title: Altered regulation of cyclic AMP-dependent protein kinase in a mouse lymphoma cell line.
abstract: The ability of cyclic AMP to inhibit growth, cause cytolysis and induce synthesis of cyclic AMP-phosphodiesterase in S49.1 mouse lymphoma cells is deficient in cells selected on the basis of their resistance to killing by 2 mM dibutyryl cyclic AMP. The properties of the cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) in the cyclic AMP-sensitive (S) and cyclic AMP-resistant (R) lymphoma cells were comparatively studied. The cyclic AMP-dependent protein kinase activity or R cells cytosol exhibits an apparent Ka for activation by cyclic AMP 100-fold greater than that of the enzyme from the parental S cells. The free regulatory and catalytic subunits from both S and R kinase are thermolabile, when associated in the holoenzyme the two subunits are more stable to heat inactivation in R kinase than in S kinase. The increased heat stability of R kinase is observed however only for the enzyme in which the catalytic and cyclic AMP-binding activities are expressed at high cyclic AMP concentrations (10(-5)--10(-4) M), the activities expressed at low cyclic AMP concentrations (10(-9)--10(-6) M) being thermolabile. The regulatory subunit of S kinase can be stabilized against heat inactivation by cyclic AMP binding both at 2-10(-7) and 10(-5) M cyclic AMP concentrations. In contrast, the regulatory subunit-cyclic AMP complex from R kinase is stable to heat inactivation only when formed in the presence of high cyclic AMP concentrations (10(-5)M). The findings indicate that the transition from a cyclic AMP-sensitive to a cyclic AMP-resistant lymphoma cell phenotype is related to a structural alteration in the regulatory subunit of the cyclic AMP-dependent protein kinase which has affected the protein's affinity for cyclic AMP and its interaction with the catalytic subunit.
mesh_terms: D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology*; D004351:Drug Resistance; D004789:Enzyme Activation; D006358:Hot Temperature; D007700:Kinetics; D008223:Lymphoma / Q000201:enzymology; D046911:Macromolecular Substances; D051379:Mice; D011485:Protein Binding; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D000242:Cyclic AMP; D011494:Protein Kinases