SUMO 2 the rescue: how SUMO2 regulates the mitochondria via Drp1 modification

Mitochondria are dynamic powerhouses of cells and their fission and fusion must be tightly regulated for normal cell function. Mitochondrial fission is mediated by the GTPase, Drp1, and mis-regulation of Drp1 leads to mitochondrial hyper-fragmentation, a known marker of disease. It has been reported that Drp1 is modified by SUMO1 and SUMO2/3, however, the mechanisms of Drp1 regulation by individual SUMO paralogs remain to be fully understood. Here, we have used CRISPR/Cas9 derived SUMO1 and SUMO2 knockout (KO) cell lines, to perform a systematic investigation of paralog-specific effects on mitochondrial maintenance and function. In contrast to expectations, we observed multiple mitochondrial defects specifically in SUMO2 KO, but not SUMO1 KO, cells. SUMO2 KO cells had reduced mitochondrial activity based on results of MTT assays. By immunofluorescence microscopy, we also observed an increase in mitochondrial fragmentation in SUMO2 KO cells. Paradoxically, increased fragmentation occurred despite reduced levels of Drp1 protein expression and sequestration of Drp1 in large cytosolic foci. Taken together, our findings indicate that SUMO2 plays a non-redundant, paralog-specific role in regulating mitochondrial function, in part through effects on Drp1. We anticipate that a more detailed understanding of the molecular effects of SUMO2 on Drp1 may lead to novel therapeutic approaches to treat or prevent ischemic injury, neurodegeneration, and other mitochondrial-related maladies.