Heat shock protein
Heat shock proteins (HSP) are a group of proteins induced by heat shock, the most prominent members of this group are a class of functionally related proteins involved in the folding and unfolding of other proteins. Their expression is increased when cells are exposed to elevated temperatures or other stress. This increase in expression is transcriptionally regulated. The dramatic upregulation of the heat shock proteins is a key part of the heat shock response and is induced primarily by heat shock factor (HSF). HSPs are found in virtually all living organisms, from bacteria to humans.
Heat-shock proteins are named according to their molecular weight. For example, Hsp60, Hsp70 and Hsp90 (the most widely-studied HSPs) refer to families of heat shock proteins on the order of 60, 70, and 90 kilodaltons in size, respectively. The small 8-kilodalton protein ubiquitin, which marks proteins for degradation, also has features of a heat shock protein.
It is known that rapid heat hardening can be elicited by a brief exposure of cells to sub-lethal high temperature, which in turn provides protection from subsequent and more severe temperature. In 1962, Italian geneticist Ferruccio Ritossa reported that heat and the metabolic uncoupler 2,4-dinitrophenol induced a characteristic pattern of puffing in the chromosomes of Drosophila. This discovery eventually led to the identification of the heat-shock proteins (HSP) or stress proteins whose expression these puffs represented. Increased synthesis of selected proteins in Drosophila cells following stresses such as heat shock was first reported in 1974.
Beginning in the mid-1980s, investigators recognized that many HSPs function as molecular chaperones and thus play a critical role in protein folding, intracellular trafficking of proteins, and coping with proteins denatured by heat and other stresses. Therefore, the study of stress proteins has undergone explosive growth.
Upregulation in stress 
Production of high levels of heat shock proteins can also be triggered by exposure to different kinds of environmental stress conditions, such as infection, inflammation, exercise, exposure of the cell to toxins (ethanol, arsenic, trace metals, and ultraviolet light, among many others), starvation, hypoxia (oxygen deprivation), nitrogen deficiency (in plants), or water deprivation. As a consequence, the heat shock proteins are also referred to as stress proteins and their upregulation is sometimes described more generally as part of the stress response.
The mechanism by which heat-shock (or other environmental stressors) activates the heat shock factor has been determined in bacteria. During heat stress outer membrane proteins (OMPs) do not fold and cannot insert correctly into the outer membrane. They accumulate in the periplasmic space. These OMP's are detected by DegS, an inner membrane protease, that passes the signal through the membrane to the sigmaE transcription factor. However, some studies suggest that an increase in damaged or abnormal proteins brings HSPs into action.
Role as chaperone 
Several heat shock proteins function as intra-cellular chaperones for other proteins. They play an important role in protein-protein interactions such as folding and assisting in the establishment of proper protein conformation (shape) and prevention of unwanted protein aggregation. By helping to stabilize partially unfolded proteins, HSPs aid in transporting proteins across membranes within the cell.
Some members of the HSP family are expressed at low to moderate levels in all organisms because of their essential role in protein maintenance.
Heat-shock proteins also occur under non-stressful conditions, simply "monitoring" the cell's proteins. Some examples of their role as "monitors" are that they carry old proteins to the cell's "recycling bin" (proteasome) and they help newly synthesised proteins fold properly.
These activities are part of a cell's own repair system, called the "cellular stress response" or the "heat-shock response".
A downstream kinase of the nitric oxide cell signalling pathway, protein kinase G, phosphorylates a small heat shock protein, hsp20. Hsp20 phosphorylation correlates well with smooth muscle relaxation and is one significant phosphoprotein involved in the process. Hsp20 appears significant in development of the smooth muscle phenotype during development. Hsp20 also serves a significant role in preventing platelet aggregation, cardiac myocyte function and prevention of apoptosis after ischemic injury, and skeletal muscle function and muscle insulin response.
Hsp27 is a major phosphoprotein during muscle contraction. Hsp27 functions in smooth muscle migration and appears to serve an integral role.
Clinical significance 
Heat Shock Factor 1 (HSF1) is a transcription factor that is involved in the upregulation of Hsp70 protein expression. Recently it was discovered that HSF1 is a powerful multifaceted modifier of carcinogenesis. HSF1 knockout mice show significantly decreased incidence of skin tumor after topical application of DMBA (7,12-dimethylbenzanthracene), a mutagen.
