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Aims: Thymic carcinoma is a rare type of cancer without an established standard pharmaceutical treatment. This study investigated the antitumor effect of dimethyl itaconate (DI), a cell-permeable derivative of itaconate, on human thymic carcinoma cell line., Main Methods: Human thymic carcinoma cell line Ty82 was used to evaluate the effect of DI on cell viability. Western blotting and immunohistochemistry were performed to determine the molecular mechanism of antitumor effects of DI on Ty82., Key Findings: DI suppressed cell growth and promoted apoptosis of Ty82. The suppressive effect of DI on Ty82 was mediated by the downregulation of lactate dehydrogenase A (LDHA), and the subsequent decrease in the activity of mechanistic target of rapamycin (mTOR). DI exhibited synergistic antitumor effects with a specific inhibitor of large neutral amino acid transporter 1 (LAT1), an amino acid transporter currently being investigated as a novel target for cancer therapy., Significance: Our findings demonstrate that DI is a novel potential strategy for thymic carcinoma treatment., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Thymic carcinoma is a rare malignant disease and standard treatment for advanced or metastatic thymic carcinoma previously treated with platinum-based chemotherapy has not been established. Lenvatinib is a novel multi-targeted inhibitor of VEGFR, FGFR, RET, c-Kit, and other kinases. The aim of this trial was to assess the activity and safety of lenvatinib as a second-line treatment in thymic carcinoma., Methods: This single-arm, phase 2 trial done in eight institutions in Japan (five cancer centres, two medical university hospitals, and one public hospital) enrolled patients with pathologically confirmed unresectable advanced or metastatic thymic carcinoma that progressed following at least one platinum-based chemotherapy. Key inclusion criteria were age 20 years or older, at least one measurable lesion as defined by the Response Evaluation Criteria in Solid Tumors version 1.1, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received 24 mg of lenvatinib orally once daily in 4-week cycles until disease progression or occurrence of unacceptable adverse events. The primary endpoint was objective response rate evaluated at the data cutoff date (Feb 22, 2019), by independent central review in the intention-to-treat population. This trial is registered on JMACCT, JMA-IIA00285, and on UMIN-CTR, UMIN000026777., Findings: Between April 21, 2017, and Feb 22, 2018, 42 patients were enrolled and all patients were included in the activity and safety analysis. The median follow-up period was 15·5 months (IQR 13·1-17·5). The objective response rate was 38% (90% CI 25·6-52·0, p<0·0001). 16 (38%) of 42 patients had a partial response and 24 (57%) had stable disease. The most frequent grade 3 treatment-related adverse events were hypertension (27 [64%]) and palmar-plantar erythrodysaesthesia syndrome (three [7%]). No patient died from adverse events., Interpretation: The activity and safety of lenvatinib in patients with advanced or metastatic thymic carcinoma was confirmed. These results suggest that lenvatinib could become a standard treatment option for patients with previously treated advanced or metastatic thymic carcinoma., Funding: Center for Clinical Trials, Japan Medical Association., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cathepsins are a group of proteolytic enzymes of the endosomal/lysosomal pathway involved in the thymic development of T cells restricted by major histocompatibility complex class II molecules. In the normal thymus, cathepsin V (CTV) and cathepsin S (CTS) are expressed in cortical and medullary epithelial cells, respectively. To investigate whether cathepsins could serve as a diagnostic marker, we performed immunohistochemical analysis for CTV and CTS in 77 cases of thymic epithelial tumors. Almost all cases (59/60) of thymoma expressed CTV, whereas 28 of 60 cases of thymoma expressed CTS. Notably, CTS was expressed in most cases of type A and type AB thymomas, but not in type B thymoma. The expression of cathepsins in type AB thymoma showed a clear correlation with histologic features; CTV was found predominantly in the type B component, and CTS was frequently expressed in the type A component. In thymic carcinoma, CTV was expressed in less than half cases (7/17), and the ratio of CTS-positive cases was equivalent to that of thymoma (8/17). Cases of CTV-negative thymic carcinoma tended to have a higher incidence of recurrence than did CTV-positive cases. Although further studies with a larger number of cases are required to confirm the utility of cathepsin immunostaining, CTV and CTS appear to serve as auxiliary diagnostic and/or prognostic markers in thymic epithelial tumors., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Toll-like receptor (TLR) agonists have been shown to have anti-tumour activity in basic research and clinical studies. However, TLR agonist monotherapy does not sufficiently eliminate tumours. Activation of the innate immune response by TLR agonists is effective at driving adaptive immunity via interleukin-12 (IL-12) or IL-1, but is counteracted by the simultaneous induction of immunosuppressive cytokines and other molecules, including IL-10, transforming growth factor-β, and indoleamine 2,3-dioxygenase (IDO). In the present study, we evaluated the anti-cancer effect of the TLR7 agonist, imiquimod (IMQ), in the absence of IDO activity. The administration of IMQ in IDO knockout (KO) mice inoculated with tumour cells significantly suppressed tumour progression compared with that in wild-type (WT) mice, and improved the survival rate. Moreover, injection with IMQ enhanced the tumour antigen-specific T helper type 1 response in IDO-KO mice with tumours. Combination therapy with IMQ and an IDO inhibitor also significantly inhibited tumour growth. Our results indicated that the enhancement of IDO expression with TLR agonists in cancer treatment might impair host anti-tumour immunity while the inhibition of IDO could enhance the therapeutic efficacy of TLR agonists via the increase of T helper type 1 immune response., (© 2014 John Wiley & Sons Ltd.)

Background: Thymomas and thymic carcinoma are rare tumors with no approved therapies. Our purpose was to analyze the molecular features and outcomes of patients referred to the Clinical Center for Targeted Therapy (Phase I Clinic)., Methods: We retrospectively reviewed the medical records of consecutive referred patients with advanced/metastatic thymoma or thymic carcinoma, Results: Twenty-one patients were identified (median age 52 years; 10 women; median number of prior systemic therapies = 2). Six of 10 patients (60%) treated with mTOR inhibitor combination regimens achieved stable disease (SD) ≥12 months or a partial response (PR). For patients treated on mTOR inhibitor regimens (N = 10), median time to treatment failure (TTF) was 11.6 months versus 2.3 months on last conventional regimen prior to referral (p=0.024). Molecular analyses (performed by next generation sequencing in seven patients and single polymerase chain reaction (PCR)-based assays in an additional six patients) showed diverse actionable mutations: PIK3CA (1 of 12 tested; 8%); EGFR (1 of 13; 8%); RET (1 of 7; 14%); and AKT1 (1 of 7; 14%). Of two patients with PIK3CA or AKT1 mutations, one was treated with an mTOR inhibitor-based regimen and achieved 26% regression with a TTF of 17 months., Conclusion: Patients with advanced/metastatic thymoma or thymic carcinoma demonstrated prolonged TTF on mTOR inhibitor-based therapy as compared to prior conventional treatment. Heterogeneity in actionable molecular aberrations was observed, suggesting that multi-assay molecular profiling and individualizing treatment merits investigation.

