**Heat Shock Proteins in Coeliac Disease**

Erna Sziksz1,2, Leonóra Himer1,2, Gábor Veres2, Beáta Szebeni1,2, András Arató2, Tivadar Tulassay1,2 and Ádám Vannay1,2 *1Research Group for Paediatrics and Nephrology, Semmelweis University and Hungarian Academy of Sciences, Budapest, 2First Department of Paediatrics, Semmelweis University, Budapest, Hungary* 

#### **1. Introduction**

36 Celiac Disease – From Pathophysiology to Advanced Therapies

Wijeratne, S.S. & Cuppett, S.L. (2006). Lipid hydroperoxide induced oxidative stress damage

Yüce, A., Demir, H., Temizel, I.N. & Koçak, N. (2004). Serum carnitine and selenium levels

(1567-1576)

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Vol. 54, No. 12, (Jun 2006), pp. (4476-4481)

an early loss of cellular redox balance. FASEB J., Vol. 14, No. 11, (Aug 2000), pp.

and antioxidant enzyme response in Caco-2 human colon cells. *J. Agric. Food Chem.*,

in children with celiac disease. *Indian J. Gastroenterol.,* Vol. 23, No. 3, (May-Jun

Coeliac disease is a complex inflammatory disorder of the small intestine with autoimmune features in genetically predisposed individuals and triggered by chronic exposure to gluten of wheat, barley and/or rye (Trynka et al., 2010). The aim of the recent chapter is to introduce and characterize a family of proteins, called heat shock proteins (HSPs), which are known to be key molecules during stress responses (Polla & Cossarizza, 1996). We will discuss the potential involvement of HSPs in the pathomechanism of coeliac disease based on recent scientific results. We will also refer to some future directions and potential therapeutic intervention.

#### **1.1 What is coeliac disease?**

Coeliac disease also known as gluten-sensitive enteropathy or nontropical sprue is a digestive disease occurring in genetically susceptible individuals, triggered by dietary gluten and related prolamins, which damage small intestine and interfere with absorption of nutrients (Setty et al., 2008). Gluten and prolamins are present in wheat, rye and barley, but also in some products such as stamp and envelope adhesive, medicines, and vitamins (Rodrigo, 2009). The genetic predisposition has been associated with the major histocompatibility complex region on chromosome 6p21. More than 90% of coeliac disease patients express the antigen-presenting molecules human leukocyte antigen-DQ2 and the remaining coeliac patients express DQ8 (Silano et al., 2010; Schuppan et al., 2005). Approximately 1% of the population is affected by coeliac disease (it remains mostly undiagnosed) (Green, 2005). It is not clear, why the prevalence of coeliac disease increased over the last decades, but similarly to other immune mediated diseases ― such as allergy or asthma ― this tendency suggests the importance of environmental stress factors besides the genetic predisposition (Rubio-Tapia & Murray, 2010). In addition, novel and trustful diagnostic marker (tissue transglutaminase) could help to uncover previously undiagnosed cases. Coeliac disease was traditionally considered to be a childhood disease, however, most patients are diagnosed in adulthood (Virta et al., 2009). Coeliac disease often becomes active for the first time after surgery, pregnancy, childbirth, viral infection, emotional or other stress situations (Baldassarre et al., 2008). Concepts/hypothesis such as the hygiene

Heat Shock Proteins in Coeliac Disease 39

Fig. 1. Major processes of the pathogenesis of coeliac disease. (For explanation see text) Abbreviations: TG: transglutaminase; APC: antigen presenting cell; T: T lymphocyte; B: B

