Transcriptional protein binding domains governing basal expression of the rat luteinizing hormone receptor gene

The functional importance of specific protein binding domains on transcription within the GC-rich 173-base pair promoter of the luteinizing hormone receptor gene was studied by mutagenesis and gel retardation analysis. Transcription was dependent on the presence of two Sp1 elements in the promoter domain of transfected expressing mouse Leydig tumor cells (mLTC) and nonexpressing Chinese hamster ovary cells. Mutation of two protein binding domains located downstream of the Sp1 elements (M1 and C-box) revealed tissue-specific regulation of promoter activity by each domain. Also, gel retardation studies indicated the presence of multiple trans factors that bind to the C-box and M1 domains. Removal of the AP-2 element from the C-box resulted in mLTC-specific transcriptional activation that may involve an M1/C-box interaction. In addition, competition by overlapping NF-1 and AP-2 elements was demonstrable in both the C-box and upstream R domain for separate trans factors that exhibit neutral or inhibitory functions, respectively. Competition between the inhibitory and neutral DNA binding factors within both upstream and promoter domains may be responsible for a mechanism that controls the on/off state of luteinizing hormone receptor gene expression in gonadal cells. These studies reveal a complex pattern of transcriptional regulation that may reflect targeted mechanisms for the control of luteinizing hormone receptor gene expression.