Search

Gene variations in GAGA samples Single

Immunoblot and Annexin V assays of GAGA6 and GAGA6-R PDX tumors after drug treatment with AZD4547, sunitinib or 1-AKP.

Preclinical models of diffuse-type gastric cancer (DGC) that reliably predict clinical activity of novel compounds are lacking. To overcome the problem of poor tumor cellularity in DGC, we used cells from malignant ascites to establish DGC patient-derived xenograft (PDX) models that recapitulate the primary cancer. Cells in PDX model GAGA6 with FGFR2 amplification were sensitive to AZD4547, a potent FGFR inhibitor that is being clinically evaluated for FGFR-aberrant cancer types. Intermittent in vivo treatment of GAGA6 tumors with AZD4547 gave rise to PDX tumors with acquired resistance to AZD4547, GAGA6-R. Surprisingly, there were no mutations in the FGFR2 gene in GAGA6-R, negating gatekeeper mutations as a mechanism of drug resistance. Phosphorylation of FGFR2 and downstream signaling molecules AKT/PKB and MAPK/ERK remained inhibited by AZD4547. Further analysis of signaling pathways identified AKT-independent phosphorylation and inhibition of GSK3β as a mechanism of drug resistance in GAGA6-R cells. Treatment of GAGA6-R cells with protein kinase C (PKC) inhibitor H7 in combination with AZD4547 led to dephosphorylation and activation of GSK3β with concomitant downregulation of MCL-1 and BCL-XL. Combined treatment with AZD4547 and H7 in vitro synergistically enhanced cell death in GAGA6-R but not GAGA6 cells. Furthermore, midostaurin, a multikinase inhibitor with PKC-inhibiting activity, in part reversed resistance of GAGA6-R tumor to AZD4547 in vivo. Our results suggest that upon challenge with FGFR inhibitors, FGFR2-amplified tumors that are highly dependent on FGFR2 signaling for survival rapidly develop resistance by switching to a PKC-mediated inhibition of GSK3β to gain a survival advantage. Mol Cancer Ther; 17(1); 232–42. ©2017 AACR.

PDF file - 130KB, Supplementary Figure S3 shows fractionation of CD44v+ cells for limiting dilution analysis in vitro and in vivo.

PDF file - 20KB, Supplementary Table S1 shows patient clinical information.

PDF file - 36KB

PDF file - 24KB, Supplementary Table S3 shows effects of CD44 variant over-expression and knockdown on tumor initiation potential.

PDF file - 25KB, Supplementary Table S2 shows estimation of CSC frequency in unsorted, EpCAM+CD133+ and EpCAM+CD133- fractions from GC16 xenografts.

PDF file - 118KB, Supplementary Figure S1 shows gating strategies for flow cytometry, quantitation for EpCAM expression level and EpCAM+ cells initiated tumors in mice.

PDF file - 33KB

PDF file - 20KB, Supplementary Table S4 shows p53 mutation status and proportion of CD44+ cells in gastric tumor xenografts.

PDF file - 126KB, Supplementary Figure S2 shows characterization of CD44v8-10 antibody by flow cytometry and gating strategy and isotype control for Figure 3.

PDF file - 93KB, Supplementary Figure S4 shows gating strategy for sorting of CD44 depleted TMK1 cells for tumor initiation assay and xenograft tumors formed.

Multiple three-dimensional (3D) tumour organoid models assisted by multi-omics and Artificial Intelligence (AI) have contributed greatly to preclinical drug development and precision medicine. The intrinsic ability to maintain genetic and phenotypic heterogeneity of tumours allows for the reconciliation of shortcomings in traditional cancer models. While their utility in preclinical studies have been well established, little progress has been made in translational research and clinical trials. In this review, we identify the major bottlenecks preventing patient-derived tumour organoids (PDTOs) from being used in clinical setting. Unsuitable methods of tissue acquisition, disparities in establishment rates and a lengthy timeline are the limiting factors for use of PDTOs in clinical application. Potential strategies to overcome this include liquid biopsies via circulating tumour cells (CTCs), an automated organoid platform and optical metabolic imaging (OMI). These proposed solutions accelerate and optimize the workflow of a clinical organoid drug screening. As such, PDTOs have the potential for potential applications in clinical oncology to improve patient outcomes. If remarkable progress is made, cancer patients can finally benefit from this revolutionary technology.

Pancreatic ductal adenocarcinoma (PDAC) is the most aggressive solid tumor. Unfortunately, patients with this disease have not benefited from the advances in precision medicine seen in other malignancies. The lack of actionable mutations as well as predictive biomarkers has hampered progress in this area. Combination therapy remains the cornerstone of systemic treatment, with FOLFIRINOX being the most effective therapeutic regimen in PDAC. However, it is clear that only subset of patients are responsive, and the toxicities of this 4-drug combination are intolerable to many patients particularly in the adjuvant setting. There is a clear need for more personalized rational drug combinations that are optimized to maximize efficacy while minimizing toxicity. We have established a protocol for the generation of PDAC organoids from endoscopic ultrasound biopsies for personalizing systemic therapy based on the principle of phenotype driven oncology. Organoids generated are analyzed for KRAS and p53 mutations to confirm their tumor origin. By applying a phenotypic optimization platform (QPOP) on these organoids, we are able to identify optimized drug combinations from a pool of both FDA-approved and preclinical drugs. As expected, FOLFIRINOX did not always rank high by treatment efficacy suggesting that alternative treatment may be more beneficial for these patients. In addition, we identified that the efficacy of FOLFIRINOX was driven by two-drug synergistic combinations which varied between patients. This can potentially advise modifications to this regimen when toxicity arises. From a discovery perspective, our platform has the capability of deriving novel drug combinations. The combination of gemcitabine and Abraxane with a WEE1-inhibitor was found to be synergistic in selected PDAC patients. Furthermore, patients with similar drug response profiles can be studied together to identify predictive markers of sensitivity. To demonstrate that this platform can indeed be applied to prospectively recommend treatment strategies for patients with progressive disease on first-line chemotherapy, we are establishing a clinical trial to personalize second-line therapy, with the endpoint of overall response rate. Overall, by combining patient-derived organoids with rational optimized drug combinations, we aim to personalize therapy for patients with PDAC to improve overall survival. Citation Format: Claire Alexandra Zhen Chew, Li Min Tay, Lissa Hooi, Edward Kai-Hua Chow, Glenn K. Bonney, Shing Leng Chan. Patient-derived pancreatic cancer organoids as in-vitro cancer models for personalizing therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3929.

