HIV-1 Tat regulates endothelial cell cycle progression via activation of the Ras/ERK MAPK signaling pathway

• Published in: Molecular biology of the cell 2006-04, Vol.17 (4), p.1985-1994
• Main Authors: Toschi, Elena, Bacigalupo, Ilaria, Strippoli, Raffaele, Chiozzini, Chiara, Cereseto, Anna, Falchi, Mario, Nappi, Filomena, Sgadari, Cecilia, Barillari, Giovanni, Mainiero, Fabrizio, Ensoli, Barbara
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - metabolism; Cell Cycle; Cell Proliferation; Cells, Cultured; Endothelial Cells - cytology; Endothelial Cells - enzymology; Endothelial Cells - virology; Enzyme Activation; Gene Products, tat - physiology; GRB2 Adaptor Protein - metabolism; HIV-1 - physiology; Human immunodeficiency virus 1; Humans; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Oligopeptides - metabolism; Phosphorylation; ras Proteins - metabolism; Sarcoma, Kaposi - enzymology; Sarcoma, Kaposi - virology; Shc Signaling Adaptor Proteins; Signal Transduction; Src Homology 2 Domain-Containing, Transforming Protein 1; tat Gene Products, Human Immunodeficiency Virus
• ISSN: 1059-1524; 1939-4586; 1059-1524
• DOI: 10.1091/mbc.E05-08-0717

Tat, the transactivator of HIV-1 gene expression, is released by acutely HIV-1-infected T-cells and promotes adhesion, migration, and growth of inflammatory cytokine-activated endothelial and Kaposi's sarcoma cells. It has been previously demonstrated that these effects of Tat are due to its ability to bind through its arginine-glycine-aspartic (RGD) region to the alpha5beta1 and alphavbeta3 integrins. However, the signaling pathways linking Tat to the regulation of cellular functions are incompletely understood. Here, we report that Tat ligation on human endothelial cells results in the activation of the small GTPases Ras and Rac and the mitogen-activated protein kinase ERK, specifically through its RGD region. In addition, we demonstrated that Tat activation of Ras, but not of Rac, induces ERK phosphorylation. We also found that the receptor proximal events accompanying Tat-induced Ras activation are mediated by tyrosine phosphorylation of Shc and recruitment of Grb2. Moreover, Tat enabled endothelial cells to progress through the G1 phase in response to bFGF, and the process is linked to ERK activation. Taken together, these data provide novel evidence about the ability of Tat to activate the Ras-ERK cascade which may be relevant for endothelial cell proliferation and for Kaposi's sarcoma progression.