Protein kinase R (PKR) plays a pro-viral role in porcine reproductive and respiratory syndrome virus (PRRSV) replication by modulating viral gene transcription.

Protein kinase R (PKR) is involved in apoptotic cell death and antiviral activities in response to many virus infections. To reveal the role of PKR in the replication of porcine reproductive and respiratory syndrome virus (PRRSV), we first examined the kinetics of PKR phosphorylation during PRRSV infection. The results showed that PRRSV transiently activates PKR at 12 and 24 h postinfection. Surprisingly, eIF-2α, the well-known downstream target of PKR, was significantly phosphorylated compared to mock-infected cells only at 48 and 72 h postinfection. Reduced viral gene transcription, viral protein synthesis, and virus titer were detected in cells transfected with PKR silencing RNA prior to PRRSV infection compared to control silencing RNA transfected cells, indicating a role of PKR in facilitating virus replication. Overall, our data suggest that PKR is not a major contributor to the phosphorylation of eIF-2α during PRRSV infection, but it plays a pro-viral role in PRRSV replication by modulating primarily viral gene transcription.

Role of phosphatidylinositol 3-kinase (PI3K) and Akt1 kinase in porcine reproductive and respiratory syndrome virus (PRRSV) replication.

We have previously reported that inhibition of phosphatidylinositol 3-kinase (PI3K) reduces porcine reproductive and respiratory syndrome (PRRSV) replication. Here, we further investigate the mechanism by which PI3K inhibition affects virus replication and the role of Akt1 kinase in virus replication. We found that PI3K inhibition reduced viral gene transcription by approximately 1.5-fold. Accordingly, viral protein synthesis was significantly reduced by PI3K inhibition. Interestingly, cells overexpressing the dominant negative mutant Akt1 exhibited a significant reduction in viral gene transcription compared to cells overexpressing the constitutively active Akt1. Viral protein synthesis was also enhanced in cells overexpressing the constitutively active Akt1. Overall, our data show that both PI3K and Akt1 play a role in viral gene expression, leading to an increase in virus replication.

Mesenchymal stromal cells with chimaeric antigen receptors for enhanced immunosuppression.

Allogeneic mesenchymal stromal cells (MSCs) are a safe treatment option for many disorders of the immune system. However, clinical trials using MSCs have shown inconsistent therapeutic efficacy, mostly owing to MSCs providing insufficient immunosuppression in target tissues. Here we show that antigen-specific immunosuppression can be enhanced by genetically modifying MSCs with chimaeric antigen receptors (CARs), as we show for E-cadherin-targeted CAR-MSCs for the treatment of graft-versus-host disease in mice. CAR-MSCs led to superior T-cell suppression and localization to E-cadherin+ colonic cells, ameliorating the animals' symptoms and survival rates. On antigen-specific stimulation, CAR-MSCs upregulated the expression of immunosuppressive genes and receptors for T-cell inhibition as well as the production of immunosuppressive cytokines while maintaining their stem cell phenotype and safety profile in the animal models. CAR-MSCs may represent a widely applicable therapeutic technology for enhancing immunosuppression.

MyD88 is an essential regulator of NK cell-mediated clearance of MCMV infection.

The signaling adapter MyD88 is critical for immune cell activation in response to viral or bacterial pathogens via several TLRs, IL-1ßR and IL-18R. However, the essential role of MyD88 during activations mediated by germline-encoded NK cell receptors (NKRs), such as Ly49H or NKG2D, has yet to be investigated. To define the NK cell-intrinsic function of MyD88, we generated a novel NK cell conditional knockout mouse for MyD88 (Myd88fl/flNcr1Cre/+). Phenotypic characterization of these mice demonstrated that MyD88 is dispensable for NK cell development and maturation. However, the MyD88-deficient NK cells exhibited significantly reduced cytotoxic potentials in vivo. In addition, the lack of MyD88 significantly reduced the NKG2D-mediated inflammatory cytokine production in vitro. Consistent with this, mice lacking MyD88 were unable to respond and clear MCMV infection. Transcriptomic analyses of splenic NK cells following MCMV infection revealed that inflammatory gene signatures were upregulated in Ly49H+. In contrast, Ly49H- NK cells have significant enrichment in G2M checkpoint genes, revealing distinct transcriptomic profiles of these subsets. Our results identify a central role for MyD88 in Ly49H-dependent gene signatures, including alterations in genes regulating proliferation in Ly49H+ NK cells. In summary, our study reveals a previously unknown function of MyD88 in Ly49H-dependent signaling and in vivo functions of NK cells.

In Vivo Assessment of NK Cell-Mediated Cytotoxicity by Adoptively Transferred Splenocyte Rejection.