may be involved in different pathological conditions, such as neurodegenerative disorders (Malorni et al., 2008), tumour progression (Chhabra et al., 2009), autoimmune and inflammatory diseases (Elli et al., 2009). Due to its activity neutral glutamine residues of the gluten protein will be deamidated and can be converted into negatively charged glutamic acids, creating epitopes with increased immunostimulatory potential (Briani et al., 2008). Some of the deamidated gliadins may cross-link to transglutaminase and form covalently linked complexes (Alaedini & Green, 2008; Fleckenstein et al, 2004). Antigen presenting immune cells such as macrophages, dendritic cells and B lymphocytes present the deamidated peptides or complexes through their disease associated human leukocyte antigen-DQ2 and human leukocyte antigen-DQ8 molecules to CD4+ T helper cells in the lamina propria (Qiao et al, 2009). Activated T cells promote B cell maturation, isotype switch, and differentiation into plasma cells producing anti-gluten and antitransglutaminase 2 antibodies (Sollid, 2000). Furthermore activated T cells express proinflammatory cytokines, such as tumor necrosis factor alpha and interferon gamma, which trigger the release of matrix metalloproteinases by fibroblasts causing epithelial cell damage, degradation of the mucosal matrix and tissue remodeling (Schuppan et al., 2009). Interleukin-15 secreted by epithelial cells in response to gluten exposure activates intraepithelial CD8+ T lymphocytes called cytotoxic T cells, which can destroy epithelial

lymphocyte; Fb: fibroblast; IEL: intraepithelial lymphocyte

hypothesis, perhaps changes in wheat or other cereals may lead to the increased prevalence of coeliac disease. The disease leads to intestinal inflammation, villous atrophy, and crypt hyperplasia of the small intestine (Kaukinen et al, 2010). Furthermore coeliac disease may be associated with various extra-intestinal complications, including isolated iron deficiency anemia (Doganci & Bozkurt, 2004), bone and skin disease (Maniar et al., 2010; Reunala, 2001), infertility, endocrine and neurologic disorders (Gupta & Kohli, 2010). Presumed disease is mainly detected by serologic screening for the presence of tissue transglutaminase specific immunglobulin A antibodies, and this should be followed by taking biopsy samples from the small intestine mucosa to establish a definite diagnosis (Rostom et al., 2005). In the pathomechanism of coeliac disease both the adaptive and innate immunity may be involved. The importance of the adaptive immune response to gluten has been well established, but recent observations also suggest the central role for the gluten-induced innate stress response in the pathogenesis of coeliac disease (Jabri & Sollid, 2006). It is characterized by the presence of lymphocytic infiltration in the epithelial membrane and the lamina propria, and expression of multiple cytokines and signaling proteins (Briani et al., 2008). Recently gluten-free diet is the most effective mode to treat coeliac disease (Fric et al., 2011).

#### **1.2 How is stress involved in the development and pathomechanism of coeliac disease?**

As mentioned above there is a broad spectrum of environmental, genetic and immunologic factors, which may be involved in the development of coeliac disease. Here we focus on the common effects of different stress factors in the pathogenesis of coeliac disease. Stress is an acute menace to the homeostasis of an organism that may have both a short- and long-term influence on the function of the organs. Stress evokes adaptive responses that serve to defend the stability of the internal environment and to ensure the survival of the organism (Bhatia & Tandon, 2005). There are several types of stress circumstances: intrinsic, such as genetic and endoplasmic reticulum stress; extrinsic/environmental including heat-, toxin-, radiation-, infection- and injury-induced stress, mechanical and regenerative stress; metabolic stress such as hypoxia-induced, osmotic and oxidative stress. Under normal circumstances the epithelial cells are connected to each other with tight junctions and adherent junctions in the small intestine and in the large bowel as well. These structures of the epithelial cells serve as a barrier and inhibit the transcellular and paracellular permeation of molecules (Turner, 2009). Mechanical, chemical or oxidative stress can impair mucosal integrity (Lewis, 2009), modulate gut motility, epithelial barrier function (John et al., 2011) and inflammatory states (Lyte et al., 2011) and in genetically susceptible persons may lead to the development of coeliac disease (Szaflarska-Poplawska et al., 2011), because incompletely digested peptides of wheat gluten (gliadin and glutenins) and related proteins, as dietary antigens, can be transported across the epithelium and enter into the lamina propria of the small intestine (Alaedini & Green, 2005). The major processes of the pathogenesis of coeliac disease are shown on Figure 1.

