title: Soluble histone H2AX is induced by DNA replication stress and sensitizes cells to undergo apoptosis.
abstract: BACKGROUND
  Chromatin-associated histone H2AX is a key regulator of the cellular responses to DNA damage. However, non-nucleosomal functions of histone H2AX are poorly characterized. We have recently shown that soluble H2AX can trigger apoptosis but the mechanisms leading to non-chromatin-associated H2AX are unclear. Here, we tested whether stalling of DNA replication, a common event in cancer cells and the underlying mechanism of various chemotherapeutic agents, can trigger increased soluble H2AX.
  
  
  RESULTS
  Transient overexpression of H2AX was found to lead to a detectable fraction of soluble H2AX and was associated with increased apoptosis. This effect was enhanced by the induction of DNA replication stress using the DNA polymerase alpha inhibitor aphidicolin. Cells manipulated to stably express H2AX did not contain soluble H2AX, however, short-term treatment with aphidicolin (1 h) resulted in detectable amounts of H2AX in the soluble nuclear fraction and enhanced apoptosis. Similarly, soluble endogenous H2AX was detected under these conditions. We found that excessive soluble H2AX causes chromatin aggregation and inhibition of ongoing gene transcription as evidenced by the redistribution and/or loss of active RNA polymerase II as well as the transcriptional co-activators CBP and p300.
  
  
  CONCLUSIONS
  Taken together, these results show that DNA replication stress rapidly leads to increased soluble H2AX and that non-chromatin-associated H2AX can sensitize cells to undergo apoptosis. Our findings encourage further studies to explore H2AX and the cellular pathways that control its expression as anti-cancer drug targets.
authors.affiliation: Molecular Virology Program, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA. yliu52003@yahoo.com
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Parry
authors.forename: Anna
authors.initials: A
authors.lastname: Chin
authors.forename: Stefan
authors.initials: S
authors.lastname: Duensing
authors.forename: Anette
authors.initials: A
authors.lastname: Duensing
mesh_terms: D017209:Apoptosis; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D012995:Solubility; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D002843:Chromatin; D006657:Histones