title: Insulin and insulin like growth factor II endocytosis and signaling via insulin receptor B.
abstract: BACKGROUND
  Insulin and insulin-like growth factors (IGFs) act on tetrameric tyrosine kinase receptors controlling essential functions including growth, metabolism, reproduction and longevity. The insulin receptor (IR) binds insulin and IGFs with different affinities triggering different cell responses.
  
  
  RESULTS
  We showed that IGF-II induces cell proliferation and gene transcription when IR-B is over-expressed. We combined biotinylated ligands with streptavidin conjugated quantum dots and visible fluorescent proteins to visualize the binding of IGF-II and insulin to IR-B and their ensuing internalization. By confocal microscopy and flow cytometry in living cells, we studied the internalization kinetic through the IR-B of both IGF-II, known to elicit proliferative responses, and insulin, a regulator of metabolism.
  
  
  CONCLUSIONS
  IGF-II promotes a faster internalization of IR-B than insulin. We propose that IGF-II differentially activates mitogenic responses through endosomes, while insulin-activated IR-B remains at the plasma membrane. This fact could facilitate the interaction with key effector molecules involved in metabolism regulation.
authors.affiliation: Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales (FCEN), Universidad de Buenos Aires (UBA), IQUIBICEN, CONICET, Buenos Aires, Argentina. federico@fbmc.fcen.uba.ar.
authors.forename: Jimena
authors.initials: J
authors.lastname: Giudice
authors.forename: Lucia Soledad
authors.initials: LS
authors.lastname: Barcos
authors.forename: Francisco F
authors.initials: FF
authors.lastname: Guaimas
authors.forename: Alberto
authors.initials: A
authors.lastname: Penas-Steinhardt
authors.forename: Luciana
authors.initials: L
authors.lastname: Giordano
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Jares-Erijman
authors.forename: Federico
authors.initials: F
authors.lastname: Coluccio Leskow