CONCLUSION

The more we look into Nef functions, the more details we find, seemingly confusing our understanding of the actions of this small viral protein. It is likely that the picture is even more complex than anticipated.

REFERENCES

1. Ahmad, N. and Venkatesan, S., Nef protein of HIV-1 is a transcriptional repressor of HIV-1 LTR, Science, 241, 1481-1485, 1988.

2. Kestler, H.W., III, Ringler, D.J., Mori, K., Panicali, D.L., Sehgal, P.K., Daniel, M.D., and Desrosiers, R.C., Importance of the Nef gene for maintenance of high virus loads and for development of AIDS, Cell, 65, 651-662, 1991.

3. Deacon, N.J., Tsykin, A., Solomon, A., Smith, K., Ludford-Menting, M., Hooker, D.J., McPhee, D.A., Greenway, A. L., Ellett, A., Chatfield, C., Lawson, V.A., Crowe, S., Maerz, A., Souza, S., Learmont,

J., Sullivan, J.S., Cunningham, A., Dwyer, D., Druton, D., and Mills, J., Genomic structure of an attenuated quasi species of HIV-1 from a blood transfusion donor and recipients, Science, 270, 988-991, 1995.

4. Kirchhoff, F., Greenough, T.C., Brettler, D.B., Sullivan, J.L., and Desrosiers, R.C., Brief report: absence of intact Nef sequences in a long-term survivor with nonprogressive HIV-1 infection, N. Engl. J. Med., 332, 228-232, 1995.

5. Hanna, Z., Kay, D.G., Rebai, N., Guimond, A., Jothy, S., and Jolicoeur, P., Nef harbors a major determinant of pathogenicity for an AIDS-like disease induced by HIV-1 in transgenic mice, Cell, 95, 163-175, 1998.

6. Wu, Y. and Marsh, J.W., Selective transcription and modulation of resting T cell activity by preinte­grated HIV DNA, Science, 293, 1503-1506, 2001.

7. Arold, S.T. and Baur, A.S., Dynamic Nef and Nef dynamics: how structure could explain the complex activities of this small HIV protein, Trends Biochem. Sci., 26, 356-363, 2001.

8. Lu, X., Yu, H., Liu, S.H., Brodsky, F.M., and Peterlin, B.M., Interactions between HIV1 Nef and vacuolar ATPase facilitate the internalization of CD4, Immunity, 8, 647-656, 1998.

9. Baur, A.S., Sass, G., Laffert, B., Willbold, D., Cheng-Mayer, C., and Peterlin, B.M., The N-terminus of Nef from HIV-1/SIV associates with a protein complex containing Lck and a serine kinase, Immunity, 6, 283-291, 1997.

10. Garcia, J.V. and Miller, A.D., Serine phosphorylation-independent downregulation of cell-surface CD4 by Nef, Nature, 350, 508-511, 1991.

11. Doms, R.W., and Trono, D., The plasma membrane as a combat zone in the HIV battlefield, Genes Dev., 14, 2677-2688, 2000.

12. Geyer, M., Yu, H., Mandic, R., Linnemann, T., Zheng, Y.H., Fackler, O.T., and Peterlin, B.M., Subunit H of the V-ATPase binds to the medium chain of adaptor protein complex 2 and connects Nef to the endocytic machinery, J. Biol. Chem., 277, 28521-28529, 2002.

13. Piguet, V., Gu, F., Foti, M., Demaurex, N., Gruenberg, J., Carpentier, J.L., and Trono, D., Nef-induced CD4 degradation: a diacidic-based motif in Nef functions as a lysosomal targeting signal through the binding of -COP in endosomes, Cell, 97, 63-73, 1999.

14. Swigut, T., Shohdy, N., and Skowronski, J., Mechanism for down-regulation of CD28 by Nef, EMBO J., 20, 1593-1604, 2001.

15. Swigut, T., Greenberg, M., and Skowronski, J., Cooperative interactions of simian immunodeficiency virus Nef, AP-2, and CD3- mediate the selective induction of T-cell receptor-CD3 endocytosis, J. Virol., 77, 8116-8126, 2003.