Background: Thymic epithelial tumors include several entities with different biologic behavior. Chemotherapy is indicated in advanced disease, but limited data exist on gene expression correlation with the response to chemotherapeutic agents., Patients and Methods: A series of 69 thymic neoplasms (7 A-, 6 AB-, 6 B1-, 10 B2-, 14 B3-thymomas, 22 carcinomas and 4 combined tumors) was collected to assess gene expression of thymidylate synthase (TS), excision repair cross complementing-1 (ERCC1), ribonucleotide reductase subunit 1 (RRM1), topoisomerase 2α (TOP2A) and mTOR., Results: A strong linear correlation between TS gene and protein expression was observed (P<0.0001, R=0.40). TS expression was significantly lower in pure A-thymomas and thymic carcinomas (P<0.0001) and progressively decreasing from B1-type to thymic carcinomas (B1>B2>B3>C; P<0.0001). RRM1 and TOP2A mRNA expression levels were significantly correlated with TS levels (both P=0.03) with a similar trend of expression among histotypes. RRM1 and TOP2A high levels were significantly correlated with high TS (P=0.03) and low tumor stages (I-II) (P<0.0001 and P<0.01, respectively). No relevant changes of ERCC1 and mTOR were detected., Conclusions: Low TS and, to a minor extent, RRM1 and TOP2A expression were detected in aggressive thymic tumors. These findings should be prospectively considered in selecting the most appropriate chemotherapy., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Background: To investigate the expression and clinical significance of protein tyrosine phosphatase nonreceptor 22 (PTPN22) in thymoma, as well as the relationship between thymoma and myasthenia gravis (MG)., Methods: The expression of PTPN22 in normal thymus (35 cases), thymoma without MG (50 cases), and thymoma with MG (45 cases) treated with surgery were detected by the EnVision two-step immunohistochemical staining method. We analyzed the relationship of thymoma with MG as well as some clinical factors, such as the Osserman classification for MC, age, gender, and course of disease before surgery. All data were analyzed using the SPSS software., Results: The positive rates of PTPN22 expression in thymoma with and without MG were 11.1% (5/45) and 24.0% (12/50), respectively, which were significantly lower than in the normal thymus (74.3%, 26/35). A significant difference was found between the positive rates of thymoma with and without MG. The expression level of PTPN22 had no relation to thymoma with MG and to the Osserman classification for MG, age, gender, and course of disease of the patient., Conclusions: Minimal or no PTPN22 expression in thymoma may play an important role in the development of thymoma with MG, provide basis for further genetic research.

Recently, a proteasome β subunit expressed exclusively in thymic cortical epithelial cells was discovered in mice and humans. This subunit, designated β5t, is a component of the thymoproteasome, a specialized type of proteasome implicated in thymic positive selection. To investigate whether β5t could serve as a marker for the differential diagnosis of thymic epithelial tumors, we performed immunohistochemical analysis using anti-β5t antibody in 54 cases of thymic epithelial tumors comprising 41 cases of thymomas and 13 cases of thymic carcinomas. β5t was detected in the neoplastic epithelial cells of thymomas. Among the subtypes of thymoma, expression of β5t was observed in most cases of type B thymoma (20 of 21) but not in type A thymomas (0 of 3). In type AB thymomas, β5t expression was variable (6 of 17). Type B3 thymomas (4 cases) were positive for β5t but negative for CD5, c-kit, and glucose transporter 1 (GLUT-1), which are known as diagnostic markers for thymic carcinomas. In contrast, thymic carcinomas were negative for β5t (0 of 13) but expressed at least one and usually all of CD5, c-kit, and GLUT-1. Thus, β5t and CD5/c-kit/GLUT-1 were differentially expressed in type B3 thymoma and thymic carcinoma. We tested β5t expression in 39 cases of tumors arising from other organs, which showed the specific expression of β5t in thymic epithelial tumors. This study demonstrates that β5t is expressed in most type B and in some type AB thymomas and is a marker useful in differentiating type B3 thymomas from thymic carcinomas when used in combination with other diagnostic markers.

Background: Thymic carcinoma (TC) is a rare aggressive tumour. Median survival with current treatments is only 2 years. Sunitinib is a multi-targeted tyrosine kinase inhibitor that has shown benefit in various other cancers., Methods: Laboratory analyses of snap-frozen tumour tissues were performed to detect activation and genetic mutations of receptor tyrosine kinases (RTKs) in TC samples. On the basis of molecular analyses showing activation of multiple RTKs in their tumour, four patients with metastatic TCs refractory to conventional therapies were treated with sunitinib according to standard protocols., Results: RTK analysis in three of the patients showed activation of multiple RTKs, including platelet-derived growth factor-beta and vascular endothelial growth factor 3. Mutations of EGFR, c-KIT, KRAS, and BRAF genes were not found. Administration of sunitinib yielded a partial remission (lasting 2 to 18+ months) according to the RECIST criteria in three patients and stable disease with excellent metabolic response in 18F-FDG-PET in another one. The overall survival with sunitinib treatment ranges from 4 to 40+ months. Withdrawal of the drug in one patient prompted rapid tumour progression that could be controlled by re-administration of sunitinib., Conclusions: Sunitinib is an active treatment for metastatic TC. A panel of molecular analyses may be warranted for optimal patient selection.

A blockade of CD44 can interfere with haematopoietic and leukemic stem cell homing, the latter being considered as a therapeutic option in haematological malignancies. We here aimed to explore the molecular mechanism underlying the therapeutic efficacy of anti-CD44. We noted that in irradiated mice reconstituted with a bone marrow cell transplant, anti-CD44 exerts a stronger effect on haematopoietic reconstitution than on T lymphoma (EL4) growth. Nonetheless, in the non-reconstituted mouse anti-CD44 suffices for a prolonged survival of EL4-bearing mice, where anti-CD44-prohibited homing actively drives EL4 cells into apoptosis. In vitro, a CD44 occupancy results in a 2-4-fold increase in apoptotic EL4 cells. Death receptor expression (CD95, TRAIL, TNFRI) remains unaltered and CD95 cross-linking-mediated apoptosis is not affected. Instead, CD44 ligation promotes mitochondrial depolarization that is accompanied by caspase-9 cleavage and is inhibited in the presence of a caspase-9 inhibitor. Apoptosis becomes initiated by activation of CD44-associated phosphatase 2A (PP2A) and proceeds via ERK1/2 dephosphorylation without ERK1/2 degradation. Accordingly, CD44-induced apoptosis could be mimicked by ERK1/2 inhibition, that also promotes EL4 cell apoptosis through the mitochondrial pathway. Thus, during haematopoietic stem cell reconstitution care should be taken not to interfere by a blockade of CD44 with haematopoiesis, which could be circumvented by selectively targeting leukemic CD44 isoforms. Beyond homing/settlement in the bone marrow niche, anti-CD44 drives leukemic T cells into apoptosis via the mitochondrial death pathway by CD44 associating with PP2A. Uncovering this new pathway of CD44-induced leukemic cell death provides new options of therapeutic interference.

We showed previously that Tyk2(-/-) natural killer cells lack the ability to lyse leukemic cells. As a consequence, the animals are leukemia prone. Here, we show that the impaired tumor surveillance extends to T cells. Challenging Tyk2(-/-) mice with EL4 thymoma significantly decreased disease latency. The crucial role of Tyk2 for CTL function was further characterized using the ovalbumin-expressing EG7 cells. Tyk2(-/-) OT-1 mice developed EG7-induced tumors significantly faster compared with wild-type (wt) controls. In vivo assays confirmed the defect in CD8(+) cytotoxicity on Tyk2 deficiency and clearly linked it to type I IFN signaling. An impaired CTL activity was only observed in IFNAR1(-/-) animals but not on IFNgamma or IL12p35 deficiency. Accordingly, EG7-induced tumors grew faster in IFNAR1(-/-) and Tyk2(-/-) but not in IFNgamma(-/-) or IL12p35(-/-) mice. Adoptive transfer experiments defined a key role of Tyk2 in CTL-mediated tumor surveillance. In contrast to wt OT-1 cells, Tyk2(-/-) OT-1 T cells were incapable of controlling EG7-induced tumor growth.

