title: MicroRNA-18a attenuates DNA damage repair through suppressing the expression of ataxia telangiectasia mutated in colorectal cancer.
abstract: BACKGROUND
  miR-18a is one of the most up-regulated miRNAs in colorectal cancers (CRC) based on miRNA profiling. In this study, we examined the functional significance of miR-18a in CRC.
  
  
  METHODS
  Expression of miR-18a was investigated in 45 CRC patients. Potential target genes of miR-18a were predicted by in silico search and confirmed by luciferase activity assay and Western blot. DNA damage was measured by comet assay. Gene function was measured by cell viability, colony formation and apoptosis assays.
  
  
  RESULTS
  The up-regulation of miR-18a was validated and confirmed in 45 primary CRC tumors compared with adjacent normal tissues (p<0.0001). Through in silico search, the 3'UTR of Ataxia telangiectasia mutated (ATM) contains a conserved miR-18a binding site. Expression of ATM was down-regulated in CRC tumors (p<0.0001) and inversely correlated with miR-18a expression (r = -0.4562, p<0.01). Over-expression of miR-18a in colon cancer cells significantly reduced the luciferase activity of the construct with wild-type ATM 3'UTR but not that with mutant ATM 3'UTR, inferring a direct interaction of miR-18a with ATM 3'UTR. This was further confirmed by the down-regulation of ATM protein by miR-18a. As ATM is a key enzyme in DNA damage repair, we evaluated the effect of miR-18a on DNA double-strand breaks. Ectopic expression of miR-18a significantly inhibited the repair of DNA damage induced by etoposide (p<0.001), leading to accumulation of DNA damage, increase in cell apoptosis and poor clonogenic survival.
  
  
  CONCLUSIONS
  miR-18a attenuates cellular repair of DNA double-strand breaks by directly suppressing ATM, a key enzyme in DNA damage repair.
authors: Institute of Digestive Disease and Department of Medicine and Therapeutics, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Hong Kong, Special Administrative Region, People's Republic of China.
authors: Chung-Wah
authors: CW
authors: Wu
authors: Yu-Juan
authors: YJ
authors: Dong
authors: Qiao-Yi
authors: QY
authors: Liang
authors: Xin-Qi
authors: XQ
authors: He
authors: Simon S M
authors: SS
authors: Ng
authors: Francis K L
authors: FK
authors: Chan
authors: Joseph J Y
authors: JJ
authors: Sung
authors: Jun
authors: J
authors: Yu
mesh_terms: D020413:3' Untranslated Regions; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D064007:Ataxia Telangiectasia Mutated Proteins; D020029:Base Pairing; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics*; D005047:Etoposide / Q000494:pharmacology / Q000633:toxicity; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008297:Male; D035683:MicroRNAs / Q000235:genetics*; D008875:Middle Aged; D009367:Neoplasm Staging; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D034622:RNA Interference; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: D020413:3' Untranslated Regions; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C581632:MIRN18 microRNA, human; D035683:MicroRNAs; D025521:Tumor Suppressor Proteins; D005047:Etoposide; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases