Expression of Cav1.3 Calcium Channel in the Human and Mouse Colon: Posttranscriptional Inhibition by IFNγ

It has been hypothesized that apically expressed L-type Ca channel Ca1.3 (encoded by CACNA1D gene) contributes toward an alternative TRPV6-independent route of intestinal epithelial Ca absorption, especially during digestion when high luminal concentration of Ca and other nutrients limit TRPV6 contribution. We and others have implicated altered expression and activity of key mediators of intestinal and renal Ca (re)absorption as contributors to negative systemic Ca balance and bone loss in intestinal inflammation. Here, we investigated the effects of experimental colitis and related inflammatory mediators on colonic Ca1.3 expression. We confirmed Ca1.3 expression within the segments of the mouse and human gastrointestinal tract. Consistent with available microarray data (GEO database) from inflammatory bowel disease (IBD) patients, mouse colonic expression of Ca1.3 was significantly reduced in trinitrobenzene sulfonic acid (TNBS) colitis. In vitro, IFNγ most potently reduced Ca1.3 expression. We reproduced these findings in vivo with wild-type and Stat1 mice injected with IFNγ. The observed effect in Stat1 suggested a noncanonical transcriptional repression or a posttranscriptional mechanism. In support of the latter, we observed no effect on the cloned Ca1.3 gene promoter activity and accelerated Ca1.3 mRNA decay rate in IFNγ-treated HCT116 cells. While the relative contribution of Ca1.3 to intestinal Ca absorption and its value as a therapeutic target remain to be established, we postulate that Ca1.3 downregulation in IBD may contribute to the negative systemic Ca balance, to increased bone resorption, and to reduced bone mineral density in IBD patients.