Partial activation of gene activity and chromatin remodeling of the human 14q32.1 serpin gene cluster by HNF-1 alpha and HNF-4 in fibroblast microcell hybrids.
The genes encoding alpha 1-antitrypsin (alpha 1AT, gene symbol P I) and corticosteroid-binding globulin (CBG) are part of a cluster of serine protease inhibitor (serpin) genes on human chromosome 14q32.1. Both genes are highly expressed in the liver and in cultured hepatoma cells, and the approximately 100-kb region around these genes contains an extensive array of expression-associated DNase I-hypersensitive sites (DHSs). Activation of human alpha 1AT and CBG transcription occurred when human chromosome 14 was transferred from nonexpressing cells to rat hepatoma cells. This activation event was accompanied by long-range chromatin reorganization of the entire region and the de novo formation of 17 expression-associated DHSs. Both gene activation and chromatin remodeling in hepatic cells required the liver-enriched transactivators hepatocyte nuclear factors-1 alpha and -4 (HNF-1 alpha and HNF-4). In this study, we tested whether ectopic expression of HNF-1 alpha and HNF-4 in nonexpressing cells could activate alpha 1AT and/or CBG transcription, and we monitored the chromatin structure of the locus in stably transfected fibroblasts. We report that both alpha 1AT and CBG mRNAs were expressed in fibroblast transfectants that stably expressed HNF-1 alpha and HNF-4, but expression was only approximately 1-10% of that observed in hepatic cells. Gene activation in these cells was accompanied by partial chromatin remodeling, as 6 of 17 expression-associated DHSs were formed. The potential implications of these results are discussed.
Rollini
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P
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.
Xu
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L
Fournier
R E
RE
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015152:Blotting, Northern; D002460:Cell Line; D002843:Chromatin / Q000235:genetics*; D002883:Chromosomes, Human, Pair 14; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000378:metabolism / Q000648:ultrastructure; D005786:Gene Expression Regulation / Q000502:physiology; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D006822:Hybrid Cells; D005810:Multigene Family; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000502:physiology*; D051381:Rats; D015843:Serpins / Q000235:genetics*; D014157:Transcription Factors / Q000502:physiology*; D015533:Transcriptional Activation
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D002843:Chromatin; D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D051557:Hepatocyte Nuclear Factor 4; C496489:Hnf1a protein, rat; C403128:MLX protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D015843:Serpins; D014157:Transcription Factors; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta