Suppression of aberrant transient receptor potential cation channel, subfamily V, member 6 expression in hyperproliferative colonic crypts by dietary calcium

Abstract

Dietary calcium is believed to reduce colon cancer risk, but the mechanism by which this occurs is poorly understood. Employing the Citrobacter rodentium-induced transmissible murine colonic hyperplasia (TMCH) model, we previously showed that a high-calcium diet (hCa) significantly abrogated hyperplasia in the distal colons of NIH-Swiss mice. Here, we explored the mechanism of dietary protection by hCa by analyzing the expression of genes involved in the regulation of Ca uptake/flux in the intestinal epithelium, including the Ca-sensing receptor, vitamin D receptor, Ca binding protein, and transient receptor potential cation channels, subfamily V, members 5 and 6 (TRPV5/6). Interestingly, while TRPV6 expression increased significantly during TMCH, the expression of the other gene products was unchanged. This elevated TRPV6 expression was significantly abrogated by a hCa diet. Immunofluorescence revealed apical membrane localization of TRPV6 in the normal colon, whereas during TMCH we observed intense apical pole and cytoplasmic staining along the entire longitudinal crypt axis, including the expanded proliferating zone. The hCa diet reversed this effect. In humans, overexpression of TRPV6 was associated with early-stage colon cancer, and in colon carcinoma cells, inhibition of TRPV6 expression by small interfering RNA inhibited their proliferation and induced apoptosis. TRPV6 small interfering RNA also diminished the transcriptional activity of the calcium-dependent nuclear factors in activated T cells. Thus the aberrant overexpression of TRPV6 contributes to colonic crypt hyperplasia in mice and to colon cancer cell proliferation in humans. Therefore, it is likely that suppression of TRPV6 by a hCa diet is required for its protective effects in the colon.

TRPV6 channel modulates proliferation of insulin secreting INS-1E beta cell line

“…The link between TRPV6 and NFAT activity was also reported in the human colon carcinoma Caco-2 cells [41]. It is known that NFAT interacts with calcium-signaling.…”

Active vitamin D (1,25-dihydroxyvitamin D3) increases host susceptibility toCitrobacter rodentiumby suppressing mucosal Th17 responses

“…It has previously been shown that mice treated with high-dose 1,25(OH) 2 D 3 (75 ng, 3 times/wk) developed exaggerated crypt hyperplasia at day 12 postinfection with C. rodentium; however, other aspects of disease were not reported (54). We found that 1,25(OH) 2 D 3 -treated infected mice suffered from increased C. rodentium burdens and exag- gerated colonic tissue damage, compared with vehicle-treated mice.…”

Citrobacter Infection and Wnt Signaling

“…Since hyper-activation of Wnt signaling is a hallmark of colon cancer and of many other human cancers, our findings clearly suggest that the TMCH model can be used as an excellent template to study the early stages of colon carcinogenesis. Indeed, we have shown recently that following CR infection, aberrant overexpression of a calcium channel TRPV6 (transient receptor potential vanilloid-type) contributes to colonic crypt hyperplasia in mice and to colon cancer cell proliferation in humans [97]. Blocking TRPV6 with high calcium diet (1%) causes almost complete abrogation of hyperplasia.…”

“…As proof of principle, we also investigated TRPV6 expression in adenomatous polyps (stage I) and advanced human cancers (stages III/IV) to determine if similarities exist with regard to TMCH model. A significant increase in TRPV6 expression, compared to normal mucosa, was observed in stage I tumor while stages III and IV cancers were negative for TRPV6 thus linking TRPV6 to early stages of colon cancer [97]. The remarkable parallel with TMCH also suggests that TMCH is not unique but shares a common final pathway in response to diverse initiating events.…”