title: Rad51 overexpression contributes to chemoresistance in human soft tissue sarcoma cells: a role for p53/activator protein 2 transcriptional regulation.
abstract: We investigated whether Rad51 overexpression plays a role in soft tissue sarcoma (STS) chemoresistance as well as the regulatory mechanisms underlying its expression. The studies reported here show that Rad51 protein is overexpressed in a large panel of human STS specimens. Human STS cell lines showed increased Rad51 protein expression, as was also observed in nude rat STS xenografts. STS cells treated with doxorubicin exhibited up-regulation of Rad51 protein while arrested in the S-G(2) phase of the cell cycle. Treatment with anti-Rad51 small interfering RNA decreased Rad51 protein expression and increased chemosensitivity to doxorubicin. Because we previously showed that reintroduction of wild-type p53 (wtp53) into STS cells harboring a p53 mutation led to increased doxorubicin chemosensitivity, we hypothesized that p53 participates in regulating Rad51 expression in STS. Reintroduction of wtp53 into STS cell lines resulted in decreased Rad51 protein and mRNA expression. Using luciferase reporter assays, we showed that reconstitution of wtp53 function decreased Rad51 promoter activity. Deletion constructs identified a specific Rad51 promoter region containing a p53-responsive element but no p53 consensus binding site. Electrophoretic mobility shift assays verified activator protein 2 (AP2) binding to this region and increased AP2 binding to the promoter in the presence of wtp53. Mutating this AP2 binding site eliminated the wtp53 repressive effect. Furthermore, AP2 knockdown resulted in increased Rad51 expression. In light of the importance of Rad51 in modulating STS chemoresistance, these findings point to a potential novel strategy for molecular-based treatments that may be of relevance to patients burdened by STS.
authors.affiliation: Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Jonathan A F
authors.initials: JA
authors.lastname: Hannay
authors.forename: Juehui
authors.initials: J
authors.lastname: Liu
authors.forename: Quan-Sheng
authors.initials: QS
authors.lastname: Zhu
authors.forename: Svetlana V
authors.initials: SV
authors.lastname: Bolshakov
authors.forename: Lan
authors.initials: L
authors.lastname: Li
authors.forename: Peter W T
authors.initials: PW
authors.lastname: Pisters
authors.forename: Alexander J F
authors.initials: AJ
authors.lastname: Lazar
authors.forename: Dihua
authors.initials: D
authors.lastname: Yu
authors.forename: Raphael E
authors.initials: RE
authors.lastname: Pollock
authors.forename: Dina
authors.initials: D
authors.lastname: Lev
mesh_terms: D002453:Cell Cycle; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D006801:Humans; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051135:Rad51 Recombinase / Q000378:metabolism / Q000502:physiology*; D020218:Response Elements; D012509:Sarcoma / Q000188:drug therapy*; D012983:Soft Tissue Neoplasms / Q000188:drug therapy*; D050656:Transcription Factor AP-2 / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
chemical_list: D034741:RNA, Small Interfering; C495901:TP53 protein, human; D050656:Transcription Factor AP-2; D016159:Tumor Suppressor Protein p53; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D046988:Proteasome Endopeptidase Complex