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Proc. Natl. Acad. Sci. USA, Published online before print October 25, 2017 | doi: 10.1073/pnas.1706489114 Increased intracellular Ca2+ concentrations prevent membrane localization of PH domains through the formation of Ca2+-phosphoinositides

Jin Ku Kang^a, Ok-Hee Kim^a, June Hur^a, So Hee Yu^a, Santosh Lamichhane^a, Jin Wook Lee^a, Uttam Ojha^a, Jeong Hee Hong^a, Cheol Soon Lee^a, Ji-Young Cha^b, Young Jae Lee^b, Seung-Soon lm^c, Young Joo Park^d, Cheol Soo Choi^a, Dae Ho Lee^a, In-Kyu Lee^e, and Byung-Chul Oh^a,1^aDepartment of Physiology, Lee Gil Ya Cancer and Diabetes Institute, Gachon University College of Medicine, Incheon 21999, Republic of Korea;

^bDepartment of Biochemistry, Lee Gil Ya Cancer and Diabetes Institute, Gachon University College of Medicine, Incheon 21999, Republic of Korea;

^cDepartment of Physiology, Keimyung University School of Medicine, Daegu 704-701, Republic of Korea;

^dDepartment of Internal Medicine, Seoul National University College of Medicine, Seoul 03080, Republic of Korea;

^eDepartment of Internal Medicine, Graduate School of Medicine, Kyungpook National University, Daegu 702-701, Republic of Korea
¹To whom correspondence should be addressed.

Abstract

Insulin resistance, a key etiological factor in metabolic syndrome, is closely linked to ectopic lipid accumulation and increased intracellular Ca²⁺ concentrations in muscle and liver. However, the mechanism by which dysregulated intracellular Ca²⁺ homeostasis causes insulin resistance remains elusive. Here, we show that increased intracellular Ca²⁺ acts as a negative regulator of insulin signaling. Chronic intracellular Ca²⁺ overload in hepatocytes during obesity and hyperlipidemia attenuates the phosphorylation of protein kinase B (Akt) and its key downstream signaling molecules by inhibiting membrane localization of pleckstrin homology (PH) domains. Pharmacological approaches showed that elevated intracellular Ca²⁺ inhibits insulin-stimulated Akt phosphorylation and abrogates membrane localization of various PH domain proteins such as phospholipase Cδ and insulin receptor substrate 1, suggesting a common mechanism inhibiting the membrane targeting of PH domains. PH domain-lipid overlay assays confirmed that Ca²⁺ abolishes the binding of various PH domains to phosphoinositides (PIPs) with two adjacent phosphate groups, such as PI(3,4)P₂, PI(4,5)P₂, and PI(3,4,5)P₃. Finally, thermodynamic analysis of the binding interaction showed that Ca²⁺-mediated inhibition of targeting PH domains to the membrane resulted from the tight binding of Ca²⁺ rather than PH domains to PIPs forming Ca²⁺-PIPs. Thus, Ca²⁺-PIPs prevent the recognition of PIPs by PH domains, potentially due to electrostatic repulsion between positively charged side chains in PH domains and the Ca²⁺-PIPs. Our findings provide a mechanistic link between intracellular Ca²⁺ dysregulation and Akt inactivation in insulin resistance.

membrane localization, PH domain, Ca2+-phosphoinositides, intracellular Ca2+ concentration, insulin resistance

논문정보

형식Research article
게재일2017년 10월 (BRIC 등록일 2017-11-07)
연구진국내 연구진
분야 생명과학 > 생리학

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