title: 53BP1 loss induces chemoresistance of colorectal cancer cells to 5-fluorouracil by inhibiting the ATM-CHK2-P53 pathway.
abstract: OBJECTIVE
  Loss of P53 binding protein 1 (53BP1) is considered a poor prognostic factor for colorectal cancer. However, its effect on chemosensitivity of colorectal cancer to 5-fluorouracil (5-FU) remains elusive. This study aimed to examine the association of 53BP1 expression with chemosensitivity of colorectal cancer cells to 5-FU.
  
  
  METHODS
  Immunohistochemistry was performed on 30 metastatic colorectal cancer samples to assess the associations of 53BP1 levels with clinical therapeutic effects. In vitro, IC50values for 5-FU and 53BP1 levels were determined by MTT assay and Western blot in 5 colorectal cancer cell lines. Then, 53BP1 was silenced in HCT116 and HT29 cells, and cell proliferation, apoptosis and cell cycle distribution were evaluated. Relative protein levels of ATM-CHK2-P53 pathway effectors and Bcl-2 family members were measured by Western blot. Finally, the effects of 53BP1 knockdown on tumor growth and 5-FU chemoresistance were investigated in vivo.
  
  
  RESULTS
  53BP1 expression was closely related to time to progression (TTP) after first-line chemotherapy. Namely, 53BP1 downregulation resulted in reduced TTP. In addition, 53BP1 silencing increased proliferation, inhibited apoptosis and induced S phase arrest in HCT116 and HT29 cells after 5-FU treatment. Moreover, 53BP1 knockdown also reduced the protein levels of ATM-CHK2-P53 apoptotic pathway effectors, caspase9 and caspase3, while increasing Bcl-2 expression. In vivo, 53BP1 silencing accelerated tumor proliferation in nude mice and enhanced resistance to 5-FU.
  
  
  CONCLUSIONS
  These findings confirmed that 53BP1 loss might be a negative factor for chemotherapy efficacy, promoting cell proliferation and inhibiting apoptosis by suppressing ATM-CHK2-P53 signaling, and finally inducing 5-FU resistance.
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Yao
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Ai
authors.initials: A
authors.lastname: Huang
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Xiumei
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Yang
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1277 JieFang Avenue, Wuhan, 430022, Hubei, China. wudajianzhu2004@163.com.
authors.forename: Hong
authors.initials: H
authors.lastname: Ma
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins / Q000235:genetics*; D049109:Cell Proliferation; D064447:Checkpoint Kinase 2 / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005472:Fluorouracil / Q000008:administration & dosage; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D015398:Signal Transduction / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*; D000071857:Tumor Suppressor p53-Binding Protein 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*
chemical_list: C495901:TP53 protein, human; C498301:TP53BP1 protein, human; D016159:Tumor Suppressor Protein p53; D000071857:Tumor Suppressor p53-Binding Protein 1; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D005472:Fluorouracil
keywords: 53BP1; ATM–CHK2–P53 pathway; Chemoresistance; Colorectal cancer; DNA damage repair