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Roles of Extracellular HSPs as Biomarkers in Immune Surveillance and Immune Evasion

by Eman A. Taha 1,2,3,†, Kisho Ono 4,† and Takanori Eguchi 1,5,*,†
1
Department of Dental Pharmacology, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8525, Japan
2
Department of Medical Bioengineering, Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan
3
Department of Biochemistry, Ain Shams University Faculty of Science, Cairo 11566, Egypt
4
Department of Oral and Maxillofacial Surgery, Okayama University Hospital, Okayama 700-0914, Japan
5
Advanced Research Center for Oral and Craniofacial Sciences, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8525, Japan
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Int. J. Mol. Sci. 2019, 20(18), 4588; https://doi.org/10.3390/ijms20184588
Received: 16 August 2019 / Revised: 13 September 2019 / Accepted: 14 September 2019 / Published: 17 September 2019
(This article belongs to the Special Issue Molecular Chaperones 2.0)
Extracellular heat shock proteins (ex-HSPs) have been found in exosomes, oncosomes, membrane surfaces, as well as free HSP in cancer and various pathological conditions, also known as alarmins. Such ex-HSPs include HSP90 (α, β, Gp96, Trap1), HSP70, and large and small HSPs. Production of HSPs is coordinately induced by heat shock factor 1 (HSF1) and hypoxia-inducible factor 1 (HIF-1), while matrix metalloproteinase 3 (MMP-3) and heterochromatin protein 1 are novel inducers of HSPs. Oncosomes released by tumor cells are a major aspect of the resistance-associated secretory phenotype (RASP) by which immune evasion can be established. The concepts of RASP are: (i) releases of ex-HSP and HSP-rich oncosomes are essential in RASP, by which molecular co-transfer of HSPs with oncogenic factors to recipient cells can promote cancer progression and resistance against stresses such as hypoxia, radiation, drugs, and immune systems; (ii) RASP of tumor cells can eject anticancer drugs, targeted therapeutics, and immune checkpoint inhibitors with oncosomes; (iii) cytotoxic lipids can be also released from tumor cells as RASP. ex-HSP and membrane-surface HSP (mHSP) play immunostimulatory roles recognized by CD91+ scavenger receptor expressed by endothelial cells-1 (SREC-1)+ Toll-like receptors (TLRs)+ antigen-presenting cells, leading to antigen cross-presentation and T cell cross-priming, as well as by CD94+ natural killer cells, leading to tumor cytolysis. On the other hand, ex-HSP/CD91 signaling in cancer cells promotes cancer progression. HSPs in body fluids are potential biomarkers detectable by liquid biopsies in cancers and tissue-damaged diseases. HSP-based vaccines, inhibitors, and RNAi therapeutics are also reviewed. View Full-Text
Keywords: heat shock protein (HSP); exosome; oncosome; alarmin; immunology; immune evasion; resistance-associated secretory phenotype (RASP); immune surveillance; hypoxia; biomarker heat shock protein (HSP); exosome; oncosome; alarmin; immunology; immune evasion; resistance-associated secretory phenotype (RASP); immune surveillance; hypoxia; biomarker
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MDPI and ACS Style

Taha, E.A.; Ono, K.; Eguchi, T. Roles of Extracellular HSPs as Biomarkers in Immune Surveillance and Immune Evasion. Int. J. Mol. Sci. 2019, 20, 4588.

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