The Role of Early Growth Response Gene Egr3 in Prostate Cancer

Members of the early growth response (Egr) family of transcription factors are known to play diverse functions in response to many cellular stimuli, including growth, stress, and inflammation. Egr family member Egr1 is a known oncogene in prostate cancer, but Egr family member Egr3 has never been studied in prostate cancer before. To test the hypothesis that Egr3 is important for prostate cancer initiation or progression a variety of in-silico and in-vitro cell culture methods were employed. Egr3 mRNA expression was analyzed in the SPECS prostate tissue gene expression dataset. Egr3 was found to be over-expressed in non-relapse prostate cancer compared to normal prostate tissue and to be significantly decreased in relapse prostate cancer. Genes correlating with this bi-phasic expression pattern were identified, and were found to be enriched with inflammatory genes such as IL-6 and IL-8.;The human prostate cell line M12, which expresses high levels of Egr3, was used as a cell culture model of prostate cancer. Stable knockdown of Egr3 protein levels in M12 cells resulted in reduced cell growth and reduced anchorage independence. Affymetrix whole genome expression analysis was performed on two M12 Egr3 knockdown clones. Again, knockdown of Egr3 expression was associated with decreased expression of a large number of inflammatory genes. A complimentary experiment of Egr3 over-expression was performed in the immortalized human 267B1 prostate cell line. 24 genes were identified as being significantly decreased in M12 Egr3 knockdown cells and significantly increased in 267B1 Egr3 over-expressing cells. Among these genes were the inflammatory mediators IL-6 and IL-8.;Because IL-6 and IL-8 were identified as correlating with the bi-phasic Egr3 expression pattern in the SPECS prostate tissue (Chapter 2), Egr3 knockdown in M12 cells, and Egr3 over-expression in 267B1 cells (Chapter 3), they were identified as likely Egr3 target genes. Multiple Egr binding sites were identified in the IL-6 and IL-8 promoters. In addition, IL-6 was shown to stimulate cell growth of M12 cells. Control of autocrine growth factors such as IL-6 and IL-8 by Egr3 in prostate cancer may be an important mechanism of prostate cancer initiation or early progression.