SIRT1 overexpression antagonizes cellular senescence with activated ERK/S6k1 signaling in human diploid fibroblasts

Abstract

Sir2, a NAD-dependent deacetylase, modulates lifespan in yeasts, worms and flies. The SIRT1, mammalian homolugue of Sir2, regulates signaling for favoring survival in stress. But whether SIRT1 has the function to influence cell vaibility and senescence under non-stresses conditions in human diploid fibroblasts is far from unknown. Our data showed that enforced SIRT1 expression promoted cell prolifferation and antagonized cellular senescence with the characteristics features od delayed Senescence-Associated β-galactosides (SA-β-gal) staining, reduced Senescence-Associated Heterochromatic Foci (SAHF) formation and G1 phase arrest, increased cell growth rate nad extended cellular lifespan in human fibroblasts, while dominant negative SIRT1 allele (H363Y) did not significantly affect the cell growth and senescence but displayed a bit decreased lifespan. Western blot results showed that SIRT1 reduced the expression of p16INK4A and promoted phosphorylation of Rb. Our data also exposed that overexpression of SIR1 was accompanied by enhance activation of ERK and S6K1 signaling. These effects were mimicked in both W138 cells and 2BS cells by concentration-dependent resveratrol, a SIRT1 activator. It was noted that treatment of SIRT1 transfected cells with Rapamycin, a mTOR inhibitor, reduced the phosphorylation of S6K1 and the expression of ld1, implying that SIRT1-induced phosphorylation of S6K1 may be party for the decreased expression of p16INK4A and promoted phosphorylation of Rb in 2BS. It was also observed that the expression of SIRT1 and phosphorylation of ERK and S6K1 was declined in senescent 2BS. These findings suggested that SIRT1-promoted cell proliferation and antagonized cellular senescene in human diploid fibroblasts may be, in part, via the activation of ERK/S6K1 signaling. © 2008 Huang et al.