Tissue transglutaminase 2 enzymes, which are the components of endomysium, become activated in the intestinal mucosa (lamina propria) (Schuppan et al., 2009). Transglutaminase 2 is a calcium-dependent enzyme which catalyzes protein cross-linking, polyamination or deamidation at selective glutamine residues (Caccamo et al., 2010) and

hypothesis, perhaps changes in wheat or other cereals may lead to the increased prevalence of coeliac disease. The disease leads to intestinal inflammation, villous atrophy, and crypt hyperplasia of the small intestine (Kaukinen et al, 2010). Furthermore coeliac disease may be associated with various extra-intestinal complications, including isolated iron deficiency anemia (Doganci & Bozkurt, 2004), bone and skin disease (Maniar et al., 2010; Reunala, 2001), infertility, endocrine and neurologic disorders (Gupta & Kohli, 2010). Presumed disease is mainly detected by serologic screening for the presence of tissue transglutaminase specific immunglobulin A antibodies, and this should be followed by taking biopsy samples from the small intestine mucosa to establish a definite diagnosis (Rostom et al., 2005). In the pathomechanism of coeliac disease both the adaptive and innate immunity may be involved. The importance of the adaptive immune response to gluten has been well established, but recent observations also suggest the central role for the gluten-induced innate stress response in the pathogenesis of coeliac disease (Jabri & Sollid, 2006). It is characterized by the presence of lymphocytic infiltration in the epithelial membrane and the lamina propria, and expression of multiple cytokines and signaling proteins (Briani et al., 2008). Recently gluten-free diet is the most effective mode to treat coeliac disease (Fric et al.,

**1.2 How is stress involved in the development and pathomechanism of coeliac** 

pathogenesis of coeliac disease are shown on Figure 1.

As mentioned above there is a broad spectrum of environmental, genetic and immunologic factors, which may be involved in the development of coeliac disease. Here we focus on the common effects of different stress factors in the pathogenesis of coeliac disease. Stress is an acute menace to the homeostasis of an organism that may have both a short- and long-term influence on the function of the organs. Stress evokes adaptive responses that serve to defend the stability of the internal environment and to ensure the survival of the organism (Bhatia & Tandon, 2005). There are several types of stress circumstances: intrinsic, such as genetic and endoplasmic reticulum stress; extrinsic/environmental including heat-, toxin-, radiation-, infection- and injury-induced stress, mechanical and regenerative stress; metabolic stress such as hypoxia-induced, osmotic and oxidative stress. Under normal circumstances the epithelial cells are connected to each other with tight junctions and adherent junctions in the small intestine and in the large bowel as well. These structures of the epithelial cells serve as a barrier and inhibit the transcellular and paracellular permeation of molecules (Turner, 2009). Mechanical, chemical or oxidative stress can impair mucosal integrity (Lewis, 2009), modulate gut motility, epithelial barrier function (John et al., 2011) and inflammatory states (Lyte et al., 2011) and in genetically susceptible persons may lead to the development of coeliac disease (Szaflarska-Poplawska et al., 2011), because incompletely digested peptides of wheat gluten (gliadin and glutenins) and related proteins, as dietary antigens, can be transported across the epithelium and enter into the lamina propria of the small intestine (Alaedini & Green, 2005). The major processes of the

Tissue transglutaminase 2 enzymes, which are the components of endomysium, become activated in the intestinal mucosa (lamina propria) (Schuppan et al., 2009). Transglutaminase 2 is a calcium-dependent enzyme which catalyzes protein cross-linking, polyamination or deamidation at selective glutamine residues (Caccamo et al., 2010) and

2011).

