title: Connexins and cyclooxygenase-2 crosstalk in the expression of radiation-induced bystander effects.
abstract: BACKGROUND
  Signalling events mediated by connexins and cyclooxygenase-2 (COX-2) have important roles in bystander effects induced by ionising radiation. However, whether these proteins mediate bystander effects independently or cooperatively has not been investigated.
  
  
  METHODS
  Bystander normal human fibroblasts were cocultured with irradiated adenocarcinoma HeLa cells in which specific connexins (Cx) are expressed in the absence of endogenous Cx, before and after COX-2 knockdown, to investigate DNA damage in bystander cells and their progeny.
  
  
  RESULTS
  Inducible expression of gap junctions composed of connexin26 (Cx26) in irradiated HeLa cells enhanced the induction of micronuclei in bystander cells (P<0.01) and reduced the coculture time necessary for manifestation of the effect. In contrast, expression of connexin32 (Cx32) conferred protective effects. COX-2 knockdown in irradiated HeLa Cx26 cells attenuated the bystander response due to connexin expression. However, COX-2 knockdown resulted in enhanced micronucleus formation in the progeny of the bystander cells (P<0.001). COX-2 knockdown delayed junctional communication in HeLa Cx26 cells, and reduced, in the plasma membrane, the physical interaction of Cx26 with MAPKKK, a controller of the MAPK pathway that regulates COX-2 and connexin.
  
  
  CONCLUSIONS
  Junctional communication and COX-2 cooperatively mediate the propagation of radiation-induced non-targeted effects. Characterising the mediating events affected by both mechanisms may lead to new approaches that mitigate secondary debilitating effects of cancer radiotherapy.
authors.affiliation: Department of Radiology, Rutgers University, New Jersey Medical School, Cancer Center, Newark, NJ 07103, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Radiology, Rutgers University, New Jersey Medical School, Cancer Center, Newark, NJ 07103, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: de Toledo
authors.affiliation: Department of Radiology, Rutgers University, New Jersey Medical School, Cancer Center, Newark, NJ 07103, USA.
authors.forename: G
authors.initials: G
authors.lastname: Hu
authors.affiliation: Center for Radiological Research, Department of Radiation Oncology, Columbia University Medical Center, New York, NY 10032, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Hei
authors.affiliation: Department of Radiology, Rutgers University, New Jersey Medical School, Cancer Center, Newark, NJ 07103, USA.
authors.forename: E I
authors.initials: EI
authors.lastname: Azzam
mesh_terms: D024201:Bystander Effect / Q000528:radiation effects*; D018920:Coculture Techniques; D000072259:Connexin 26; D017630:Connexins / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D017629:Gap Junctions / Q000378:metabolism / Q000528:radiation effects; D006367:HeLa Cells; D006801:Humans
chemical_list: D017630:Connexins; C000607042:GJB2 protein, human; D000072259:Connexin 26; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human