Abstract
We have investigated the molecular basis of intracellular Ca(2+) handling in human colon carcinoma cells (HT29) versus normal human mucosa cells (NCM460) and its contribution to cancer features. We found that Ca(2+) stores in colon carcinoma cells are partially depleted relative to normal cells. However, resting Ca(2+) levels, agonist-induced Ca(2+) increases, store-operated Ca(2+) entry (SOCE), and store-operated currents (ISOC) are largely enhanced in tumor cells. Enhanced SOCE and depleted Ca(2+) stores correlate with increased cell proliferation, invasion, and survival characteristic of tumor cells. Normal mucosa cells displayed small, inward Ca(2+) release-activated Ca(2+) currents (ICRAC) mediated by ORAI1. In contrast, colon carcinoma cells showed mixed currents composed of enhanced ICRAC plus a nonselective ISOC mediated by TRPC1. Tumor cells display increased expression of TRPC1, ORAI1, ORAI2, ORAI3, and STIM1. In contrast, STIM2 protein was nearly depleted in tumor cells. Silencing data suggest that enhanced ORAI1 and TRPC1 contribute to enhanced SOCE and differential store-operated currents in tumor cells, whereas ORAI2 and -3 are seemingly less important. In addition, STIM2 knockdown decreases SOCE and Ca(2+) store content in normal cells while promoting apoptosis resistance. These data suggest that loss of STIM2 may underlie Ca(2+) store depletion and apoptosis resistance in tumor cells. We conclude that a reciprocal shift in TRPC1 and STIM2 contributes to Ca(2+) remodeling and tumor features in colon cancer.