DIFFERENTIATION OF Y79 CELLS INDUCED BY PROLONGED EXPOSURE TO INSULIN

Y79 human retinoblastoma cells are known to contain receptors for both insulin and insulin-like growth factors (IGFs), to produce these cyto kines and release them in the culture medium. Previously we have demon strated that IGFs and insulin stimulate Y79 cell proliferation through the involvement of type I IGF receptor and Insulin Receptor Substrate 1 (IRS-1). This paper studies the effect of prolonged exposure to ins ulin on Y79 cells. Cells grown for 10 days in the presence of insulin were reseeded and incubated once more with insulin. In the reseeded ce lls proliferation lowered and morphological changes appeared. After 10 days of reseeding, cells stopped proliferating and showed long ramify ing neurite processes and varicosities consistent with neuronal differ entiation. Morphological differentiation was accompanied by a marked i ncrease in the content of total protein and in that of tubulin, the ma jor protein constituent of microtubules, a marked increase in the cont ent of specialized protein markers of dopaminergic and cholinergic dif ferentiation (dopamine beta-hydroxylase and choline acetyltransferase activities, respectively); a contemporaneous decrease in the content o f glial fibrillary acidic protein (GFAP), a specific marker of glial c ells, was also observed. Our results demonstrate that prolonged exposu re to insulin induces Y79 cells to differentiate into a neuronal-like phenotype. At this moment it is not possible to establish the mechanis m by which insulin induces this differentiative effect.