Sp1 and Sp3 transactivate the human lipoprotein lipase gene promoter through binding to a CT element: synergy with the sterol regulatory element binding protein and reduced transactivation of a naturally occurring promoter variant.
Lipoprotein lipase (LPL) is a key enzyme in lipoprotein and energy metabolism and, therefore, regulation of its expression could have an important bearing on these processes. We have identified an evolutionarily conserved 5'-CCTCCCCCC-3' motif (from -91 to -83, CT element) in the human LPL gene promoter, deletion or mutation of which caused approximately 70-80% decrease in promoter activity. We found that Sp1 and Sp3 in THP-1 nuclear protein extracts bind specifically to this element. Co-transfection with Sp1 and Sp3 expression plasmids transactivated the LPL promoter via the CT element in Drosophila SL2 cells devoid of Sp proteins. Sp3 moderately repressed Sp1-mediated LPL promoter activation when both were co-expressed in SL2 cells. Furthermore, co-expression of an active sterol regulatory element binding protein (SREBP-1), with Sp1, but not with Sp3, synergistically activated the LPL promoter in SL2 cells. We previously reported a naturally occurring T-->G substitution at position -93 of the human LPL promoter which reduces promoter activity by 40-50% in transient transfection assays. In this study, we showed that this substitution results in reduced binding affinity to Sp1/Sp3 and in diminished transactivation by Sp1/Sp3 alone and by the synergistic action of Spl and SREBP-1 In conclusion, recruitment of Sp1/Sp3 by the CT element may play an important role in expression of the human lipoprotein lipase gene. Synergistic transcriptional activation by Sp1 and SREBP-1 may provide a mechanism for cross-talk between cholesterol and triglyceride metabolic pathways.
Yang
W S
WS
Department of Genetics, University of Washington, Seattle 98195, USA.
Deeb
S S
SS
D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D004357:Drug Synergism; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D008071:Lipoprotein Lipase / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009687:Nuclear Proteins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D016415:Sequence Alignment; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D051705:Sp3 Transcription Factor; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015533:Transcriptional Activation; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C497121:SP3 protein, human; C497387:SREBF1 protein, human; D016329:Sp1 Transcription Factor; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; D051705:Sp3 Transcription Factor; D008071:Lipoprotein Lipase