Preclinical models of diffuse-type gastric cancer (DGC) that reliably predict clinical activity of novel compounds are lacking. To overcome the problem of poor tumor cellularity in DGC, we used cells from malignant ascites to establish DGC patient-derived xenograft (PDX) models that recapitulate the primary cancer. Cells in PDX model GAGA6 with FGFR2 amplification were sensitive to AZD4547, a potent FGFR inhibitor that is being clinically evaluated for FGFR-aberrant cancer types. Intermittent in vivo treatment of GAGA6 tumors with AZD4547 gave rise to PDX tumors with acquired resistance to AZD4547, GAGA6-R. Surprisingly, there were no mutations in the FGFR2 gene in GAGA6-R, negating gatekeeper mutations as a mechanism of drug resistance. Phosphorylation of FGFR2 and downstream signaling molecules AKT/PKB and MAPK/ERK remained inhibited by AZD4547. Further analysis of signaling pathways identified AKT-independent phosphorylation and inhibition of GSK3β as a mechanism of drug resistance in GAGA6-R cells. Treatment of GAGA6-R cells with protein kinase C (PKC) inhibitor H7 in combination with AZD4547 led to dephosphorylation and activation of GSK3β with concomitant downregulation of MCL-1 and BCL-XL. Combined treatment with AZD4547 and H7 in vitro synergistically enhanced cell death in GAGA6-R but not GAGA6 cells. Furthermore, midostaurin, a multikinase inhibitor with PKC-inhibiting activity, in part reversed resistance of GAGA6-R tumor to AZD4547 in vivo. Our results suggest that upon challenge with FGFR inhibitors, FGFR2-amplified tumors that are highly dependent on FGFR2 signaling for survival rapidly develop resistance by switching to a PKC-mediated inhibition of GSK3β to gain a survival advantage. Mol Cancer Ther; 17(1); 232–42. ©2017 AACR.

ZBTB transcription factors orchestrate gene transcription during tissue development. However, their roles in glioblastoma (GBM) remain unexplored. Here, through a functional screening of ZBTB genes, we identify that BCL6 is required for GBM cell viability and that BCL6 overexpression is associated with worse prognosis. In a somatic transgenic mouse model, depletion of Bcl6 inhibits the progression of KrasG12V-driven high-grade glioma. Transcriptome analysis demonstrates the involvement of BCL6 in tumor protein p53 (TP53), erythroblastic leukemia viral oncogene homolog (ErbB), and MAPK signaling pathways. Indeed, BCL6 represses the expression of wild-type p53 and its target genes in GBM cells. Knockdown of BCL6 augments the activation of TP53 pathway in response to radiation. Importantly, we discover that receptor tyrosine kinase AXL is a transcriptional target of BCL6 in GBM and mediates partially the regulatory effects of BCL6 on both MEK-ERK (mitogen-activated protein/extracellular signal-regulated kinase kinase-extracellular signal-regulated kinase) and S6K-RPS6 (ribosomal protein S6 kinase-ribosomal protein S6) axes. Similar to BCL6 silencing, depletion of AXL profoundly attenuates GBM proliferation both in vitro and in vivo. Moreover, targeted inhibition of BCL6/nuclear receptor corepressor 1 (NCoR) complex by peptidomimetic inhibitor not only significantly decreases AXL expression and the activity of MEK-ERK and S6K-RPS6 cascades but also displays a potent antiproliferative effect against GBM cells. Together, these findings uncover a glioma-promoting role of BCL6 and provide the rationale of targeting BCL6 as a potential therapeutic approach.

SUMMARY RUNX3 functions as a tumor suppressor in the gastric epithelium, where its inactivation is frequently observed during carcinogenesis. We identified IL23A as a RUNX3 target gene in gastric epithelial cells. This was confirmed in a series of in vitro analyses in gastric epithelial cell lines. In elucidating the underlying regulatory network, we uncovered a prominent role for the TNF-α/NF-κB pathway in activating IL23A transcription. Moreover, the activating effect of TNF-α was markedly augmented by the infection of Helicobacter pylori, the primary cause of human gastritis. Of note, H. pylori utilized the CagA/SHP2 pathway to activate IL23A, as well as the induction of the NOD1 pathway by iE-DAP. Importantly, RUNX3 synergized strongly with these physiologically relevant stimuli to induce IL23A. Lastly, we present evidence for the secretion of IL23A by gastric epithelial cells in a form that is distinct from canonical IL-23 (IL23A/IL12B).

The surface marker CD44 has been identified as one of several markers associated with cancer stem cells (CSC) in solid tumors, but its ubiquitous expression in many cell types, including hematopoietic cells, has hindered its use in targeting CSCs. In this study, 28 paired primary tumor and adjacent nontumor gastric tissue samples were analyzed for cell surface protein expression. Cells that expressed pan-CD44 were found to occur at significantly higher frequency in gastric tumor tissues. We identified CD44v8-10 as the predominant CD44 variant expressed in gastric cancer cells and verified its role as a gastric CSC marker by limiting dilution and serial transplantation assays. Parallel experiments using CD133 failed to enrich for gastric CSCs. Analyses of another 26 primary samples showed significant CD44v8-10 upregulation in gastric tumor sites. Exogenous expression of CD44v8-10 but not CD44 standard (CD44s) increased the frequency of tumor initiation in immunocompromised mice. Reciprocal silencing of total CD44 resulted in reduced tumor-initiating potential of gastric cancer cells that could be rescued by CD44v8-10 but not CD44s expression. Our findings provide important functional evidence that CD44v8-10 marks human gastric CSCs and contributes to tumor initiation, possibly through enhancing oxidative stress defense. In addition, we showed that CD44v8-10 expression is low in normal tissues. Because CD44 also marks CSCs of numerous human cancers, many of which may also overexpress CD44v8-10, CD44v8-10 may provide an avenue to target CSCs in other human cancers. Cancer Res; 74(9); 2630–41. ©2014 AACR.

