SKP2 Inactivation Suppresses Cell Proliferation and Regulates AR/FOXA1 Expression in PCa Cells

Abstract

Increased levels of SKP2 (S‐phase kinase‐associated protein 2), an E3 ubiquitin ligase, is frequently seen in advanced stages of prostate cancer (PCa). Correlations between SKP2 and the ubiquitin‐mediated degradation of key cell cycle regulators such as p21 and p27, as well as between SKP2 and the regulation of androgen receptor (AR) activity is frequently observed in PCa progression. Despite these associations, the molecular mechanisms responsible for the proto‐oncogenic effects of SKP2 in PCa remain elusive. The transcription factor FOXA1 (Forkhead box protein A1) is known to induce AR activity, and by doing so cause the activation of AR target genes. Deregulation of the AR/FOXA1 complex has been found to contribute to the progression of PCa and castration‐resistant prostate cancer (CRPC). We hypothesized that SKP2 impacts the function of the AR/FOXA1 complex contributing to the progression of CRPC. Using shRNA technology, we established stable SKP2 knockdown PCa cell lines to investigate the effects of SKP2 on CRPC growth. Our results demonstrate that SKP2 plays a critical role in the regulation of AR and FOXA1 expression in CRPC cell lines. SKP2 knockdown increased AR and FOXA1 levels in C4‐2B and 22RV1 cells, two CRPC cell lines. Furthermore, SKP2 knockdown significantly inhibited cellular proliferation and restored sensitivity to the AR antagonist (MDV3100) in C4‐2B and 22RV1 cells. Combined exposure to the AR antagonist (MDV3100) and a SKP2 inhibitor significantly reduced cellular proliferation, a result of cell cycle arrest and cellular senescence in C4‐2B and 22RV1. Endogenous and Myc‐tagged SKP2 as well as Flag‐tagged FOXA1 immunoprecipitation displayed a physical interaction between SKP2 and FOXA1. In vivo ubiquitination assay was performed using HEK293T cells transfected with HA‐Ub constructs demonstrating a SKP2 E3 ubiquitin ligase function for FOXA1. Our findings present a potential SKP2‐AR/FOXA1 signaling pathway that may be targeted therapeutically to inhibit CRPC malignancy.Support or Funding Information2U54CA163066MVTCP CA163069This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.