title: Combined chemical-genetic approach identifies cytosolic HSP70 dependence in rhabdomyosarcoma.
abstract: Cytosolic and organelle-based heat-shock protein (HSP) chaperones ensure proper folding and function of nascent and injured polypeptides to support cell growth. Under conditions of cellular stress, including oncogenic transformation, proteostasis components maintain homeostasis and prevent apoptosis. Although this cancer-relevant function has provided a rationale for therapeutically targeting proteostasis regulators (e.g., HSP90), cancer-subtype dependencies upon particular proteostasis components are relatively undefined. Here, we show that human rhabdomyosarcoma (RMS) cells, but not several other cancer cell types, depend upon heat-shock protein 70 kDA (HSP70) for survival. HSP70-targeted therapy (but not chemotherapeutic agents) promoted apoptosis in RMS cells by triggering an unfolded protein response (UPR) that induced PRKR-like endoplasmic reticulum kinase (PERK)-eukaryotic translation initiation factor α (eIF2α)-CEBP homologous protein (CHOP) signaling and CHOP-mediated cell death. Intriguingly, inhibition of only cytosolic HSP70 induced the UPR, suggesting that the essential activity of HSP70 in RMS cells lies at the endoplasmic reticulum-cytosol interface. We also found that increased CHOP mRNA in clinical specimens was a biomarker for poor outcomes in chemotherapy-treated RMS patients. The data suggest that, like human epidermal growth factor receptor 2 (HER2) amplification in breast cancer, increased CHOP in RMS is a biomarker of decreased response to chemotherapy but enhanced response to targeted therapy. Our findings identify the cytosolic HSP70-UPR axis as an unexpected regulator of RMS pathogenesis, revealing HSP70-targeted therapy as a promising strategy to engage CHOP-mediated apoptosis and improve RMS treatment. Our study highlights the utility of dissecting cancer subtype-specific dependencies on proteostasis networks to uncover unanticipated cancer vulnerabilities.
authors.affiliation: Department of Pediatrics, University of California, San Francisco, CA 94143; Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA 94143;
authors.forename: Amit J
authors.initials: AJ
authors.lastname: Sabnis
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260;
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Guerriero
authors.affiliation: Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA 94143; Department of Medicine, University of California, San Francisco, CA 94143;
authors.forename: Victor
authors.initials: V
authors.lastname: Olivas
authors.affiliation: Department of Medicine, University of California, San Francisco, CA 94143;
authors.forename: Anin
authors.initials: A
authors.lastname: Sayana
authors.affiliation: Department of Medicine, University of California, San Francisco, CA 94143;
authors.forename: Jonathan
authors.initials: J
authors.lastname: Shue
authors.affiliation: Department of Medicine, University of California, San Francisco, CA 94143;
authors.forename: Jennifer
authors.initials: J
authors.lastname: Flanagan
authors.affiliation: Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA 94143; Department of Medicine, University of California, San Francisco, CA 94143;
authors.forename: Saurabh
authors.initials: S
authors.lastname: Asthana
authors.affiliation: Research Centre for Infectious Diseases, School of Biological Sciences, University of Adelaide, Adelaide 5005, Australia;
authors.forename: Adrienne W
authors.initials: AW
authors.lastname: Paton
authors.affiliation: Research Centre for Infectious Diseases, School of Biological Sciences, University of Adelaide, Adelaide 5005, Australia;
authors.forename: James C
authors.initials: JC
authors.lastname: Paton
authors.affiliation: Institute for Neurodegenerative Disease, University of California, San Francisco, CA 94143;
authors.forename: Jason E
authors.initials: JE
authors.lastname: Gestwicki
authors.affiliation: Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143; Howard Hughes Medical Institute, University of California, San Francisco, CA 94143;
authors.forename: Peter
authors.initials: P
authors.lastname: Walter
authors.affiliation: Howard Hughes Medical Institute, University of California, San Francisco, CA 94143; Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143;
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Weissman
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260.
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260;
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Brodsky
authors.affiliation: Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, CA 94143; Department of Medicine, University of California, San Francisco, CA 94143; trever.bivona@ucsf.edu.
authors.forename: Trever G
authors.initials: TG
authors.lastname: Bivona
mesh_terms: D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D006801:Humans; D000072041:PAX3 Transcription Factor / Q000502:physiology; D012208:Rhabdomyosarcoma / Q000188:drug therapy / Q000209:etiology* / Q000473:pathology; D051742:Transcription Factor CHOP / Q000502:physiology; D056811:Unfolded Protein Response
chemical_list: C497249:DDIT3 protein, human; D018840:HSP70 Heat-Shock Proteins; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051742:Transcription Factor CHOP
keywords: HSP70; cancer; chaperone; sarcoma; unfolded protein response