Cardiovirus leader proteins retarget RSK kinases toward alternative substrates to perturb nucleocytoplasmic traffic

Nanomedicine-enhanced SCAP hybrid spheroids: A novel approach for improved stem cell survival

In regenerative medicine, the therapeutic potential of mesenchymal stem cells (MSC), such as stem cells from human apical papilla (SCAP), is well-documented and largely attributed to their secretome. However, their poor survival post-transplantation limits their efficacy. This study hypothesized that combining SCAP spheroids with nanomedicines loaded with NecroX-5 (an anti-necrotic drug) and rapamycin (an immunosuppressive agent) would enhance SCAP survival in vivo. The approach aimed to reduce oxidative stress-related cell death and suppress immune reactions towards xeno-/allogenic cells. Two types of nanocarriers, polymeric nanoparticles (NP) and lipid nanocapsules (LNC), were compared to encapsulate NecroX-5 and rapamycin. A magnetic-dependent method was employed to associate SCAP with nanomedicines, involving co-encapsulation of drugs and Super Paramagnetic Iron Oxide Nanoparticles (SPIONs) in the nanocarriers and cell magnetization using Nanoshuttle™. In vivo, SCAP hybrid spheroids expressing Luciferase, when injected subcutaneously into immunocompetent mice, showed increased bioluminescence signals compared to regular spheroids. These results provide proof-of-concept that magnetic-driven association of cells and nanomedicines into hybrid spheroids is feasible and suggest that delivering SCAP as hybrid spheroids can enhance their survival.

High Internal Phase Emulsion-Templated Hydrophilic Polyphosphoester Scaffolds: Tailoring the Porosity and Degradation for Soft Tissue Engineering

Synthetic porous scaffolds are key elements in tissue engineering (TE), requiring controlled porosity for cell colonization, along with a degradation rate aligned with tissue growth. While biodegradable polyester scaffolds are widely used in TE, they are primarily hydrophobic and suited for semirigid to hard tissue applications. This work broadens the scope of TE by introducing porous scaffolds made of polyphosphoesters (PPEs), degradable polymers with adaptable physicochemical properties. PPE hydrogels were shaped into 3D scaffolds using an emulsion templating method, yielding hydrophilic matrices with controlled porosity and tunable Young's moduli for soft tissues. Degradation assays at physiological pH confirmed the scaffolds' biodegradability. Cytotoxicity tests with PPE scaffolds showed excellent cell viability, while RGD functionalization further enhanced cell adhesion. Scaffold colonization, low inflammation, and angiogenesis were demonstrated in vivo through subcutaneous implantation of the scaffolds in mice and histological analysis. These results highlight PPE-based scaffolds as promising candidates for regenerative medicine.

The "DDVF" motif used by viral and bacterial proteins to hijack RSK kinases mimics a short linear motif (SLiM) found in proteins related to the RAS-ERK MAP kinase pathway

Proteins of pathogens such as cardioviruses, Kaposi sarcoma-associated herpes virus, varicella zoster virus and bacteria of the genus Yersinia were previously shown to use a common "DDVF" (D/E-D/E-V-F) short linear motif (SLiM) to hijack cellular kinases of the RSK (p90 ribosomal S6 kinases) family. Notably, the leader (L) protein of Theiler's murine encephalomyelitis virus (TMEV), a cardiovirus, and protein YopM of Yersinia species were shown to act as adapters to retarget RSKs toward unconventional substrates, nucleoporins and pyrin, respectively. Remarkable conservation of the SLiM docking site targeted by pathogens' proteins in RSK sequences suggested a physiological role for this site. Using SLiM prediction tools and AlphaFold docking, we screened the human proteome for proteins that would interact with RSKs through a DDVF-like SLiM. Co-immunoprecipitation experiments show that two candidates previously known as RSK partners, FGFR1 and SPRED2, as well as two candidates identified as novel RSK partners, GAB3 and CNKSR2 do interact with RSKs through a similar interface as the one used by pathogens, as was recently documented for SPRED2. FGFR1 employs a DSVF motif to bind RSKs and phosphorylation of the serine in this motif slightly increased RSK binding. FGFR1, SPRED2, GAB3 and CNKSR2 act upstream of RSK in the RAS-ERK MAP kinase pathway. Analysis of ERK activation in cells expressing a mutated form of RSK lacking the DDVF-docking site suggests that RSK might interact with the DDVF-like SLiM of several partners to provide a negative feed-back to the ERK MAPK pathway. Moreover, after TMEV infection, ERK phosphorylation was altered by the L protein in a DDVF-dependent manner. Taken together, our data suggest that, in addition to retargeting RSKs toward unconventional substrates, pathogens' proteins carrying a DDVF-like motif can compete with endogenous DDVF-containing proteins for RSK binding, thereby altering the regulation of the RAS-ERK MAP kinase pathway.

Involvement of paraspeckle components in viral infections

Paraspeckles are non-membranous subnuclear bodies, formed through the interaction between the architectural long non-coding RNA (lncRNA) nuclear paraspeckle assembly transcript 1 (NEAT1) and specific RNA-binding proteins, including the three Drosophila Behavior/Human Splicing (DBHS) family members (PSPC1 (Paraspeckle Component 1), SFPQ (Splicing Factor Proline and Glutamine Rich) and NONO (Non-POU domain-containing octamer-binding protein)). Paraspeckle components were found to impact viral infections through various mechanisms, such as induction of antiviral gene expression, IRES-mediated translation, or viral mRNA polyadenylation. A complex involving NEAT1 RNA and paraspeckle proteins was also found to modulate interferon gene transcription after nuclear DNA sensing, through the activation of the cGAS-STING axis. This review aims to provide an overview on how these elements actively contribute to the dynamics of viral infections.

