title: Plant HDAC inhibitor chrysin arrest cell growth and induce p21WAF1 by altering chromatin of STAT response element in A375 cells.
abstract: BACKGROUND
  Chrysin and its analogues, belongs to flavonoid family and possess potential anti-tumour activity. The aim of this study is to determine the molecular mechanism by which chrysin controls cell growth and induce apoptosis in A375 cells.
  
  
  METHODS
  Effect of chrysin and its analogues on cell viability and cell cycle analysis was determined by MTT assay and flowcytometry. A series of Western blots was performed to determine the effect of chrysin on important cell cycle regulatory proteins (Cdk2, cyclin D1, p53, p21, p27). The fluorimetry and calorimetry based assays was conducted for characterization of chrysin as HDAC inhibitor. The changes in histone tail modification such as acetylation and methylation was studied after chrysin treatment was estimated by immuno-fluorescence and western blot analysis. The expression of Bcl-xL, survivin and caspase-3 was estimated in chrysin treated cells. The effect of chrysin on p21 promoter activity was studied by luciferase and ChIP assays.
  
  
  RESULTS
  Chrysin cause G1 cell cycle arrest and found to inhibit HDAC-2 and HDAC-8. Chrysin treated cells have shown increase in the levels of H3acK14, H4acK12, H4acK16 and decrease in H3me2K9 methylation. The p21 induction by chrysin treatment was found to be independent of p53 status. The chromatin remodelling at p21WAF1 promoter induces p21 activity, increased STAT-1 expression and epigenetic modifications that are responsible for ultimate cell cycle arrest and apoptosis.
  
  
  CONCLUSIONS
  Chrysin shows in vitro anti-cancer activity that is correlated with induction of histone hyperacetylation and possible recruitment of STAT-1, 3, 5 proteins at STAT (-692 to -684) region of p21 promoter. Our results also support an unexpected action of chrysin on the chromatin organization of p21WAF1 promoter through histone methylation and hyper-acetylation. It proposes previously unknown sequence specific chromatin modulations in the STAT responsive elements for regulating cell cycle progression negatively via the induction of the CDK inhibitor p21WAF1.
authors.affiliation: Department of Chemical Biology, Indian Institute of Chemical Technology, Hyderabad, India. manikapb@gmail.com
authors.forename: Manika
authors.initials: M
authors.lastname: Pal-Bhadra
authors.forename: M Janaki
authors.initials: MJ
authors.lastname: Ramaiah
authors.forename: T Lakshminarayan
authors.initials: TL
authors.lastname: Reddy
authors.forename: Anita
authors.initials: A
authors.lastname: Krishnan
authors.forename: S N C V L
authors.initials: SN
authors.lastname: Pushpavalli
authors.forename: K Suresh
authors.initials: KS
authors.lastname: Babu
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Tiwari
authors.forename: J Madhusudana
authors.initials: JM
authors.lastname: Rao
authors.forename: Jhillu S
authors.initials: JS
authors.lastname: Yadav
authors.forename: Utpal
authors.initials: U
authors.lastname: Bhadra
mesh_terms: D000107:Acetylation; D017209:Apoptosis / Q000187:drug effects; D001483:Base Sequence; D059447:Cell Cycle Checkpoints / Q000187:drug effects*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002877:Chromosomes, Human / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D023061:Gene Order; D056572:Histone Deacetylase Inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D006657:Histones / Q000378:metabolism; D006801:Humans; D008745:Methylation; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D020218:Response Elements; D050791:STAT Transcription Factors / Q000378:metabolism
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D005419:Flavonoids; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D050791:STAT Transcription Factors; C043561:chrysin