VPU-MEDIATED PROTEOLYSIS OF GP160 CD4 CHIMERIC ENVELOPE GLYCOPROTEINSIN THE ENDOPLASMIC-RETICULUM - REQUIREMENT OF BOTH THE ANCHOR AND CYTOPLASMIC DOMAINS OF CD4/

The Vpu protein of HIV-1 induces degradation of CD4 in the endoplasmic reticulum. Previous studies have elucidated the role of the CD4 cytop lasmic domain in the Vpu-induced degradation process, and the minimal Vpu responsive element mapped to a small region in the CD4 tail. In th e present study, we have carried our: both biochemical and biological experiments to analyze the role of the CD4 anchor domain in the Vpu-in duced degradation process. We generated chimeric proteins that possess ed the ecto-anchor domains of gp160 and the cytoplasmic domain of CD4. The chimeric envelope glycoproteins were functionally active in the f usion of HeLa CD4+ cells, with the exception of those having the argin ine to isoleucine (R to I) substitution in the gp160 anchor domain. Co expression studies revealed that these chimeric glycoproteins were sta ble and functionally active in the presence of Vpu, as opposed to thos e having the anchor-cytoplasmic domains of CD4. The half-life of Vpu-s ensitive chimeric glycoproteins was calculated to be approximately 60- 90 min, whereas Vpu-resistant envelope glycoproteins exhibited relativ ely longer half-lives in the presence of Vpu. Taken together, these st udies strongly suggest that the CD4 anchor domain appears to provide c ritical sequence or structural elements through which the Vpu protein could access CD4 or glycoproteins bearing the Vpu responsive element f or degradation in the endoplasmic reticulum. (C) 1994 Academic Press, Inc.