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Obesity (Silver Spring). 2008 Mar;16(3):531-8. doi: 10.1038/oby.2007.98. Epub 2008 Jan 17.

SIK2 can be activated by deprivation of nutrition and it inhibits expression of lipogenic genes in adipocytes.

Author information

1
Brown Medical School, Department of Medicine, Hallett Center for Diabetes and Endocrinology, Providence, RI, USA.

Abstract

OBJECTIVE:

Determine the biological function of SIK2 in 3T3-L1 adipocytes.

METHODS AND PROCEDURES:

3T3-L1 adipocytes were treated with serum-free, serum/glucose-free, or complete Dulbecco's Modified Eagle's Medium (DMEM) for 15 min, or 10 microg/ml oligomycin in serum-free DMEM for 15 min, or different doses of 5-amino-4-imidazolecarboxamide (AICAR) for different periods of time in serum-free DMEM. After treatment, SIK2 kinase activity was measured by examining phosphorylation of a peptide substrate. SIK2 was overexpressed and knocked down in 3T3-L1 CAR adipocytes using adenovirus-mediated gene transfer for the assessment of lipogenic gene expression and triglyceride content. Electroporation was used to transiently transfect 3T3-L1 adipocytes with fatty acid synthase (FAS) promoter-driven luciferase construct to evaluate the effect of SIK2 on FAS transcription.

RESULTS:

In 3T3-L1 adipocytes, SIK2 can be activated by nutrient deprivation, inhibition of ATP synthesis, and treatment of AICAR. Overexpression of SIK2 repressed the expression of lipogenic genes, including FAS, acetyl CoA carboxylase 2 (ACC2), and stearoyl CoA desaturase 1 (SCD1), and reduced triglyceride content. Reduction of endogenous SIK2 expression through RNA interference increased the expression of FAS, ACC2, and SCD1. This effect is independent of adenosine monophosphate-activated protein kinase (AMPK) since neither phosphorylation state nor protein level of AMPKalpha1 and AMPKalpha2 was affected by SIK2 overexpression. SIK2 inhibits the expression of FAS-promoter driven luciferase reporter gene, and this effect can be reversed by overexpression of constitutively active sterol regulatory element binding protein-1 (SREBP-1). Furthermore, SIK2 also reduces the nuclear translocation of endogenous SREBP-1.

DISCUSSION:

Our results support a role for SIK2 in adipocyte energy metabolism. SIK2 may function similarly to AMPK for turning off lipogenesis in low-energy state.

PMID:
18239551
DOI:
10.1038/oby.2007.98
[Indexed for MEDLINE]
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