Effect of the 3' flanking sequences of rat beta-casein and human growth hormone genes on gene expression in mammary epithelial cells

Abstract

P-Casein gene is expressed by the synergistic action of lactogenic hormones in a murine mammary epithelial cell line, HC11. We previously reported that the expression of transfected rat p-casein promoter/human growth hormone ftision gene (pChGH) in HC11 cells is induced by the synergistic action of glucocorticoid and insulin [Yu, D.-Y.，Lee, C.-S., Kim, J.-Y.，and Lee, K-K (1991) Mol. Cells 11, 459464]. In this study the 3' flanking sequence of the fusion gene in pChGH was replaced by that of SV40 early gene (in pCShGH) and that of rat p-caseip gene (in pCChGH). The effects of those 3r flanking sequences on the expression level of the fusion gene were compared by Northern blot hybridization and radioimmunoassay with HC11 cells transfected by the three plasmids. Northern blot hybridization results showed that transcriptions of all the three fusion genes were induced in the similar fashion by the synergistic action of prolactin, insulin, and glucocorticoid hormone. However, according to radioimmunoassay results, the fusion gene in pCShGH yielded a lower amount of protein than that in pChGH or pCChGH. Thus the 3f flanking sequences of human growth hormone and rat g-casein genes would increase the gene expression level, probably via post-transcriptional mechanism, compared to the SV40 early gene sequence.