CHARACTERIZATION OF A CAMP-DEPENDENT PROTEIN-KINASE MUTANT RESISTANT TO CISPLATIN

The signal transduction pathway of cAMP, mediated by the cAMP-dependen t protein kinase (PKA), is involved in the regulation of metabolisms, cell growth and differentiation and gene expression, Isolated PKA muta nts from Chinese hamster ovary (CHO) cells were used in our laboratory to study the role of cAMP in the development of drug resistance in ca ncer, We have found that PKA mutants harboring a defective regulatory (RI alpha) subunit, but not the catalytic (C) subunit, are more resist ant to the chemotherapeutic drug cisplatin. To clarify the role of PKA in cisplatin resistance, we have performed a step-wise selection with a CHO RI alpha subunit mutant cell line, 10248, for further resistanc e to cisplatin. A representative clone (10248/CDDPR-5) was used for fu rther characterization. These cisplatin-resistant PKA mutant cells rem ained refractory to cAMP-induced growth inhibition and had decreased P KA activity comparable to the parental 10248 mutant cells. Furthermore , 10248/CDDPR-5 also exhibited cross-resistance to the nitrogen mustar d melphalan but maintained the same sensitivity as wild-type cells to non-DNA-damaging agents such as methotrexate. The mechanism of resista nce may be due to increased DNA repair as assessed by the host cell re activation assay, We speculate that mutation and functional inactivati on of PKA may result in deregulated growth response to cAMP, as well a s the acquisition of resistance to cisplatin and other DNA-damaging ag ents in cancer. (C) 1997 Wiley-Liss, lnc.