Abstract 1667: Prostatitis related mitogenic stimuli cause loss of NKX3.1: Increased risk for prostate cancer

Abstract NKX3.1 is a haploinsufficient prostate cancer suppressor which has been shown to be reduced in most of the primary human prostate cancers. Reduced NKX3.1 expression in luminal epithelial cells was already observed in pre-neoplastic lesions like prostate intraepithelial neoplasia (PIN) and in early tumor stages. Since the NKX3.1 knock out mouse model displayed a higher incidence of PIN formation it is assumed that the loss of NKX3.1 is involved in the initiation of in prostate cancer. Another potential risk factor for the initiation of prostate cancer is a chronic inflammation of the prostate (prostatitis). However, a clear link between prostatitis and prostate cancer initiation has not yet been established. To estimate whether a loss of NKX3.1 in inflamed prostate tissue might be the basis for PIN formation and subsequent tumor initiation, we compared the NKX3.1 expression levels in postatitis, prostate cancer and normal tissue. We observed a pronounced reduction of NKX3.1 in areas which are positive for B cell and MPS markers CD20 and CD68, respectively. Stimulation of PCa cancer cell lines with cytokines and growth factors known to be expressed by those infiltrating cells revealed a distinct reduction of NKX3.1 expression in PCa cells stimulated with either TNFa or IL1a. Furthermore, the loss of NKX3.1 protein and mRNA was far more pronounced in PCa cells treated with the epidermal growth factor (EGF). Since EGF has a mitogenic function we also tested the impact of a combinatory stimulation of LNCaP cells with the strong mitogen phorbol-12-myristate-13-acetate (PMA) and the calcium ionophor Ionomycin on NKX3.1 expression. Similar to EGF stimulation, PMA+Ionomycin caused a dramatic reduction of NKX3.1 protein as well as mRNA level. NKX3.1 target genes were found to be derepressed upon EGF or P+I stimulation while androgen receptor mRNA expression was found to be decreased. EGF or P+I induced NKX3.1 loss in PCa cell lines appears to depend on two different mechanisms. While the decrease of NKX3.1 mRNA levels largely remained unaffected upon pretreatment with MG132 or Bortezomib, the stabilization of NKX3.1 protein after co-treatment with EGF/P+I and MG132 or Bortezomib suggests the participation of the proteasomal pathway in this process. In addition, the decline in NKX3.1 mRNA levels appears to be independent from a reduced NKX3.1 promoter activity as determined by luciferase reporter assays. Taken together our results imply that a mitogenic stimulus might be the cause for reduced NKX3.1 levels in luminal prostate epithelial cells. Since the production of mitogenic growth factors are increased in inflammatory sites the growth factor induced loss of NKX3.1 might be the connection between prostatitis and prostate cancer initiation. Citation Format: Josua Decker, Garima Jain, Philip Harazim, Tina Kießling, Peter Möller, Ralf Marienfeld. Prostatitis related mitogenic stimuli cause loss of NKX3.1: Increased risk for prostate 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 1667. doi:10.1158/1538-7445.AM2014-1667