title: Phosphorylation of serine 399 in LKB1 protein short form by protein kinase Cζ is required for its nucleocytoplasmic transport and consequent AMP-activated protein kinase (AMPK) activation.
abstract: Two splice variants of LKB1 exist: LKB1 long form (LKB1(L)) and LKB1 short form (LKB1(S)). In a previous study, we demonstrated that phosphorylation of Ser-428/431 (in LKB1(L)) by protein kinase Cζ (PKCζ) was essential for LKB1-mediated activation of AMP-activated protein kinase (AMPK) in response to oxidants or metformin. Paradoxically, LKB1S also activates AMPK although it lacks Ser-428/431. Thus, we hypothesized that LKB1(S) contained additional phosphorylation sites important in AMPK activation. Truncation analysis and site-directed mutagenesis were used to identify putative PKCζ phosphorylation sites in LKB1(S). Substitution of Ser-399 to alanine did not alter the activity of LKB1(S), but abolished peroxynitrite- and metformin-induced activation of AMPK. Furthermore, the phosphomimetic mutation (S399D) increased the phosphorylation of AMPK and its downstream target phospho-acetyl-coenzyme A carboxylase (ACC). PKCζ-dependent phosphorylation of Ser-399 triggered nucleocytoplasmic translocation of LKB1(S) in response to metformin or peroxynitrite treatment. This effect was ablated by pharmacological and genetic inhibition of PKCζ, by inhibition of CRM1 activity and by substituting Ser-399 with alanine (S399A). Overexpression of PKCζ up-regulated metformin-mediated phosphorylation of both AMPK (Thr-172) and ACC (Ser-79), but the effect was ablated in the S399A mutant. We conclude that, similar to Ser-428/431 (in LKB1(L)), Ser-399 (in LKB1(S)) is a PKCζ-dependent phosphorylation site essential for nucleocytoplasmic export of LKB1(S) and consequent AMPK activation.
authors.affiliation: Section of Molecular Medicine, Department of Medicine, Oklahoma City, Oklahoma 73013.
authors.forename: Huaiping
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Section of Molecular Medicine, Department of Medicine, Oklahoma City, Oklahoma 73013.
authors.forename: Cate M
authors.initials: CM
authors.lastname: Moriasi
authors.affiliation: Section of Molecular Medicine, Department of Medicine, Oklahoma City, Oklahoma 73013.
authors.forename: Miao
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Section of Molecular Medicine, Department of Medicine, Oklahoma City, Oklahoma 73013.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Section of Molecular Medicine, Department of Medicine, Oklahoma City, Oklahoma 73013; Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73013. Electronic address: ming-hui-zou@ouhsc.edu.
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Zou
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D019943:Amino Acid Substitution; D002467:Cell Nucleus / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D008687:Metformin / Q000494:pharmacology; D020125:Mutation, Missense; D030421:Peroxynitrous Acid / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D012694:Serine; D000097606:Exportin 1 Protein
chemical_list: D000091162:AMP-Activated Protein Kinase Kinases; D055372:AMP-Activated Protein Kinases; D007004:Hypoglycemic Agents; D028884:Karyopherins; D008687:Metformin; D030421:Peroxynitrous Acid; D051744:Protein Kinase C-epsilon; D017346:Protein Serine-Threonine Kinases; D018160:Receptors, Cytoplasmic and Nuclear; D012694:Serine; D000097606:Exportin 1 Protein; C109790:STK11 protein, human
keywords: AMP-activated Kinase (AMPK); LKB; Metformin; Peroxynitrite; Phosphorylation; Protein Kinase C (PKC); Signal Transduction