Salt-inducible Kinase 3 Signaling Is Important for the Gluconeogenic Programs in Mouse Hepatocytes

• Published in: The Journal of biological chemistry Vol. 290; no. 29; pp. 17879 - 17893
• Main Authors: Itoh, Yumi, Sanosaka, Masato, Fuchino, Hiroyuki, Yahara, Yasuhito, Kumagai, Ayako, Takemoto, Daisaku, Kagawa, Mai, Doi, Junko, Ohta, Miho, Tsumaki, Noriyuki, Kawahara, Nobuo, Takemori, Hiroshi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 17.07.2015; American Society for Biochemistry and Molecular Biology
• Subjects: AMP-activated kinase (AMPK); Animals; cAMP response element-binding protein (CREB); Cells, Cultured; CRTC; Female; Gene Knockout Techniques; gluconeogenesis; Gluconeogenesis - drug effects; Glucose - metabolism; hepatocyte; Hepatocytes - drug effects; Hepatocytes - metabolism; Indans - pharmacology; liver kinase B1 (LKB1); Metabolism; Mice; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - chemistry; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Signal Transduction; SIK; Transcription Factors - metabolism; CRTC; liver kinase B1 (LKB1); cAMP response element-binding protein (CREB); hepatocyte; SIK; AMP-activated kinase (AMPK); gluconeogenesis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.640821

Salt-inducible kinases (SIKs), members of the 5′-AMP-activated protein kinase (AMPK) family, are proposed to be important suppressors of gluconeogenic programs in the liver via the phosphorylation-dependent inactivation of the CREB-specific coactivator CRTC2. Although a dramatic phenotype for glucose metabolism has been found in SIK3-KO mice, additional complex phenotypes, dysregulation of bile acids, cholesterol, and fat homeostasis can render it difficult to discuss the hepatic functions of SIK3. The aim of this study was to examine the cell autonomous actions of SIK3 in hepatocytes. To eliminate systemic effects, we prepared primary hepatocytes and screened the small compounds suppressing SIK3 signaling cascades. SIK3-KO primary hepatocytes produced glucose more quickly after treatment with the cAMP agonist forskolin than the WT hepatocytes, which was accompanied by enhanced gluconeogenic gene expression and CRTC2 dephosphorylation. Reporter-based screening identified pterosin B as a SIK3 signaling-specific inhibitor. Pterosin B suppressed SIK3 downstream cascades by up-regulating the phosphorylation levels in the SIK3 C-terminal regulatory domain. When pterosin B promoted glucose production by up-regulating gluconeogenic gene expression in mouse hepatoma AML-12 cells, it decreased the glycogen content and stimulated an association between the glycogen phosphorylase kinase gamma subunit (PHKG2) and SIK3. PHKG2 phosphorylated the peptides with sequences of the C-terminal domain of SIK3. Here we found that the levels of active AMPK were higher both in the SIK3-KO hepatocytes and in pterosin B-treated AML-12 cells than in their controls. These results suggest that SIK3, rather than SIK1, SIK2, or AMPKs, acts as the predominant suppressor in gluconeogenic gene expression in the hepatocytes. Salt-inducible kinases (SIKs) are capable of suppressing gluconeogenic gene expression in hepatocytes when they are overexpressed. However, enhanced gluconeogenic programs are observed only in SIK3-defective hepatocytes. SIK3 is the major kinase that down-regulates gluconeogenesis. The present study proposes that SIK3 could be a new target of diabetic care.