ENHANCED PROTEOLYTIC PROCESSING OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE PROTEIN IN MURINE LTK(-) CELLS

Proteolytic processing of the human immunodeficiency virus type 1 (HIV -1) envelope (Env) precursor glycoprotein (gp160) to produce the matur e gp120 and gp41 proteins is required for virus infection and virus-in duced cell fusion. It has also been suggested that cleavage of gp120 a t the immunodominant V3 loop region is required for virus-to-cell and cell-to-cell fusion. In this investigation we have studied the proteol ytic processing of the HIV-1 Env in cells of various origins (human, m onkey, and mouse) infected with a vaccinia virus recombinant expressin g the entire gp160 protein (VV-env-1). We have observed that in murine Ltk(-) cells, in addition to the proteolytic cleavage of gp160 at the gp120/gp41 site, there is also extensive intracellular proteolytic pr ocessing of gp160 at the V3 loop and at a novel site located at the C terminus of gp41. Similar proteolytic processing of the Env precursor was observed after treatment of extracts of VV-env-1-infected monkey c ells with thrombin, a trypsin-like protease that has been shown to cle ave the gp120 at the V3 loop. Our findings suggest that murine Ltk(-) cells could be a good model system for structural studies of Env with different HIV isolates and in searches for proteinase inhibitors that could prevent HIV-1 infection of susceptible cells by blocking proteol ysis of Env.