Effect of peroxisome proliferator-activated receptor alpha on human angiotensinogen promoter

The renin-angiotensin system plays a key role in the regulation of blood pressure. Angiotensinogen (ANG), mainly synthesized in the liver, is the first substrate of renin-angiotensin system. We had previously found that hepatocyte nuclear factor 4 (HNF-4) dramatically activates the human ANG promoter. It is generally known that HNF-4 and peroxisome proliferator-activated receptor alpha (PPARalpha) bind to response elements composed of two core motifs, RG(G/T)TCA, or a closely related sequence separated by 1 nucleotide (DR1 element). To examine whether or not PPARalpha activates the human ANG promoter, we used the reporter gene containing the sequence from -1222 to +44 of the human ANG gene promoter. PPARalpha and RXR heterodimer activated this promoter, and the PPARalpha responsive region was the same site that we had previously mapped as a binding site for HNF-4. Although the human ANG promoter was not induced by PPARalpha ligand bezafibrate in HepG2 cells, this reporter gene was inducible by bezafibrate treatment in HeLa cells, which do not express endogenous HNF-4. We suspected that the high level expression of HNF-4 in HepG2 cells might interfere with the effect of bezafibrate on the human ANG promoter. To confirm this model, we cotransfected HNF-4 expression vector with PPARalpha expression vector into HeLa cells. The bezafibrate-dependent activation of the ANG promoter was inhibited by HNF-4. These results suggest that PPARalpha and HNF-4 competitively affect the human ANG promoter through the C region.     

Functional conserved elements mediate intestinal-type fatty acid binding protein (I-FABP) expression in the gut epithelia of zebrafish larvae.

Intestinal-type fatty acid binding protein (I-FABP) plays an important role in the intracellular binding and trafficking of long chain fatty acids in the intestine. The aim of this study, therefore, was to elucidate the regulation and spatiotemporal expression of the I-FABP gene during zebrafish larval development. We performed in vivo reporter-gene analysis in zebrafish by using a transient and transgenic approach. Green fluorescent protein-reporter analyses revealed that the proximal 192-bp region of the I-FABP promoter is sufficient to direct intestine-specific expression during zebrafish larval development. Functional dissection of a 41-bp region within this 192-bp promoter revealed that one C/EBP and two GATA-like binding sites, along with a novel 15-bp element within it are required for I-FABP gene expression in vivo. In addition, the six consensus sites (CCACATCAGCATGAA) in the 15-bp element are critical for I-FABP gene regulation in the zebrafish gut epithelia. Comparison analyses of the orthologous 15-bp element from mammalian I-FABP genes suggests that these mammalian elements are functionally equivalent to the zebrafish 15 element. These results provide the first in vivo evidence that these binding sites (C/EBP and GATA) and the novel 15-bp element contribute to intestine-specific gene expression and that they are functionally conserved across vertebrate evolution.