title: The effects of NBS1 knockdown by small interfering RNA on the ionizing radiation-induced apoptosis in human lymphoblastoid cells with different p53 status.
abstract: Mutations of NBS1 are responsible for the human hereditary disease Nijmegen breakage syndrome (NBS), which is characterized by an extremely high cancer rate. In this study, we investigated the influence of NBS1 on ionizing radiation (IR) induced apoptosis. Using small interfering RNA (siRNA) transfection, we knocked down NBS1 protein in three closely related human lymphoblastoid cell lines differing in p53 status: TK6 with a wild-type p53, NH32 with a null mutation of p53, and WTK1 with a mutant p53. We found that up to 48h after 5Gy IR, all three lines showed an obvious induction of apoptosis regardless of the p53 status. The magnitude of apoptosis induction was TK6>NH32>WTK1. This suggested that although p53 is an important modulator of IR-induced apoptosis, other p53-independent apoptosis pathway also exists. Moreover, NBS1 knockdown led to reduction of IR-induced apoptosis in all three lines and both NBS1/ATM/p53/BAX and NBS1/ATM/CHK2/E2F1 apoptosis pathways were partially inactivated. Our results suggest that NBS1 plays an important role in IR-induced apoptosis via both p53-dependent and p53-independent mechanisms. The impaired apoptosis response to DNA damage in NBS1 deficient cells might be one of the important mechanisms of cancer predisposition in NBS patients.
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA. ying.zhang@colostate.edu
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.forename: Chang U K
authors.initials: CU
authors.lastname: Lim
authors.forename: Junqing
authors.initials: J
authors.lastname: Zhou
authors.forename: Howard H
authors.initials: HH
authors.lastname: Liber
mesh_terms: D017209:Apoptosis / Q000235:genetics / Q000502:physiology / Q000528:radiation effects*; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D064447:Checkpoint Kinase 2; D004268:DNA-Binding Proteins / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000378:metabolism; D005720:Gamma Rays; D005838:Genotype; D006801:Humans; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; C112156:NBN protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases