Regulation of E-cadherin and beta-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 Ca(2+). In neither the siRNA-transfected cells nor the Ca(2+)-nonresponsive variant cells did inclusion of Ca(2+) in the culture medium inhibit proliferation or induce morphological alterations. Extracellular Ca(2+) 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 Ca(2+)-responsive variant line derived from the same parental CBS cells, Ca(2+) 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 mock-transfected cells and in the Ca(2+)-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 Ca(2+)-nonresponsive variant cells upon Ca(2+) 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 beta-catenin was observed. Where CaSR expression was reduced, beta-catenin surface expression was likewise reduced.
Bhagavathula
Narasimharao
N
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Hanosh
Andrew W
AW
Nerusu
Kamalakar C
KC
Appelman
Henry
H
Chakrabarty
Subhas
S
Varani
James
J
D015820:Cadherins / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D034741:RNA, Small Interfering / Q000235:genetics; D044169:Receptors, Calcium-Sensing / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D051176:beta Catenin / Q000378:metabolism*
D015820:Cadherins; D034741:RNA, Small Interfering; D044169:Receptors, Calcium-Sensing; D051176:beta Catenin; D002118:Calcium