IL-4 upregulates IL-1-induced chemokine gene expression in bone marrow stromal cells by enhancing NF-kB activation

Bone marrow stromal cells play a critical role in the proliferation and differentiation of hematopoietic stem and progenitor cells by secreting numerous hematopoietic growth factors and colony-stimulating factors (CSFs). We have previously reported that monocyte chemotactic protein-1 (MCP-1 or MCP-1/JE) and interferon-inducible protein 10 KD (IP-10) are both induced in murine bone marrow stromal cell line +/(+)-1.LDA11 upon stimulation with various inflammatory agents, including IL-1 alpha, IFN-gamma, TNF-alpha, or LPS. In addition, the expression of MCP-1/JE and IP-10 mRNA by these inducers is potentiated by IL-4 and TGF-beta 1. In the present study we have investigated the mechanism of IL-4-mediated upregulation of MCP-1/JE gene expression. Our results of nuclear run-on experiments show that IL-4 enhances the IL-1-induced transcription of MCP-1/JE gene. Because the transcription of genes is regulated by DNA binding nuclear factors and binding sites for transcription factors AP-1 and SP-1, and NF-kB in the enhancer region of MCP-1/JE have been demonstrated, we examined the effect of IL-4 on the levels of these factors in stromal cells stimulated with IL-1. Whereas AP-1 and SP-1 are constitutively expressed in stromal cells, NF-kB is detected only after stimulation with IL-1. Furthermore, while unable to induce the activation of NF-kB alone, IL-4 enhanced the activation of NF-kB by IL-1. Taken together, these data suggest that upregulation of NF-kB may be the mechanism by which IL-4 increases the transcription of MCP-1/JE gene resulting in overabundance of the chemokine mRNA.