Sorting of Marburg virus surface protein and virus release take place at opposite surfaces of infected polarized epithelial cells

Marburg virus, a filovirus, causes severe hemorrhagic fever with hitherto p oorly understood molecular pathogenesis. We have investigated here the vect orial transport of the surface protein GP of Marburg virus in polarized epi thelial cells. To this end, we established an MDCKII cell line that was abl e to express GP permanently (MDCK-GP). The functional integrity of GP expre ssed in these cells was analyzed using vesicular stomatitis virus pseudotyp es. Further experiments revealed that GP is transported in MDCK-GP cells ma inly to the apical membrane and is released exclusively into the culture me dium facing the epical membrane. When MDCKII cells were infected with Marbu rg virus, the majority of GP was also transported to the apical membrane, s uggesting that the protein contains an autonomous apical transport signal. Release of infectious progeny virions, however, took place exclusively at t he basolateral membrane of the cells, Thus, vectorial budding of Marburg vi rus is presumably determined by factors other than the surface protein.