VIRUS-MEDIATED RELEASE OF ENDOSOMAL CONTENT IN-VITRO - DIFFERENT BEHAVIOR OF ADENOVIRUS AND RHINOVIRUS SEROTYPE-2

Endosomal penetration by nonenveloped viruses might be accomplished by either local breakdown of the endosomal membrane (e.g., adenovirus) o r formation of a membrane-spanning pore by capsid proteins. Uncoating of the nonenveloped virus human rhinovirus serotype 2 (HRV2) has been shown to occur from late endosomes and to be entirely dependent on the acidic pH in this compartment (Prchla, E., E. Kuechler, D. Blaas, and R. Fuchs. 1994. J. Virol. 68: 3713-3723). To investigate further the mechanism of uncoating of HRV2, an in vitro assay was established to t est viruses or virus-derived peptides for their capacity to release co internalized biotin-dextran of different molecular mass (10 and 70 kD) from isolated endosomes. The suitability of the: assay was demonstrat ed by use of a fusogenic peptide derived from influenza virus hemagglu tinin (GALA-INF3). Whereas adenovirus induced a low pH-dependent relea se of up to 46% of the internalized biotin-dextran and did not show an y significant size selectivity (as expected for endosome disruption), HRV2 mediated release of 27% of the 10 kD dextran and only traces of t he 70-kD dextran. Similarly, GALA-INF3-induced release of biotin-dextr an was also size dependent. The potential role of the capsid protein V P1 in HRV2 uncoating in vivo was also substantiated in our in vitro sy stem using an amphipatic, NH2-terminal peptide of VP1. Taken together, these data favor the model of a specific pore-forming mechanism for H RV2 uncoating which is in contrast to the membrane-disrupting mechanis m of adenovirus.