Figure 5

Modulation of survivin expression in TSC^−/− A⁺ cells by IGF-1 and EGF. A,B: The cells were cultured for 48 h in standard medium, or in the same medium devoid of EGF in the presence or absence of IGF-1 (50 ng/mL). C: After 24 h in serum-deprived medium, IGF-1 (50 ng/mL), LY294002 (LY, 100 µM), or both were added to the serum-deprived medium for 2 or 6 h, and survivin, Smac/DIABLO, caspase-3, and the phosphorylated form of S6 were assessed by means of Western blotting. Removing EGF from the growth medium (A), or adding IGF-1 in the presence or absence of EGF (B), triggered the expression of survivin. The expression of proapoptotic Smac/DIABLO in A⁺ cells was down-regulated by IGF-1, but only in the presence of EGF (B). The omission of EGF counteracted the suppressive action of IGF-1 on Smac/DIABLO expression (B). Serum-deprivation and LY, a PI3K inhibitor, did not inhibit the rapid IGF-1 induction of survivin expression, which was already evident 2 h after drug exposure (C).