Hsp70 protein | |||||||||
---|---|---|---|---|---|---|---|---|---|
Identifiers | |||||||||
Symbol | HSP70 | ||||||||
Pfam | PF00012 | ||||||||
Pfam clan | CL0108 | ||||||||
InterPro | IPR013126 | ||||||||
PROSITE | PDOC00269 | ||||||||
SCOP2 | 3hsc / SCOPe / SUPFAM | ||||||||
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The 70 kilodalton heat shock proteins (Hsp70s or DnaK) are a family of conserved ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms. Intracellularly localized Hsp70s are an important part of the cell's machinery for protein folding, performing chaperoning functions, and helping to protect cells from the adverse effects of physiological stresses. [2] [3] Additionally, membrane-bound Hsp70s have been identified as a potential target for cancer therapies [4] and their extracellularly localized counterparts have been identified as having both membrane-bound and membrane-free structures. [5]
Members of the Hsp70 family are very strongly upregulated by heat stress and toxic chemicals, particularly heavy metals such as arsenic, cadmium, copper, mercury, etc. Heat shock was originally discovered by Ferruccio Ritossa in the 1960s when a lab worker accidentally boosted the incubation temperature of Drosophila (fruit flies). When examining the chromosomes, Ritossa found a "puffing pattern" that indicated the elevated gene transcription of an unknown protein. [6] [7] This was later described as the "Heat Shock Response" and the proteins were termed the "Heat Shock Proteins" (Hsps).
The Hsp70 proteins have three major functional domains:
Protein phosphorylation, a post-translational modification, helps to regulate protein function and involves the phosphorylation of amino acids with hydroxyl groups in their side chains (among eukaryotes). Serine, threonine, and tyrosine amino acids are common targets of phosphorylation. Phosphorylation of Hsp70 has become a point of greater exploration in scientific literature relatively recently. A 2020 publication suggests that phosphorylation of a serine residue between the NBD and substrate binding domain in yeast Hsp70s leads to a dramatic reduction of the normal Hsp70 heat shock response. [10] This deactivation via phosphorylation of a protein is a common motif in protein regulation, and demonstrates how relatively small changes to protein structure can have biologically significant effects on protein function.
The Hsp70 system interacts with extended peptide segments of proteins as well as partially folded proteins to cause aggregation of proteins in key pathways to downregulate activity. [11] [8] When not interacting with a substrate peptide, Hsp70 is usually in an ATP bound state. Hsp70 by itself is characterized by a very weak ATPase activity, such that spontaneous hydrolysis will not occur for many minutes. As newly synthesized proteins emerge from the ribosomes, the substrate binding domain of Hsp70 recognizes sequences of hydrophobic amino acid residues, and interacts with them. This spontaneous interaction is reversible, and in the ATP bound state Hsp70 may relatively freely bind and release peptides. However, the presence of a peptide in the binding domain stimulates the ATPase activity of Hsp70, increasing its normally slow rate of ATP hydrolysis. When ATP is hydrolyzed to ADP the binding pocket of Hsp70 closes, tightly binding the now-trapped peptide chain. Further speeding ATP hydrolysis are the so-called J-domain cochaperones: primarily Hsp40 in eukaryotes, and DnaJ in prokaryotes. These cochaperones dramatically increase the ATPase activity of Hsp70 in the presence of interacting peptides.
By binding tightly to partially synthesized peptide sequences (incomplete proteins), Hsp70 prevents them from aggregating and being rendered nonfunctional. Once the entire protein is synthesized, a nucleotide exchange factor (prokaryotic GrpE, eukaryotic BAG1 and HspBP1 are among those which have been identified) stimulates the release of ADP and binding of fresh ATP, opening the binding pocket. The protein is then free to fold on its own, or to be transferred to other chaperones for further processing. [12] HOP (the Hsp70/Hsp90 Organizing Protein) can bind to both Hsp70 and Hsp90 at the same time, and mediates the transfer of peptides from Hsp70 to Hsp90. [13]
Hsp70 also aids in transmembrane transport of proteins, by stabilizing them in a partially folded state. It is also known to be phosphorylated [14] which regulates several of its functions. [15] [16] [17]
Hsp70 proteins can act to protect cells from thermal or oxidative stress. These stresses normally act to damage proteins, causing partial unfolding and possible aggregation. By temporarily binding to hydrophobic residues exposed by stress, Hsp70 prevents these partially denatured proteins from aggregating, and inhibits them from refolding. Low ATP is characteristic of heat shock and sustained binding is seen as aggregation suppression, while recovery from heat shock involves substrate binding and nucleotide cycling. In a thermophile anaerobe (Thermotoga maritima) the Hsp70 demonstrates redox sensitive binding to model peptides, suggesting a second mode of binding regulation based on oxidative stress.
