出版社:American Society for Biochemistry and Molecular Biology
摘要:ABCA7 is highly homologous to ABCA1 and mediates cellular cholesteroland phospholipid release by apolipoproteins when transfectedin vitro. However, expression of ABCA7 was downregulated byincreased cellular cholesterol while ABCA1 was upregulated,and the results were consistent by forced expression or downregulationof sterol-responsive/regulatory element (SRE) binding proteins(SREBPs). We analyzed the promoter of the ABCA7 gene and identifiedthe new exon encoding 96 bp (mouse) and 95 bp (human) of the5' untranslated region and the transcription start site at 1,122bp (mouse) and 1,260 bp (human) upstream of the initiation methioninecodon. At 5' upstream of this exon is the ABCA7 proximal promotercontaining multiple binding sites of transcription factors forhematopoiesis and SRE of 9 bp at 212 bp (mouse) and 179 bp (human)upstream of the new exon. The apolipoprotein A-I-mediated lipidrelease was not influenced by suppression of the endogenousABCA7 with small interfering RNA in mouse fibroblasts or byits increase in ABCA1-deficient mouse cells. In contrast, phagocyticactivity was altered in parallel to the ABCA7 expression inthese cells. When phagocytosis was induced, the messages increasedfor SREBP2, ABCA7, and other SREBP2-regulated proteins. TheABCA1 message decreased in this condition. We conclude thatthe ABCA7 gene is regulated by sterol in the opposite directionto ABCA1 through SRE/SREBP2 and that expression of ABCA7 bythis regulation is associated with phagocytic activity.Supplementary key words ATP binding cassette transporter A7 • ATP binding cassette transporter A1 • cholesterol • high density lipoprotein • sterol-responsive/regulatory element • sterol-responsive/regulatory element binding protein • promoter
Abbreviations: apoA-I, apolipoprotein A-I; ChIP, chromatin immunoprecipitation; DF medium, 1:1 mixture of Dulbecco's modified Eagle's medium and Ham's F12 medium; FCS, fetal calf serum; LPDS, lipoprotein-deficient serum; LXR, liver X receptor; 5'RACE, rapid amplification of 5' cDNA ends; siRNA, small interfering RNA; SRE, sterol-responsive/regulatory element; SREBP, sterol-responsive/regulatory element binding protein; UTR, untranslated region