Promoter variants and transcriptional regulation of the intestinal fatty acid binding protein gene (FABP2)
The human intestinal fatty acid binding protein (FABP2) is a cytosolic 15 kDa protein and is involved in resorption of long-chain fatty acids. Phenotyping of FABP2 knock-out mice and association analysis of promoter haplotypes revealed FABP2 as a susceptibility gene for insulin resistance and related traits. Relevant FABP2 promoter polymorphisms -80Del>T, -136AGTAG>Del, -168AAG>T, -260G>A, -471G>A, and -778G>T result in two haplotypes A and B. Haplotype B possesses 2-3 fold lower transcriptional activity than A in Caco-2 cells. The aim of this work was to investigate the general and haplotype-specific transcriptional regulation of the human FABP2 promoter. For this purpose, reporter gene assays in human colonic carcinoma Caco-2, cervix carcinoma Hela and hepatoma Huh7 cells, site-directed mutagenesis, electrophoretic mobility shift assays and supershift-assays were used. Data show that FABP2 is strongly activated by the transcriptional factor HNF-1a and HNF-4a via identified functional recognition elements within FABP2 promoter region -185/-165 and -336/-324, respectively. This seems to be of importance in the control of FABP2 expression by differentiation and nutrients, e.g. dietary lipids. Furthermore it was demonstrated that polymorphism -80Del>T, together with -136AGTAG>Del and -168AAG>T, essentially determines different activities of FABP2 promoter haplotypes. GATA factors bind less efficiently to the –80B allele compared to A. This results in two-fold lower activation of haplotype B by these factors. GATA factors play a major role in development and differentiation and therefore very likely mediate a differential activation of FABP2 promoter haplotypes also in-vivo. Taken together, the work provides insights into the molecular basis of the general and variant specific transcriptional regulation of the diabetes type 2 associated human FABP2 gene.