FIGURE 3.

MST1 enhances p53 transcriptional activity. A, H1299 cells were co-transfected with a 14*p53 artificial luciferase construct and p53, MST1, MST1-K59R, or Sirt1 as indicated. Lysates were assayed for dual luciferase activity (t test; n = 4, p < 0.01). Error bars represent the mean ± S.E. MST1 expression decreases Sirt1-mediated repression of p53 transcriptional activation. B, H1299 cells were co-transfected with a p21-luciferase promoter construct and p53, MST1, or Sirt1 plasmids as indicated. Lysates were assayed for dual luciferase activity as in A (t test; n = 3, p < 0.05). Sirt1 reduces p53-mediated p21 expression, and MST1 expression can reverse Sirt1-mediated repression of p53-induced p21 expression. C, U2OS cells were transfected with plasmids encoding MST1 together with Sirt1 or an empty control vector. Apoptosis was analyzed after 36-h etoposide treatment by annexin V staining followed by flow cytometry (t test; n = 3, p < 0.01). D, U2OS cells were transfected with either si-Sirt1, si-MST1, or both si-Sirt1 and si-MST1, or the control vector. Apoptosis was analyzed after 36-h etoposide treatment by annexin V staining followed by flow cytometry (t test; n = 3, p < 0.01).