Positive cross talk between protein kinase D and β-catenin in intestinal epithelial cells: impact on β-catenin nuclear localization and phosphorylation at Ser552

Given the fundamental role of beta-catenin signaling in intestinal epithelial cell proliferation and the growth-promoting function of protein kinase D1 (PKD1) in these cells, we hypothesized that PKDs mediate cross talk with beta-catenin signaling. The results presented here provide several lines of evidence supporting this hypothesis. We found that stimulation of intestinal epithelial IEC-18 cells with the G protein-coupled receptor (GPCR) agonist angiotensin II (ANG II), a potent inducer of PKD activation, promoted endogenous beta-catenin nuclear localization in a time-dependent manner. A significant increase was evident within 1 h of ANG II stimulation (P < 0.01), peaked at 4 h (P < 0.001), and declined afterwards. GPCR stimulation also induced a marked increase in beta-catenin-regulated genes and phosphorylation at Ser(552) in intestinal epithelial cells. Exposure to preferential inhibitors of the PKD family (CRT006610 or kb NB 142-70) or knockdown of the isoforms of the PKD family prevented the increase in beta-catenin nuclear localization and phosphorylation at Ser(552) in response to ANG II. GPCR stimulation also induced the formation of a complex between PKD1 and beta-catenin, as shown by coimmuno-precipitation that depended on PKD1 catalytic activation, as it was abrogated by cell treatment with PKD family inhibitors. Using transgenic mice that express elevated PKD1 protein in the intestinal epithelium, we detected a marked increase in the localization of beta-catenin in the nucleus of crypt epithelial cells in the ileum of PKD1 transgenic mice, compared with nontransgenic littermates. Collectively, our results identify a novel cross talk between PKD and beta-catenin in intestinal epithelial cells, both in vitro and in vivo.