An actin remodeling role for Arabidopsis processing bodies revealed by their proximity interactome.

Cellular condensates can comprise membrane-less ribonucleoprotein assemblies with liquid-like properties. These cellular condensates influence various biological outcomes, but their liquidity hampers their isolation and characterization. Here, we investigated the composition of the condensates known as processing bodies (PBs) in the model plant Arabidopsis thaliana through a proximity-biotinylation proteomics approach. Using in situ protein-protein interaction approaches, genetics and high-resolution dynamic imaging, we show that processing bodies comprise networks that interface with membranes. Surprisingly, the conserved component of PBs, DECAPPING PROTEIN 1 (DCP1), can localize to unique plasma membrane subdomains including cell edges and vertices. We characterized these plasma membrane interfaces and discovered a developmental module that can control cell shape. This module is regulated by DCP1, independently from its role in decapping, and the actin-nucleating SCAR-WAVE complex, whereby the DCP1-SCAR-WAVE interaction confines and enhances actin nucleation. This study reveals an unexpected function for a conserved condensate at unique membrane interfaces.

IFN-Stimulated Gene 15 Is an Alarmin that Boosts the CTL Response via an Innate, NK Cell-Dependent Route.

Type I IFN is produced upon infection and tissue damage and induces the expression of many IFN-stimulated genes (ISGs) that encode host-protective proteins. ISG15 is a ubiquitin-like molecule that can be conjugated to proteins but is also released from cells in a free form. Free, extracellular ISG15 is suggested to have an immune-regulatory role, based on disease phenotypes of ISG15-deficient humans and mice. However, the underlying mechanisms by which free ISG15 would act as a "cytokine" are unclear and much debated. We, in this study, demonstrate in a clinically relevant mouse model of therapeutic vaccination that free ISG15 is an alarmin that induces tissue alert, characterized by extracellular matrix remodeling, myeloid cell infiltration, and inflammation. Moreover, free ISG15 is a potent adjuvant for the CTL response. ISG15 produced at the vaccination site promoted the vaccine-specific CTL response by enhancing expansion, short-lived effector and effector/memory differentiation of CD8+ T cells. The function of free ISG15 as an extracellular ligand was demonstrated, because the equivalents in murine ISG15 of 2 aa recently implicated in binding of human ISG15 to LFA-1 in vitro were required for its adjuvant effect in vivo. Moreover, in further agreement with the in vitro findings on human cells, free ISG15 boosted the CTL response in vivo via NK cells in the absence of CD4+ T cell help. Thus, free ISG15 is part of a newly recognized innate route to promote the CTL response.

Radiotherapy and Cisplatin Increase Immunotherapy Efficacy by Enabling Local and Systemic Intratumoral T-cell Activity.

To increase cancer immunotherapy success, PD-1 blockade must be combined with rationally selected treatments. Here, we examined, in a poorly immunogenic mouse breast cancer model, the potential of antibody-based immunomodulation and conventional anticancer treatments to collaborate with anti-PD-1 treatment. One requirement to improve anti-PD-1-mediated tumor control was to promote tumor-specific cytotoxic T-cell (CTL) priming, which was achieved by stimulating the CD137 costimulatory receptor. A second requirement was to overrule PD-1-unrelated mechanisms of CTL suppression in the tumor microenvironment (TME). This was achieved by radiotherapy and cisplatin treatment. In the context of CD137/PD-1-targeting immunotherapy, radiotherapy allowed for tumor elimination by altering the TME, rather than intrinsic CTL functionality. Combining this radioimmunotherapy regimen with low-dose cisplatin improved CTL-dependent regression of a contralateral tumor outside the radiation field. Thus, systemic tumor control may be achieved by combining immunotherapy protocols that promote T-cell priming with (chemo)radiation protocols that permit CTL activity in both the irradiated tumor and (occult) metastases.