Local production of macrophage inflammatory protein-1beta (MIP-1beta), a beta-chemokine that blocks human immunodeficiency virus type 1 (HIV-1) entry into CD4+ CC chemokine receptor 5+ target cells, may be a significant factor in resistance to HIV-1 infection and control of local viral spread. The mechanisms governing MIP-1beta expression in T cells, however, are not well understood. Our results suggest that MIP-1beta RNA expression in T cells is dynamically regulated by transcriptional factors of the cyclic adenosine monophosphate (cAMP) responsive element (CRE)-binding (CREB)/modulator family. Transient transfection of primary human T cells with 5' deletion and site-specific mutants of the human MIP-1beta promoter identified an activated protein-1 (AP-1)/CRE-like motif at position -74 to -65 base pairs, relative to the TATA box as a vital cis-acting element and a binding site for inducible cAMP early repressor (ICER). Ectopic expression of ICER or induction of endogenous ICER with the cAMP agonists forskolin and prostaglandin E2 resulted in the formation of ICER-containing complexes, including an ICER:CREB heterodimer to the AP-1/CRE-like site and inhibition of MIP-1beta promoter activity. Our data characterize an important binding site for the dominant-negative regulator ICER in the MIP-1beta promoter and suggest that dynamic changes in the relative levels of ICER and CREB play a crucial role in cAMP-mediated attenuation of MIP-1beta transcription in human T cells.
Abstract IFN-α-2b, known as potent immune modulator, can either inhibit or enhance immune cell activity within the tightly regulated microenvironment of inflammation, depending upon the concentration of the cytokine and the activation stage of the cell. Chemokine receptors, which not only mediate chemotaxis of immune cells to the site of inflammation but also affect cellular activation by transferring corresponding signals, represent yet another level of immune regulation. Here we demonstrate that IFN-α increases the expression of CCR1 and CCR3 in primary mononuclear phagocytes, as well as in the monocytoid cell line U937. Enhanced receptor mRNA expression correlated with functional readouts such as increased intracellular calcium mobilization and cell migration in response to ligands. Expression of CCR2b, CCR4, CCR5, and CXCR4 was unchanged or decreased after IFN-α treatment. These observations indicate a differentially regulated cellular signaling relationship of IFN-α pathways and chemokine receptor expression. We also provide evidence that, under these conditions, IFN-α treatment increased the expression of CD95 (Fas, Apo1), resulting in enhanced susceptibility to apoptosis. Taken together, these data add important information for the rational application of IFN-α (2b) in immune and cancer therapies.
IFN-alpha-2b, known as potent immune modulator, can either inhibit or enhance immune cell activity within the tightly regulated microenvironment of inflammation, depending upon the concentration of the cytokine and the activation stage of the cell. Chemokine receptors, which not only mediate chemotaxis of immune cells to the site of inflammation but also affect cellular activation by transferring corresponding signals, represent yet another level of immune regulation. Here we demonstrate that IFN-alpha increases the expression of CCR1 and CCR3 in primary mononuclear phagocytes, as well as in the monocytoid cell line U937. Enhanced receptor mRNA expression correlated with functional readouts such as increased intracellular calcium mobilization and cell migration in response to ligands. Expression of CCR2b, CCR4, CCR5, and CXCR4 was unchanged or decreased after IFN-alpha treatment. These observations indicate a differentially regulated cellular signaling relationship of IFN-alpha pathways and chemokine receptor expression. We also provide evidence that, under these conditions, IFN-alpha treatment increased the expression of CD95 (Fas, Apo1), resulting in enhanced susceptibility to apoptosis. Taken together, these data add important information for the rational application of IFN-alpha (2b) in immune and cancer therapies.
