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The autophosphorylation of specific tyrosine residues occurs in the cytoplasmic region of the insulin receptor (IR) upon insulin binding, and this in turn initiates signal transduction. The R3 subfamily (Ptprb, Ptprh, Ptprj and Ptpro) of receptor-like protein tyrosine phosphatases (RPTPs) is characterized by an extracellular region with 6-17 fibronectin type III-like repeats and a cytoplasmic region with a single phosphatase domain. We herein identified the IR as a substrate for R3 RPTPs by using the substrate-trapping mutants of R3 RPTPs. The co-expression of R3 RPTPs with the IR in HEK293T cells suppressed insulin-induced tyrosine phosphorylation of the IR. In vitro assays using synthetic phosphopeptides revealed that R3 RPTPs preferentially dephosphorylated a particular phosphorylation site of the IR: Y960 in the juxtamembrane region and Y1146 in the activation loop. Among four R3 members, only Ptprj was co-expressed with the IR in major insulin target tissues, such as the skeletal muscle, liver and adipose tissue. Importantly, the activation of IR and Akt by insulin was enhanced, and glucose and insulin tolerance was improved in Ptprj-deficient mice. These results demonstrated Ptprj as a physiological enzyme that attenuates insulin signalling in vivo, and indicate that an inhibitor of Ptprj may be an insulin-sensitizing agent. [ABSTRACT FROM AUTHOR]

The discovery of microRNAs (miRNAs) has revealed a new layer of gene expression regulation that affects many normal and pathologic biological systems. Among the malignancies affected by the dysregulation of miRNAs, there are cancers of lymphoid origin in which miRNAs are thought to have tumor suppressive or tumor promoting activities, depending on the nature of their specific targets. In the last four to five years, the experimental field that provided the deepest insights into the in vivo biology of miRNAs is that of mouse modeling, in which transgenic and knockout animals mimic over-expression or down-regulation, respectively, of specific miRNAs involved in human leukemia/lymphoma. This review discusses recent advances in our understanding of lymphoid malignancies based on the natural and engineered mouse models of three different miRNAs: miR-15a/16-1 cluster, miR-155, and miR-17-92 cluster. [ABSTRACT FROM AUTHOR]

Ptprj is a ubiquitously expressed murine gene encoding a receptor-type protein tyrosine phosphatase, which has recently been proposed as a candidate gene on the locus Scc1 for colon cancer susceptibility. It has been demonstrated that PTPRJ, the human homologue of Ptprj, is involved in the control of cell growth and adhesion, being furthermore altered in several types of cancer including mammary, thyroid, lung, colon, and pancreatic cancers. To investigate the biological functions of Ptprj, we have generated mice deficient in this receptor protein tyrosine phosphatase. Ptprj-deficient mice are viable, fertile, and show no gross anatomical alterations. Furthermore, neither changes in life span nor spontaneous tumor appearance were observed in Ptprj-null mice. Our results indicate that Ptprj is dispensable for normal growth and development in mice. [ABSTRACT FROM AUTHOR]

The WWOX (WW domain containing oxidoreductase) gene at the common fragile site, FRA16D, is altered in many types of cancer, including lung cancer. We have examined the tumor suppressor function of WWOX in preclinical lung cancer models. The WWOX gene was expressed in lung cancer cell lines through recombinant adenovirus (Ad) infection (Ad-WWOX), and through a drug [ponasterone A, (ponA)]-inducible system. After WWOX restoration in vitro, endogenous WWOX protein-negative cell lines (A549, H460, and H1299) underwent apoptosis through activation of the intrinsic apoptotic caspase cascade in A549 and H460 cells. Ectopic expression of WWOX caused dramatic suppression of tumorigenicity of A549, H460, and H1299 cells in nude mice after Ad-WWOX infection and after ponA induction of WWOX expression in H1299 lung cancer cells. Tumorigenicity and in vitro growth of U2020 (WWOX-positive) lung cancer cells was unaffected by WWOX overexpression. This study confirms that WWOX is a tumor suppressor gene and is highly effective in preventing growth of lung cancer xenografts, whether introduced through viral infection or by induction of a silent WWOX transgene. [ABSTRACT FROM AUTHOR]

The Testin (TES) gene was previously identified as a putative human tumor suppressor gene at 7q31.2, a region that is frequently deleted in hematopoietic malignancies, as well as in epithelial tumors. To determine whether TES acts as a tumor suppressor in vivo, we generated a Tes knockout mouse and then used it in an established model of carcinogen-induced gastric cancer. In mice a zinc-deficient (ZD) diet enhances cellular proliferation in the forestomach and susceptibility to N-nitrosomethyl- benzylamine (NMBA)-induced carcinogenesis. Five-week-old Tes wild-type (+/+), heterozygous (+/-). and homozygous (-/-) mice were divided into four groups: mice fed a zinc-sufficient diet (ZS); mice fed a ZD diet ZS fed plus NMBA-treated mice (ZS+NMBA), and ZD fed plus NMBA-treated mice (ZD+NMBA). After 4 weeks, the ZS+ NMBA and ZD+ NMBA groups were treated with three intragastric doses of NMBA. Animals were killed 8 weeks after NMBA administration: 25% of +/+ mice developed benign lesions; 88% of +/- showed multiple papillomas, atypical glandular metaplasia, and squamous cell carcinomasl; and 81 % of -/- mice displayed very large papillomas, squamous cell carcinomas, and adenocarcinomas. A statistically significant difference in tumor incidence was found between +/- versus +/+ and -/- versus +/+ (P < 0.0001). These data suggest that Tes functions as a tumor suppressor gene in vivo. [ABSTRACT FROM AUTHOR]

