BACKGROUND Lens epithelium-derived growth factor p75 (LEDGF/p75) is a stress survival transcription co-activator and autoantigen that is overexpressed in tumors, including prostate cancer (PCa). This oncoprotein promotes resistance to cell death induced by oxidative stress and chemotherapy by mechanisms that remain unclear. To get insights into these mechanisms we identified candidate target stress genes of LEDGF/p75 using pathway-specific gene expression profiling in PCa cells. METHODS A “Human oxidative stress and antioxidant defense” qPCR array was used to identify genes exhibiting significant expression changes in response to knockdown or overexpression of LEDGF/p75 in PC-3 cells. Validation of array results was performed by additional qPCR and immunoblotting. RESULTS Cytoglobin (CYGB), Phosphoinositide-binding protein PIP3-E/IPCEF-1, superoxidase dismutase 3 (SOD3), thyroid peroxidase (TPO), and albumin (ALB) exhibited significant transcript down- and up-regulation in response to LEDGF/p75 knockdown and overexpression, respectively. CYGB gene was selected for further validation based on its emerging role as a stress oncoprotein in human malignancies. In light of previous reports indicating that LEDGF/p75 regulates peroxiredoxin 6 (PRDX6), and that PRDXs exhibit differential expression in PCa, we also examined the relationship between these proteins in PCa cells. Our validation data revealed that changes in LEDGF/p75 transcript and protein expression in PCa cells closely paralleled those of CYGB, but not those of the PRDXs. CONCLUSIONS Our study identifies CYGB and other genes as stress genes potentially regulated by LEDGF/p75 in PCa cells, and provides a rationale for investigating their role in PCa and in promoting resistance to chemotherapy- and oxidative stress-induced cell death.

Chronic inflammation in the prostate microenvironment, with its associated increase in oxidative stress, is critical for prostate carcinogenesis since it leads to DNA mutations and epigenetic changes, as well as deregulation of stress and antioxidant proteins that protect prostate cells against oxidative damage and cell death. The lens epithelium-derived growth factor p75 (LEDGF/p75), an oxidative stress-induced transcription coactivator, is overexpressed in prostate tumors and other tumor types. LEDGF/p75 is emerging as a stress oncoprotein that protects cancer cells against lysosomal cell death and promotes resistance to chemotherapeutic drugs. We hypothesize that the pro-survival function of LEDGF/p75 is associated with its ability to promote the transcriptional activation of protective stress genes. To date, only very few candidate target genes of LEDGF/p75 have been identified in cancer cells. Towards this goal we initiated a stress focused gene profiling analysis of PC3 prostate cancer cells overexpressing or lacking LEDGF/p75, using the Real Time PCR Array System (SABiosciences). We selected an array that contained 80 genes involved in the cellular stress response and antioxidant defense. siRNA oligos targeting the C-terminus of the LEDGF/p75 mRNA sequence were used to induce transient LEDGF/p75 knockdown in PC3 cell. LEDGF/p75 was also stably overexpressed in PC3 cells by transduction with a lentiliviral vector. Both transient siRNA-mediated knockdown and overexpression of LEDGF/p75 were associated with significant changes in the expression of several stress/antioxidant genes, using a cutoff fold change value of 1.5 (P<0.001). We selected for further analysis common genes that were significantly downregulated when LEDGF/p75 was knocked down and upregulated when this protein was overexpressed. These genes are phosphoinositide-binding protein E, cytoglobulin, superoxide dismutase 3, thyroid peroxidase, titin, glutathione transferase zeta1 and albumin. The expression of these genes in response to LEDGF/p75 expression was further validated using real-time RT-PCR. This study identifies candidate stress genes potentially regulated by LEDGF/p75 in PC3 cells, and provides a rationale for investigating the mechanisms by which this emerging stress oncoprotein promotes resistance to lysosomal cell death and chemotherapy in prostate tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2092. doi:10.1158/1538-7445.AM2011-2092