**disease?** 

Fig. 1. Major processes of the pathogenesis of coeliac disease. (For explanation see text) Abbreviations: TG: transglutaminase; APC: antigen presenting cell; T: T lymphocyte; B: B lymphocyte; Fb: fibroblast; IEL: intraepithelial lymphocyte

may be involved in different pathological conditions, such as neurodegenerative disorders (Malorni et al., 2008), tumour progression (Chhabra et al., 2009), autoimmune and inflammatory diseases (Elli et al., 2009). Due to its activity neutral glutamine residues of the gluten protein will be deamidated and can be converted into negatively charged glutamic acids, creating epitopes with increased immunostimulatory potential (Briani et al., 2008). Some of the deamidated gliadins may cross-link to transglutaminase and form covalently linked complexes (Alaedini & Green, 2008; Fleckenstein et al, 2004). Antigen presenting immune cells such as macrophages, dendritic cells and B lymphocytes present the deamidated peptides or complexes through their disease associated human leukocyte antigen-DQ2 and human leukocyte antigen-DQ8 molecules to CD4+ T helper cells in the lamina propria (Qiao et al, 2009). Activated T cells promote B cell maturation, isotype switch, and differentiation into plasma cells producing anti-gluten and antitransglutaminase 2 antibodies (Sollid, 2000). Furthermore activated T cells express proinflammatory cytokines, such as tumor necrosis factor alpha and interferon gamma, which trigger the release of matrix metalloproteinases by fibroblasts causing epithelial cell damage, degradation of the mucosal matrix and tissue remodeling (Schuppan et al., 2009). Interleukin-15 secreted by epithelial cells in response to gluten exposure activates intraepithelial CD8+ T lymphocytes called cytotoxic T cells, which can destroy epithelial

Heat Shock Proteins in Coeliac Disease 41

Role in protein folding, decrease the amount of nonnative proteins and unwanted intermolecular

Help to eliminate misfolded and irreversibly aggregated

Necessary to repair DNA damage and failures, that occur

and reorganization during and

Sustain cellular structures such

Table 1. Functional classification of proteins induced by heat stress response. For

explanations see text. Abbreviations: HSP: heat shock protein; NADH: nicotinamide adenine dinucleotide; CREB: cAMP response element-binding; Fas: FS7-associated cell surface antigen; HSF: heat shock factor; ABC: ATP binding cassette. (Based on review of Richter K.

degradation of the targeted protein by 26S proteasome complex (Glickman & Ciechanover, 2002). The third functional class of proteins (involved in the response to stress) is the group of DNA/RNA modifying enzymes. They are essential to repair DNA damage that occurs during stress (Jantschitsch & Trautinger, 2003; Biamonti & Caceres, 2009). The fourth class is that of metabolic enzymes, which are involved in cell energy supply stabilization and reorganization during and after stress. Malmendal et al. characterized the metabolomic profile of Drosophila melanogaster after heat stress exposure, and found relatively reduced level of some metabolites following shock compared to controls, which were involved in energy metabolism (Malmendal et al., 2006). They described that following heat stress energy storage were decreased in the form of reduced glycogen and fatty acid-like or lipidlike molecules and glucose levels (Malmendal et al., 2006). During stress response regulating proteins such as transcription factors and kinases play also crucial role. They are involved in further initiation of signaling pathways in response to stress or have role in ribosome biogenesis and assembly (Al Refaii & Alix, 2009). One family of the most important transcription factors involved in stress response is that of heat shock factors (Akerfelt et al., 2007). Heat shock factors play significant role in suppressing protein misfolding in cells by the induction of classical as well as of nonclassical heat shock genes, both of which might be required to maintain protein homeostasis (Fujimoto & Nakai, 2010). Proteins involved in

to regulate stress responses

Stabilization of membrane structure and function

interactions

proteins

4. Metabolic enzymes Cell energy supply stabilization

5. Regulatory proteins Transcription factors or kinases

after stress

as cytoskeleton

during stress

**Function Examples Reference** 

HSP90

HSP (heat shock protein) 60, HSP70,

Lap4 (vacuolar aminopeptidase), Yps6 (aspartic protease)

