HIV Nef Increases T Cell ERK MAP Kinase Activity

Abstract

The human immunodeficiency regulatory protein Nef enhances viral replication and is central to viral pathogenesis. Although Nef has displayed a capacity to associate with a diverse assortment of cellular molecules and to increase T cell activity, the biochemical activity of Nef in T cells remains poorly defined. In this report we examine the bioactivity of Nef in primary CD4 T cells and, in particular, focus on the biochemical pathways known to be central to T cell activity. The extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase pathway was dramatically affected by Nef expression with increases in ERK, MEK, and Elk induction. The capacity of Nef to increase the MAP kinase pathway activity was dependent on T cell receptor stimulation. By increasing ERK MAP kinase activity, Nef is functionally associated with a kinase known to affect T cell activity, viral replication, and viral infectivity. The human immunodeficiency regulatory protein Nef enhances viral replication and is central to viral pathogenesis. Although Nef has displayed a capacity to associate with a diverse assortment of cellular molecules and to increase T cell activity, the biochemical activity of Nef in T cells remains poorly defined. In this report we examine the bioactivity of Nef in primary CD4 T cells and, in particular, focus on the biochemical pathways known to be central to T cell activity. The extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase pathway was dramatically affected by Nef expression with increases in ERK, MEK, and Elk induction. The capacity of Nef to increase the MAP kinase pathway activity was dependent on T cell receptor stimulation. By increasing ERK MAP kinase activity, Nef is functionally associated with a kinase known to affect T cell activity, viral replication, and viral infectivity. Most of the viral gene products of HIV 1HIV-1human immunodeficiency virus type 1ERKextracellular signal-regulated kinaseMAPmitogen-activated proteinMEKextracellular signal-regulated kinase kinase 1/2MKKMAP kinase kinaseJNKc-Jun N-terminal kinaseSEK1stress-activated kinase kinase 1IL-2interleukin-2CCDcharge-coupled deviceAMacetoxymethyl ester have established structural or biochemical functions. Nef, which is the predominant early transcript (1Robert-Guroff M. Popovic M. Gartner S. Markham P. Gallo R.C. Reitz M.S. J. Virol. 1990; 64: 3391-3398Crossref PubMed Google Scholar, 2Guatelli J.C. Gingeras T.R. Richman D.D. J. Virol. 1990; 64: 4093-4098Crossref PubMed Google Scholar), is largely defined by cellular and viral phenotypes and by in vivo effects. Nef expression modulates cell surface receptors (3Garcia J.V. Miller A.D. Nature. 1991; 350: 508-511Crossref PubMed Scopus (658) Google Scholar, 4Schwartz O. Marechal V., Le Gall S. Lemonnier F. Heard J.M. Nat. Med. 1996; 2: 338-342Crossref PubMed Scopus (883) Google Scholar), enhances virion infectivity (5de Ronde A. Klaver B. Keulen W. Smit L. Goudsmit J. Virology. 1992; 188: 391-395Crossref PubMed Scopus (144) Google Scholar, 6Spina C.A. Kwoh T.J. Chowers M.Y. Guatelli J.C. Richman D.D. J. Exp. Med. 1994; 179: 115-123Crossref PubMed Scopus (364) Google Scholar, 7Miller M.D. Warmerdam M.T. Gaston I. Greene W.C. Feinberg M.B. J. Exp. Med. 1994; 179: 101-113Crossref PubMed Scopus (479) Google Scholar), and enhances in vivo viral replication and pathogenesis (8Kestler H.W. Ringler D.J. Mori K. Panicali D.L. Sehgal P.K. Daniel M.D. Desrosiers R.C. Cell. 1991; 65: 651-662Abstract Full Text PDF PubMed Scopus (1438) Google Scholar). The study of CD4 and the major histocompatibility antigen I down-modulation has been the most productive and has resulted in identification of numerous cellular moieties, largely restricted to endocytotic machinery, that can associate with Nef (for reviews, see Refs. 9Piguet V. Schwartz O., Le Gall S. Trono D. Immunol. Rev. 1999; 168: 51-63Crossref PubMed Scopus (179) Google Scholar and10Skowronski J. Greenberg M.E. Lock M. Mariani R. Salghetti S. Swigut T. Iafrate A.J. Cold Spring Harbor Symp. Quant. Biol. 1999; 64: 453-463Crossref PubMed Scopus (24) Google Scholar). From this work, it has been suggested that Nef serves as an adapter for coupling endocytotic molecules to the targeted membrane receptors. human immunodeficiency virus type 1 extracellular signal-regulated kinase mitogen-activated protein extracellular signal-regulated kinase kinase 1/2 MAP kinase kinase c-Jun N-terminal kinase stress-activated kinase kinase 1 interleukin-2 charge-coupled device acetoxymethyl ester The study of Nef-mediated effects on activation pathways has been less conclusive. Studies addressing Nef function in T cells define capacities that both inhibit and enhance T cell activity (for review, see Refs. 10Skowronski J. Greenberg M.E. Lock M. Mariani R. Salghetti S. Swigut T. Iafrate A.J. Cold Spring Harbor Symp. Quant. Biol. 1999; 64: 453-463Crossref PubMed Scopus (24) Google Scholar and 11Marsh J.W. Arch. Biochem. Biophys. 