The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected millions of people worldwide, igniting an unprecedented effort from the scientific community to understand the biological underpinning of COVID19 pathophysiology. In this Review, we summarize the current state of knowledge of innate and adaptive immune responses elicited by SARS-CoV-2 infection and the immunological pathways that likely contribute to disease severity and death. We also discuss the rationale and clinical outcome of current therapeutic strategies as well as prospective clinical trials to prevent or treat SARS-CoV-2 infection.

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To study the binding specificity of Src homology 3 (SH3) domains, we have screened a mouse embryonic expression library for peptide fragments that interact with them. Several clones were identified that express fragments of proteins which, through proline-rich binding sites, exhibit differential binding specificity to various SH3 domains. Src-SH3-specific binding uses a sequence of 7 aa of the consensus RPLPXXP, in Protein-protein interactions are central events in cellular signal transduction. These interactions are often mediated by noncatalytic conserved domains, three of which are the Src homology regions 2 and 3 (SH2 and SH3), first identified as part of the Rous sarcoma viral oncogene product (1, 2), and the plekstrin homology (PH) domain, more recently identified by protein sequence alignments (3, 4). To date, the best understood protein interactions are those mediated by the SH2 domains, which bind to phosphotyrosine residues on proteins that have been primed for signaling through phosphorylation.The function of SH3 domains is less clear. In relation to the oncogenic potential of protein-tyrosine kinases, these domains play an inhibitory role because mutation or deletion of them activates the transforming potential of c-Src and c-Abl protooncoproteins (5-7). The first clue to the function of SH3 domains was obtained by the cloning of fragments of two protein ligands for the Abl SH3: 3BP1 and 3BP2 (8). In these proteins, proline-rich peptides only 10 aa long serve as targets of SH3 binding (9). Since then, a number of interactions between SH3 domains and proline-rich ligands have been described, showing that SH3 domains are involved in epidermal growth factor receptor signaling (10), cellular localization of cytoplasmic proteins (11), upregulation of the GTPase activity of dynamin (12), and activation of phosphatidylinositol 3-kinase in response to IgM crosslinking (13).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.From these and other reports it is now clear that interactions between SH3s and their ligands occur through proline-rich sites. It is less clear, however, how the specificity of interaction is achieved. In this study we report the isolation of peptide fragments from proteins that exhibit differential binding specificity to various SH3s. Specificity of interaction is mediated by unique sequences that interact with binding pockets found on the surface of SH3 domains. Our data correlate well with recent reports that identify specific artificial ligands for different SH3 domains from chemically synthesized and phage display libraries (14-16) and suggest that these ligands do occur in vivo. MATERIALS AND METHODSLibrary Screening. A 16-day mouse embryo cDNA expression library (Novagen) was screened for SH3-binding proteins according to the manufacturer's protocols and as previously described (8). Biotinylated glutathione S-transfe...

The highly invasive behavior of glioblastoma cells contributes to the morbidity and mortality associated with these tumors. The integrin-mediated adhesion and migration of glioblastoma cells on brain matrix proteins is enhanced by stimulation with growth factors, including platelet-derived growth factor (PDGF). As focal adhesion kinase (FAK), a nonreceptor cytoplasmic tyrosine kinase, has been shown to promote cell migration in various other cell types, we analysed its role in glioblastoma cell migration. Forced overexpression of FAK in serumstarved glioblastoma cells plated on recombinant (rec)-osteopontin resulted in a twofold enhancement of basal migration and a ninefold enhancement of PDGF-BBstimulated migration. Both expression of mutant FAK(397F) and the downregulation of FAK with small interfering (si) RNA inhibited basal and PDGF-stimulated migration. FAK overexpression and PDGF stimulation was found to increase the phosphorylation of the Crk-associated substrate (CAS) family member human enhancer of filamentation 1 (HEF1), but not p130CAS or Src-interacting protein (Sin)/Efs, although the levels of expression of these proteins was similar. Moreover downregulation of HEF1 with siRNA, but not p130CAS, inhibited basal and PDGF-stimulated migration. The phosphorylated HEF1 colocalized with vinculin and was associated almost exclusively with 0.1% Triton X-100 insoluble material, consistent with its signaling at focal adhesions. FAK overexpression promoted invasion through normal brain homogenate and siHEF1 inhibited this invasion. Results presented here suggest that HEF1 acts as a necessary and specific downstream effector of FAK in the invasive behavior of glioblastoma cells and may be an effective target for treatment of these tumors.

Ruane et al. demonstrate a role for the microbiota in modulating protective immunity to intranasal vaccination via the ability of lung dendritic cells to induce B cell IgA class switching.