Heat shock factor 1 (Hsf1) belongs to a family of heat shock transcription factors that activate the transcription of genes encoding products required for protein folding, processing, targeting, degradation, and function.¹The up-regulation of Hsp expression by stressors is achieved at the level of transcription through a heat shock element (HSE) and a transcription factor.^2,3,4Most Hsfs have highly conserved amino acid sequences. On all Hsfs there is a DNA binding domain at the N-terminus. Hydrophobic repeats located adjacent to this binding domain are essential for the formation of active trimers. Towards the C-terminal region another short hydrophobic repeat exists and is thought to be necessary for suppression of trimerization.⁵There are two main Hsfs, 1 and 2. Murine Hsf1 exists as two isoforms, however in higher eukaryotes Hsf1 is found in a diffuse cytoplasmic and nuclear distribution in unstressed cells. Once exposed to a multitude of stressors, it localizes to discrete nuclear granules within seconds. As it recovers from stress, Hsf1 dissipates from these granules to a diffuse nucleoplasmic distribution. Hsf2 on the other hand is similar to murine Hsf1, as it exists as two isoforms, the α form being more transcriptionally active than the smaller β form.^6,7Various experiments have suggested that Hsf2 may have roles in differentiation and development.^8,9,10

1.Morano, K.A., and Thiele, D.J.Heat shock factor function and regulation in response to cellular stress, growth, and differentiation signalsGene Expression7271-282(1998) 2.Tanaka, K.I., Namba, T., Arai, Y., et al.Genetic evidence for a protective role for heat shock factor 1 and heat shock protein 70 against colitisThe Journal of Biological Chemisty(2007) 3.Morimoto, R.I.Regulation of the heat shock transcriptional response: Cross talk between a family of heat shock factors, molecular chaperones, and negative regulatorsGenes & Development123788-3796(1998) 4.McMillan, D.R., Xiao, X., Shao, L., et al.Targeted disruption of heat shock transcription factor 1 abolishes thermotolerance and protection against heat-inducible apoptosisThe Journal of Biological Chemisty273(13)7523-7528(1998) 5.Jolly, C., Usson, Y., and Morimoto, R.I.Rapid and reversible relocalization of heat shock factor 1 within seconds to nuclear stress granulesProceedings of the National Academy of Sciences of the United States of America966769-6774(1999) 6.Fiorenza, M.T., Farkas, T., Dissing, M., et al.Complex expression of murine heat shock transcription factorsNucleic Acids Research23(3)467-474(1995) 7.Goodson, M.L., Park-Sarge, O.K., and Sarge, K.D.Tissue-dependent expression of heat shock factor 2 isoforms with distinct transcriptional activitesMolecular and Cellular Biology15(10)5288-5293(1995) 8.Rallu, M., Loones, M., Lallemand, Y., et al.Function and regulation of heat shock factor 2 during mouse embryogenesisProceedings of the National Academy of Sciences of the United States of America942392-2397(1997) 9.Sarge, K.D., Park-Sarge, O.K., Kirby, J.D., et al.Expression of heat shock factor 2 in mouse testis: Potential role as a regulator of heat-shock protein gene expression during spermatogenesisBiology of Reproduction501334-1343(1994) 10.Murphy, S.P., Gorzowski, J.J., Sarge, K.D., et al.Characterization of constitutive HSF2 DNA-binding activity in mouse embryonal carcinoma cellsMolecular and Cellular Biology14(8)5309-5317(1994)