Hsp70 seems to be able to participate in disposal of damaged or defective proteins. Interaction with CHIP (Carboxyl-terminus of Hsp70 Interacting Protein)–an E3 ubiquitin ligase–allows Hsp70 to pass proteins to the cell's ubiquitination and proteolysis pathways. [18]
Finally, in addition to improving overall protein integrity, Hsp70 directly inhibits apoptosis. [19] One hallmark of apoptosis is the release of cytochrome c, which then recruits Apaf-1 and dATP/ATP into an apoptosome complex. This complex then cleaves procaspase-9, activating caspase-9 and eventually inducing apoptosis via caspase 3 activation. Hsp70 inhibits this process by blocking the recruitment of procaspase-9 to the Apaf-1/dATP/cytochrome c apoptosome complex. It does not bind directly to the procaspase-9 binding site, but likely induces a conformational change that renders procaspase-9 binding less favorable. Hsp70 is shown to interact with Endoplasmic reticulum stress sensor protein IRE1alpha thereby protecting the cells from ER stress - induced apoptosis. This interaction prolonged the splicing of XBP-1 mRNA thereby inducing transcriptional upregulation of targets of spliced XBP-1 like EDEM1, ERdj4 and P58IPK rescuing the cells from apoptosis. [20] Other studies suggest that Hsp70 may play an anti-apoptotic role at other steps, but is not involved in Fas-ligand-mediated apoptosis (although Hsp 27 is). Therefore, Hsp70 not only saves important components of the cell (the proteins) but also directly saves the cell as a whole. Considering that stress-response proteins (like Hsp70) evolved before apoptotic machinery, Hsp70's direct role in inhibiting apoptosis provides an interesting evolutionary picture of how more recent (apoptotic) machinery accommodated previous machinery (Hsps), thus aligning the improved integrity of a cell's proteins with the improved chances of that particular cell's survival.
In mice, exogenous recombinant human Hsp70 (eHsp70), delivered intranasally, increases lifespan. Although the maximum lifespan increased only moderately, the overall mortality rate in treated animals was much lower compared with the control group. Also this eHsp70-treatment improves learning and memory of mice in old age, increases their curiosity. [21]
Hsp70 is overexpressed in malignant melanoma [22] and underexpressed in renal cell cancer. [23] [24] In breast cancer cell line (MCF7) has been found that not only Hsp90 interacted with estrogen receptor alpha (ERα) but also Hsp70-1 and Hsc70 interacted with ERα too. [25]
Given the role of heat shock proteins as an ancient defense system for stabilizing cells and eliminating old and damaged cells, this system has been co-opted by cancer cells to promote their growth. [26] Increased Hsp70 in particular has been shown to inhibit apoptosis of cancer cells, [27] and increased Hsp70 has been shown to be associated with or directly induce endometrial, [28] lung, [29] colon, [30] prostate, [31] and breast [32] cancer, as well as leukemia. [33] Hsp70 in cancer cells may be responsible for tumorigenesis and tumor progression by providing resistance to chemotherapy. Inhibition of Hsp70 has been shown to reduce the size of tumors and can cause their complete regression. [34] Hsp70/Hsp90 is a particularly attractive target for therapeutics, because it is regulated by the inhibition of its ATPase activity, while other HSPs are regulated by nucleotides. [35] Several inhibitors have been designed for Hsp70 that are currently in clinical trials, [36] though as of now HSP90 inhibitors have been more successful. [37] In addition, Hsp70 has been shown to be a regulator of the immune system, activating the immune system as an antigen. [38] Thus, tumor-derived Hsp70 has been suggested as a potential vaccine [39] or avenue to target for immunotherapy. [40] Given the increased expression of Hsp70 in cancer, it has been suggested as a biomarker for cancer prognostics, with high levels portending poor prognosis. [41] An oncogenic mechanism illustrates how extracellular vesicles expressing HSP70 are produced by proliferative Acute Lymphoblastic Leukemia cells and can target and compromise a healthy hematopoiesis system during leukemia development. [42]
Both Hsp70 and HSP47 were shown to be expressed in dermis and epidermis following laser irradiation, and the spatial and temporal changes in HSP expression patterns define the laser-induced thermal damage zone and the process of healing in tissues. Hsp70 may define biochemically the thermal damage zone in which cells are targeted for destruction, and HSP47 may illustrate the process of recovery from thermally induced damage. [43] HSP70 helps in protecting skin against the increased melanin and wrinkled formation induced due to UV exposure. [44]