16. Lama, J., Mangasarian, A., and Trono, D., Cell-surface expression of CD4 reduces HIV-1 infectivity by blocking Env incorporation in a Nef- and Vpu-inhibitable manner, Curr. Biol., 9, 622-631, 1999.

17. Ross, T.M., Oran, A.E., and Cullen, B.R., Inhibition of HIV-1 progeny virion release by cell-surface CD4 is relieved by expression of the viral Nef protein, Curr. Biol., 9, 613-621, 1999.

18. Lama, J., The physiological relevance of CD4 receptor down-modulation during HIV infection, Curr. HIV Res., 1, 167-184, 2003.

19. Schwartz, O., Marechal, V., Le Gall, S., Lemonnier, F., and Heard, J.M., Endocytosis of major histocompatibility complex class I molecules is induced by the HIV-1 Nef protein, Nat. Med., 2, 338-342, 1996.

20. Blagoveshchenskaya, A.D., Thomas, L., Feliciangeli, S.F., Hung, C.H., and Thomas, G., HIV-1 Nef downregulates MHC-I by a PACS-1- and PI3K-regulated ARF6 endocytic pathway, Cell, 111, 853-866, 2002.

21. Collins, K.L., Chen, B.K., Kalams, S.A., Walker, B.D., and Baltimore, D., HIV-1 Nef protein protects infected primary cells against killing by cytotoxic T lymphocytes, Nature, 391, 397-401, 1998.

22. Xu, X.N., Screaton, G.R., and McMichael, A.J., Virus infections: escape, resistance, and counterattack, Immunity, 15, 867-870, 2001.

23. Baur, A.S., Sawai, E.T., Dazin, P., Fantl, W.J., Cheng-Mayer, C., and Peterlin, B.M., HIV-1 Nef leads to inhibition or activation of T cells depending on its intracellular localization, Immunity, 1, 373-384, 1994.

24. Simmons, A., Aluvihare, V., and McMichael, A., Nef triggers a transcriptional program in T cells imitating single-signal T cell activation and inducing HIV virulence mediators, Immunity, 14, 763-777,

2001.

25. Fackler, O.T., and Baur, A.S., Live and let die: Nef functions beyond HIV replication, Immunity, 16, 493-497, 2002.

26. Xu, X.N., Laffert, B., Screaton, G.R., Kraft, M., Wolf, D., Kolanus, W., Mongkolsapay, J., McMichael, A.J., and Baur, A.S., Induction of Fas ligand expression by HIV involves the interaction of Nef with the T cell receptor chain, J. Exp. Med., 189, 1489-1496, 1999.

27. Fackler, O.T., Luo, W., Geyer, M., Alberts, A.S., and Peterlin, B.M., Activation of Vav by Nef induces cytoskeletal rearrangements and downstream effector functions, Mol. Cell, 3, 729-739, 1999.

28. Sawai, E.T., Baur, A., Struble, H., Peterlin, B.M., Levy, J.A., and Cheng-Mayer, C., Human immun­odeficiency virus type 1 Nef associates with a cellular serine kinase in T lymphocytes, Proc. Natl. Acad. Sci. U.S.A., 91, 1539-1543, 1994.

29. Smith, B.L., Krushelnycky, B.W., Mochly-Rosen, D., and Berg, P., The HIV Nef protein associates with protein kinase C, J. Biol. Chem., 271, 16753-16757, 1996.

30. Janardhan, A., Swigut, T., Hill, B., Myers, M.P., and Skowronski, J., HIV-1 Nef binds the DOCK2- ELMO1 complex to activate Rac and inhibit lymphocyte chemotaxis, PLoS Biol., 2, 2(1):E6, 2004.

31. Schrager, J.A., Der Minassian, V., and Marsh, J.W., HIV Nef increases T cell ERK MAP kinase activity, J. Biol. Chem., 277, 6137-6142, 2002.

32. Wang, J.K., Kiyokawa, E., Verdin, E., and Trono, D., The Nef protein of HIV-1 associates with rafts and primes T cells for activation, Proc. Natl. Acad. Sci. U.S.A., 97, 394-399, 2000.