1999; 365: 192-198Crossref PubMed Scopus (34) Google Scholar). From work with a CD8-Nef fusion protein, it was proposed that cellular location defined whether Nef expression resulted in negative or positive effects on T cell activity (12Baur A.S. Sawai E.T. Dazin P. Fantl W.J. Cheng-Mayer C. Peterlin B.M. Immunity. 1994; 1: 373-384Abstract Full Text PDF PubMed Scopus (279) Google Scholar). Recent efforts from our laboratory have demonstrated that the opposing effects of Nef on T cell activation are also mediated by different Nef concentrations (13Liu X. Schrager J.A. Lange G.D. Marsh J.W. J. Biol. Chem. 2001; 276: 32763-32770Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar). Nef can increase T cell interleukin-2 synthesis in both T cell lines and human primary CD4 T cells (14Rhee S.S. Marsh J.W. J. Immunol. 1994; 152: 5128-5134PubMed Google Scholar, 15Alexander L., Du, Z. Rosenzweig M. Jung J.U. Desrosiers R.C. J. Virol. 1997; 71: 6094-6099Crossref PubMed Google Scholar, 16Schrager J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar, 17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar). Furthermore, Nef has been shown to increase both T cell nuclear factor of activated T cells (17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar,18Manninen A. Renkema G.H. Saksela K. J. Biol. Chem. 2000; 275: 16513-16517Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar) and NF-κB (17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar) reporter activities. Thus, there is evolving support for Nef as a positive T cell factor. Attempts to define the biochemical capacity of Nef are numerous. Nef can bind to a number of cellular signaling moieties. For example, Nef binds to and activates the tyrosine kinase Hck (19Briggs S.D. Sharkey M. Stevenson M. Smithgall T.E. J. Biol. Chem. 1997; 272: 17899-17902Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar, 20Moarefi I. LaFevre-Bernt M. Sicheri F. Huse M. Lee C.H. Kuriyan J. Miller W.T. Nature. 1997; 385: 650-653Crossref PubMed Scopus (541) Google Scholar), and the co-expression of Nef and Hck in Rat-2 fibroblasts resulted in cellular transformation, although Nef expression alone had no effect (19Briggs S.D. Sharkey M. Stevenson M. Smithgall T.E. J. Biol. Chem. 1997; 272: 17899-17902Abstract Full Text Full Text PDF PubMed Scopus (180) Google Scholar). In a macrophage cell line, Nef, through Hck and MAP kinase, induces the transcription factor activating protein-1 (21Biggs T.E. Cooke S.J. Barton C.H. Harris M.P. Saksela K. Mann D.A. J. Mol. Biol. 1999; 290: 21-35Crossref PubMed Scopus (56) Google Scholar). Hck is not expressed in T cells, but with regard to T cell kinases, Nef has been shown to bind and inhibit Lck and MAP kinase activity (22Greenway A. Azad A. Mills J. McPhee D. J. Virol. 1996; 70: 6701-6708Crossref PubMed Google Scholar). Nef expression has also been demonstrated to alter calcium signaling. When expressed in NIH3T3 cells, Nef inhibited inositol trisphosphate-mediated calcium flux (23De S.K. Marsh J.W. J. Biol. Chem. 1994; 269: 6656-6660Abstract Full Text PDF PubMed Google Scholar), an effect similar to that seen in a Jurkat cell expressing a Nef-CD8 fusion protein (12Baur A.S. Sawai E.T. Dazin P. Fantl W.J. Cheng-Mayer C. Peterlin B.M. Immunity. 1994; 1: 373-384Abstract Full Text PDF PubMed Scopus (279) Google Scholar). However, in Nef-expressing transgenic murine thymocytes, T cell stimulation resulted in elevated calcium responses (24Skowronski J. Parks D. Mariani R. EMBO J. 1993; 12: 703-713Crossref PubMed Scopus (256) Google Scholar), a finding more consistent with T cell activation enhancement. Nef also binds to an activated serine kinase, p21-activated kinase or Pak (25Nunn M.F. Marsh J.W. J. Virol. 1996; 70: 6157-6161Crossref PubMed Google Scholar), and this association occurs in HIV-infected primary T cells (26Brown A. Wang X. Sawai E. Cheng-Mayer C. J. Virol. 