title: DNA damage induced by oridonin involves cell cycle arrest at G2/M phase in human MCF-7 cells.
abstract: OBJECTIVE
  To study the mechanisms of inhibition of cell growth and induction of DNA damage in oridonin-treated MCF-7 human breast cancer cells.
  
  
  METHODS
  The cytotoxicity of oridonin-treated MCF-7 cells was measured by MTT assay. Cell cycle phase distribution was analyzed by flow cytometry. P-ATM, P-CHK2, γH2AX and P-P53 protein expressions were detected by Western blot analysis. The expression of r-h2ax and P-ATM was also detected by immunofluorescence staining. The degree of cellular damage of oridonin-induced MCF-7 human breast cancer cells was confirmed by the comet assay analysis of DNA fragmentation.
  
  
  RESULTS
  Oridonin inhibited cell growth in a time- and dose-dependent manner. The IC50 values at 48 and 72 hours were 78.3 and 31.62 µmol/l, respectively. Oridonin induced G2/M phase arrest in MCF-7 cells. MCF-7 cells treated with oridonin showed significant DNA damage as shown by an increase in olive tail moment (OTM). The protein expression levels of P-ATM, P-CHK2, γH2AX and P-P53 were increased significantly in a dose-dependent manner.
  
  
  CONCLUSIONS
  DNA damage provokes p53-mediated G2/M cell cycle arrest in oridonin-induced MCF-7 cells through the mechanism of CHK2 activation by activated ATM protein kinase, which is induced by oridonin.
authors.affiliation: Central Research Laboratory, the First Affiliated Hospital of Jilin University, Changchun, China ; School of Basic Medical Sciences, Jiamusi University, No. 148 Xuefu Street, Jiamusi City, Heilongjiang Province, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Tan
authors.forename: Rui
authors.initials: R
authors.lastname: Zhao
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Liu
keywords: ATM; CHK2; apoptosis; cell cycle; oridonin; p53