ABSTRACT
The first step of herpesviruses virion assembly occurs in the nucleus. However, the exact site where nucleocapsids are assembled, where the genome and the inner tegument are acquired, remains controversial. We created a recombinant VZV expressing ORF23 (homologous to HSV-1 VP26) fused to the eGFP and dually fluorescent viruses with a tegument protein additionally fused to a red tag (ORF9, ORF21 and ORF22 corresponding to HSV-1 UL49, UL37 and UL36). We identified nuclear dense structures containing the major capsid protein, the scaffold protein and maturing protease, as well as ORF21 and ORF22. Correlative microscopy demonstrated that the structures correspond to capsid aggregates and time-lapse video imaging showed that they appear prior to the accumulation of cytoplasmic capsids, presumably undergoing the secondary egress, and are highly dynamic. Our observations suggest that these structures might represent a nuclear area important for capsid assembly and/or maturation before the budding at the inner nuclear membrane.
Subject(s)
Capsid/metabolism , Cell Nucleus/virology , Herpesvirus 3, Human/physiology , Macromolecular Substances/metabolism , Virus Assembly , Artificial Gene Fusion , Cell Line , Genes, Reporter , Humans , Luminescent Proteins/analysis , Luminescent Proteins/genetics , Microscopy, Fluorescence , Microscopy, Video , Recombinant Fusion Proteins/analysis , Recombinant Fusion Proteins/genetics , Viral Proteins/genetics , Viral Proteins/metabolismABSTRACT
SHIP-1 is an inositol phosphatase predominantly expressed in hematopoietic cells. Over the ten past years, SHIP-1 has been described as an important regulator of immune functions. Here, we characterize a new inhibitory function for SHIP-1 in NOD2 signaling. NOD2 is a crucial cytoplasmic bacterial sensor that activates proinflammatory and antimicrobial responses upon bacterial invasion. We observed that SHIP-1 decreases NOD2-induced NF-κB activation in macrophages. This negative regulation relies on its interaction with XIAP. Indeed, we observed that XIAP is an essential mediator of the NOD2 signaling pathway that enables proper NF-κB activation in macrophages. Upon NOD2 activation, SHIP-1 C-terminal proline rich domain (PRD) interacts with XIAP, thereby disturbing the interaction between XIAP and RIP2 in order to decrease NF-κB signaling.
Subject(s)
NF-kappa B/metabolism , Nod2 Signaling Adaptor Protein/metabolism , Phosphoric Monoester Hydrolases/metabolism , Receptor-Interacting Protein Serine-Threonine Kinase 2/metabolism , X-Linked Inhibitor of Apoptosis Protein/metabolism , Cell Line, Tumor , Down-Regulation , Epithelial Cells/cytology , Gene Expression Regulation , Humans , Immune System , Inflammation , Inositol Polyphosphate 5-Phosphatases , Macrophages/cytology , Macrophages/metabolism , Models, Biological , Monocytes/cytology , Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases , Protein Structure, Tertiary , Signal TransductionABSTRACT
PI3K cascade is a central signaling pathway regulating cell proliferation, growth, differentiation, and survival. Tight regulation of the PI3K signaling pathway is necessary to avoid aberrant cell proliferation and cancer development. Together with SHIP-1, the inositol phosphatases PTEN and SHIP-2 are the gatekeepers of this pathway. In this review, we will focus on SHIP-1 functions. Negative regulation of immune cell activation by SHIP-1 is well characterized. Besides its catalytic activity, SHIP-1 also displays non-enzymatic activity playing role in several immune pathways. Indeed, SHIP-1 exhibits several domains that mediate protein-protein interaction. This review emphasizes the negative regulation of immune cell activation by SHIP-1 that is mediated by its protein-protein interaction.
