AbstractThe dynamic nature of mitochondrial fusion and fission allows rapid adaptability to changing metabolic demands and stress to restore homeostasis. The principal fission protein is the cytosolic GTPase dynamin related protein-1 (DRP1), which binds to the outer membrane receptors mitochondrial fission protein 1 (Fis1), mitochondrial dynamics proteins (MiD49/51) and mitochondrial fission factor (MFF). MFF is the predominant pro-fission receptor, whereas MiD proteins sequester inactive DRP1 and form a trimeric complex of DRP1-MiD-MFF.
The fusion and fission machinery are subject to multiple forms of post-translational modifications (PTM) to regulate mitochondrial function. AMPK phosphorylation of MFF at S155/S172 promotes fission under energetic stress, and parkin-mediated ubiquitination promotes mitophagy. The small ubiquitin-like modifier (SUMO) isoform SUMO-1 promotes DRP1 recruitment, whereas SUMO-2/3-DRP1 represses fission during oxygen/glucose deprivation (OGD).
I present a novel finding that MFF is SUMOylated at K151, which is enhanced by phosphorylation at S155. A SUMO-deficient MFF mutant (K151R) has reduced ubiquitination, which occurs at a separate site to K151, suggesting SUMOylation promotes ubiquitination. The K151R mutant has reduced binding to DRP1, but surprisingly, the MFF phospho-null and phospho-mimetic mutants also have reduced binding. SUMOylation of MFF reduces the association of MFF with MiD proteins, and I present a model whereby the degree of SUMOylation mediates the ratio of MiD in the DRP1-MiD-MFF complex. Intriguingly, expression of the K151R mutant in primary neurons enhances dendritic mitochondrial size and reduces density, with no effect on axonal mitochondria, suggesting differential compartment-specific regulation and/or roles of MFF SUMOylation. My data indicate that MFF SUMOylation is enhanced following OGD and is required for DRP1 binding following mitochondrial depolarisation. Taken together, these results demonstrate that there is substantial crosstalk between the PTMs of MFF, and MFF SUMOylation is required to regulate the fine-tuning of mitochondrial dynamics under basal conditions and is also involved in the stress response.
|Date of Award||23 Jan 2020|
|Supervisor||Jeremy M Henley (Supervisor)|