title: Non-apoptotic function of caspases in a cellular model of hydrogen peroxide-associated colitis.
abstract: Oxidative stress, caused by reactive oxygen species (ROS), is a major contributor to inflammatory bowel disease (IBD)-associated neoplasia. We mimicked ROS exposure of the epithelium in IBD using non-tumour human colonic epithelial cells (HCEC) and hydrogen peroxide (H2 O2 ). A population of HCEC survived H2 O2 -induced oxidative stress via JNK-dependent cell cycle arrests. Caspases, p21(WAF1) and γ-H2AX were identified as JNK-regulated proteins. Up-regulation of caspases was linked to cell survival and not, as expected, to apoptosis. Inhibition using the pan-caspase inhibitor Z-VAD-FMK caused up-regulation of γ-H2AX, a DNA-damage sensor, indicating its negative regulation via caspases. Cell cycle analysis revealed an accumulation of HCEC in the G1 -phase as first response to oxidative stress and increased S-phase population and then apoptosis as second response following caspase inhibition. Thus, caspases execute a non-apoptotic function by promoting cells through G1 - and S-phase by overriding the G1 /S- and intra-S checkpoints despite DNA-damage. This led to the accumulation of cells in the G2 /M-phase and decreased apoptosis. Caspases mediate survival of oxidatively damaged HCEC via γ-H2AX suppression, although its direct proteolytic inactivation was excluded. Conversely, we found that oxidative stress led to caspase-dependent proteolytic degradation of the DNA-damage checkpoint protein ATM that is upstream of γ-H2AX. As a consequence, undetected DNA-damage and increased proliferation were found in repeatedly H2 O2 -exposed HCEC. Such features have been associated with neoplastic transformation and appear here to be mediated by a non-apoptotic function of caspases. Overexpression of upstream p-JNK in active ulcerative colitis also suggests a potential importance of this pathway in vivo.
authors.affiliation: Department of Pathology, Otto-von-Guericke University, Magdeburg, Germany. angela.poehlmann@med.ovgu.de
authors.forename: Angela
authors.initials: A
authors.lastname: Poehlmann
authors.forename: Kathrin
authors.initials: K
authors.lastname: Reissig
authors.forename: Andrea
authors.initials: A
authors.lastname: Just
authors.forename: Diana
authors.initials: D
authors.lastname: Walluscheck
authors.forename: Roland
authors.initials: R
authors.lastname: Hartig
authors.forename: Antje
authors.initials: A
authors.lastname: Schinlauer
authors.forename: Wiebke
authors.initials: W
authors.lastname: Lessel
authors.forename: Thomas
authors.initials: T
authors.lastname: Guenther
authors.forename: Andrew
authors.initials: A
authors.lastname: Silver
authors.forename: Pablo
authors.initials: P
authors.lastname: Steinberg
authors.forename: Albert
authors.initials: A
authors.lastname: Roessner
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D003092:Colitis / Q000139:chemically induced* / Q000378:metabolism; D003106:Colon / Q000201:enzymology; D020552:Comet Assay; D004249:DNA Damage; D004847:Epithelial Cells / Q000166:cytology; D006657:Histones / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007150:Immunohistochemistry; D007249:Inflammation; D015212:Inflammatory Bowel Diseases / Q000201:enzymology*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; C468783:H2AX protein, human; D006657:Histones; D017382:Reactive Oxygen Species; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D006861:Hydrogen Peroxide; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D048670:MAP Kinase Kinase 4; D020169:Caspases
keywords: ATM degradation; DNA-damage checkpoints; JNK-dependent cell cycle arrests; hydrogen peroxide-associated colitis; inflammation; neoplastic transformation; non-apoptotic caspase function; γ-H2AX