The expression of the receptor protein tyrosine phosphatase r-PTP?is drastically reduced in rat and human malignant thyroid cells, whereas its restoration reverts the neoplastic phenotype of retrovirally transformed rat thyroid cells. Moreover, reduced levels and loss of heterozygosity of DEP-1, the human homolog of r-PTP?, have been found in many human neoplasias. Here, we report that the r-PTP?protein binds to c-Src in living cells and dephosphorylates the c-Src inhibitory tyrosine phosphorylation site (Tyr 529), thereby increasing c-Src tyrosine kinase activity in malignant rat thyroid cells stably transfected with r-PTP?. Tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin was enhanced in r-PTP?-expressing cells. This was associated with increased adhesion of malignant r-PTP?-transfected thyroid cells vs both untransfected cells and cells stably transfected with an inactive r-PTP?mutant. Treatment of rat thyroid cells with the c-Src inhibitor PP2 decreased cell adhesion to a higher extent in r-PTP?-transfected cells than in mock-transfected or stably transfected cells with the inactive r-PTP?mutant, indicating that r-PTP?regulates cell-substratum adhesion by activating c-Src. Interestingly, the extent of both c-Src dephosphorylation at Tyr 529, FAK and paxillin phosphorylation, and the increased cell adhesion were associated with the degree of r-PTP?expression.Oncogene (2005) 24, 3187-3195. doi:10.1038/sj.onc.1208510 Published online 21 February 2005 [ABSTRACT FROM AUTHOR]

Common fragile sites are regions that show elevated susceptibility to DNA damage, leading to alterations that can contribute to cancer development. FRA3B, located at chromosome region 3p14.2, is the most frequently expressed human common fragile site, and allelic losses at FRA3B have been observed in many types of cancer. The FHIT gene, encompassing the FRA3B region, is a tumorsuppressor gene. To identify the features of FHIT/FRA3B that might contribute to fragility, sequences of the human FHIT and the flanking PTPRG gene were compared with those of murine Fhitand Ptprg. Human and mouse orthologous genes, FHIT and Fhit, are more highly conserved through evolution than PTPRG/Ptprg and yet contain more sequence elements that are exquisitely sensitive to genomic rearrangements, such as high-flexibility regions and long interspersed nuclear element 1s, suggesting that common fragile sites serve a function. The conserved AT-rich high-flexibility regions are the most characteristic of common fragile sites. [ABSTRACT FROM AUTHOR]

In an effort to identify tumor suppressor gene(s) associated with the frequent loss of heterozygosity observed on chromosome 6q25-q27, we constructed a contig derived from the sequences of bacterial artificial chromosome/P1 bacteriophage artificial chromosome clones defined by the genetic interval D6S1581-D6S1579D6S305-D6S1599-D6S1008. Sequence analysis of this contig found it to contain eight known genes, including the complete genomic structure of the Parkin gene. Loss of heterozygosity (LOH) analysis of 40 malignant breast and ovarian tumors identified a common minimal region of loss, including the markers D6S305 (50%) and D6S1599 (32%). Both loci exhibited the highest frequencies of IOH in this study and are each located within the Parkin genomic structure. Whereas mutation analysis revealed no missense substitutions, expression of the Parkin gene appeared to be downregulated or absent in the tumor biopsies and tumor cell lines examined. In addition, the identification of two truncating deletions in 3 of 20 ovarian tumor samples, as well as homozygous deletion of exon 2 in the lung adenocarcinoma cell lines Calu-3 and H-1573, supports the hypothesis that hemizygous or homozygous deletions are responsible for the abnormal expression of Parkin in these samples. These data suggest that the LOH observed at chromosome 6q25-q26 may contribute to the initiation and/or progression of cancer by inactivating or reducing the expression of the Parkin gene. Because Parkin maps to FRA6E, one of the most active common fragile sites in the human genome, it represents another example of a large tumor suppressor gene, like FHIT and WWOX, located at a common fragile site. [ABSTRACT FROM AUTHOR]

