A trans-Activation Domain in Yeast Heat Shock Transcription Factor Is Essential for Cell Cycle Progression during Stress

Abstract

Gene expression in response to heat shock is mediated by the heat shock transcription factor (HSF), which in yeast harbors both amino- and carboxyl-terminal transcriptional activation domains. Yeast cells bearing a truncated form of HSF in which the carboxyl-terminal transcriptional activation domain has been deleted [HSF(1-583)] are temperature sensitive for growth at 37°C, demonstrating a requirement for this domain for sustained viability during thermal stress. Here we demonstrate that HSF(1-583) cells undergo reversible cell cycle arrest at 37°C in the G₂/M phase of the cell cycle and exhibit marked reduction in levels of the molecular chaperone Hsp90. As in higher eukaryotes, yeast possesses two nearly identical isoforms of Hsp90: one constitutively expressed and one highly heat inducible. When expressed at physiological levels in HSF(1-583) cells, the inducible Hsp90 isoform encoded by HSP82 more efficiently suppressed the temperature sensitivity of this strain than the constitutively expressed gene HSC82, suggesting that different functional roles may exist for these chaperones. Consistent with a defect in Hsp90 production, HSF(1-583) cells also exhibited hypersensitivity to the Hsp90-binding ansamycin antibiotic geldanamycin. Depletion of Hsp90 from yeast cells wild type for HSF results in cell cycle arrest in both G₁/S and G₂/M phases, suggesting a complex requirement for chaperone function in mitotic division during stress.

ACKNOWLEDGMENTS

We gratefully acknowledge Susan Lindquist, Diane Robins, Donald McDonnell, and William Pratt for generously providing materials and Robert Fuller for helpful advice and use of the fluorescence microscope. We thank Anne Marie Des Lauriers from the University of Michigan BRCF Flow Cytometry Core for flow cytometric analysis, Susan Lillie for helpful advice, and Chen Kuang for technical assistance. We also thank William Pratt, Phillip C. C. Liu and Xiao-Dong Liu for comments on the manuscript.

K. A. Morano was supported by the Cancer Biology Training Program at the University of Michigan Comprehensive Cancer Center (NIH 5T32CA09676-06) and NIH NRSA (1F32 GM19195-01). N. Santoro is supported by a predoctoral fellowship from the United States Environmental Protection Agency (U 914826-01-2). This work was supported in part by the Taisho Excellence in Research Program, Taisho Pharmaceuticals Co., Ltd., and the University of Michigan Comprehensive Cancer Center. D. J. Thiele is a Burroughs Wellcome Toxicology Scholar.