Regulation of androgen receptor stability by the β₁Pix/STUB1 complex

Abstract

The androgen receptor (AR) is essential in the development and differentiation of testes and male genitalia. AR expression is tightly regulated at the translational and posttranslational levels. AR posttranscriptional regulation is a major determinant of AR availability since AR is a direct target of E3 ubiquitin ligase STUB1. Our work indicated that the Rac/Cdc42 guanosine triphosphatase guanine nucleotide exchange factor, β1Pix, enhanced AR levels after AR stimulation in HEK293 and HeLa cells. AR stimulation decreased AR ubiquitination which is accompanied by increased β1Pix binding to AR. Ectopic expression of β1Pix decreased AR ubiquitination in Tm4 and HEK293 cells. We demonstrated that the formation of a multimolecular complex comprised of AR/β1Pix/STUB1 responded in a time‐dependent manner to AR stimulation. β1Pix binding dissociated STUB1 from AR and thus prevented STUB1 from catalyzing receptor ubiquitination. β1Pix enhanced AR transcriptional activity and increased AR target gene expression. Irrespective of treatment, immunofluorescence analysis showed a strong nuclear colocalization of endogenous AR and endogenous βPix in Tm4 cells. However, using Tm4 cell fractionation, AR stimulation decreased βPix/AR association in the cytosolic fraction and increased binding of AR to βPix in the nuclear fraction. To support the role of β1Pix in androgen regulation, we found that individuals lacking this gene have a significant increase in genitourinary malformations associated with androgen dysfunction. Our data indicate that β1Pix is an important modulator of AR stability and ligand‐dependent AR transcriptional activity. We propose that β1Pix could serve as a promising therapeutic target to modulate AR signaling.