Inhibitory cross-talk by cAMP kinase on the calmodulin-dependent protein kinase cascade.
The calmodulin-dependent kinase (CaM-K) cascade, a Ca2+-triggered system involving phosphorylation and activation of CaM-KI and CaM-KIV by CaM kinase kinase (CaM-KK), regulates transcription through direct phosphorylation of transcription factors such as cAMP response element-binding protein. We have shown previously that activated CaM-KIV can activate the mitogen-activated protein kinases (Enslen, H., Tokumitsu, H., Stork, P. J. S., Davis, R. J., and Soderling, T. R. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 10803-10808), and the present paper describes a novel regulatory cross-talk between cAMP kinase (PKA) and CaM-KK. PKA gave rapid phosphorylation in vitro and in cells of recombinant CaM-KK, resulting in 50-75% inhibition of CaM-KK activity, part of which was due to suppression of CaM-binding by phosphorylation of Ser458 in the CaM-binding domain. However, the Ser458 --> Ala mutant, or a truncation mutant in which the CaM-binding and autoinhibitory domains were deleted, was still partially suppressed by PKA-mediated phosphorylation. The second inhibitory site was identified as Thr108 by site-specific mutagenesis. Treatments of COS-7, PC12, hippocampal, or Jurkat cells with the PKA activators forskolin or isoproterenol gave 30-90% inhibition of either endogenous or transfected CaM-KK and/or CaM-KIV activities. These results demonstrate that the CaM kinase cascade is negatively regulated in cells by the cAMP/PKA pathway.
Wayman
G A
GA
Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201, USA.
Tokumitsu
H
H
Soderling
T R
TR
D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D010766:Phosphorylation; D018411:Spodoptera
D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases