Activation of C-kinase eta through its cholesterol-3-sulfate-dependent phosphorylation by casein kinase I in vitro.
The physiological correlation between casein kinase I (CK-I) and an isoform eta of protein kinase C ( C-kinase eta) was investigated in vitro, since it has been reported that (i) cholesterol-3-sulfate (CH-3S) effectively activates C-kinase eta rather than the other isoforms ( C-kinase epsilon and C-kinase delta) in vitro; and (ii) CK-I efficiently phosphorylates CH-3S-binding proteins, such as high mobility group protein 1 ( HMG1), in the presence of CH-3S in vitro. We found that (i) CK-I phosphorylated Thr in preference to Ser on recombinant human C-kinase isoform eta (rhC-kinase eta) in the presence of CH-3S; (ii) this phosphorylation was selectively inhibited by CK-I-7 (a CK-I inhibitor); and (iii) the activity (phosphorylation of protamine sulfate) of rhC-kinase eta was approx. 3.2-fold stimulated by its full phosphorylation by CK-I in the presence of 3 microM CH-3S. These results suggest that CK-I is a protein kinase responsible for the activation of rhC-kinase eta in the presence of CH-3S in vitro.[1]References
- Activation of C-kinase eta through its cholesterol-3-sulfate-dependent phosphorylation by casein kinase I in vitro. Okano, M., Yokoyama, T., Miyanaga, T., Ohtsuki, K. Biol. Pharm. Bull. (2004) [Pubmed]
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