title: Effects of insulin, insulin-like growth factor-I and -II on proliferation and intracellular signaling in endometrial carcinoma cells with different expression levels of insulin receptor isoform A.
abstract: BACKGROUND
  Hyperinsulinemia, insulin-like growth factor (IGF)-I and -II (IGF-II) are associated with increased risk of endometrial carcinoma. Insulin receptor isoform A (IR-A) is more frequently expressed in endometrial carcinoma than in normal endometrial tissues. To better understand their roles in endometrial carcinoma, we investigated the effects of insulin, IGF-I, and IGF-II in endometrial carcinomas cells with different IR-A expression levels.
  
  
  METHODS
  To explore the role of IR-A in mediating the activity of IGF-I, IGF-II, and insulin, we investigate the cellular proliferation of endometrial carcinoma cell lines RL95-2 and RL95-2-IR-A by MTS assays. Then we examined the protein kinase Akt phosphorylation and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in both cell lines by Western blotting. The effect of IGF-II and AG1024 on cell cycle progression and apoptosis was assessed by flowcytometry. To examine whether the effects of IGFs were mediated by IR-A, we blocked IGF-I receptor (IGF-IR) in both cell lines using AG1024, an IGF-IR-specific inhibitor.
  
  
  RESULTS
  IGF-I and IGF-II significantly enhanced proliferation of both cell lines (P < 0.05). By contrast, insulin significantly increased proliferation of RL95-2-IR-A cells only (P < 0.05). IGF-I and IGF-II significantly increased pAkt levels in RL95-2 cells and pERK1/2 levels in RL95-2-IR-A cells (all, P < 0.05). Insulin increased pERK1/2 levels in RL95-2-IR-A cells only (P < 0.05). LY294002 and PD98059 inhibited the specific signaling activities and cellular proliferation. After AG1024 pretreatment, neither IGF-I nor IGF-II affected pAkt levels in RL95-2 cells. IGF-II, but not IGF-I, increased pERK1/2 levels in RL95-2-IR-A cells. After AG1024 pretreatment, the proliferation rate and DNA content corresponding to the S phase increased and apoptosis decreased significantly in IGF-II-treated RL95-2-IR-A cells only (P < 0.05).
  
  
  CONCLUSIONS
  The proliferation effect of insulin is mediated by IR-A. When IR-A dominates in a cell line, IGF-II activated cell proliferation mainly through the ERK1/2 pathway. On the other hand, IGF-II activated cell proliferation mainly through the Akt pathway. IR-A can at least partly mediate the proliferative and anti-apoptotic effects of IGF-II through the ERK1/2 pathway.
authors.affiliation: Department of Obstetrics and Gynecology, Peking University People's Hospital, Beijing 100044, China.
authors.forename: Chun-fang
authors.initials: CF
authors.lastname: Wang
authors.forename: Guo
authors.initials: G
authors.lastname: Zhang
authors.forename: Li-jun
authors.initials: LJ
authors.lastname: Zhao
authors.forename: Xiao-ping
authors.initials: XP
authors.lastname: Li
authors.forename: Wen-juan
authors.initials: WJ
authors.lastname: Qi
authors.forename: Jian-liu
authors.initials: JL
authors.lastname: Wang
authors.forename: Li-hui
authors.initials: LH
authors.lastname: Wei
mesh_terms: D015703:Antigens, CD / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D016889:Endometrial Neoplasms / Q000378:metabolism / Q000473:pathology*; D005260:Female; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D042541:Intracellular Space / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D011972:Receptor, Insulin / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D015703:Antigens, CD; D007328:Insulin; D020033:Protein Isoforms; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; C435941:INSR protein, human; D011972:Receptor, Insulin