A ROLE FOR GUANYL NUCLEOTIDE-BINDING REGULATORY PROTEIN BETA-SUBUNIT AND GAMMA-SUBUNIT IN THE EXPRESSION OF THE ADRENOCORTICOTROPIN RECEPTOR

Mutant Y1 mouse adrenocortical tumor cells, isolated on the basis of t heir resistance to the growth-inhibitory effects of forskolin, arise f rom single mutational events. These mutants present complex phenotypes in which the activity of G beta/gamma is impaired, ACTH receptor gene expression is markedly diminished, and ACTH-responsive adenylyl cycla se activity is lost. In this study, we have tested the hypothesis that the impairment in G beta/gamma activity is responsible for the loss o f ACTH receptor gene expression and ACTH-responsive adenylyl cyclase a ctivity. Transfection of one of the mutant clones with expression vect ors encoding either G beta 1 or G beta 2 together with G gamma 2 incre ased ACTH receptor expression and restored ACTH-responsive adenylyl cy clase activity. Interestingly, either G beta 2 or G gamma 2 alone was effective. These results thus support the hypothesis that the impairme nt in G beta/gamma activity is responsible for the loss of ACTH recept or expression. A luciferase reporter plasmid driven by the proximal pr omoter region df the mouse ACTH receptor gene was expressed poorly in the mutants compared with parental Y1 cells, suggesting that the G bet a/gamma defect compromised transcriptional activity at the proximal pr omoter region of the ACTH receptor gene.