Regulation of insulin-like growth factor-II expression and its role in autocrine growth of human neuroblastoma cells

Abstract

Insulin‐like growth factor‐II (IGF‐II) is highly expressed in fetal tissues and may act as an autocrine growth factor during early embryogenesis. The SH‐SY5Y human neuroblastoma cell line also expresses IGF‐II and its receptors and responds to exogenous IGF‐II with increased DNA synthesis, cell division, and neuritic outgrowth. For this study, we tested the hypothesis that IGF‐II mediates autocrine growth of SH‐SY5Y cells in serum‐free media. SH‐SY5Y cells plated at high densities proliferated in serum‐free media, whereas sparsely plated cells did not. IGF‐II mRNA levels increased within 24 hours of serum deprivation and were associated with increased immunoreactive IGF‐II protein. Exogenous addition of IGF‐II increased ³H‐TdR incorporation and cell number in a dose‐ and time‐dependent fashion. By nuclear labelling experiments using 5‐Bromo‐2′ deoxyuridine (BrdU), we detected a twofold higher percentage of S phase nuclei after a 24‐hour incubation in IGF‐II. Treatment of SH‐SY5Y cells with anti‐IGF‐II antibodies in serum‐free media inhibited cell proliferation, and this inhibition was partially overcome by the addition of increasing concentrations of IGF‐II. Collectively, our results indicate that IGF‐II mediates an autocrine growth mechanism in SH‐SY5Y cells that is associated with increased IGF‐II expression.