The Coxsackie- and adenovirus receptor (CAR) is a transmembrane cell adhesion molecule with two extracellular immunoglobulin domains. It is located at cell-cell contacts, for example at intercalated discs between cardiomyocytes or at tight junctions in lung and intestines. CAR forms homodimers with its membrane-distal immunoglobulin domain D1 and is involved in cell adhesion, proliferation, and migration. It acts as a pathfinder protein during embryogenesis and during tissue remodelling after injuries. Next to its physiological functions, CAR aroused interest due to its role in cell entry and attachment of Coxsackie- and adenoviruses. Both viruses use CAR D1 as binding site and are a major cause for viral-induced myocarditis.<br />I investigated three different mechanisms that might influence CAR´s interaction with viruses. First, five genetic variants in the CAR-coding gene that are most frequent in human population were analysed regarding their influence on cell adhesion and proliferation as well as on virus internalisation. No differences were observed among the variants compared to wild type CAR. This gives further evidence to the idea of CAR as an indispensable protein during embryogenesis, for which until now no pathogenic genetic variant has been described.<br />Second, I designed peptides to use them as virus entry inhibitors. Synthetic peptides that inhibit virus-receptor interactions have not been described for adenoviruses yet. In this work, peptides based on known interaction motifs either of CAR D1 or of adenovirus binding knob were used. No peptide inhibited adenovector cell entry significantly. Probably, peptide binding was too weak to compete with virus-CAR interaction.<br />Third, several soluble proteases that are secreted by immune cells during myocarditis were tested for their ability to shed CAR, i.e. to release its extracellular domain through proteolysis. Soluble CAR extracellular domain could function as a virus trap and inhibit ongoing viral infections. I used human soluble or membranous CAR expressed by *E. coli* or mammalian cells to screen for potential ectodomain sheddases. For neutrophil elastase, both incubation time and protease concentration comply with a physiologically relevant process. CAR cleavage products comprise complete D1 domain, which could make them biologically active virus traps. Thus, CAR-shedding through neutrophil elastase, which is described here for the first time, might be a host defense mechanism against Coxsackie- and adenoviruses.
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