Wood W M, Dowding J M, Sarapura V D, McDermott M T, Gordon D F, Ridgway E C
Department of Medicine/Endocrinology, University of Colorado Health Sciences Center, Denver 80262, USA.
Mol Cell Endocrinol. 1998 Jul 25;142(1-2):141-52. doi: 10.1016/s0303-7207(98)00110-5.
Transcription of the glycoprotein hormone alpha-subunit gene in the pituitary is governed by different promoter elements in thyrotropes and gonadotropes. We recently identified an upstream enhancer that directs a high level of cell type specific expression in transgenic mice and stimulates proximal promoter activity in cultured alphaTSH and alphaT3 cells. To assess the contribution of promoter sequences that functionally interact with the enhancer, we mutated two proximal elements shown to be important in both thyrotrope and gonadotrope cells. Disruption of the pituitary glycoprotein hormone basal element (PGBE), which binds a LIM homeodomain protein, resulted in a decrease in basal promoter activity in both alphaTSH and alphaT3 cells. Enhancer function was completely abolished by the PGBE site mutation in alphaT3 gonadotropes, whereas some stimulatory activity remained in alphaTSH thyrotropes. Mutation of the gonadotrope specific element (GSE), which binds SF1 and is important for basal activity in gonadotropes and TRH response in thyrotropes, resulted in declines in basal and enhanced promoter activity only in alphaT3 cells and not in alphaTSH cells. Despite this decrease in enhanced activity, the GSE mutated promoter still retained some enhancer stimulated activity, suggesting that the PGBE site still functionally interacts in the absence of an intact GSE. This mutation had no effect in alphaTSH cells. These data suggest that although the enhancer works in both cell types it exhibits cell type specific functional characteristics.
