title: Downregulation of histone H3 lysine 9 methyltransferase G9a induces centrosome disruption and chromosome instability in cancer cells.
abstract: BACKGROUND
  Modifications of the histone amino-terminal tails affect access of regulatory factors and complexes to chromatin and thereby influence biological processes. Cancer cells are characterized by prominent epigenetic dysregulation, including histone modifications. However, the functional roles of the histone methyltransferases (HMT) in cancer remain unclear.
  
  
  RESULTS
  We studied RNAi-based inhibition (knockdown, KD) of 2 different H3K9 HMTs, SUV39H1 and G9a. Knockdown of the 2 HMTs in PC3 cancer cell line markedly inhibited cell growth and caused profound morphological changes with loss of telomerase activity and shortened telomeres. SUV39H1 KD cells showed substantial increase in G2/M fraction. G9a KD cells showed increased DNA content (1.7-fold in 2 independent clones) compared with FACS analyses to control. Karyotype analyses showed that this was due to an increased number of chromosomes (from 61 to 102) in G9a KD cells compared to parental PC3. Intriguingly, we found abnormal centrosome morphology and number in about 25% of the G9a KD cells, while centrosomes were morphologically normal in control cells. Microarray analyses after KD of SUV39H1 or G9a showed very few genes up-regulated among the 39,000 genes. The silenced tumor-suppressor genes p16 and RASSF1A were not activated in KD cells.
  
  
  CONCLUSIONS
  These data suggest that the 2 HMTs, SUV39H1 and G9a are required to perpetuate the malignant phenotype. Furthermore, G9a plays a critical role in regulating centrosome duplication presumably through chromatin structure rather than through affecting gene expression in cancer cells. Targeting these histone methyltransferases may be of therapeutic benefit in cancers.
authors.affiliation: Division of Molecular Oncology, Aichi Cancer Center Research Institute, Nagoya, Japan. ykondo@aichi-cc.jp
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kondo
authors.forename: Lanlan
authors.initials: L
authors.lastname: Shen
authors.forename: Saira
authors.initials: S
authors.lastname: Ahmed
authors.forename: Yanis
authors.initials: Y
authors.lastname: Boumber
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Sekido
authors.forename: Bassem R
authors.initials: BR
authors.lastname: Haddad
authors.forename: Jean-Pierre J
authors.initials: JP
authors.lastname: Issa
mesh_terms: D045744:Cell Line, Tumor; D018385:Centrosome / Q000201:enzymology*; D043171:Chromosomal Instability; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics*; D044127:Epigenesis, Genetic; D015972:Gene Expression Regulation, Neoplastic; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D008780:Methyltransferases / Q000235:genetics; D009369:Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D011496:Protein Methyltransferases; D012097:Repressor Proteins / Q000235:genetics; D016615:Telomere / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics
chemical_list: D019941:Cyclin-Dependent Kinase Inhibitor p16; D006657:Histones; C411762:RASSF1 protein, human; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; C407843:SUV39H1 protein, human; D000076983:Histone Methyltransferases; D008780:Methyltransferases; D011496:Protein Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; D008239:Lysine