Insulin-like growth factor II in human neuroblastoma cell growth.

Insulin-like growth factor-II (IGF-II) is a mitogenic polypeptide which shares structural and functional homology with insulin. IGF-II and its receptors are produced during mammalian embryogenesis, and may serve an important role in neuronal maturation. In this thesis, production of IGF-II and IGF receptor expression in human SH-SY5Y neuroblastoma cells was assayed. It was hypothesized that IGF-II and IGF receptor production is regulated together with changes in growth rate and the IGF-II may exhibit autocrine growth promoting effects. Incubation of SH-SY5Y cells in serum-free media for six days and subsequent radioimmunoassay of conditioned media showed a three-fold increase in secretion of this peptide. This increase in IGF-II protein was associated with a 30-fold rise in 6.0 kb IGF-II mRNA over the same incubation period, as determined by Northern analysis of total RNA, suggesting increased IGF-II biosynthesis which may be important in regulating cell growth. Anti-IGF-II antibody inhibited SH-SY5Y cell proliferation, which was partially overcome by addition of IGF-II, indicating that IGF-II is necessary for SH-SY5Y cell growth in serum-free media. Exogenously added IGF-II stimulated $\sp3$H-TdR incorporation and BrdU nuclear labelling index, suggesting IGF-II promotes entry of SH-SY5Y cells into S phase. IGF-II did not alter the distribution of cells within the cell cycle, a finding which is inconsistent with the stimulatory effect of IGF-II on DNA synthesis. Treatment of SH-SY5Y cells with the antiproliferative cytokine IFN-$\gamma$ inhibited $\sp3$H-TdR incorporation and induced a serum-dependent decrease in cell number. We detected two-fold decreases in 6.0 kb IGF-II mRNA and secreted IGF-II protein after three-day treatment with IFN-$\gamma$ (100 U/ml). Type I IGF receptor mRNA was increased three-fold by IFN-$\gamma$ in the presence of serum and 1.5-fold in the absence of serum, whereas type II IGF receptor mRNA was unchanged. IGF-II prevented IFN-$\gamma$ inhibition of DNA synthesis, but only in serum-free media. Collectively, our data support the hypothesis that IGF-II is an autocrine growth factor in SH-SY5Y cells and that IGF-II and type I IGF receptor expression is regulated by serum factors which regulate proliferation, including IFN-$\gamma$.PhDNeuroscienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103269/1/9308393.pdfDescription of 9308393.pdf : Restricted to UM users only