Regulation of MCP-1 gene transcription by Smads and HIV-1 Tat in human glial cells.
Expression of several cytokines involved in signal transduction such as TGFbeta-1 and the inflammatory chemokines including MCP-1 is elevated during the course of AIDS progression. The enhancement of these cellular proteins in astrocytic cells is mediated, at least in part, by HIV-1 Tat protein. Here, we investigate the possible regulation of MCP-1 transcription by Tat and the Smad family of transcription factors whose activities are induced by the TGFbeta-1 pathway. Results from transfection studies revealed that Smad-3 stimulates basal and Tat-mediated transcription of MCP-1 in human astrocytic cells. Smad-4, on the other hand, had no effect on the basal activity of the MCP-1 promoter, but showed the ability to decrease both Smad-3 and Tat-induced transcription of the MCP promoter. Results from protein-binding studies revealed the ability of both Smad-3 and Smad-4 to associate with the region of Tat spanning residues 1-40. Examination of the transcriptional activity of the various domains of Smad including MH1, at the N-terminus, and MH2, at the C-terminus of the protein indicated that neither MH1 or MH2 alone positively cooperate with Tat in modulating MCP-1 transcription. However, ectopic expression of MH1 and, more notably, MH2 severely suppressed transcriptional activation of MCP-1 by Tat in astrocytic cells. Binding studies revealed that similar to the full-length Smad protein, both MH1 and MH2 associate with Tat protein and that the residues between 1 and 40 of Tat are important for their interaction. These observations reveal a novel mechanism for Tat-mediated transcriptional activation via TGFbeta signaling pathway and provide evidence for regulation of MCP-1 gene transcription by this signaling pathway in human astrocytic cells.
Abraham
Selvajothi
S
Center for Neurovirology and Cancer Biology, College of Science and Technology, Temple University, 1900 North 12th Street, 015-96, Room 203, Philadelphia, PA 19122, USA.
Sawaya
Bassel E
BE
Safak
Mahmut
M
Batuman
Olcay
O
Khalili
Kamel
K
Amini
Shohreh
S
D001253:Astrocytes / Q000378:metabolism*; D002460:Cell Line; D018932:Chemokine CCL2 / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D015696:Gene Products, tat / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015398:Signal Transduction; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism
D018932:Chemokine CCL2; D004268:DNA-Binding Proteins; D015696:Gene Products, tat; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta