title: An inhibitory mono-ubiquitylation of the Drosophila initiator caspase Dronc functions in both apoptotic and non-apoptotic pathways.
abstract: Apoptosis is an evolutionary conserved cell death mechanism, which requires activation of initiator and effector caspases. The Drosophila initiator caspase Dronc, the ortholog of mammalian Caspase-2 and Caspase-9, has an N-terminal CARD domain that recruits Dronc into the apoptosome for activation. In addition to its role in apoptosis, Dronc also has non-apoptotic functions such as compensatory proliferation. One mechanism to control the activation of Dronc is ubiquitylation. However, the mechanistic details of ubiquitylation of Dronc are less clear. For example, monomeric inactive Dronc is subject to non-degradative ubiquitylation in living cells, while ubiquitylation of active apoptosome-bound Dronc triggers its proteolytic degradation in apoptotic cells. Here, we examined the role of non-degradative ubiquitylation of Dronc in living cells in vivo, i.e. in the context of a multi-cellular organism. Our in vivo data suggest that in living cells Dronc is mono-ubiquitylated on Lys78 (K78) in its CARD domain. This ubiquitylation prevents activation of Dronc in the apoptosome and protects cells from apoptosis. Furthermore, K78 ubiquitylation plays an inhibitory role for non-apoptotic functions of Dronc. We provide evidence that not all of the non-apoptotic functions of Dronc require its catalytic activity. In conclusion, we demonstrate a mechanism whereby Dronc's apoptotic and non-apoptotic activities can be kept silenced in a non-degradative manner through a single ubiquitylation event in living cells.
authors.affiliation: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
authors.forename: Hatem Elif
authors.identifier: 0000-0002-2366-9837
authors.initials: HE
authors.lastname: Kamber Kaya
authors.affiliation: Institute for Genetics and Molecular Medicine, Edinburgh Cancer Research Centre, The University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Mark
authors.initials: M
authors.lastname: Ditzel
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, Institute of Cancer Research, Mary-Jean Mitchell Green Building, Chester Beatty Laboratories, London, United Kingdom.
authors.forename: Pascal
authors.initials: P
authors.lastname: Meier
authors.affiliation: Department of Molecular, Cell and Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
authors.forename: Andreas
authors.identifier: 0000-0002-9134-871X
authors.initials: A
authors.lastname: Bergmann
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D053143:Caspase 2 / Q000235:genetics; D053453:Caspase 9 / Q000235:genetics; D020169:Caspases / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics; D011485:Protein Binding; D000072417:Protein Domains / Q000235:genetics; D059748:Proteolysis; D054875:Ubiquitination / Q000235:genetics*
chemical_list: D029721:Drosophila Proteins; D053143:Caspase 2; D053453:Caspase 9; D020169:Caspases; C118731:dronc protein, Drosophila