Enhancement of bovine leukemia virus-induced syncytia formation by di- and tripeptides.

Short hydrophobic peptides were previously shown to inhibit infectivity of para-
and orthomyxoviruses. We tested the ability of a series of di- and tripeptides to
interfere with cell fusion induced by bovine leukemia virus (BLV). Peptides
containing a hydrophobic contribution and/or a positive net charge strongly
enhanced syncytia formation induced by BLV on CC81 indicator cells. The size of
the multinucleated cells was strongly increased (up to 10-fold) in the presence
of the enhancer peptides whereas no effect was observed on the indicator cells in
the absence of BLV. The peptides thus amplified the fusion process initiated by
BLV envelope glycoproteins. The effect was dose-dependent at concentrations
ranging from 20 to 640 microM and did not result from an increased expression of
BLV proteins. The peptides did not compete with anti-gp51 monoclonal antibodies
for the recognition of eight well-defined epitopes of gp51. We consequently
hypothesize that the enhancer peptides interact with the membrane of
BLV-producing cells and/or indicator cells and propose a model based on molecular
modeling.