Title: Comparative interactomes of HSF1 in stress and disease reveal a role for CTCF in HSF1-mediated gene regulation
Abstract: Heat shock transcription factor 1 (HSF1) orchestrates cellular stress protection by activating or repressing gene transcription in response to protein misfolding, oncogenic cell proliferation, and other environmental stresses. HSF1 is tightly regulated via intramolecular repressive interactions, post-translational modifications, and protein-protein interactions. How these HSF1 regulatory protein interactions are altered in response to acute and chronic stress is largely unknown. To elucidate the profile of HSF1 protein interactions under normal growth and chronic and acutely stressful conditions, quantitative proteomics studies identified interacting proteins in the response to heat shock or in the presence of a poly-glutamine aggregation protein cell-based model of Huntington's disease. These studies identified distinct protein interaction partners of HSF1 as well as changes in the magnitude of shared interactions as a function of each stressful condition. Several novel HSF1-interacting proteins were identified that encompass a wide variety of cellular functions, including roles in DNA repair, mRNA processing, and regulation of RNA polymerase II. One HSF1 partner, CTCF, interacted with HSF1 in a stress-inducible manner and functions in repression of specific HSF1 target genes. Understanding how HSF1 regulates gene repression is a crucial question, given the dysregulation of HSF1 target genes in both cancer and neurodegeneration. These studies expand our understanding of HSF1-mediated gene repression and provide key insights into HSF1 regulation via protein-protein interactions. Heat shock transcription factor 1 (HSF1) orchestrates cellular stress protection by activating or repressing gene transcription in response to protein misfolding, oncogenic cell proliferation, and other environmental stresses. HSF1 is tightly regulated via intramolecular repressive interactions, post-translational modifications, and protein-protein interactions. How these HSF1 regulatory protein interactions are altered in response to acute and chronic stress is largely unknown. To elucidate the profile of HSF1 protein interactions under normal growth and chronic and acutely stressful conditions, quantitative proteomics studies identified interacting proteins in the response to heat shock or in the presence of a poly-glutamine aggregation protein cell-based model of Huntington's disease. These studies identified distinct protein interaction partners of HSF1 as well as changes in the magnitude of shared interactions as a function of each stressful condition. Several novel HSF1-interacting proteins were identified that encompass a wide variety of cellular functions, including roles in DNA repair, mRNA processing, and regulation of RNA polymerase II. One HSF1 partner, CTCF, interacted with HSF1 in a stress-inducible manner and functions in repression of specific HSF1 target genes. Understanding how HSF1 regulates gene repression is a crucial question, given the dysregulation of HSF1 target genes in both cancer and neurodegeneration. These studies expand our understanding of HSF1-mediated gene repression and provide key insights into HSF1 regulation via protein-protein interactions. Organisms are constantly challenged with adapting to stressful conditions such as protein misfolding, inflammation, environmental toxicants, increased temperature, and rapid cell proliferation. A crucial player in the cellular stress response is heat shock transcription factor 1 (HSF1), a regulator of stress-protective gene transcription (1Gomez-Pastor R. Burchfiel E.T. Thiele D.J. Regulation of heat shock transcription factors and their roles in physiology and disease.Nat. Rev. Mol. Cell Biol. 2018; 19: 4-19Crossref PubMed Scopus (190) Google Scholar, 2Akerfelt M. Morimoto R.I. Sistonen L. Heat shock factors: integrators of cell stress, development and lifespan.Nat. Rev. Mol. 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Previous studies conducted in HD cellular and mouse models revealed that the impairment of HSF1 arises, in part, from inappropriate protein interactions that result in HSF1 degradation (33Gomez-Pastor R. Burchfiel E.T. Neef D.W. Jaeger A.M. Cabiscol E. McKinstry S.U. Doss A. Aballay A. Lo D.C. Akimov S.S. Ross C.A. Eroglu C. Thiele D.J. Abnormal degradation of the neuronal stress-protective transcription factor HSF1 in Huntington's disease.Nat. Commun. 2017; 8: 14405Crossref PubMed Scopus (52) Google Scholar). In HD, elevated expression of protein kinase CK2α' and E3 ligase component FBXW7 promote the phosphorylation-dependent degradation of HSF1 (33Gomez-Pastor R. Burchfiel E.T. Neef D.W. Jaeger A.M. Cabiscol E. McKinstry S.U. Doss A. Aballay A. Lo D.C. Akimov S.S. Ross C.A. Eroglu C. Thiele D.J. Abnormal degradation of the neuronal stress-protective transcription factor HSF1 in Huntington's disease.Nat. Commun. 2017; 8: 14405Crossref PubMed Scopus (52) Google Scholar). 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BAG3 affects the nucleocytoplasmic shuttling of HSF1 upon heat stress.Biochem. Biophys. Res. Commun. 2015; 464: 561-567Crossref PubMed Scopus (0) Google Scholar), whereas RPA70 facilitates basal HSF1 binding at the Hsp70 locus by recruiting histone chaperone FACT (50Fujimoto M. Takaki E. Takii R. Tan K. Prakasam R. Hayashida N. Iemura S. Natsume T. Nakai A. RPA assists HSF1 access to nucleosomal DNA by recruiting histone chaperone FACT.Mol. Cell. 2012; 48: 182-194Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar). In addition to illuminating regulatory mechanisms imposed on HSF1 by interacting proteins, the study of other protein interactors has revealed roles for HSF1 in new pathways, including DNA repair (53Huang J. Nueda A. Yoo S. Dynan W.S. Heat shock transcription factor 1 binds selectively in vitro to Ku protein and the catalytic subunit of the DNA-dependent protein kinase.J. Biol. 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Taken together, these and other studies demonstrate how protein regulators of HSF1 can significantly alter HSF1 activity, function, and degradation. However, many of these regulatory interactions have been explored exclusively in response to heat shock, highlighting the need for a systematic proteomics approach in which the HSF1 interactome can be simultaneously investigated under different stress conditions, including chronic protein misfolding. To decipher new aspects of HSF1 regulation via protein partners under distinct cellular stress states, the HSF1 interactome was examined during normal growth conditions, acute heat shock, and the chronic protein misfolding stress encountered in HD. HSF1 interacts with an array of proteins with diverse cellular functions, including mRNA processing, chromatin mod