Vav exchange factor counteracts the HIV-1 Nef-mediated decrease of plasma membrane GM1 and NF-AT activity in T cells.
Several findings support the importance of GM1-enriched lipid microdomains of plasma membrane and of Vav, an essential regulator of actin cytoskeletal rearrangement, in the regulation of T cell activation. Moreover, a functional link among lipid microdomains, Vav and the HIV product Nef has been described. These observations suggest that Nef can modify plasma membrane GM1, affecting the behavior of HIV-infected cells towards antigen recognition and Vav towards counteracting such an effect. We observed that Nef expression, either following viral infection or ectopic expression, significantly decreased the level of plasma membrane GM1 in unstimulated T cells. This down-regulation was associated with the inhibition of NF-AT activation, but not with NF-kappaB activation induced by TCR engagement. Dissecting the signaling pathway that regulates NF-AT activation, we found that Nef inhibited exclusively the Ca(2+)/calcineurin cascade, whereas the JNK cascade and AP-1 transcriptional activity were not affected. Our evidence that Vav overexpression counteracted both the Nef-induced decrease of GM1 expression and the inhibition of NF-AT activity, suggests a novel mechanism by which Nef may interfere with TCR-mediated activation through the modulation of intracellular trafficking and clustering of GM1-enriched microdomains at the cell surface.
Tuosto
Loretta
L
Department of Cellular and Developmental Biology, La Sapienza University, Rome, Italy.
Marinari
Barbara
B
Andreotti
Mauro
M
Federico
Maurizio
M
Piccolella
Enza
E
D020013:Calcium Signaling; D018797:Cell Cycle Proteins; D002462:Cell Membrane / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005677:G(M1) Ganglioside / Q000378:metabolism*; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D016328:NF-kappa B / Q000378:metabolism; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D054311:nef Gene Products, Human Immunodeficiency Virus
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D015693:Gene Products, nef; D016328:NF-kappa B; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011948:Receptors, Antigen, T-Cell; D014157:Transcription Factors; C496618:VAV1 protein, human; D054311:nef Gene Products, Human Immunodeficiency Virus; D005677:G(M1) Ganglioside