Diffuse-type gastric cancer (DGC) is a histologic subtype characterized by poor cellular cohesiveness, increased metastasis and poor prognosis. As preclinical models of DGC that reliably predict clinical activity of novel compounds are lacking, we generated patient-derived xenograft (PDX) models using malignant ascites from DGC patients that closely recapitulated the primary cancer. To uncover novel therapeutic targets, we applied the concept of synthetic lethality and asked if DGCs require DNA repair proteins for survival. Major DNA repair kinases ATM, ATR and DNA-PKcs in established DGC cell lines and ex vivo cell lines from PDXs (GAGA3, GAGA6 and GAS24) were inhibited using small-molecule inhibitors KU55933, VE-821 and KU60648, respectively. Interestingly, most diffuse-type gastric cells exhibited elevated lethality when DNA-PKcs, a central kinase that regulates the non-homologous end joining pathway (NHEJ), was inhibited by KU60648 as compared to the nontransformed gastric epithelial line, HFE-145. We confirmed that genetic depletion of DNA-PKcs by siRNA resulted in cell death in two PDX lines GAS24 and GAGA6 cells but not in HFE-145 cells, suggesting the dependence of these cells on DNA-PKcs for survival. Two mechanisms appear to sensitize DGC cells to DNA-PKcs inhibition; firstly, impaired homologous recombination repair in GAS24 and GAGA6 as shown by compromised ability to resolve radiation-induced γH2AX foci, and secondly, transcriptional downregulation of the mismatch repair protein, MSH6, in GAGA3 and GAGA6. Knockdown of MSH6 in GAS24 cells enhanced their sensitivity to KU60648, suggesting a functional link between MSH6 and DNA-PK function. Lastly, to develop MSH6 as a biomarker for predicting DNA-PKcs sensitivity, we analyzed MSH6 levels by immunohistochemical staining in formalin-fixed, paraffin-embedded (FFPE) tissue sample sections derived from PDXs. In these preliminary studies, MSH6 expression was lower with high heterogeneity in GAGA3 and GAGA6 compared to GAS24. In this study, we show for the first time the downregulation of DNA mismatch protein MSH6 in sporadic diffuse gastric cancer, and its potential as a therapeutic predictor for DNA-PKcs inhibition treatment. Citation Format: Vaidehi Krishnan, Wen Min Lau, Eileen Teng, Jin Wei Tan, Haresh Sankar, Debbie Xiu En Lim, Crystal Kok Yan Pang, Ming Teh, Jimmy Bok Yan So, Patrick Tan, Yoshiaki Ito, Shing Leng Chan. Loss of mismatch repair protein MSH6 sensitizes diffuse-type gastric cancer cells to DNA-PKcs inhibitor KU60648 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1570.

Introduction: Gastric cancer is a leading cause of global cancer mortality with an overall 5-year survival rate of approximately 20% and is particularly prevalent in many Asian countries. ASC amino acid transporter 2 (ASCT2), also known as SLC1A5, is a Na+-dependent glutamine/neutral amino acid transporter. ASCT2 acts as a high-affinity transporter of L-glutamine (Gln) and has been reported to be upregulated in a variety of cancerous tissues, including stomach. Several studies have shown that glutamine is a major nutrient contributing to cancer cell growth, so the glutamine metabolism pathway is an attractive target for gastric cancer treatment. In this study, we evaluated the efficacy of a novel anti-ASCT2 humanized monoclonal antibody, KM8094, as a therapeutic agent against gastric cancer and explored predictive biomarker candidates using patient-derived xenograft (PDX) mouse models. Materials and Methods: The tumor tissues from which the PDX models were generated were provided by Dr. Chan Shing Leng (NUS, Singapore). For the glutamine uptake assay, PDX-tumor cells were incubated with 3H-glutamine in the presence of KM8094. Intracellular 3H-glutamine was measured by liquid scintillation spectrophotometry. In vitro ADCC activity against human gastric cancer cells (SNU-16) was evaluated using human peripheral blood mononuclear cells (PBMC) from either gastric cancer patients or healthy controls as effector cells. In vivo antitumor activity of KM8094 was examined using PDX models. Mice were treated with KM8094 at 10 mg/kg i.v. or phosphate-buffered saline once weekly for 2-3 weeks. Finally, omics analyses of PDX tumor tissues were performed via a gene expression array analysis, DNA methylation array analysis, and metabolomics analysis. Results: All five gastric cancer PDX models histologically expressed ASCT2. KM8094 significantly inhibited the 3H-glutamine uptake in vitro and showed in vivo antitumor efficacy in the gastric cancer PDX models. In addition, KM8094 showed in vitro ADCC activity against gastric cancer cells using PBMCs from gastric cancer patients. These results indicated that KM8094 is a potential new therapeutic agent for gastric cancer treatment. Finally, we explored predictive biomarker candidates of KM8094 by a multi-omics analysis on the PDX models, and a few candidates were selected by genomic analyses. In addition, a metabolomics analysis revealed clear differences in the intracellular energy and redox status between responsive and nonresponsive PDX models. Conclusions: These results demonstrated the therapeutic potential of KM8094 for the treatment of gastric cancer and provide some insight into predictive biomarker candidates for antitumor efficacy. Citation Format: Noriyuki Kasai, Aya Sasakawa, Kenta Hosomi, Tze Wei Poh, Bernadette Lynn Chua, Wei Peng Yong, Jimmy So, Shing Leng Chan, Richie Soong, Koji Kono, Toshihiko Ishii, Kazuya Yamano. Evaluation of a novel monoclonal antibody targeting ASC amino acid transporter 2 using patient-derived xenograft mouse models of gastric cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B035.

