Inhibition of tumor necrosis factor-alpha transcription in macrophages exposed to febrile range temperature - A possible role for heat shock factor-1as 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 trans cription 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 respon se to endotoxin (LPS) was comparable in the 37 and 39.5 degrees C cell cult ures, peaking within 10 min of LPS stimulation. However, the duration of tr anscriptional 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 o f the TNF alpha gene revealed that the proximal 85-nucleotide promoter sequ ence and the 5'-untranslated region were sufficient for temperature sensiti vity. This sequence contains six heat shock response element (HRE) half-sit es but no complete HREs, Electrophoretic mobility shift and immunoblot assa ys 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 i n the absence of heat shock protein-70 gene activation. The proximal TNF al pha promoter/5'-untranslated region sequence competed for HSF binding to a classic HRE. Overexpression of HSF-1 reduced activity of the TNF alpha prom oter. These data suggest that partial activation of HSF-I during exposure t o febrile, sub-heat shock temperatures may block TNF alpha transcription by binding to its proximal promoter or 5'-untranslated region.