Crosstalk between protein kinase C α and transforming growth factor β signaling mediated by Runx2 in intestinal epithelial cells

Tight coordination of growth regulatory signaling is required for intestinal epithelial homeostasis. Protein kinase C alpha (PKC alpha) and transforming growth factor beta (TGF beta) are nega-tive regulators of proliferation with tumor suppressor proper-ties in the intestine. Here, we identify novel crosstalk between PKC alpha and TGF beta signaling. RNA-Seq analysis of non -transformed intestinal crypt-like cells and colorectal cancer cells identified TGF beta receptor 1 (TGF beta R1) as a target of PKC alpha signaling. RT-PCR and immunoblot analysis confirmed that PKC alpha positively regulates TGFfiR1 mRNA and protein expression in these cells. Effects on TGF beta R1 were dependent on Ras-extracellular signal-regulated kinase 1/2 (ERK) signaling. Nascent RNA and promoter-reporter analysis indi-cated that PKC alpha induces TGFfiR1 transcription, and Runx2 was identified as an essential mediator of the effect. PKC alpha promoted ERK-mediated activating phosphorylation of Runx2, which preceded transcriptional activation of the TGFfiR1 gene and induction of Runx2 expression. Thus, we have identified a novel PKC alpha -> ERK -> Runx2 -> TGF beta R1 signaling axis. In further support of a link between PKC alpha and TGF beta signaling, PKC alpha knockdown reduced the ability of TGF beta to induce SMAD2 phosphorylation and cell cycle arrest, and inhibition of TGF beta R1 decreased PKC alpha-induced upregulation of p21Cip1 and p27Kip1 in intestinal cells. The physiological relevance of these findings is also supported by The Cancer Genome Atlas data showing correlation between PKCa, Runx2, and TGFfiR1 mRNA expression in human colorectal cancer. PKC alpha also regulated TGF beta R1 in endometrial cancer cells, and PKCa, Runx2, and TGFfiR1 expression correlates in uterine tumors, indicating that crosstalk between PKC alpha and TGF beta signaling may be a common mechanism in diverse epithelial tissues.

Automated summary

This study identified a novel crosstalk between PKC alpha and TGF beta signaling, which regulates the expression of TGF beta receptor 1 and affects intestinal epithelial cell proliferation and tumor development. The crosstalk between PKC alpha and TGF beta signaling is not only present in the intestine, but also in other epithelial tissues.