ABSTRACT
Replication of immunodeficiency viruses (HIV-1 and SIV) in immature dendritic cell (DC)-T cell cocultures is dependent on Nef. In contrast, mature DCs promote the replication of wild-type and nef-defective SIV in concert with CD4(+) T cells. Transcription factor activation occurs on DC maturation and this study aimed to investigate whether Nef triggers similar events in immature DCs, rendering them more like mature DCs. Recombinant HIV nef-expressing adenovirus was used to selectively introduce nef into immature human or macaque DCs. These data provide the first evidence that the expression of HIV nef in immature DCs induced selective activation of STAT3 and, to a lesser extent, NF-kappaB. This highlights how Nef can signal primary immature DCs, suggesting one way in which Nef may modulate immature DCs to drive virus replication in the DC-T cell milieu.
Subject(s)
DNA-Binding Proteins/metabolism , Dendritic Cells/metabolism , Gene Products, nef/metabolism , Trans-Activators/metabolism , Transcriptional Activation , Adenoviridae/genetics , Animals , Cells, Cultured , Dendritic Cells/cytology , Gene Products, nef/genetics , Genetic Vectors , Humans , Macaca , Male , NF-kappa B/metabolism , Recombination, Genetic , STAT3 Transcription FactorABSTRACT
Stats1 and 3 (signal transducers and activators of transcription) can be activated simultaneously, although not necessarily to the same degree or duration, by the interaction of cells with the same polypeptide ligand (EGF, PDGF, or high concentrations of IL-6, for example). However, these two Stat proteins can mediate opposing effects on cell growth and survival. Stat1 activation slows growth and promotes apoptosis. In contrast, activated Stat3 can protect cells from apoptosis. Furthermore, a constitutively active form of Stat3, Stat3-C (bridged by S-S linkages between cysteines instead of phosphotyrosines) can induce cellular transformation of fibroblasts. We have determined that fibroblasts transformed by Stat3-C are more resistant to proapoptotic stimuli than nontransformed cells. Also, to examine the potential opposing roles in apoptosis of Stat1 and Stat3, we studied the cervical carcinoma-derived cell line, Me180, which undergoes Stat1-dependent, IFN gamma-induced apoptosis. Me180 cells that express Stat3-C are protected against IFN gamma-mediated apoptosis.
Subject(s)
Apoptosis , DNA-Binding Proteins/metabolism , Signal Transduction , Trans-Activators/metabolism , 3T3 Cells , Animals , Cell Line, Transformed , Culture Media, Serum-Free , DNA-Binding Proteins/genetics , Fibroblasts/cytology , Fibroblasts/metabolism , Growth Inhibitors/pharmacology , Humans , Interferon-gamma/pharmacology , Mice , Oncogene Protein pp60(v-src)/genetics , Oncogene Protein pp60(v-src)/metabolism , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins c-bcl-2/genetics , STAT1 Transcription Factor , STAT3 Transcription Factor , Trans-Activators/genetics , Tumor Cells, Cultured , Ultraviolet Rays , bcl-2-Associated X Protein , bcl-X ProteinABSTRACT
STATs are latent transcription factors that mediate cytokine- and growth factor-directed transcription. In many human cancers and transformed cell lines, Stat3 is persistently activated, and in cell culture, active Stat3 is either required for transformation, enhances transformation, or blocks apoptosis. We report that substitution of two cysteine residues within the C-terminal loop of the SH2 domain of Stat3 produces a molecule that dimerizes spontaneously, binds to DNA, and activates transcription. The Stat3-C molecule in immortalized fibroblasts causes cellular transformation scored by colony formation in soft agar and tumor formation in nude mice. Thus, the activated Stat3 molecule by itself can mediate cellular transformation and the experiments focus attention on the importance of constitutive Stat3 activation in human tumors.