1999; 73: 9899-9907Crossref PubMed Google Scholar). In a recent exploration of Nef activity, it was demonstrated that the co-expression of Nef with Vav, through Pak, increased c-Jun N-terminal kinase (JNK) activity in NIH3T3 cells (27Fackler O.T. Luo W. Geyer M. Alberts A.S. Peterlin B.M. Mol. Cell. 1999; 3: 729-739Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar). However, it is unclear how relevant these studies are to the activity of Nef in peripheral CD4 T cells, the main target of HIV infection. The biochemistry of T cell activation is highly complex, but many of the molecular pathways leading to IL-2 expression have been characterized (for reviews, see Refs. 28van Leeuwen J.E.M. Samelson L.E. Curr. Opin. Immunol. 1999; 11: 242-248Crossref PubMed Scopus (217) Google Scholar and 29Kane L.P. Lin J. Weiss A. Curr. Opin. Immunol. 2000; 12: 242-249Crossref PubMed Scopus (428) Google Scholar). As used here, IL-2 is both a reporter for the metabolic activity of a T cell and the end-product of a highly characterized and dissectible biochemical process of the CD4 T cell. Per se, an increase in IL-2 levels does not significantly contribute to HIV replication (30Kovacs J.A. Vogel S. Albert J.M. Falloon J. Davey R.T., Jr. Walker R.E. Polis M.A. Spooner K. Metcalf J.A. Baseler M. Fyfe G. Lane H.C. N. Engl. J. Med. 1996; 335: 1350-1356Crossref PubMed Scopus (400) Google Scholar). However, with a recent demonstration that Nef, as expressed from HIV infection, increased T cell activity (as defined by IL-2 secretion) and viral production (31Wu Y. Marsh J.W. Science. 2001; 293: 1503-1506Crossref PubMed Scopus (307) Google Scholar), an understanding of the biochemical activity of Nef in these contexts appears relevant. Events mediated by engagement of the T cell receptor and CD28 co-receptor result in activation of the MAP kinases extracellular signal-regulated kinase (ERK), JNK, and p38, in addition to phosphorylation of IκB, of and activation of the kinase The pathways leading to these signaling are in The of kinases and signaling molecules is on the that Nef, as a protein, affect pathways in this cellular The was also to the to Nef effects. of a that HIV Nef concentrations similar to seen in HIV (13Liu X. Schrager J.A. Lange G.D. Marsh J.W. J. Biol. Chem. 2001; 276: 32763-32770Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar) in of an pathway in primary CD4 T cells that relevant molecular In this we that Nef expression in primary CD4 T cells increases activity of the ERK MAP kinase The peripheral from was by and from the of the of C. L. J. Immunol. 1997; Google Scholar) and as J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar). in with 1 and to of CD4 T cells was by the addition of CD28 on J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar). CD4 T cells with the (3Garcia J.V. Miller A.D. Nature. 1991; 350: 508-511Crossref PubMed Scopus (658) Google Scholar) expressing the Nef or the Nef which was by a to B. Y. K. A. M.P. Virology. 1990; PubMed Scopus Google Scholar). in Nef was by J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar). For T cell the cells to be similar to the cells, as J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar). and positive for Nef For cell activation from cell of the cells, by to a no to The was through this process or The cells in with and The cells in 1 of of or was with defined cells for and the cell was in of for and for to and similar to a The was to and with or or of was by and and with of on an with a For with For of ERK phosphorylation of cells in 1 of cells activated by the addition of as defined cells for and the cell was 1 of 1 1 1 1 1 1 and for and the was for kinase or cellular protein in the was by protein and to be in protein kinase was used to ERK kinase from the cell by an in kinase protein (as in from for was as For this we the of the calcium was by the for acetoxymethyl ester J. Biol. Chem. Full Text PDF PubMed Google Scholar), but the from with of was in with 1 and cells in a through the addition of of and calcium levels by of on a with a and a of calcium was the addition of and as B.M. W. K. M. C. D.J. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar, T. T.J. Nature. PubMed Scopus Google Scholar), but a of was used for For cell number and on a primary CD4 T cells with type Nef or the of Nef expression The has been demonstrated to T cell capacity J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar, 17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar) but serves as a for the cellular of and the used in this the cell to a cell. and cells expressed Nef protein X. Schrager J.A. Lange G.D. Marsh J.W. J. Biol. Chem. 2001; 276: 32763-32770Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar and 16Schrager J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google not of the ERK MAP kinase pathway is for IL-2 synthesis R. B. EMBO J. 1993; 12: PubMed Scopus Google Scholar, M. S. D. J. Exp. Med. 1994; PubMed Scopus Google Scholar). ERK is also central to the of cellular transcription and and activation of A.J. Nature. 