33. Zack, J.A., Arrigo, S.J., Weitsman, S.R., Go, A.S., Haislip, A., and Chen, I.S., HIV-1 entry into quiescent primary lymphocytes: molecular analysis reveals a labile, latent viral structure, Cell, 61, 213-222, 1990.

34. Kinoshita, S., Chen, B.K., Kaneshima, H., and Nolan, G.P., Host control of HIV-1 parasitism in T cells by the nuclear factor of activated T cells, Cell, 95, 595-604, 1998.

35. Fackler, O.T., Wolf, D., Weber, H.O., Laffert, B., DfAloja, P., Schuler-Thurner, B., Geffin, R., Saksela,

K., Geyer, M., Peterlin, B.M., Schuler, G.

36. Messmer, D., Jacque, J.M., Santisteban, C., Bristow, C., Han, S.Y., Villamide-Herrera, L., Mehlhop, E., Marx, P.A., Steinman, R.M., Gettie, A., and Pope, M., Endogenously expressed Nef uncouples cytokine and chemokine production from membrane phenotypic maturation in dendritic cells, J. Immunol., 169, 4172-4182. 2002.

37. Petit, C., Buseyne, F., Boccaccio, C., Abastado, J.P., Heard, J.M., and Schwartz, O., Nef is required for efficient HIV-1 replication in cocultures of dendritic cells and lymphocytes, Virology, 286, 225-236, 2001.

38. Kane, L.P. and Weiss, A., The PI-3 kinase/Akt pathway and T cell activation: pleiotropic pathways downstream of PIP3, Immunol. Rev., 192, 7-20, 2003.

39. Cooray, S., The pivotal role of phosphatidylinositol 3-kinase-Akt signal transduction in virus survival, J. Gen. Virol., 85, 1065-1076, 2004.

40. Fruman, D.A., Meyers, R.E., and Cantley, L.C., Phosphoinositide kinases, Annu. Rev. Biochem., 67, 481-507, 1998.

41. Marsden, V.S. and Strasser, A., Control of apoptosis in the immune system: Bcl-2, BH3-only proteins and more, Annu. Rev. Immunol., 21, 71-105, 2003.

42. Jones, R.G., Parsons, M., Bonnard, M., Chan, V.S., Yeh, W.C., Woodgett, J.R., and Ohashi, P.S., Protein kinase B regulates T lymphocyte survival, nuclear factor B activation, and Bcl-X(L) levels in vivo, J. Exp. Med., 191, 1721-1734, 2000.

43. Green, D.R., Droin, N., and Pinkoski, M., Activation-induced cell death in T cells, Immunol. Rev., 193, 70-81, 2003.

44. Andreola, G., Rivoltini, L., Castelli, C., Huber, V., Perego, P., Deho, P., Squarcina, P., Accornero, P., Lozupone, F., Lugini, L., Stringaro, A., Molinari, A., Arancia, G., Gentile, M., Parmiani, G., and Fais, S., Induction of lymphocyte apoptosis by tumor cell secretion of FasL-bearing microvesicles, J. Exp. Med., 195, 1303-1316, 2002.

45. Benedict, C.A., Norris, P.S., and Ware, C.F., To kill or be killed: viral evasion of apoptosis, Nat. Immunol., 3, 1013-1018, 2002.

46. Tschopp, J., Thome, M., Hofmann, K., and Meinl, E., The fight of viruses against apoptosis, Curr. Opin. Genet. Dev., 8, 82-87, 1998.

47. Dahl, J., Jurczak, A., Cheng, L.A., Baker, D.C., and Benjamin, T.L., Evidence of a role for phosphati­dylinositol 3-kinase activation in the blocking of apoptosis by polyomavirus middle T antigen, J. Virol., 72, 3221-3226, 1998.

48. Meinl, E., Fickenscher, H., Thome, M., Tschopp, J., and Fleckenstein, B., Anti-apoptotic strategies of lymphotropic viruses, Immunol. Today, 19, 474-479, 1998.

