title: Increased levels of the Akt-specific phosphatase PH domain leucine-rich repeat protein phosphatase (PHLPP)-1 in obese participants are associated with insulin resistance.
abstract: OBJECTIVE
  We determined the contribution to insulin resistance of the PH domain leucine-rich repeat protein phosphatase (PHLPP), which dephosphorylates Akt at Ser473, inhibiting its activity. We measured the abundance of PHLPP in fat and skeletal muscle from obese participants. To study the effect of PHLPP on insulin signalling, PHLPP (also known as PHLPP1) was overexpressed in HepG2 and L6 cells.
  
  
  METHODS
  Subcutaneous fat samples were obtained from 82 morbidly obese and ten non-obese participants. Skeletal muscle samples were obtained from 12 obese and eight non-obese participants. Quantification of PHLPP-1 in human tissues was performed by immunoblotting. The functional consequences of recombinant PHLPP1 overexpression in hepatoma HepG2 cells and L6 myoblasts were investigated.
  
  
  RESULTS
  Of the 82 obese participants, 31 had normal fasting glucose, 33 impaired fasting glucose and 18 type 2 diabetes. PHLPP-1 abundance was twofold higher in the three obese groups than in non-obese participants (p = 0.004). No differences were observed between obese participants with normal fasting glucose, impaired fasting glucose or type 2 diabetes. PHLPP-1 abundance was correlated with basal Akt Ser473 phosphorylation (r = -0.48; p = 0.001), BMI (r = 0.44; p < 0.0001), insulin (r = 0.35; p < 0.0001) and HOMA (r = 0.38; p < 0.0001). PHLPP-1 abundance was twofold higher in the skeletal muscle of 12 obese participants than in that of eight non-obese participants (p < 0.0001). Insulin treatment of HepG2 cells resulted in a dose- and time-dependent upregulation of PHLPP-1. Overexpression of PHLPP1 in HepG2 cells and L6 myoblasts resulted in impaired insulin signalling involving Akt/glycogen synthase kinase 3, glycogen synthesis and glucose transport.
  
  
  CONCLUSIONS
  Increased abundance of PHLPP-1, production of which is regulated by insulin, may represent a new molecular defect in insulin-resistant states such as obesity.
authors: Department of Experimental and Clinical Medicine, University Magna Græcia of Catanzaro, Viale Europa, 88100 Catanzaro, Italy.
authors: F
authors: F
authors: Andreozzi
authors: C
authors: C
authors: Procopio
authors: A
authors: A
authors: Greco
authors: G C
authors: GC
authors: Mannino
authors: C
authors: C
authors: Miele
authors: G A
authors: GA
authors: Raciti
authors: C
authors: C
authors: Iadicicco
authors: F
authors: F
authors: Beguinot
authors: A E
authors: AE
authors: Pontiroli
authors: M L
authors: ML
authors: Hribal
authors: F
authors: F
authors: Folli
authors: G
authors: G
authors: Sesti
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D005260:Female; D056945:Hep G2 Cells; D006801:Humans; D066298:In Vitro Techniques; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D009765:Obesity / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D055815:Young Adult
chemical_list: D009687:Nuclear Proteins; D051057:Proto-Oncogene Proteins c-akt; C400601:PHLPP1 protein, human; C541572:PHLPP2 protein, human; D010749:Phosphoprotein Phosphatases