DNA helicase, RNAse p subunit, topoisomerase

acetyl-CoA hydrolase, NADH ubiquinone oxidoreductase

claudin, actin, Las 17 (actin patch protein)

MarR (antibiotic resistance), ABC transporters

Tiroli-Cepeda & Ramos, 2011

Maupin-Furlow et

, Jantschitsch & Trautinger, 2003; Biamonti & Caceres,

Malmendal et al.,

Levitsky et al., 2008

Vigh et al., 2007

al., 2000

2009

2006

CREB, Fas, HSF Akerfelt et al., 2007

**# Functional protein class name** 

chaperones (HSPs)

2. Proteolytic system components

modifying enzymes

6. Cell organisatory proteins

modulating proteins

7. Transport, detoxifying, membrane-

et al., 2010)

3. DNA/RNA

1. Molecular

cells, that express stress-induced non-classical major histocompatibility complex class I ligands and human leukocyte antigen E molecules (Briani et al., 2008; Jabri et al., 2005). Gliadin peptides can also directly elicit innate immune responses in macrophages and dendritic cells via pattern recognition receptors such as Toll-like receptor 2 and 4 (Szebeni et al., 2007). Mammalian Toll-like receptors comprise a family of type I transmembrane receptors, which originally recognize conserved pathogen-associated molecular patterns of different microorganisms (Medzhitov, 2001). Activation of Toll-like receptors leads to the upregulation of major histocompatibility complexes, costimulatory molecules and expression of proinflammatory cytokines and chemokines (Takeda et al, 2003). These stressinduced reactions lead to damage of the epithelial cells in the small intestine, which results in increased permeability, loss of barrier function and aggravation of the disease (Sollid & Jabri, 2005).

#### **2. Stress inducible proteins: their role and classification**

There are some major key molecules or processes, namely basement membrane degradation, oxidative stress, apoptosis, effect of matrix metalloproteinases and dysregulation of proliferation and differentiation, which are thought to play role in the pathophysiology of coeliac disease (Diosdado et al., 2004), however the exact pathomechanism is not fully understood. Here we focus on stress circumstances, as critical factors in the initiation and pathogenesis of coeliac disease (Lewis & McKay, 2009). Among several other diseases there are increasing evidences between stress and various gastrointestinal disorders, such as inflammatory bowel disease, irritable bowel syndrome, peptic ulcer disease, gastrointestinal reflux disease (Levenstein et al., 2000; Gué et al., 1997). Organisms must be able to sense and respond rapidly to changes in their environment in order to maintain homeostasis and survive. Therefore as consequence of stress several processes and molecules become activated. Based on the review by Richter K. et al. these proteins can be grouped into classes, namely molecular chaperones (called as HSPs), components of the proteolytic system, RNA/DNA modifying enzymes, metabolic enzymes, regulatory proteins, cell organisatory proteins and transport, detoxifying and membrane-modulating proteins (Richter et al., 2010) (Table 1).

The first discovered stress inducible proteins, called HSPs are recently referred to as "molecular chaperones" (discussed in details later). They are involved in adequate folding of proteins, which means, that these ubiquitous, conserved proteins help other proteins and macromolecules to fold or re-fold and reach their final, native conformation (Papp et al., 2003). Cells are equipped with an efficient surveillance system to selectively eliminate abnormally folded, damaged proteins (Mishra et al., 2009). First with the help of molecular chaperones the cell tries to refold the unfolded proteins (Bukau et al, 2006), but if the refolding is no more possible, the misfolded or irreversibly aggregated proteins will be degraded by the ubiquitin proteasome system (Shang & Taylor, 2011). In the second class of proteins belong the components of the ubiquitin-proteasome pathway, which is the primary cytosolic proteolytic machinery for the selective degradation of various forms of damaged proteins, so it is an important protein quality control mechanism (Dantuma & Lindsten, 2010). Degradation of the target protein by ubiquitin proteasome system is a multistep process consisting of activating, conjugating, and ligating enzymes to ensure covalent attachment of multiple molecules of ubiquitin to the target proteins, which finally leads to

