title: Identification of the antibiotic ionomycin as an unexpected peroxisome proliferator-activated receptor γ (PPARγ) ligand with a unique binding mode and effective glucose-lowering activity in a mouse model of diabetes.
abstract: OBJECTIVE
  Existing thiazolidinedione (TZD) drugs for diabetes have severe side effects. The aim of this study is to develop alternative peroxisome proliferator-activated receptor γ (PPARγ) ligands that retain the benefits in improving insulin resistance but with reduced side effects.
  
  
  METHODS
  We used AlphaScreen assay to screen for new PPARγ ligands from compound libraries. In vitro biochemical binding affinity assay and in vivo cell-based reporter assay were used to validate ionomycin as a partial ligand of PPARγ. A mouse model of diabetes was used to assess the effects of ionomycin in improving insulin sensitivity. Crystal structure of PPARγ complexed with ionomycin revealed the unique binding mode of ionomycin, which elucidated the molecular mechanisms allowing the discrimination of ionomycin from TZDs.
  
  
  RESULTS
  We found that the antibiotic ionomycin is a novel modulating ligand for PPARγ. Both the transactivation and binding activity of PPARγ by ionomycin can be blocked by PPARγ specific antagonist GW9662. Ionomycin interacts with the PPARγ ligand-binding domain in a unique binding mode with properties and epitopes distinct from those of TZD drugs. Ionomycin treatment effectively improved hyperglycaemia and insulin resistance, but had reduced side effects compared with TZDs in the mouse model of diabetes. In addition, ionomycin effectively blocked the phosphorylation of PPARγ at Ser273 by cyclin-dependent kinase 5 both in vitro and in vivo.
  
  
  CONCLUSIONS
  Our studies suggest that ionomycin may represent a unique template for designing novel PPARγ ligands with advantages over current TZD drugs.
authors.affiliation: State Key Laboratory of Cellular Stress Biology, School of Life Sciences, Xiamen University, Fujian, China.
authors.forename: W
authors.initials: W
authors.lastname: Zheng
authors.forename: X
authors.initials: X
authors.lastname: Feng
authors.forename: L
authors.initials: L
authors.lastname: Qiu
authors.forename: Z
authors.initials: Z
authors.lastname: Pan
authors.forename: R
authors.initials: R
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: D
authors.initials: D
authors.lastname: Hou
authors.forename: L
authors.initials: L
authors.lastname: Jin
authors.forename: Y
authors.initials: Y
authors.lastname: Li
mesh_terms: D000813:Anilides / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000737:chemistry / Q000627:therapeutic use*; D015759:Ionomycin / Q000737:chemistry / Q000627:therapeutic use*; D008297:Male; D051379:Mice; D047495:PPAR gamma / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding
chemical_list: C457499:2-chloro-5-nitrobenzanilide; D000813:Anilides; D001786:Blood Glucose; D007004:Hypoglycemic Agents; D047495:PPAR gamma; D015759:Ionomycin