The conserved dileucine- and tyrosine-based motifs in MLV and MPMV envelope glycoproteins are both important to regulate a common Env intracellular trafficking.

BACKGROUND: Retrovirus particles emerge from the assembly of two structural protein components, Gag that is translated as a soluble protein in the cytoplasm of the host cells, and Env, a type I transmembrane protein. Because both components are translated in different intracellular compartments, elucidating the mechanisms of retrovirus assembly thus requires the study of their intracellular trafficking. RESULTS: We used a CD25 (Tac) chimera-based approach to study the trafficking of Moloney murine leukemia virus and Mason-Pfizer monkey virus Env proteins. We found that the cytoplasmic tails (CTs) of both Env conserved two major signals that control a complex intracellular trafficking. A dileucine-based motif controls the sorting of the chimeras from the trans-Golgi network (TGN) toward endosomal compartments. Env proteins then follow a retrograde transport to the TGN due to the action of a tyrosine-based motif. Mutation of either motif induces the mis-localization of the chimeric proteins and both motifs are found to mediate interactions of the viral CTs with clathrin adaptors. CONCLUSION: This data reveals the unexpected complexity of the intracellular trafficking of retrovirus Env proteins that cycle between the TGN and endosomes. Given that Gag proteins hijack endosomal host proteins, our work suggests that the endosomal pathway may be used by retroviruses to ensure proper encountering of viral structural Gag and Env proteins in cells, an essential step of virus assembly.

Targeted retroviral vectors displaying a cleavage site-engineered hemagglutinin (HA) through HA-protease interactions.

We report here a targeting method that exploits the expression pattern of cell surface proteases to induce gene delivery to specific tissues. We describe retroviral vectors harboring modified surface glycoproteins derived from an avian influenza virus hemagglutinin (HA) for which the cell entry properties, dependent on HA cleavage by producer cells, were conditionally blocked at a postbinding step by insertion of matrix metalloproteinase (MMP) substrates. We demonstrate that such vectors induce gene transfer, both in vitro and in mice harboring human tumor xenografts, only through contact with target cells expressing MMPs that cleave the substrate introduced into the recombinant HA. This selective gene transfer in MMP-rich cells was specifically inhibited by 1,10-phenanthroline, a broad-range MMP inhibitor. Importantly, such MMP-activatable vectors selectively transduced MMP-rich cells in heterogeneous populations containing MMP-rich and MMP-poor cells. These vectors will allow useful gene transfer applications into target cells exhibiting specific protease activities.