During viral infections, the sites

During viral infections, the sites of virus replication
represent complex microenvironments whose effects on
viral infection remain to be understood. In contrast to
cytokines (Stark et al., 1998), the implication of proteases,
which are produced in large amounts by inflammatory
cells (Steinhoff et al., 2005), still remains enigmatic.
Extracellular proteases are known to increase infectivity
of several viruses through the cleavage of virion proteins
necessary to pursue the viral life cycle (Zhirnov et al.,
2002), but the possibility that such a phenomenon could be
mediated through cell signalling has never been documented.
The aim of our study was to test this hypothesis by
using the herpesvirus model of Pseudorabies virus (PRV)
(Klupp et al., 2004; Mettenleiter, 2002; Ray & Enquist,
2004). We report here that trypsin increases viral production
by PRV-infected cells through activation of the
ERK1/2 pathway.