McCormick A, Wu D, Castrillo J L, Dana S, Strobl J, Thompson E B, Karin M
Department of Pharmacology, School of Medicine, University of California, San Diego, La Jolla 92093.
Cell. 1988 Oct 21;55(2):379-89. doi: 10.1016/0092-8674(88)90061-x.
Growth hormone (GH) expression in pituitary-derived cells has been attributed to the presence of a positive trans-activator, GHF-1, which binds to two sites on the GH promoter. Somatic cell hybridization of non-GH-expressing L cells with pituitary-derived GH3 cells usually results in extinction of GH production. While previous studies showed that extinction occurs at the level of GH transcription, the exact mechanism remained elusive. We therefore characterized two parental cell lines and three hybrids, two of which extinguish GH expression and one in which GH is reexpressed after loss of mouse chromosomal material. Using in vivo transfections, in vitro transcription, DNAase I footprints, and immunoblotting experiments, no evidence for a direct repressor of GH transcription was found. Rather, extinction of GH expression in fibroblast x pituitary hybrids was accompanied by loss of GHF-1 protein and mRNA expression, suggesting that extinction occurs by repression of this trans-activator.
垂体来源细胞中生长激素（GH）的表达归因于一种正向反式激活因子GHF-1的存在，该因子与GH启动子上的两个位点结合。非GH表达的L细胞与垂体来源的GH3细胞进行体细胞杂交通常会导致GH产生的消失。虽然先前的研究表明消失发生在GH转录水平，但确切机制仍然难以捉摸。因此，我们对两个亲代细胞系和三个杂种细胞系进行了表征，其中两个杂种细胞系的GH表达消失，另一个杂种细胞系在丢失小鼠染色体物质后GH重新表达。通过体内转染、体外转录、DNA酶I足迹和免疫印迹实验，未发现直接抑制GH转录的证据。相反，成纤维细胞×垂体杂种细胞中GH表达的消失伴随着GHF-1蛋白和mRNA表达的丧失，这表明消失是通过抑制这种反式激活因子而发生的。