NK cells are innate lymphocytes that are vital to clearance of virally infected or malignantly transformed cells. Assessment of the cytotoxic response is an important component of NK cell research and investigation of human disease. Standard assays of NK cell-mediated cytotoxicity of CD107a degranulation or 51Cr release assay utilize cultured or freshly isolated NK cell populations in vitro. In addition to requirements to maintain multiple target cell lines and radioactivity precautions in the case of 51Cr, these are in vitro evaluations of a complex in vivo function. Here, we describe the in vivo assessment of NK cell-mediated cytotoxicity through the adoptive transfer of splenocytes and their subsequent rejection. This protocol offers rapid, quantitative, and concurrent assessment of NK cell-mediated cytotoxicity against the prototypic NK stimulations of "missing-self" and "nonself."

Natural Killer Cells: Development, Maturation, and Clinical Utilization.

Natural killer (NK) cells are the predominant innate lymphocyte subsets that mediate anti-tumor and anti-viral responses, and therefore possess promising clinical utilization. NK cells do not express polymorphic clonotypic receptors and utilize inhibitory receptors (killer immunoglobulin-like receptor and Ly49) to develop, mature, and recognize "self" from "non-self." The essential roles of common gamma cytokines such as interleukin (IL)-2, IL-7, and IL-15 in the commitment and development of NK cells are well established. However, the critical functions of pro-inflammatory cytokines IL-12, IL-18, IL-27, and IL-35 in the transcriptional-priming of NK cells are only starting to emerge. Recent studies have highlighted multiple shared characteristics between NK cells the adaptive immune lymphocytes. NK cells utilize unique signaling pathways that offer exclusive ways to genetically manipulate to improve their effector functions. Here, we summarize the recent advances made in the understanding of how NK cells develop, mature, and their potential translational use in the clinic.

IQ Domain-Containing GTPase-Activating Protein 1 Regulates Cytoskeletal Reorganization and Facilitates NKG2D-Mediated Mechanistic Target of Rapamycin Complex 1 Activation and Cytokine Gene Translation in Natural Killer Cells.

Natural killer (NK) cells are innate lymphocytes that play essential roles in mediating antitumor immunity. NK cells respond to various inflammatory stimuli including cytokines and stress-induced cellular ligands which activate germline-encoded activation receptors (NKRs), such as NKG2D. The signaling molecules activated downstream of NKRs are well defined; however, the mechanisms that regulate these pathways are not fully understood. IQ domain-containing GTPase-activating protein 1 (IQGAP1) is a ubiquitously expressed scaffold protein. It regulates diverse cellular signaling programs in various physiological contexts, including immune cell activation and function. Therefore, we sought to investigate the role of IQGAP1 in NK cells. Development and maturation of NK cells from mice lacking IQGAP1 (Iqgap1-/- ) were mostly intact; however, the absolute number of splenic NK cells was significantly reduced. Phenotypic and functional characterization revealed a significant reduction in the egression of NK cells from the bone marrow of Iqagp1-/- mice altering their peripheral homeostasis. Lack of IQGAP1 resulted in reduced NK cell motility and their ability to mediate antitumor immunity in vivo. Activation of Iqgap1-/- NK cells via NKRs, including NKG2D, resulted in significantly reduced levels of inflammatory cytokines compared with wild-type (WT). This reduction in Iqgap1-/- NK cells is neither due to an impaired membrane proximal signaling nor a defect in gene transcription. The levels of Ifng transcripts were comparable between WT and Iqgap1-/- , suggesting that IQGAP1-dependent regulation of cytokine production is regulated by a post-transcriptional mechanism. To this end, Iqgap1-/- NK cells failed to fully induce S6 phosphorylation and showed significantly reduced protein translation following NKG2D-mediated activation, revealing a previously undefined regulatory function of IQGAP1 via the mechanistic target of rapamycin complex 1. Together, these results implicate IQGAP1 as an essential scaffold for NK cell homeostasis and function and provide novel mechanistic insights to the post-transcriptional regulation of inflammatory cytokine production.

IQGAP1: insights into the function of a molecular puppeteer.

The intracellular spatiotemporal organization of signaling events is critical for normal cellular function. In response to environmental stimuli, cells utilize highly organized signaling pathways that are subject to multiple layers of regulation. However, the molecular mechanisms that coordinate these complex processes remain an enigma. Scaffolding proteins (scaffolins) have emerged as critical regulators of signaling pathways, many of which have well-described functions in immune cells. IQGAP1, a highly conserved cytoplasmic scaffold protein, is able to curb, compartmentalize, and coordinate multiple signaling pathways in a variety of cell types. IQGAP1 plays a central role in cell-cell interaction, cell adherence, and movement via actin/tubulin-based cytoskeletal reorganization. Evidence also implicates IQGAP1 as an essential regulator of the MAPK and Wnt/ß-catenin signaling pathways. Here, we summarize the recent advances on the cellular and molecular biology of IQGAP1. We also describe how this pleiotropic scaffolin acts as a true molecular puppeteer, and highlight the significance of future research regarding the role of IQGAP1 in immune cells.