Neutralizing antibodies could be antivirals against COVID-19 pandemics. Here, we report isolation of four human-origin monoclonal antibodies from a convalescent patient, all of which display neutralization abilities. B38 and H4 block the binding between virus S-protein RBD and cellular receptor ACE2. A competition assay indicates their different epitopes on the RBD, making them a potential virus-targeting MAb-pair to avoid immune escape in future clinical applications. Moreover, a therapeutic study in a mouse model validated that these antibodies can reduce virus titers in infected lungs. The RBD-B38 complex structure revealed that most residues on the epitope overlap with the RBD-ACE2 binding interface, explaining the blocking effect and neutralizing capacity. Our results highlight the promise of antibodybased therapeutics and provide a structural basis for rational vaccine design.

Highlights d Cryo-EM structure of SARS-CoV-2 nsp12-nsp7-nsp8 core polymerase complex d The core complex of SARS-CoV-2 has lower enzymatic activity than SARS-CoV d SARS-CoV-2 nsp7-8-12 subunits are less thermostable than the SARS-CoV counterpart

An avian-origin human-infecting influenza (H7N9) virus was recently identified in China. We have evaluated the viral hemagglutinin (HA) receptor-binding properties of two human H7N9 isolates, A/Shanghai/1/2013 (SH-H7N9) (containing the avian-signature residue Gln(226)) and A/Anhui/1/2013 (AH-H7N9) (containing the mammalian-signature residue Leu(226)). We found that SH-H7N9 HA preferentially binds the avian receptor analog, whereas AH-H7N9 HA binds both avian and human receptor analogs. Furthermore, an AH-H7N9 mutant HA (Leu(226) → Gln) was found to exhibit dual receptor-binding property, indicating that other amino acid substitutions contribute to the receptor-binding switch. The structures of SH-H7N9 HA, AH-H7N9 HA, and its mutant in complex with either avian or human receptor analogs show how AH-H7N9 can bind human receptors while still retaining the avian receptor-binding property.

Autophagy is involved in the replication of viruses, especially those that perform RNA assembly on the surface of cytoplasmic membrane in host cells. However, little is known about the regulatory role of autophagy in influenza A virus replication. Using fluorescence and electron microscopy, we observed that autophagosomes can be induced and identified upon influenza A virus infection. The virus increased the amount of the autophagosome marker protein microtubule-associated protein light chain 3-II (LC3-II) and enhanced autophagic flux. When autophagy was pharmacologically inhibited by either 3-methylademine or wortmannin, the titers of influenza A virus were remarkably decreased. Viral reduction via autophagy inhibition was further confirmed by RNA interference, through which two different proteins required for autophagy were depleted. Noticeably, the compounds utilized had no marked effect on virus entry or cell viability, either of which might limit viral replication. Furthermore, alteration of cellular autophagy via pharmacological reagents or RNA interference impaired viral protein accumulation. Taken together, these findings indicate that autophagy is actively involved in influenza A virus replication.

Activating transcription factor 4 (ATF4) is a critical mediator of metabolic and oxidative homeostasis and cell survival. ATF4 is elevated in response to diverse microenvironmental stresses, including starvation, ER stress damages and exposure to toxic factors. Here we show that ATF4 expression fosters the malignancy of primary brain tumors (WHO grade III and IV gliomas) and increases proliferation and tumor angiogenesis. Hence, ATF4 expression promotes cell migration and anchorage-independent cell growth, whereas siRNA-mediated knockdown of ATF4 attenuates these features of malignancy in human gliomas. Further experiments revealed that ATF4-dependent tumor promoting effects are mediated by transcriptional targeting the glutamate antiporter xCT/SCL7A11 (also known as system Xc-). Thus, xCT is elevated as a consequence of ATF4 activation. We further found evidence that ATF4-induced proliferation can be attenuated by pharmacological or genetic xCT inhibition and ferroptosis inducers such as sorafenib, erastin and GPx4 inhibitor RSL3. Further, fostered xCT expression promotes cell survival and growth in ATF4 knockdown cells. Moreover, increased xCT levels ameliorate sorafenib and erastin-induced ferroptosis. Conversely, ATF4 knockdown renders cells susceptible for erastin, sorafenib and RSL3-induced ferroptosis. We further identified that ATF4 promotes tumor-mediated neuronal cell death which can be alleviated by xCT inhibition. Moreover, elevated ATF4 expression in gliomas promotes tumor angiogenesis. Noteworthy, ATF4-induced angiogenesis could be diminished by ferroptosis inducers erastin and by GPx4 inhibitor RSL3. Our data provide proof-of-principle evidence that ATF4 fosters proliferation and induces a toxic microenvironmental niche. Furthermore, ATF4 increases tumor angiogenesis and shapes the vascular architecture in a xCT-dependent manner. Thus, inhibition of ATF4 is a valid target for diminishing tumor growth and vasculature via sensitizing tumor cells for ferroptosis.

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder in which the loss of dystrophin causes progressive degeneration of skeletal and cardiac muscle. Potential therapies that carry substantial risk, such as gene and cell-based approaches, must first be tested in animal models, notably the mdx mouse and several dystrophin-deficient breeds of dogs, including golden retriever muscular dystrophy (GRMD). Affected dogs have a more severe phenotype, in keeping with that of DMD, so may better predict disease pathogenesis and treatment efficacy. We and others have developed various phenotypic tests to characterize disease progression in the GRMD model. These biomarkers range from measures of strength and joint contractures to magnetic resonance imaging. Some of these tests are routinely used in clinical veterinary practice, while others require specialized equipment and expertise. By comparing serial measurements from treated and untreated groups, one can document improvement or delayed progression of disease. Potential treatments for DMD may be broadly categorized as molecular, cellular, or pharmacologic. The GRMD model has increasingly been used to assess efficacy of a range of these therapies. While some of these studies have largely provided general proof-of-concept for the treatment under study, others have demonstrated efficacy using the biomarkers discussed. Importantly, just as symptoms in DMD vary among patients, GRMD dogs display remarkable phenotypic variation. While confounding statistical analysis in preclinical trials, this variation offers insight regarding the role that modifier genes play in disease pathogenesis. By correlating functional and mRNA profiling results, gene targets for therapy development can be identified.

Highlights d Endothelial loss of pfkfb3 impairs ischemic muscle revascularization and regeneration d EC-derived lactate instructs MCT1-dependent macrophage functional polarization d Lactate-polarized macrophages promote muscle revascularization and regeneration d Restoring lactate levels improves macrophage polarization and recovery from ischemia

Multiple surface envelope proteins are involved in the human herpes simplex virus type 1 entry and fusion. Among them, glycoprotein D (gD) has an important role by binding to the host receptors such as herpes virus entry mediator and nectin-1. Although the complex structure of gD with herpes virus entry mediator has been established, the binding mode of gD with the nectin-1 is elusive. Nectin-1 is a member of the immunoglobulin (Ig)-like (three Ig-like domains) cell adhesion molecules and is believed to form a homodimer to exert its functions. Here we report the complex structure of gD and nectin-1 (three Ig domains), revealing that gD binds the fi rst Ig domain of nectin-1 in a similar mode to the nectin-1 homodimer interaction. The key amino acids responsible for nectin-1 dimerization are also used for gD / nectin-1 binding. This result indicates that binding of gD to nectin-1 would preclude the nectin-1 dimerization, consequently abolishing its cell adhesion function.