title: Connexin-43 downregulation in G2/M phase enriched tumour cells causes extensive low-dose hyper-radiosensitivity (HRS) associated with mitochondrial apoptotic events.
abstract: Enrichment of tumour cells in G2/M phases in vitro is known to be associated with low-dose hyper-radiosensitivity (HRS). These cell cycle phases also involve reduced expression of adhesion protein connexin-43 (Cx43). Therefore, we investigated the role of Cx43 in HRS. Asynchronous or G2/M enriched tumour cells (U87, BMG-1, HeLa) and normal primary fibroblasts (HDFn) were γ-irradiated at varying doses, with an asynchronous group separately subjected to Cx43-knockdown prior to irradiation. Cx43 level, gap junctional activity, clonogenic cell survival, cell growth/viability, mitochondrial alterations and other apoptosis-regulating events were studied. G2/M enrichment reduced Cx43 level by ~50% and caused considerable HRS at doses 10 cGy-30 cGy in all tumour cell lines. Cx43-knockdown to the same level (~60%) also elicited prominent HRS response in these cells. Quite important, radiosensitivity of primary HDFn cells remained unaltered by all these treatments. In Cx43-knockdown tumour cells, low-dose irradiation caused significant growth inhibition and apoptosis involving loss of MMP, cytochrome-c release and caspase-3 activation, thereby demonstrating the important cytoprotective role of Cx43. Therefore, this study significantly shows that Cx43 downregulation (a constitutive feature of G2/M phase) selectively renders tumour cells hypersensitive to low-dose radiation, and presents connexins as potential therapeutic targets.
authors.affiliation: Natural Radiation Response Mechanisms Group, Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig. Mazumdar Road, Delhi 110054, India.
authors.forename: Soma
authors.initials: S
authors.lastname: Ghosh
authors.affiliation: Natural Radiation Response Mechanisms Group, Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig. Mazumdar Road, Delhi 110054, India.
authors.forename: Ashish
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Natural Radiation Response Mechanisms Group, Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig. Mazumdar Road, Delhi 110054, India. Electronic address: sudhirchandna@yahoo.com.
authors.forename: Sudhir
authors.initials: S
authors.lastname: Chandna
mesh_terms: D017209:Apoptosis / Q000528:radiation effects*; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation / Q000528:radiation effects; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D015536:Down-Regulation; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D059565:G2 Phase Cell Cycle Checkpoints / Q000528:radiation effects*; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D021381:Protein Transport; D034622:RNA Interference; D013997:Time Factors; D014162:Transfection; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: C494826:BAX protein, human; D018031:Connexin 43; C500216:GJA1 protein, human; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; C505407:CASP3 protein, human; D053148:Caspase 3
keywords: Connexin-43; Differential radiation response; G2/M enrichment; Low-dose hyper-radiosensitivity; Radiation-induced apoptosis