Evasion of apoptosis plays an important role in colon cancer progression. Following loss of the Apc tumor suppressor gene in mice, the gene encoding Fem1b is upregulated early in neoplastic intestinal epithelium. Fem1b is a pro-apoptotic protein that interacts with Fas, TNFR1 and Apaf-1, and increased expression of Fem1b induces apoptosis of cancer cells. Fem1b is a homolog of FEM-1, a protein in Caenorhabditis elegans that is negatively regulated by ubiquitination and proteasomal degradation. To study Fem1b regulation in colon cancer progression, we used apoptotis-sensitive SW480 cells, derived from a primary colon cancer, and their isogenic, apoptosis-resistant counterparts SW620 cells, derived from a subsequent metastatic lesion in the same patient. Treatment with proteasome inhibitor increased Fem1b protein levels in SW620 cells, but not in SW480 cells. In SW620 cells we found that endogenous Fem1b co-immunoprecipitates in complexes with RACK1, a protein known to mediate ubiquitination and proteasomal degradation of other pro-apoptotic proteins and to be upregulated in colon cancer. Full-length Fem1b, or the N-terminal region of Fem1b, associated with RACK1 when co-expressed in HEK293T cells, and RACK1 stimulated ubiquitination of Fem1b. RACK1 overexpression in SW620 cells led to downregulation of Fem1b protein levels. Conversely, downregulation of RACK1 led to upregulation of Fem1b protein levels, associated with induction of apoptosis, and this apoptosis was inhibited by blocking Fem1b protein upregulation. In conclusion, RACK1 downregulates levels of the pro-apoptotic protein Fem1b in metastatic, apoptosis-resistant colon cancer cells, which may promote apoptosis-resistance during progression of colon cancer.

Valproic acid (VPA) is a histone deacetylase inhibitor previously shown to promote the proliferation and self-renewal of CD34(+) hematopoietic cells. We tested the effect of VPA in conjunction with the selective amplification technology developed by Viacell Inc. Stem cells enriched from frozen cord blood were cultured for 7 d, subjected to reselection and grown in fresh medium for a further 7 d. Treatment with VPA resulted in an average two-fold higher expansion of CD45(+)34(+) cells compared with control. Furthermore, VPA-treatment induced higher numbers of CD45(+)34(+) cells to reside in the S phase than control cultured cells and resulted in a 2.5-fold upregulation in HOXB4 expression. Importantly, VPA-treated cells reconstituted hematopoiesis in non-obese diabetic/severe combined immunodeficient mice with a six-fold higher efficiency than control cells. Collectively, our results indicate that VPA, already used clinically for neurologic disorder treatment, is a useful additive for the ex vivo culture of hematopoietic stem/progenitor cells to enhance engraftment efficiency.

The ratio of the levels of pro-survival and pro-apoptotic members of the Bcl-2 protein family is thought to be an important regulatory factor for determining the sensitivity of the mammalian cells to apoptotic stimuli. High levels of expression of pro-survival members such as Bcl(XL) in human cancers were frequently found to be a good prognostic indicator predicting poor response to chemotherapy. The pro-survival members of the Bcl-2 family mediate their effects through heterodimerization with the BH3 region of the pro-apoptotic members. Structural analyses of the binding complex of the BH3 peptide and Bcl(XL) showed that a hydrophobic groove termed the BH3 binding cleft is the docking site for the BH3 region. Chemical mimetics of the BH3 region such as BH3I-1 that target the BH3 binding cleft indeed exhibit pro-apoptotic activities. Chelerythrine (CHE) and sanguinarine (SAN) are natural benzophenanthridine alkaloids that are structurally homologous to each other. CHE was previously identified as an inhibitor of Bcl(XL) function from a high-throughput screen of natural products, but its mode of interaction with Bcl(XL) is not known. By determining the effect of site-directed mutagenesis on ligand binding and using saturation transfer difference (STD) NMR experiments, we have verified locations of these docked ligands. Surprisingly, CHE and SAN bind separately at the BH groove and BH1 region of Bcl(XL) respectively, different from the BH3 binding cleft where other known inhibitors of Bcl(XL) target. Interestingly, certain residues on the flexible loop between helices alpha1 and alpha2 of Bcl(XL) are also perturbed upon CHE, but not SAN or BH3I-1 binding. Although CHE and SAN are similarly effective as BH3I-1 in displacing bound BH3 peptide, they are much more effective in inducing apoptosis, raising the possibility that CHE and SAN might be able to antagonize other pro-survival mechanisms in addition to the one that involves BH3 region binding.

Apoptotic stimuli induce conformational changes in Bax and trigger its translocation from cytosol to mitochondria. Upon assembling into the mitochondrial membrane, Bax initiates a death program through a series of events, culminating in the release of apoptogenic factors such as cytochrome c . Although it is known that Bax is one of the key factors for integrating multiple death signals, the mechanism by which Bax functions in mitochondria remains controversial. We have previously identified modulator of apoptosis-1 (MAP-1) as a Bax-associating protein, but its functional relationship with Bax in contributing to apoptosis regulation remains to be established. In this study, we show that MAP-1 is a critical mitochondrial effector of Bax. MAP-1 is a mitochondria-enriched protein that associates with Bax only upon apoptotic induction, which coincides with the release of cytochrome c from mitochondria. Small interfering RNAs that diminish MAP-1 levels in mammalian cell lines confer selective inhibition of Bax-mediated apoptosis. Mammalian cells with stable expression of MAP-1 small interfering RNAs are resistant to multiple apoptotic stimuli in triggering apoptotic death as well as in inducing conformation change and translocation of Bax. Similar to Bax-deficient cells, MAP-1-deficient cells exhibit aggressive anchorage-independent growth. Remarkably, recombinant Bax- or tBid-mediated release of cytochrome c from isolated mitochondria is significantly compromised in the MAP-1 knockdown cells. We propose that MAP-1 is a direct mitochondrial target of Bax.

1. Proteins of the Bcl-2 family are central regulators of apoptosis and are thought to act primarily on the mitochondria. 2. Members of the Bcl-2 family possess either anti-apoptotic or pro-apoptotic function. They are characterized by the presence of conserved sequence motifs, known as Bcl-2 homology (BH) domains. Anti-apoptotic members share all four BH domains, designated as BH1-4; the multidomain pro-apoptotic members contain BH1-3 domains, whereas another subgroup of pro-apoptotic members only have a BH3 domain. 3. The BH3-only proteins act as sensors for distinct apoptosis pathways, whereas multidomain pro-apoptotic Bax and Bak are executioners of death orders relayed by the BH3-only proteins. 4. Anti-apoptotic Bcl-2 family members appear to function, at least in part, by interacting with and antagonizing pro-apoptotic family members. The BH1-3 domains of BclXL form an elongated hydrophobic groove, which is the docking site for the BH3 domains of pro-apoptotic binding partners. 5. The deregulation of the various Bcl-2 proteins has been implicated in many pathological conditions. 6. Knowledge derived from the understanding of the function and regulation of the Bcl-2 family of proteins has allowed us to contemplate new therapeutic strategies for diseases where apoptosis signalling mechanisms can potentially be manipulated. 7. The anti-apoptotic Bcl-2 members have been targeted successfully using an antisense approach, BH3-peptides and small molecular weight chemicals that are inhibitors of their anti-apoptotic function.

