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

Abstract

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 β‐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 β‐catenin distribution from the cytoplasm to the cell membrane. Additionally, down‐regulation of c‐myc and cyclin D1 expression was observed in mock‐transfected cells 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 β‐catenin was observed. Where CaSR expression was reduced, β‐catenin surface expression was likewise reduced. © 2007 Wiley‐Liss, Inc.

Epigenetic inactivation of calcium-sensing receptor in colorectal carcinogenesis

“…11,14 In a small series of colorectal cancer tissues (n ¼ 6), a relationship between CASR expression and b-catenin staining pattern was reported. 14 In this study, nuclear/cytoplasmic b-catenin expression was more frequently observed in cases with reduced CASR expression than in cases with normal CASR expression. As various genetic and epigenetic alterations are involved in b-catenin/T-cell factor activation, the relationship between b-catenin expression and CASR expression seems not to be simple.…”

“…CASR reportedly controls proliferation and differentiation in the human colonic epithelium and colon carcinoma cells. [10][11][12][13][14][15][16][17][18] Increased thymidylate synthase expression is one the most important mechanisms underlying the resistance to 5-fluorouracil (FU) in colorectal cancer. 19,20 Interestingly, activation of CASR reportedly downregulates the expression of thymidylate synthase and survivin, and upregulates cellular sensitivity to 5-FU in human colorectal cancer cell lines.…”

Effects of potential calcium sensing receptor inducers on promoting chemosensitivity of human colon carcinoma cells

“…Since CaSR not only suppressed protein expression of survivin and TS, but also inhibited gene promoter transcription of these proteins, we suggested that the suppression of the genes by CaSR mainly occurred at the level of transcriptional promotion and initiation. Activation of CaSR also stimulates the expression of E-cadherin (8,9,36). E-cadherin is a major classical trans-membrane protein in epithelial cells.…”

“…Human colon carcinoma cell line CBS, Moser, Fet, and SW480 cells were maintained in SMEM medium (Sigma, St. Louis, MO) as described previously (7)(8)(9). To assess the effect of the compounds indicated on the cytotoxic response to anticancer drugs, the medium of actively growing cells was replenished with medium containing the compounds at the doses indicated in the figures and FOLFIRI (5-FU 60 μM, leucovorin 28 μM, SN-38 40 μM).…”

“…As the epithelial cells differentiate and migrate upward to the top of the crypt, the cells acquire a gradient increase in the expression of the CaSR (5,6). In colon cancer, welldifferentiated carcinoma cells express observable levels of CaSR, whereas undifferentiated carcinoma cells have little or no CaSR expression (7)(8)(9)(10). Since undifferentiated status is one of the mechanisms underlying drug resistance, we have hypothesized in our previous studies that CaSR is involved in chemosensitivity of human colon carcinoma cells and found that activation or induction of CaSR in the cells significantly promoted the sensitivity of the cells to anticancer drug treatment (11,12).…”