Redox regulation of casein kinase II autophosphorylation and its effect on Jun-DNA binding

In previous studies we showed that an oxido-reductase is involved in the restoration of contact inhibition in fibrosacoma cells, implicating the redox state in growth control. In the present report we demonstrate that autophosphorylation of casein kinase II (CKII) is redox-dependent. We have also shown that phosphorylation of the transcription factor Jun by CKII is regulated by the redox state. In vitro kinase assays revealed that CKII-catalyzed phosphorylation increased the affinity of Jun for the DNA. In conformational analyses, CKII maintained an intact structure only within the redox range permissive to its autophosphorylation. Collectively, these data suggest that the redox state profoundly influences the ability of CKII to phosphorylate its substrate Jun and may do so by affecting the autophosphorylation as well as the structure of CKII. To demonstrate the biological relevance of these observations, redox potentials of fibroblast nuclei from different stages of growth were measured. Results indicated that as cell density increased, the intranuclear environment gradually became less reducing. Redox-dependent behaviors of growth-associated proteins such as Jun and CKII, together with evidence for in vivo changes in the nuclear redox state suggest that a redox mechanism may be involved in the regulation of cell growth.