Transcriptional suppression of human microsomal triglyceride transfer protein by hypolipidemic insulin sensitizers.
Microsomal triglyceride transfer protein (MTP) catalyzes the assembly and secretion of liver triglyceride-rich lipoproteins. The human MTP (hMTP) promoter activity is reported here to be suppressed by HNF-4alpha ligand antagonists (e.g., Medica analogs) or by PPARgamma ligand agonists (e.g., thiazolidinediones), thus accounting for their hypolipidemic activity in humans. Suppression of liver hMTP by Medica analogs or by thiazolidinediones was mediated by the TAAA sequence that serves as non-canonical TATA box of the hMTP core promoter. MTP suppression was evident in the specific context of the wild type hMTP core promoter, but not in the context of the mutated rodent-conforming hMTP core promoter governed by a canonical TATA box conjoined with its proximal (-50/-38)DR-1 element. hMTP suppression by Medica analogs or thiazolidinediones mediated by hMTP TAAA was independent of HNF-4alpha or PPARgamma. hMTP suppression by Medica analogs, but not by thiazolidinediones, was further complemented by inhibition of HNF-4alpha transcriptional activity transduced by the distal (-83/-70)DR-1 element of hMTP promoter. hMTP promoter activity was unaffected by PPARalpha activation. Furthermore, in contrast to hMTP, the promoter activity of the rodent-conforming hMTP was robustly activated by Wy-14,643-activated PPARalpha or by thiazolidinedione-activated PPARgamma. Transcriptional activation by PPARalpha or PPARgamma of the rodent-conforming, but not the wild type hMTP gene promoter, resulted from the species-specific context of the respective proximal DR-1 elements. Hence, suppression of hMTP transcription by hypolipidemic insulin sensitizers requires the specific context of hMTP core promoter. In light of the species-specific context of MTP core promoters, the rodent MTP promoter may not substitute for the human promoter when searching for hypolipidemic MTP suppressors.
Sheena
Vered
V
Department of Human Nutrition and Metabolism, Hebrew University Medical School, Jerusalem 91120, Israel.
Hertz
Rachel
R
Berman
Ina
I
Nousbeck
Janna
J
Bar-Tana
Jacob
J
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D002460:Cell Line; D051557:Hepatocyte Nuclear Factor 4 / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D000960:Hypolipidemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism; D008024:Ligands; D051379:Mice; D047492:Peroxisome Proliferator-Activated Receptors / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D051381:Rats; D014158:Transcription, Genetic / Q000187:drug effects*
D002352:Carrier Proteins; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D000960:Hypolipidemic Agents; D007328:Insulin; D008024:Ligands; D047492:Peroxisome Proliferator-Activated Receptors; C106092:microsomal triglyceride transfer protein