Identification of an interaction between the TPalpha and TPbeta isoforms of the human thromboxane A2 receptor with protein kinase C-related kinase (PRK) 1 : implications for prostate cancer.

In humans, thromboxane (TX)A2 signals through the TPalpha and TPbeta isoforms of the TXA2 receptor, or TP. Herein, the RhoA effector protein kinase C-related kinase (PRK) 1 was identified as an interactant of both TPalpha and TPbeta involving common and unique sequences within their respective carboxyl-terminal (C)-tail domains and the kinase domain of PRK1 (PRK1640-942). While the interaction with PRK1 is constitutive, agonist-activation of TPalpha/TPbeta did not regulate the complex per se but enhanced PRK1 activation leading to phosphorylation of its general substrate histone H1 in vitro. Altered PRK1 and TP expression and signalling are increasingly implicated in certain neoplasms, particularly in androgen-associated prostate carcinomas. Agonist-activation of TPalpha/TPbeta led to phosphorylation of histone H3 at Thr11 (H3Thr11), a previously recognized specific marker of androgen induced-chromatin remodeling, in the prostate LNCaP and PC-3 cell lines but not in primary vascular smooth muscle or endothelial cells. Moreover, this effect was augmented by dihydrotestosterone in androgen-responsive LNCaP but not in non-responsive PC-3 cells. Furthermore, PRK1 was confirmed to constitutively interact with TPalpha/TPbeta in both LNCaP and PC-3 cells and targeted disruption of PRK1 impaired TPalpha/TPbeta-mediated H3Thr11 phosphorylation in, and cell migration of, both prostate cell types. Collectively, considering the role of TXA2 as a potent mediator of RhoA signalling, the identification of PRK1 as a bone fide interactant of TPalpha/TPbeta, and leading to H3Thr11 phosphorylation to regulate cell migration, has broad functional significance such as within the vasculature and in neoplasms in which both PRK1 and the TPs are increasingly implicated.