HIF-1α and Nrf2 regulates hypoxia induced overexpression of DDAH1 through promoter activation in prostate cancer

Dimethylarginine dimethylaminohydrolase-1 (DDAH1) is overexpressed in prostate cancer (PCa) and promotes PCa progression in in vivo through the ADMA-NO pathway by degrading nitric oxide synthase (NOS) inhibitors such as asymmetric dimethylarginine (ADMA) and monomethylamine arginine (L-NMMA). In this study, we investigated the molecular mechanism involved in the overexpression of DDAH1 in PCa and examined its potential role as a therapeutic target. We observed that DDAH1expression is elevated in PCa (PC3, LNCaP, and DU145) cell lines under hypoxia. ChIP and reporter assay results confirmed that DDAH1 expression is positively regulated by HIF-1 alpha through directly binding to the hypoxia response elements (HRE) located within the promoter region between - 1242/-1238 upstream of its transcription start site (TSS). Under hypoxia, HIF-1 alpha is translocated into the nucleus and activates its target gene expression in PC3 cells. Interestingly, in the event of HIF-1 alpha inhibition or siRNA-mediated knockdown, an alternative transcription factor Nrf2 promotes DDAH1 expression through antioxidant response elements (AREs) on its promoter. ChIP assay results showed that Nrf2 binds to AREs located between -1016 /-1008 bp from the TSS of DDAH1. Furthermore, knockdown of PCa therapeutic target HSP90, an essential co-factor for both HIF-1 alpha and Nrf2 causes attenuation of hypoxia induced DDAH1 overexpression in PCa cells. These results demonstrate that hypoxia induced upregulation of DDAH1 expression is positively regulated by HIF-1 alpha and Nrf2 in association with HSP90. Therefore, targeting tumor angiogenesis promoting DDAH1 along with standard androgen receptor (AR) targeted therapy may offer an effective strategy to prevent PCa progression.

Automated summary

This study found that DDAH1 overexpression in prostate cancer cells is positively regulated by HIF-1 alpha and Nrf2. Under hypoxia, HIF-1 alpha activates DDAH1 expression by binding to the HRE in the promoter region, while in the absence of HIF-1 alpha, Nrf2 promotes DDAH1 expression through AREs.