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Feeding and Fasting Signals Converge on the LKB1-SIK3 Pathway to Regulate Lipid Metabolism in Drosophila.

Choi S, Lim DS, Chung J - PLoS Genet. (2015)

Bottom Line: Interestingly, we found that the LKB1-SIK3-HDAC4 signaling axis is modulated by dietary conditions.In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibits the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induces HDAC4 nuclear localization and brummer gene expression.However, under prolonged fasting conditions, AKH-independent signaling decreases the activity of the LKB1-SIK3 pathway to induce lipolytic responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejon, Republic of Korea; National Creative Research Initiatives Center for Energy Homeostasis Regulation, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea.

ABSTRACT
LKB1 plays important roles in governing energy homeostasis by regulating AMP-activated protein kinase (AMPK) and other AMPK-related kinases, including the salt-inducible kinases (SIKs). However, the roles and regulation of LKB1 in lipid metabolism are poorly understood. Here we show that Drosophila LKB1 mutants display decreased lipid storage and increased gene expression of brummer, the Drosophila homolog of adipose triglyceride lipase (ATGL). These phenotypes are consistent with those of SIK3 mutants and are rescued by expression of constitutively active SIK3 in the fat body, suggesting that SIK3 is a key downstream kinase of LKB1. Using genetic and biochemical analyses, we identify HDAC4, a class IIa histone deacetylase, as a lipolytic target of the LKB1-SIK3 pathway. Interestingly, we found that the LKB1-SIK3-HDAC4 signaling axis is modulated by dietary conditions. In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibits the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induces HDAC4 nuclear localization and brummer gene expression. However, under prolonged fasting conditions, AKH-independent signaling decreases the activity of the LKB1-SIK3 pathway to induce lipolytic responses. We also identify that the Drosophila insulin-like peptides (DILPs) pathway, related to mammalian insulin pathway, regulates SIK3 activity in feeding conditions independently of increasing LKB1 kinase activity. Overall, these data suggest that fasting stimuli specifically control the kinase activity of LKB1 and establish the LKB1-SIK3 pathway as a converging point between feeding and fasting signals to control lipid homeostasis in Drosophila.

No MeSH data available.


Related in: MedlinePlus

Activation of insulin receptor increases phosphorylation of SIK3 by Akt.(A) Immunoblot analyses showing the effect of 4 hr fasting and constitutively active insulin receptor (InRCA) on Thr196 phosphorylation of SIK3 protein in larvae (top three panels). Anti-phospho-Thr196 SIK3, -Myc (SIK3 protein), and -β-tubulin (TUB) antibodies were used. Densitometry of phospho-Thr196 SIK3 bands (bottom panel). FB-Gal4 was used to drive transgene expression in the fat body. (B) Immunoblot analyses showing the effect of constitutively active insulin receptor (InRCA) on Akt-dependent phosphorylation of SIK3 protein in larvae (top four panels). The lysates were immunoprecipitated with an anti-Myc (SIK3 protein) antibody, and then immunoblotted with an anti-phospho-Akt substrate antibody. Densitometry of phospho-SIK3 bands (bottom panel). (C) A schematic model for LKB1 and SIK3 function to regulate lipid homeostasis in Drosophila fat body. LKB1 regulates the nucleocytoplasmic localization of HDAC4 via SIK3-dependent phosphorylation. Under feeding condition, DILPs-induced Akt activation leads to SIK3 activation, thereby inhibiting HDAC4 activity by phosphorylation. Under short-term fasting conditions, the AKH pathway inhibits the kinase activity of LKB1 in phosphorylating SIK3 Thr196 residue and controls SIK3 activity via PKA-dependent phosphorylation. Unphosphorylated and nuclear localized HDAC4 deacetylates and activates FOXO to increase bmm expression [19], thereby reducing lipid storage. AKH-independent signaling modulates the LKB1-SIK3-HDAC4 pathway to induce bmm expression when fasting is prolonged. Data are presented as mean ± SEM (*P < 0.05; **P < 0.01; NS, non-significant).
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pgen.1005263.g006: Activation of insulin receptor increases phosphorylation of SIK3 by Akt.(A) Immunoblot analyses showing the effect of 4 hr fasting and constitutively active insulin receptor (InRCA) on Thr196 phosphorylation of SIK3 protein in larvae (top three panels). Anti-phospho-Thr196 SIK3, -Myc (SIK3 protein), and -β-tubulin (TUB) antibodies were used. Densitometry of phospho-Thr196 SIK3 bands (bottom panel). FB-Gal4 was used to drive transgene expression in the fat body. (B) Immunoblot analyses showing the effect of constitutively active insulin receptor (InRCA) on Akt-dependent phosphorylation of SIK3 protein in larvae (top four panels). The lysates were immunoprecipitated with an anti-Myc (SIK3 protein) antibody, and then immunoblotted with an anti-phospho-Akt substrate antibody. Densitometry of phospho-SIK3 bands (bottom panel). (C) A schematic model for LKB1 and SIK3 function to regulate lipid homeostasis in Drosophila fat body. LKB1 regulates the nucleocytoplasmic localization of HDAC4 via SIK3-dependent phosphorylation. Under feeding condition, DILPs-induced Akt activation leads to SIK3 activation, thereby inhibiting HDAC4 activity by phosphorylation. Under short-term fasting conditions, the AKH pathway inhibits the kinase activity of LKB1 in phosphorylating SIK3 Thr196 residue and controls SIK3 activity via PKA-dependent phosphorylation. Unphosphorylated and nuclear localized HDAC4 deacetylates and activates FOXO to increase bmm expression [19], thereby reducing lipid storage. AKH-independent signaling modulates the LKB1-SIK3-HDAC4 pathway to induce bmm expression when fasting is prolonged. Data are presented as mean ± SEM (*P < 0.05; **P < 0.01; NS, non-significant).