The identification of small molecule inhibitors of antiapoptotic Bcl-2 family members has opened up new therapeutic opportunities, while the vast diversity of chemical structures and biological activities of natural products are yet to be systematically exploited. Here we report the identification of chelerythrine as an inhibitor of BclXL-Bak Bcl-2 homology 3 (BH3) domain binding through a high throughput screening of 107,423 extracts derived from natural products. Chelerythrine inhibited the BclXL-Bak BH3 peptide binding with IC50 of 1.5 micro m and displaced Bax, a BH3-containing protein, from BclXL. Mammalian cells treated with chelerythrine underwent apoptosis with characteristic features that suggest involvement of the mitochondrial pathway. While staurosporine, H7, etoposide, and chelerythrine released cytochrome c from mitochondria in intact cells, only chelerythrine released cytochrome c from isolated mitochondria. Furthermore BclXL-overexpressing cells that were completely resistant to apoptotic stimuli used in this study remained sensitive to chelerythrine. Although chelerythrine is widely known as a protein kinase C inhibitor, the mechanism by which it mediates apoptosis remain controversial. Our data suggest that chelerythrine triggers apoptosis through a mechanism that involves direct targeting of Bcl-2 family proteins.

Hypoxia promotes stem cell maintenance and tumor progression, but it remains unclear how it regulates long-term adaptation toward these processes. We reveal a striking downregulation of the hypoxia-inducible histone H3 lysine 9 (H3K9) demethylase JMJD1A as a hallmark of clinical human germ cell-derived tumors, such as seminomas, yolk sac tumors, and embryonal carcinomas. Jmjd1a was not essential for stem cell self-renewal but played a crucial role as a tumor suppressor in opposition to the hypoxia-regulated oncogenic H3K9 methyltransferase G9a. Importantly, loss of Jmjd1a resulted in increased tumor growth, whereas loss of G9a produced smaller tumors. Pharmacological inhibition of G9a also resulted in attenuation of tumor growth, offering a novel therapeutic strategy for germ cell-derived tumors. Finally, Jmjd1a and G9a drive mutually opposing expression of the antiangiogenic factor genes Robo4, Igfbp4, Notch4, and Tfpi accompanied by changes in H3K9 methylation status. Thus, we demonstrate a novel mechanistic link whereby hypoxia-regulated epigenetic changes are instrumental for the control of tumor growth through coordinated dysregulation of antiangiogenic gene expression.

The expression of winter flounder liver-type antifreeze protein (wflAFP) genes is tissue-specific and under seasonal and hormonal regulation. The only intron of the major wflAFP gene was demonstrated to be a liver-specific enhancer in both mammalian cell lines and flounder hepatocytes. Element B, the core enhancer sequence, was shown to interact specifically with a liver-enriched transcription factor, CCAAT/enhancer-binding protein α (C/EBPα), as well as a presumptive antifreeze enhancer-binding protein (AEP). In this study, the identity of the rat AEP ortholog was revealed via its DNA–protein interaction with element B. It is a helicase-domain-containing protein, 988 amino acids in length, and is homologous to mouse Smubp-2, hamster Rip-1 and human Smubp-2. The specific binding between element B and AEP was confirmed by South-Western analysis and gel retardation assays. Residues in element B important to this interaction were identified by methylation interference assays. Mutation on one of the residues disrupted the binding between element B and AEP and its enhancer activity was significantly reduced, suggesting that AEP is essential for the transactivation of the wflAFP gene intron. The rat AEP is ubiquitously expressed in various tissues, and the flounder homolog is present as shown by genomic Southern analysis. The potential role of AEP in regulating the flounder AFP gene expression is discussed.

Apoptosis is an evolutionarily conserved process that is critical for tissue homeostasis and development including sex determination in essentially all multicellular organisms. Here, we report the cloning of an ankyrin repeat-containing protein, termed F1Aalpha, in a yeast two-hybrid screen using the cytoplasmic domain of Fas (CD95/APO-1) as bait. Amino acid sequence analysis indicates that F1Aalpha has extensive homology to the sex-determining protein FEM-1 of the Caenorhabditis elegans, which is required for the development of all aspects of the male phenotype. F1Aalpha associates with the cytoplasmic domains of Fas and tumor necrosis factor receptor 1, two prototype members of the "death receptor" family. The F1Aalpha protein also oligomerizes. Overexpression of F1Aalpha induces apoptosis in mammalian cells, and co-expression of Bcl-XL or the dominant negative mutants of either FADD or caspase-9 blocks this effect. Deletion analysis revealed the center region of F1Aalpha, including a cluster of five ankyrin repeats to be necessary and sufficient for maximum apoptotic activity, and the N-terminal region appears to regulate negatively this activity. Furthermore, F1Aalpha is cleaved by a caspase-3-like protease at Asp(342), and the cleavage-resistant mutant is unable to induce apoptosis upon overexpression. F1Aalpha is therefore a member of a growing family of death receptor-associated proteins that mediates apoptosis.

The winter flounder antifreeze protein (AFP) intron contains a liver-specific enhancer (Element B) which was shown earlier to bind CCAAT/enhancer binding protein (C/EBP)alpha. In contrast, as demonstrated in the present studies, the intron of the skin-type AFP gene acted as a ubiquitous enhancer and contained a TA insertion at similar region to Element B (Element S) which destroyed its interaction with C/EBPalpha. Furthermore, a TA insertion of Element B by site-directed mutagenesis decreased its liver enhancer activity. The presence or absence of C/EBPalpha binding motifs in Element B and Element S, respectively, may provide a mechanism for their differential expression.

