Suppression of Leishmania RNA virus replication by capsid protein overexpression.

Some strains of the protozoan parasite genus Leishmania are persistently infected with single-segmented double-stranded RNA viruses, which are termed LRV. The function of these cytoplasmic viruses is unknown. In order to address the question of whether LRV affects the parasite's phenotype, pairs of isogenic LRV(+)-LRV- lines are required. Since the persistent nature of these viruses precludes de novo infection of virus-negative strains, LRV(+)-LRV- strains were transformed with a Leishmania expression vector expressing the LRV capsid protein with the aim of determining if LRV- promastigotes support capsid assembly and if LRV replication is affected by excess capsid protein. I found that in LRV- promastigotes, capsid protein was capable of self-assembly into virus-like capsids and that capsid overexpression in a naturally infected LRV+ line resulted in a progressive reduction in LRV copy number. Clonal lines derived from an LRV+ capsid overexpressor had no detectable levels of LRV. These results demonstrate that LRV replication can be inhibited and that a significant reduction of viral copy number has no effect on the parasite's viability in liquid medium.