Inhibition of intracellular cAMP-dependent protein kinase using mutant genes of the regulatory type I subunit.

Expression vectors were constructed that code for mutated forms of the regulatory type 1 subunit (RI) of cyclic AMP-dependent protein kinase. These mutations alter a specific amino acid which is present in each of two homologous cAMP-binding domains of the RI protein. When these expression vectors were introduced into NIH 3T3 and Y1 adrenocortical tumor cells a mutant RI protein was produced that acted in a dominant fashion to cause a 20-400-fold inhibition of cAMP-dependent protein kinase activation. In addition, processes controlled by cAMP in adrenal cells were blocked; cells became resistant to the growth-inhibitory effects of cAMP and defective in steroid synthesis. Expression of mutant RI genes in cells provides a specific means to explore the role of cAMP and protein phosphorylation in the process of intracellular signalling.