Stringent time-dependent transregulation of calcium calmodulin kinase II (CaMKII) is implicated in anti-apoptotic control

Abstract

Induction of apoptosis by the PP1/PP2A inhibitor calyculin A was inhibited if the CaMKII inhibitor KN-93 was added no later than 10 min after addition of calyculin A. The physiological relevance and mechanism of CaMKII during apoptosis, however, remains largely unclear. Here we show in MDCK and gastric parietal cells that normal transregulation of CaMKII terminates the initial burst of autophosphorylation after only 10 min. The kinetics of CaMKII involved transregulation by PP1, PP2A, PP2B and PKCalpha. Transregulation of CaMKII resulted in two kinetic phases for phosphorylation of the autoactivation site at T286/287. During the initial phase, there was a clear peak of phosphorylation that lasted 10 min. This phase was subsequently followed by a half but constant level of T286/287 phosphorylation. Calyculin A perturbed this transregulation, resulting in a hyperphosphorylated CaMKII. This effect of CA on the kinetics of CaMKII was observed in vivo as well as in vitro using isolated tubulovesicles. Calyculin A-induced hyperphosphorylation of CaMKII appears to be at least one mechanism used by cells to trigger apoptosis. Therefore, stringent limitation of CaMKII autophosphorylation at T286/287 by transregulation and prevention of hyperphosphorylation seems to restrict apoptosis.

Regulation of stathmin phosphorylation in mouse liver progenitor‐29 cells during proteasome inhibition

“…Stathmin activity has been shown to be regulated by the phosphorylation of four serine residues, which are substrates of different protein kinases, such as CAMKII, CDK2, and ERK1/2 56–58 that participate in the regulation of central cellular processes. CaMKII has been associated to apoptosis 59, 60, and its activation may lead to the accumulation of reactive oxygen species, as has been associated to proteasome inhibition 61. In MLP‐29 cells MG132 and epoxomicin activate transiently CaMKII by autophosphorylation on Thr286 62, suggesting that calcium‐calmodulin (CAM) kinase pathway may be involved in the induction of apoptosis mediated by proteasome inhibitors.…”