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A Promoter Recruitment Mechanism for Tumor Necrosis Factor-α-induced Interleukin-8 Transcription in Type II Pulmonary Epithelial Cells

The alveolar macrophage-derived peptide tumor necrosis factor-α (TNFα) initiates pulmonary inflammation through its ability to stimulate interleukin-8 (IL-8) synthesis in alveolar epithelial cells through an incompletely described transcriptional mechanism. In this study, we use the technique of ligation-mediated polymerase chain reaction (LMPCR) to record changes in transcription factor occupancy of the IL-8 promoter after TNFα stimulation of A549 human alveolar cells. Using dimethylsulfate/LMPCR, no detectable proteins bind the TATA box in unstimulated cells. By contrast, TNFα rapidly induces protection of G residues at −79 and −80 coincident with endogenous IL-8 gene transcription. Using DNase I/LMPCR, we observe inducible protection of nucleotides −60 to −99 (the TNF response element) and nucleotides −3 to −32 (containing the TATA box). Surprisingly, extensive TATA box protection is only seen after TNFα stimulation. Using a two-step microaffinity isolation/Western immunoblot DNA binding assay, we observe that the NF-κB subunits Rel A, NF-κB1, and c-Rel inducibly bind the TNF response element; these proteins undergo rapid TNFα-inducible increases in nuclear abundance as a consequence of IκBα proteolysis. Furthermore, the peptide aldehyde N-acetyl-Leu-Leu-norleucinal, an agent that blocks both IκBα proteolysis and NF-κB subunit translocation, abrogates recombinant human TNFα-inducible IL-8 gene transcription. These studies demonstrate that IL-8 is activated by a promoter recruitment mechanism in alveolar epithelial cells, where NF-κB subunit translocation is required for (and coincident with) binding of the constitutively active TATA box-binding proteins.