Inhibition of Hsp90 leads to Hsp70 and Hsp40 upregulation, which can channel misfolded protein for proteasome degradation, which can potentially inhibit the progression of neurodegenerative diseases. [45] For example, Hsp70 overexpression in human neuroglioma cells transfected with mutant alpha-synuclein led to 50% less oligomeric alpha-synuclein species, [46] pointing towards the possibility that increasing its expression could diminish the spread of Parkinson's disease. Similarly, Hsp70 overexpression suppressed poly-Q dependent aggregation and neurodegeneration in cell cultures, yeast, [47] fly, [48] and mouse [49] models, and deletion of hsp70 increased the size of polyQ inclusion bodies, [50] suggesting that increasing its expression could help to prevent Huntington's disease. Similarly, reductions in Hsp70 have been shown in transgenic mouse models of ALS and patients with sporadic ALS. [51] Lastly, increased expression or activity of Hsp70 has been proposed as a method to prevent the progression of Alzheimer's disease, because knock down of Hsp70 promoted A-beta toxicity, [52] and Hsp70 was shown to promote tau stability, while Hsp70 levels are decreased in tauopathies like Alzheimer's disease. [53] Given the complex interplay between the different chaperone proteins, therapeutic development in this field is aimed at investigating how the chaperone network as a whole can be manipulated and the effect of this manipulation on the progression of neurodegenerative disease, but the balance of Hsp70 and Hsp90 levels appears to be central in this pathophysiology.
The fluctuations in the levels of chaperone HSP70 affect the homeostasis. Diabetes leads to several microvasculature and microvasculature diseases like retinopathy, Toll like receptors are integral part of innate immune system and eHSP70 binds to toll like receptors and activates the MyD88 pathway, further stimulating NF-kB, cytokines like TNFα and IL1 β, increased production of reactive oxygen species contributing to insulin resistance and diabetes. Whereas there is decrease in the levels of iHSP70. [54]
HSP70 is a chaperone with ubiquitous presence. [55] It is crucial in the cardiovascular system. HSP70 normally aids in protein folding and aggregation; when present in the cell, functioning as an anti-inflammatory molecule; however, under stress conditions, it is localized to the extracellular milieu, where it is involved in inducing inflammatory pathways and contributes to disease pathogenesis. [56] It is well established that intracellular HSP70 (iHSP70) levels play a protective role, whereas extracellular HSP70 (eHSP70) levels in circulating blood are linked to pathophysiology in micro and microvasculature, which results in a variety of cardiovascular illnesses. HSP70 homologues identified in human cytosol includes HSPA1A, HSPA1B, HSPA1L, HSPA12B, HSPA13, HSPA14 whereas HSPA9 in mitochondria. The HSP70 acts as DAMP and activates innate immune response which as involved in cardiovascular disease progression. [57]
The chaperone protein acts as auto antigen in atherosclerosis. Increased oxidative stress causes the formation of high-density oxidized LDL, the first event in the formation of plaque. This activates HSP70 and its promoter in the endothelial and smooth muscle cells, which contributes to atherosclerosis by inducing JAK/STAT pathway expression. [58] [59]
HSP70 is also linked to high blood pressure, a worldwide concern and risk factor for a variety of cardiovascular diseases. Hypertension causes endothelial dysfunction and vascular wall damage, both of which contribute to arterial stiffness and atherosclerosis. [60] HSPA1A, HSPA1B, and HSPA1L are three genes in humans that encode HSP70, and their polymorphism is linked to the onset of high blood pressure and cardiovascular disease. [61] Angiotensin II, endothelin-1, or phenylepinephrine cause HSP70 overexpression, which activates several molecular pathways, resulting in increased production of ROS, CRP, IL-10, TNF-alpha, and IL-6 [62] [61] These inflammatory signals interfere with the antioxidant machinery and results in rapid disease progression.
HSP70 expression increases after the coronary bypass surgery. Exercise has a positive and protective impact on cardiovascular disorders and stimulates the increased production of chaperone protein together known to be cardioprotective.