Winter flounder, Pleuronectes americanus, produces antifreeze proteins (AFPs) to avoid freezing during winter. The AFP in the blood is synthesized by the liver and its annual level is regulated by environmental factors and somatotropin. The only intron (+106 to +602) of the AFP gene contains putative binding sites for liver-enriched transcription activators. Due to the lack of an appropriate fish liver cell line, a mammalian model system was used to demonstrate the liver-specific enhancer activity of the intron. Deletion analysis of the intron indicated nucleotide sequences between +192 bp and +334 bp were important for the enhancer activity. Further refinement showed that the element B (+303 to +322 bp) resided in this region interacted with proteins from rat nuclear extracts by DNase I footprinting and mobility shift analysis. Gel retardation with competition and supershift experiments defined element B to include binding sites for CCAAT/enhancer binding protein a (C/EBP alpha), a liver-enriched transcription factor, and a novel activator protein-1 (AP-1) site binding protein, designated as antifreeze enhancer binding protein (AEP). Residues important to DNA-protein interaction in element B were mapped by methylation interference. Mutations in element B by site-directed mutagenesis destroyed the enhancer activity of the intron. Ultraviolet crosslinking experiments using element B revealed the specific binding of two proteins of approximately 43 and 80 kDa. The present findings provide a mechanism(s) by which the tissue specificity of AFP gene expression can be achieved. Integration of the present information with the somatotropin-mediated signal transduction pathways has generated a working model for the hormonal regulation and seasonal expression of the AFP gene.

Limited preclinical data are available regarding development of resistance to FGFR kinase inhibitors, several of which are currently evaluated in clinical trials. We generated a patient-derived xenograft (PDX) model for diffuse type gastric cancer and demonstrated that the GAGA6 PDX model with high FGFR2 amplification was very sensitive to AZD4547, a potent small molecule (SMOL) inhibitor of FGFR1, FGFR2, and FGFR3 kinase currently in development for FGFR aberrant cancer types. Intermittent in vivo treatment of GAGA6 tumors with AZD4547 gave rise to PDX tumors with acquired resistance to AZD4547, GAGA6-R. Surprisingly, no mutations were found in the FGFR2 gene in GAGA6-R, excluding gatekeeper mutations as a mechanism of drug resistance. In addition, phosphorylation of FGFR2 and the downstream signaling molecules AKT/PKB and MAPK/ERK were still inhibited by AZD4547 in GAGA6-R tumors suggesting alternative pathways for development of resistance toward AZD4547. Further analysis of signaling pathways identified an AKT-independent inhibition of GSK3β as a mechanism of drug resistance in GAGA6-R. In contrast to GAGA6, phosphorylation of GSK3β at the deactivating serine 9 (S9) position in GAGA6-R cells was not affected by de-phosphorylation of AKT, a known modulator of GSK3β activity. Inhibition of GSK3β kinase activity with 1-azakenpaullone (1-AKP) conferred AZD4547 drug resistance in GAGA6 tumor-derived cells while overexpression of constitutively active GSK3β S9A mutant in GAGA6-R tumor-derived cells sensitized them to AZD4547 treatment. As a direct activator of GSK3β is not available, we tested a different strategy to overcome drug resistance in the GAGA6-R PDX model. Since wild-type FGFR2 remained highly expressed in GAGA6-R tumor cells, we tested the anti-tumor effect of an antibody-drug conjugate (ADC), FGFR2-ADC BAY 1187982, on GAGA6-R tumors in vivo. BAY 1187982 consists of the fully human anti-FGFR2 antibody BAY 1179470 conjugated via a stable linker to a novel auristatin payload. A first-in-human study with BAY 1187982 is currently recruiting (NCT02368951). Weekly treatment (Q7Dx3) of GAGA6-R tumors with 7.5mg/kg of FGFR2-ADC in monotherapy was found to efficaciously inhibit tumor growth in GAGA6-R (88% tumor growth inhibition (TGI), P In conclusion, our findings reveal that tumor cells harboring an amplification of the FGFR2 gene are highly dependent on FGFR2 signaling for survival, but rapidly develop alternative signaling pathways when challenged with an FGFR small molecule inhibitor. An FGFR2-ADC such as BAY 1187982 clearly provides an efficient avenue to overcome such acquired mechanisms of drug resistance. Citation Format: Wen Min Lau, Eileen Teng, Kie Kyon Huang, Jin Wei Tan, Ming Teh, Wei Peng Yong, Anette Sommer, Christoph A. Schatz, Patrick Tan, Shing Leng Chan, Jimmy So. High efficacy of BAY 1187982, an FGFR2-ADC, in overcoming drug resistance in a diffuse type gastric cancer patient-derived xenograft model with acquired resistance to pan-FGFR inhibitor AZD4547. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-117.

The transcription factor RUNX3 functions as a tumor suppressor in the gastrointestinal epithelium, where its loss is an early event in carcinogenesis. While RUNX3 acts concurrently as a mediator of TGF-β signaling and an antagonist of Wnt, the cellular changes that follow its loss and their contribution to tumorigenicity are not fully understood. Here, we report that the loss of Runx3 in gastric epithelial cells results in spontaneous epithelial-mesenchymal transition (EMT). This produces a tumorigenic stem cell-like subpopulation, which remarkably expresses the gastric stem cell marker Lgr5. This phenomenon is due to the compounding effects of the dysregulation of the TGF-β and Wnt pathways. Specifically, Runx3−/−p53−/− gastric epithelial cells were unexpectedly sensitized for TGF-β-induced EMT, during which the resultant induction of Lgr5 was enhanced by an aberrantly activated Wnt pathway. These data demonstrate a protective role for RUNX3 in safeguarding gastric epithelial cells against aberrant growth factor signaling and the resultant cellular plasticity and stemness.

Background: Gastric carcinogenesis has been well documented in the step-wise histopathological model, known as Correa pathway. Several biomarkers including CD44, Musashi-1 and CD133 have been reported as putative stem cell (PSC) markers. Methods: We investigated expression of PSC markers CD44, Musashi-1 and CD133 in relation to gastric carcinogenesis and prognosis and chemoresponse. Immunohistochemistry staining was performed in gastric cancer (GC) clinical specimens representing different steps of the Correa pathway. Gastric cancer samples taken before and after neoadjuvant chemotherapy with docetaxel, cisplatin and capecitabine (DCX) were also evaluated for PSC marker expression. Results: We showed that the expression of three PSC markers was significantly elevated in GC relative to normal gastric mucosa (P

