Incorporation of wild-type and C-terminally truncated human epidermal growth factor receptor into human immunodeficiency virus-like particles: insight into the processes governing glycoprotein incorporation into retroviral particles.

Previous results have indicated that incorporation of surface glycoprotein into retroviral particles is not a specific process and that many heterologous viral and cellular glycoproteins can be incorporated as long as they do not have long cytoplasmic C-terminal regions which were presumed to be sterically inhibitory. In this study, this concept has been directly examined by analyzing the incorporation of the wild-type human epidermal growth factor receptor (Wt-EGFR) and of a C-terminally truncated mutant of Wt-EGFR (Tr-EGFR) into human immunodeficiency virus (HIV)-like particles. Incorporation was directly analyzed at the protein level and by immunogold labelling of enriched HIV-like particles. In agreement with the above concept, Tr-EGFR, with only 7 C-terminal amino acids (aa), was efficiently incorporated into HIV-like particles. Incorporation of the Wt-EGFR species, with 542 C-terminal cytoplasmic aa, was reduced by a factor of about 5 in comparison to that of the Tr-EGFR species. However, the Wt-EGFR species was still very significantly present in the HIV-like particles. A series of control experiments verified that this represents genuine incorporation of Wt-EGFR into the membrane of HIV-like particles. These observations allow further speculation as to the processes governing glycoprotein incorporation into retroviral particles and indicate that the internal virus structure of HIV (in particular the matrix layer [MA]) can accommodate much larger heterologous cytoplasmic domains in incorporated glycoproteins than previously assumed.