A replication-deficient adenovirus enhances liposome-mediated nucleic acid transfer into a stable cell line expressing T7 RNA polymerase

Rotavirus capsid protein VP5* permeabilizes membranes

Proteolytic cleavage of the VP4 outer capsid spike protein into VP8* and VP5* proteins is required for rotavirus infectivity and for rotavirus-induced membrane permeability. In this study we addressed the function of the VP5* cleavage fragment in permeabilizing membranes. Expressed VP5* and truncated VP5* proteins were purified by nickel affinity chromatography and assayed for their ability to permeabilize large unilamellar vesicles (LUVs) preloaded with carboxyfluorescein (CF). VP5* and VP5* truncations, but not VP4 or VP8*, permeabilized LUVs as measured by fluorescence dequenching of released CF. Similar to virus-induced CF release, VP5*-induced CF release was concentration and temperature dependent, with a pH optimum of 7.35 at 37 degrees C, but independent of the presence of divalent cations or cholesterol. VP5*-induced permeability was completely inhibited by VP5*-specific neutralizing monoclonal antibodies (2G4, M2, or M7) which recognize conformational epitopes on VP5* but was not inhibited by VP8*-specific neutralizing antibodies. In addition, N-terminal and C-terminal VP5* truncations including residues 265 to 474 are capable of permeabilizing LUVs. These findings demonstrate that VP5* permeabilizes membranes in the absence of other rotavirus proteins and that membrane-permeabilizing VP5* truncations contain the putative fusion region within predicted virion surface domains. The ability of recombinant expressed VP5* to permeabilize membranes should permit us to functionally define requirements for VP5*-membrane interactions. These findings indicate that VP5* is a specific membrane-permeabilizing capsid protein which is likely to play a role in the cellular entry of rotaviruses.

Mechanism of adenovirus improvement of cationic liposome-mediated gene transfer

Substantial effort has been focused on the development of highly efficient gene transfer strategies. Although viral and non-viral methods have been elaborated, mechanisms of gene delivery are still poorly understood. We exploited our recent observation that replication-deficient type 5 adenovirus dramatically enhances lipofectAMINE-mediated gene transfer (lipoadenofection) in differentiated cells to elucidate the mechanism of adenovirus action in this process. Heat-induced denaturation of viral capsid abolishes adenovirus action whereas inactivation of viral genome by short treatment with UV has no effect. Electron microscopic observations reveal the formation of a complex containing adenovirus and lipofectAMINE which probably carries DNA into cells via endocytosis. Anti-adenovirus antiserum or monoclonal anti-alpha(v)beta3 integrin antibody inhibits lipoadenofection, at least partially. Neutralization of endosomal compartments with chloroquine, ammonium chloride or monensin does not prevent adenovirus improvement of gene transfer. Hence, adenovirus-lipofectAMINE-DNA complexes in which viral particles are each encompassed by three lipid layers, penetrate cells via an endocytic pathway involving probably the adenovirus receptor and alpha(v)beta3 integrin. The resulting efficient transfer and expression of plasmid DNA proceeds from a mechanism in which adenoviral endosomolytic activity appears to be required while viral genome is not essential.