Elk-1, C/EBPalpha, and Pit-1 confer an insulin-responsive phenotype on prolactin promoter expression in Chinese hamster ovary cells and define the factors required for insulin-increased transcription.
The transcription factor(s) that mediate insulin-increased gene transcription are not well defined. These studies use phenotypic conversion of Rat2 and Chinese hamster ovary (CHO) cells with transcription factors to identify components required for regulation of prolactin promoter activity and its control by insulin. The pituitary-derived GH4 cells contain all of the transcription factors required for insulin-increased prolactin-chloramphenicol acetyltransferase (CAT) expression while HeLa cells require only Pit-1, a pituitary-specific factor. However, Rat2 and CHO cells require additional factors. We had determined previously that the transcription factor that mediates insulin-increased prolactin gene expression was likely an Ets-related protein. Elk-1 and Sap-1 were the only Ets-related transcription factors tested as chimeras with LexA DNA-binding domain that were able to mediate insulin-increased expression of a LexA-CAT reporter plasmid. Elk-1 and Sap-1 are expressed in GH4 and HeLa cells but Rat2 and CHO cells express Sap-1, but not Elk-1. Expression of Elk-1 made Rat2 cells (but not CHO cells) insulin responsive. C/EBPalpha also binds to the prolactin promoter at a sequence overlapping the binding site for Elk-1. Expression of both C/EBPalpha and Pit-1 in CHO cells is required for high basal transcription of prolactin-CAT. Expression of Elk-1 converts CHO cells into a phenotype in which prolactin gene expression is increased by insulin treatment. Finally, antisense mediated reduction of Elk-1 in GH4 cells decreased insulin-increased prolactin gene expression and confirmed the requirement for Elk-1 for insulin-increased prolactin gene expression. Thus, both C/EBPalpha and Pit-1 were required for high basal transcription while insulin sensitivity required Elk-1.
Jacob
K K
KK
Department of Medicine, New York University School of Medicine, 550 First Ave., New York, NY 10016, USA.
Stanley
F M
FM
D016475:3T3 Cells; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000494:pharmacology*; D016466:CHO Cells; D002352:Carrier Proteins / Q000494:pharmacology*; D006224:Cricetinae; D004268:DNA-Binding Proteins; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D006023:Glycoproteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008565:Membrane Proteins; D051379:Mice; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D049294:Phospholipid Transfer Proteins; D011388:Prolactin / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D049231:Saposins; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D049128:Sphingolipid Activator Proteins; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000187:drug effects*; D050807:ets-Domain Protein Elk-1; D000099160:LexA Repressor Protein
D001426:Bacterial Proteins; D022763:CCAAT-Enhancer-Binding Protein-alpha; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006023:Glycoproteins; D007328:Insulin; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D049294:Phospholipid Transfer Proteins; D011388:Prolactin; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049231:Saposins; D012697:Serine Endopeptidases; D049128:Sphingolipid Activator Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D000099160:LexA Repressor Protein; C494112:ELK1 protein, human; C494113:Elk1 protein, mouse; C494114:Elk1 protein, rat; C483345:PSAP protein, human; C483344:Psap protein, mouse; C483347:Psap protein, rat