COMPARATIVE PROCESSING OF BOVINE LEUKEMIA-VIRUS ENVELOPE GLYCOPROTEINGP72 BY SUBTILISIN KEXIN-LIKE MAMMALIAN CONVERTASES/

Intracellular proteolytic processing of bovine leukemia virus (BLV) en velope glycoprotein precursor (gp72) at the C-terminal end of the RVRR (268)down arrow site is an essential step for virus infectivity. Subti lisin/kexin-like convertases cleave proproteins at preferred RX(WR)R d own arrow sites, including those commonly found in viral envelope glyc oprotein precursors, We first demonstrated that gp72 is processed into gp51/gp30 in both CV1 cells and the furin-deficient LoVo cells, leadi ng us to compare the ability of mammalian convertases to cleave BLV gp 72 in vitro. In contrast to the inability of the neuroendocrine PC1 to cleave gp72, the convertases furin, PACE4, PC5-A and PCS-B, which pro cess constitutively secreted precursors, can effectively cleave gp72 i nto gp51/gp30, N-terminal sequence analysis of the convertase-generate d gp30 demonstrated that cleavage occurs at the in vivo-utilized RVRR down arrow SPV site, Such furin-, PACE4- and PC5-mediated processing w as completely inhibited by the alpha(1)-antitrypsin variant alpha 1-PD X. Mutagenesis of the gp72 cleavage site into RVRG-TPV resulted in com plete abrogation of gp72 processing by endogenous CV-1 cells and by co nvertases in vitro. Since our in vitro data suggest a redundancy in th e ability of the convertases to cleave gp72, RT-PCR analysis was used to define the convertases expressed in B-lymphocytes, representing one of the major targets of BLV infection. Our data revealed that only fu rin and the newly discovered PC7 mRNAs are expressed in Raji, B-Jab an d LG2 cell lines. (C) 1997 Federation of European Biochemical Societie s.