Protein kinase A-mediated phosphorylation regulates STAT3 activation and oncogenic EZH2 activity

Abstract

Polycomb Repressive Complex 2 (PRC2) member enhancer of zeste homologue 2 (EZH2) trimethylates histone H3 lysine 27 (H3K27me3), alters chromatin structure and contributes to epigenetic regulation of gene expression in normal and disease processes. Phosphorylation of EZH2 augmented EZH2 oncogenic activity in cancer but observations have been limited to serine 21 (S21) residue by protein kinase B. In addition, phosphorylation of the evolutionarily conserved T372 motif of EZH2 by p38 resulted in EZH2 interaction with Ying Yang 1 and promoted muscle stem cell differentiation. In the present study, we used epithelial ovarian cancer (OC) cells as a model to demonstrate that phosphorylation of EZH2 at T372 by protein kinase A (PKA) induced a dominant-negative EZH2 phenotype, inhibited OC cell proliferation and migration in vitro and decreased ovarian xenograft tumor growth in vivo. Phosphorylation of T372 by PKA enhanced the interaction between EZH2 and signal transducer and activator of transcription 3 (STAT3), and STAT3 binding to pT372-EZH2 reduced cellular levels of pSTAT3 and downregulated interleukin 6 receptor expression in OC. Furthermore, PKA-mediated pT372-EZH2 decreased ATP levels and altered mitochondrial gene expression, resulting in mitochondrial dysfunction and reduced OC cell growth. These findings demonstrate that PKA-mediated T372 phosphorylation reduces oncogenic EZH2 activity and reveal a novel role for pT372 in regulating EZH2 in OC and possibly other cancers.

Cyclic AMP Regulates Key Features of Macrophages via PKA: Recruitment, Reprogramming and Efferocytosis

“…Corroborating our data, Koscso and colleagues demonstrated that adenosine, which binds to A2A and A2B receptors and stimulate the adenylyl cyclase to produce cAMP, has synergistic effect with IL-10 in inducing macrophage polarization towards an M2c profile in a STAT3-dependent manner [93]. Moreover, recent studies have argued that STAT3 activation can occur via PKA [94,95]. Although we have not investigated here whether db-cAMP-induced STAT3 activation was via PKA, we can hypothesize that PKA activation may be occurring in our settings of macrophage reprogramming.…”

Activation of STAT3 and STAT5 Signaling in Epithelial Ovarian Cancer Progression: Mechanism and Therapeutic Opportunity

“…Interestingly, upon Tyr372 phosphorylation of EZH2 by protein kinase A, pY372-EZH2 efficiently interacted with STAT3 protein. This non-canonical EZH2 interaction reduced cellular levels of STAT3 and altered STAT3 activation, leading to the downregulation of downstream target IL-6R in EOC [46]. Furthermore, tyrosine phosphorylation of EZH2 by JAK3 in lymphoid neoplasia was reported to promote dissociation of the polycomb repressive complex 2 (PRC2) complex leading to decreased global H3K27me3 levels while it switches EZH2 to a transcriptional activator [47], but studies in EOC are lacking.…”

Peer Review #1 of "EZH2/H3K27Me3 and phosphorylated EZH2 predict chemotherapy response and prognosis in ovarian cancer (v0.2)"

“…A recent study reported that EZH2 phosphorylation at T372 reduced ovarian cancer cell proliferation, migration and tumor formation (Wan et al, 2018). The levels of EZH2-T372 phosphorylation in primary ovarian tumor samples were significantly lower than that in normal ovarian surface epithelium (Ozes et al, 2018). Wan et al reported that EZH2 phosphorylation at T311 by AMPK suppressed PRC2 activity and EZH2-pT311 correlated with better survival in ovarian and breast cancer patients (Wan et al, 2018).…”