PKCλ in liver mediates insulin-induced SREBP-1c expression and determines both hepatic lipid content and overall insulin sensitivity
Michihiro Matsumoto, Wataru Ogawa, Kazunori Akimoto, Hiroshi Inoue, Kazuaki Miyake, Kensuke Furukawa, Yoshitake Hayashi, Haruhisa Iguchi, Yasushi Matsuki, Ryuji Hiramatsu, Hitoshi Shimano, Nobuhiro Yamada, Shigeo Ohno, Masato Kasuga, Tetsuo Noda
Michihiro Matsumoto, Wataru Ogawa, Kazunori Akimoto, Hiroshi Inoue, Kazuaki Miyake, Kensuke Furukawa, Yoshitake Hayashi, Haruhisa Iguchi, Yasushi Matsuki, Ryuji Hiramatsu, Hitoshi Shimano, Nobuhiro Yamada, Shigeo Ohno, Masato Kasuga, Tetsuo Noda
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Article Endocrinology

PKCλ in liver mediates insulin-induced SREBP-1c expression and determines both hepatic lipid content and overall insulin sensitivity

Abstract

PKCλ is implicated as a downstream effector of PI3K in insulin action. We show here that mice that lack PKCλ specifically in the liver (L-λKO mice), produced with the use of the Cre-loxP system, exhibit increased insulin sensitivity as well as a decreased triglyceride content and reduced expression of the sterol regulatory element–binding protein-1c (SREBP-1c) gene in the liver. Induction of the hepatic expression of Srebp1c and of its target genes involved in fatty acid/triglyceride synthesis by fasting and refeeding or by hepatic expression of an active form of PI3K was inhibited in L-λKO mice compared with that in control animals. Expression of Srebp1c induced by insulin or by active PI3K in primary cultured rat hepatocytes was inhibited by a dominant-negative form of PKCλ and was mimicked by overexpression of WT PKCλ. Restoration of PKCλ expression in the liver of L-λKO mice with the use of adenovirus-mediated gene transfer corrected the metabolic abnormalities of these animals. Hepatic PKCλ is thus a determinant of hepatic lipid content and whole-body insulin sensitivity.

Authors

Michihiro Matsumoto, Wataru Ogawa, Kazunori Akimoto, Hiroshi Inoue, Kazuaki Miyake, Kensuke Furukawa, Yoshitake Hayashi, Haruhisa Iguchi, Yasushi Matsuki, Ryuji Hiramatsu, Hitoshi Shimano, Nobuhiro Yamada, Shigeo Ohno, Masato Kasuga, Tetsuo Noda

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Effects of dominant-negative and WT PKCλ on the expression of Srebp1, Fa...
Effects of dominant-negative and WT PKCλ on the expression of Srebp1, Fas, Pck1, and G6pc in primary cultured rat hepatocytes. (a, c, and d) Cells that had been infected (or not) with an adenoviral vector for a dominant-negative form of PKCλ (AxCAλKD) at the indicated MOI (in PFU/cell) were incubated in the absence or presence of insulin, dexamethasone (Dex), or T0901317, plus pCPT-cAMP (these two agents were used to induce the expression of Pck1 and G6pc), as indicated. Total cell lysates were then subjected to immunoblot analysis with antibodies to PKCλ, and total RNA extracted from the cells was subjected to Northern blot analysis with probes specific for Srebp1, Fas, Pck1, or G6pc mRNA’s. (b) Cells that had been infected (or not) with an adenovirus encoding a constitutively active form of PI3K (AxCAMyr-p110) at an MOI of three plaque-forming units/cell were then infected with AxCAλKD at the indicated MOI. Total cell lysates were subjected to immunoblot analysis with antibodies to PKCλ or to Myc (for the detection of Myr-p110), and total RNA extracted from the cells was subjected to Northern blot analysis with a probe specific for Srebp1 mRNA. (e) Cells were infected (or not) with an adenovirus encoding WT PKCλ (AxCAλWT) at the indicated MOI, after which cell lysates were subjected to immunoblot analysis with antibodies to PKCλ and total RNA extracted from the cells was subjected to Northern blot analysis with probes specific for Srebp1 or Fas mRNAs. All data are representative of at least three independent experiments.