cells, that express stress-induced non-classical major histocompatibility complex class I ligands and human leukocyte antigen E molecules (Briani et al., 2008; Jabri et al., 2005). Gliadin peptides can also directly elicit innate immune responses in macrophages and dendritic cells via pattern recognition receptors such as Toll-like receptor 2 and 4 (Szebeni et al., 2007). Mammalian Toll-like receptors comprise a family of type I transmembrane receptors, which originally recognize conserved pathogen-associated molecular patterns of different microorganisms (Medzhitov, 2001). Activation of Toll-like receptors leads to the upregulation of major histocompatibility complexes, costimulatory molecules and expression of proinflammatory cytokines and chemokines (Takeda et al, 2003). These stressinduced reactions lead to damage of the epithelial cells in the small intestine, which results in increased permeability, loss of barrier function and aggravation of the disease (Sollid &

There are some major key molecules or processes, namely basement membrane degradation, oxidative stress, apoptosis, effect of matrix metalloproteinases and dysregulation of proliferation and differentiation, which are thought to play role in the pathophysiology of coeliac disease (Diosdado et al., 2004), however the exact pathomechanism is not fully understood. Here we focus on stress circumstances, as critical factors in the initiation and pathogenesis of coeliac disease (Lewis & McKay, 2009). Among several other diseases there are increasing evidences between stress and various gastrointestinal disorders, such as inflammatory bowel disease, irritable bowel syndrome, peptic ulcer disease, gastrointestinal reflux disease (Levenstein et al., 2000; Gué et al., 1997). Organisms must be able to sense and respond rapidly to changes in their environment in order to maintain homeostasis and survive. Therefore as consequence of stress several processes and molecules become activated. Based on the review by Richter K. et al. these proteins can be grouped into classes, namely molecular chaperones (called as HSPs), components of the proteolytic system, RNA/DNA modifying enzymes, metabolic enzymes, regulatory proteins, cell organisatory proteins and transport, detoxifying and membrane-modulating proteins (Richter et al., 2010)

The first discovered stress inducible proteins, called HSPs are recently referred to as "molecular chaperones" (discussed in details later). They are involved in adequate folding of proteins, which means, that these ubiquitous, conserved proteins help other proteins and macromolecules to fold or re-fold and reach their final, native conformation (Papp et al., 2003). Cells are equipped with an efficient surveillance system to selectively eliminate abnormally folded, damaged proteins (Mishra et al., 2009). First with the help of molecular chaperones the cell tries to refold the unfolded proteins (Bukau et al, 2006), but if the refolding is no more possible, the misfolded or irreversibly aggregated proteins will be degraded by the ubiquitin proteasome system (Shang & Taylor, 2011). In the second class of proteins belong the components of the ubiquitin-proteasome pathway, which is the primary cytosolic proteolytic machinery for the selective degradation of various forms of damaged proteins, so it is an important protein quality control mechanism (Dantuma & Lindsten, 2010). Degradation of the target protein by ubiquitin proteasome system is a multistep process consisting of activating, conjugating, and ligating enzymes to ensure covalent attachment of multiple molecules of ubiquitin to the target proteins, which finally leads to

**2. Stress inducible proteins: their role and classification** 

Jabri, 2005).

(Table 1).