Mentions: LKB1 is ubiquitously expressed and constitutively active in mammalian cells [15], which raises the question of how dietary conditions change the activity of LKB1 and SIK3 to control lipid homeostasis. Our findings suggested that fasting and the AKH pathway inhibit LKB1 activity to regulate SIK3 Thr196 phosphorylation (Figs 4C and 6C). It is possible that fasting- and AKH-induced inhibition of LKB1 activity can be achieved by altered subcellular localization, protein conformation, stability, and/or protein-protein interactions of LKB1 and its associated proteins. Interestingly, in HEK-293 cells, fasting triggers autophosphorylation of human LKB1 at Thr336 [30] that corresponds to Thr460 in Drosophila LKB1 [31]. This phosphorylation promotes the protein-protein interaction between LKB1 and 14-3-3 proteins [30] and inhibits the ability of LKB1 for suppressing cell growth [31].


Feeding and Fasting Signals Converge on the LKB1-SIK3 Pathway to Regulate Lipid Metabolism in Drosophila.

Choi S, Lim DS, Chung J - PLoS Genet. (2015)

Activation of insulin receptor increases phosphorylation of SIK3 by Akt.(A) Immunoblot analyses showing the effect of 4 hr fasting and constitutively active insulin receptor (InRCA) on Thr196 phosphorylation of SIK3 protein in larvae (top three panels). Anti-phospho-Thr196 SIK3, -Myc (SIK3 protein), and -β-tubulin (TUB) antibodies were used. Densitometry of phospho-Thr196 SIK3 bands (bottom panel). FB-Gal4 was used to drive transgene expression in the fat body. (B) Immunoblot analyses showing the effect of constitutively active insulin receptor (InRCA) on Akt-dependent phosphorylation of SIK3 protein in larvae (top four panels). The lysates were immunoprecipitated with an anti-Myc (SIK3 protein) antibody, and then immunoblotted with an anti-phospho-Akt substrate antibody. Densitometry of phospho-SIK3 bands (bottom panel). (C) A schematic model for LKB1 and SIK3 function to regulate lipid homeostasis in Drosophila fat body. LKB1 regulates the nucleocytoplasmic localization of HDAC4 via SIK3-dependent phosphorylation. Under feeding condition, DILPs-induced Akt activation leads to SIK3 activation, thereby inhibiting HDAC4 activity by phosphorylation. Under short-term fasting conditions, the AKH pathway inhibits the kinase activity of LKB1 in phosphorylating SIK3 Thr196 residue and controls SIK3 activity via PKA-dependent phosphorylation. Unphosphorylated and nuclear localized HDAC4 deacetylates and activates FOXO to increase bmm expression [19], thereby reducing lipid storage. AKH-independent signaling modulates the LKB1-SIK3-HDAC4 pathway to induce bmm expression when fasting is prolonged. Data are presented as mean ± SEM (*P < 0.05; **P < 0.01; NS, non-significant).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4440640&req=5

