Identification of Egr1 as the oncostatin M-induced transcription activator that binds to sterol-independent regulatory element of human LDL receptor promoter.
Previously, we identified the low density lipoprotein receptor (LDLR) promoter region -17 to -1 as a novel sterol-independent regulatory element (SIRE) that mediates the stimulating effect of oncostatin M (OM). The goal of this study was to identify the OM-induced transcription activator that binds to the SIRE sequence. By conducting a electrophoretic mobility shift assay (EMSA) followed by UV crosslinking and SDS-PAGE, we show that a protein with a molecular mass of 85 kDa was present in the OM-induced SIRE DNA-protein complex. Western blotting and supershift assays reveal that the 85 kDa factor is early growth response gene 1 (Egr1). The interaction of Egr1 with the SIRE sequence was further confirmed in vivo by chromatin immunoprecipitation assays. The functional role of Egr1 in LDLR transcription was assessed by cotransfection of an Egr1 expression vector with an LDLR promoter reporter construct. We show that overexpression of Egr1 significantly increases LDLR promoter activity when cotransfected with CCAAT/enhancer binding protein beta (c/EBPbeta) or with cAMP-responsive element binding protein (CREB) expression vectors. Our studies clearly demonstrate that Egr1 is the OM-induced transcription factor that binds to the SIRE sequence of the LDLR promoter and also suggest that Egr1 may have a functional role in OM-induced upregulation of LDLR transcription through interaction with other SIRE binding proteins such as c/EBPbeta or CREB.
Zhang
Fang
F
Department of Veterans Affairs, Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
Ahlborn
Thomas E
TE
Li
Cong
C
Kraemer
Fredric B
FB
Liu
Jingwen
J
D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051766:Early Growth Response Protein 1; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D017874:Immediate-Early Proteins; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D053683:Oncostatin M; D010455:Peptides / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011973:Receptors, LDL / Q000235:genetics*; D020218:Response Elements / Q000235:genetics*; D013261:Sterols; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; C508351:OSM protein, human; D010455:Peptides; D011973:Receptors, LDL; D013261:Sterols; D014157:Transcription Factors; D053683:Oncostatin M; D020928:Mitogen-Activated Protein Kinases