Mitochondria are essential for a variety of cellular functions, including ATP production, lipid biosynthesis and calcium homeostasis. Moreover, a number of major cell signaling pathways, including apoptosis, require mitochondria. Consistent with a major role of mitochondria in the control of cell function, mitochondrial defects result in a variety of malignant pathologies. Thus, the molecular components that control mitochondrial homeostasis are likely to be major determinants of cell fate and the well being of the whole organism. However, despite their importance, the mechanisms of mitochondrial quality control, as well as the signaling mechanisms between mitochondria and other cell compartments, are largely unknown. We have identified MARCH5 and IBRDC2, two novel mitochondrial E3 ubiquitin ligases, and have determined that these two proteins are essential for the regulation of mitochondrial function in apoptosis and mitochondrial division, respectively. These results implicate a family of novel mitochondrial membrane-associated RING finger E3 ubiquitin ligases in the regulation of mitochondrial homeostasis through ubiquitin-dependent mechanisms. The present proposal seeks to elucidate the functions of IBRDC2 and MARCH5, and their roles in mitochondrial protein regulation and in membrane dynamics, both in healthy cells and during apoptosis. Biochemical and cellular studies, imaging investigations using time-lapse methods, new fluorescent tools developed by the PI (including photoactivable fluorescent proteins), and a variety of molecular genetic methodologies will be utilized to address the following three questions: 1) What are the biochemical properties of IBRDC2 and MARCH5? The sub-mitochondrial localization, membrane topology and substrate specificity of IBRDC2 and MARCH5 will be determined. 2) How do IBRDC2 and MARCH5 work in the mitochondria of living cells? Studies exploiting gain- and loss-of-function approaches will test the roles of IBRDC2 and MARCH5 in proteasome-dependent mitochondrial protein degradation, as well as in the regulation of membrane dynamics and apoptosis-related mitochondrial protein complexes. These studies will also identify mitochondrial proteins that are under regulatory control of IBRDC2 and MARCH5. 3) What is the influence of IBRDC2 and MARCH5 on specific molecular events in the apoptotic cascade? These studies will determine to what degree IBRDC2 and MARCH5 activities are required for progression of distinct steps of apoptosis. Addressing these questions will improve our general understanding of mitochondrial function and, in the long term, are likely to contribute to the development of novel pharmacological approaches to treat diseases stemming from mitochondrial dysfunction. The proposed studies are part of our long- term effort to understand the normal functions of mitochondria and how mitochondrial defects contribute to disease. Public Health Relevance: We have identified MARCH5 and IBRDC2, two novel mitochondrial E3 ubiquitin ligases, and have determined that these two proteins are essential for the regulation of mitochondrial function in apoptosis and mitochondrial division, respectively. These results implicate a family of novel mitochondrial membrane-associated RING finger E3 ubiquitin ligases in the regulation of mitochondrial homeostasis through ubiquitin-dependent mechanisms. The present proposal seeks to elucidate the functions of IBRDC2 and MARCH5, and their roles in mitochondrial protein regulation and in membrane dynamics, both in healthy cells and during apoptosis. The results of these studies, should improve our general understanding of mitochondrial function and, in the long term, are likely to contribute to the development of novel pharmacological approaches to treat diseases stemming from mitochondrial dysfunction.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM083131-04
Application #
7922531
Study Section
Membrane Biology and Protein Processing (MBPP)
Program Officer
Gindhart, Joseph G
Project Start
2008-09-01
Project End
2013-08-31
Budget Start
2010-09-01
Budget End
2011-08-31
Support Year
4
Fiscal Year
2010
Total Cost
$267,300
Indirect Cost
Name
University of Maryland Baltimore
Department
Biochemistry
Type
Schools of Medicine
DUNS #
188435911
City
Baltimore
State
MD
Country
United States
Zip Code
21201
Cherok, Edward; Xu, Shan; Li, Sunan et al. (2017) Novel regulatory roles of Mff and Drp1 in E3 ubiquitin ligase MARCH5-dependent degradation of MiD49 and Mcl1 and control of mitochondrial dynamics. Mol Biol Cell 28:396-410
Xu, Shan; Cherok, Edward; Das, Shweta et al. (2016) Mitochondrial E3 ubiquitin ligase MARCH5 controls mitochondrial fission and cell sensitivity to stress-induced apoptosis through regulation of MiD49 protein. Mol Biol Cell 27:349-59
Li, Sunan; Xu, Shan; Roelofs, Brian A et al. (2015) Transient assembly of F-actin on the outer mitochondrial membrane contributes to mitochondrial fission. J Cell Biol 208:109-23
Karbowski, Mariusz; Cleland, Megan M; Roelofs, Brian A (2014) Photoactivatable green fluorescent protein-based visualization and quantification of mitochondrial fusion and mitochondrial network complexity in living cells. Methods Enzymol 547:57-73
Chen, Zhiliang; Zhong, Yongwang; Wang, Yang et al. (2013) Ubiquitination-induced fluorescence complementation (UiFC) for detection of K48 ubiquitin chains in vitro and in live cells. PLoS One 8:e73482
Neutzner, Albert; Li, Sunan; Xu, Shan et al. (2012) The ubiquitin/proteasome system-dependent control of mitochondrial steps in apoptosis. Semin Cell Dev Biol 23:499-508
Karbowski, Mariusz; Neutzner, Albert (2012) Neurodegeneration as a consequence of failed mitochondrial maintenance. Acta Neuropathol 123:157-71
Neutzner, Albert; Neutzner, Melanie; Benischke, Anne-Sophie et al. (2011) A systematic search for endoplasmic reticulum (ER) membrane-associated RING finger proteins identifies Nixin/ZNRF4 as a regulator of calnexin stability and ER homeostasis. J Biol Chem 286:8633-43
Xu, Shan; Peng, Guihong; Wang, Yang et al. (2011) The AAA-ATPase p97 is essential for outer mitochondrial membrane protein turnover. Mol Biol Cell 22:291-300
Cleland, M M; Norris, K L; Karbowski, M et al. (2011) Bcl-2 family interaction with the mitochondrial morphogenesis machinery. Cell Death Differ 18:235-47

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