Cooperative interaction of C/EBP beta and Tat modulates MCP-1 gene transcription in astrocytes.
The chemoattractant protein 1 (MCP-1) is one of the most potent monocyte chemoattractants whose level is elevated during the course of AIDS dementia. Earlier studies showed that HIV-1 Tat protein is able to induce transcription of the MCP-1 promoter in astrocytic cells. Furthermore, the TGFbeta-1 signaling pathway through its regulatory proteins, Smads, modulates Tat activation of MCP-1. Here, we demonstrate that C/EBPbeta, whose activity is enhanced by a variety of cytokines during the course of viral infection, can stimulate basal- and Tat-mediated transcription of MCP-1 in human astrocytic cells. Results using promoter deletion mutants suggested the importance of multiple C/EBPbeta binding sites scattered within -200 to +1 of the MCP-1 promoter in the observed activity. Results from DNA binding studies have shown that the interaction of C/EBPbeta with its DNA motif is diminished by the C/EBPbeta homologous protein, CHOP, which possesses the ability to suppress the stimulatory effect of C/EBPbeta on MCP-1 transcription. Tat, which possesses the ability to interact with C/EBPbeta, alleviates the negative effect of CHOP and restores C/EBPbeta interaction with the DNA. Furthermore, Smad3 and its C-terminal regulatory motif, MH2, interact with C/EBPbeta and modulate its DNA binding and transcriptional activity on the MCP-1 promoter. Our results show that the physical and functional interactions of C/EBPbeta and Tat are severely affected by the presence of Smad3 and MH2. Altogether, these observations identify C/EBPbeta as a new partner for Tat in stimulating MCP-1 transcription in astrocytes and suggest that the delicate balance among the downstream regulatory proteins of several cytokines and immunomodulators can dictate the level of expression of chemoattractants, including MCP-1. Hence, inappropriate expression and function of regulatory proteins such as C/EBPbeta and Smads by Tat may induce MCP-1 production in astrocytes and contribute to the neuropathogenesis of AIDS through stimulation of inflammation in the CNS.
Abraham
Selvajothi
S
Center for Neurovirology and Cancer Biology, Temple University, 1900 North 12th Street, 015-96, Room 203, Philadelphia, PA 19122, USA.
Sweet
Thersa
T
Sawaya
Bassel E
BE
Rappaport
Jay
J
Khalili
Kamel
K
Amini
Shohreh
S
D021581:Active Transport, Cell Nucleus / Q000235:genetics; D020816:Amino Acid Motifs / Q000235:genetics; D001253:Astrocytes / Q000276:immunology* / Q000378:metabolism* / Q000821:virology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism / Q000502:physiology*; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D018932:Chemokine CCL2 / Q000235:genetics* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D015696:Gene Products, tat / Q000378:metabolism / Q000502:physiology*; D005982:Glutathione Transferase / Q000235:genetics; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D017384:Sequence Deletion; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D051900:Smad3 Protein; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology; D054322:tat Gene Products, Human Immunodeficiency Virus
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D018932:Chemokine CCL2; C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D015696:Gene Products, tat; D011993:Recombinant Fusion Proteins; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D054322:tat Gene Products, Human Immunodeficiency Virus; D051742:Transcription Factor CHOP; D005982:Glutathione Transferase