Estrogen suppresses transcription of lipoprotein lipase gene - Existence of a unique estrogen response element on the lipoprotein lipase promoter

Estrogen exerts a variety of effects not only on female reproductive organs but also on nonreproductive organs, including adipose tissue. Estrogen inh ibits obesity triggered by ovariectomy in rodents. We studied the mechanism underlying this estrogen-dependent inhibition of obesity. Estrogen markedl y decreased the amounts of fat accumulation and lipoprotein lipase (LPL) mR NA as well as triglyceride accumulation in genetically manipulated 3T3-L1 a dipocytes stably expressing the estrogen receptor (ER), A pLPL(1980)-CAT co nstruct, along with an ER expression vector, was introduced into differenti ated 3T3-L1 cells, and CAT activities were determined, ER, mostly ligand-de pendently, inhibited the basal LPL promoter activity by 7-fold. We searched the LPL promoter for an estrogen-responsive suppressive element by employi ng a set of 5'-deletion mutants of the pLPL-CAT reporter. Although there wa s no classical estrogen response element, it was demonstrated that an AP-1- like TGAATTC sequence located at (-1856/-1850) was responsible for the supp ression of the LPL gene transcription by estrogen, An electrophoretic mobil ity shift assay probed with the TGAATTC sequence demonstrated formation of a specific DNA-nuclear protein complex. Interestingly, this complex was not affected by the addition of any antibodies against ER, c-Jun, c-Fos, JunB, or JunD, Because this TGAATTC element responded to phorbol ester and overe xpression of CREB-binding protein abrogated the suppressive effect of estro gen on the LPL promoter, we conclude that a unique protein that is related to the AP-1 transcription factor families may be involved in the complex th at binds to the TGAATTC element.