Caratterizzazione dell'impatto della fosforilazione sulle funzioni del recettore degli androgeni

The androgen receptor (AR) is a member of the steroid hormone receptors (SHRs) subfamily of nuclear receptors (NRs), and the main mediator of androgen signalling. In its inactive state, AR localizes in the cytosol, associated with chaperones and co-chaperones which form the foldosome complex. The foldosome complex through a reversible three-step process (early, intermediate and mature) assists AR folding, keeping it ready to bind androgens. As a transcription factor, AR activation must be tightly regulated together with its rapid inactivation and degradation. However, the fine regulation of AR synthesis, maturation, activation, and degradation remains poorly understood. AR activity is strongly regulated by several post-translational modifications, with phosphorylation being the most common. Any disruption in the balance between AR activation and degradation leads to several disease conditions, including cancer. Notably, males have a higher risk of developing clear cell renal cell carcinoma (ccRCC), suggesting the involvement of AR in ccRCC pathogenesis. The central hypothesis of this work is that phosphorylation affects the balance between folding and degradation by altering AR protein-protein interactions (PPIs). Moreover, given the importance of phosphorylation in regulating AR function, we hypothesized that it may contribute to ccRCC development. We showed that both phosphorylation at specific sites and androgen levels directly influence the binding with specific co-chaperones, like PP5, STUB1 and MDM2, providing a signal for AR degradation. Moreover, we found that AR also interacts with the tumour suppressor Von Hippel Lindau protein (VHL) protein, whose loss-of-function (LOF) mutation is associated with ccRCC. VHL is the substrate recognition particle of the E3-ubiquitin ligase complex, involved in the degradation of HIF-1α. We demonstrate that VHL promotes AR degradation in an isoform-specific manner, a process that may disrupted in ccRCC tumor harboring VHL LOF mutations. Using an AR negative ccRCC cell line, named ACHN, stably expressing AR and different AR phospho-mutants, we observed different effects on tumor growth. This implies that AR phosphorylation influences tumor growth and that AR regulates gene expression based on its phosphorylation status. Our findings provide new insights into the mechanisms regulating AR activity and contribute to the understanding of ccRCC pathogenesis, potentially offering new perspectives for targeted therapeutic strategies.