Identification of small molecule chemical inhibitors of the collagen-specific chaperone Hsp47

Targeting HSP47 for cancer treatment

Heat shock protein 47 (HSP47) serves as an endoplasmic reticulum residing collagen-specific chaperone and plays an important role in collagen biosynthesis and structural assembly. HSP47 is encoded by the SERPINH1 gene, which is located on chromosome 11q13.5, one of the most frequently amplified regions in human cancers. The expression of HSP47 is regulated by multiple cellular factors, including cytokines, transcription factors, microRNAs, and circular RNAs. HSP47 is frequently upregulated in a variety of cancers and plays an important role in tumor progression. HSP47 promotes tumor stemness, angiogenesis, growth, epithelial-mesenchymal transition, and metastatic capacity. HSP47 also regulates the efficacy of tumor therapies, such as chemotherapy, radiotherapy, and immunotherapy. Inhibition of HSP47 expression has antitumor effects, suggesting that targeting HSP47 is a feasible strategy for cancer treatment. In this review, we highlight the function and expression of regulatory mechanisms of HSP47 in cancer progression and point out the potential development of therapeutic strategies in targeting HSP47 in the future.

Benzbromarone Induces Targeted Degradation of HSP47 Protein and Improves Hypertrophic Scar Formation

Fibrotic diseases are characterized by the abnormal accumulation of collagen in the extracellular matrix, leading to the functional impairment of various organs. In the skin, excessive collagen deposition manifests as hypertrophic scars and keloids, placing a substantial burden on patients and the healthcare system worldwide. HSP47 is essential for proper collagen assembly and contributes to fibrosis. However, identifying clinically applicable HSP47 inhibitors has been a major pharmaceutical challenge. In this study, we identified benzbromarone (BBR) as an HSP47 inhibitor for hypertrophic scarring treatment. BBR inhibited collagen production and secretion in fibroblasts from patients with keloid by binding to HSP47 and inhibiting the interaction between HSP47 and collagen. Interestingly, BBR not only inhibits HSP47 but also acts as a molecular glue degrader that promotes its proteasome-dependent degradation. Through these molecular mechanisms, BBR effectively reduced hypertrophic scarring in mini pigs and rats with burns and/or excisional skin damage. Thus, these findings suggest that BBR can be used to clinically treat hypertrophic scars and, more generally, fibrotic diseases.

The Synthesis and Biological Applications of the 1,2,3-Dithiazole Scaffold

The 1,2,3-dithiazole is an underappreciated scaffold in medicinal chemistry despite possessing a wide variety of nascent pharmacological activities. The scaffold has a potential wealth of opportunities within these activities and further afield. The 1,2,3-dithiazole scaffold has already been reported as an antifungal, herbicide, antibacterial, anticancer agent, antiviral, antifibrotic, and is a melanin and Arabidopsis gibberellin 2-oxidase inhibitor. These structure activity relationships are discussed in detail, along with insights and future directions. The review also highlights selected synthetic strategies developed towards the 1,2,3-dithiazole scaffold, how these are integrated to accessibility of chemical space, and to the prism of current and future biological activities.

Therapeutic Strategies to Overcome Fibrotic Barriers to Nanomedicine in the Pancreatic Tumor Microenvironment

Pancreatic cancer is notorious for its dismal prognosis. The enhanced permeability and retention (EPR) effect theory posits that nanomedicines (therapeutics in the size range of approximately 10-200 nm) selectively accumulate in tumors. Nanomedicine has thus been suggested to be the "magic bullet"-both effective and safe-to treat pancreatic cancer. However, the densely fibrotic tumor microenvironment of pancreatic cancer impedes nanomedicine delivery. The EPR effect is thus insufficient to achieve a significant therapeutic effect. Intratumoral fibrosis is chiefly driven by aberrantly activated fibroblasts and the extracellular matrix (ECM) components secreted. Fibroblast and ECM abnormalities offer various potential targets for therapeutic intervention. In this review, we detail the diverse strategies being tested to overcome the fibrotic barriers to nanomedicine in pancreatic cancer. Strategies that target the fibrotic tissue/process are discussed first, which are followed by strategies to optimize nanomedicine design. We provide an overview of how a deeper understanding, increasingly at single-cell resolution, of fibroblast biology is revealing the complex role of the fibrotic stroma in pancreatic cancer pathogenesis and consider the therapeutic implications. Finally, we discuss critical gaps in our understanding and how we might better formulate strategies to successfully overcome the fibrotic barriers in pancreatic cancer.

