Selective Role of an NH2-Terminal WxxLF Motif for Aberrant Androgen Receptor Activation in Androgen Depletion–Independent Prostate Cancer Cells

Abstract

Systemic prostate cancer therapy requires androgen ablation, which inhibits the production or action of androgens. Prostate cancer ultimately relapses during androgen ablation, and an androgen depletion-independent (ADI) phenotype emerges. Aberrant androgen receptor (AR) activation underlies therapy resistance at this stage of the disease, and mounting evidence implicates the large and highly disordered AR NH 2 -terminal domain (NTD) as a key mediator of this activity. In this study, we investigated the role of the NTD transactivation unit 5 (TAU5) domain in mediating AR transcriptional activity in cell-based models of prostate cancer progression. AR replacement and Gal4-based promoter tethering experiments revealed that AR TAU5 had a dichotomous function, inhibiting ligand-dependent AR activity in androgen-dependent prostate cancer cells, while enhancing ligand-independent AR activity in ADI prostate cancer cells. Molecular dissection of TAU5 showed that a WxxLF motif was fully responsible for its ligandindependent activity. Mechanistically, WxxLF did not rely on an interaction with the AR ligand-binding domain to mediate ligand-independent AR activity. Rather, WxxLF functioned as an autonomous transactivation domain. These data show that ligand-dependent and ligand-independent AR activation rely on fundamentally distinct mechanisms, and define WxxLF as the major transactivation motif within the AR TAU5 domain.

Androgen and Prostate Cancer: Is the Hypothesis Dead?

“…Two epidemiologic studies examined polymorphic variants of the AR gene and its coactivator AIB1 in cases and controls, with mixed results (11,21). Studies on androgen receptor coactivators in prostate cancer showed that androgen receptor coactivators are associated with disease aggressiveness and poor prognosis (22), with androgen receptor activation related to androgen-refractory disease (23), and with resistance to antiandrogen (24,25). The role of androgen receptor corepressors in prostate cancer is not yet well-defined.…”

Androgen Receptor Exon 1 Mutation Causes Androgen Insensitivity by Creating Phosphorylation Site and Inhibiting Melanoma Antigen-A11 Activation of NH2- and Carboxyl-terminal Interaction-dependent Transactivation

“…2) implicated in the androgen-dependent AR N/C interaction and transcriptional activity (13,(21)(22)(23). Expression studies using wild-type and mutant AR and select AR fragments ( Fig.…”

“…The AR N/C interaction is modulated by primate-specific melanoma antigen-A11 (MAGE-11) that binds the AR FXXLF motif and functions synergistically with the AR N/C interaction, coregulators, and transcription factors (16 -20). An AR NH 2 -terminal WXXLF motif contributes to the AR N/C interaction through mechanisms not well understood (21,22). Disruption of the AR N/C interaction by mutating the AR NH 2 -terminal FXXLF motif inhibits AR transcriptional activation of androgen-responsive reporter genes (23).…”

“…9). The WXXLF motif has been linked to AR transcriptional activity and is a site of somatic mutations in prostate cancer, although the mechanisms by which the WXXLF motif increases AR activity were unclear (13,21,22,64,65). Absence of an inhibitory effect of the R405S mutation on WXXLF motif binding to AF2 and on androgen-dependent AR stabilization suggested that the AR R405S mutation does not interfere with the androgen-dependent AR N/C interaction.…”

The biological and clinical advances of androgen receptor function in age-related diseases and cancer [Review]

“…In the LBD, the binding of androgen hormone to AR is promoted [8]. AF2 domain in the LBD interacts with co-regulators with LXXLL motif [9][10][11]. In the absence of hormone, AR forms a complex in the cytoplasm with the heat shock protein (Hsp) family that functions as molecular chaperones.…”