title: Functional analysis of the involvement of apurinic/apyrimidinic endonuclease 1 in the resistance to melphalan in multiple myeloma.
abstract: BACKGROUND
  Melphalan resistance has been considered one of the major obstacles to improve outcomes in multiple myeloma (MM) therapy; unfortunately, the mechanistic details of this resistance remain unclear. Melphalan is a highly effective alkylating agent which causes many types of DNA lesions, including DNA base alkylation damage that is repaired by base excision repair (BER). We postulated that human apurinic/apyrimidinic endonuclease 1 (APE1), an essential BER enzyme, plays a vital role in acquired melphalan resistance. However, because APE1 is a multifunctional protein with redox activity and acetylation modification in addition to its major repair activity, the particular APE1 function that may play a more important role in melphalan resistance is unknown.
  
  
  METHODS
  Two MM cell lines, RPMI-8226 and U266 were used to measure the difference in APE1 levels in melphalan-resistant and sensitive derivatives. APE1 functional mutants for DNA repair, redox and acetylation were employed to investigate the roles of individual APE1 activities in acquired melphalan resistance.
  
  
  RESULTS
  Our results indicate that APE1 is overexpressed in both MM melphalan-resistant cells. Knocking down APE1 sensitizes the melphalan resistant MM cells to melphalan treatment. The exogenous expression of DNA repair mutant H309N and acetylation mutant K6R/K7R of APE1 failed to restore the melphalan resistance of the APE1 knockdown RPMI-8226 cells. The AP endonuclease activity and multidrug resistance protein 1 (MDR1) regulatory activity may play roles in the melphalan resistance of MM cells.
  
  
  CONCLUSIONS
  The present study has identified that the DNA repair functions and the acetylation modification of APE1 are involved in melphalan resistance of MM cells and has also shed light on future therapeutic strategies targeting specific APE1 functions by small molecule inhibitors.
authors.affiliation: Cancer Center, Research Institute of Surgery, Daping Hospital, Third Military Medical University, Chongqing 400042, P,R China. xiejia505@sina.com.
authors.forename: Jiayin
authors.initials: J
authors.lastname: Xie
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.forename: Mengxia
authors.initials: M
authors.lastname: Li
authors.forename: Jia
authors.initials: J
authors.lastname: Du
authors.forename: Liwei
authors.initials: L
authors.lastname: Zhou
authors.forename: Senlin
authors.initials: S
authors.lastname: Yang
authors.forename: Linli
authors.initials: L
authors.lastname: Zeng
authors.forename: Zengpeng
authors.initials: Z
authors.lastname: Li
authors.forename: Ge
authors.initials: G
authors.lastname: Wang
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000107:Acetylation; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008558:Melphalan / Q000494:pharmacology*; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D009154:Mutation; D010084:Oxidation-Reduction; D034622:RNA Interference; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018906:Antineoplastic Agents, Alkylating; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D008558:Melphalan