The treatment of advanced stage thymomas and thymic carcinomas is a multimodal therapy. New therapeutic targets are currently under investigation, including the epidermal growth factor receptor (EGFR) as well as KIT. A number of studies have shown protumorigenic potential of Cyclooxygenase-2 (COX-2) in a variety of human malignancies, but so far it is unknown whether COX-2 is expressed in primary malignancies of the thymus. Using tissue microarrays, the expression of COX-2, microsomal-PGES-1 and -PGES-2 (mPGES-1 and mPGES-2), as well as EGFR was evaluated in different subtypes of thymoma and thymic carcinomas. COX-2 was expressed in all subtypes as determined by immunohistochemistry. Some cases of type B2 and thymic carcinomas had COX-2 staining levels classified as mild to moderate. However, when measuring the optical color intensity, no significant differences could be detected. Concerning the expression levels, a weak correlation between the expression of COX-2, mPGES-1 and mPGES-2 as well as EGFR was found. Furthermore, additional cases of thymomas and thymic carcinomas were analyzed by COX-2 Western immunoblot analysis and were compared to normal thymi. The analysis showed that thymomas and thymic carcinomas had a significantly stronger COX-2 expression than that of the normal thymi (p < 0.04). In summary, COX-2 is expressed in all subtypes of thymomas and thymic carcinomas and thus represents, in addition to EGFR and KIT, a potential therapeutic target. Further studies are needed in order to determine whether a combined therapy using COX-2 inhibitors in addition to the evolving anti-EGFR antibody therapy may be considered as a treatment option.

Objective: To study the relationship between activation of pro-MMP-2 and expression of matrix metalloproteinases (MMP)-2, MT1-MMP and tissue inhibitor of metalloproteinases (TIMP)-2 mRNA in thymoma and thymic carcinoma; and to study the molecular mechanism of invasion and metastasis of thymic epithelial tumors., Methods: Fresh tissue specimens of thymoma, thymic carcinoma and normal thymus were included. The mRNA expression of MMP-2, MT1-MMP and TIMP-2 were analyzed by real-time reverse transcription polymerase chain reaction. The pro-MMP-2 activation ratio and its localization were determined by gelatin zymography and film in-situ gelatin-Zymography, respectively. Correlation of mRNA expression of MMP-2, MT1-MMP and TIMP-2 was investigated in tumors with different histological subtypes and clinical stages., Results: There were no significant differences in the expressions of MMP-2, MT1-MMP and TIMP-2 mRNA between I and II stage or III and IV stage thymomas (P > 0.05). However, significant differences of the expressions were observed between three tumor groups: I-II stage, III-IV stage and thymic carcinomas (P < 0.005), and between three histological subtypes: AB-B1 (lymphocyte-rich and mixed types), B2-B3 (cortical and predominantly polygonal cells types) and thymic carcinomas (P < 0.05). Expression levels of MT1-MMP and TIMP-2 mRNA were correlated with pro-MMP-2 activation ratio (Spearman rank correlation: r = 0.7235, r = 0.7647, P < 0.005). The expression of MMP-9 did not show significant differences between thymomas and thymic carcinomas., Conclusions: MMP-2, MT1-MMP and TIMP-2 mRNA expression levels are correlated with the histologic subtypes and clinical stages of thymoma. The mRNA expressions of MT1-MMP and TIMP-2 are correlated with the activation ratio of pro-MMP-2. It is speculated that upregulation of MT1-MMP gene expression may induce an activation of pro-MMP-2 through TIMP-2.

The roles played by host-derived nitric oxide (NO) in the growth and subsequent immune rejection of a immunogenic murine lymphoma were investigated by growing the tumor in mice in which the gene for either inducible NO synthase (iNOS) or endothelial NOS (eNOS) had been ablated. This showed that NO from tumor-infiltrating host cells had no significant effect on either tumor growth or immune rejection, although measurements of tumor nitrite levels and protein nitration showed that there had been significant NO production in the rejected tumors, in both the eNOS and iNOS knockout mice. Inhibition of both tumor and host NOS activities, with an iNOS-selective inhibitor (1400W), a nonselective NOS inhibitor [Nomega-nitro-L-arginine methyl ester (L-NAME)], or scavenging NO with a ruthenium-based scavenger, significantly delayed tumor rejection, while having no appreciable effect on tumor growth. Incubation of tumor cells with medium taken from cultured splenocytes, that had been isolated from immunized animals and activated by incubating them with irradiated tumor cells, resulted in an increase in tumor cell NOS activity and an increase in tumor cell apoptosis, which could be inhibited using L-NAME. We propose that, during the immune rejection of this tumor model, there is induction of tumor NOS activity by cytokines secreted by activated lymphocytes within the tumor and that this results in increased levels of tumor NO that induce tumor cell apoptosis and facilitate immune rejection of the tumor.

Peroxiredoxin-3 (Prdx3) is a mitochondrial member of the antioxidant family of thioredoxin peroxidases that uses mitochondrial thioredoxin-2 (Trx2) as a source of reducing equivalents to scavenge hydrogen peroxide (H(2)O(2)). Low levels of H(2)O(2) produced by the mitochondria regulate physiological processes, including cell proliferation, while high levels of H(2)O(2) are toxic to the cell and cause apoptosis. WEHI7.2 thymoma cells with stable overexpression of Prdx3 displayed decreased levels of cellular H(2)O(2) and decreased cell proliferation without a change in basal levels of apoptosis. Prdx3-transfected cells showed a marked resistance to hypoxia-induced H(2)O(2) formation and apoptosis. Prdx3 overexpression also protected the cells against apoptosis caused by H(2)O(2), t-butylhydroperoxide, and the anticancer drug imexon, but not by dexamethasone. Thus, mitochondrial Prdx3 is an important cellular antioxidant that regulates physiological levels of H(2)O(2), leading to decreased cell growth while protecting cells from the apoptosis-inducing effects of high levels of H(2)O(2).

Purpose: Thymoma is one of the most common solid tumors in the mediastinum. However, there is no definitive consensus regarding the optimal adjuvant chemotherapy for advanced thymoma., Methods: To predict tumor sensitivity to 5-fluorouracil (5-FU) in thymoma, we investigated the mRNA levels of thymidylate synthase (TS), the key enzyme that catalyzes the methylation of deoxyuridine monophosphate, and correlates with the resistance of 5-FU and dihydropyrimidine dehydrogenase (DPD), which degrades 5-FU in thymoma. We used real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) using the LightCycler to monitor the TS and DPD gene expression levels in thymoma tissue specimens from patients, coamplified with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as an internal standard., Results: In the resected tumor specimens, TS and DPD mRNA levels were 3.876 and 14.651, respectively. Both the TS and DPD mRNA levels were significantly higher in the tumor tissue specimens than in the normal adjacent thymus tissue specimens. No significant correlations were observed between the TS or DPD levels and other clinicopathological factors., Conclusions: The combined use of measurements of TS and DPD mRNA levels using real-time RT-PCR analyses may provide an indication of the selective cytoxicity of 5-FU on thymoma. In general, 5-FU itself is not considered to be a useful treatment for thymoma. The usufulness of DPD-inhibiting fluoropyrimidine (DIF) drugs for thymoma should therefore be further considered.

