Insulin-like growth factor-I protects neuroblastoma against starvation-induced apoptosis and is associated with increased Bcl-2 expression.
OBJECTIVE
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.
Beierle
Elizabeth A
EA
University of Florida, Gainesville, FL, USA.
Strande
Louise F
LF
Chen
Mike K
MK
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling / Q000379:methods; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D009447:Neuroblastoma / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016895:Culture Media, Serum-Free; D019253:Proto-Oncogene Proteins c-bcl-2; D007334:Insulin-Like Growth Factor I