Journal of Virology, May 2001, p. 4150-4157, Vol. 75, No. 9
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.9.4150-4157.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Molecular Virology Laboratory, Centre for Immunology and Cancer Research, P.A. Hospital,1 and Queensland Cancer Fund Laboratory of Experimental Oncology, Department of Pathology,2 University of Queensland, Brisbane, Australia
Received 8 November 2000/Accepted 1 February 2001
The initial step in viral infection is the attachment of the virus
to the host cell via an interaction with its receptor. We have
previously shown that a receptor for human papillomavirus is the
6
integrin. The
6 integrin is involved in the attachment of epithelial
cells with the basement membrane, but recent evidence suggests that
ligation of many integrins results in intracellular signaling events
that influence cell proliferation. Here we present evidence that
exposure of A431 human epithelial cells to human papillomavirus type 6b
L1 virus-like particles (VLPs) results in a dose-dependent increase in
cell proliferation, as measured by bromodeoxyuridine incorporation.
This proliferation is lost if VLPs are first denatured or incubated
with a monoclonal antibody against L1 protein. The MEK1 inhibitor
PB98059 inhibits the VLP-mediated increase in cell proliferation,
suggesting involvement of the Ras-MAP kinase pathway. Indeed, VLP
binding results in rapid phosphorylation of the
4 integrin upon
tyrosine residues and subsequent recruitment of the adapter protein Shc
to
4. Within 30 min, the activation of Ras, Raf, and Erk2 was
observed. Finally, the upregulation of c-myc mRNA was
observed at 60 min. These data indicate that human papillomavirus type
6b is able to signal cells via the Ras-MAP kinase pathway to induce
cell proliferation. We hypothesize that such a mechanism would allow
papillomaviruses to infect hosts more successfully by increasing the
potential pool of cells they are able to infect via the initiation of
proliferation in resting keratinocyte stem and suprabasal cells.
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