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J. Biol. Chem., Vol. 282, Issue 10, 7077-7086, March 9, 2007

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Heat Shock Factor 2 (HSF2) Contributes to Inducible Expression of hsp Genes through Interplay with HSF1^*

Päivi Östling¹, Johanna K. Björk^¶1, Pia Roos-Mattjus^¶, Valérie Mezger^||, and Lea Sistonen^¶2

From the Departments of Biochemistry & Pharmacy and ^¶Biology, Åbo Akademi University and the Turku Centre for Biotechnology, Åbo Akademi University and University of Turku, FI-20521 Turku, Finland and the ^||Laboratoire de Biologie Moléculaire du Stress, CNRS UMR8541, Ecole Normale Supérieure, 75005 Paris, France

The heat shock response is a defense reaction activated by proteotoxic damage induced by physiological or environmental stress. Cells respond to the proteotoxic damage by elevated expression of heat shock proteins (Hsps) that function as molecular chaperones and maintain the vital homeostasis of protein folds. Heat shock factors (HSFs) are the main transcriptional regulators of the stress-induced expression of hsp genes. Mammalian HSF1 was originally identified as the transcriptional regulator of the heat shock response, whereas HSF2 has not been implicated a role in the stress response. Previously, we and others have demonstrated that HSF1 and HSF2 interact through their trimerization domains, but the functional consequence of this interaction remained unclear. We have now demonstrated on chromatin that both HSF1 and HSF2 were able to bind the hsp70 promoter not only in response to heat shock but also during hemin-induced differentiation of K562 erythroleukemia cells. In both cases an intact HSF1 was required in order to reach maximal levels of promoter occupancy, suggesting that HSF1 influences the DNA binding activity of HSF2. The functional consequence of the HSF1-HSF2 interplay was demonstrated by real-time reverse transcription-PCR analyses, which showed that HSF2 was able to modulate the HSF1-mediated expression of major hsp genes. Our results reveal, contrary to the predominant model, that HSF2 indeed participates in the transcriptional regulation of the heat shock response.

Received for publication, August 8, 2006 , and in revised form, December 22, 2006.

^* This study was supported in part by grants from the Academy of Finland, the Finnish Cancer Organizations, the Sigrid Jusélius Foundation, the Finnish Life and Pension Insurance Companies, and Åbo Akademi University (to L. S.), from the Magnus Ehrnrooth Foundation (to P. R.-M. and P.Ö.) and the OskarÖflund Foundation (to J. K. B., P. R.-M., and P.Ö.), and also from the K. Albin Johansson Foundation (to P. R.-M.) and the Waldemar von Frenckell Foundation (to P.Ö.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by the Turku Graduate School of Biomedical Sciences. These authors should be considered equal contributors.

² To whom correspondence should be addressed: Turku Centre for Biotechnology, P. O. Box 123, FI-20521 Turku, Finland. Tel.: 358-2-333-8028; Fax: 358-2-333-8000; E-mail: lea.sistonen{at}btk.fi.

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