Background: Telomerase is a nucleoprotein complex that caps the physical termini of all eukaryotic chromosomes. It is suggested that telomerase play important roles in unlimited cell division acquisition of the malignant phenotype. We studied the relation of telomerase activity in thymoma and thymic carcinoma to the clinicopathological features of these lesions., Methods: Tissue specimens were surgically resected from patients with thymoma and thymic carcinoma. Telomerase activity was evaluated according to a modified telomeric repeat amplification protocol (TRAP) assay., Results: Telomerase activity was detected in all thymic epithelial tumors. The activity (mean +/- SD: unit/microgram.protein) in thymoma (n = 17) was significantly higher than that in thymic carcinoma (n = 7) [431.8 +/- 400.1 vs. 68.8 +/- 39.8: p < 0.01]. Telomerase activities in thymoma and thymic carcinoma were significantly higher than that in primary lung adenocarcinoma (33.5 +/- 39.2: n = 47), studied as control (p < 0.01). In patients with thymoma, telomerase activity did not correlate with tumor stage according to Masaoka classification (p = 0.776). In patients with thymic carcinoma, however, telomerase activity positively correlated with tumor stage (p = 0.02). In thymoma, telomerase activity positively correlated with the ratio of induced lymphocytes according to Rosai's classification (p = 0.045)., Conclusion: In thymoma, telomerase activity reflects the presence of immature T-cell lymphocytes in tumor tissue rather than tumor stage or malignant phenotype. In thymic carcinoma, telomerase activity derived directly from cancer cells may relate to tumor stage.

The abzyme activity of mAb35 and pQ1-209 was compared with that of normal rabbit IgG and serum IgG from patients with various forms of myasthenia. It was found that mAb35 and pQ1-209 and IgG from patients with myasthenia possess catalytic activity. IgG from myasthenia patients with thymomas possess creatine phosphokinase activity, which 2-fold surpassed the control.

Background: Caspase activation is a critical early step in the onset of apoptosis. Cell-permeable fluorogenic caspase substrates have proven valuable in detecting caspase activation by flow cytometry. Nevertheless, detection of early low-level caspase activation has been difficult using conventional area or peak fluorescence analysis by flow cytometry, despite the apparent presence of these cells as observed by microscopy. We describe a method utilizing maximum fluorescence pixel analysis by laser scanning cytometry (LSC) to detect early apoptotic cells., Methods: The PhiPhiLux-G(1)D(2) caspase 3/7 substrate was used in combination with DNA dye exclusion and annexin V binding to identify several stages of apoptosis in EL4 murine thymoma cells by both traditional flow and LSC. LSC analysis of maximum pixel brightness in individual cells demonstrated an intermediate caspase-low subpopulation not detectable by flow or LSC integral analysis. LSC analysis of caspase activity was then carried out using the larger UMR-106 rat osteosarcoma cell line to determine if this apparent early caspase activity could be correlated with localized, punctate caspase activity observed by microscopy., Results: The caspase-low subpopulation found in apoptotic EL4 cells was also observable in UMR-106 cells. Relocation to cells with low fluorescence due to caspase activity and subsequent examination by microscopy demonstrated that these latter cells indeed show punctate, highly localized caspase activation foci that might represent an early stage in caspase activation., Conclusions: Cells with low-level, localized caspase expression can be detected using maximum pixel analysis by LSC. This methodology allows an early step of apoptotic activation to be resolved for further analysis., (Copyright 2002 Wiley-Liss, Inc.)

Background: Telomerase is a nucleoprotein complex that caps the physical termini of all eukaryotic chromosomes. Because most malignant cells and reproductive cells have telomerase activity, which elongates telomeric DNA, telomerase may play important roles in unlimited cell division acquisition of the malignant phenotype. The current study examined the relation of telomerase activity in thymoma and thymic carcinoma with the clinicopathologic features of these lesions., Methods: Tissue specimens were surgically resected from patients with thymoma and thymic carcinoma. Telomerase activity was evaluated according to a modified telomeric repeat amplification protocol assay. Paraffin sections of tumor were immunostained by MIC2 antibody, a marker of immature T cells., Results: Telomerase activity was detected in all thymic epithelial tumors. The activity (mean +/- SD; unit per microg protein) in thymoma (n = 17) was significantly higher than that in thymic carcinoma (n = 7) (431.8 +/- 400.1 vs. 68.8 +/- 39.8; P < 0.01). Telomerase activities in thymoma and thymic carcinoma were significantly higher than that in primary lung adenocarcinoma (33.5 +/- 39.2, n = 47), studied as a control (P < 0.01). In patients with thymoma, telomerase activity did not correlate with tumor stage according to Masaoka classification (P = 0.776). In patients with thymic carcinoma, however, telomerase activity positively correlated with tumor stage (P = 0.02). In thymoma, telomerase activity positively correlated with the ratio of induced lymphocytes according to Rosai's classification (P = 0.045). MIC2-positive lymphocytes were identified in all cases of thymoma (n = 12). In contrast, lymphocytes infiltrating thymic carcinoma did not react with MIC2., Conclusions: In thymoma, telomerase activity reflects the presence of immature T-cell lymphocytes in tumor tissue rather than tumor stage or malignant phenotype. In thymic carcinoma, telomerase activity derived directly from cancer cells may relate to tumor stage., (Copyright 2002 American Cancer Society.)

Glucocorticoids are used for the treatment of lymphoid neoplasms, taking advantage of the well-known ability of these compounds to cause apoptosis in lymphoid tissues. Previously, we have shown that dexamethasone, a synthetic glucocorticoid, causes a down-regulation of several antioxidant defense enzymes and proteins, including catalase and thioredoxin, concomitant with the induction of apoptosis in WEHI7.2 mouse thymoma cells. To test whether this down-regulation plays a critical role in the mechanism of steroid-induced apoptosis, WEHI7.2 cells were transfected with rat catalase. Two clones, expressing 1.4-fold and 2.0-fold higher catalase specific activity, respectively, when compared with vectoronly transfectants were selected for further study. An increase to 1.4-fold parental cell catalase activity delayed cell loss after dexamethasone treatment, whereas a 2.0-fold parental catalase activity prevented dexamethasone-induced cell loss for 48 h after treatment. Dexamethasone treatment of the WEHI7.2 cells stimulated a release of cytochrome c into the cytosol. Catalase-overexpressing cells showed a delay or lack of cytochrome c release from the mitochondria, which correlated temporally with the delay or prevention of cell loss in the culture after dexamethasone treatment. A decreased amount of cell death from WEHI7.2 cells overexpressing catalase was also seen in tumor xenografts in severe combined immunodeficient mice when compared with tumors from vector-only transfected cells. Similarly, thioredoxin-overexpressing WEHI7.2 cells, shown previously to be apoptosis resistant, showed decreased cell death in tumor xenografts. This resulted in larger tumors from cells overexpressing these proteins. Cell death in control transfectant tumor xenografts was primarily attributable to apoptosis. In contrast, the cell death we observed in tumors from thioredoxin- or catalase-overexpressing cells had a higher frequency of a nonapoptotic, nonnecrotic type of cell death termed para-apoptosis. These data suggest that: (a) oxidative stress plays a critical role in steroid-induced apoptosis prior to the commitment of the cells to undergo apoptosis; and (b) resistance to oxidative stress can contribute to tumor growth.

Unlabelled: BACKGROUND AND OBJECTS: Matrix degradation, which is a critical event in the process of tumor invasion and metastasis, is considered to be caused by the action of proteolytic enzymes., Methods: We examined the gelatinolytic activity of matrix metalloproteinase (MMP)-9, and the activity of active and inactive forms of MMP-2 in five thymi, five noninvasive thymomas, eight invasive thymomas, and five thymic carcinomas by quantitative gelatinolytic zymography., Results: The gelatinolytic activity of active MMP-2 in five thymi was zero. The mean gelatinolytic activity of active MMP-2 was 0.020 +/- 0.015 in noninvasive thymoma, 0.084 +/- 0.098 in invasive thymoma and 0.246 +/- 0.194 in thymic carcinoma. The gelatinolytic activity of active MMP-2 correlated with the invasiveness of thymic epithelial tumors (Spearman rank correlation: r-value = 0.532). The gelatinolytic activity of active MMP-2 in three thymoma cases with microscopic capsular invasion was the same as that of noninvasive thymoma. When thymoma cases showing microscopic capsular invasion were classified into the "macroscopically noninvasive thymoma" group, the gelatinolytic activity of active MMP-2 correlated with the invasiveness of thymic epithelial tumors (Spearman rank correlation: r-value = 0.621)., Conclusions: The gelatinolytic activity of active MMP-2 significantly correlated with the invasiveness in thymic epithelial tumors. J. Surg. Oncol. 2001;76:169-175., (Copyright 2001 Wiley-Liss, Inc.)

