Antibodies targeting the spike (S) and nucleocapsid (N) proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential tools. In addition to important roles in the treatment and diagnosis of infection, the availability of high-quality specific antibodies for the S and N proteins is essential to facilitate basic research of virus replication and in the characterization of mutations responsible for variants of concern. We have developed panels of mouse and rabbit monoclonal antibodies (mAbs) to the SARS-CoV-2 spike receptor-binding domain (S-RBD) and N protein for functional and antigenic analyses. The mAbs to the S-RBD were tested for neutralization of native SARS-CoV-2, with several exhibiting neutralizing activity. The panels of mAbs to the N protein were assessed for cross-reactivity with the SARS-CoV and Middle East respiratory syndrome (MERS)-CoV N proteins and could be subdivided into sets that showed unique specificity for SARS-CoV-2 N protein, cross-reactivity between SARS-CoV-2 and SARS-CoV N proteins only, or cross-reactivity to all three coronavirus N proteins tested. Partial mapping of N-reactive mAbs were conducted using truncated fragments of the SARS-CoV-2 N protein and revealed near complete coverage of the N protein. Collectively, these sets of mouse and rabbit monoclonal antibodies can be used to examine structure/function studies for N proteins and to define the surface location of virus neutralizing epitopes on the RBD of the S protein.

Human cytomegalovirus (HCMV) modulates numerous cellular pathways to facilitate infection, including key components in cellular iron homeostasis. Iron is essential to many cellular processes but, if present in excess, drives cell death through ferroptosis. Ferroptosis is a process that is dependent upon the accumulation of oxidatively damaged phospholipids (lipid peroxides); when these lipid peroxides accumulate in membranes, this culminates in plasma membrane rupture and eventual cell lysis. Here, we demonstrate that HCMV infection downregulates the expression of a key modulator of lipid peroxidation, glutathione peroxidase 4 (GPX4). HCMV infection also markedly increased levels of lipid peroxides within infected cells. Despite the marked downregulation of GPX4 by HCMV, further inhibition of GPX4 impaired virus replication. Interestingly, overexpression of GPX4 did not reduce the production of lipid peroxides within infected cells. In contrast, lipid peroxide levels were reduced by treatment with ferrostatin-1, a ferrous iron-dependent scavenger of alkoxyl radicals, indicating a role for iron in the production of lipid peroxides. HCMV-infected cells became less sensitive to GPX4 inhibition as infection progressed, requiring substantially higher levels of GPX4 inhibitors to induce ferroptosis compared to uninfected cells. This observed difference in sensitivity to ferroptosis upon infection correlated with a large increase in lipid production by infected cells. Therefore, the marked stimulation of lipid peroxidation by HCMV likely proceeds through a pathway that is independent of GPX4 regulation, but the ability of lipid peroxides to stimulate ferroptosis by modulating plasma membrane rupture is likely blunted by the massive increase in lipid production during HCMV infection. IMPORTANCE: Human cytomegalovirus (HCMV) infection is intimately linked with countless host cell pathways that are modulated in a coordinated fashion to facilitate infection. Here, we describe HCMV-induced regulation of lipid peroxidation, a precursor of the iron-regulated cell death pathway known as ferroptosis, during human cytomegalovirus infection. These studies reveal hitherto unidentified changes in metabolism mediated by HCMV that decrease sensitivity to ferroptosis, despite increases in lipid peroxidation and transient increases in intracellular iron levels in infected cells.

Human coronavirus 229E (HCoV-229E) is an alpha coronavirus that infects humans and bats. In common with all positive-strand RNA viruses, 229E infection causes rearrangements of the host’s intracellular membranes to form replication organelles, a highly conserved and vital step in the viral replication cycle. Here, we investigated the role of the ESCRT protein VPS4A in 229E infection. We found that functional VPS4A was required for the formation of replication organelles and localizing viral RNA to these structures in host cells to facilitate viral genome replication. We validated this effect using small molecule inhibitors to VPS4A, significantly reducing virus replication. We also showed that other ESCRTS, like CHMP4B, were required for the virus replication step, whereas VPS37A was involved in the post-replication stages. The absence of a functional VPS4A prevented the remodeling of membranes to form viral replication centers and, therefore, exposed the viral RNA, triggering an inflammatory immune response as indicated by elevated levels of IL-6. Interestingly, we observed the role of VPS4A to be similar for the OC43 coronavirus, indicating it could be conserved across all four coronavirus genera, including SARS-CoV-2. Understanding more about the replication of coronaviruses is imperative to finding more effective ways to control them.