Peptides derived from plant virus VPg protein inhibit eIF4E oncogene

Viruses of the Potyviridae family have VPg protein covalently attached to the 5′ end of their linear RNA genome. The protein interacts with the host translation initiation factor eIF4E that occurs in plant cells in two isoforms, one being the preferable target of a given VPg, the remaining one still acting in host protein synthesis. In animal cells only one form of eIF4E is directly involved in protein synthesis. The human eIF4E is known to be an oncogene; elevated expression of eIF4E leads to oncogenic transformation, cancers in animal models and poor prognosis in human cancers, while reduction of the eIF4E level can reverse the transformed phenotype. We show that VPg protein delivery to cells containing only one eIF4E isoform involved in protein synthesis resulted in immobilization of eIF4E in the cytoplasm. The region of VPg involved in the interaction with eIF4E has been partially identified. Peptides derived from this region interacted better with eIF4E than complete VPg protein. Here we characterized one of VPg peptides, VPg5 and we show that VPg5 delivered to colon carcinoma HCT116 cells is able to inhibit cell growth, which is accompanied by reduction in eIF4E level.