THE ROLE OF EUKARYOTIC SUBTILISIN-LIKE ENDOPROTEASES FOR THE ACTIVATION OF HUMAN-IMMUNODEFICIENCY-VIRUS GLYCOPROTEINS IN NATURAL HOST-CELLS

Proteolytic activation of the precursor envelope glycoproteins gp160 o f human immunodeficiency virus type 1 (HIV-1) and gp140 of HIV-2, a pr erequisite for viral infection, results in the formation of gp120/gp41 and gp125/gp36, respectively. Cleavage is mediated by cellular protea ses. Furin, a member of the eukaryotic subtilisin family, has been sho wn to be an activating protease for HIV. Here, we compared the presenc e of furin and other mammalian subtilisins in lymphatic cells and tiss ues. Northern blot analyses revealed that furin and the recently disco vered protease LPC/PC7 were the only subtilisin-like enzymes transcrib ed in such cells. Furin was identified as an enzymatically active endo protease present in different lymphocytic, as well as monocytic, cell lines. When expressed from vaccinia virus vectors, the proprotein conv ertases were correctly processed, transported, and secreted into the m edia and enzymatically active. Coexpression of different subtilisins w ith the HIV envelope precursors revealed that furin and LPC/PC7 are ab le to cleave HIV-1 gp160. Moreover, both enzymes proteolytically proce ssed the envelope precursor of HIV-2. gp140 was also cleaved to some e xtent by PC1, which is not, however, present in lymphatic cells. Furin - and LPC/PC7-catalyzed cleavage of HIV-1 gp160 resulted in biological ly active envelope protein. In conclusion, among the known members of the subtilisin family, only furin and LPC/PC7 fulfill the requirements of a protease responsible for in vivo activation of HIV envelope glyc oproteins.