Molecular mechanism of estrogen action to inhibit obesity

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Estrogen is known to regulate adipogenesis in rodents. Estrogen administration in ovariectomized rodents reduces lipoprotein lipase (LPL) gene expression in fat tissues. In this study we studied the mechanisms of transcriptional regulation of the murine LPL gene by estrogen. The 5'-flanking region of LPL gene (-1980 bp) was fused to CAT reporter gene, introduced into COS-1 cells with estrogen receptor expression vector and CAT activities were determined in the presence or the absence of estradiol. Estradiol at 10^<-6> M suppressed pLPL- (-1980) -CAT activity by 20-fold in COS-1 cells. We next determined the estrogen-suppressive element on the LPL promoter by systematically deleting the 5'-flanking region. The most potent region for the estrogen-dependent suppression was located between -1980 and -1570 bp. We narrowed down the region using 50 - 410 bp fragments between -1980 and -1570 bp fused to the minimal promoter-CAT gene. We found that the 50-bp- (-1620/-1570) element was important for estrogen-dependent suppression in LPL gene transcription. When this 50-bp element was deleted from the pLPL (-1980) -CAT construct, estrogen-dependent suppressiveness was decreased to 5-fold. Nuclear proteins from COS-1 cells specifically bound to this 50-bp element were observed by the electrophoretic mobility shift assay. These results collectively suggest that the 50-bp (-1620/-1570) element, which harbors no conventional estrogen-responsive element, may contain a novel cis-acting element which is crucial for estrogen-dependent suppression of the murine LPL gene transcription.