Luciferase transduction and selection protocol for reliable in vivo bioluminescent measurements in cancer research

Bioluminescence imaging has become an essential non-invasive tool in cancer research for monitoring various cellular processes and tumor progression in vivo. In this article, we aimed to propose a transduction and selection protocol for reliable in vivo bioluminescent measurements in immunocompetent mouse models. Using two different heterogenous luciferase-expressing cell models, we underlined factors influencing transduction. The protocol was tested through an in vitro luciferase activity assay as well as using in vivo longitudinal monitoring of metastases formation (In Vivo Imaging System®). The data were cross validated with histological assessment. Our results demonstrated stable and proportional in vitro and in vivo bioluminescent signals correlating with actual metastatic burden. Furthermore, ex vivo analysis confirmed the accuracy of bioluminescent imaging in quantifying metastatic surface area. This protocol should ensure reliable and reproducible measurements in cancer research utilizing luciferase-positive cell lines, confirming the validity and accuracy of preclinical studies in immunocompetent models.

Assessment of Kinome-Wide Activity Remodeling upon Picornavirus Infection

Picornaviridae represent a large family of single-stranded positive RNA viruses of which different members can infect both humans and animals. These include the enteroviruses (e.g., poliovirus, coxsackievirus, and rhinoviruses) as well as the cardioviruses (e.g., encephalomyocarditis virus). Picornaviruses have evolved to interact with, use, and/or evade cellular host systems to create the optimal environment for replication and spreading. It is known that viruses modify kinase activity during infection, but a proteome-wide overview of the (de)regulation of cellular kinases during picornavirus infection is lacking. To study the kinase activity landscape during picornavirus infection, we here applied dedicated targeted mass spectrometry-based assays covering ∼40% of the human kinome. Our data show that upon infection, kinases of the MAPK pathways become activated (e.g., ERK1/2, RSK1/2, JNK1/2/3, and p38), while kinases involved in regulating the cell cycle (e.g., CDK1/2, GWL, and DYRK3) become inactivated. Additionally, we observed the activation of CHK2, an important kinase involved in the DNA damage response. Using pharmacological kinase inhibitors, we demonstrate that several of these activated kinases are essential for the replication of encephalomyocarditis virus. Altogether, the data provide a quantitative understanding of the regulation of kinome activity induced by picornavirus infection, providing a resource important for developing novel antiviral therapeutic interventions.

Picornavirus security proteins promote the release of extracellular vesicle enclosed viruses via the modulation of host kinases

The discovery that extracellular vesicles (EVs) serve as carriers of virus particles calls for a reevaluation of the release strategies of non-enveloped viruses. Little is currently known about the molecular mechanisms that determine the release and composition of EVs produced by virus-infected cells, as well as conservation of these mechanisms among viruses. We previously described an important role for the Leader protein of the picornavirus encephalomyocarditis virus (EMCV) in the induction of virus-carrying EV subsets with distinct molecular and physical properties. EMCV L acts as a 'viral security protein' by suppressing host antiviral stress and type-I interferon (IFN) responses. Here, we tested the ability of functionally related picornavirus proteins of Theilers murine encephalitis virus (TMEV L), Saffold virus (SAFV L), and coxsackievirus B3 (CVB3 2Apro), to rescue EV and EV-enclosed virus release when introduced in Leader-deficient EMCV. We show that all viral security proteins tested were able to promote virus packaging in EVs, but that only the expression of EMCV L and CVB3 2Apro increased overall EV production. We provide evidence that one of the main antiviral pathways counteracted by this class of picornaviral proteins, i.e. the inhibition of PKR-mediated stress responses, affected EV and EV-enclosed virus release during infection. Moreover, we show that the enhanced capacity of the viral proteins EMCV L and CVB3 2Apro to promote EV-enclosed virus release is linked to their ability to simultaneously promote the activation of the stress kinase P38 MAPK. Taken together, we demonstrate that cellular stress pathways involving the kinases PKR and P38 are modulated by the activity of non-structural viral proteins to increase the release EV-enclosed viruses during picornavirus infections. These data shed new light on the molecular regulation of EV production in response to virus infection.

Identification of RSK substrates using an analog-sensitive kinase approach

The p90 ribosomal S6 kinases (RSK) family of serine/threonine kinases comprises four isoforms (RSK1-4) that lie downstream of the ERK1/2 mitogen-activated protein kinase pathway. RSKs are implicated in fine tuning of cellular processes such as translation, transcription, proliferation, and motility. Previous work showed that pathogens such as Cardioviruses could hijack any of the four RSK isoforms to inhibit PKR activation or to disrupt cellular nucleocytoplasmic trafficking. In contrast, some reports suggest nonredundant functions for distinct RSK isoforms, whereas Coffin-Lowry syndrome has only been associated with mutations in the gene encoding RSK2. In this work, we used the analog-sensitive kinase strategy to ask whether the cellular substrates of distinct RSK isoforms differ. We compared the substrates of two of the most distant RSK isoforms: RSK1 and RSK4. We identified a series of potential substrates for both RSKs in cells and validated RanBP3, PDCD4, IRS2, and ZC3H11A as substrates of both RSK1 and RSK4, and SORBS2 as an RSK1 substrate. In addition, using mutagenesis and inhibitors, we confirmed analog-sensitive kinase data showing that endogenous RSKs phosphorylate TRIM33 at S1119. Our data thus identify a series of potential RSK substrates and suggest that the substrates of RSK1 and RSK4 largely overlap and that the specificity of the various RSK isoforms likely depends on their cell- or tissue-specific expression pattern.