CCAAT-enhancer-binding protein beta (C/EBP beta) activates CCR5 promoter: Increased C/EBP beta and CCR5 in T lymphocytes from HIV-1-infected individuals

C/EBP beta is a member of a family of leucine zipper transcription factors that are involved in regulating the expression of several cytokines, including IL-1, IL-6, IL-8, TNF, and macrophage-inflammatory protein-1 alpha. We identified multiple C/EBP beta binding sites within the gene for CCR5, suggesting that C/EBP beta may be involved in its regulation. Transient transfection experiments in both myeloid and lymphoid cells showed an increase in CCR5 promoter-driven green fluorescent protein production in the presence of C/EBP beta. Deletion analysis identified two C/EBP beta -responsive regions in the CCR5 gene, one in the promoter region and one at the 3' part of the intron. We provide evidence that, in myeloid cells (U937), C/EBP beta independently activates CCR5 expression through sites located either in the promoter region or in the intron of the CCR5 gene. In contrast, in lymphoid cells (jurkat) the presence of the intronic cis-regulatory regions is required for C/EBP beta -mediated activation. In agreement with the functional data, EMSA demonstrated that in both myeloid and lymphoid cells C/EBP beta binds specifically to sites present in the intron, whereas interaction with the sites located in the promoter was cell type specific and was detected only in myeloid cells. Analysis of C/EBP beta in primary PBMCs obtained from HIV-1-infected individuals revealed a significant increase in C/EBP beta expression. The enhanced C/EBP beta activity correlated with a higher frequency of circulating CCR5(+) lymphocytes in AIDS patients and with a decline in CD4 lymphocyte numbers. Taken together, these results suggest that C/FBP beta is an important regulator of CCR5 expression and may play a relevant role in the pathogenesis of HIV disease.

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