Although murine embryonic fibroblasts (MEFs) with Bax or Bak deleted displayed no defect in apoptosis signaling, MEFs with Bax and Bak double knock-out (DKO) showed dramatic resistance to diverse apoptotic stimuli, suggesting that Bax and Bak are redundant but essential regulators for apoptosis signaling. Chelerythrine has recently been identified as a Bcl-xL inhibitor that is capable of triggering apoptosis via direct action on mitochondria. Here we report that in contrast to classic apoptotic stimuli, chelerythrine is fully competent in inducing apoptosis in the DKO MEFs. Wild-type and DKO MEFs are equally sensitive to chelerythrine-induced morphological and biochemical changes associated with apoptosis phenotype. Interestingly, chelerythrine-mediated release of cytochrome c is rapid and precedes Bax translocation and integration. Although the BH3 peptide of Bim is totally inactive in releasing cytochrome c from isolated mitochondria of DKO MEFs, chelerythrine maintains its potency and efficacy in inducing direct release of cytochrome c from these mitochondria. Furthermore, chelerythrine-mediated mitochondrial swelling and loss in mitochondrial membrane potential (ΔΨm) are inhibited by cyclosporine A, suggesting that mitochondrial permeability transition pore is involved in chelerythrine-induced apoptosis. Although certain apoptotic stimuli have been shown to elicit cytotoxic effect in the DKO MEFs through alternate death mechanisms, chelerythrine does not appear to engage necrotic or autophagic death mechanism to trigger cell death in the DKO MEFs. These results, thus, argue for the existence of an alternative Bax/Bak-independent apoptotic mechanism that involves cyclosporine A-sensitive mitochondrial membrane permeability.

Mesenchymal stem cells have been implicated as playing an important role in stem cell engraftment. Recently, a new pluripotent population of umbilical cord blood (UCB) cells, unrestricted somatic stem cells (USSCs), with intrinsic and directable potential to develop into mesodermal, endodermal, and ectodermal fates, has been identified. In this study, we evaluated the capacity of ex vivo expanded USSCs to influence the homing of UCB-derived CD34+ cells into the marrow and spleen of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. USSCs induced a significant enhancement of CD34+ cell homing to both bone marrow and spleen (2.2 ± 0.3- and 2.4 ± 0.6-fold, respectively; p < .05), with a magnitude similar to that induced by USSCs that had been thawed prior to transplantation. The effect of USSCs was dose-dependent and detectable at USSC:CD34+ ratios of 1:1 and above. Enhanced marrow homing by USSCs was unaltered by extensive culture passaging of the cells, as similar enhancement was observed for both early-passage (passage 5 [p5]) and late-passage (p10) USSCs. The homing effect of USSCs was also reflected in an increased proportion of NOD/SCID mice exhibiting significant human cell engraftment 6 weeks after transplantation, with a similar distribution of myeloid and lymphoid components. USSCs enhanced the homing of cellular products of ex vivo expanded UCB lineage-negative (lin−) cells, generated in 14-day cultures by Selective Amplification. The relative proportion of homing CD34+ cells within the culture-expanded cell population was unaltered by USSC cotransplantation. Production of stromal-derived factor-1 (SDF-1) by USSCs was detected by both gene expression and protein released into culture media of these cells. Knockdown of SDF-1 production by USSCs using lentiviral-SiRNA led to a significant (p < .05) reduction in USSC-mediated enhancement of CD34+ homing. Our findings thus suggest a clinical potential for using USSCs in facilitating homing and engraftment for cord blood transplant recipients.

Diffuse gastric cancer (DGC) is a poorly differentiated adenocarcinoma characterized by infiltration of signet ring cells into the stomach wall and a lack of tumor mass formation. DGC has rapid disease progression with a dismally poor prognosis and is resistant to chemo- and radiotherapy. There is no available targeted therapy, and preclinical models that reliably predict clinical activity of novel compounds are also lacking. In addition, molecular analyses of DGC have been hampered by difficulty in obtaining primary tumors of sufficient tumor cellularity without contaminating normal fibroblasts. To overcome the scarcity of cancer cells and the abundance of surrounding stromal tissue, we isolated cancer cells from malignant ascites of DGC patients. Red blood cells were removed by Ficoll separation and CD45+ hematopoietic cells were depleted using antibody-conjugated magnetic beads. Exome sequencing was performed on cancer cells and peripheral blood cells from the same patient to identify somatic alterations in DGC. We also generated patient-derived xenografts (PDX) using isolated cancer cells to establish preclinical cancer models for DGC. Exome sequencing revealed FGFR2 and KRAS amplifications as well as p53 mutations. Cancer cells isolated from malignant ascites formed subcutaneous tumors that recapitulated the histology of primary DGC tumors with characteristic signet ring cells and intracellular mucin. FGFR2 amplification in PDX tumors was confirmed by fluorescence in situ hybridization (FISH), with correspondingly high levels of FGFR2 transcripts and protein expression. We performed drug treatments on PDX tumors using FGFR2 inhibitor AZD4547 and found that FGFR2 amplification status alone was sufficient to predict the sensitivity of PDX tumors to AZD4547. Tumor volume of FGFR2-amplified tumors decreased or remained the same following AZD4547 treatment compared to vehicle-treated tumors which showed increased tumor volume. In contrast, AZD4547 treatment had little or no effect on tumor growth of non-FGFR2 amplified tumors. Furthermore, these PDX tumors regardless of FGFR2 amplification status responded poorly to cisplatin, a standard drug currently used for treatment of DGC. In conclusion, we report a high prevalence of FGFR2 gene amplification in DGC and the establishment of reliable PDX models that can predict tumor response to targeted therapy. Citation Format: Wen Min Lau, Zhijiang Zang, Eileen Teng, Kakoli Das, Wei Peng Yong, Ming Teh, Tania Chia, Jin Wei Tan, Amy Tay, Asim Shabbir, Koji Kono, Jimmy So, Patrick Tan, Shing Leng Chan. Clinical relevance of FGFR2 amplification in diffuse gastric cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1228. doi:10.1158/1538-7445.AM2014-1228

Recent data on gene deletion analyses revealed that cells derived from animals that are deficient in both Bax and Bak (two key members of the “multidomain” proapoptotic Bcl-2 subfamily), but not cells lacking one of the two genes, are completely resistant to apoptotic death triggered by diverse stimuli. These data suggest that engagement of a “multidomain” proapoptotic member, BAX or BAK, is essential for apoptotic signaling. To gain further understanding of the molecular functions of the “multidomain” proapoptotic molecules, we used yeast two hybrid screen to identify protein partners of BAX. A proapoptotic protein, termed MAP-1 (Modulator of Apoptosis), was identified as a BAX-interacting protein from a human brain cDNA library. MAP-1 is a member of a growing family of proteins that were initially identified as onconeural antigens. MAP-1 contains a BH3-like motif and mediates caspase-dependent death in mammalian cells when overexpressed. Mutagenesis analyses revealed that the BH3-like domain of MAP-1 is required for association with BAX and for mediating apoptosis. Interestingly, in contrast to all other previously identified BAX-associating proteins that require only one of the three BH domains of BAX for binding, all the three BH (BH1, BH2 and BH3) domains of BAX are necessary for binding to MAP-1. Taken together, these data suggest that MAP-1 may mediate its proapoptotic function by engaging its BH3-like domain in binding the Bc1-XL-like hydrophobic pocket of BAX.