49. Herbein, G., Mahlknecht, U., Batliwalla, F., Gregersen, P., Pappas, T., Butler, J., O'Brien, W.A., and Verdin, E., Apoptosis of CD⁺ T cells is mediated by macrophages through interaction of HIV gp120 with chemokine receptor CXCR4, Nature, 395, 189-194, 1998.

50. Geleziunas, R., Xu, W., Takeda, K., Ichijo, H., and Greene, W.C., HIV-1 Nef inhibits ASK1-dependent death signalling providing a potential mechanism for protecting the infected host cell, Nature, 410, 834-838, 2001.

51. Chang, H.Y., Nishitoh, H., Yang, X., Ichijo, H., and Baltimore, D., Activation of apoptosis signal­regulating kinase 1 (ASK1) by the adapter protein Daxx, Science, 281, 1860-1863, 1998.

52. Tobiume, K., Matsuzawa, A., Takahashi, T., Nishitoh, H., Morita, K., Takeda, K., Minowa, O., Miyazono, K., Noda, T., and Ichijo, H., ASK1 is required for sustained activations of JNK∕p38 MAP kinases and apoptosis, EMBO Rep., 2, 222-228, 2001.

53. Wolf, D., Witte, V., Laffert, B., Blume, K., Stromer, E., Trapp, S., d'Aloja, P., Schurmann, A., and Baur, A.S., HIV-1 Nef associated PAK and PI3-kinases stimulate Akt-independent Bad-phosphoryla­tion to induce anti-apoptotic signals, Nat. Med., 7, 1217-1224, 2001.

54. Finkel, T.H., Tudor-Williams, G., Banda, N.K., Cotton, M.F., Curiel, T., Monks, C., Baba, T.W., Ruprecht, R.M., and Kupfer, A., Apoptosis occurs predominantly in bystander cells and not in productively infected cells of HIV- and SIV-infected lymph nodes, Nat. Med., 1, 129-134, 1995.

55. Xu, X.N., Screaton, G.R., Gotch, F.M., Dong, T., Tan, R., Almond, N., Walker, B., Stebbings, R., Kent, K., Nagata, S., Stott, J.E., and McMichael, A.J., Evasion of cytotoxic T lymphocyte (CTL) responses by Nef-dependent induction of Fas ligand (CD95L) expression on simian immunodeficiency virus-infected cells, J. Exp. Med., 186, 7-16, 1997.

56. Combadiere, B., Freedman, M., Chen, L., Shores, E.W., Love, P., and Lenardo, M.J., Qualitative and quantitative contributions of the T cell receptor chain to mature T cell apoptosis, J. Exp. Med., 183, 2109-2117, 1996.

57. Ross, T.M., Using death to one's advantage: HIV modulation of apoptosis, Leukemia, 15, 332-341, 2001.

58. Steinman R.M., DC-SIGN: a guide to some mysteries of dendritic cells. Cell, 2000 Mar 3;100(5): 491-4.

59. Fujii, Y., Otake, K., Tashiro, M., and Adachi, A., Soluble Nef antigen of HIV-1 is cytotoxic for human CD4⁺ T cells, FEBS Lett., 393, 93-96, 1996.

60. Okada, H., Takei, R., and Tashiro, M., Nef protein of HIV-1 induces apoptotic cytolysis of murine lymphoid cells independently of CD95 (Fas) and its suppression by serine/threonine protein kinase inhibitors, FEBS Lett., 417, 61-64, 1997.

61. James, C.O., Huang, M.B., Khan, M., Garcia-Barrio, M., Powell, M.D., and Bond, V.C., Extracellular Nef protein targets CD4⁺ T cells for apoptosis by interacting with CXCR4 surface receptors, J. Virol., 78, 3099-3109, 2004.

62. Mueller, Y.M., De Rosa, S.C., Hutton, J.A., Witek, J., Roederer, M., Altman, J.D., and Katsikis, P.D., Increased CD95∕Fas-induced apoptosis of HIV-specific CD8(+) T cells, Immunity, 15, 871-882, 2001.