INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR EXPRESSION AND FUNCTION IN NERVE GROWTH-FACTOR - DIFFERENTIATED PC12 CELLS

Receptors for insulin-like growth factor I (IGF-I) were studied on PC1 2EY cells, a subclone of PC12. Differentiation of PC12EY cells with ne rve growth factor (NGF) did not alter either the number of IGF-I recep tors nor their affinity for IGF-I. IGF-I receptors remained fully func tional during differentiation, promoting increases in thymidine incorp oration, 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 function al, IGF-I fails to induce cell proliferation in differentiated PC12 ce lls.