Direct selection of hepatoma cell variants deficient in ?1-antitrypsin gene expression

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Abstract
Expression plasmids containing the human α1-antitrypsin (α1 AT) promoter fused to either adenine phosphoribosyltransferase (aprt) or xanthine-guanine phosphoribosyltransferase (gpt) coding sequences were sequentially introduced into APRT− HPRT− rat hepatoma cells. Stable transfectants expressing both transgenes were isolated and characterized. Nonexpressing variants were subsequently obtained by selecting against expression of one or both transgenes. Variants isolated by selecting against expression of either transgene alone generally displayed deficiency phenotypes incis, as only three of 20 clones tested were affected for expression of α1AT mRNA. In contrast, double selection yielded predominantlytrans effects: 12 of 14 lines tested showed impaired ability to express their chromosomal α1AT genes. Furthermore, expression of several other liver genes, including the gene encoding the HNF-1trans-activator, was repressed in many of the variant lines. Thus, double selection using chimeric transgenes is a useful approach for generating variant cell lines deficient in expression of specific mammalian genes.