Abstract
Purpose: :
Previous work suggests that the Retinal Pigment Epithelium (RPE) is more susceptible to Adenoviral infection than most other epithelia in the organism. The purpose of this study was to investigate the molecular mechanisms responsible for such phenotype.
Methods: :
Fully polarized epithelial cell lines of kidney, renal, lung, thyroid and RPE origins were infected from the apical surface with a GFP-encoding, replication-deficient serotype-5 Adenovirus and infections were quantified by fluorometry. The surface localization of the Coxsackie and Adenovirus Receptor (CAR), a basolateral and tight junctional protein in all epithelia studied to date, was visualized by immunofluorescence and its intracellular trafficking was tracked by microscopy and biochemical assays.
Results: :
The increased susceptibility of RPE to adenovirus infection correlated with the absence of the clathrin adaptor AP1B, and the striking apical localization of CAR. Additional experiments showed that in other epithelia, CAR is unavailable to apical adenoviruses because AP1B sorts CAR towards the basolateral membrane. Knock-down of AP1B in the kidney cell line MDCK promoted mistargeting of CAR from recycling endosomes to the apical surface and increased infectivity with apical adenoviruses.
Conclusions: :
In summary, we have demonstrated that RPE cells lack a major clathrin adaptor employed by most epithelia to target proteins to the basolateral plasma membrane. This results in apical localization of the adenovirus receptor CAR, a basolateral and tight junctional protein in most epithelia, to the apical surface or RPE, and higher susceptibility to infection by these viruses. Our findings illustrate how normal variations in the trafficking machinery result in changes in tissue-specific infection.
Keywords: retinal pigment epithelium • CAR • adenovirus