THE INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR PROTECTS TUMOR-CELLS FROM APOPTOSIS IN-VIVO

The role of the insulin-like growth factor I receptor (IGF-IR) in prog rammed cell death has been investigated in vivo in a biodiffusion cham ber, where the extent of cell death could be determined quantitatively . We found that a decrease in the number of IGF-IRs causes massive apo ptosis in vivo in several transplantable tumors, either from humans or rodents. Conversely, an overexpressed IGF-IR protects cells from apop tosis in vivo. We also show that the same conditions that in vitro cau se only partial growth arrest with a minimum of cell death, induce in vivo almost complete cell death. We conclude that the IGF-IR activated by its ligands plays a very important protective role in programmed c ell death, and that its protective action is even more striking in viv o than in vitro.