Fas ligand gene expression is directly regulated by stress-inducible heat shock transcription factor-1

Abstract

Heat shock transcription factor-1 (HSF-1) is the primary stress responsive transcription factor that regulates expression of heat shock proteins (Hsps) in response to elevated temperature. We show that the transcriptional activity of HSF-1 can also directly mediate hyperthermia-induced Fas ligand (FasL) expression in activated T cells. We identify a conserved region within the human FasL promoter spanning from -276 to -236 upstream of the translational start site that contains two 15 bp non-identical adjacent HSF-1-binding sites or heat shock elements (HSEs) separated by 11 bp. Both the distal HSE (HSE1) (extending from À276 to -262) and the proximal HSE (HSE2) (spanning from À250 to -236) consist of two perfect and one imperfect nGAAn pentamers. We show the direct binding of HSF-1 to these elements and that mutation of these sites abrogates the ability of HSF-1 to bind and drive promoter activity. HSF-1 associates with these elements in a cooperative manner to mediate optimal promoter activity. We propose that the ability of HSF-1 to mediate stress-inducible expression of FasL extends its classical function as a regulator of Hsps to encompass a function for this transcription factor in the regulation of immune function and homeostasis. Cell Death and Differentiation (2010) 17, 1034-1046 doi:10.1038/cdd.2010 published online 12 February 2010 Mammalian heat shock transcription factor-1 (HSF-1) exists constitutively as a non-DNA-binding cytosolic monomer that when activated by heat stress, forms active homotrimers that translocate to the nucleus and associate with consensusbinding sites within the promoters of its target genes.

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