Extensive C-terminal Deletion in Human Immunodeficiency Virus Type 1 Env Glycoprotein Arising After Long-term Culture of Chronically Infected Cells

Abstract

Human immunodeficiency virus type 1 (HIV-1) chronically infected (CI) cell lines were established from HIV-1,~B/LA~-infected MT-4 cells that survived acute infection. The HIV env gene expressed in the two longterm cultured cell lines differed from that of the lines cultured for shorter periods, by coding for a glycoprotein gpl60 that had the C terminus deleted. One long-term cultured cell line, CI-17, was studied in detail. An insertion of a premature stop codon in the env gene caused about 90 % of gpl60 molecules to be truncated (gpl60x), lacking both cytoplasmic and transmembrane domains; these species were secreted into the cell medium, and could form oligomers with other truncated gpl60 molecules as well as with their normal counterparts. CI-17 cells constantly yielded high levels of viral protein and relatively low quantities of infectious virus, without cytopathicity. However, acute infection of fresh MT-4 cells with CI-17-derived virus led to cytopathicity, the rate of which as well as the Env glycoprotein pattern depended on multiplicity: (i) using an infection dose of 10 -4 IDs0/cell, cells died 7 to 8 days post-infection with normal gpl60 synthesis predominating; (ii) with l0 -2 IDs0, gpl60x was produced as early as 48 h postinfection and cell death was delayed. Predominant gpl60x formation occurred again when new CI cell lines were obtained with CI-17-derived virus. Thus, two human immunodeficiency virus variants, a normal and a defective one, are persistently expressed in CI-17 cells. The other long-term cultured CI cell line also expressed gpl60 with a similar (albeit slightly longer) deletion of a C-terminal region in most molecules, but the cell lines that were cultured for shorter periods did not. These results suggest that the emergence of HIV variants with a C-terminal deletion in the Env glycoprotein, which coexist with normal virus, may play a role in maintaining the long-term growth capacity and viability of CI ceils.

Identification of Two Sequences in the Cytoplasmic Tail of the Human Immunodeficiency Virus Type 1 Envelope Glycoprotein That Inhibit Cell Surface Expression

“…7). Due to a direct interaction between Env and viral matrix proteins, the carboxy-terminal end of the gp41 cytoplasmic domain appears to influence the incorporation of glycoproteins into virions (13,15,16,22,25,28,39,72,73). Thus, the gp160 mutant with the short internal deletion of is1 and is2, syngp160⌬is1-2, which is considerably more highly expressed at the cell surface in comparison to wild-type Env, should still be incorporated into virus particles.…”

“…Deletion of the carboxy terminus, which has been observed after long-term culture of chronically HIV-1-infected cells, increases both protein transport and processing of gp160 but leads to a decreased incorporation of glycoproteins into virions, probably because of a direct interaction between Env and viral matrix proteins (13,15,18,22,25,28,39,72,73). Moreover, deletion of the cytoplasmic domain appears to reduce infectivity of virions due to postentry events (26,72).…”