The human chorionic somatomammotropin enhancers form a composite silencer in pituitary cells in vitro.

The human GH (GH) gene family includes the pituitary-specific hGH-1, placental-specific chorionic somatomammotropin (hCS-5, hCS-2, and hCS-1), and hGH-2 genes. These duplicated, nearly identical genes are localized on approximately 50 kb of DNA on chromosome 17q23-q24. An enhancer (CSEn2), located downstream of the hCS-2 gene, participates in mediating placental-specific hCS gene expression. In the preceding paper we demonstrated that CSEn2 activity derives from the cooperative binding of transcription factor-1, TEF-1, and a placental-specific factor CSEF-1 to multiple enhansons, Enh1-Enh5, that are related to the SV40 GT-IIC and SphI/SphII enhansons. Here we demonstrate that two copies of CSEn2 or a single copy of CSEn2 linked to either of the other two enhancers in the hGH/hCS locus, CSEn1 and CSEn5, act cooperatively to enhance hCS promoter activity in choriocarcinoma (BeWo) cells, but silence the promoter in pituitary GC cells. Mutation of Enh4, an essential GT-IIC-like enhanson in the context of the intact enhancer, abolishes silencer activity, and multimerized GT-IIC enhansons mimic the intact CSEn enhancer/silencer activities in BeWo and GC cells, respectively. By antibody-mediated supershift, Western, and far Western analyses, we identified TEF-1 as the GT-IIC-binding factor in pituitary cells. The data suggest that TEF-1 may be involved in pituitary-specific repression of placental GH/CS gene transcription through long-range interactions between the multiple CS enhancers present on the GH/CS gene locus.