PML-II recruits ataxin-3 to PML-NBs and inhibits its deubiquitinating activity
Introduction
PML-NBs are PML protein-based discrete heterogeneous and dynamic nuclear spherical structures ranging in size from 0.1 to 1.0 μm that have been implicated in a variety of important functions, including apoptosis, transcription and viral defense [[1], [2], [3]]. The PML protein is the essential structural component of PML-NBs. It has at least 6 nuclear isoforms, designated PML-I through PML-VI, that contain the same N-terminal RBCC region but differ in their C-termini [4]. Increasing evidence has suggested that the N-terminus performs a function that is shared by different isoforms and that the variability of the PML C-termini contributes greatly to the functional diversity of PML-NBs [5]. Consistent with this, some isoform-specific functions of PML have been identified. For instance, PML-IV can specifically interact with p53 and regulate oncogene-induced premature senescence [6]. PML-V has been shown to control the mobility of PML-NBs [7].
Apart from PML-I, PML-II is another abundant isoform with a longer C-terminus [4]. It is unique from the other five isoforms in that it can localize to the inner nuclear membrane in some types of cells [8]. Most studies concerning PML-II have shown interactions with adenovirus [9] and herpes simplex virus [10] that appear to suggest an antiviral effect of PML-II. Recent studies have found that PML-II associates with lipid droplet formation [11,12] and accelerates the aging process [13] through its unique C-terminus. Indeed, our previous data have suggested that PML-II can direct PML nuclear bodies to cellular sites to which its C-terminus specifically binds. However, the components of the binding site remain unclear. All of the above results indicate that the unique C-terminal domain of PML-II plays an important role in PML-NB function.
To identify the unknown binding site or other potential proteins that specifically interact with PML-II, we used a yeast two-hybrid assay and identified a novel PML–II–interacting protein, ataxin-3. In this study, we report that the C-terminus of PML-II specifically interacts with ataxin-3 and that PML-II can recruit wild-type or pathological ataxin-3 to PML-NBs. Importantly, the deubiquitinase activity of ataxin-3 was inhibited by PML-II. Our results suggest that PML-II may be a negative regulator of ataxin-3.
Section snippets
Construction of plasmids and transfection
The plasmids pcDNA3-Myc-ataxin-3-13Q and pcDNA3-Myc-ataxin-3-79Q were obtained from Dr. Masaki Matsumoto (Kyushu University, Fukuoka, Japan). The plasmids GFP-SOD-N85R and p3∗Flag-ataxin-3(C14A) were obtained from Dr. Guanghui Wang (Soochow University, Jiangsu, China). For plasmids used for the yeast two-hybrid analysis, Myc-ataxin-3 was cloned into the yeast expression vector PACT2 (Clontech), and the pGBKT7 plasmids expressing PML-CT (1–5) and FLAG-PML-(I-VI) were described previously [7].
The C-terminus of PML-II interacts with ataxin-3
To search for potential binding partners for the PML-II isoform, we performed a yeast two-hybrid screen of a human cDNA library generated from human leukemia cells with the unique C-terminal region of PML-II as bait. One potential PML–II–interacting protein was ataxin-3, which is a member of the polyQ disease-related proteins responsible for spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease [15]. To determine whether the interaction between ataxin-3 and PML was PML-II
Discussion
In polyglutamine diseases, accumulation of misfolded polyQ-expansion proteins induces the formation of neuronal intranuclear inclusions (NIs), which is a hallmark of SCA3 and other polyQ-expansion diseases [16,19]. Promyelocytic leukemia protein (PML), a major component of nuclear bodies, has been shown to be associated with polyQ diseases in both in vivo and in vitro studies. For instance, in transfected cells, pathological ataxin-7 colocalizes with PML [20], and the characteristic
Declaration of competing Interest
The authors declare that they have no conflicts of interest with the research and/or publication of this article.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (31371351), the Natural Science Foundation of Hebei Province (C2020423052) and the Project of Excellent Young Teacher Fundamental Research of Hebei University of Chinese Medicine (YQ2019003).
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PML isoforms: a molecular basis for PML pleiotropic functions
2022, Trends in Biochemical SciencesCitation Excerpt :Specifically, PMLII promotes transcription of major histocompatibility complex (MHC) II genes by protecting the class II transactivator CIITA from proteasomal degradation [63], modulating the activity of IFN-β-responsive genes by increased recruitment of IRF3, NFκB, and STAT1 to gene promoters [64], and regulating apoptosis downstream IFN-α by enhancing ERK and AKT signaling [65]. In addition to its immune regulatory function, PMLII has been more recently involved in aging and neurodegeneration by accelerating progerin-mediated senescence [23] and inhibiting the activity of wild type and poly-Q repeat-containing ataxin-3 [66]. Finally, in specific cell types that include hepatic cells, PMLII localizes to the inner nuclear membrane where it promotes the budding of nuclear lipid droplets involved in lipid synthesis [24,67] (Figure 2C).