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-1(IIIB/LAI)-infected MT-4 cells t hat survived acute infection The HIV env gene expressed in the two lon g-term cultured cell lines differed from that of the lines cultured fo r shorter periods, by coding for a glycoprotein gp160 that had the C t erminus deleted. One long-term cultured cell line, CI-17, was studied in detail. An insertion of a premature stop codon in the env gene caus ed about 90 % of gp160 molecules to be truncated (gpl60x), lacking bot h cytoplasmic and transmembrane domains; these species were secreted i nto the cell medium, and could form oligomers with other truncated gp1 60 molecules as well as with their normal counterparts. CI-17 cells co nstantly yielded high levels of viral protein and relatively low quant ities of infectious virus, without cytopathicity. However, acute infec tion 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 o n multiplicity: (i) using an infection dose of 10(-4) ID50/cell, cells died 7 to 8 days post-infection with normal gp160 synthesis predomina ting; (ii) with 10(-2) ID50, gpl60x was produced as early as 48 h post infection and cell death was delayed. Predominant gpl60x formation occ urred again when new CI cell lines were obtained with CI-17-derived vi rus. Thus, two human immunodeficiency virus variants, a normal and a d efective one, are persistently expressed in CI-17 cells. The other lon g-term cultured CI cell line also expressed gp160 with a similar (albe it slightly longer) deletion of a C-terminal region in most molecules, but the cell lines that were cultured for shorter periods did not. Th ese results suggest that the emergence of HIV variants with a C-termin al deletion in the Env glycoprotein, which coexist with normal virus, may play a role in maintaining the long-term growth capacity and viabi lity of CI cells.