Figure 1.

Prolonged insulin-like growth factor-1 (IGF-1) treatment induces senescence-like phenotypes. (A) Schematic of experimental design and reference time frame. (B, C) MEFs and IMR90 cells were serum-starved for 4 days, and then treated with or without 50 ng mL⁻¹ IGF-1 for 6 days under serum-starvation conditions. Cells were stained for SA-β-Gal activity, photographed (B), and quantitated as the percentage of SA-β-Gal-positive cells over total cell number (C). Results are presented as means and SE from three experiments performed in triplicate. (D) IMR90 cells were serum-starved for 4 days, and then treated with or without IGF-1 for 6 days under serum-starvation conditions. Whole-cell lysates were subjected to western blot analysis, as shown. (E–G) IMR90 cells were serum-starved for 4 days, then treated with or without IGF-1 for 6 days under serum-starvation conditions, and then grown for an additional 3 days in the presence of 10% FBS. Cells were assayed for BrdU incorporation (E) and quantified (F), or grown for three more days in the presence of 10% FBS and measured for cell proliferation (G). Results are presented as means and SE from three experiments performed in triplicate. **P < 0.01.