FAM3B/PANDER inhibits cell death and increases prostate tumor growth by modulating the expression of Bcl-2 and Bcl-XL cell survival genes.

BACKGROUND: FAM3B/PANDER is a novel cytokine-like protein that induces apoptosis in insulin-secreting beta-cells. Since in silico data revealed that FAM3B can be expressed in prostate tumors, we evaluated the putative role of this cytokine in prostate tumor progression. METHODS: FAM3B expression was analyzed by quantitative PCR in tumor tissue clinical samples and prostate tumor cell lines. Culture growth and viability of DU145 cell line were evaluated after treatment with either exogenous FAM3B protein obtained from conditioned media (CM) of 293 T cells overexpressing FAM3B or a recombinant FAM3B protein produced in a bacterial host. DU145 cells overexpressing FAM3B protein were produced by lentiviral-mediated transduction of full-length FAM3B cDNA. Cell viability and apoptosis were analyzed in DU145/FAM3B cells after treatment with several cell death inducers, such as TNF-alpha, staurosporine, etoposide, camptothecin, and serum starvation conditions. Anchorage-independent growth in soft agarose assay was used to evaluate in vitro tumorigenicity. In vivo tumorigenicity and invasiveness were evaluated by tumor xenograft growth in nude mice. RESULTS: We observed an increase in FAM3B expression in prostate tumor samples when compared to normal tissues. DU145 cell viability and survival increased after exogenous treatment with recombinant FAM3B protein or FAM3B-secreted protein. Overexpression of FAM3B in DU145 cells promoted inhibition of DNA fragmentation and phosphatidylserine externalization in a time and dose-dependent fashion, upon apoptosis triggered by TNF-alpha. These events were accompanied by increased gene expression of anti-apoptotic Bcl-2 and Bcl-XL, decreased expression of pro-apoptotic Bax and diminished caspase-3, -8 and -9 proteolytic activities. Furthermore, inhibition of Bcl-2 anti-apoptotic family proteins with small molecules antagonists decreases protective effects of FAM3B in DU145 cells. When compared to the respective controls, cells overexpressing FAM3B displayed a decreased anchorage- independent growth in vitro and increased tumor growth in xenografted nude mice. The immunohistochemistry analysis of tumor xenografts revealed a similar anti-apoptotic phenotype displayed by FAM3B-overexpressing tumor cells. CONCLUSIONS: Taken together, by activating pro-survival mechanisms FAM3B overexpression contributes to increased resistance to cell death and tumor growth in nude mice, highlighting a putative role for this cytokine in prostate cancer progression.

Antiapoptotic and Prometastatic Roles of Cytokine FAM3B in Triple-Negative Breast Cancer.

BACKGROUND: Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer. FAM3B, a secreted protein, has been extensively studied in various types of tumors. However, its function in breast cancer remains poorly understood. METHODS: We analyzed FAM3B expression data from breast cancer patients available at TCGA database and overall survival was analyzed by using the Kaplan-Meier plotter. MDA-MB-231 TNBC tumor cell line and hormone-responsive MCF-7 cell lines were transfected to overexpress FAM3B. We assessed cell death, tumorigenicity, and invasiveness in vitro through MTT analysis, flow cytometry assays, anchorage-independent tumor growth, and wound healing assays, respectively. We performed in vivo evaluation by tumor xenograft in nude mice. RESULTS: In silico analysis revealed that FAM3B expression was lower in all breast tumors. However, TNBC patients with high FAM3B expression had a poor prognosis. FAM3B overexpression protected MDA-MB-231 cells from cell death, with increased expression of Bcl-2 and Bcl-xL, and reduced caspase-3 activity. MDA-MB-231 cells overexpressing FAM3B also exhibited increased tumorigenicity and migration rates in vitro, displaying increased tumor growth and reduced survival rates in xenotransplanted nude mice. This phenotype is accompanied by the upregulation of EMT-related genes Slug, Snail, TGFBR2, vimentin, N-cadherin, MMP-2, MMP-9, and MMP-14. However, these effects were not observed in the MCF-7 cells overexpressing FAM3B. CONCLUSION: FAM3B overexpression contributes to tumor growth, promotion of metastasis, and, consequently, leads to a poor prognosis in the most aggressive forms of breast cancer. Future clinical research is necessary to validate FAM3B as both a diagnostic and a therapeutic strategy for TNBC.