Specific inhibition of mTOR reduced the incidence of S-phase entry induced by rhGGF2. A, A histogram of the level of BrdU labeling in epithelia that were treated with rapamycin (Rap) at 1, 5, and 20 nm in the presence of rhGGF2. B, The inhibitory effect of 20 nm rapamycin on S-phase entry was reversed by FK506, which competes with rapamycin for the same binding site of the immunophilin FKBP12. FK506 was added 1 hr before rapamycin, rhGGF2, and BrdU. When tested together with rhGGF2, FK506 did not change the level of S-phase entry significantly from the level induced by rhGGF2 alone. Each bar represents data from 20 to 44 pieces of epithelium.