GPR56 regulates the expression of key androgen-target genes via G13-Rho-PKN1 axis and is overexpressed in prostate cancer.

Androgens and the androgen receptor (AR) play critical roles in prostate cancer (PCa) development and progression. Consequently, primary treatment strategies target either androgen synthesis or androgen-AR interactions. Although initially effective, tumors frequently recur as androgen-independent and more aggressive disease. In recurrent tumors, AR signaling often remains active through AR mutations or activation of alternative signaling pathways. Earlier studies from our laboratory had identified GPR56 (ADGRG1/GPCR205), an adhesion GPCR, as a possible membrane androgen receptor. Here, we demonstrate that GPR56, is significantly overexpressed in PCa tissues at both the transcript and protein levels and is associated with poor patient survival. Functional studies revealed that GPR56 promotes PCa cell proliferation and migration. Furthermore, GPR56 regulates the expression of key androgen-responsive genes, including KLK3 (PSA), FOXA1, TMPRSS2, and NKX3.1 and many others, across multiple prostate cell models. This study demonstrates that Testosterone (T) stimulation of cells expressing GPR56, activates the G13-RhoA-PKN1 signaling pathway, resulting in enhanced PKN1 expression and activation. This leads to AR-PKN1 interaction and increased transcriptional activity of AR target genes. Further T-stimulation activates serum response factor (SRF)-dependent transcription activating the RhoA-ROCK1-MLCK axis, leading to robust actin polymerization, a process associated with increased tumor cell motility and metastatic potential. Collectively, these findings shed light on the role of GPR56 in AR signaling and PCa. Further, the identification of a previously unrecognized GPR56-G13-PKN1 axis which interacts with AR and possibly SRF to enhance AR target gene activity, presents GPR56 as a promising therapeutic target especially in case of advanced PCa.