Prokaryotes express three Hsp70 proteins: DnaK, HscA (Hsc66), and HscC (Hsc62). [63]
Eukaryotic organisms express several slightly different Hsp70 proteins. All share the common domain structure, but each has a unique pattern of expression or subcellular localization. These are, among others:
The following is a list of human Hsp70 genes and their corresponding proteins: [2]
gene | protein | synonyms | subcellular location |
---|---|---|---|
HSPA1A | Hsp70 | HSP70-1, Hsp72 | Nuc/Cyto |
HSPA1B | Hsp70 | HSP70-2 | Nuc/Cyto |
HSPA1L | Hsp70 | ? | |
HSPA2 | Hsp70-2 | ? | |
HSPA5 | Hsp70-5 | BiP/Grp78 | ER |
HSPA6 | Hsp70-6 | ? | |
HSPA7 | Hsp70-7 | ? | |
HSPA8 | Hsp70-8 | Hsc70 | Nuc/Cyto |
HSPA9 | Hsp70-9 | Grp75/mtHsp70 | Mito |
HSPA12A | Hsp70-12a | ? | |
HSPA14 | Hsp70-14 | ? |
HSP70s are found in many plants including Arabidopsis, soybean (Glycine max), barley (Hordeum vulgare) and wheat (Triticum aestivum). [64]
Hsp90s are essential for protein remodeling, similar to Hsp70 proteins, and play an especially vital role in eukaryotes, where it has been suggested that Hsp90 interacts with the DnaK system (composed of DnaK, GrpE, and either DnaJ or CbpA) to facilitate the process of protein remodeling. [65] In E. coli, Hsp90s works collaboratively with Hsp70s to facilitate protein remodeling and activation. Hsp90Ec and DnaK are chaperones of Hsp90 and Hsp70, respectively. DnaK initially binds and stabilizes the misfolded protein before working collaboratively with Hsp90Ec to refold this substrate and cause its activation. Given conditions of excess DnaK, this chaperone has been found to inhibit remodeling of proteins. However, the presence of Hsp90Ec can mitigate this effect and enable protein remodeling despite conditions of excess DnaK. [66]
The Hsp70 superfamily also includes a family of Hsp110/Grp170 (Sse) proteins, which are larger proteins related to Hsp70. [67] The Hsp110 family of proteins have divergent functions: yeast Sse1p has little ATPase activity but is a chaperone on its own as well as a nucleotide exchange factor for Hsp70, while the closely related Sse2p has little unfoldase activity. [12]
The following is a list of currently named human HSP110 genes. HSPH2-4 are proposed names and the current name is linked: [67]
gene | synonyms | subcellular location |
---|---|---|
HSPH1 | HSP105 | Cyto |
HSPH2 | HSPA4; APG-2; HSP110 | Cyto |
HSPH3 | HSPA4L; APG-1 | Nuc |
HSPH4 | HYOU1/Grp170; ORP150; HSP12A | ER |
In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assist large proteins in proper protein folding during or after synthesis, and after partial denaturation. Chaperones are also involved in the translocation of proteins for proteolysis.
Heat shock proteins (HSPs) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including exposure to cold, UV light and during wound healing or tissue remodeling. Many members of this group perform chaperone functions by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell 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.
Hsp90 is a chaperone protein that assists other proteins to fold properly, stabilizes proteins against heat stress, and aids in protein degradation. It also stabilizes a number of proteins required for tumor growth, which is why Hsp90 inhibitors are investigated as anti-cancer drugs.
Stress-induced-phosphoprotein 1 also Hsp70-Hsp90 organising protein (Hop) is encoded in the human by the STIP1 gene. It functions as a co-chaperone which reversibly links together the protein chaperones Hsp70 and Hsp90.
The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal cell, proteostasis must be maintained because proteins are the main functional units of the cell. Many proteins take on a defined configuration in a process known as protein folding in order to perform their biological functions. If these structures are altered, critical processes could be affected, leading to cell damage or death. The heat shock response can be employed under stress to induce the expression of heat shock proteins (HSP), many of which are molecular chaperones, that help prevent or reverse protein misfolding and provide an environment for proper folding.
Geldanamycin is a 1,4-benzoquinone ansamycin antitumor antibiotic that inhibits the function of Hsp90 by binding to the unusual ADP/ATP-binding pocket of the protein. HSP90 client proteins play important roles in the regulation of the cell cycle, cell growth, cell survival, apoptosis, angiogenesis and oncogenesis.
Heat shock 70 kDa protein 8 also known as heat shock cognate 71 kDa protein or Hsc70 or Hsp73 is a heat shock protein that in humans is encoded by the HSPA8 gene on chromosome 11. As a member of the heat shock protein 70 family and a chaperone protein, it facilitates the proper folding of newly translated and misfolded proteins, as well as stabilize or degrade mutant proteins. Its functions contribute to biological processes including signal transduction, apoptosis, autophagy, protein homeostasis, and cell growth and differentiation. It has been associated with an extensive number of cancers, neurodegenerative diseases, cell senescence, and aging.
Heat shock protein 27 (Hsp27) also known as heat shock protein beta-1 (HSPB1) is a protein that in humans is encoded by the HSPB1 gene.
