ABSTRACT
Homeostatic maintenance of cellular mitochondria requires a dynamic balance between fission and fusion, and controlled changes in morphology are important for processes such as apoptosis and cellular division. Interphase mitochondria have been described as an interconnected network that fragments as cells enter mitosis, and this mitotic mitochondrial fragmentation is known to be regulated by the dynamin-related GTPase Drp1 (dynamin-related protein 1), a key component of the mitochondrial division machinery. Loss of Drp1 function and the subsequent failure of mitochondrial division during mitosis lead to incomplete cytokinesis and the unequal distribution of mitochondria into daughter cells. During mitotic exit and interphase, the mitochondrial network reforms. Here we demonstrate that changes in mitochondrial dynamics as cells exit mitosis are driven in part through ubiquitylation of Drp1, catalyzed by the APC/C(Cdh1) (anaphase-promoting complex/cyclosome and its coactivator Cdh1) E3 ubiquitin ligase complex. Importantly, inhibition of Cdh1-mediated Drp1 ubiquitylation and proteasomal degradation during interphase prevents the normal G1 phase regrowth of mitochondrial networks following cell division.
Subject(s)
Cadherins/metabolism , Cytokinesis , Mitochondria/enzymology , Mitochondrial Proteins/metabolism , Mitosis , Ubiquitin-Protein Ligase Complexes/metabolism , Anaphase-Promoting Complex-Cyclosome , Antigens, CD , Cadherins/antagonists & inhibitors , Cadherins/genetics , Dynamins , Enzyme Stability , G1 Phase/genetics , GTP Phosphohydrolases/deficiency , GTP Phosphohydrolases/genetics , Gene Expression , Gene Silencing , HEK293 Cells , HeLa Cells , Humans , Interphase/genetics , Microtubule-Associated Proteins/deficiency , Microtubule-Associated Proteins/genetics , Mitochondria/genetics , Mitochondrial Proteins/deficiency , Mitochondrial Proteins/genetics , Proteasome Endopeptidase Complex/metabolism , RNA, Small Interfering/metabolism , Transfection , Ubiquitin-Protein Ligase Complexes/antagonists & inhibitors , Ubiquitin-Protein Ligase Complexes/genetics , Ubiquitin-Protein Ligases/antagonists & inhibitors , Ubiquitin-Protein Ligases/genetics , Ubiquitin-Protein Ligases/metabolism , UbiquitinationABSTRACT
Xenopus oocyte death is partly controlled by the apoptotic initiator caspase-2 (C2). We reported previously that oocyte nutrient depletion activates C2 upstream of mitochondrial cytochrome c release. Conversely, nutrient-replete oocytes inhibit C2 via S135 phosphorylation catalyzed by calcium/calmodulin-dependent protein kinase II. We now show that C2 phosphorylated at S135 binds 14-3-3zeta, thus preventing C2 dephosphorylation. Moreover, we determined that S135 dephosphorylation is catalyzed by protein phosphatase-1 (PP1), which directly binds C2. Although C2 dephosphorylation is responsive to metabolism, neither PP1 activity nor binding is metabolically regulated. Rather, release of 14-3-3zeta from C2 is controlled by metabolism and allows for C2 dephosphorylation. Accordingly, a C2 mutant unable to bind 14-3-3zeta is highly susceptible to dephosphorylation. Although this mechanism was initially established in Xenopus, we now demonstrate similar control of murine C2 by phosphorylation and 14-3-3 binding in mouse eggs. These findings provide an unexpected evolutionary link between 14-3-3 and metabolism in oocyte death.