Table 1. Functional classification of proteins induced by heat stress response. For explanations see text. Abbreviations: HSP: heat shock protein; NADH: nicotinamide adenine dinucleotide; CREB: cAMP response element-binding; Fas: FS7-associated cell surface antigen; HSF: heat shock factor; ABC: ATP binding cassette. (Based on review of Richter K. et al., 2010)

degradation of the targeted protein by 26S proteasome complex (Glickman & Ciechanover, 2002). The third functional class of proteins (involved in the response to stress) is the group of DNA/RNA modifying enzymes. They are essential to repair DNA damage that occurs during stress (Jantschitsch & Trautinger, 2003; Biamonti & Caceres, 2009). The fourth class is that of metabolic enzymes, which are involved in cell energy supply stabilization and reorganization during and after stress. Malmendal et al. characterized the metabolomic profile of Drosophila melanogaster after heat stress exposure, and found relatively reduced level of some metabolites following shock compared to controls, which were involved in energy metabolism (Malmendal et al., 2006). They described that following heat stress energy storage were decreased in the form of reduced glycogen and fatty acid-like or lipidlike molecules and glucose levels (Malmendal et al., 2006). During stress response regulating proteins such as transcription factors and kinases play also crucial role. They are involved in further initiation of signaling pathways in response to stress or have role in ribosome biogenesis and assembly (Al Refaii & Alix, 2009). One family of the most important transcription factors involved in stress response is that of heat shock factors (Akerfelt et al., 2007). Heat shock factors play significant role in suppressing protein misfolding in cells by the induction of classical as well as of nonclassical heat shock genes, both of which might be required to maintain protein homeostasis (Fujimoto & Nakai, 2010). Proteins involved in

Heat Shock Proteins in Coeliac Disease 43

(Morandi et al., 1989). The HSP chaperone machinery may stabilize the target protein to degradation by the ubiquitin-proteasome pathway of proteolysis (Pratt et al., 2004). These functions of HSPs are important during cell repair process after damage. Generally there are two major groups of HSPs, constitutive, which are continually present in the cell, and inducible HSPs (Petrof et al., 2004). HSPs are rapidly induced by a variety of cellular stressors, such as heat, UV light, or cytotoxic agents (Rajaiah & Moudgil, 2009; Aufricht, 2004), ischaemia-reperfusion injury, oxidative stress and nutritional stress (Akerfelt et al, 2010). Recently our knowledge about their roles have been expanded, including their involvement in the modulation of immune responses (Hauet-Broere et al., 2006; Johnson & Fleshner, 2006), autoimmunity (Rajaiah & Moudgil, 2009), cell signaling (Csermely et al., 2007), cell proliferation (Pechan, 1991), and apoptosis (Padmini & Lavanya, 2011). The expression of HSPs has been reported in several tissues and cell types, including heart (Ghayour-Mobarhan, 2009), brain (Stetler, 2010), muscle (Geiger & Gupte, 2011), lung (Wong & Wispé, 1997), kidney (Kelly, 2005), liver (Tashiro, 2009) and intestinum (Asano et al., 2009). It is also known, that HSPs are overexpressed in a wide range of human cancers and are implicated in tumour cell proliferation, differentiation, invasion, metastasis, death, and recognition by the immune system (Ciocca & Calderwood, 2005). HSPs can be classified into five major families, namely HSP60s, HSP70s, HSP90s, HSP100s and small HSPs (Richter et al., 2010; Roberts et al., 2010) based on their molecular weight. There are also some not ubiquitous HSPs, for example redox-regulated chaperon HSP33, which can not be ranked into these classical groups (Graf & Jakob, 2002). Major families of HSPs can be seen on Table

**Example members Cellular localization** 

plasma membrane

cytoplasm, nucleus, mitochondria, endoplasmic reticulum

cytoplasm, nucleus, mitochondria, endoplasmic reticulum, lysosomes and extracellular compartments

cytoplasm, nucleus

1. HSP100 80-110 kDa HSP100, HSP104 cytoplasm, nucleus, mitochondia,

HSP90β

HSP73, HSP80

alphaB-crystallin, HSP25, HSP27, ubiquitin

various HSP33 various

Table 2. Major families of HSPs. For explanations see text. (Based on review of Roberts et al.,

The HSP100 proteins belong to the superfamily of AAA (ATPase associated with various cellular activities) + domain-containing ATPases (Mayer, 2010). They are localized to

4. HSP60 58-65 kDa HSP60, HSP65 mitochondria

2.

6.