Background & Aims: VEGF is a key stimulator of angiogenesis and promotes the growth colon tumors via increased nutrient and oxygen supply. A recent study demonstrated that colorectal cancer (CRC) cells have increased expression of VEGF and its receptors VEGFR1 & VEGF-R2, which indicates a possibility of direct stimulation of CRC cell growth by VEGF. However, the role of VEGF in CRC cell proliferation by an autocrine mechanism has not been fully explored in depth. We hypothesized that VEGF secreted by CRC cells binds to VEGF-R1 & VEGF-R2 on CRC cells and: 1) promotes proliferation of these cells through an autocrine pathway, 2) inhibits CRC apoptosis. Methods: We used: (1) human CRC cell lines HCT116 & HT29 and (2) normal colonic epithelial cells NCM356 & NCM460 cultured in nutrient media. Studies: 1) VEGF, VEGF-R1 & VEGF-R2 mRNA and protein expression of by Real-Time RT-PCR and immunoblotting; 2) VEGF165 secretion into the culture media by ELISA; 3) cell proliferation by BrdU assay; 4) apoptosis by TUNEL staining and assessment of activated caspases 3 and 9; 5) Inhibition of VEGF receptor function using AAL993 inhibitor, which blocks function of VEGF-R1 and VEGF-R2; 6) assessment of phosphorylation of EGF receptor (EGF-R) to test its transactivation by VEGF. Results: 1) Normal colonic cells do not secrete VEGF (< 35 pg/ml culture media) while CRC cells express and secrete high levels of VEGF (840 1500 pg/ml culture media); 2) Normal colonic epithelial cell lines expressed no or minimal VEGF-R1 & VEGF-R2 mRNA and protein while CRC cell lines exhibit strong expression of VEGF-R1 & VEGF-R2 vs. normal colonic epithelial cells by 14and 24-fold, respectively (all p < 0.001); 3) CRC cell lines have significantly increased cell proliferation by 31% (p < 0.01) and decreased apoptosis vs. normal colonic epithelial cells; 3) Inhibition of both VEGF-R1 & VEGF-R2 receptors using AAL-993 significantly decreased CRC cell proliferation by (2.2-fold) ; 4) Treatment of CRC cells with AAL-993 decreased phosphorylation of EGF-R by 1.9-fold (p < 0.01). Conclusions: 1) VEGF and its VEGF-R1 & VEGF-R2 receptors are increased in CRC cell lines; 2) CRC cells secrete VEGF, which stimulates CRC cell proliferation via an autocrine mechanism by its VEGF-R1 & VEGF-R2 receptors and also inhibits apoptosis; 3) VEGF receptor signaling pathway is critical for activating EGF-R in CRC cells; 4) These studies suggest a cross-talk between VEGF receptor and EGF-R signaling in CRC cells, which promotes these cells' proliferation.

In Caenorhabditis elegans, fem-1, fem-2, and fem-3 play pivotal roles in sex determination. Recently, a mammalian homologue of the C. elegans sex-determining protein FEM-1, F1Aalpha, has been described. Although there is little evidence to link F1Aalpha to sex determination, F1Aalpha and FEM-1 both promote apoptosis in mammalian cells. Here we report the identification and characterization of a human homologue of the C. elegans sex-determining protein FEM-2, hFEM-2. Similar to FEM-2, hFEM-2 exhibited PP2C phosphatase activity and associated with FEM-3. hFEM-2 shows striking similarity (79% amino acid identity) to rat Ca(2+)/calmodulin (CaM)-dependent protein kinase phosphatase (rCaMKPase). hFEM-2 and FEM-2, but not PP2Calpha, were demonstrated to dephosphorylate CaM kinase II efficiently in vitro, suggesting that hFEM-2 and FEM-2 are specific phosphatases for CaM kinase. Furthermore, hFEM-2 and FEM-2 associated with F1Aalpha and FEM-1 respectively. Overexpression of hFEM-2, FEM-2, or rCaMKPase all mediated apoptosis in mammalian cells. The catalytically active, but not the inactive, forms of hFEM-2 induced caspase-dependent apoptosis, which was blocked by Bcl-XL or a dominant negative mutant of caspase-9. Taken together, our data suggest that hFEM-2 and rCaMKPase are mammalian homologues of FEM-2 and they are evolutionarily conserved CaM kinase phosphatases that may have a role in apoptosis signaling.

A novel Bax-associating protein, named MAP-1 (Modulator of Apoptosis), has been identified in a yeast two-hybrid screen. MAP-1 contains a BH3-like (BH: Bcl-2 homology) motif and mediates caspase-dependent apoptosis in mammalian cells when overexpressed. MAP-1 homodimerizes and associates with the proapoptotic Bax and the prosurvival Bcl-2 and Bcl-X(L) of the Bcl-2 family in vitro and in vivo in mammalian cells. Mutagenesis analyses revealed that the BH3-like domain in MAP-1 is not required for its association with Bcl-X(L) but is required for association with Bax and for mediating apoptosis. Interestingly, in contrast to other Bax-associating proteins such as Bcl-X(L) and Bid, which require the BH3 and BH1 domains of Bax, respectively, for binding, the binding of MAP-1 to Bax appears to require all three BH domains (BH1, BH2, and BH3) of Bax, because point mutation of the critical amino acid in any one of these domains is sufficient to abolish its binding to MAP-1. These data suggest that MAP-1 mediates apoptosis through a mechanism that involves binding to Bax.