Identification of HSP47 Binding Site on Native Collagen and Its Implications for the Development of HSP47 Inhibitors

HSP47 (heat shock protein 47) is a collagen-specific molecular chaperone that is essential for procollagen folding and function. Previous studies have shown that HSP47 binding requires a critical Arg residue at the Y position of the (Gly-Xaa-Yaa) repeats of collagen; however, the exact binding sites of HSP47 on native collagens are not fully defined. To address this, we mapped the HSP47 binding sites on collagens through an ELISA binding assay using collagen toolkits, synthetic collagen peptides covering the entire amino acid sequences of collagen types II and III assembled in triple-helical conformation. Our results showed that HSP47 binds to only a few of the GXR motifs in collagen, with most of the HSP47 binding sites identified located near the N-terminal part of the triple-helical region. Molecular modelling and binding energy calculation indicated that residues flanking the key Arg in the collagen sequence also play an important role in defining the high-affinity HSP47 binding site of collagen. Based on this binding mode of HSP47 to collagen, virtual screening targeting both the Arg binding site and its neighboring area on the HSP47 surface, and a subsequent bioassay, we identified two novel compounds with blocking activity towards HSP47 binding of collagen. Overall, our study revealed the native HSP47 binding sites on collagen and provided novel information for the design of small-molecule inhibitors of HSP47.

Silencing Heat Shock Protein 47 (HSP47) in Fibrogenic Precision-Cut Lung Slices: A Surprising Lack of Effects on Fibrogenesis?

Idiopathic pulmonary fibrosis (IPF) is a chronic disease that is characterized by the excessive deposition of scar tissue in the lungs. As currently available treatments are unable to restore lung function in patients, there is an urgent medical need for more effective drugs. Developing such drugs, however, is challenging because IPF has a complex pathogenesis. Emerging evidence indicates that heat shock protein 47 (HSP47), which is encoded by the gene Serpinh1, may be a suitable therapeutic target as it is required for collagen synthesis. Pharmacological inhibition or knockdown of HSP47 could therefore be a promising approach to treat fibrosis. The objective of this study was to assess the therapeutic potential of Serpinh1-targeting small interfering RNA (siRNA) in fibrogenic precision-cut lung slices prepared from murine tissue. To enhance fibrogenesis, slices were cultured for up to 144 h with transforming growth factor β1. Self-deliverable siRNA was used to knockdown mRNA and protein expression, without affecting the viability and morphology of slices. After silencing HSP47, only the secretion of fibronectin was reduced while other aspects of fibrogenesis remained unaffected (e.g., myofibroblast differentiation as well as collagen secretion and deposition). These observations are surprising as others have shown that Serpinh1-targeting siRNA suppressed collagen deposition in animals. Further studies are therefore warranted to elucidate downstream effects on fibrosis upon silencing HSP47.

HSP47: a potential target for fibrotic diseases and implications for therapy

Introduction: Chronic fibrotic disorders are challenging clinical problems. The major challenge is the identification of specific targets expressed selectively in fibrotic tissues. Collagen accumulation is the hallmark fibrosis. HSP47 is a collagen-specific chaperon with critical role in collagen folding. This review discusses the anti-fibrotic potential of HSP47. Areas covered: This review compiles data retrieved from the PubMed database with keywords 'HSP47+fibrosis' from 01/2005 to 06/2020. We examined 1) collagen biology and its role in fibrotic diseases, 2) HSP47 role in fibrosis, 3) HSP47 inhibition strategies and 4) clinical investigations. The identification of the HSP47-collagen binding site led to the development of methods to screen HSP47 inhibitors with anti-fibrotic potential. Specific in vivo  delivery systems of HSP47 siRNA to fibrotic tissue reduced collagen production/secretion associated with fibrosis inhibition in preclinical models. This strategy is about to be tested in clinical trials. Expert opinion: As a collagen-specific chaperon, HSP47 is a promising therapeutic target in fibrosis. Preclinical models have shown encouraging anti-fibrotic results. Anti-HSP47 strategies need to be further evaluated in clinical trials. The increase in circulating-HSP47 in lung fibrosis patients highlights the potential of HSP47 as a noninvasive biomarker and may represent an important step toward personalized medicine in fibrotic disorders.

