Vitamin D mediates its action in human colon carcinoma cells in a calcium‐sensing receptor‐dependent manner: downregulates malignant cell behavior and the expression of thymidylate synthase and survivin and promotes cellular sensitivity to 5‐FU

Abstract

Vitamin D (VD) protects against colon carcinogenesis by mechanisms not fully understood. We had earlier reported on the similarity in the biologic action of VD and that of the calcium-sensing receptor (CaSR) in human colon carcinoma cells. At the molecular level, the CaSR gene contains 2 VD response elements and VD stimulates the expression of CaSR. In this study, we investigated on the relationship between VD action and CaSR function. We determined and compared the action of VD in human colon carcinoma cells (CBS, Moser, Caco-2 and HCT116) and their CaSR knocked-down counterparts. VD inhibited cellular proliferation, cellular invasion, and anchorage-independent growth and stimulated the expression of p21/Waf1 but not in CaSR knocked-down cells. These results demonstrate, for the first time, that the known tumor-suppressive function of VD requires functional CaSR and knocking down CaSR expression abrogated this function of VD. We recently reported that activation of CaSR in human colon carcinoma cells downregulated the expression of thymidylate synthase (TS) and survivin and promoted a significant increase in sensitivity to cytotoxic drugs. We now demonstrate, for the first time, that VD suppressed the expression of TS and survivin, TS and survivin gene transcriptional activities and promoted a cytotoxic response to 5-FU in a CaSR-dependent manner. Ectopic expression of wild-type CaSR in colon carcinoma cells also inhibited the expression of TS and survivin and enhanced cellular sensitivity to 5-FU. VD, however, could no longer enhance cellular sensitivity to 5-FU in cells overexpressing CaSR.

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

“…Calcipotriol and lentinan promote chemosensitivity in a CaSRdependent manner. As we have recently reported, CaSR is required in mediating calcitriol-promoted chemosencitivity in human colon carcinoma cells (12). We hypothesized that the same mechanism governed the effects of calcipotriol and lentinan.…”

“…We have recently reported that induction of CaSR in human colon carcinoma cells by calcitriol promoted the sensitivity of the cells to the anticancer drug 5-FU (12). Since calcipotriol and lentinan exhibited similar effects in inducing CaSR expression as calcitriol, we hypothesized that these compounds may also be able to strengthen chemosensitivity in human colon carcinoma cells.…”

“…We hypothesized that the same mechanism governed the effects of calcipotriol and lentinan. Using the CaSR knock-down cell model that we have previously prepared (11,12) and maintained in good condition, as shown in Fig. 3a, we determined the effects of calcipotriol or lentinan in the cell models.…”

“…In colon cancer, welldifferentiated carcinoma cells express observable levels of CaSR, whereas undifferentiated carcinoma cells have little or no CaSR expression (7-10). 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).The human CaSR gene has two promoters (P1 and P2) and each promoter has a transcriptional start site (4,13-15). Both promoters contain the vitamin D (VD) response element (VDRE), which is recognized and bound by the complex of VD receptor (VDR) activated and bound by VD (15).…”

Epigenetic inactivation of calcium-sensing receptor in colorectal carcinogenesis

“…15 Moreover, it has been reported that vitamin D mediates its action in human colorectal cancer cells in a CASR-dependent manner and downregulates malignant cell behavior. 21 Ion transport systems are often altered in human cancer. Downregulation of CASR protein expression has been reported in colorectal cancer tissues.…”