title: Characterization of GAB1 expression over the menstrual cycle in women with and without polycystic ovarian syndrome provides a new insight into its pathophysiology.
abstract: BACKGROUND
  In a previous microarray analysis, GRB2-associated binding protein 1 (GAB1), a docking protein closely related to the insulin receptor substrate, was down-regulated in endometrium of women with polycystic ovary syndrome (PCOS).
  
  
  OBJECTIVE
  The objective of the study was to characterize the cyclic expression of endometrial GAB1 in vivo in normal women and those with PCOS as well as investigate the possible mechanisms of endometrial regulation of GAB1 expression and action in vitro.
  
  
  METHODS
  This was an experimental and case-control study.
  
  
  METHODS
  The study was conducted at a tertiary university hospital.
  
  
  METHODS
  Normal proven fertile women (controls; n = 31) and women with PCOS (cases; n = 26) participated in the study.
  
  
  METHODS
  INTERVENTIONS included timed endometrial biopsies at different phases of the menstrual cycle. Ishikawa cells were cultured with β-estradiol (E2), medroxyprogesterone acetate, and E2 + medroxyprogesterone acetate. Transfection of small interfering RNA for GAB1 in Ishikawa cells incubated with or without insulin.
  
  
  METHODS
  GAB1 mRNA expression in Ishikawa cells and in endometrium of cases and controls was measured. Protein expression of phosphorylated MAPK by Western blot was also measured. Immunohistochemical localization and expression of phosphorylated GAB1 in endometrium was also measured, using a digital histological score.
  
  
  RESULTS
  In endometrial tissue, GAB1 mRNA was reduced in the proliferative phase of PCOS women, compared with controls (P = .003; ANOVA). When all the phases of the menstrual cycle were grouped, GAB1 protein expression was reduced in endometrium of PCOS women (P < .0001; Student t test). E2 increases GAB1 mRNA expression in Ishikawa cells (P = .001; ANOVA). Phosphorylated MAPK is reduced in cells transfected with small interfering RNA for GAB1 (P = .008; ANOVA) and incubated with insulin.
  
  
  CONCLUSIONS
  GAB1 mRNA expression is positively modulated by E2. Endometrial GAB1 protein and mRNA expression are reduced in women with PCOS, suggesting that the endometrium of PCOS women have a defect in insulin signaling due to GAB1 down-regulation.
authors.affiliation: Department of Obstetrics and Gynecology (K.L.R., S.L.Y.), University of North Carolina, Chapel Hill, North Carolina 27599; and Departamento de Ginecologia e Obstetrícia (R.F.S.), Universidade Federal do Rio Grande do Sul 90035-903, Brazil.
authors.forename: K L
authors.initials: KL
authors.lastname: Roemer
authors.forename: S L
authors.initials: SL
authors.lastname: Young
authors.forename: R F
authors.initials: RF
authors.lastname: Savaris
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D016022:Case-Control Studies; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004717:Endometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006801:Humans; D017258:Medroxyprogesterone Acetate / Q000494:pharmacology; D008597:Menstrual Cycle / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011085:Polycystic Ovary Syndrome / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D055815:Young Adult
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C098587:GAB1 protein, human; D004958:Estradiol; D017258:Medroxyprogesterone Acetate