Inhibition of tumor necrosis factor-α transcription in macrophages exposed to febrile range temperature -: A possible role for heat shock factor-1 as a negative transcriptional regulator

We previously reported that expression of tumor necrosis factor-alpha (TNF alpha) was attenuated in macrophages exposed to febrile range temperatures. In this study, we analyzed the influence of temperature on TNF alpha transcription in the Raw 264.7 macrophage cell line during incubation at 37 and 39.5 degrees C, The initial activation of TNF alpha transcription in response to endotoxin (LPS) was comparable in the 37 and 39.5 degrees C cell cultures, peaking within 10 min of LPS stimulation. However, the duration of transcriptional activation was markedly reduced in the 39.5 degrees C cells (30-60 min) compared with the 37 degrees C cells (2-4 h), Deletion mapping of the TNF alpha gene revealed that the proximal 85-nucleotide promoter sequence and the 5'-untranslated region were sufficient for temperature sensitivity. This sequence contains six heat shock response element (HRE) half-sites but no complete HREs, Electrophoretic mobility shift and immunoblot assays demonstrated that nuclear transclocation of heat shock factor (HSF) and its activation to a DNA-binding form occurred in the 39.5 degrees C cells in the absence of heat shock protein-70 gene activation. The proximal TNF alpha promoter/5'-untranslated region sequence competed for HSF binding to a classic HRE. Overexpression of HSF-1 reduced activity of the TNF alpha promoter. These data suggest that partial activation of HSF-I during exposure to febrile, sub-heat shock temperatures may block TNF alpha transcription by binding to its proximal promoter or 5'-untranslated region.