SIRT1 modulates the levels of H4K16ac and γ-H2AX and is in complex with TPX2.

(A) siRNA-mediated loss of SIRT1 in HeLa cells increases H4K16ac levels and decreases ionizing radiation-dependent γ-H2AX levels when compared to controls. (B) Overexpression of SIRT1 in MCF7 cells decreases H4K16ac levels and increases ionizing radiation-dependent γ-H2AX levels when compared to controls. (C) Co-immunoprecipitations with TPX2 antibodies from HeLa cells with and without ionizing radiation treatment as indicated and in the absence or presence of ethidium bromide (EtBr). (The Input for TPX2 is from a longer exposure of the same blot.) (D) Co-immunoprecipitations with SIRT1 antibodies from HeLa cells with and without ionizing radiation treatment as indicated. Beads without antibodies (No Ab) were used as controls. Cells were treated with 10 Gy (or left untreated) and harvested after 1h recovery (A-B) or as indicated (C-D). See text for details. Levels of H2AX and H4 were used as loading controls. IR: ionizing radiation.