A 50-kDa membrane protein mediates sialic acid-independent binding and infection of conjunctival cells by adenovirus type 37

The ocular tropism of adenovirus type 37 (Ad37) does not correlate with the wide distribution of the 46-kDa coxsackievirus and adenovirus receptor (CA R), the major receptor for most adenovirus serotypes. We previously found t hat Ad37 infects and binds well to conjunctival cells (Chang C), but poorly to lung epithelial (A549) cells that express CAR and hypothesized that thi s serotype uses a distinct receptor that is selectively expressed on conjun ctival cells. To test this, we produced particles of a fiber-deleted Ad5 ve ctor containing the Ad37 fiber protein. The pseudotyped" vector infected Ch ang C cells better than A549 cells using a CAR-independent pathway. Ad37 bi nding was calcium-dependent and was abolished by protease digestion of cell surface proteins. Using a virus overlay protein blot assay (VOPBA), we det ected calcium-dependent Ad37 binding to 50- and 60-kDa membrane proteins on permissive Chang C cells. In contrast, calcium-dependent binding was detec ted with only the 60-kDa protein on nonpermissive A549 cells. Ad19p, a clos ely related serotype that failed to bind to conjunctival cells, recognized the 60-kDa, but not the 50-kDa, protein. Ad37 has been reported to use sial ic acid instead of CAR as a cell receptor on A549 cells. Pretreatment of Ch ang C cells with neuraminidase abolished Ad37 binding to only the 60-kDa pr otein, suggesting that sialic acid mediates Ad37 binding to the 60-kDa prot ein. The pseudotyped Ad37 vector was also able to infect neuraminidase-trea ted Chang C cells. Thus, subgroup D adenoviral binding to the 50-kDa protei n is calcium-dependent and cell type- and serotype-specific, whereas bindin g to the 60-kDa protein is not necessary for infection of conjunctival cell s. Together. these data suggest that the 50-kDa protein is the major recept or for Ad37 on conjunctival cells. (C) 2001 Academic Press.