TRANSCRIPTIONAL PROTEIN-BINDING DOMAINS GOVERNING BASAL EXPRESSION OFTHE RAT LUTEINIZING-HORMONE RECEPTOR GENE

The functional importance of specific protein binding domains on trans cription within the CC-rich 173-base pair promoter of the luteinizing hormone receptor gene was studied by mutagenesis and gel retardation a nalysis. Transcription was dependent on the presence of two Sp1 elemen ts 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 activit y by each domain. Also, gel retardation studies indicated the presence of multiple trans factors that bind to the C-box and M1 domains. Remo val of the AP-2 element from the C-box resulted in mLTC-specific trans criptional activation that may involve an M1/C-box interaction. In add ition, competition by overlapping NF-1 and AP-2 elements was demonstra ble in both the C-box and upstream R domain for separate trans factors that exhibit neutral or inhibitory functions, respectively. Competiti on 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 express ion in gonadal cells. These studies reveal a complex pattern of transc riptional regulation that may reflect targeted mechanisms for the cont rol of luteinizing hormone receptor gene expression.