Regulation of gene expression mediated by Ca^<2+>/calmodulin-dependent protein kinase cascade

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Ca^<2+>/calmodulin-dependent protein kinases (CaM-Ks) constitute a diverse group of enzymes, which are involved in many cellular responses mediated by an increase in the concentration of intracellular calcium. Previous studies have demonstrated that two multifunctionla CaM-kinases, CaM-KI and IV, are activated byphosphorylation of an activation loop Thr residue by an upstream CaM-kinase (CaM-KK) resulting in a large increase in catalytic efficiency. In this study, we have found that Ile441 in CaM-KKα is essential for the autoinhibition of CaM-KK and the binding orientation of CaM to CaM-KKα is not critical for relief of the autoinhibition. The unique binding orientation of CaM to CaM-KKα which was originally discovered using NMR analysis, was also confirmed with C.elegans CaM-KK by using X-ray crystallography. In contrast to CaM-KKα, CaM-KKβ-isoform has shown to exhibit enhanced Ca^<2+>/CaM-independent activity which is due to the second regulatory domain (residues 129-151) located in N-terminal of the catalytic domain. This domain inhibits the autoinhibition of CaM-KKβ resulting in generation of its autonomous activity. We also have generated C.elegans carrying CRE-GFP reporter gene and cloned C.elegans CREB. C.elegans CREB-mediated gene expression was induced by C.elegans CaM-K cascade (CaM-KK/CaM-KI) in transfected cells. In living worm, GFP-expression was induced by overexpression of C.elegans CaM-KI 1-295 (constitutively active mutant) in some neurons, which was not observed in CREB-deficient worm. This indicates that CaM-K cascade mediats CREB-dependent transcriptional activation is conserved in C.elegans.