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Kevin D. Sarge
Research Interests Research Focus We are interested in how cells protect themselves when they are exposed to stress conditions, which is happening constantly in our bodies. The system we are studying is the induction of hsp70i protein expression in response to stress. This is a critically important response because hsp70i and the other induced hsp’s bind to proteins that have been misfolded in response to stress to prevent their aggregation and also to help these proteins re-fold back to their native functional state. Without the induction of these hsp’s many proteins would be lost when stress occurs and cell death would likely occur. We are studying a family of transcription factors called heat shock factors that regulate the expression of heat shock protein genes by binding to DNA sequences called heat shock elements (HSEs) in their promoters. The two HSFs we study the most are HSF1 and HSF2. Both HSFs are important for hsp gene expression, but they function in very different ways. HSF1 is the HSF that is responsible for activating expression of hsp genes when stress occurs. Stress causes HSF1 to be converted from a inactive monomeric form to a trimeric form that binds the hsp promoter HSE’s to turn on their transcription, resulting in a large increase in levels of cytoprotective hsp70i protein in the cell. HSF2, in contrast, appears to function in hsp gene regulation, at least in part, by doing something to the hsp70i promoter called “bookmarking”, which we describe in a recent paper in Science. Briefly, what we found is that HSF2 functions to prevent the hsp70i promoter from being compacted during mitosis, in contrast to most of the genomic DNA which is tightly compacted. Our results suggest that this lack of compaction is important because it provides cells with the ability to turn on transcription of the hsp70i gene even in early G1 phase if a stress occurs. Otherwise, the cell would be unable to protect itself until it could de-compact the promoter region. Indeed, our results show that blocking HSF2-mediated bookmarking by performing HSF2 siRNA treatment results in a significant in killing of these cells if they are stressed while in G1. Our results suggest that HSF2 prevents compaction of the hsp70i promoter by binding to its HSEs at the beginning of mitosis, recruiting protein phosphatase 2A, and interacting with a subunit of the enzyme called condensin that is important for mitotic DNA compaction, so that the HSF2-associated PP2A can dephosphorylate and inactivate the condensin to prevent compaction of this specific region of the chromosome. We are continuing our studies of both HSF1 and HSF2 in order to obtain further insight into the regulation of heat shock protein gene expression. Why we want to understand how heat shock protein genes are turned on First, induction of hsp gene expression protects us from stresses we experience everyday, ranging from the stress of elevated temperature (fever and heat stroke), oxidative stress occurring constantly in our cells that is a major cause of aging-related decline, cytotoxic side effects of medically prescribed drugs, not to mention the many harmful chemicals found in our environment and sometimes even our food. Second, hsp’s are critical players in the battle against human diseases. Many human diseases, including Alzheimer’s disease, Huntingtin’s disease, and the prion disease Creutzfeld-Jacob disease (human counterpart of Mad Cow disease), are caused by problems in the folding of certain cellular proteins. Fortunately, our cells have a mechanism, called the cellular stress response, that allows them to combat these diseases by preventing protein misfolding, thus dramatically reducing the incidence of these diseases relative to what would occur if cells did not have this mechanism. However, as cells get older they lose the ability to mount this cellular stress response, which could explain why these diseases are much more prevalent later in life. For this reason there has been a strong impetus to find ways to block the decline in the stress response that occurs with age and thus hopefully significantly reduce the incidence of these diseases. So, by learning how hsp genes are turned on we hope to develop ways to turn them on whenever we want, as potential treatments for the medical conditions described above.
