2nd National Conference Human Retroviruses and Related Infections Washington, DC - January 29 - February 2, 1995

Natl Conf Hum Retrovir Relat Infect 1995 Jan 29-Feb 2;2: (abstract no. 26)

Bour S, Schubert U, Strebel K
Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, MD, USA

We have recently demonstrated that co-expression of Vpu and CD4 in HeLa cells results in the degradation of CD4 in the endoplasmic reticulum. The sensitivity of CD4 to Vpu- mediated degradation is conferred by the presence of specific sequences located between amino acids 402 and 420 in the CD4 cytoplasmic domain. In order to better define the mechanisms involved in CD4 degradation, we investigated the existence and functional relevance of direct interactions between CD4 and Vpu.Co-immunoprecipitation experiments showed that Vpu specifically binds to the cytoplasmic tail of CD4. This phenomenon is relevant to the mechanism of CD4 degradation since the ability of CD8/CD4 chimera and various CD4 mutants to form complexes with Vpu correlates with their sensitivity to degradation. Accordingly, we found that amino acid residues in the CD4 cytoplasmic tail previously shown to be important for degradation are necessary and sufficient for Vpu binding. We further demonstrate that a deletion mutant of Vpu as well as a phosphorylation mutant, both biologically inactive with regard to CD4 degradation, retained the capacity to interact with the CD4 cytoplasmic domain. Taken together, these results indicate that Vpu binding is necessary to trigger CD4 degradation. However, the binding to target molecules is not sufficient per se to cause degradation. Interaction between CD4 and Vpu is thus likely to be an early event critical in triggering a multi-step process leading to CD4 degradation. We also clarified the post-binding events of Vpu-mediated degradation of CD4 by examining the requirement of ATP in this process and are currently investigating the identity of the protease activities involved.

Keywords: AIDS Vaccines, Animals, Antigens, CD4, Antigens, CD8, Base Sequence, Endoplasmic Reticulum, HIV, HIV Envelope Protein gp160, HIV-1, Hela Cells, Humans, genetics, immunology, metabolism

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1995-01-29
26

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