A Tale of Usurpation and Subversion: SUMO-Dependent Integrity of Promyelocytic Leukemia Nuclear Bodies at the Crossroad of Infection and Immunity

Abstract

Promyelocytic leukemia nuclear bodies (PML NBs) are multi-protein assemblies representing distinct sub-nuclear structures. As phase-separated molecular condensates, PML NBs exhibit liquid droplet-like consistency. A key organizer of the assembly and dynamics of PML NBs is the ubiquitin-like SUMO modification system. SUMO is covalently attached to PML and other core components of PML NBs thereby exhibiting a glue-like function by providing multivalent interactions with proteins containing SUMO interacting motifs (SIMs). PML NBs serve as the catalytic center for nuclear SUMOylation and SUMO-SIM interactions are essential for protein assembly within these structures. Importantly, however, formation of SUMO chains on PML and other PML NB-associated proteins triggers ubiquitylation and proteasomal degradation which coincide with disruption of these nuclear condensates. To date, a plethora of nuclear activities such as transcriptional and post-transcriptional regulation of gene expression, apoptosis, senescence, cell cycle control, DNA damage response, and DNA replication have been associated with PML NBs. Not surprisingly, therefore, SUMO-dependent PML NB integrity has been implicated in regulating many physiological processes including tumor suppression, metabolism, drug-resistance, development, cellular stemness, and anti-pathogen immune response. The interplay between PML NBs and viral infection is multifaceted. As a part of the cellular antiviral defense strategy, PML NB components are crucial restriction factors for many viruses and a mutual positive correlation has been found to exist between PML NBs and the interferon response. Viruses, in turn, have developed counterstrategies for disarming PML NB associated immune defense measures. On the other end of the spectrum, certain viruses are known to usurp specific PML NB components for successful replication and disruption of these sub-nuclear foci has recently been linked to the stimulation rather than curtailment of antiviral gene repertoire. Importantly, the ability of invading virions to manipulate the host SUMO modification machinery is essential for this interplay between PML NB integrity and viruses. Moreover, compelling evidence is emerging in favor of bacterial pathogens to negotiate with the SUMO system thereby modulating PML NB-directed intrinsic and innate immunity. In the current context, we will present an updated account of the dynamic intricacies between cellular PML NBs as the nuclear SUMO modification hotspots and immune regulatory mechanisms in response to viral and bacterial pathogens.

The interactions between PML nuclear bodies and small and medium size DNA viruses

“…SUMO conjugation involves SUMO activating enzyme E1, SUMO conjugating enzyme UBC9 (ubiquitin-conjugating enzyme 9), and SUMO E3 ligase, summarized in [ 63 ]. The N-terminal RING finger domain of PML is essential for its interaction with the UBC9 protein [ 64 ].…”

The PML hub: An emerging actor of leukemia therapies

“…1 ). PML plays a significant role in antiviral responses ( Geoffroy and Chelbi-Alix, 2011 ; Patra and Müller, 2021 ) through both a direct interference with replication of multiple viruses, but also by enhancing global IFN response through enhancement of STAT1 signaling ( Scherer and Stamminger, 2016 ). Interestingly, several PML NB client proteins are also IFN-inducible and modulate antiviral responses, including Sp100, Daxx, or SUMO ( Grötzinger et al, 1996 ; Sahin et al, 2014a ).…”

SUMOylated Golgin45 associates with PML-NB to transcriptionally regulate lipid metabolism genes during heat shock stress

“…One of the well characterized roles for protein SUMOylation is regulation of promyelocytic leukemia nuclear bodies (PML-NBs) formation, which undergoes dynamic regulation by protein SUMOylation 10 – 12 . PML-NBs are involved in various genome maintenance pathway and cellular stress response, including the DNA damage response, innate immunity during viral infection, DNA repair, telomere homeostasis, cellular senescence and p53-associated apoptosis 13 – 16 .…”