title: Transcriptional and post-transcriptional induction of the TGFalpha gene in transformed rat liver epithelial cells.
abstract: Although TGFalpha mRNA and protein are frequently elevated in neoplastic cells, neither the level at which deregulation occurs nor the mechanism(s) responsible have been well characterized. As a first step, we examined the induction of TGFalpha mRNA in two series of clonally-derived rat liver epithelial cell lines that were transformed either by exposure to chemical carcinogen or stable transfection of activated Ha-ras. We found that steady-state levels of TGFalpha mRNA in both series of transformed lines were induced 25- to 50-fold over those in the respective normal parental cells. This induction, which occurred without amplification of the TGF alpha gene, was accompanied by at least a five- to 10-fold increase in transcription along the entire length of the gene with no evidence of a transcriptional attenuation or arrest mechanism in the normal cells. Analysis of the TGFalpha promoter and flanking regions did not support a correlation between the extent of methylation and the level of expression, but did reveal several DNase I hypersensitive sites spanning from -14 to +8 kilobases. Two of these sites were differentially observed in cells displaying high and low TGFalpha gene transcription, while a third site correlated with TPA-induced expression. Finally, measurement of TGFalpha mRNA decay in the presence of Actinomycin D revealed a consistent 1.5- to 3.2-fold increase in the half-life of the TGFalpha transcript in the various transformed cell lines. These results indicate that transformation-mediated induction of TGFalpha gene expression in rat liver epithelial cells occurs through both transcriptional and post-transcriptional mechanisms, but is primarily the result of TGFalpha promoter activation.
authors.affiliation: Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill 27599-7295, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Berkowitz
authors.forename: M A
authors.initials: MA
authors.lastname: Hissong
authors.forename: D C
authors.initials: DC
authors.lastname: Lee
mesh_terms: D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D003850:Deoxyribonuclease I / Q000378:metabolism; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D014158:Transcription, Genetic; D016211:Transforming Growth Factor alpha / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D016211:Transforming Growth Factor alpha; D003850:Deoxyribonuclease I