Abstract
BackgroundFAM3B/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.MethodsFAM3B 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.ResultsWe 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.ConclusionsTaken 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.
Highlights
FAM3B/PANcreatic-DERived factor (PANDER) is a novel cytokine-like protein that induces apoptosis in insulin-secreting beta-cells
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
FAM3B is expressed by human prostate tumors and prostate tumor cell lines We evaluated FAM3B expression at Messenger Ribonucleic acid (RNA) (mRNA) level in prostatic normal tissue and tumor samples as well as in prostate tumor cell lines
Summary
FAM3B/PANDER is a novel cytokine-like protein that induces apoptosis in insulin-secreting beta-cells. There is a great need to identify molecular prognostic factors that allow stratification of prostate cancer patients in groups that are more homogeneous [1]. Pancreatic-derived factor (FAM3B/PANDER, or FAM3B), is a novel secreted protein discovered through in silico screening for novel cytokine families based on a highly conserved four-helix bundle secondary structure [2, 3]. Initial characterization evaluating the role of FAM3B on pancreatic islets revealed induction of pancreatic β-cell apoptosis via caspase- 3 and cyclin-dependent kinase inhibitor 1A (p21) pathways, suggesting that FAM3B is a potential activator in a setting of type 1 diabetes [6]. Recent evidence using a FAM3B knockout mouse model revealed another biological role for this protein in the regulation of glycaemia via regulation of liver and pancreas functions [7]. Additional studies have demonstrated that FAM3B is significantly regulated by both glucose and insulin, supporting a biological role in glycemic control and regulation of lipogenesis [8,9,10,11,12]
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