Efecto de la proteína Tat de VIH-1 en los mecanismos de activación de los linfocitos T

Abstract

HIV-1-Tat affects cellular gene expression through modulation of the activity of different transcription factors. However, the molecular mechanisms by which intracellular Tat affects gene expression are not fully understood. Here, we have investigated the role of Tat on the cooperation between nuclear factor of activated T cells (NFAT) and activator protein 1 (AP-1) transcription factors. Constitutive or transient Tat expression in Jurkat T cells enhanced cooperative NFAT/AP-1, but not AP-1, dependent transcription independently of its ability to transactivate the HIV long terminal repeat (LTR). Furthermore, transactivation of a NFAT/AP-1 reporter by transfection of NFAT and c-Jun was strongly enhanced by simultaneous Tat transfection. Moreover, intracellular Tat expression increased the binding of NFAT/AP- 1 complexes to the interleukin 2 (IL-2) promoter. HIV-1-Tat interacted with NFAT but not c-Jun. These results indicate that Tat interacts with NFAT affecting its cooperation with AP- 1 . Transiently expression of HIV-1-Tat enhanced the transactivation activity of the aminoterminal transactivation domain (TAD-A) of NFATc2. We mapped this functional interaction in the first 144 aminoacids of NFATc2 TAD-A. Moreover, Tat cooperated with the kinases Cok, PKCç and NIK and with the coactivator CBP/p300 in this increase. Furthermore, the transiently transfection of a constitutive active form of calcineurin enhanced synergistically the effect of Tat upon NFATc2 Tat, however, calcineurin and Tat there was no interaction between both of them. The over-expression of HDAC1 increased the transcriptional activity of NFATc2. Tat cooperates with proteins that activates the transcriptional activity of NFAT, increasing their effects. Furthermore, Tat-stably expressing cells had less surface expression of the HIV- 1 correceptor in T-cells CXCR4 in presence of fetal calf serum (FCS) but did not affect to CXCR4 transcription. Tat increased the internalization of the receptor in the presence of its ligand, stromal cell-derived factor 1 (SDF-1), but did not affect the internalization of other T cell receptors in the same way. These results indicate that Tat modulates the expression of CXCR4 in the surface of Tat-expressing cells. 3