Selective Modulation of Protein Kinase Isozymes by the Site-Selective Analog 8-chloroadenosine 3′,5′-cyclic Monophosphate Provides a Biological Means for Control of Human Colon Cancer Cell Growth

Differential expression of type I and type II cAMP-dependent protein kinase isozymes has been linked to growth regulation and differentiation. We examined the expression of protein kinase isozymes in the LS 174T human colon cancer cell line during 8-chloroadenosine 3′,5′-cyclic monophosphate (8-Cl-cAMP)-induced growth inhibition. Two species of RII (the regulatory subunit of protein kinase type II) with apparent Mr 52,000 (R52II) and Mr 56,000 (R56II) and a single species of RI (the regulatory subunit of protein kinase type I) with Mr 48,000 were identified in the cancer cells. RI and both forms of RII were covalently labeled with 8-azidoadenosine 3′,5′-cyclic [32P]monophosphate, and two anti-RII antibodies that exclusively recognize either R52II or R56II resolved two forms of the RII receptors. 8-Cl-cAMP treatment induced a decrease of RI and an increase of both R52II and R56II in the cytosols of cancer cells and rapid translocation (within 10 min) of R52II from the cytosol to nucleus. 8-Cl-cAMP caused transcriptional activation of the R52II receptor gene and inactivation of the RI receptor gene. It also exhibited high-affinity site-1-selective binding to the purified preparations of both RII receptor proteins. Thus, differential regulation of various forms of cAMP receptor proteins is involved in 8-Cl-cAMP-induced regulation of cancer cell growth, and nuclear translocation of R52II receptor protein appears to be an early event in such differential regulation.