MULTIPLE HORMONE RESPONSE ELEMENTS CAN CONFER GLUCOCORTICOID REGULATION ON THE HUMAN INSULIN-RECEPTOR GENE

Glucocorticoids have been shown to increase the levels of cell surface insulin receptors and their mRNA in many, different cell types. Previously, we have reported that glucocorticoids induce the transcription of the human insulin receptor (hIR) gene in rat 208F cells and we also identified a putative glucocorticoid response element (GRE) to which the glucocorticoid receptor binds in a specific manner. In this study we have mapped four additional regions of the hIR promoter to which glucocorticoid receptor binds specifically; one resides at -1340 and the others are distributed within a 100 base pair region from -750 to -650. Within each DNase I footprinting region resides at least one putative GRE sequence. They function as GREs to confer glucocorticoid inducibility when fused to a heterologous promoter-chloramphenicol acetyltransferase reporter construct. The functional significance of these putative GREs was further substantiated by mutational analysis. Taken together, our results indicate that these GREs are capable of conferring glucocorticoid-dependent transcriptional induction similar to those observed in vivo. Therefore, the increase of hlR mRNA and insulin binding to surface receptor in response to glucocorticoids is likely mediated by enhancement of transcription. The functional redundancy of the GREs may reflect the biological mechanism which ensures the glucocorticoid regulation of the hIR gene at the transcriptional level.