Expression of human endogenous retrovirus type K envelope glycoprotein in insect and mammalian cells.
The human endogenous retrovirus type K (HERV-K) family codes for the human teratocarcinoma-derived retrovirus (HTDV) particles. The existence of the envelope protein (ENV) of HERV-K encoded by the subgenomic env mRNA has not yet been demonstrated. To study the genetic requirements for successful expression of ENV, we have constructed a series of recombinant HERV-K env expression vectors for infection and transfection experiments in insect cells and mammalian cells, respectively. Six baculovirus constructs bearing full-length or truncated HERV-K env with or without homologous or heterologous signal peptides were used for infections of insect cells. All recombinant baculoviruses yielded ENV proteins with the expected molecular masses. The full-length 80- to 90-kDa HERV-K ENV protein including the cORF leader sequence was glycosylated in insect cells. In addition, the 14-kDa cORF protein was expressed due to splicing of the full-length env mRNA. The ENV precursor protein is not cleaved to the surface (SU) and transmembrane (TM) glycoproteins; it does not appear on the surface of infected insect cells and is not secreted into the medium. For ENV expression in COS cells, plasmid vectors harboring the cytomegalovirus immediate-early promoter/intron A element and the tissue plasminogen activator (t-PA) signal peptide or the homologous HERV-K signal peptide upstream of the env gene were employed. Glycosylated and uncleaved ENV was expressed as in GH teratocarcinoma cells but at higher levels. The heterologous t-PA signal sequence was instrumental for expression of HERV-K ENV on the cell surface. Hence, we have shown for the first time that the HERV-K env gene has the potential to be expressed as a full-length envelope protein with appropriate glycosylation. In addition, our data provide explanations for the lack of infectivity of HERV-K/HTDV particles.
Tönjes
R R
RR
Paul-Ehrlich-Institut, Langen, Germany. Toenjes@em.uni-frankfurt.de
Limbach
C
C
Löwer
R
R
Kurth
R
R
D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology; D001483:Base Sequence; D019556:COS Cells; D003001:Cloning, Molecular; D004279:DNA, Viral; D015870:Gene Expression; D015686:Gene Products, env / Q000235:genetics* / Q000276:immunology; D006031:Glycosylation; D006801:Humans; D008969:Molecular Sequence Data; D011817:Rabbits; D012190:Retroviridae / Q000235:genetics* / Q000276:immunology; D018411:Spodoptera / Q000166:cytology; D014407:Tumor Cells, Cultured
D000914:Antibodies, Viral; D004279:DNA, Viral; D015686:Gene Products, env