We present evidence here that the proinflammatory cytokine, interleukin-1 beta (IL-1 beta) stimulates a significant increase in protein kinase C (PKC)-epsilon and PKC-delta protein levels and increases PKC-epsilon, but not PKC-delta, transcripts in EL4 thymoma cells. Incubation of EL4 cells with IL-1 beta induced protein synthesis of PKC-epsilon (6-fold increase) by 7 h and had a biphasic effect on PKC-delta levels with peaks at 4 h (2-fold increase) and 24 h (4-fold increase). At the level of mRNA, PKC-epsilon, but not PKC-delta levels, were induced after incubation of EL4 cells with IL-1 beta. The signalling mechanisms utilized by IL-1 beta to induce the synthesis of these PKC isoforms were investigated. Two phosphatidylinositol (PI) 3-kinase-specific inhibitors, wortmannin and LY294002, inhibited IL-1 beta-induced synthesis of PKC-epsilon. However, the PI 3-kinase inhibitors had little effect on the IL-1 beta-induced synthesis of PKC-delta in these cells. Our results indicate that IL-1 beta induced both PKC-delta and PKC-epsilon expression over different time periods. Furthermore, our evidence suggests that IL-1 beta induction of PKC-epsilon, but not PKC-delta, may occur via the PI 3-kinase pathway., (Copyright 2001 S. Karger AG, Basel)

In vitro effects of folic acid (10(-5), 10(-4), and 10(-3)M) on activities of gamma-glutamyltransferase and glutathione reductase, the enzymes involved in glutathione metabolism, were studied in tissue samples obtained after surgical treatment of the lungs and thymus. Folic acid did not change gamma-glutamyltransferase activity in lung cancer tissue, but in thymoma tissue this substance in a concentration of 10(-3)M inhibited it by 16%. Folic acid had no effects on glutathione reductase activity in benign tumors and normal lung and thymus tissues, but increased this activity in thymoma and lung cancer tissues. Activation of glutathione reductase was probably related to binding of folic acid in the allosteric center of the enzyme, which probably induced conformational changes in the catalytic center, acceleration of electron transport from NADPH(2) to oxidized glutathione via flavin adenine nucleotide, and intense production of reduced glutathione.

Simian virus 40 T-tumor antigen (SV40 T-ag) can induce a wide variety of tumors in hamsters and neonatal mice. These tumorigenic effects are predominantly due to the activity of early viral gene products, large T-antigen and small t-antigen. We have analyzed the expression of a DNA repair gene, N-methylpurine-DNA glycosylase (MPG), from different tissues of a non-transgenic (control) and SV40 T-ag expressing transgenic mice at the mRNA level. Expression of the transgene in thymus of adult mice was also detected by the presence of SV40 T-ag mRNA. Non-transgenic mice did not express the SV40 T-ag gene in their thymus, while the mRNA for MPG was found in thymus from both of transgenic and non-transgenic mice. The MPG gene was expressed in various tissues and is regulated in a tissue-specific manner. Northern blot analysis revealed that the transgenic mice showed considerably higher expression of MPG in the thymic carcinomas. The level of MPG mRNA in the thymic carcinoma was elevated about 5.7 fold, as compared with those found in the control thymus. MPG expression was significantly increased, either directly or indirectly, by the SV40 T-ag gene product. These findings provide the first in vivo observations that the SV40 T-ag gene induced thymic carcinomas associated with the activation of the DNA repair gene, MPG.

Cyclin-dependent kinase-6 (CDK6) is the earliest inducible member of the CDK family in human T lymphocytes, involved in growth factor stimulation and cell cycle progression. CDK6 is one of the targets of p16 and p15, CDK inhibitors encoded by MTS1 and MTS2, two tumor suppressor genes that are frequently deleted in T-cell leukemia. In this study we have investigated CDK6 expression in normal and neoplastic lymphoid tissues using immunohistochemistry and flow cytometry. In normal (six samples) and hyperplastic (four samples) thymuses, strong CDK6 expression was observed in a discrete proportion of cortical thymocytes (10 to 15%), mainly located in the peripheral (subcapsular) zone of the cortex. All tested cases of T-cell lymphoblastic lymphoma/leukemia (T-LBL/ALL) showed strong CDK6 expression in the majority (up to 100%) of neoplastic lymphoid cells. Western blot analysis confirmed the expected CDK6 protein size (40 kd). According to Southern blot analysis, CDK6 overexpression in neoplastic T lymphoblasts was not due to gene amplification. In all other lymphomas investigated (28 peripheral T-cell non-Hodgkin's lympohomas (T-NHLs), 7 CD30+ anaplastic NHLs, 22 high-grade B-NHLs, 15 low-grade B-NHLs, 25 B-cell precursor ALLs), CDK6 was not expressed or expressed at low levels, with the only exception of three nasal angiocentric T-NHLs, all exhibiting CDK6 immunoreactivity comparable to that observed in T-LBL/ALL. These data provide evidence that CDK6 is abnormally expressed in T-LBL/ALL and may be involved in the pathogenesis of this malignancy. In addition, the quantitative difference of CDK6 expression between neoplastic and non-neoplastic cortical thymocytes can be potentially useful in the differential diagnosis of thymic neoplasms on histological and cytological specimens.

Telomerase is an enzyme that stabilizes telomere length in transformed cells and tumors. Its role in tumor development is far from clear. In this paper, a new experimental model to study telomerase activity during tumorigenesis is presented. After infection with Polyoma virus, AKR mice developed thymomas and mammary gland adenocarcinomas. Polyoma antigens were observed by the peroxidase-antiperoxidase technique on tissue sections, and by Western blot on tumor extracts. The TRAP assay was performed to detect telomerase activity. It was not present in normal mammary gland, but it was positive in mammary gland adenocarcinomas. A different pattern was seen in thymic tissues: normal thymus had higher telomerase activity than thymomas. The incubation of thymoma extracts with normal thymus extracts decreased telomerase activity in the latter. These results demonstrate two different patterns of telomerase activity in tumors induced by Polyoma virus, and suggest the presence of telomerase inhibitory factors in thymomas.

Stimulation of sensitive EL4 mouse thymoma cells (s-EL4) with phorbol esters results in production of interleukin 2 (IL-2), adherence to a plastic substrate, and growth inhibition, whereas a phorbol ester-resistant variant (r-EL4) fails to respond. Previous studies revealed substantially decreased expression of protein kinase C (PKC) epsilon in the r-EL4 versus s-EL4 cells. This work has been extended to examine the more recently described PKC isozymes. Western and Northern analyses revealed a marked decrease in PKC eta and theta in r-EL4 as compared to s-EL4 cells. Treatment of these lines with phorbol ester for 24 h resulted in down-regulation of all PKC isozymes examined except PKC eta, which was up-regulated in the s-EL4 cells at the time of maximal IL-2 production. Two newly isolated EL4 clones, resistant to phorbol ester-induced growth inhibition but still exhibiting the phorbol ester-induced adherence and IL-2 production, both expressed PKC eta and theta. Collectively, these observations suggest a dissociation of growth inhibition from adherence and IL-2 production pathways and a potential role for PKC eta in the latter.

