HMGB1increases radiosensitivity by interacting with HDAC1

Objective To study the nuclear protein association of high-mobility group box-1 (HMGB1) and histone deacetylase 1 (HDAC1),and the effect of interaction on radiosensitivity in human breast cancer cells.Methods The protein-protein interaction was determined by immunoprecipitationWestern blot and glutathione-S-transferase capture assays.Cell growth was examined by MTT (methyl thiazolyl tetrazolium)assay and clonogenic assay.Histone deacetylase activity was analyzed by histone deacetylase assay.Results A significant increase of HMGB1 protein and radiosensitivity was observed in MDA-MB-231 and MDA-MB-468 cells transfected with a pCMV-Tag2B expression vector carrying with a full-length of HMGB1 cDNA.HMGB1 binding to HDAC1 was demonstrated as GST (glutathione Stransferase)-pull down and immunoprecipitation Western blot assay,and the association was elevated by irradiation.An LXCXE motif was required for the HMGB1-HADC1 interaction and HMGB1 radiosensitization.A significant difference of IC50 value was observed,for example,1.8 and 2.2 Gy (wtHMGB1 transfectants,P ＜ 0.05),3.6 and 3.8 Gy (HMGB1/C103F transfectants,P ＞ 0.05),both compared with 3.9 and 4.1 Gy (pCMV-Tag2B transfectants) in MDA-MB-231 and MDA-MB-468 cells,respectively.A specific HDAC1 inhibitor trichostatin A markedly reduced the HMGB1-mediated radiosensitivity,0.5 Gy in the presence of trichostatin A versus 1.8 Gy in absence of trichostatin A in MDA-MB-231 transfectants,1.2 Gy (with trichostatin A) versus 2.2 Gy (without trichostatin A) in MDA-MB-468 transfectants,P ＜ 0.05.Histone deacetylase activity was also detected in immunoprecipitates prepared from these cells with antibodies to HMGB1,and this activity was abolished by the histone trichostatin A.Conclusions These results suggest a previous unanticipated role for HDAC1 in modification of HMGB1-mediated radiosensitivity by its direct interaction with HMGB1.