Role of insulin-like growth factors in autocrine growth of human retinoblastoma Y79 cells.
In this study, we have demonstrated that human retinoblastoma Y79 cells produce insulin-like growth factors (IGFs) type I and type II and release them into the medium. We have also ascertained, by means of competitive studies and cross-linking procedure, that Y79 cells contain the type-I IGF receptor (IGF-IR). Furthermore, surface-bound IGF-I is internalised by the receptor, then degraded to amino acids. Insulin, IGF-I and IGF-II caused down-regulation of IGF-IR; the effect is concentration and time dependent. Scatchard analysis demonstrated that incubation with insulin markedly decreased the binding capacity measured for IGF-I while the apparent Kd value calculated for IGF-I binding was not significantly modified. IGF-I, IGF-II and insulin induced tyrosine phosphorylation of IGF-IR. Tyrosine phosphorylation of this receptor with, however, a less strong signal, was detectable even in cells cultured in serum-free medium without the addition of any exogenous growth factor. Similar results have been found concerning the tyrosine phosphorylation of insulin receptor substrate-1 (IRS 1). Tyrosine phosphorylation of both IGF-IR and IRS 1, either under basal conditions or after stimulation with growth factors, was strongly inhibited when alpha-IR3, a monoclonal antibody to IGF-IR, was added to the culture. IGF-I was capable of inducing Y79 cell proliferation and its effect was entirely inhibited by the addition of alpha-IR3. This antibody also markedly reduced the proliferation of Y79 cells cultured in serum-free medium not supplemented with stimulatory factors. Our results indicate that IGF-I and IGF-IR mediate an autocrine growth mechanism in Y79 cells.
Giuliano
M
M
Institute of Biological Chemistry, University of Palermo, Italy.
Vento
R
R
Lauricella
M
M
Calvaruso
G
G
Carabillo
M
M
Tesoriere
G
G
D001667:Binding, Competitive; D002455:Cell Division / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000502:physiology*; D012175:Retinoblastoma / Q000473:pathology*; D015398:Signal Transduction
C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D019000:Phosphotyrosine; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1