The capacity of pretherapeutically assessed neuron-specific enolase (NSE) to differentiate between small cell lung cancer (SCLC) and mediastinal tumors was investigated retrospectively in a series of 320 patients. NSE was found to be increased in 95/130 (73.1%) patients with SCLC, in 4/62 (6.5%) patients with Hodgkin's disease, in 10/58 (17.2%) patients with non-Hodgkin's lymphoma, in 5/16 (31.3%) patients with teratoma, and in 6/54 (11.1%) patients with thymoma. The cut-off value, defined as the 95% percentile of a reference population suffering from benign pulmonary disorders (n = 192), was set at 13.8 ng/ml. When this discrimination level was increased to 26.4 ng/ml, which corresponds to a 95% specificity versus the total group with mediastinal tumors, SCLC was recognized with a detection rate of only 49.2%. In conclusion, increased NSE concentrations in a patient with a hilar mass and/or mediastinal widening on X-ray are not always diagnostic of SCLC due to the high rate of elevated NSE values associated with mediastinal tumors. However, in a patient who presents with a hilar mass and a high NSE level, bronchoscopy is always indicated to obtain adequate specimens for histology in order to plan an appropriate therapeutic regimen.

A secreted dibasic cleaving peptidase capable of converting dynorphins into Leu-enkephalin-Arg6 was purified from the medium of EL-4 mouse thymoma cells. The enzyme is a novel metalloendopeptidase with a neutral pH optimum (6.9) and a molecular weight of approximately 130 000. The dibasic cleaving enzyme was completely inhibited in the presence of 20-50 mM amine buffers, 0.1 mM EDTA, 0.5 mM 1,10-phenanthroline, 0.5 mM N-ethylmaleimide, and 1mM DTNB. Unlike the Kex2 family of proteases, Ca2+ did not activate the endopeptidase, but high concentrations (1 mM) of metal ions such as Cu2+, Ni2+, Zn2+, and Co2+ completely inhibited the enzyme. Inhibition was not seen with 0.2 mM TLCK, 1 mM DTT, and 1 mM PMSF. The enzyme will cleave Arg-Arg and Arg-Lys bonds, but not Lys-Arg or Lys-Lys bonds in identical environments, and no aminopeptidase or carboxypeptidase activity was seen. The size of the substrate does not seem to be a determining factor, since dynorphin A(1-12) is cleaved at a rate similar to prodynorphin B(228-256) containing 29 amino acids. The identity of the residues on either side of the cleavage site influences the rate of processing, as noted by different rates of cleavage for the same size peptides dynorphin A(1-13) vs dynorphin A(1-9) vs beta-neoendorphin. The presence of proline in the P3' (alpha-neoendorphin), P4' (dynorphin A(1-11)), or P5' (bovine adrenal medulla dodecapeptide) position does not prevent cleavage, but neurotensin and its (1-11) fragment containing both P2 and P2' proline residues are not cleaved.

The cross-linking by antibody of some glycosyl-phosphatidyl-inositol (GPI)-anchored proteins on the plasma membrane of T cells leads to cell activation. Phosphorylation of proteins on tyrosine residues has a central role in the control of T cell activation, and non-receptor protein tyrosine kinases can be coprecipitated with immune complexes of GPI-anchored proteins in T cell lysates. In order to investigate the nature of this interaction, two recombinant GPI-anchored proteins were constructed (using the GPI signal sequence from Thy-1), and their associations with protein tyrosine kinases in stable transfectants of a mouse thymoma have been investigated. One recombinant GPI protein is the extracellular domain of the human complement receptor-1, normally an integral membrane protein, and the other is the secreted protein, human tissue inhibitor of metalloproteinases. The latter protein should be foreign to the cell surface and yet has been expressed as a GPI-anchored protein at levels equivalent to the highly expressed antigens Thy-1 and Ly6.A2 on mouse thymoma cells. Neither of the two recombinant proteins, when immunoprecipitated from NP40 lysates of transfected cells, was associated with protein tyrosine kinases in contrast with the natural endogenous GPI-anchored proteins Thy-1 and Ly6.A2 in non-transfected parental cells. Moreover, high expression of foreign recombinant GPI protein appears to interfere with the association of the natural GPI proteins with protein tyrosine kinases.

The R1.1 mouse thymoma cell line expresses a high-affinity kappa opioid binding site. Opioid binding to this site is inhibited by guanine nucleotides, suggesting that the receptor is coupled to a guanine nucleotide-binding protein. Here, we present evidence that the kappa opioid binding site on R1.1 cell membranes is negatively coupled to adenylyl cyclase. The kappa-selective agonists (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)- cyclohexyl]benzeneacetamide methane-sulfonate hydrate [(-)-U50,488], (5 alpha,7 alpha, 8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxas- piro(4,5)dec-8-yl)benzeneacetamide (U69,593) and several dynorphin peptides inhibited basal and forskolin-stimulated cyclic AMP production by up to 40% in R1.1 cell membranes. The order of potency for the inhibition of adenylyl cyclase activity by opioid agonists correlated with their Ki values for the inhibition of [3H]U69,593 binding. Opioid-mediated inhibition of adenylyl cyclase activity was stereoselective, as (-)-U50,488 was more potent than the (+) isomer, and the inhibition was blocked by the kappa-selective antagonist nor-binaltorphimine. The opioid-mediated inhibition of adenylyl cyclase activity was also completely blocked by incubating R1.1 cells with Bordetella pertussis toxin (PTX). Incubation of R1.1 cell membranes with PTX and [adenylate-32P]NAD+ resulted in the exclusive labeling of a 41-kDa protein, as determined by separating the membrane proteins under reducing conditions on a SDS polyacrylamide gel, followed by autoradiography. These results suggest that a PTX-sensitive inhibitory guanine nucleotide-binding protein mediates the link between the thymoma kappa opioid receptor and adenylyl cyclase.

The disialogangliosides of WHT/Ht mouse thymomas, which were obtained by subcutaneous transplantation of a thymoma that developed spontaneously in a WHT/Ht mouse, were purified and characterized. From the results of sugar-composition analysis, a permethylation study, enzymatic hydrolysis followed by TLC-immunostaining, negative-ion fast atom bombardment mass spectrometry (FAB/MS), and 1H-NMR spectroscopy, the structure of one of the five purified disialogangliosides was determined to be IV3 alpha(NeuGc alpha 2-8NeuGc)-Gg4Cer. The other 4 disialogangliosides were tentatively characterized on the basis of sialidase treatment followed by TLC-immunostaining with cholera toxin B subunit and anti-Gg4Cer antibody to be IV alpha(NeuAc alpha-NeuGc)-Gg4Cer, IV alpha(NeuGc alpha-NeuAc)-Gg4Cer, IV alpha NeuAc,II3 alpha NeuAc-Gg4Cer, and IV alpha NeuGc,II3 alpha NeuGc-Gg4Cer. In addition, another component exhibiting one spot on TLC was a mixture of IV alpha NeuGc,II3 alpha NeuAc-Gg4Cer and IV alpha NeuAc,II3 alpha NeuGc-Gg4Cer. Then the occurrence of these gangliosides in WHT/Ht mouse thymocytes was examined. As one of two major disialogangliosides, the thymocytes contained IV3 alpha(NeuGc alpha 2-8NeuGc)-Gg4Cer, which was characterized with a mass spectrum and mass chromatograms obtained by micro high-performance liquid chromatography-FAB/MS. The other major disialoganglioside was tentatively characterized to be II3 alpha-(NeuGc alpha-NeuGc)-Gg4Cer by sialidase treatment followed by TLC-immunostaining. A sialidase-susceptible monosialoganglioside, IV3 alpha NeuGc-Gg4Cer [GM1b(NeuGc)], had been reported to be characteristic of mouse immune tissues [Nakamura, K. et al. (1988) J. Biochem, 103, 201-208]. Taken together, the results suggest that the pathway from Gg4Cer to IV3 alpha(NeuGc alpha 2-8NeuGc)-Gg4Cer through GM1b(NeuGc) is quite active in mouse immune tissues.

