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HDAC6-dependent deacetylation of SAE2 enhances SUMO1 conjugation for mitotic integrity.

Mammalian cells express three conjugatable SUMO variants: SUMO1 and the closely related SUMO2 and SUMO3 (together referred to as SUMO2/3). While some substrates are modified by both, others show a clear preference, though the basis for this selectivity remains unclear. Here, we examine a modification of the catalytic component of the human SUMO activation enzyme, SAE2. We find that lysine 164 of SAE2 undergoes HDAC6-dependent deacetylation during mitosis. A non-deacetylatable acetyl-mimetic mutant, SAE2-K164Q, selectively enhances SUMO2 over SUMO1 activation and conjugation, and distinguishes between SUMO1 and SUMO2/3 based on differences in their C-terminal tails. Complementation of SAE2-deficient or inhibited cells with SAE2-K164Q suppresses mitotic SUMO1 conjugation and promotes multipolar spindle formation. We identify NuMA as a SUMO E1-dependent substrate and demonstrate that mitotic defects caused by SAE2-K164Q or HDAC6 inhibition are rescued by SUMO1 overexpression or expression of a GFP-SUMO1-NuMA-K1766R fusion. These results support a model in which SAE1:SAE2 deacetylation during early mitosis promotes SUMO1 conjugation to ensure mitotic fidelity, highlighting a regulatory role for the SUMO-activating enzyme in the selection of SUMO proteins.

Humans

Epigenetic regulation of transgenes.

Gene therapy holds significant potential for treating genetic disorders, but the use of viral vectors is limited by factors such as immunogenicity, payload capacity, and high manufacturing costs. Nonviral gene delivery (NVGD) using plasmid DNA presents an attractive alternative; however, it typically provides a limited magnitude or duration of transgene expression. One potential reason for these shortcomings is the host cell's epigenetic regulation mechanisms, which can silence both viral and nonviral transgenes. Specifically, when foreign DNA enters the nucleus, it is detected by nuclear DNA sensors, such as IFI16, which initiate the assembly of a "restrictosome" or nuclear domain 10 (ND10) body. This multiprotein complex contains several components, such as PML, Speckled Proteins (e.g., SP100), DAXX, and ATRX that act as a scaffold for recruiting various epigenetic modifiers that subsequently deposit repressive histone modifications like H3K9me3 and H3K27me3 on the transgene chromatin. These marks induce DNA methylation and the subsequent condensation of plasmids or episomes into heterochromatin, which represses transgene expression. Alternatively, unmethylated CpG motifs in bacterial plasmid DNA can trigger innate immune responses in the cytosol, but this review will specifically focus on the detailed mechanisms of epigenetic regulation responsible for silencing plasmid DNA within the host cell nucleus. Addressing these nuclear defense mechanisms, potentially through strategies that manipulate DNA methylation or inhibit restrictosome activity, is crucial for advancing the development of safe, effective, and long-lasting plasmid viral and non-viral gene therapies.

Epigenesis, Genetic