Abstract
Leptin controls food intake and energy expenditure by regulating hypothalamic neuron activities. Leptin exerts its actions through complex signaling pathways including STAT3 phosphorylation, nuclear translocation, and binding to target gene promoter/cofactor complexes. Deficient or defective leptin signaling leads to obesity, which may be caused by insufficient leptin levels and/or resistance to leptin signaling. To understand the molecular mechanisms of leptin resistance, we studied the regulation of pro-opiomelanocortin (POMC) gene expression by leptin. We show that phospho-STAT3 activates POMC promoter in response to leptin signaling through a mechanism that requires an SP1-binding site in the POMC promoter. Furthermore, FoxO1 binds to STAT3 and prevents STAT3 from interacting with the SP1.POMC promoter complex, and consequently, inhibits STAT3-mediated leptin action. Our study suggests that leptin action could be inhibited at a step downstream of STAT3 phosphorylation and nuclear translocation, and provides a potential mechanism of leptin resistance in which an increased FoxO1 antagonizes STAT3-mediated leptin signaling.
Highlights
Leptin, a hormone secreted from adipose tissue, regulates food intake and energy expenditure [1]
Administration of recombinant leptin can reverse the phenotypes associated with lack of leptin production in humans and mice, the pharmaceutical significance of leptin is limited in the majority of obese subjects [5, 26, 27]
In most of the obese humans and animals, circulating leptin is often higher than their lean counterparts, but the body fails to respond to leptin because of impaired leptin signaling or leptin resistance [8, 10]
Summary
Animal Welfare and Diet-treated Animals—All of the experiments involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Agency for Science, Technology and Research Biomedical Sciences Institutes. For STAT3-FoxO1 interaction in 293-OBRb cells, 293OBRb cells transfected with expression vectors of pXJ40FLAG-mSTAT3 and pcDNA3-Myc-mFoxO1 were serumstarved and treated with leptin (50 nM) for 30 min and lysed in lysis buffer. The immunoprecipitates were washed four times in lysis buffer and subjected to SDS-PAGE and immunoblotting with antibodies against FLAG or Myc. 5% of cell lysate used in each co-IP sample was loaded as input. For STAT3-FoxO1 interaction using mouse hypothalamic extracts, hypothalamus from 14 C57BL/6 mice that were fed with HFD for 5 weeks was homogenized in chilled whole cell buffer containing 20 mM HEPES, pH 7.9, 280 mM KCl, 1 mM EDTA, 10% glycerol, 0.5% Nonidet P-40, and 20 mM NaF, supplemented with 1 mM Na3VO4, 1 mM dithiothreitol, 1 mM phenylmethylsulfonyl fluoride, and protease inhibitors. The significance limit was set at p Ͻ 0.05
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