Phorbol esters (TPA) and concanavalin A (ConA) are known to induce granulocyte-macrophage colony-stimulating factor (GM-CSF) production in murine thymoma EL-4 cells by mRNA stabilization. The role of the 3'-untranslated region (3'-UTR) in GM-CSF mRNA stabilization induced by TPA and ConA in EL-4 cells was examined by transfection studies using chloramphenicol acetyltransferase (CAT) constructions. The GM-CSF 3'-UTR contains a 63-nucleotide region at its 3' end with repeating ATTTA motifs which is responsible for mRNA degradation in a variety of cell types (Shaw, G., and Kamen, R. (1986) Cell 46, 659-666). We produced constructs containing most of the GM-CSF 3'-UTR (303 nucleotides, pRSV-CATgm) or the 3'-terminal AT-rich region (116 nucleotides, pRSV-CATau) and measured CAT enzyme activity and CAT mRNA after transient transfection into EL-4 and NIH 3T3 cells. Low levels of CAT activity were seen in both cells with either plasmid compared with levels of CAT activity obtained with pRSV-CAT. TPA treatment caused an approximately 10-fold increase in CAT activity and mRNA in EL-4 cells transfected with pRSV-CATgm. No increases were seen in EL-4 cells transfected with pRSV-CATau or pRSV-CAT. No response to TPA was detected in transfected NIH 3T3 cells, indicating that the response to TPA is relatively cell-specific. There was no increase in CAT activity after ConA treatment in EL-4 or NIH 3T3 cells transfected with any of the constructs suggesting that the GM-CSF 3'-UTR lacks elements that can respond alone to ConA. Nuclear run-on and actinomycin D chase experiments in EL-4 cells showed that TPA induces CAT activity via mRNA stabilization. By linker-substitution mutagenesis we show that TPA inducibility depends on a 60-nucleotide region of the 3'-UTR whose 5' end is located 160 nucleotides upstream of the 5' end of the AU-rich region.

Alkaline phosphatase (ALP) was secreted and expressed at the cell surface of the lymphoma A/63-2 cell line but not on another clone A/63-1 deriving from a single thymoma (A/63) induced by a wild-type Abelson-Moloney viral complex. The enzyme was heat-sensitive and strongly inhibited by L-p-bromotetramisole and L-homoarginine but not by L-phenylalanine. All these data indicated that this enzyme was most likely identical to the L/B/K ALP isoenzyme. Southern blot analysis showed that neither amplification nor polymorphism were responsible for the high expression of the ALP gene observed in A/63-2 cells. On the opposite, the mRNA transcripts of ALP were only detected in A/63-2 cells indicating that a modulation of the ALP gene transcription occurred which could be due to the insertion of the v-abl gene within or near the 5'-flanking region of the ALP promotor in A/63-2 cells. Butyrate strongly increased both the secretion and the expression of the enzyme on A/63-2 cell surface. This induction was strongly inhibited by cordycepin, an RNA biosynthesis inhibitor, and at a lesser degree by cycloheximide, a translation inhibitor suggesting that butyrate induction occurs both at the transcriptional and the translational level.

To investigate whether differential protein kinase C isozyme expression in phorbol ester-sensitive and -resistant EL4 thymoma cells could account for the difference in phorbol ester responsiveness, we purified and characterized isozymes from the two cell lines. In both cell types, two peaks of protein kinase C activity were resolved on hydroxylapatite following DEAE-cellulose and phenyl-Superose chromatography. Western blot analysis showed that the first peak corresponded to protein kinase C-beta and the second to protein kinase C-alpha. Two-dimensional phosphotryptic mapping of the purified alpha and beta isozymes did not reveal any reproducible differences between sensitive and resistant EL4 cells. Nor were any differences between the cell types observed in the cytosolic versus membrane localization of alpha and beta protein kinase C. Northern blot analysis showed the expression of mRNA for protein kinase C-alpha, -beta, -delta and -epsilon in both cell lines, and the absence of mRNA for gamma or zeta. Although no major differences in expression of alpha, beta, or delta mRNA between sensitive and resistant EL4 cells were detectable, expression of protein kinase C-epsilon mRNA in resistant cells was only 20-25% of that in sensitive. Western blot analysis with anti-protein kinase C-epsilon antibodies showed the presence of the epsilon-isozyme in sensitive cells and the absence of detectable amounts in resistant cells. Although protein kinase C-epsilon constitutes only a small portion of the total protein kinase C in sensitive cells, the possibility is raised that decreased protein kinase C-epsilon expression may contribute to the failure of resistant EL4 cells to respond to phorbol esters.

Phorbol esters, acting via activation of the protein kinase C family of protein serine/threonine kinases, are able to exert profound effects on various cellular functions. In this study, we used the EL4 thymoma cell line to study the potential role of "downstream" protein serine/threonine kinases in cellular responses to phorbol esters. In wild-type EL4 cells, addition of phorbol ester caused a rapid activation of kinase activity toward RRLSSLRA (S6P). This increased activity was maintained for at least 15 min but diminished to control levels by 60 min. Activation of a myelin basic protein (MBP) kinase was also seen in response to phorbol ester. In a variant EL4 cell line in which phorbol ester does not induce interleukin 2 transcription, phorbol ester failed to activate either the S6P kinase or MBP kinase. Partial purification of the activated S6P and MBP kinases from wild-type cells showed that they represent separate enzymes that are distinct from protein kinase C. Although the variant cells had reduced levels of protein kinase C as compared with the wild-type cells, the amount of membrane-bound enzyme increased in response to phorbol 12-myristate 13-acetate in both wild-type and variant cells. Treatment of intact cells with phorbol ester resulted in phosphorylation of some of the same protein substrates in both cell lines. Okadaic acid, a phosphatase inhibitor, increased S6P and MBP kinase activities in both wild-type and variant cells. Thus, phorbol ester failed to activate the S6P and MBP kinases in the variant cells even though these cells express activatable protein kinase C, S6P kinase, and MBP kinase. Two protein kinase inhibitors, staurosporine and H-7, inhibited the activity of all three kinases in vitro, while a peptide inhibitor (PKC 19-31) showed specificity for protein kinase C. In summary, these results suggest that activation of messenger-independent protein kinases may be critical for certain protein kinase C-dependent responses.

Amylases were purified and characterized from three amylase-producing human tumors. The relative molecular mass of the amylases was estimated to be 54 000 on sodium dodecyl sulfate/polyacrylamide gel electrophoresis, different from human salivary amylase (61 000 and 64 000) and human pancreatic amylase (60 000). The tumor amylases had completely identical antigenicities with human salivary and pancreatic amylases against antibody to human salivary amylase, while the intensity of the tumor amylases was less than 20% of that of human salivary and pancreatic amylases on single radial immunodiffusion. On isoelectric focusing, two of the three tumor amylases showed a major peak at pH 6.4, which corresponded to a major peak of human salivary amylase, the other showed a major peak at pH 6.4, which corresponded to a minor peak of human salivary amylase. The three tumor amylases showed similar amino acid composition, different from those of human salivary and pancreatic amylases. These findings suggest that tumor amylases have a tertiary structure similar to that of normal human amylases, but differ from them in amino acid composition.