Co-chaperones are proteins that assist chaperones in protein folding and other functions. Co-chaperones are the non-client binding molecules that assist in protein folding mediated by Hsp70 and Hsp90. They are particularly essential in stimulation of the ATPase activity of these chaperone proteins. There are a great number of different co-chaperones however based on their domain structure most of them fall into two groups: J-domain proteins and tetratricopeptide repeats (TPR).
Heat shock 70 kDa protein 1, also termed Hsp72, is a protein that in humans is encoded by the HSPA1A gene. As a member of the heat shock protein 70 family and a chaperone protein, it facilitates the proper folding of newly translated and misfolded proteins, as well as stabilize or degrade mutant proteins. In addition, Hsp72 also facilitates DNA repair. Its functions contribute to biological processes including signal transduction, apoptosis, protein homeostasis, and cell growth and differentiation. It has been associated with an extensive number of cancers, neurodegenerative diseases, cell senescence and aging, and inflammatory diseases such as Diabetes mellitus type 2 and rheumatoid arthritis.
Heat shock protein HSP 90-alpha is a protein that in humans is encoded by the HSP90AA1 gene.
Human gene HSPA1B is an intron-less gene which encodes for the heat shock protein HSP70-2, a member of the Hsp70 family of proteins. The gene is located in the major histocompatibility complex, on the short arm of chromosome 6, in a cluster with two paralogous genes, HSPA1A and HSPA1L. HSPA1A and HSPA1B produce nearly identical proteins because the few differences in their DNA sequences are almost exclusively synonymous substitutions or in the three prime untranslated region, heat shock 70kDa protein 1A, from HSPA1A, and heat shock 70kDa protein 1B, from HSPA1B. A third, more modified paralog to these genes exists in the same region, HSPA1L, which shares a 90% homology with the other two.
Heat shock factor protein 1 is a protein that in humans is encoded by the HSF1 gene. HSF1 is highly conserved in eukaryotes and is the primary mediator of transcriptional responses to proteotoxic stress with important roles in non-stress regulation such as development and metabolism.
Heat shock protein HSP 90-beta also called HSP90beta is a protein that in humans is encoded by the HSP90AB1 gene.
Binding immunoglobulin protein (BiPS) also known as 78 kDa glucose-regulated protein (GRP-78) or heat shock 70 kDa protein 5 (HSPA5) is a protein that in humans is encoded by the HSPA5 gene.
DnaJ homolog subfamily B member 1 is a protein that in humans is encoded by the DNAJB1 gene.
Heat shock 70 kDa protein 1L is a protein that in humans is encoded by the HSPA1L gene on chromosome 6. As a member of the heat shock protein 70 (Hsp70) family and a chaperone protein, it facilitates the proper folding of newly translated and misfolded proteins, as well as stabilize or degrade mutant proteins. Its functions contribute to biological processes including signal transduction, apoptosis, protein homeostasis, and cell growth and differentiation. It has been associated with an extensive number of cancers, neurodegenerative diseases, cell senescence and aging, and Graft-versus-host disease.
Peptidylprolyl isomerase D (cyclophilin D), also known as PPID, is an enzyme which in humans is encoded by the PPID gene on chromosome 4. As a member of the peptidyl-prolyl cis-trans isomerase (PPIase) family, this protein catalyzes the cis-trans isomerization of proline imidic peptide bonds, which allows it to facilitate folding or repair of proteins. In addition, PPID participates in many biological processes, including mitochondrial metabolism, apoptosis, redox, and inflammation, as well as in related diseases and conditions, such as ischemic reperfusion injury, AIDS, and cancer.
Proteostasis is the dynamic regulation of a balanced, functional proteome. The proteostasis network includes competing and integrated biological pathways within cells that control the biogenesis, folding, trafficking, and degradation of proteins present within and outside the cell. Loss of proteostasis is central to understanding the cause of diseases associated with excessive protein misfolding and degradation leading to loss-of-function phenotypes, as well as aggregation-associated degenerative disorders. Therapeutic restoration of proteostasis may treat or resolve these pathologies.
An Hsp90 inhibitor is a substance that inhibits that activity of the Hsp90 heat shock protein. Since Hsp90 stabilizes a variety of proteins required for survival of cancer cells, these substances may have therapeutic benefit in the treatment of various types of malignancies. Furthermore, a number of Hsp90 inhibitors are currently undergoing clinical trials for a variety of cancers. Hsp90 inhibitors include the natural products geldanamycin, Retaspimycin hydrochloride and radicicol as well as semisynthetic derivatives 17-N-Allylamino-17-demethoxygeldanamycin (17AAG).
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