GRB10 sustains AR activity by interacting with PP2A in prostate cancer cells

• Published in: International journal of cancer Vol. 148; no. 2; pp. 469 - 480
• Main Authors: Hao, Jun, Ci, Xinpei, Wang, Yong, Choi, Stephen Yiu Chuen, Sullivan, Sarah E., Xue, Hui, Wu, Rebecca, Dong, Xin, Haegert, Anne M., Collins, Colin C., Lin, Dong, Wang, Yuzhuo
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 15.01.2021; Wiley Subscription Services, Inc
• Subjects: Androgen receptors; Androgens; AR phosphorylation; Cancer; Castration; Gene expression; GRB10; Immunoprecipitation; Kinases; Mass spectroscopy; Medical research; Phosphorylation; PP2A; Prostate cancer; prostate cancer (PCa); Serine; Transcription; Xenografts
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.33335

Prostate cancer (PCa) progression is driven by androgen receptor (AR) signaling. Unfortunately, androgen‐deprivation therapy and the use of even more potent AR pathway inhibitors (ARPIs) cannot bring about a cure. ARPI resistance (ie, castration‐resistant PCa, CRPC) will inevitably develop. Previously, we demonstrated that GRB10 is an AR transcriptionally repressed gene that functionally contributes to CRPC development and ARPI resistance. GRB10 expression is elevated prior to CRPC development in our patient‐derived xenograft models and is significantly upregulated in clinical CRPC samples. Here, we analyzed transcriptomic data from GRB10 knockdown in PCa cells and found that AR signaling is downregulated. While the mRNA expression of AR target genes decreased upon GRB10 knockdown, AR expression was not affected at the mRNA or protein level. We further found that phosphorylation of AR serine 81 (S81), which is critical for AR transcriptional activity, is decreased by GRB10 knockdown and increased by its overexpression. Luciferase assay using GRB10‐knockdown cells also indicate reduced AR activity. Immunoprecipitation coupled with mass spectrometry revealed an interaction between GRB10 and the PP2A complex, which is a known phosphatase of AR. Further validations and analyses showed that GRB10 binds to the PP2Ac catalytic subunit with its PH domain. Mechanistically, GRB10 knockdown increased PP2Ac protein stability, which in turn decreased AR S81 phosphorylation and reduced AR activity. Our findings indicate a reciprocal feedback between GRB10 and AR signaling, implying the importance of GRB10 in PCa progression. What's new? Androgen receptor (AR) signaling is the dominant driver of AR‐dependent castration‐resistant prostate cancer (CRPC) development and progression, even with continuous androgen deprivation therapy. The mechanisms causing the reactivation of AR signaling in CRPC remain unclear. Here, the authors demonstrate that the adaptor protein GRB10 sustains AR activity in CRPC. Data from high‐throughput proteomics analysis indicate that the reported tumor suppressor PP2A is a mediator of AR modulation by GRB10. GRB10 interacts with PP2A and promotes its degradation, thereby protecting phosphorylated AR from dephosphorylation and sustaining active AR signaling. Inhibiting GRB10 therapeutically could potentially improve CRPC management.