THU496 A Positive Relationship Exists Between CARF And AR In Prostate Cancer

Disclosure: K.M. Hasan: None. H. Khambati: None. R.R. Huerta: None. J. Vadgama: None. A.P. Sinha-Hikim: None. T.C. Friedman: None. Prostate cancer (PCa) is the second most prevalent cancer among men worldwide. Since PCa onset is androgen dependent, androgen deprivation therapy (ADT) is the first treatment choice for a primary tumor or metastatic PCa. However, ADT eventually leads to the development of castration resistant PCa (CRPC), which is the leading cause of higher mortality in PCa. Thus, there is a need to identify the underlying mechanisms of CRPC to manage this aggressive disease. Increased androgen receptor (AR) expression is one of the most important factors contributing to the development of CRPC. It has been shown that tumor suppressor p53 negatively regulates the expression of AR. So, loss of p53 functions has been associated with increased expression of AR in advanced PCa. However, the mechanism of p53-mediated inhibition of AR is not well understood. In this study, we demonstrated that CARF (CDKN2AIP), a p53 pathway regulatory protein, is highly expressed in PCa, but its significance in PCa development is unknown. Since, like AR, CARF is negatively regulated by p53, we hypothesize that a reciprocal relationship between CARF and p53 could regulate AR expression in PCa cells. Indeed, we found that activation of p53 by DNA damage stress inhibited both CARF and AR in LnCap and 22RV1, AR-positive, and wtp53 cell lines. Our result indicated that CARF and AR were decreased dose-dependent manner, and presumably, that could trigger cell death. Consistent with this speculation, we found that silencing CARF by ShRNA in LnCap triggered apoptosis and inhibition of cell proliferation. With great interest, we further demonstrated that silencing of CARF downregulated the AR level in LnCap and 22RV1 cells suggesting that CARF regulates the expression of AR in PCa. RT-PCR results showed that AR transcripts remained unchanged in CARF-depleted LnCap cells. This result indicated that CARF could regulate the AR stability but not the transcription. Intriguingly, we found that the expression of NEDD4, one of the AR-targeting E3 ligases, was increased in CARF-depleted cells. Therefore, by enhancing the stability, CARF could positively regulate the expression of AR in PCa cells. Further studies are in progress to know more details about the CARF-mediated AR regulation and its impact on androgen-independent PCa development and progression. Presentation: Thursday, June 15, 2023