Intracellular Signaling and Desmoglein 2 Shedding Triggered by Human Adenoviruses Ad3, Ad14, and Ad14P1

Abstract

We recently discovered that desmoglein 2 (DSG2) is a receptor for human adenovirus species B serotypes Ad3, Ad7, Ad11, and Ad14. Ad3 is considered to be a widely distributed human pathogen. Ad3 binding to DSG2 triggers the transient opening of epithelial junctions. Here, we further delineate the mechanism that leads to DSG2-mediated epithelial junction opening in cells exposed to Ad3 and recombinant Ad3 fiber proteins. We identified an Ad3 fiber knob-dependent pathway that involves the phosphorylation of mitogen-activated protein (MAP) kinases triggering the activation of the matrix-metalloproteinase ADAM17. ADAM17, in turn, cleaves the extracellular domain of DSG2 that links epithelial cells together. The shed DSG2 domain can be detected in cell culture supernatant and also in serum of mice with established human xenograft tumors. We then extended our studies to Ad14 and Ad14P1. Ad14 is an important research and clinical object because of the recent appearance of a new, more pathogenic strain (Ad14P1). In a human epithelial cancer xenograft model, Ad14P1 showed more efficient viral spread and oncolysis than Ad14. Here, we tested the hypothesis that a mutation in the Ad14P1 fiber knob could account for the differences between the two strains. While our X-ray crystallography studies suggested an altered three-dimensional (3D) structure of the Ad14P1 fiber knob in the F-G loop region, this did not significantly change the fiber knob affinity to DSG2 or the intracellular signaling and DSG2 shedding in epithelial cancer cells. IMPORTANCE A number of widely distributed adenoviruses use the epithelial junction protein DSG2 as a receptor for infection and lateral spread. Interaction with DSG2 allows the virus not only to enter cells but also to open epithelial junctions which form a physicalbarrier to virus spread. Our study elucidates the mechanism beyond virus-triggered junction opening with a focus on adenovirus serotype 3. Ad3 binds to DSG2 with its fiber knob domain and triggers intracellular signaling that culminates in the cleavage of the extracellular domain of DSG2, thereby disrupting DSG2 homodimers between epithelial cells. We confirmed this pathway with a second DSG2-interacting serotype, Ad14, and its recently emerged strain Ad14P1. These new insights in basic adenovirus biology can be employed to develop novel drugs to treat adenovirus infection as well as be used as tools for gene delivery into epithelial tissues or epithelial tumors. W e recently discovered that desmoglein 2 (DSG2) is a receptor for human adenovirus species B serotypes Ad3, Ad7, Ad11, and Ad14 (1-3). DSG2 is a calcium-binding transmembrane glycoprotein belonging to the cadherin protein family. In epithelial cells of the respiratory, gastrointestinal, and urinary tracts, DSG2 is a component of the cell-cell adhesion structure (4). It is well established that in addition to maintaining cell adhesion, DSG2 is also involved in intracellular signaling (5). Its cytoplasmic tail interacts with a series of proteins, including plakoglobi...

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“…It has been well documented that the sheddase disintegrin and metalloproteinase 17 (ADAM17) plays an important role in the pathogenesis of cancer and is highly up‐regulated in many malignancies, including SCCs of the skin, esophagus, head and neck, and lung (34–36). Furthermore, ADAM17 targets and cleaves Dsg2, resulting in a shed ~95‐kDa ectodomain and a membrane‐anchored ~65‐kDa fragment, similar in size to the product detected here in EVs (37, 38). We posit that loss of the full‐length Dsg2 in SCC EVs may result from higher levels of ADAM17 activation.…”

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