Newborn C57BL mice exposed to RadLV at birth were followed and periodically sampled for thymus and bone marrow TdT activity. Tumors detected at or before 100 days had mostly low TdT levels. Large thymic lymphocytic tumors detected after 100 days had elevated total TdT content per gland. Serial samples showed a changing TdT pattern with time. The mid period shifted from low levels to normal-to-high levels for both TdT content and total TdT per gland. No unusual bone marrow TdT activity change preceded the appearance of thymomas. TdT marks a unique precursor cell highly sensitive to RadLV associated with lymphomagenesis. RadLV induced both TdT+ and TdT- thymic lymphomas and both types were found to occur after lymphoma initiation by injection of RadLV into newborns.

A DNA polymerase which was active with unprimed poly(dC) as a template was detected in the DNA polymerase alpha fraction from rat thymoma tissue. The activity was dependent on rGTP and associated with ribonucleotide polymerizing activity. The activity was partially sensitive to aphidicolin and dideoxy GTP and resistant to alpha-amanitin. Thus, this is a rat "replicase" which is very similar to that found in mouse cells. The replicase activity with poly(dT) or phage fd single stranded circular DNA was greatly enhanced by the mouse replicase-stimulating factor beyond the species difference.

The purification and kinetic characterization of an NAD(P)+-malic enzyme from 22aH mouse hepatoma mitochondria are described. The enzyme was purified 328-fold with a final yield of 51% and specific activity of 38.1 units/mg of protein by employing DEAE-cellulose chromatography and an ATP affinity column. Sephadex G-200 chromatography yielded a native Mr = 240,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major subunit with Mr = 61,000, suggesting a tetrameric structure, and also showed that the preparation contained less than 10% polypeptide impurities. Use of the ATP affinity column required the presence of MnCl2 and fumarate (an allosteric activator) in the elution buffers. In the absence of fumarate, the Michaelis constants for malate, NAD+, and NADP+ were 3.6 mM, 55 microM, and 72 microM, respectively; in the presence of fumarate (2 mM), the constants were 0.34 mM, 9 microM, and 13 microM, respectively. ATP was shown to be an allosteric inhibitor, competitive with malate. However, the inhibition by ATP displayed hyperbolic competitive kinetics with a KI (ATP) of 80 microM (minus fumarate) and 0.5 mM (plus 2 mM fumarate). The allosteric properties of the enzyme are integrated into a rationale for its specific role in the pathways of malate and glutamate oxidation in tumor mitochondria.

The number of cells from which murine thymic leukemias (thymomas) develop after neonatal injection with a mink cell focus-inducing recombinant virus was studied in AKR mice heterozygous at the X-linked phosphoglycerate kinase (PGK) locus. Because only one of the two X-chromosomes is active in XX somatic cells, thymic leukemias that are clonal should display either type A or type B PGK but not both, whereas those with a multicellular origin may exhibit both enzymes. In 23 of 25 animals studied, thymomas expressed exclusively (11 animals) or predominantly (12 animals) a single enzyme in contrast to normal tissue which expressed both enzyme types in approximately equal ratios. In the 12 thymomas expressing a minor enzyme component, the predominant enzyme in the original tumor always predominated in the thymomas arising in animals transplanted with the original tumors, indicating that this minor PGK component was not contributed by malignant cells. The results indicate that the great majority of recombinant virus-induced AKR leukemias are clonal.

The extent and distribution of alfa-naphthyl acetate esterase (ANAE) activity in both normal thymuses and thymuses or thymomas from patients with myasthenia gravis were investigated by enzyme histochemistry. In all a closely similar distribution of ANAE activity was recognizable. ANAE positive thymic lymphocytes were distributed preferentially at the cortico-medullary junction and in the medulla. Their numbers at these sites were higher in myasthenic patients than in normal adults (P less than 0.001) and lowest in fetuses. The relative numbers of cells showing both ANAE activity and EN-rosette-forming capacity was lower in thymocytes than peripheral lymphocytes but was increasing higher in thymuses from fetal, adult and myasthenic patients and in thymomas. These findings are discussed in relation to the stage of maturity of thymocytes and the importance of intrathymic immunological challenge in the attainment of these cells of functional properties usually acquired in the periphery.

The induction of ornithine decarboxylase (ODC) activity in lymphocytes is associated with activation and the initiation of cellular proliferation. ODC is also an essential component in tumor promotion. Phorbol myristic acetate (PMA) is a mitogen for lymphocytes, but can also promote tumor formation. Tumor promotion is linked to the generation of free radicals induced by PMA. Modulation of intracellular glutathione is associated lymphocyte activation and in protection of cells from damage due to oxygen radicals. We examined the interaction between ODC activity and intracellular glutathione concentrations in EL4 murine lymphoblastoid cells. The intracellular glutathione concentration could be augmented in EL4 cells when cultured with the cysteine delivery agents 2-oxothiazolidine 4-carboxylate (OTC) and 2-mercaptoethanol (2-ME) and suppressed with the gamma-glutamylcysteine synthetase inhibitor buthionine sulfoximine (BSO). OTC and 2-ME suppressed ODC activity in fresh serum and PMA-activated EL4 cells. BSO had no effect on ODC activity of EL4 cells cultured in the presence of PMA. While both OTC and 2-ME augmented the total intracellular glutathione concentration, PMA enhanced only the level of oxidized glutathione. To determine if the mechanism by which PMA or fresh serum altered intracellular glutathione and ODC activity was through the generation of oxygen radicals, EL4 cells were cultured with free radical scavengers. The nonpermeant electron acceptor potassium ferricyanide, and the H2O2 scavenger catalase, lowered ODC activity in both serum-stimulated and PMA-activated EL4 cells. Similarly, incubation of EL4 cells with either potassium ferricyanide or catalase elevated intracellular glutathione concentrations. These data suggest that (a) modulation of intracellular glutathione in the EL4 lymphoblastoid cell line alters ODC activity induced by fresh serum and by the mitogen PMA; (b) activation of EL4 cells by PMA alone alters intracellular glutathione metabolism, which may be associated with its role as a mitogen in lymphocyte activation; and (c) the generation of free radicals in EL4 cells may play a positive role in cellular activation.

Since evidence indicates that phorbol ester-induced production of interleukin 2 requires transcription, we investigated the possibility that the phorbol ester receptor acts directly in the nuclei of EL4 thymoma cells. Using a procedure that minimized plasma membrane contamination (as measured by 5'-nucleotidase activity) and maintained the integrity of the double nuclear membrane, we were unable to detect specific binding of [3H]phorbol 12,13-dibutyrate in nuclei of unstimulated cells. Treatment of cells with phorbol 12,13-dibutyrate (100 nM, 37 degrees C) for up to 6 h did not cause appearance of phorbol ester binding capacity in nuclei (4 +/- 8% of homogenate value; 5'-nucleotidase activity = 10 +/- 3%) despite translocation of 40% of the cytosolic binding capacity to the plasma membrane fraction. The failure to detect nuclear binding capacity in treated cells was not due to occupation of nuclear sites with unlabeled ligand; effective exchange binding was demonstrated by recovery of total homogenate binding capacity in treated cells of 82 +/- 13% of that in untreated cells. Treatment of isolated nuclei with DNase to liberate DNA binding proteins also failed to reveal any nuclear phorbol ester binding capacity. Assay of nuclei for protein kinase C enzymatic activity gave similar negative results. These data argue strongly against a direct action of the intact phorbol ester receptor (or the phorbol ester binding fragment) in the transcriptional activation of interleukin 2 in EL4 cells but cannot rule out the possibility of a role for the catalytic fragment.