EXPRESSION OF INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-6 COMPLEMENTARY-DNA ALTERS NEUROBLASTOMA CELL-GROWTH

Insulin-like growth factors I and II (IGF-I and IGF-IZ) are actively i nvolved in neuroblastoma cell growth. In all biological fluids, they a re noncovalently bound to high-affinity binding proteins. At least six species of these IGF-binding proteins (IGFBPs) have been identified, but their precise roles remain unclear. One of them, IGFBP-6, is produ ced by neuroblastoma cells in culture under certain experimental condi tions and seems to be associated with the arrest of cell growth. We st ably transfected IGR-N-91 and SK-N-SH neuroblastoma cells with an expr ession vector comprising IGFBP-6 cDNA, whose expression was placed und er the control of the constitutive and ubiquitous cytomegalovirus prom oter. Analyses of the cell cycle (flux cytofluorometry), mitogenic act ivity (radiolabeled thymidine incorporation), and the number of viable cells (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test ) showed that the mitogenic effects of serum, IGF-I, IGF-II, and des ( 1-3) IGF-I, a truncated IGF-I analogue with no affinity for IGFBP-6, w ere depressed in both transfected cell lines. With s.c, injection of t ransfected IGR-N-91 cells into nude mice, tumors developed in only 50- 70% of cases, 1 or 2 weeks after those in controls, and were 60-90% sm aller. Our findings show that IGFBP-6 influences neuroblastoma cell gr owth, both in vitro and in experimental xenograft development.