Regulation of MCP-1 expression by C/EBPbeta and HIV Tat

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DESCRIPTION (provided by applicant): HIV-1 infection of the central nervous system leads to the development of dementia, also known as HIV-1 associated dementia, HAD, in greater than 30% of AIDS patients. Infiltration of monocytes and macrophages to the brain correlating with the development and progression of dementia is among the key pathologic features of the HAD. Monocyte chemoattractant protein 1, MCP-1, a beta chemokine, has received special attention due to its elevated levels in brain tissue and in cerebrospinal fluid of patients with HAD. It is believed that the increased expression of MCP-1 in the brain promotes the attraction of activated monocytes and macrophages to the brain where they cause neuronal cell death by releasing several inflammatory cytokines and immunomodulators. Earlier studies by several laboratories including ours have indicated that the HIV-1 regulatory protein, Tat, has the ability to augment transcription of the MCP-1 gene and the secretion of this chemoattractant protein in primary human astrocytes. However, the mechanism involved in the activation of MCP-1 by Tat remains unknown. Our recent studies have established the capacity of C/EBPbeta DNA binding transcription factor in stimulating expression of the MCP-1 promoter in astrocytes. C/EBP-beta is a ubiquitous regulatory protein whose activity can be modulated through its association with partners such as CHOP, cmyb, and Spl. Further, our results demonstrate the ability of Tat to specifically interact with C/EBP-beta, and cooperate with C/EBP-beta in enhancing transcription of the MCP-1 promoter in human astrocytes. On the other hand, Tat has been shown to stimulate transcription of genes encoding TNFalpha and TGFbeta-1 whose products trigger the signaling pathways causing the activation of p50/p65 subunits of NFKappaB and Smads family of transcription factors, respectively. Examination of NFrJ3 and Smads activities upon the MCP-1 promoter in human astrocytes revealed that by associating with C/EBP-beta, p50/p65 elevates transcription of MCP-1, whereas the interaction of Smad3 with C/EBPbeta suppresses the level of MCP-1 gene transcription. This observation implies that the delicate balance between the two signaling event induced by Tat can dictate, via C/EBP-beta, the level of MCP-1 gene expression. These observations led us to hypothesize that Tat modulates transcription of MCP-1 in the CNS directly by associating with C/EBP-beta and its partners and/or indirectly by stimulating cytokine signaling pathways that communicate with C/EBP-beta. To test this hypothesis, we will perform a comprehensive series of structural and functional experiments using a variety of molecular biology and cell biology in vitro and in vivo techniques to decipher the mechanism involved in Tat-induced activation of MCP-1 in astrocytes and microglia. The outcome of these mechanistic studies will provide important information that can be utilized for devising molecular therapeutic tools for interfering with the activation of MCP-1 gene expression in the CNS.