Biology Reference
In-Depth Information
cells with EV1 can cause a rapid clustering of the integrins on the plasma
membrane.
16
The receptor clustering might be an important mechanism
triggering integrin signaling and initiating virus entry (Fig. 1).
In contrast to many other viruses and their integrin receptors, bind-
ing of the
2I domain to EV1 does not directly induce uncoating of
the virus.
16
Instead, the interaction seems to stabilize the virus. Therefore,
it seems likely that the conditions needed for viral uncoating exist only
inside cellular structures. Our sucrose gradient sedimentation analysis of
the viral particles suggested that, while inside membrane vesicles, viral
uncoating starts approximately 30 min post infection (p.i.), when
approximately 25% of the virus particles are in the 80S form and repre-
sent capsids that have released their RNA genome.
9
α
1 Integrin Leads to Rapid
Internalization of the Virus-Receptor Complexes
Clustering of
α
2
β
We have recently tested the hypothesis that the integrin-mediated
entry of EV1 is initiated by virus-dependent receptor clustering. For
this purpose, we have used antibodies against
integrin and sec-
ondary antibodies to initiate clustering, and then followed living cells
under a confocal microscope (Fig. 2.; Upla
et al
., 2004; see http://
www.molbiolcell.org/cgi/content/full/E03-08-0588/DC1 for the
live cell videos). Immediately after the clusters formed they started a lat-
eral movement along the cell surface. During the process smaller clusters
seemed to have the tendency to fuse together. Based on the imaging of
cells expressing actin-green fluorecent protein (GFP) chimeras, we
propose that the integrin clusters may follow microfilaments. Already
during the first 15 minutes after the formation of integrin clusters
their internalization started. Thus the antibody-dependent integrin
clusters were internalized in the same way as EV1, suggesting that
receptor clustering is sufficient to initiate the entry process.
α 2β 1
EV1 Internalization and Integrin Signaling
The binding of integrins to their ligands can induce both a conforma-
tional change in the receptors and receptor clustering. The integrins
