title: IGF-IR internalizes with Caveolin-1 and PTRF/Cavin in HaCat cells.
abstract: BACKGROUND
  Insulin-like growth factor-I receptor (IGF-IR) is a tyrosine kinase receptor (RTK) associated with caveolae, invaginations of the plasma membrane that regulate vesicular transport, endocytosis and intracellular signaling. IGF-IR internalization represents a key mechanism of down-modulation of receptors number on plasma membrane. IGF-IR interacts directly with Caveolin-1 (Cav-1), the most relevant protein of caveolae. Recently it has been demonstrated that the Polymerase I and Transcript Release Factor I (PTRF/Cavin) is required for caveolae biogenesis and function. The role of Cav-1 and PTRF/Cavin in IGF-IR internalization is still to be clarified.
  
  
  RESULTS
  We have investigated the interaction of IGF-IR with Cav-1 and PTRF/Cavin in the presence of IGF1in human Hacat cells. We show that IGF-IR internalization triggers Cav-1 and PTRF/Cavin translocation from plasma membrane to cytosol and increases IGF-IR interaction with these proteins. In fact, Cav-1 and PTRF/Cavin co-immunoprecipitate with IGF-IR during receptor internalization. We found a different time course of co-immunoprecipitation between IGF-IR and Cav-1 compared to IGF-IR and PTRF/Cavin. Cav-1 and PTRF/Cavin silencing by siRNA differently affect surface IGF-IR levels following IGF1 treatment: Cav-1 and PTRF/Cavin silencing significantly affect IGF-IR rate of internalization, while PTRF/Cavin silencing also decreases IGF-IR plasma membrane recovery. Since Cav-1 phosphorylation could have a role in IGF-IR internalization, the mutant Cav-1Y14F lacking Tyr14 was transfected. Cav-1Y14F transfected cells showed a reduced internalization of IGF-IR compared with cells expressing wild type Cav-1. Receptor internalization was not impaired by Clathrin silencing. These findings support a critical role of caveolae in IGF-IR intracellular traveling.
  
  
  CONCLUSIONS
  These data indicate that Caveolae play a role in IGF-IR internalization. Based on these findings, Cav-1 and PTRF/Cavin could represent two relevant and distinct targets to modulate IGF-IR function.
authors.affiliation: Department of Endocrinology and Medicine (DiSEM), University of Genova, Genova, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Salani
authors.forename: Mario
authors.initials: M
authors.lastname: Passalacqua
authors.forename: Sara
authors.initials: S
authors.lastname: Maffioli
authors.forename: Lucia
authors.initials: L
authors.lastname: Briatore
authors.forename: Meriem
authors.initials: M
authors.lastname: Hamoudane
authors.forename: Paola
authors.initials: P
authors.lastname: Contini
authors.forename: Renzo
authors.initials: R
authors.lastname: Cordera
authors.forename: Davide
authors.initials: D
authors.lastname: Maggi
mesh_terms: D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004705:Endocytosis; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D018613:Microscopy, Confocal; D009154:Mutation; D011485:Protein Binding / Q000187:drug effects; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection
chemical_list: C497835:CAVIN1 protein, human; D051242:Caveolin 1; D016601:RNA-Binding Proteins; D049452:Green Fluorescent Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1