βArrestin1 regulates glucocorticoid receptor mitogenic signaling in castration‐resistant prostate cancer

Abstract

Background: Prostate cancer (PC) is the most commonly diagnosed malignancy and the second leading cause of cancer-related deaths in males. The disease is initially treated with methods that inhibit androgen receptor (AR) signal transduction.Laboratory-based and clinical studies have identified alternative pathways that cause the failure of AR signal inhibition and consequent development of castrationresistant prostate cancer (CRPC). Glucocorticoid receptor (GR) signaling is activated in certain PC patients and promotes the emergence of CRPC, although by as yet incompletely understood mechanisms. We have previously demonstrated that ubiquitous βarrestin1 (βArr1) expression levels are linked to PC progression. Here, we consider the possibility that βArr1 interacts with and activates GR in model CRPC cells.Methods: Bioinformatic analysis of tumor xenograft and human PC datasets was used to correlate the expression of βArr1 and GR. Western blot, immunohistochemistry and immunofluorescence microscopy, and subcellular fractionation were used to determine protein expression level and localization. Immunoprecipitation was applied to detect protein-protein interactions. RNA expression levels were determined using quantitative reverse transcription-polymerase chain reaction. Prostate sphere analysis was used to assess the rate of growth and invasion. The xenograft tumor implantation method was used to determine the tumor growth rate, local invasion, and metastasis.Results: Elevated expression of βArr1 positively correlated with increased GR expression and function in CRPC xenograft and in human PC patients. βArr1 is expressed in the cell cytosol and nucleus, and it formed a complex with GR in the nucleus and not cytosol. Depletion of βArr1 in AR-null CRPC cells inhibited GR function and CRPC growth and invasion in both in vitro and in vivo settings.Conclusions: βArr1 binds GR that initiates mitogenic signaling cascades involved in the progression of PC to CRPC. The targeting of the βArr1-GR axis may provide a new opportunity to better manage the CRPC disease.

Advances in the Current Understanding of the Mechanisms Governing the Acquisition of Castration-Resistant Prostate Cancer

“…Hoshi et al demonstrated that the GR-mediated upregulation of GLUT4 is associated with the progression of the CRPC [ 107 ]. In addition, Purayil et al found that βArr1 can play a role in the progression of prostate cancer to CRPC by binding to the GR to initiate a mitogenic signaling cascade [ 108 ]. As such, GR can bypass the AR pathway and promote the development of CRPC.…”