NF-κB and STAT5 Play Important Roles in the Regulation of Mouse Toll-Like Receptor 2 Gene Expression

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Abstract
Toll-like receptor 2 (TLR2) is involved in the innate immunity by recognizing various bacterial components. We have previously reported that TLR2 gene expression is rapidly induced by LPS or inflammatory cytokines in macrophages, and by TCR engagement or IL-2/IL-15 stimulation in T cells. Here, to investigate the mechanisms governing TLR2 transcription, we cloned the 5′ upstream region of the mouse TLR2 (mTLR2) gene and mapped its transcriptional start site. The 5′ upstream region of the mTLR2 gene contains two NF-κB, two CCAAT/enhancer binding protein, one cAMP response element-binding protein, and one STAT consensus sequences. In mouse macrophage cell lines, deletion of both NF-κB sites caused the complete loss of mTLR2 promoter responsiveness to TNF-α. NF-κB sites were also important but not absolutely necessary for LPS-mediated mTLR2 promoter activation. In T cell lines, mTLR2 responsiveness to IL-15 was abrogated by the 3′ NF-κB mutation, whereas 5′ NF-κB showed no functional significance. The STAT binding site also seemed to contribute, as the deletion of this sequence significantly reduced the IL-15-mediated mTLR2 promoter activation. EMSAs confirmed nuclear protein binding to both NF-κB sites in macrophages following LPS and TNF-α stimulation and to the 3′ NF-κB site in T cells after IL-15 treatment. Thus, NF-κB activation is important but differently involved in the regulation of mTLR2 gene expression in macrophages and T cells following LPS or cytokine stimulation.