Canine adenovirus type 2 attachment and internalization: Coxsackievirus-adenovirus receptor, alternative receptors, and an RGD-independent pathway

The best-characterized receptors for adenoviruses (Ads) are the coxsackievirus-ad receptor (CAR) and integrins alpha (v)beta (5) and alpha (v)beta (3), which facilitate entry. The alpha (v) integrins recognize an Arg-Gly-Asp (RGD) motif found in some extracellular matrix proteins and in the penton base in most human Ads. Using a canine adenovirus type 2 (CAV-2) vector, we found that CHO cells that express CAR but not wild-type CHO cells are susceptible to CAV-2 transduction. Cells expressing alpha (M)beta (2) integrins or major histocompatibiIity complex class I (MHC-I) molecules but which do not express CAR were not transduced. Binding assays showed that CAV-2 attaches to a recombinant soluble form of CAR and that Ad type 5 (Ad5) fiber, penton base, and an anti-CAR antibody partially blocked attachment. Using fluorescently labeled CAV-2 particles, we found that in some cells nonpermissive for transduction, inhibition was at the point of internalization and not attachment. The transduction efficiency of CAV 2, which lacks an RGD motif, surprisingly mimicked that of Ad5 when tested in cells selectively expressing alpha (v)beta (5) and alpha (v)beta (3) integrins. Our results demonstrate that CAV-2 transduction is augmented by CAR and possibly by alpha (v)beta (5), though transduction can be CAR and alpha (v)beta (3/5) independent but is alpha (M)beta (2), MHC-I, and RGD independent, demonstrating a transduction mechanism which is distinct from that of Ad2/5.