Extinction of alpha1-antitrypsin expression in cell hybrids is independent of HNF1alpha and HNF4 and involves both promoter and internal DNA sequences

Nucleic Acids Res. 1999 Feb 15;27(4):1190-7. doi: 10.1093/nar/27.4.1190.

Abstract

In rat hepatoma x fibroblast somatic cell hybrids, extinction of rat alpha1-antitrypsin (alpha1AT) gene expression is accompanied by the loss of liver-enriched transcription factors hepatocyte nuclear factor 1 (HNF1alpha) and hepatocyte nuclear factor 4 (HNF4). Previous analysis showed that forced expression of functional HNF1alpha failed to prevent extinction of the rat alpha1AT locus in cell hybrids. Here I show that ectopic co-expression of HNF1alpha plus HNF4 fails to prevent extinction of either rat or human alpha1AT genes in cell hybrids. A 40 kb human alpha1AT minilocus integrated into the rat genome is fully silenced in cell hybrids in the presence of transacting factors. The integrated alpha1AT promoter, but not a viral or ubiquitously active promoter, is repressed 35-fold in the cell hybrids. In addition, position effects also contributed to extinction of many integrated transgenes in a cell type-dependent manner. Finally, internal DNA sequences within the human alpha1AT gene contributed dramatically to the extinction phenotype, resulting in a further 10- to 30-fold reduction in alpha1AT gene expression in cell hybrids. Thus, multiple mechanisms contribute to silencing of tissue-specific gene expression of the alpha1AT gene in cell hybrids.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Cell Line
  • DNA
  • DNA-Binding Proteins*
  • Gene Expression Regulation
  • Hepatocyte Nuclear Factor 1
  • Hepatocyte Nuclear Factor 1-alpha
  • Hepatocyte Nuclear Factor 1-beta
  • Hepatocyte Nuclear Factor 4
  • Humans
  • Hybrid Cells
  • Nuclear Proteins*
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Promoter Regions, Genetic*
  • Rats
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Tumor Cells, Cultured
  • alpha 1-Antitrypsin / genetics*

Substances

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • DNA-Binding Proteins
  • HNF1A protein, human
  • HNF1B protein, human
  • Hepatocyte Nuclear Factor 1-alpha
  • Hepatocyte Nuclear Factor 4
  • Hnf1a protein, rat
  • MLX protein, human
  • Nuclear Proteins
  • Phosphoproteins
  • Transcription Factors
  • alpha 1-Antitrypsin
  • Hepatocyte Nuclear Factor 1
  • Hepatocyte Nuclear Factor 1-beta
  • DNA