Insulin-Like Growth Factor I Receptor Expression and Function in Nerve Growth Factor-Differentiated PC12 Cells

Abstract: Receptors for insulin-like growth factor I (IGF-I) were studied on PC12EY cells, a subclone of PC12. Differentiation of PC12EY cells with nerve growth factor (NGF) did not alter either the number of IGF-I receptors nor their affinity for IGF-I. IGF-I receptors remained fully functional during differentiation, promoting increases in thymidine incorporation, glucose uptake, amino acid uptake, and the phosphorylation of the S6 protein of the ribosomes. IGF-I also increased the proportion of differentiated cells found in S-phase. But although the addition of IGF-I to naive cells caused an increase in cell number, there was no comparable increase when IGF-I was added to differentiated cells. Thus, although the receptor for IGF-I continues to be present and functional, IGF-I fails to induce cell proliferation in differentiated PC12 cells.