Figure 5.

SIRT1 inhibits c-Myc–induced cellular transformation. (a) Colony formation assays were performed using HO15 and Myc3 Rat1 cells infected with retrovirus encoding SIRT1 and SIRT1-H363Y. Colony formation was examined 2 wk later. The results shown are mean ± SEM and are representative of three independent assays. (b) Soft agar colony formation assay was performed using Myc3 Rat1 cells infected with retrovirus encoding SIRT1 and SIRT1-H363Y. The figure is representative of three independent assays. (c) HO15 cells were stably transfected with the indicated vectors. Cell growth was quantified at the indicated time. (d) Myc3 cells were transfected with Ras-encoding constructs together with vector or SIRT1-encoding constructs. Transfected cells were implanted into nude mice, and tumor formation was monitored. *, P < 0.05; **, P < 0.01 by two-tailed Student's t test. (e) Model of how c-Myc–SIRT1 loop regulates cell growth. Ac, acetylation.