Figure 1. mTORC1 activity is enhanced with loss of p53 function independent of AMPK.

(A) Phosphorylation of S6K1 is higher in p53 null cells. p53+/+ and p53−/− HCT116 cells were treated with vehicle (DMSO) or 20 μM VP16 for 24 hrs and p53 and p-T389 S6K1 levels were assessed by immunoblotting. (B) Loss of p53 does not alter activation of AMPK. Three subconfluent cultures of HCT116 cells wt and null for p53 were separately harvested and lysates probed by immunoblotting. (C) p53 null cells have higher mTORC1-dependent phosphorylation of 4EBP1 and reduced 4EBP1 function. m⁷GTP pulldowns were performed on 3 independent replicate HCT116 cell lysates followed by immunoblot analysis of the eIF4E and 4EBP1 captured by the beads, as well as the corresponding lysates. (D) Silencing of p53 augments mTORC1 signaling. HCT116 and two NSCLC cell lines, H460 and A549, were transfected with scrambled or p53-specific siRNA for 48 hrs and cell extracts were analyzed by immunoblotting.