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97 T-Cell Receptor-Mediated HIV-1 LTR Activation Is Strongly Up-Regulated upon CD43 Cross-Linking: Involvement of NFAT and NF?B
C. Barat, J. Roy*, and M. J. Tremblay
Laval Univ., Ste-Foy, Québec, Canada
Background: CD43 (sialophorin) is a sialoglycoprotein expressed on the surface of a wide variety of blood cells including T lymphocytes, monocytes, neutrophils, and platelets. Numerous studies reported that CD43 ligation induces activation and proliferation of T cells, monocytes, and dendritic cells. Considering that CD43 is the most abundant membrane protein of leucocytes, we investigated the effect of CD43-mediated signaling events on both HIV-1 transcription and replication.
Methods: Using monoclonal antibodies against the CD43 molecule, we assessed the effect of CD43 cross-linking on HIV-1 LTR activity through luciferase-based reporter gene assays in Jurkat cells. Nuclear proteins were extracted from anti-CD43-treated human T lymphoid and primary CD4+ T cells and then used in EMSA with 32P-labelled region of the HIV-1 enhancer sequence. The involvement of different intracellular components (i.e., p56lck, LAT, SLP-76, and Ca++) were assessed using different Jurkat-derived deficient cell lines (i.e., JCAM1.6, JCAM2, J14-V29, and CJ, respectively).
Results: We demonstrated that cross-linking of CD43 with monoclonal antibodies induced a potentiation of the TCR-mediated HIV-1 LTR activation in both transfection assays and HIV-1-infected cells. To achieve transcriptional activation, a suboptimal concentration of anti-CD3 antibody was required. In addition, EMSA experiments demonstrated that CD43-mediated signaling events induce NFAT and NF?B binding activities to the HIV-1 enhancer. Moreover, p56lck, LAT, SLP-76, and Ca++ were shown to be important for CD43-mediated costimulation of HIV-1 LTR activity.
Conclusions: These results are the first demonstration that CD43 can act as a potent costimulating molecule to TCR-mediated HIV-1 LTR activation and this effect is independent of CD28. The suboptimal concentration of anti-CD3 suggested that CD43-mediated signaling could lower the threshold for TCR/CD3 activation. Overall, our results enlarged our understanding of signaling events leading to HIV-1 LTR activation and provided new insights in regard to the 2-signal model in human T cells. Such an understanding of T-cell biology could lead to the design of better drugs and to the development of more efficient vaccines.
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