Cancer vaccine adjuvant 
Given their role in antigen presentation, HSPs are useful as immunologic adjuvants in boosting the response to a vaccine. Furthermore, some researchers speculate that HSPs may be involved in binding protein fragments from dead malignant cells and presenting them to the immune system. Therefore HSPs may be useful for increasing the effectiveness of cancer vaccines.
Anticancer therapeutics 
Intracellular heat shock proteins are highly expressed in cancerous cells and are essential to the survival of these cell types. Hence small molecule inhibitors of HSPs, especially Hsp90 show promise as anticancer agents. The potent Hsp90 inhibitor 17-AAG is currently in clinical trials for the treatment of several types of cancer. HSPgp96 also shows promise as an anticancer treatment and is currently in clinical trials against non-small cell lung cancer.
Researchers are also investigating the role of HSPs in conferring stress tolerance to hybridized plants, hoping to address drought and poor soil conditions for farming.
|Approximate molecular weight
|Prokaryotic proteins||Eukaryotic proteins||Function|
|20-30 kDa||GrpE||The HspB group of Hsp. Eleven members in mammals including Hsp27, HSPB6 or HspB1 |
|40 kDa||DnaJ||Hsp40||Co-factor of Hsp70|
|60 kDa||GroEL, 60kDa antigen||Hsp60||Involved in protein folding after its post-translational import to the mitochondrion/chloroplast|
|70 kDa||DnaK||The HspA group of Hsp including Hsp71, Hsp70, Hsp72, Grp78 (BiP), Hsx70 found only in primates||Protein folding and unfolding, provides thermotolerance to cell on exposure to heat stress. Also prevents protein folding during post-translational import into the mitochondria/chloroplast.|
|90 kDa||HtpG, C62.5||The HspC group of Hsp including Hsp90, Grp94||Maintenance of steroid receptors and transcription factors|
|100 kDa||ClpB, ClpA, ClpX||Hsp104, Hsp110||Tolerance of extreme temperature|
Although the most important members of each family are tabulated here, it should be noted that some species may express additional chaperones, co-chaperones, and heat shock proteins not listed. In addition, many of these proteins may have multiple splice variants (Hsp90α and Hsp90β, for instance) or conflicts of nomenclature (Hsp72 is sometimes called Hsp70).
See also 
- De Maio A (January 1999). "Heat shock proteins: facts, thoughts, and dreams". Shock (Augusta, Ga.) 11 (1): 1–12. doi:10.1097/00024382-199901000-00001. PMID 9921710.
- Wu C (1995). "Heat shock transcription factors: structure and regulation". Annual review of cell and developmental biology 11: 441–69. doi:10.1146/annurev.cb.11.110195.002301. PMID 8689565.
- Li Z, Srivastava P (February 2004). "Heat-shock proteins". Current Protocols in Immunology. Appendix 1: Appendix 1T. doi:10.1002/0471142735.ima01ts58. ISBN 0-471-14273-5. PMID 18432918.
- Raboy B, Sharon G, Parag HA, Shochat Y, Kulka RG (1991). "Effect of stress on protein degradation: role of the ubiquitin system". Acta biologica Hungarica 42 (1–3): 3–20. PMID 1668897.
- Ritossa F (1962). "A new puffing pattern induced by temperature shock and DNP in drosophila". Cellular and Molecular Life Sciences (CMLS) 18 (12): 571–573. doi:10.1007/BF02172188.
- Ritossa F (June 1996). "Discovery of the heat shock response". Cell Stress Chaperones 1 (2): 97–8. doi:10.1379/1466-1268(1996)001<0097:DOTHSR>2.3.CO;2. PMC 248460. PMID 9222594.
- Schlesinger, MJ (1990-07-25). "Heat shock proteins". The Journal of Biological Chemistry 265 (21): 12111–12114. PMID 2197269.
- Santoro MG (January 2000). "Heat shock factors and the control of the stress response". Biochemical pharmacology 59 (1): 55–63. doi:10.1016/S0006-2952(99)00299-3. PMID 10605935.
- Walsh NP; Alba, BM; Bose, B; Gross, CA; Sauer, RT (April 2003). "OM peptide signals initiate the envelope stress response by activating DegS protease via relief of inhibition mediated by its PDZ domain". Cell 113 (1): 61–71. doi:10.1016/S0092-8674(03)00203-4. PMID 12679035.
- Narberhaus F (2010). "Translational control of bacterial heat shock and virulence genes by temperature-sensing mRNAs". RNA Biol 7 (1): 84–9. doi:10.4161/rna.7.1.10501. PMID 20009504.
