The role of chromatin-associated heat-shock protein 90 in transcriptional response to stress
Cell Biology
Final Report Abstract
Chaperones are proteins that help other proteins fold. Usually protein folding takes place in the cytoplasm, and that is the location where chaperones have been mostly studied. However chaperones are also found in the nucleus, a compartment where proteins enter after being completely folded. This project addresses an important aspect of chaperone biology: the role of molecular chaperones in the nucleus. We focus on a particular chaperone called heat-shock protein 90 (HSP90), that is a therapeutic target for cancer and is involved in late-stage protein folding. Our previous work had suggested that chaperones are required to stabilize transcriptional regulators on chromatin. We now have identified HSP90 interactome in the nucleus of human cells. This interactome consists of regulators of the chaperone as well as client proteins that depend on chaperones on their stability, assembly, folding or function. Indeed, using functional assays we report that Host Cell Factor C1 (HCFC1) is a major target of HSP90 in the nucleus. HCFC1 binds to promoters of cell cycle genes and is required for the continued expression of cell cycle genes in proliferating cells. When HSP90 is inhibited by small molecule inhibitors that are in clinical trials as anti-cancer agents, HCFC1 is readily degraded reducing the expression of cell-cycle genes. HCFC1 is over-expressed in many cancers and is one of the ten genes that are in the 'death-by-cancer' signature. That means HCFC1-overexpressing cancers are likely to be aggressive and lethal. Thus identification of HSP90 as a chaperone required for stabilization is an important milestone in understanding of HSP90 inhibitors as cancer therapeutics. Along with HCFC1, we also identified a role of known HSP90 client, NELF, in regulating transcriptional response to stress. NELF is recruited to promoters of genes downregulated during stress, and causes RNA pol II to be stabilized at promoters, reducing the transcription of target genes. How NELF senses stress is not clear, but may involve nuclear chaperones. It is plausible that chaperones keep NELF in an inactive form, and upon stress chaperone activity is compromised releasing NELF to perform the function of transcriptional repression. More experiments will be needed to ascertain this model.
Publications
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(2017) High capacity of the endoplasmic reticulum to prevent secretion and aggregation of amyloidogenic proteins. EMBO. e201695841
Vincenz-Donnelly L, Holthusen H, Körner R, Hansen EC, Presto J, Johansson J, Sawarkar R, Hartl FU, Hipp MS
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(2018) Chromatin Immunoprecipitation (ChIP) of Heat Shock Protein 90 (Hsp90). Methods Mol Biol. 1709: 221-231
Yoveva A, Sawarkar R
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(2019) Heat-shock protein 90 controls the expression of cell-cycle genes by stabilizing metazoan-specific Host-Cell Factor HCFC1. Cell Reports. 29(6):1645-1659
Antonova A, Hummel B, Khavaran A, Redhaber D, Aprile-Garcia F, Rawat P, Gundel K, Schneck M, Hansen E, Mitschke J, Mittler G, Miething C and Sawarkar R
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(2019) Nascent-protein ubiquitination is required for heat-shock induced gene downregulation. Nature Structural and Molecular Biology. 26(2):137-146
Aprile-Garcia F, Tomar P, Hummel B, Khavaran A and Sawarkar R
