title: Knockdown of c-Myc expression by RNAi inhibits MCF-7 breast tumor cells growth in vitro and in vivo.
abstract: BACKGROUND
  Breast cancer is the leading cause of cancer death in women worldwide. Elevated expression of c-Myc is a frequent genetic abnormality seen in this malignancy. For a better understanding of its role in maintaining the malignant phenotype, we used RNA interference (RNAi) directed against c-Myc in our study. RNAi provides a new, reliable method to investigate gene function and has the potential for gene therapy. The aim of the study was to examine the anti-tumor effects elicited by a decrease in the protein level of c-Myc by RNAi and its possible mechanism of effects in MCF-7 cells.
  
  
  METHODS
  A plasmid-based polymerase III promoter system was used to deliver and express short interfering RNA (siRNA) targeting c-myc to reduce its expression in MCF-7 cells. Western blot analysis was used to measure the protein level of c-Myc. We assessed the effects of c-Myc silencing on tumor growth by a growth curve, by soft agar assay and by nude mice experiments in vivo. Standard fluorescence-activated cell sorter analysis and TdT-mediated dUTP nick end labelling assay were used to determine apoptosis of the cells.
  
  
  RESULTS
  Our data showed that plasmids expressing siRNA against c-myc markedly and durably reduced its expression in MCF-7 cells by up to 80%, decreased the growth rate of MCF-7 cells, inhibited colony formation in soft agar and significantly reduced tumor growth in nude mice. We also found that depletion of c-Myc in this manner promoted apoptosis of MCF-7 cells upon serum withdrawal.
  
  
  CONCLUSIONS
  c-Myc has a pivotal function in the development of breast cancer. Our data show that decreasing the c-Myc protein level in MCF-7 cells by RNAi could significantly inhibit tumor growth both in vitro and in vivo, and imply the therapeutic potential of RNAi on the treatment of breast cancer by targeting overexpression oncogenes such as c-myc, and c-myc might be a potential therapeutic target for human breast cancer.
authors.affiliation: Laboratory of Cell and Molecular Biology, Cancer Institute & Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, PR China. Yihua_wang@hotmail.com
authors.forename: Yi-hua
authors.initials: YH
authors.lastname: Wang
authors.forename: Shuang
authors.initials: S
authors.lastname: Liu
authors.forename: Guo
authors.initials: G
authors.lastname: Zhang
authors.forename: Cui-qi
authors.initials: CQ
authors.lastname: Zhou
authors.forename: Hong-xia
authors.initials: HX
authors.lastname: Zhu
authors.forename: Xiao-bo
authors.initials: XB
authors.lastname: Zhou
authors.forename: Lan-ping
authors.initials: LP
authors.lastname: Quan
authors.forename: Jin-feng
authors.initials: JF
authors.lastname: Bai
authors.forename: Ning-zhi
authors.initials: NZ
authors.lastname: Xu
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D016259:Genes, myc; D015316:Genetic Therapy / Q000379:methods; D006801:Humans; D010641:Phenotype; D010957:Plasmids; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis*; D034622:RNA Interference; D012320:RNA Polymerase III / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D016271:Proto-Oncogene Proteins c-myc; D012320:RNA Polymerase III
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