title: The AMPK-related kinase SIK2 is regulated by cAMP via phosphorylation at Ser358 in adipocytes.
abstract: SIK2 (salt-inducible kinase 2) is a member of the AMPK (AMP-activated protein kinase) family of kinases and is highly expressed in adipocytes. We investigated the regulation of SIK2 in adipocytes in response to cellular stimuli with relevance for adipocyte function and/or AMPK signalling. None of the treatments, including insulin, cAMP inducers or AICAR (5-amino-4-imidazolecarboxamide riboside), affected SIK2 activity towards peptide or protein substrates in vitro. However, stimulation with the cAMP-elevating agent forskolin and the β-adrenergic receptor agonist CL 316,243 resulted in a PKA (protein kinase A)-dependent phosphorylation and 14-3-3 binding of SIK2. Phosphopeptide mapping of SIK2 revealed several sites phosphorylated in response to cAMP induction, including Ser(358). Site-directed mutagenesis demonstrated that phosphorylation of Ser(358), but not the previously reported PKA site Ser(587), was required for 14-3-3 binding. Immunocytochemistry illustrated that the localization of exogenously expressed SIK2 in HEK (human embryonic kidney)-293 cells was exclusively cytosolic and remained unchanged after cAMP elevation. Fractionation of adipocytes, however, revealed a significant increase of wild-type, but not Ser358Ala, HA (haemagglutinin)-SIK2 in the cytosol and a concomitant decrease in a particulate fraction after CL 316,243 treatment. This supports a phosphorylation-dependent relocalization in adipocytes. We hypothesize that regulation of SIK2 by cAMP could play a role for the critical effects of this second messenger on lipid metabolism in adipocytes.
authors.affiliation: The Department of Experimental Medical Science, Lund University, BMC C11, 221 84 Lund, Sweden. emma.henriksson@med.lu.se
authors.forename: Emma
authors.initials: E
authors.lastname: Henriksson
authors.forename: Helena A
authors.initials: HA
authors.lastname: Jones
authors.forename: Kashyap
authors.initials: K
authors.lastname: Patel
authors.forename: Mark
authors.initials: M
authors.lastname: Peggie
authors.forename: Nicholas
authors.initials: N
authors.lastname: Morrice
authors.forename: Kei
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Olga
authors.initials: O
authors.lastname: Göransson
mesh_terms: D016475:3T3 Cells; D000091162:AMP-Activated Protein Kinase Kinases; D017667:Adipocytes / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D000242:Cyclic AMP / Q000235:genetics / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation / Q000502:physiology; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology; D012694:Serine / Q000235:genetics / Q000378:metabolism*
chemical_list: D012694:Serine; D000242:Cyclic AMP; D011494:Protein Kinases; C551842:salt-inducible kinase-2, human; D017346:Protein Serine-Threonine Kinases; D000091162:AMP-Activated Protein Kinase Kinases