A hyperfusogenic gibbon ape leukemia envelope glycoprotein: targeting of a cytotoxic gene by ligand display.
An important goal in cancer gene therapy is the development of novel targeted cytotoxic genes. The observation that transfection of a GaLV envelope glycoprotein lacking an R peptide into human cells results in considerable cell-cell fusion and subsequent cell death prompted us to explore the potential for using this fusogenic membrane glycoprotein (FMG) as a targeted cytotoxic gene. As proof of principle, we therefore displayed epidermal growth factor (EGF) on the N terminus of GaLV envelope glycoproteins both with and without an R peptide (GaLV R+ and GaLV R-). Transfection of the GaLVR+ envelope expression plasmids did not cause cell-cell fusion. The GaLV R+ envelopes were incorporated into retroviral vectors whose infectivity was investigated on EGF receptor-positive and -negative cells. The vector incorporating an N-terminally unmodified envelope was able to infect all human cell lines tested. Infectivity of the vector incorporating an envelope on which EGF was displayed was restricted on EGF receptor-positive cells (but not on EGF receptor-negative cells) and could be restored by protease cleavage of the displayed domain or competition with exogenous ligand. The cell-cell fusion capacity of the GaLV R- envelope glycoproteins (N-terminally unmodified and with N-terminal display of both EGF and insulin-like growth factor I [IGF-I]) was investigated by plasmid DNA transfection. While the N-terminally unmodified GaLV R- fused all human cell types tested, fusogenicity of GaLV R- on which EGF or IGF-I was displayed was considerably restricted on receptor-positive cells. "Reciprocal" competition experiments showed that fusogenicity could be restored by competition only with the relevant exogenous ligand. Thus the specificity of cell-cell fusion by a hyperfusogenic GaLV envelope glycoprotein can be regulated by N-terminal display of growth factor ligands. There is therefore significant potential for further development of the targeting of the cell-killing capability of this fusogenic viral glycoprotein by using strategies similar to those we have developed for the targeting of retroviral vectors.
Fielding
A K
AK
Hematology and Molecular Medicine, Mayo Clinic, Rochester, MN 55902, USA.
Chapel-Fernandes
S
S
Chadwick
M P
MP
Bullough
F J
FJ
Cosset
F L
FL
Russell
S J
SJ
D000595:Amino Acid Sequence; D000818:Animals; D016923:Cell Death; D002459:Cell Fusion; D004815:Epidermal Growth Factor / Q000235:genetics / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006023:Glycoproteins / Q000235:genetics*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D017989:Leukemia Virus, Gibbon Ape / Q000235:genetics*; D008024:Ligands; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics*; D014759:Viral Envelope Proteins / Q000235:genetics*
D006023:Glycoproteins; D008024:Ligands; D009842:Oligopeptides; C080708:R peptide; D011993:Recombinant Fusion Proteins; D014759:Viral Envelope Proteins; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D066246:ErbB Receptors