IGFBP-3 mediates p53-induced apoptosis during serum starvation

Insulin-like growth factor binding protein (IGFBP)-3, a p53-response gene, can induce apoptosis in an IGF-independent manner. Here we demonstrate that IGFBP-3 mediates p53-induced apoptosis during serum starvation using two foil neoplastic cell models: one which introduces p53 activity and one which eliminates it. We created a doxycycline-inducible p53 model from the p53-negative PC-3 prostate cancer cell line. Doxycycline treatment increased both p53 and IGFBP-3 levels. It also augmented apoptosis, but not during insulin-like growth factor-I co-treatment. In a second model, lung carcinoma H460 cells expressing fully functional p53 were stably transfected with E6, which targets p53 for degradation. H460-E6 cells contained less p53 and IGFBP-3 than control neo-transfected cells, and proteasome blockade restored both. In serum deprivation, H460-E6 cells had enhanced growth and less apoptosis than did H460-neo cells. Reductions in H460-neo apoptosis, comparable in magnitude to H460-E6, were achieved by adding anti-IGFBP- 3 -antibody or IGFBP-3 antisense oligomers, but not non-specific immunoglobulin or IGFBP-3 sense oligomers. In summary, turning p53 'on' in two foil neoplastic cell models induced IGFBP-3 expression and increased apoptosis during serum starvation, an effect inhibited by insulin-like growth factor-I treatment and specific IGFBP-3 blockade. This is the first demonstration of inhibition of p53 action by antagonizing IGFBP-3.