Regulation of E-cadherin and β-catenin by Ca2+ in colon carcinoma is dependent on calcium-sensing receptor expression and function

An siRNA directed against the extracellular calcium-sensing receptor (CaSR) was used to down-regulate this protein in CBS colon carcinoma cells. In additional studies, we utilized a variant of the parental CBS line that demonstrates CaSR expression but does not upregulate this protein in response to extracellular Ca2+ In neither the siRNA-transfected cells nor the Ca2+-nonresponsive variant cells did inclusion of Ca2+ in the culture medium inhibit proliferation or induce morphological alterations. Extracellular Ca2+ also failed to induce E-cadherin production or a shift in beta-catenin from the cytoplasm to the cell membrane. In mock-transfected cells and in a Ca2+- responsive variant line derived from the same parental CBS cells, Ca2+ treatment resulted in growth-reduction. This was accompanied by increased E-cadherin production and a shift in beta-catenin distribution from the cytoplasm to the cell membrane. Additionally, down-regulation of c-myc and cyclin D1 expression was observed in truck-transfected calls and in the Ca2+-responsive variant line (along with reduced T cell factor transcriptional activation). Neither c-myc nor cyclin D1 was significantly down- regulated in the siRNA-transfected cells or in the Ca2+-nonresponsive variant cells upon Ca2+ stimulation. In histological sections of human colon carcinoma CaSR was significantly reduced as compared to the level in normal colonic crypt epithelial cells. Where CaSR expression was high, strong surface staining for E-cadherin and P-catenin was observed. Where CaSR expression was reduced, P-catenin surface expression was likewise reduced. (C) 2007 Wiley-Liss, Inc.