Differential gene regulation of StarD4 and StarD5 cholesterol transfer proteins. Activation of StarD4 by sterol regulatory element-binding protein-2 and StarD5 by endoplasmic reticulum stress.
The StarD4 and StarD5 proteins share approximately 30% identity, and each is a steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain. We previously showed StarD4 expression is sterol-repressed, consistent with regulation by sterol regulatory element-binding proteins (SREBPs), whereas StarD5 is not sterol-regulated. Here we further address the regulation and function of StarD4 and StarD5. Unlike StAR, the START family prototype, StarD4 and StarD5 were not induced by steroidogenic stimuli in Leydig cells. However, StarD4 and StarD5 showed StAR-like activity in a cell culture steroidogenesis assay, indicating cholesterol transfer. In transgenic mice expressing active SREBPs, StarD4 was predominantly activated by SREBP-2 rather than SREBP-1a. The mouse and human StarD4 proximal promoters share approximately 70% identity, including several potential sterol regulatory elements (SREs). Reporters driven by the StarD4 promoter from either species were transfected into NIH-3T3 cells, and reporter activity was highly repressed by sterols. Site-directed mutagenesis of potential SREs identified a conserved functional SRE in the mouse (TCGGTCCAT) and human (TCATTCCAT) promoters. StarD5 was not sterol-repressed via SREBPs nor was it sterol-activated via liver X receptors (LXRs). Even though StarD4 and StarD5 were not LXR targets, their overexpression stimulated LXR reporter activity, suggesting roles in cholesterol metabolism. StarD5 expression increased 3-fold in free cholesterol-loaded macrophages, which activate the endoplasmic reticulum (ER) stress response. When NIH-3T3 cells were treated with agents to induce ER stress, StarD5 expression increased 6-8-fold. Because StarD4 is regulated by sterols via SREBP-2, whereas StarD5 is activated by ER stress, they likely serve distinct functions in cholesterol metabolism.
Soccio
Raymond E
RE
Laboratory of Biochemical Genetics and Metabolism, Rockefeller University, New York, New York 10021, USA.
Adams
Rachel M
RM
Maxwell
Kara N
KN
Breslow
Jan L
JL
D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D019556:COS Cells; D002352:Carrier Proteins; D002784:Cholesterol / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D008099:Liver / Q000378:metabolism; D000071518:Liver X Receptors; D008156:Luciferases / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D041681:NIH 3T3 Cells; D057093:Orphan Nuclear Receptors; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D013261:Sterols / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D019076:Transgenes
D033942:Adaptor Proteins, Vesicular Transport; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; D026901:Membrane Transport Proteins; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; C456544:STARD4 protein, human; C456546:STARD5 protein, human; C497388:Srebf1 protein, mouse; C497391:Srebf2 protein, mouse; C499209:Stard4 protein, mouse; C499212:Stard5 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D013261:Sterols; D014157:Transcription Factors; D002784:Cholesterol; D008156:Luciferases