Human immunodeficiency virus type 1 Vpu protein induces degradation of CD4 in vitro: the cytoplasmic domain of CD4 contributes to Vpu sensitivity (original) (raw)

Abstract

CD4 is an integral membrane glycoprotein which functions as the human immunodeficiency virus (HIV) receptor for infection of human host cells. We have recently demonstrated that Vpu, an HIV type 1 (HIV-1) encoded integral membrane phosphoprotein, induces rapid degradation of CD4 in the endoplasmic reticulum. In this report, we describe an in vitro model system that allowed us to define important parameters for Vpu-dependent CD4 degradation. The rate of CD4 decay in rabbit reticulocyte lysate was approximately one-third of that observed previously in tissue culture experiments in the presence of Vpu (40 versus 12 min) and required no other HIV-1 encoded proteins. Degradation was contingent on the presence of microsomal membranes in the assay and the coexpression of Vpu and CD4 in the same membrane compartment. By using the in vitro degradation assay, the effects of specific mutations in CD4, including C-terminal truncations and glycosylation mutants, were analyzed. The results of these experiments indicate that Vpu has the capacity to induce degradation of glycosylated as well as nonglycosylated membrane-associated CD4. Truncation of 13 C-terminal amino acids of CD4 did not affect the ability of Vpu to induce its degradation. However, the removal of 32 amino acids from the C-terminus of CD4 completely abolished sensitivity to Vpu. This suggests that Vpu targets specific sequences in the cytoplasmic domain of CD4 to induce its degradation. We also analyzed the effects of mutations in Vpu on its biological activity in the in vitro CD4 degradation assay. The results of these experiments suggest that sequences critical for this function of Vpu are located in its hydrophilic C-terminal domain.

