Extensive C-terminal deletion in human immunodeficiency virus type 1 Env glycoprotein arising after long-term culture of chronically infected cells.

Human immunodeficiency virus type 1 (HIV-1) chronically infected (CI) cell lines were established from HIV-1HIB/LAI-infected MT-4 cells that survived acute infection. The HIV env gene expressed in the two long-term cultured cell lines differed from that of the lines cultured for shorter periods, by coding for a glycoprotein gp 160 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 gp160 molecules to be truncated (gp160x), lacking both cytoplasmic and transmembrane domains; these species were secreted into the cell medium, and could form oligomers with other truncated gp160 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) ID50/cell, cells died 7 to 8 days post-infection with normal gp160 synthesis predominating; (ii) with 10(-2) ID50, gp160x was produced as early as 48 h post-infection and cell death was delayed. Predominant gp160x 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 gp160 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 cells.

[Pathological cleavage of human immunodeficiency virus gp160 protein in infected cells as a probable factor for infection becoming chronic]. / Pathologicheskoe razrezanie belka gp160 birusa immunodefitsita cheloveka v zarazhennykh kletkakh kak veroiatnyi faktor khronizatsii infektsii.

The synthesis of HIV-1 (IIIb isolate) structural protein in chronically (CI) and acutely infected (AI) MT4 cells was studied. During long-term cultivation the CI system was characterized by high involvement of the cells into infection (up to 100%), high level of virus-specific protein synthesis, moderate virus yield, but absence of any virus-induced cytopathic effects and normal growth potential of infected cells. AI cells demonstrated a similar level of synthesis of virus specific proteins, higher virus yield, and rapid progression of cytopathicity followed by total cell death. Most of the HIV gp160 protein molecules undergo rapid cleavage in the region between the point of conventional cleavage and the transmembrane domain, being removed from the physiologically competent pool, but a small portion of gp160s undergo apparently normal intracellular development. According to our data, the two HIV variants (normal and defective) persist in CI system and pathological cleavage of defective virus gp160 protein results most probably in chronization of infection.