Elevated endosomal pH in HeLa cells overexpressing mutant dynamin can affect infection by pH-sensitive viruses

Many viruses gain access to the cell via the endosomal route and require lo w endosomal pH for infectivity. The GTPase dynamin is essential for clathri n-dependent endocytosis, and in HeLa cells overexpressing the nonfunctional dynamin(K44A) mutant the formation of clathrin-coated vesicles is halted. HRV2, a human minor group rhinovirus, is internalized by members of the low -density lipoprotein receptor family in a clathrin-independent manner. The low endosomal pH then leads to conversion of the capsid to C-antigen, which is required for release (uncoating) and transfer of the viral RNA into the cytosol and de novo synthesis of infectious virus. We here demonstrate tha t overexpression of dynamin(K44A) reduces this antigenic conversion and res ults in diminished viral synthesis. In contrast, lysosomal degradation is u naffected. The kinetics of the formation of C-antigen in vitro and in vivo suggest that the pH in endosomes is elevated by about 0.4 units upon overex pression of dynamin(K44A). As a consequence, HRV2 uncoating is diminished e arly after internalization but attains control levels upon prolonged intern alization. Thus, overexpression of dynamin(K44A), in addition to traffickin g defects, results in an elevated endosomal pH and thereby affects virus in fection and most likely endosomal sorting and processing.