2000; PubMed Scopus Google Scholar). In T cells, stimulation of the T cell receptor is not to ERK activity M. S.J. D. J. Exp. Med. 1993; PubMed Scopus Google Scholar). T cell activation ERK and of different molecular and of this kinase is by phosphorylation of a of and tyrosine of ERK A.J. P. J. EMBO J. 1991; PubMed Scopus Google Scholar). was by on from of cell and Nef-expressing primary CD4 T cells by stimulation with on to the cells from and As shown in of both and are stimulation with The of activated ERK was dramatically increased in Nef-expressing cells, but not in the Nef cell. this for ERK protein displayed no that the Nef-mediated increase in and activity was not to in ERK For we have the of ERK activity with The of the Nef to the Nef increase in ERK activity is consistent with of effect on T cell activation J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar, 17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar). The ERK activity was increased by Nef in cells from different and, in was in cells by not T cells also MAP kinases, and is in T cells by CD28 B. E. M. T. M. Y. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar). activation in T cells is by known as phosphorylation of a and tyrosine in B. J. Science. PubMed Scopus Google Scholar). primary human CD4 T cells with and CD28 As shown in activation was dependent on stimulation. the activity of MAP kinase ERK, there is no effect on activity in primary CD4 T cells by HIV of protein is also displayed in A. MAP kinase, p38, is also activated by phosphorylation J. Lee L. Science. 1994; PubMed Scopus Google Scholar, J. S. M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). to ERK, the phosphorylation of was less and As shown in activation of in the or of Nef was kinase known as protein kinase is of activity and is on by a kinase kinase L. K. D. F. P. J. Science. PubMed Scopus Google Scholar) and on by A. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar). of the surface receptors resulted in the phosphorylation of as shown in and Nef expression to have no The NF-κB transcription factor is to the factor D. Science. PubMed Scopus Google Scholar). The phosphorylation of T. S. EMBO J. PubMed Scopus Google Scholar, K. S. L. G. U. Science. PubMed Scopus Google Scholar) to and of which with NF-κB nuclear T cell activation K. C. M. D.J. Mol. Cell. Biol. PubMed Google Scholar, A. S.J. W. C.H. J. Immunol. 1999; Google Scholar). examine the effect of Nef on Nef-expressing and cells with and to as and by of cells to phosphorylation of and expression of Nef to no in this of the T cell receptor also in a of a effect of activity. calcium was by of calcium by of and Nef cells to T cell receptor stimulation resulted in similar cellular calcium as shown in D. Nef increased the of ERK MAP kinase but not to affect define pathway we the of and the T cell kinases for ERK and JNK, As with the T cells activated by engagement of the T cell ERK, phosphorylation was to be with the levels with the and the Nef cells, the Nef-expressing cells displayed an increase in the of activity, as by of the serine phosphorylation by As with the ERK we not see Nef-mediated activation in the of T cell receptor stimulation. of the of the kinase in the demonstrated a similar on surface receptor stimulation with the of Nef on activity was by Nef The increased phosphorylation of ERK by and of by the pathway by Nef phosphorylation define to ERK MAP ERK MAP kinase induces numerous transcription the phosphorylation of M. O. C. C. EMBO J. PubMed Scopus Google Scholar). on the of activated and Nef-expressing primary CD4 T phosphorylation of the was in the Nef-expressing cells, with the Nef cell or cells not The increased phosphorylation of Elk was not to an increase in Elk protein levels in the cell. In addition to MAP kinase ERK, can be by the MAP kinases and R. T. EMBO J. 1997; PubMed Scopus Google Scholar, M.A. R. EMBO J. 1996; PubMed Scopus Google Scholar, A.J. A.D. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar), although activation of or in these studies does not to be affected by in an in kinase phosphorylation by ERK kinase activity that was from and from of activated As shown in there was an increased of ERK MAP kinase activity in Nef-expressing T cells T cell consistent with increased phosphorylation in Nef-expressing cells that the ERK MAP kinase activation is in Nef-expressing primary CD4 T The of effect on pathways from the T cell surface receptor that this activity is for the in T cell activity. In the mediated increase in ERK MAP kinase activity also Nef to characterized HIV ERK activity has been demonstrated to increase HIV expression X. Y. D. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar) and HIV replication E. P. A. C. J. Virol. PubMed Google Scholar). Furthermore, viral infectivity has been to be affected by ERK and by activation of this pathway J.M. Mann A. N. B. Stevenson M. EMBO J. PubMed Scopus Google Scholar, X. D. J. Virol. 1999; 73: PubMed Google Scholar). increases infectivity of HIV B. L. M. S. L. Gallo R.C. F. Science. PubMed Scopus Google Scholar, K. D. K. D. T. M.A. Nature. PubMed Scopus Google Scholar), and phosphorylation by ERK increases the activity of this viral regulatory protein X. D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, the capacity of Nef to increase ERK activity that a of this viral protein in virion infectivity in be to activity. work with CD4 T cells that Nef expression by does not the MAP kinase In our there is a for stimulation of the surface T cell is consistent with that the Nef-mediated IL-2 in primary human CD4 T cells activation J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar, 17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar) and that the HIV of T cell IL-2 is also dependent on T cell receptor stimulation (31Wu Y. Marsh J.W. Science. 2001; 293: 1503-1506Crossref PubMed Scopus (307) Google M. S. C. G. J. N. T. S. Verdin E. Science. 1997; 275: PubMed Scopus Google Scholar). finding appears to from a recent demonstration that co-expression of Nef with Vav, through Pak, increases activity in NIH3T3 cells (27Fackler O.T. Luo W. Geyer M. Alberts A.S. Peterlin B.M. Mol. Cell. 1999; 3: 729-739Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar). not an increase in activity with Nef in the of or T cell receptor stimulation. be the of NIH3T3 cells result in expression levels of Nef and seen in the cells Pak can in numerous cells A. J. P. M. S. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar, L. M. J. S. J. Curr. Biol. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar), Pak activity in T cells, receptor has been shown to be for ERK activity but not D. L.P. D. Weiss A. EMBO J. PubMed Scopus Google Scholar). The of Pak in ERK activity is and Nef are by the for Nef to associate with different Pak and different (26Brown A. Wang X. Sawai E. Cheng-Mayer C. J. Virol. 1999; 73: 9899-9907Crossref PubMed Google Scholar, V. R. J. J. J. B. J. J. Virol. 2000; PubMed Scopus Google Scholar, J.A. Geyer M. B. Luo W. A. Alberts A.S. 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Full Text Full Text PDF PubMed Scopus Google Scholar), but the effect of this association on kinase activity is The positive effect of Nef on T cell IL-2 stimulation has been in and human T cell as as in primary human T cells (14Rhee S.S. Marsh J.W. J. Immunol. 1994; 152: 5128-5134PubMed Google Scholar, 15Alexander L., Du, Z. Rosenzweig M. Jung J.U. Desrosiers R.C. J. Virol. 1997; 71: 6094-6099Crossref PubMed Google Scholar, 16Schrager J.A. Marsh J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 8167-8172Crossref PubMed Scopus (161) Google Scholar, 17Wang J.K. Kiyokawa E. Verdin E. Trono D. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 394-399Crossref PubMed Scopus (251) Google Scholar). The of this to the biochemical activity of Nef in T cells is by the recent demonstration that Nef from HIV also increases this T cell (31Wu Y. Marsh J.W. Science. 2001; 293: 1503-1506Crossref PubMed Scopus (307) Google Scholar). that Nef increases both murine and human T cell activity, we the that Nef expression in increased ERK activity in human T cells is by the transgenic study of Z. N. A. S. P. Cell. Full Text Full Text PDF PubMed Scopus Google Scholar). that murine phosphorylation of the phosphorylation of ERK, of activation by A.J. P. J. EMBO J. 1991; PubMed Scopus Google Scholar, R. J. J.A. J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar). Thus, the for Nef bioactivity in primary CD4 T cells to be in cellular Although the pathogenesis be this Nef activity is with a in these that is similar to the seen in studies of the molecular activity of Nef that the MAP kinase pathway is In the for ERK MAP kinase activity T cell activation pathways an for biochemical of Nef molecular activity. of the of of for for the Nef expression and and for of the