Representative Publications
Xing, H., Vanderford, N.L., and Sarge, K.D. TBP/PP2A mitotic complex bookmarks genes by preventing condensin action. Nat. Cell Biol. (in press). Zhang, Y. and Sarge, K.D. (2008) Sumoylation of amyloid precursor protein negatively regulates Ab aggregate levels. Bioc. Biop. Res. Comm. 374: 673-678.Zhang, Y. and Sarge, K.D. (2008) Sumoylation regulates lamin A function and is lost in lamin A mutants associated with familial cardiomyopathies. J. Cell. Biol. 182: 35-39. Park-Sarge, O.K., and Sarge, K.D. (in press) Detection of sumoylated proteins. Methods Mol. Biol. In “Protein Protocols Handbook” (ed. John M. Walker). Humana Press. Zhang, Y. and Sarge, K.D. (2007) Celastrol inhibits polyglutamine aggregation and toxicity through induction of the heat shock response. J. Mol. Med. 85: 1421-1428.. Skaggs, H.S., Xing, H., Wilkerson, D.C., Murphy, L.A., Hong, Y., Mayhew, C.N., and Sarge, K.D. (2007) HSF1-Tpr interaction facilitates export of stress-induced hsp70 mRNA. J. Biol. Chem. 282: 33902-33907. Wilkerson, D.C., Skaggs, H.S., and Sarge, K.D. (2007) HSF2 binds to the hsp90, hsp27, and c-fos promoters constitutively and modulates their expression. Cell Stress & Chaperones 12: 283-290. Xing, H., Hong, Y., and Sarge, K.D. (2007) Identification of the PP2A-interacting region of heat shock transcription factor 2. Cell Stress & Chaperones 12: 192-197.
Sarge, K.D. and Park-Sarge, O.K. (2005)
Gene bookmarking: keeping the pages open. Trends Biochem. Sci.
30: 605-610. Hilgarth, R.S., Murphy, L., Skaggs, H.S., Wilkerson, D.C., Xing, H., and Sarge, K.D. Regulation and function of SUMO modification. Minireview for J. Biol. Chem. 279, 53899-53902. Hilgarth, R.S., Murphy, L.A., O’Connor, C., Clark, James A., Park-Sarge, O.K., Sarge, K.D. (2004) Identification of Xenopus HSF2: Conserved role of sumoylation in regulating DNA-binding activity of HSF2 proteins. Cell Stress Chaperones 9, 214-220. Xing, H., Mayhew, C.N., Cullen, K.E., Park-Sarge, O.K., Sarge, K.D. (2004) HSF1 modulation of hsp70 mRNA polyadenylation via interaction with symplekin. Journal of Biological Chemistry 279: 10551-10555. Lubert, E. J., and Sarge, K.D. (2003) Interaction between protein phosphatase 2A and members of the importin-beta family. Biochem. Biophys. Res. Commun. 303: 908-913. Hilgarth, R.S., Hong, Y., Park-Sarge, O.K., Sarge, K.D. (2003) Insights into the regulation of heat shock transcription factor 1 SUMO-1 modification. Biochem. Biophys. Res. Commun. 303: 196-200. Gothard, L.Q., Ruffner, M.E., Woodward, J.G., Park-Sarge, O.K., Sarge, K.D. (2003) Lowered temperature set-point for activation of the cellular stress response in T-Lymphocytes. J. Biol. Chem. 278: 9322-9326. Hong, Y., Rogers, R., Matunis, M.J., Mayhew, C.N., Goodson, M.L., Park-Sarge, O.K., and Sarge, K.D. (2001) Regulation of HSF1 by stress-induced SUMO-1 modification. J. Biol. Chem. 276: 40263-40267. Lubert, E.J., Hong, Y., Sarge, K.D. (2001) Interaction between protein phosphatase 5 and the A subunit of protein phosphatase 2A: evidence for a heterotrimeric form of protein phosphatase 5. J. Biol. Chem. 276: 38582-38587. Goodson, M.L., Hong, Y., Rogers, R., Matunis, M.J., Park-Sarge, O.K., Sarge, K.D. (2001) SUMO-1 Modification Regulates the DNA-Binding Activity of Heat Shock Transcription Factor 2 (HSF2), a Promyelocytic Leukemia Nuclear Body Associated Transcription Factor. J. Biol. Chem. 276: 18513-18518. Hong, Y., Lubert, E.J., Rodgers, D.W., and Sarge, K.D. (2000) Molecular basis of competition between HSF2 and catalytic subunit for binding to the PR65/A subunit of PP2A. Biochem. Biophys. Res. Commun. 272: 84-89. |
