Protein Kinase N1 control of androgen-responsive serum response factor action provides rationale for novel prostate cancer treatment strategy

Abstract

Sustained reliance on androgen receptor (AR) after failure of AR-targeting androgen deprivation therapy (ADT) prevents effective treatment of castration-recurrent (CR) prostate cancer (CaP). Interfering with the molecular machinery by which AR drives CaP progression may be an alternative therapeutic strategy but its feasibility remains to be tested. Here, we explore targeting the mechanism by which AR, via RhoA, conveys androgen-responsiveness to Serum Response Factor (SRF), which controls aggressive CaP behavior and is maintained in CR-CaP. Following a siRNA screen and candidate gene approach, RNA-Seq studies confirmed that the RhoA effector Protein Kinase N1 (PKN1) transduces androgen-responsiveness to SRF. Androgen treatment induced SRF-PKN1 interaction, and PKN1 knockdown or overexpression severely impaired or stimulated, respectively, androgen regulation of SRF target genes. PKN1 overexpression occurred during clinical CR-CaP progression, and hastened CaP growth and shortened CR-CaP survival in orthotopic CaP xenografts. PKN1’s effects on SRF relied on its kinase domain. The multikinase inhibitor lestaurtinib inhibited PKN1 action and preferentially affected androgen regulation of SRF over direct AR target genes. In a CR-CaP patient-derived xenograft, expression of SRF target genes was maintained while AR target gene expression declined and proliferative gene expression increased. PKN1 inhibition decreased viability of CaP cells before and after ADT. In patient-derived CaP explants, lestaurtinib increased AR target gene expression but did not significantly alter SRF target gene or proliferative gene expression. These results provide proof-of-principle for selective forms of ADT that preferentially target different fractions of AR’s transcriptional output to inhibit CaP growth.

Exploration of Prognostic Biomarkers and Therapeutic Targets in The Microenvironment of Bladder Cancer Based on CXC Chemokines

“…Our study provided evidence that there is an association between CXC chemokines and the NF-κB signaling pathway during BLCA tumorigenesis and development. Our results also suggested Src family tyrosine kinases (LCK and LYN), PKN1, PRKG1, and CHEK1 might be the targets of the differential CXC chemokines, which play important roles in cell growth, division, migration, and survival signaling pathways [66][67][68][69], and mediate the carcinogenesis of several tumors [70][71][72]. Therefore, these differentially expressed CXC chemokines might modulate BLCA development and progression dependent on the above-mentioned signaling pathways by regulating these kinases.…”

Characterization of Kinase Expression Related to Increased Migration of PC-3M Cells Using Global Comparative Phosphoproteome Analysis

“…In addition, CDK inhibitors are currently being evaluated in clinical trials (45). Second, serine/threonine-protein kinase N1 (PKN1) and PKN2 have been reported to contribute to the motility of PCa cells, and PKN1 overexpression was observed during clinical CRPC progression (46)(47)(48). PKN1 and PKN2 have been suggested to be potential PCa treatment targets.…”

AR-dependent phosphorylation and phospho-proteome targets in prostate cancer

“…It is also conceivable that AR controls enzymatic activity of phosphorylation modulators without altering their expression levels. One such mechanism by which AR may steer kinase activity to specific CaP functions is its signaling, via activation of RhoA, to the Ser/Thr kinase PKN1, which then mediates androgen control to the secondary transcription factor serum response factor (SRF) (Venkadakrishnan et al 2019). SRF controls the immediate early response, cell cycle regulation, and organization of cytoskeleton.…”

“…Another important and often underappreciated limitation is that the endpoint used to measure therapeutic success is not adequate for the compound under investigation, leaving investigators essentially unable to judge the efficacy of drugs tested and to misinterpret trial results. An example of this relates to our and others' testing of the multi-kinase inhibitor, lestaurtinib, as CaP therapeutic (Venkadakrishnan et al 2019). Lestaurtinib also inhibits the kinase activity of PKN1, which drives CaP progression, and is highly expressed and activated in CRPC.…”

“…The decision not to move lestaurtinib forward clinically in CRPC was made solely based on the failure to meet the endpoint of PSA response. However, studies in vivo and in vitro CaP models have shown increased PSA production by cells that were growth-arrested by lestaurtinib (Collins et al 2007, Venkadakrishnan et al 2019). The implication is that a potentially effective agent to target AR action downstream of activated AR that has a different mechanism of action than traditional ADT and is tolerated by patients was abandoned mainly because of the use of an inappropriate biomarker to evaluate treatment response.…”