Small-molecule modulators of serine protease inhibitor proteins (serpins)

Serine protease inhibitors (serpins) are a large family of proteins that regulate and control crucial physiological processes, such as inflammation, coagulation, thrombosis and thrombolysis, and immune responses. The extraordinary impact that these proteins have on numerous crucial pathways makes them an attractive target for drug discovery. In this review, we discuss recent advances in research on small-molecule modulators of serpins, examine their mode of action, analyse the structural data from crystallised protein-ligand complexes, and highlight the potential obstacles and possible therapeutic perspectives. The application of in silico methods for rational drug discovery is also summarised. In addition, we stress the need for continued research in this field.

Intestinal stenosis in Crohn's disease shows a generalized upregulation of genes involved in collagen metabolism and recognition that could serve as novel anti-fibrotic drug targets

BACKGROUND AND AIMS

Crohn's disease (CD) can be complicated by intestinal fibrosis. Pharmacological therapies against intestinal fibrosis are not available. The aim of this study was to determine whether pathways involved in collagen metabolism are upregulated in intestinal fibrosis, and to discuss which drugs might be suitable to inhibit excessive extracellular matrix formation targeting these pathways.

METHODS

Human fibrotic and non-fibrotic terminal ileum was obtained from patients with CD undergoing ileocecal resection due to stenosis. Genes involved in collagen metabolism were analyzed using a microfluidic low-density TaqMan array. A literature search was performed to find potential anti-fibrotic drugs that target proteins/enzymes involved in collagen synthesis, its degradation and its recognition.

RESULTS

mRNA expression of collagen type I (COL1A1, 0.76 ± 0.28 versus 37.82 ± 49.85, p = 0.02) and III (COL3A1, 2.01 ± 2.61 versus 68.65 ± 84.07, p = 0.02) was increased in fibrotic CD compared with non-fibrotic CD. mRNA expression of proteins involved in both intra- and extracellular post-translational modification of collagens (prolyl- and lysyl hydroxylases, lysyl oxidases, chaperones), collagen-degrading enzymes (MMPs and cathepsin-K), and collagen receptors were upregulated in the fibrosis-affected part. A literature search on the upregulated genes revealed several potential anti-fibrotic drugs.

CONCLUSION

Expression of genes involved in collagen metabolism in intestinal fibrosis affected terminal ileum of patients with CD reveals a plethora of drug targets. Inhibition of post-translational modification and altering collagen metabolism might attenuate fibrosis formation in the intestine in CD. Which compound has the highest potential depends on a combination anti-fibrotic efficacy and safety, especially since some of the enzymes play key roles in the physiology of collagen.

Small molecule inhibitor of HSP47 prevents pro-fibrotic mechanisms of fibroblasts in vitro

Excessive extracellular matrix deposition, in particular collagen, is an important cause of lung fibrosis. Heat shock protein 47 (HSP47), a collagen-binding protein, plays an important role in the intracellular processing of procollagen. A small molecule that blocks the collagen chaperone function of HSP47 has been reported as an HSP47 inhibitor. The aim of this study was to assess the effect of the HSP47 inhibitor on collagen synthesis and other fibrotic process in vitro. We evaluated collagen expression by western blot, and determined cell viability and migration by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and scratch test, respectively, in human and mouse lung fibroblasts. Treatment of lung fibroblasts with HSP47 siRNA decreased collagen type I expression. Similarly, the HSP47 inhibitor decreased collagen type I expression in transforming growth factor beta 1 (TGF-β1)-treated lung fibroblasts in a dose-dependent manner. The inhibitor also decreased the viability and cell migration ability of TGF-β1-treated lung fibroblasts. Overall, we demonstrated that HSP47 is a potential therapeutic target for pulmonary fibrosis. The small molecule HSP47 inhibitor may mediate antifibrotic effects by suppressing the overexpression of collagen, and inhibiting the viability and migration of fibroblasts. Further research is needed to clarify the therapeutic potential of this HSP47 inhibitor for pulmonary fibrosis.

