title: Gadd45 proteins induce G2/M arrest and modulate apoptosis in kidney cells exposed to hyperosmotic stress.
abstract: Gadd45 proteins are induced by hyperosmolality in renal inner medullary (IM) cells, but their role for cell adaptation to osmotic stress is not known. We show that a cell line derived from murine renal IM cells responds to moderate hyperosmotic stress (540 mosmol/kg) by activation of G(2)/M arrest without significant apoptosis. If the severity of hyperosmotic stress exceeds the tolerance limit of this cell line (620 mosmol/kg) apoptosis is strongly induced. Using transient overexpression of ectopic Gadd45 proteins and simultaneous analysis of transfected versus non-transfected cells by laser-scanning cytometry, we were able to measure the effects of Gadd45 super-induction during hyperosmolality on G(2)/M arrest and apoptosis. Our results demonstrate that induction of all three Gadd45 isoforms inhibits mitosis and promotes G(2)/M arrest during moderate hyperosmotic stress but not in isosmotic controls. Furthermore, all three Gadd45 proteins are also involved in control of apoptosis during severe hyperosmotic stress. Under these conditions Gadd45gamma induction strongly potentiates apoptosis. In contrast, Gadd45alpha/beta induction transiently increases caspase 3/7 and annexin V binding before 12 h but inhibits later stages of apoptosis during severe hyperosmolality. These results show that Gadd45 isoforms function in common but also in distinct pathways during hyperosmolality and that their increased abundance contributes to the low mitotic index and protection of genomic integrity in cells of the mammalian renal inner medulla.
authors.affiliation: Physiological Genomics Group, Department of Animal Sciences, University of California, Davis, California 95616, USA.
authors.forename: Sally K
authors.initials: SK
authors.lastname: Mak
authors.forename: Dietmar
authors.initials: D
authors.lastname: Kültz
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D000939:Epitopes; D016195:G2 Phase; D006657:Histones / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D007668:Kidney / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism; D007834:Lasers; D051379:Mice; D008938:Mitosis; D009687:Nuclear Proteins / Q000378:metabolism*; D009995:Osmosis; D020033:Protein Isoforms; D012313:RNA / Q000378:metabolism; D013312:Stress, Physiological; D013997:Time Factors; D014162:Transfection; D014867:Water / Q000737:chemistry; D000097642:GADD45 Proteins
chemical_list: D017304:Annexin A5; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D018797:Cell Cycle Proteins; D004247:DNA; D000939:Epitopes; D006657:Histones; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012313:RNA; D014867:Water; C439070:GADD45A protein, human; D000097642:GADD45 Proteins; C499072:Gadd45a protein, mouse; C505407:CASP3 protein, human; C505520:CASP7 protein, human; C505409:Casp3 protein, mouse; C505524:Casp7 protein, mouse