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R3750 --> 792.7 --> 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. [ABSTRACT FROM AUTHOR]

Ubiquitin (Ub) regulates diverse functions in eukaryotes through its attachment to other proteins. The defining step in this protein modification pathway is the attack of a substrate lysine residue on Ub bound through its C-terminus to the active site cysteine residue of a Ub-conjugating enzyme (E2) or certain Ub ligases (E3s). So far, these E2 and E3 cysteine residues are the only enzyme groups known to participate in the catalysis of conjugation. Here we show that a strictly conserved E2 asparagine residue is critical for catalysis of E2- and E2/RING E3- dependent isopeptide bond formation, but dispensable for upstream and downstream reactions of Ub thiol ester formation. In constrast, the strictly conserved histidine and proline residues immediately upstream of the asparagine are dispensable for catalysis of isopeptide bond formation. We propose that the conserved asparagine side chain stabilizes the oxyanion intermediate formed during lysine attack. The E2 asparagine is the first non-covalent catalytic group to be proposed in any Ub conjugation factor. [ABSTRACT FROM AUTHOR]

The PML protein, identified first as part of the oncogenic PML­RARα chimera in acute promyelocytic leukemia (APL), concentrates within discrete subnuclear structures, corresponding to some types of nuclear bodies. These structures are disrupted in APL cells, and retinoic acid (RA) can trigger their reorganization, correlating with its therapeutic effect in this type of leukemia. Recently, arsenic trioxide (As2O3) was identified as a potent antileukemic agent which, similarly to RA, induces complete remissions in APL patients. Here we show that, in APL cells, As2O3 triggers rapid degradation of PML—RARα and provokes the restoration of intact nuclear bodies. In non-APL cells, the ubiquitin-like protein SUMO-1 is covalently attached to a subset of wild-type PML in a reversible and phosphorylation-dependent manner. The unmodified form of PML is found in the soluble nucleoplasmic fraction, whereas the SUMO-1-polymodified forms of PML are compartmentalized exclusively in the PML nuclear bodies. As2O3 administration strikingly increases the pool of SUMO-1—PML conjugates that, subsequently, accumulate in enlarged nuclear bodies. In contrast to PML—RARα, the overall amount of PML seems to remain unaltered up to 36 h following As2O3 treatment. These findings indicate that the conjugation of PML with SUMO-1 modulates its intracellular localization and suggest that post-translational modification by SUMO-1 may be more generally involved than previously suspected in the targeting of proteins to distinct subcellular structures. They provide additional evidence that the role of ‘ubiquitin-like’ post-translational modification is not limited to a degradation signal. [ABSTRACT FROM AUTHOR]

The article offers information on PTEN protein regarding tumor suppression. It mentions that PTEN protein is a lipid phosphatase that dephosphorylates phosphatidylinositol-3,4,5-triphosphate (PIP3). According to a study, PTEN is modified by the small ubiquitin-related modifier (SUMO). It includes that sumoylation facilitates cooperative binding of PTEN to the plasma membrane.