Regulation of androgen receptor stability by the β₁ Pix/STUB1 complex

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, β₁ Pix, enhanced AR levels after AR stimulation in HEK293 and HeLa cells. AR stimulation decreased AR ubiquitination which is accompanied by increased β₁ Pix binding to AR. Ectopic expression of β₁ Pix decreased AR ubiquitination in Tm4 and HEK293 cells. We demonstrated that the formation of a multimolecular complex comprised of AR/β₁ Pix/STUB1 responded in a time-dependent manner to AR stimulation. β₁ Pix binding dissociated STUB1 from AR and thus prevented STUB1 from catalyzing receptor ubiquitination. β₁ Pix 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 β₁ Pix 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 β₁ Pix is an important modulator of AR stability and ligand-dependent AR transcriptional activity. We propose that β₁ Pix could serve as a promising therapeutic target to modulate AR signaling.