The role of the IGF-1 receptor in the stimulation of cells by short pulses of growth factors.

Balb/c 3T3 cells require prolonged stimulation by serum or growth factors to enter DNA synthesis. However, in p6 cells, a derivative cell line from 3T3 cells which constitutively over-express the insulin-like growth factor-1 (IGF-1) receptor, a serum pulse of only 1 h is sufficient for maximal stimulation. Furthermore, maximal stimulation of DNA synthesis is also obtained when 3T3 cells, serum-stimulated for only 1 h, are subsequently incubated with IGF-1. Our results indicate that short pulses of growth factors render 3T3 cells capable of responding to IGF-1, either by increasing the number of IGF-1 receptors or by providing a new substrate for the activated receptor.