pgen.1005263.g006: Activation of insulin receptor increases phosphorylation of SIK3 by Akt.(A) Immunoblot analyses showing the effect of 4 hr fasting and constitutively active insulin receptor (InRCA) on Thr196 phosphorylation of SIK3 protein in larvae (top three panels). Anti-phospho-Thr196 SIK3, -Myc (SIK3 protein), and -β-tubulin (TUB) antibodies were used. Densitometry of phospho-Thr196 SIK3 bands (bottom panel). FB-Gal4 was used to drive transgene expression in the fat body. (B) Immunoblot analyses showing the effect of constitutively active insulin receptor (InRCA) on Akt-dependent phosphorylation of SIK3 protein in larvae (top four panels). The lysates were immunoprecipitated with an anti-Myc (SIK3 protein) antibody, and then immunoblotted with an anti-phospho-Akt substrate antibody. Densitometry of phospho-SIK3 bands (bottom panel). (C) A schematic model for LKB1 and SIK3 function to regulate lipid homeostasis in Drosophila fat body. LKB1 regulates the nucleocytoplasmic localization of HDAC4 via SIK3-dependent phosphorylation. Under feeding condition, DILPs-induced Akt activation leads to SIK3 activation, thereby inhibiting HDAC4 activity by phosphorylation. Under short-term fasting conditions, the AKH pathway inhibits the kinase activity of LKB1 in phosphorylating SIK3 Thr196 residue and controls SIK3 activity via PKA-dependent phosphorylation. Unphosphorylated and nuclear localized HDAC4 deacetylates and activates FOXO to increase bmm expression [19], thereby reducing lipid storage. AKH-independent signaling modulates the LKB1-SIK3-HDAC4 pathway to induce bmm expression when fasting is prolonged. Data are presented as mean ± SEM (*P < 0.05; **P < 0.01; NS, non-significant).
Mentions: LKB1 is ubiquitously expressed and constitutively active in mammalian cells [15], which raises the question of how dietary conditions change the activity of LKB1 and SIK3 to control lipid homeostasis. Our findings suggested that fasting and the AKH pathway inhibit LKB1 activity to regulate SIK3 Thr196 phosphorylation (Figs 4C and 6C). It is possible that fasting- and AKH-induced inhibition of LKB1 activity can be achieved by altered subcellular localization, protein conformation, stability, and/or protein-protein interactions of LKB1 and its associated proteins. Interestingly, in HEK-293 cells, fasting triggers autophosphorylation of human LKB1 at Thr336 [30] that corresponds to Thr460 in Drosophila LKB1 [31]. This phosphorylation promotes the protein-protein interaction between LKB1 and 14-3-3 proteins [30] and inhibits the ability of LKB1 for suppressing cell growth [31].

Bottom Line: Interestingly, we found that the LKB1-SIK3-HDAC4 signaling axis is modulated by dietary conditions.In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibits the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induces HDAC4 nuclear localization and brummer gene expression.However, under prolonged fasting conditions, AKH-independent signaling decreases the activity of the LKB1-SIK3 pathway to induce lipolytic responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejon, Republic of Korea; National Creative Research Initiatives Center for Energy Homeostasis Regulation, Seoul National University, Seoul, Republic of Korea; Institute of Molecular Biology and Genetics, Seoul National University, Seoul, Republic of Korea.

ABSTRACT
LKB1 plays important roles in governing energy homeostasis by regulating AMP-activated protein kinase (AMPK) and other AMPK-related kinases, including the salt-inducible kinases (SIKs). However, the roles and regulation of LKB1 in lipid metabolism are poorly understood. Here we show that Drosophila LKB1 mutants display decreased lipid storage and increased gene expression of brummer, the Drosophila homolog of adipose triglyceride lipase (ATGL). These phenotypes are consistent with those of SIK3 mutants and are rescued by expression of constitutively active SIK3 in the fat body, suggesting that SIK3 is a key downstream kinase of LKB1. Using genetic and biochemical analyses, we identify HDAC4, a class IIa histone deacetylase, as a lipolytic target of the LKB1-SIK3 pathway. Interestingly, we found that the LKB1-SIK3-HDAC4 signaling axis is modulated by dietary conditions. In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibits the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induces HDAC4 nuclear localization and brummer gene expression. However, under prolonged fasting conditions, AKH-independent signaling decreases the activity of the LKB1-SIK3 pathway to induce lipolytic responses. We also identify that the Drosophila insulin-like peptides (DILPs) pathway, related to mammalian insulin pathway, regulates SIK3 activity in feeding conditions independently of increasing LKB1 kinase activity. Overall, these data suggest that fasting stimuli specifically control the kinase activity of LKB1 and establish the LKB1-SIK3 pathway as a converging point between feeding and fasting signals to control lipid homeostasis in Drosophila.

No MeSH data available.


Related in: MedlinePlus