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Importance of autophosphorylation at Ser186 in the A‐loop of salt inducible kinase 1 for its sustained kinase activity
Author(s) -
Hashimoto Yoshiko Katoh,
Satoh Tomohiro,
Okamoto Mitsuhiro,
Takemori Hiroshi
Publication year - 2008
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.21737
Subject(s) - autophosphorylation , phosphorylation , kinase , microbiology and biotechnology , mapk14 , cyclin dependent kinase 9 , map kinase kinase kinase , phosphorylation cascade , biology , mitogen activated protein kinase kinase , map2k7 , chemistry , biochemistry , protein kinase a , cyclin dependent kinase 2 , protein phosphorylation
Autophosphorylation is an important mechanism by which protein kinases regulate their own biological activities. Salt inducible kinase 1 (SIK1) is a regulator in the feedback cascades of cAMP‐mediated gene expression, while its kinase domain also features autophosphorylation activity. We provide evidence that Ser186 in the activation loop is the site of autophosphorylation and essential for the kinase activity. Ser186 is located at the +4 position of the critical Thr residue Thr182, which is phosphorylated by upstream kinases such as LKB1. The relationship between phosphorylation at Ser186 and at Thr182 in COS‐7 cells indicates that the former is a prerequisite for the latter. Glycogen synthase kinase‐3β (GSK‐3β) phosphorylates Ser/Thr residues located at the fourth position ahead of the pre‐phosphorylated Ser/Thr residues, and inhibitors of GSK‐3β reduce the phosphorylation at Thr182. The results of an in vitro reconstitution assay also indicate that GSK‐3β could be the SIK1 kinase. However, overexpression and knockdown of GSK‐3β in LKB1‐defective HeLa cells suggests that GSK‐3β alone may not be able to phosphorylate or activate SIK1, indicating that LKB1 may play a crucial role by phosphorylating SIK1 at Thr182, possibly as an initiator of the autophosphorylation cascade, and GSK‐3β may phosphorylate SIK1 at Thr182 by recognizing the priming‐autophosphorylation at Ser186 in cultured cells. This may also be the case for the other isoform SIK2, but not for SIK3. J. Cell. Biochem. 104: 1724–1739, 2008. © 2008 Wiley‐Liss, Inc.