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  1. Adachi A., Gendelman H. E., Koenig S., Folks T., Willey R., Rabson A., Martin M. A. Production of acquired immunodeficiency syndrome-associated retrovirus in human and nonhuman cells transfected with an infectious molecular clone. J Virol. 1986 Aug;59(2):284–291. doi: 10.1128/jvi.59.2.284-291.1986. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Bonifacino J. S., Lippincott-Schwartz J. Degradation of proteins within the endoplasmic reticulum. Curr Opin Cell Biol. 1991 Aug;3(4):592–600. doi: 10.1016/0955-0674(91)90028-w. [DOI] [PubMed] [Google Scholar]
  3. Bour S., Boulerice F., Wainberg M. A. Inhibition of gp160 and CD4 maturation in U937 cells after both defective and productive infections by human immunodeficiency virus type 1. J Virol. 1991 Dec;65(12):6387–6396. doi: 10.1128/jvi.65.12.6387-6396.1991. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Crise B., Buonocore L., Rose J. K. CD4 is retained in the endoplasmic reticulum by the human immunodeficiency virus type 1 glycoprotein precursor. J Virol. 1990 Nov;64(11):5585–5593. doi: 10.1128/jvi.64.11.5585-5593.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Hoxie J. A., Alpers J. D., Rackowski J. L., Huebner K., Haggarty B. S., Cedarbaum A. J., Reed J. C. Alterations in T4 (CD4) protein and mRNA synthesis in cells infected with HIV. Science. 1986 Nov 28;234(4780):1123–1127. doi: 10.1126/science.3095925. [DOI] [PubMed] [Google Scholar]
  6. Huet T., Cheynier R., Meyerhans A., Roelants G., Wain-Hobson S. Genetic organization of a chimpanzee lentivirus related to HIV-1. Nature. 1990 May 24;345(6273):356–359. doi: 10.1038/345356a0. [DOI] [PubMed] [Google Scholar]
  7. Jabbar M. A., Nayak D. P. Intracellular interaction of human immunodeficiency virus type 1 (ARV-2) envelope glycoprotein gp160 with CD4 blocks the movement and maturation of CD4 to the plasma membrane. J Virol. 1990 Dec;64(12):6297–6304. doi: 10.1128/jvi.64.12.6297-6304.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Katz F. N., Rothman J. E., Lingappa V. R., Blobel G., Lodish H. F. Membrane assembly in vitro: synthesis, glycosylation, and asymmetric insertion of a transmembrane protein. Proc Natl Acad Sci U S A. 1977 Aug;74(8):3278–3282. doi: 10.1073/pnas.74.8.3278. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Klausner R. D., Sitia R. Protein degradation in the endoplasmic reticulum. Cell. 1990 Aug 24;62(4):611–614. doi: 10.1016/0092-8674(90)90104-m. [DOI] [PubMed] [Google Scholar]
  10. Klimkait T., Strebel K., Hoggan M. D., Martin M. A., Orenstein J. M. The human immunodeficiency virus type 1-specific protein vpu is required for efficient virus maturation and release. J Virol. 1990 Feb;64(2):621–629. doi: 10.1128/jvi.64.2.621-629.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Maddon P. J., Dalgleish A. G., McDougal J. S., Clapham P. R., Weiss R. A., Axel R. The T4 gene encodes the AIDS virus receptor and is expressed in the immune system and the brain. Cell. 1986 Nov 7;47(3):333–348. doi: 10.1016/0092-8674(86)90590-8. [DOI] [PubMed] [Google Scholar]
  12. Maddon P. J., Littman D. R., Godfrey M., Maddon D. E., Chess L., Axel R. The isolation and nucleotide sequence of a cDNA encoding the T cell surface protein T4: a new member of the immunoglobulin gene family. Cell. 1985 Aug;42(1):93–104. doi: 10.1016/s0092-8674(85)80105-7. [DOI] [PubMed] [Google Scholar]
  13. Pinto L. H., Holsinger L. J., Lamb R. A. Influenza virus M2 protein has ion channel activity. Cell. 1992 May 1;69(3):517–528. doi: 10.1016/0092-8674(92)90452-i. [DOI] [PubMed] [Google Scholar]
  14. Scheffner M., Werness B. A., Huibregtse J. M., Levine A. J., Howley P. M. The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53. Cell. 1990 Dec 21;63(6):1129–1136. doi: 10.1016/0092-8674(90)90409-8. [DOI] [PubMed] [Google Scholar]
  15. Schubert U., Schneider T., Henklein P., Hoffmann K., Berthold E., Hauser H., Pauli G., Porstmann T. Human-immunodeficiency-virus-type-1-encoded Vpu protein is phosphorylated by casein kinase II. Eur J Biochem. 1992 Mar 1;204(2):875–883. doi: 10.1111/j.1432-1033.1992.tb16707.x. [DOI] [PubMed] [Google Scholar]
  16. Schwartz S., Felber B. K., Fenyö E. M., Pavlakis G. N. Env and Vpu proteins of human immunodeficiency virus type 1 are produced from multiple bicistronic mRNAs. J Virol. 1990 Nov;64(11):5448–5456. doi: 10.1128/jvi.64.11.5448-5456.1990. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Shin J., Dunbrack R. L., Jr, Lee S., Strominger J. L. Phosphorylation-dependent down-modulation of CD4 requires a specific structure within the cytoplasmic domain of CD4. J Biol Chem. 1991 Jun 5;266(16):10658–10665. [PubMed] [Google Scholar]
  18. Shin J., Dunbrack R. L., Jr, Lee S., Strominger J. L. Signals for retention of transmembrane proteins in the endoplasmic reticulum studied with CD4 truncation mutants. Proc Natl Acad Sci U S A. 1991 Mar 1;88(5):1918–1922. doi: 10.1073/pnas.88.5.1918. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Strebel K., Klimkait T., Maldarelli F., Martin M. A. Molecular and biochemical analyses of human immunodeficiency virus type 1 vpu protein. J Virol. 1989 Sep;63(9):3784–3791. doi: 10.1128/jvi.63.9.3784-3791.1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Strebel K., Klimkait T., Martin M. A. A novel gene of HIV-1, vpu, and its 16-kilodalton product. Science. 1988 Sep 2;241(4870):1221–1223. doi: 10.1126/science.3261888. [DOI] [PubMed] [Google Scholar]
  21. Sugrue R. J., Hay A. J. Structural characteristics of the M2 protein of influenza A viruses: evidence that it forms a tetrameric channel. Virology. 1991 Feb;180(2):617–624. doi: 10.1016/0042-6822(91)90075-M. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Terwilliger E. F., Cohen E. A., Lu Y. C., Sodroski J. G., Haseltine W. A. Functional role of human immunodeficiency virus type 1 vpu. Proc Natl Acad Sci U S A. 1989 Jul;86(13):5163–5167. doi: 10.1073/pnas.86.13.5163. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Tifft C. J., Proia R. L., Camerini-Otero R. D. The folding and cell surface expression of CD4 requires glycosylation. J Biol Chem. 1992 Feb 15;267(5):3268–3273. [PubMed] [Google Scholar]
  24. Walter P., Blobel G. Preparation of microsomal membranes for cotranslational protein translocation. Methods Enzymol. 1983;96:84–93. doi: 10.1016/s0076-6879(83)96010-x. [DOI] [PubMed] [Google Scholar]
  25. Wileman T., Kane L. P., Carson G. R., Terhorst C. Depletion of cellular calcium accelerates protein degradation in the endoplasmic reticulum. J Biol Chem. 1991 Mar 5;266(7):4500–4507. [PubMed] [Google Scholar]
  26. Willey R. L., Maldarelli F., Martin M. A., Strebel K. Human immunodeficiency virus type 1 Vpu protein induces rapid degradation of CD4. J Virol. 1992 Dec;66(12):7193–7200. doi: 10.1128/jvi.66.12.7193-7200.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Willey R. L., Maldarelli F., Martin M. A., Strebel K. Human immunodeficiency virus type 1 Vpu protein regulates the formation of intracellular gp160-CD4 complexes. J Virol. 1992 Jan;66(1):226–234. doi: 10.1128/jvi.66.1.226-234.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]