- Walter S, Buchner J (April 2002). "Molecular chaperones--cellular machines for protein folding". Angewandte Chemie (International ed. in English) 41 (7): 1098–113. doi:10.1002/1521-3773(20020402)41:7<1098::AID-ANIE1098>3.0.CO;2-9. PMID 12491239.
- Borges JC, Ramos CH (April 2005). "Protein folding assisted by chaperones". Protein and peptide letters 12 (3): 257–61. doi:10.2174/0929866053587165. PMID 15777275.
- Benjamin IJ, McMillan DR (July 1998). "Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease". Circulation research 83 (2): 117–32. PMID 9686751.
- Antonova G, Lichtenbeld H, Xia T, Chatterjee A, Dimitropoulou C, Catravas JD (2007). "Functional significance of hsp90 complexes with NOS and sGC in endothelial cells". Clinical hemorheology and microcirculation 37 (1–2): 19–35. PMID 17641392.
- McLemore EC, Tessier DJ, Thresher J, Komalavilas P, Brophy CM (July 2005). "Role of the small heat shock proteins in regulating vascular smooth muscle tone". Journal of the American College of Surgeons 201 (1): 30–6. doi:10.1016/j.jamcollsurg.2005.03.017. PMID 15978441.
- Fan GC, Ren X, Qian J, Yuan Q, Nicolaou P, Wang Y, Jones WK, Chu G, Kranias EG (April 2005). "Novel cardioprotective role of a small heat-shock protein, Hsp20, against ischemia/reperfusion injury". Circulation 111 (14): 1792–9. doi:10.1161/01.CIR.0000160851.41872.C6. PMID 15809372.
- Salinthone S, Tyagi M, Gerthoffer WT (July 2008). "Small Heat Shock Proteins in Smooth Muscle". Pharmacology & therapeutics 119 (1): 44–54. doi:10.1016/j.pharmthera.2008.04.005. PMC 2581864. PMID 18579210.
- Nishikawa M, Takemoto S, Takakura Y (April 2008). "Heat shock protein derivatives for delivery of antigens to antigen presenting cells". Int J Pharm 354 (1–2): 23–7. doi:10.1016/j.ijpharm.2007.09.030. PMID 17980980.
- Xu D, Zalmas LP, La Thangue NB (July 2008). "A transcription cofactor required for the heat-shock response". EMBO Rep. 9 (7): 662–9. doi:10.1038/embor.2008.70. PMC 2475325. PMID 18451878.
- Dai C, Whitesell L, Rogers AB, Lindquist S (September 2007). "Heat Shock Factor 1 Is a Powerful Multifaceted Modifier of Carcinogenesis". Cell 130 (6): 1005–18. doi:10.1016/j.cell.2007.07.020. PMC 2586609. PMID 17889646.
- Bendz H, Ruhland SC, Pandya MJ, Hainzl O, Riegelsberger S, Braüchle C, Mayer MP, Buchner J, Issels RD, Noessner E (October 2007). "Human heat shock protein 70 enhances tumor antigen presentation through complex formation and intracellular antigen delivery without innate immune signaling". J. Biol. Chem. 282 (43): 31688–702. doi:10.1074/jbc.M704129200. PMID 17684010.
- Wall Street Journal article on company and FDA
- Binder RJ (April 2008). "Heat-shock protein-based vaccines for cancer and infectious disease". Expert Rev Vaccines 7 (3): 383–93. doi:10.1586/147605188.8.131.523. PMID 18393608.
- Didelot C, Lanneau D, Brunet M, et al. (2007). "Anti-cancer therapeutic approaches based on intracellular and extracellular heat shock proteins". Curr. Med. Chem. 14 (27): 2839–47. doi:10.2174/092986707782360079. PMID 18045130.
- Solit DB, Rosen N (2006). "Hsp90: a novel target for cancer therapy". Curr Top Med Chem 6 (11): 1205–14. doi:10.2174/156802606777812068. PMID 16842157.
- Vinocur B, Altman A (April 2005). "Recent advances in engineering plant tolerance to abiotic stress: achievements and limitations". Current opinion in biotechnology 16 (2): 123–32. doi:10.1016/j.copbio.2005.02.001. PMID 15831376.
- Kampinga, HH, Hageman, J, Vos, MJ, Kubota, H, Tanguay, RM, Bruford, EA (2009-01). "Guidelines for the nomenclature of the human heat shock proteins". Cell Stress and Chaperones 14 (1): 105–111. doi:10.1007/s12192-008-0068-7. PMC 2673902. PMID 18663603.
|Wikimedia Commons has media related to: Heat-shock proteins|