The Extracellular Calcium-Sensing Receptor Regulates the Proliferation of Colonic Epithelial Cells In Vitro and In Vivo

OSVALDO REY; WENHAN CHANG; DANIEL BIKLE; NORA ROZENGURT; PAT MOYER; ENRIQUE ROZENGURT

Congreso; Digestive Diseases Week; 2011

Background: The extracellular Ca2+-sensing receptor (CaR) is implicated in the regulation of proliferation and differentiation of intestinal epithelial cells. Indeed, CaR expression is lost in colon carcinomas and dietary Ca2+ has been proposed to reduce colon cancer risk. However, the mechanisms involved remain poorly understood. Here, we examined changes in -catenin triggered by CaR activation in colonic epithelial cells and its role in the control of colonic cell proliferation. Results: Phosphorylation of -catenin at Ser-33, Ser-37 and Ser-41 by GSK-3 promotes its degradation whereas, in contrast, its phosphorylation on Ser-552 stimulates nuclear translocation and transcriptional activity. Here we demonstrate that stimulation of the CaR by extracellular Ca2+ (5 mM) or by the calcimimetic R-568 (100 nM) produced a striking and time-dependent (30 min to 4 h) decrease (60%) in the phosphorylation of -catenin at Ser-552 in NCM-460 human-colon derived epithelial cells expressing the CaR. Concomitantly, we detected by immunofluorescence a reduced nuclear reactivity of the phospho Ser-552 antibody as well as a marked redistribution of -catenin to the plasma membrane. These effects were mediated by the CaR because extracellular Ca2+ or by R-568 did not change the level of -catenin Ser-552 phosphorylation or its distribution when the expression of the CaR was not induced in NCM-460 cells. These changes in -catenin phosphorylation and intracellular distribution were associated with cell proliferation inhibition. In Vivo studies using a recently developed CaR intestinal-specific knock out mice indicate that the genetic ablation of the CaR leads to an increase in the proliferation of colonic crypts as revealed by Ki 67 proliferation marker immunostaining. Conclusion: These studies suggest that signaling pathways emanating from the CaR play an important role in the control colonic epithelial crypt cells proliferation by a novel mechanism that involves -catenin phosphorylation/dephosphorylation cascades.