Desmosomal Cadherins in Health and Disease.

Desmosomal cadherins are a recent evolutionary innovation that make up the adhesive core of highly specialized intercellular junctions called desmosomes. Desmosomal cadherins, which are grouped into desmogleins and desmocollins, are related to the classical cadherins, but their cytoplasmic domains are tailored for anchoring intermediate filaments instead of actin to sites of cell-cell adhesion. The resulting junctions are critical for resisting mechanical stress in tissues such as the skin and heart. Desmosomal cadherins also act as signaling hubs that promote differentiation and facilitate morphogenesis, creating more complex and effective tissue barriers in vertebrate tissues. Interference with desmosomal cadherin adhesive and supra-adhesive functions leads to a variety of autoimmune, hereditary, toxin-mediated, and malignant diseases. We review our current understanding of how desmosomal cadherins contribute to human health and disease, highlight gaps in our knowledge about their regulation and function, and introduce promising new directions toward combatting desmosome-related diseases.

Astrovirus replication in human intestinal enteroids reveals multi-cellular tropism and an intricate host innate immune landscape.

Human astroviruses (HAstV) are understudied positive-strand RNA viruses that cause gastroenteritis mostly in children and the elderly. Three clades of astroviruses, classic, MLB-type and VA-type have been reported in humans. One limitation towards a better understanding of these viruses has been the lack of a physiologically relevant cell culture model that supports growth of all clades of HAstV. Herein, we demonstrate infection of HAstV strains belonging to all three clades in epithelium-only human intestinal enteroids (HIE) isolated from biopsy-derived intestinal crypts. A detailed investigation of infection of VA1, a member of the non-canonical HAstV-VA/HMO clade, showed robust replication in HIE derived from different patients and from different intestinal regions independent of the cellular differentiation status. Flow cytometry and immunofluorescence analysis revealed that VA1 infects several cell types, including intestinal progenitor cells and mature enterocytes, in HIE cultures. RNA profiling of VA1-infected HIE uncovered that the host response to infection is dominated by interferon (IFN)-mediated innate immune responses. A comparison of the antiviral host response in non-transformed HIE and transformed human colon carcinoma Caco-2 cells highlighted significant differences between these cells, including an increased magnitude of the response in HIE. Additional studies confirmed the sensitivity of VA1 to exogenous IFNs, and indicated that the endogenous IFN response of HIE to curtail the growth of strains from all three clades. Genotypic variation in the permissiveness of different HIE lines to HAstV could be overcome by pharmacologic inhibition of JAK/STAT signaling. Collectively, our data identify HIE as a universal infection model for HAstV and an improved model of the intestinal epithelium to investigate enteric virus-host interactions.

Norovirus Escape from Broadly Neutralizing Antibodies Is Limited to Allostery-Like Mechanisms.

Ideal antiviral vaccines elicit antibodies (Abs) with broad strain recognition that bind to regions that are difficult to mutate for escape. Using 10 murine norovirus (MNV) strains and 5 human norovirus (HuNoV) virus-like particles (VLPs), we identified monoclonal antibody (MAb) 2D3, which broadly neutralized all MNV strains tested. Importantly, escape mutants corresponding to this antibody were very slow to develop and were distal to those raised against our previously studied antibody, A6.2. To understand the atomic details of 2D3 neutralization, we determined the cryo-electron microscopy (cryo-EM) structure of the 2D3/MNV1 complex. Interestingly, 2D3 binds to the top of the P domain, very close to where A6.2 binds, but the only escape mutations identified to date fall well outside the contact regions of both 2D3 and A6.2. To determine how mutations in distal residues could block antibody binding, we used molecular dynamics flexible fitting simulations of the atomic structures placed into the density map to examine the 2D3/MNV1 complex and these mutations. Our findings suggest that the escape mutant, V339I, may stabilize a salt bridge network at the P-domain dimer interface that, in an allostery-like manner, affects the conformational relaxation of the P domain and the efficiency of binding. They further highlight the unusual antigenic surface bound by MAb 2D3, one which elicits cross-reactive antibodies but which the virus is unable to alter to escape neutralization. These results may be leveraged to generate norovirus (NoV) vaccines containing broadly neutralizing antibodies. IMPORTANCE The simplest and most common way for viruses to escape antibody neutralization is by mutating residues that are essential for antibody binding. Escape mutations are strongly selected for by their effect on viral fitness, which is most often related to issues of protein folding, particle assembly, and capsid function. The studies presented here demonstrated that a broadly neutralizing antibody to mouse norovirus binds to an exposed surface but that the only escape mutants that arose were distal to the antibody binding surface. To understand this finding, we performed an in silico analysis that suggested that those escape mutations blocked antibody binding by affecting structural plasticity. This kind of antigenic region-one that gives rise to broadly neutralizing antibodies but that the virus finds difficult to escape from-is therefore ideal for vaccine development.