Regulation of human particulate guanylyl cyclase gene expression by the homeodomain protein, CDX-2

Guanylyl Cyclase C is a transmembrane receptor for the E. coli heat-stable enterotoxin (ST) and the endogenous peptides guanylin and uroguanylin. In humans, GCC (hGCC) is exclusively expressed in intestinal mucosa, colorectal tumors and cell lines of intestinal origin. Although stimulation of this receptor by ST is the proximal step in mediating secretory diarrhea, a physiological role for this evolutionarily conserved receptor has not been defined. Previous reporter gene analysis of the hGCC promoter suggested that at least three discrete regions contribute to the tissue specificity of hGCC transcription. The promoter region -257 to -457 possesses several consensus sequences for the binding of cdx-2, a homeodomain protein that regulates enterocyte-specific gene expression. We examined the tissue specific expression of hGCC by performing electromobility shift assays (EMSA) on nuclear extracts of several intestinal and extraintestinal cell lines using a labeled -257 to -457 hGCC promoter fragment. EMSA revealed intestinal cell line-specific shifts that were competed by SIF1, a defined nucleotide consensus sequence for cdx-2 binding. These findings suggest that cdx-2 may participate in the intestinal specific transcription of hGCC.