LKB1 signalling attenuates early events of adipogenesis and responds to adipogenic cues

J Mol Endocrinol. 2014 Aug;53(1):117-30. doi: 10.1530/JME-13-0296. Epub 2014 May 23.

Abstract

cAMP-response element-binding protein (CREB) is required for the induction of adipogenic transcription factors such as CCAAT/enhancer-binding proteins (C/EBPs). Interestingly, it is known from studies in other tissues that LKB1 and its substrates AMP-activated protein kinase (AMPK) and salt-inducible kinases (SIKs) negatively regulate gene expression by phosphorylating the CREB co-activator CRTC2 and class IIa histone deacetylases (HDACs), which results in their exclusion from the nucleus where they co-activate or inhibit their targets. In this study, we show that AMPK/SIK signalling is acutely attenuated during adipogenic differentiation of 3T3-L1 preadipocytes, which coincides with the dephosphorylation and nuclear translocation of CRTC2 and HDAC4. When subjected to differentiation, 3T3-L1 preadipocytes in which the expression of LKB1 was stably reduced using shRNA (Lkb1-shRNA), as well as Lkb1-knockout mouse embryonic fibroblasts (Lkb1(-/-) MEFs), differentiated more readily into adipocyte-like cells and accumulated more triglycerides compared with scrambled-shRNA-expressing 3T3-L1 cells or Wt MEFs. In addition, the phosphorylation of CRTC2 and HDAC4 was reduced, and the mRNA expression of adipogenic transcription factors Cebpa, peroxisome proliferator-activated receptor γ (Pparg) and adipocyte-specific proteins such as hormone-sensitive lipase (HSL), fatty acid synthase (FAS), aP2, GLUT4 and adiponectin was increased in the absence of LKB1. The mRNA and protein expression of Ddit3/CHOP10, a dominant-negative member of the C/EBP family, was reduced in Lkb1-shRNA-expressing cells, providing a potential mechanism for the up-regulation of Pparg and Cebpa expression. These results support the hypothesis that LKB1 signalling keeps preadipocytes in their non-differentiated form.

Keywords: AMPK; CRTC2; HDACs; LKB1; SIKs; adipogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3-L1 Cells
  • AMP-Activated Protein Kinases / metabolism
  • Active Transport, Cell Nucleus
  • Adipocytes / cytology
  • Adipocytes / metabolism
  • Adipogenesis / genetics
  • Adipogenesis / physiology*
  • Animals
  • Cell Differentiation
  • Cells, Cultured
  • Gene Knockout Techniques
  • Histone Deacetylases / metabolism
  • Mice
  • Models, Biological
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / deficiency
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • Signal Transduction
  • Transcription Factors / metabolism

Substances

  • Crtc2 protein, mouse
  • RNA, Small Interfering
  • Transcription Factors
  • Stk11 protein, mouse
  • salt-inducible kinase-2, mouse
  • Protein-Serine-Threonine Kinases
  • SIK3 protein, mouse
  • AMP-Activated Protein Kinases
  • Hdac5 protein, mouse
  • Histone Deacetylases