The FHIT gene is inactivated early in the development of many human tumors, and Fhit-deficient mice have increased cancer incidence. Viral reexpression of Fhit kills Fhit-deficient cells by induction of apoptosis. Fhit, a member of branch 2 of the histidinetriad superfamily of nucleoside monophosphate hydrolases and transferases, is a diadenosine polyphosphate hydrolase, the activesite histidine of which is not required for tumor suppression. To provide a rigorous test of the hypothesis that Fhit function depends on forming a complex with substrates, we designed a series of alleles of Fhit intended to reduce substrate-binding and/or hydrolytic rates, characterized these mutants biochemically, and then performed quantitative cell-death assays on cancer cells virally infected with each allele. The allele series covered defects as great as 100,000-fold in k[sub cat] and increases as large as 30-fold in K[sub M]. Nonetheless, when mutant FHIT genes were expressed in two human cancer ceil lines containing FHIT deletions, reductions in apoptotic activity correlated exclusively with K[sub M]. Mutants with 2and 7-fold increases in K[sub M] significantly reduced apoptotic indices, whereas the mutant with a 30-fold increase in K[sub M] retained little cellular function. These data indicate that the proapoptotic function of Fhit is limited by substrate binding and is unrelated to substrate hydrolysis. [ABSTRACT FROM AUTHOR]

Examines the role of gene maps to chromosome 8p22 for the suppression of cancer cell growth. Regulation of cell mitosis; Fractionation state of cellular protein; Evaluation of the protein-protein interaction.

Clarifies the role of tumor suppressor gene FHIT in cancer development. Ability to inhibit tumor development by oral gene transfer; Potential of FHIT gene therapy as a novel clinical approach not only for treatment of early stages of cancer but also in prevention of human cancer.

The dual-specificity phosphatase PTEN/MMAC1/TEP1 has recently been identified as the tumor suppressor gene most frequently mutated and/or deleted in human tumors. Germline mutations of PTEN give rise to Cowden Disease (CD), an autosomal dominantly-inherited cancer syndrome which predisposes to increased risk of developing breast and thyroid tumors. However, PTEN mutations have rarely been detected in sporadic thyroid carcinomas. In this study, we confirm that PTEN mutations in sporadic thyroid cancer are infrequent as we found one point mutation and one heterozygous deletion of PTEN gene in 26 tumors and eight cell lines screened. However, we report that PTEN expression is reduced – both at the mRNA and at the protein level – in five out of eight tumor-derived cell lines and in 24 out of 61 primary tumors. In most cases, decreased PTEN expression is correlated with increased phosphorylation of the PTEN-regulated protein kinase Akt/PKB. Moreover, we demonstrate that PTEN may act as a suppressor of thyroid cancerogenesis as the constitutive re-expression of PTEN into two different thyroid tumor cell lines markedly inhibits cell growth. PTEN-dependent inhibition of BrdU incorporation is accompanied by enhanced expression of the cyclin-dependent kinase inhibitor p27kip1 and can be overcome by simultaneous co-transfection of an excess p27kip1 antisense plasmid. Accordingly, in a subset of thyroid primary carcinomas and tumor-derived cell lines, a striking correlation between PTEN expression and the level of p27kip1 protein was observed. In conclusion, our findings demonstrate that inactivation of PTEN may play a role in the development of sporadic thyroid carcinomas and that one key target of PTEN suppressor activity is represented by the cyclin-dependent kinase inhibitor p27kip1. Oncogene (2000) 19, 3146–3155 [ABSTRACT FROM AUTHOR]

The metabolism of T-lymphocytes has recently emerged as a pivotal area of investigation, offering insights into the supra-genic modulations that can influence the genetic mechanisms underlying lymphocyte clustering processes. Furthermore, it has become a crucial aspect in understanding lymphocyte plasticity within the immune microenvironment, both in physiological and pathological contexts. T-lymphocyte metabolism has recently emerged as a pivotal factor in both targeted therapy and the genetic signature of the T-lymphocyte, as a result of its influence on gatekeeper processes. From this perspective, the interconnections between the metabolic processes traditionally associated with energy production and the capacity to influence the genetic fate of the T lymphocyte have identified purine metabolism and nuclear/cytoplasmic signaling as pivotal elements in comprehending the intricacies of these molecular phenomena. The two aspects of purine metabolism and metabolic/molecular control of the nuclear envelope have been the subject of a number of significant studies published in recent years. However, from a certain perspective, the existing evidence remains sparse and inconclusive, hindering a comprehensive understanding of the subject matter. In this review, we endeavor to establish a connection between these aspects for the first time and to present a review of the molecular, immunological and genetic events that determine how these aspects, which have hitherto received insufficient attention, may represent a new avenue for lymphocyte reprogramming in the therapeutic field. This will be achieved by understanding the connections between nuclear control and purine flux within and outside the cell. [ABSTRACT FROM AUTHOR]

The CD4+ T‐cell population plays a vital role in the adaptive immune system by coordinating the immune response against different pathogens. A significant transformation occurs in CD4+ cells during an immune response, as they shift from a dormant state to an active state. This transformation leads to extensive proliferation, differentiation, and cytokine production, which contribute to regulating and coordinating the immune response. Th17 and Treg cells are among the most intriguing CD4+ T‐cell subpopulations in terms of genetics and metabolism. Gene expression modulation processes rely on and are linked to metabolic changes in cells. Lactylation is a new model that combines metabolism and gene modulation to drive Th17/Treg differentiation and functional processes. The focus of this review is on the metabolic pathways that impact lymphocyte gene modulation in a functionally relevant manner. [ABSTRACT FROM AUTHOR]