N. Bayer et al., Inhibition of clathrin-dependent endocytosis has multiple effects on humanrhinovirus serotype 2 cell entry, J BIOL CHEM, 276(6), 2001, pp. 3952-3962
Minor group human rhinoviruses (exemplified by human rhinovirus serotype 2
(HRV2)) use members of the low density lipoprotein receptor family for cell
entry; all these receptors possess clathrin-coated pit localization signal
s. Viral infection should thus be inhibited under conditions of impaired cl
athrin-mediated endocytosis. However, Madshus et at reported an increase in
the cytopathic effect of HRV2 infection in HEp-2 cells upon suppression of
clathrin-dependent endocytosis by hypotonic shock and potassium depletion
(Madshus, I. H., Sandvig, K., Olsnes, S., and van Deurs, B. (1987) J. Cell,
Physiol. 131, 14-22.) To resolve this apparent contradiction, we investiga
ted the binding, internalization, conformational changes, and productive un
coating of HRV2 in HeLa cells subjected to hypotonic shock and potassium de
pletion. This treatment led to an increase in HRV2 binding, with internaliz
ation being barely affected. The generation of C-antigenic particles requir
ing pH less than or equal to5.6 was strongly reduced due to an elevation of
the pH in endosomal compartments. However, K+ depletion only slightly affe
cted de novo viral protein synthesis, suggesting that productivity of viral
RNA in the cytoplasm is enhanced and thus compensates for the reduction in
C-antigenic particles. The distinct steps in the entry pathway of HRV2 are
thus differently influenced by potassium depletion. Viral internalization
under conditions of inhibited clathrin-dependent endocytosis without the ne
ed to disturb the ionic milieu was confirmed in HeLa cells overexpressing t
he nonfunctional dynamin-1 mutant K44A. Unexpectedly, overexpression of dyn
amin-1 K44A resulted in elevated endosomal pH compared with overexpression
of wild-type dynamin.