Regulation of the NK-1 receptor gene expression in human macrophage cells via an NF-κB site on its promoter

We report here that human monocytic/macrophage THP-1 cells express the neurokinin 1 receptor (NK-1R), and that exposure of these cells to the proinflammatory cytokine IL-1beta increased the expression of the NK-1R gene at the mRNA and protein levels. Because IL-1beta function involves nuclear factor KB (NF-kB) activation, these data suggest that this increase in the expression of the NK-1R gene is mediated by the NF-KB transcription factor. An earlier report noted that the promoter region of the human NK-1R gene contains a putative binding site for NF-KB [Takahashi, K., Tanaka, A., Hara, M. & Nakanishi, S. (1992) Eur. J. Biochem. 204, 1025-1033]. Here we demonstrate that this is indeed a functional NF-KB-binding site, and that NF-KB is responsible for regulating the expression of the NK-1R gene by binding to the promoter region of the NK-1R gene. To further substantiate that the observed NF-KB-dependent IL-1beta induction of the human NK-1R gene is regulated via a transcriptional event through this NF-KB site on the NK-1R gene promoter, we transfected THP-1 cells with a luciferase promoter-reporter construct containing the 5' promoter region of the human NK-1R gene. Exposure of these cells to IL-1beta or overexpression of NF-KB cDNAs resulted in a significant increase in the amount of luciferase activity that was diminished greatly in cells transfected with IKBalpha, the NF-KB inhibitor. These results directly implicate NF-KB in the regulation of the NK-1R gene and provide a molecular mechanism for the increase in expression of the NK-1R gene in responsive cells.