Insulin-like growth factor-I protects neuroblastoma against starvation-induced apoptosis and is associated with increased Bcl-2 expression

Background/Purpose: Aggressive neuroblastomas avoid apoptosis and have increased expression of the antiapoptotic protein, Bcl-2. Insulin-like growth factor-I (IGF-I) is mitogenic and may promote tumor survival by inhibiting apoptosis. The authors hypothesize that IGF-I may protect neuroblastoma cells from apoptosis by upregulating their Bcl-2 expression. Methods: Human neuroblastoma cells (IMR-32) are cultured, and 3 experimental groups are established: 1 group with cells cultured in standard growth media (control), 1 with cells grown in serum-depleted media (starvation), and 1 with neuroblastoma cells cultured in starvation media plus IGF-I. The cells are harvested at 14 and 24 hours, and cytospin slides are made. Bcl-2 expression is measured by immunohistochemistry. Apoptosis is detected with the TUNEL method. Results: Bcl-2 expression is decreased 90% in the serum starved neuroblastoma cells. In addition, apoptosis is 150 times higher in the starved neuroblastoma cells. These changes are abrogated by the addition of IGF-I, where apoptosis is decreased 50% and Bcl-2 is 14-fold higher in the IGF-I-treated group. These changes are most apparent at 24 hours. Conclusions: IGF-I protects neuroblastoma cells from apoptosis and increases Bcl-2 expression. Growth factors may have a direct role in promoting tumorigenesis by inducing the expression of antiapoptotic proteins by the tumor.