Choline Kinase Alpha as an Androgen Receptor Chaperone and Prostate Cancer Therapeutic Target

Abstract

Background:The androgen receptor (AR) is a major drug target in prostate cancer (PCa). We profiled the AR-regulated kinome to identify clinically relevant and druggable effectors of AR signaling.Methods:Using genome-wide approaches, we interrogated all AR regulated kinases. Among these, choline kinase alpha (CHKA) expression was evaluated in benign (n = 195), prostatic intraepithelial neoplasia (PIN) (n = 153) and prostate cancer (PCa) lesions (n = 359). We interrogated how CHKA regulates AR signaling using biochemical assays and investigated androgen regulation of CHKA expression in men with PCa, both untreated (n = 20) and treated with an androgen biosynthesis inhibitor degarelix (n = 27). We studied the effect of CHKA inhibition on the PCa transcriptome using RNA sequencing and tested the effect of CHKA inhibition on cell growth, clonogenic survival and invasion. Tumor xenografts (n = 6 per group) were generated in mice using genetically engineered prostate cancer cells with inducible CHKA knockdown. Data were analyzed with χ2 tests, Cox regression analysis, and Kaplan-Meier methods. All statistical tests were two-sided.Results:CHKA expression was shown to be androgen regulated in cell lines, xenografts, and human tissue (log fold change from 6.75 to 6.59, P = .002) and was positively associated with tumor stage. CHKA binds directly to the ligand-binding domain (LBD) of AR, enhancing its stability. As such, CHKA is the first kinase identified as an AR chaperone. Inhibition of CHKA repressed the AR transcriptional program including pathways enriched for regulation of protein folding, decreased AR protein levels, and inhibited the growth of PCa cell lines, human PCa explants, and tumor xenografts.Conclusions:CHKA can act as an AR chaperone, providing, to our knowledge, the first evidence for kinases as molecular chaperones, making CHKA both a marker of tumor progression and a potential therapeutic target for PCa.

Interference with the androgen receptor protein stability in therapy‐resistant prostate cancer

“…Examples include arrest‐defective protein 1 (ARD1), an oncoprotein that enhances dissociation of the ligand‐bound AR from HSP90 by acetylation of the K618 residue of AR, leading to PCa tumor growth . Recently, a novel chaperone of AR, choline kinase‐α (CHKA) is shown to be upregulated in PCa and bind directly to the AR LBD, a region where HSPs bind . Interestingly, inactivation of CHKA results in downregulation of AR protein levels.…”

“…Interestingly, inactivation of CHKA results in downregulation of AR protein levels. Accordingly, inactivation of CHKA reduced tumor growth of CRPC in xenograft mice indicating that the chaperone function of CHKA and its interaction with AR renders CHKA an interesting drug target to downregulate AR protein levels . The co‐chaperone folliculin‐interacting proteins (FNIPs) positively regulate the HSP90 chaperone cycle and are highly expressed in tumors .…”

“…30 Recently, a novel chaperone of AR, choline kinase-α (CHKA) is shown to be upregulated in PCa and bind directly to the AR LBD, a region where HSPs bind. 31 Interestingly, inactivation of CHKA results in downregulation of AR protein levels. Accordingly, inactivation of CHKA reduced tumor growth of CRPC in xenograft mice indicating that the chaperone function of CHKA and its interaction with AR renders CHKA an interesting drug target to downregulate AR protein levels.…”

“…Accordingly, inactivation of CHKA reduced tumor growth of CRPC in xenograft mice indicating that the chaperone function of CHKA and its interaction with AR renders CHKA an interesting drug target to downregulate AR protein levels. 31 The co-chaperone folliculin-interacting proteins (FNIPs) positively regulate the HSP90 chaperone cycle and are highly expressed in tumors. 32 Importantly, higher levels of FNIPs in renal cancer cells correlate with increased sensitivity to HSP90i, leading us to ponder whether FNIPs modulate HSPs-AR complex in PCa thus affecting HSP90i treatment outcome.…”

Kinase joins the chaperone club: Androgen-regulated kinome reveals choline kinase alpha as a potential drug target in prostate cancer

“…We showed that choline kinase a (CHKA) is a chaperone for the AR, promoting its stability and function. 6 This is the first report demonstrating that kinases can act as chaperones. During our studies we also identified 49 androgen-regulated kinases, of which 25 were upregulated and 24 were downregulated.…”