Roles of the endoplasmic reticulum-resident, collagen-specific molecular chaperone Hsp47 in vertebrate cells and human disease

Heat shock protein 47 (Hsp47) is an endoplasmic reticulum (ER)-resident molecular chaperone essential for correct folding of procollagen in mammalian cells. In this Review, we discuss the role and function of Hsp47 in vertebrate cells and its role in connective tissue disorders. Hsp47 binds to collagenous (Gly-Xaa-Arg) repeats within triple-helical procollagen in the ER and can prevent its local unfolding or aggregate formation, resulting in accelerating triple-helix formation of procollagen. Hsp47 pH-dependently dissociates from procollagen in the cis-Golgi or ER-Golgi intermediate compartment and is then transported back to the ER. Although Hsp47 belongs to the serine protease inhibitor (serpin) superfamily, it does not possess serine protease inhibitory activity. Whereas general molecular chaperones such as Hsp70 and Hsp90 exhibit broad substrate specificity, Hsp47 has narrower specificity mainly for procollagens. However, other Hsp47-interacting proteins have been recently reported, suggesting a much broader role for Hsp47 in the cell that warrants further investigation. Other ER-resident stress proteins, such as binding immunoglobulin protein (BiP), are induced by ER stress, whereas Hsp47 is induced only by heat shock. Constitutive expression of Hsp47 is always correlated with expression of various collagen types, and disruption of the Hsp47 gene in mice causes embryonic lethality due to impaired basement membrane and collagen fibril formation. Increased Hsp47 expression is associated with collagen-related disorders such as fibrosis, characterized by abnormal collagen accumulation, highlighting Hsp47's potential as a clinically relevant therapeutic target.

The heat shock protein 47 as a potential biomarker and a therapeutic agent in cancer research

Heat shock protein 47 (HSP47) is an important chaperone required for the correct folding and secretion of collagen. Several studies revealed that HSP47 has a role in numerous steps of collagen synthesis, preventing procollagen aggregation and inducing hydroxylation of proline and lysine residues. HSP47 is encoded by the SERPINH1 gene, which is located on chromosome 11q13.5, one of the most frequently amplified regions in human cancer. The altered expression levels of HSP47 have been correlated with several types of cancer, such as cervical, breast, pancreatic and gastric cancers. Studies have shown that HSP47 promotes tumor angiogenesis, growth, migration and metastatic capacity. In this review, we highlight the fundamental aspects of the interaction between HSP47 and collagen and the recent discoveries of the role of this chaperone in different types of malignant neoplasias. We also discuss recent treatments using HSP47 as a therapeutic target, and present evidences that HSP47 is an essential protein for cancer biology and a potential molecular target for chemotherapy.

The chaperone protein HSP47: a platelet collagen binding protein that contributes to thrombosis and hemostasis

Essentials Heat shock protein 47 (HSP47), a collagen specific chaperone is present on the platelet surface. Collagen mediated platelet function was reduced following blockade or deletion of HSP47. GPVI receptor regulated signalling was reduced in HSP47 deficient platelets. Platelet HSP47 tethers to exposed collagen thus modulating thrombosis and hemostasis.

SUMMARY

Objective Heat shock protein 47 (HSP47) is an intracellular chaperone protein that is vital for collagen biosynthesis in collagen secreting cells. This protein has also been shown to be present on the surface of platelets. Given the importance of collagen and its interactions with platelets in triggering hemostasis and thrombosis, in this study we sought to characterize the role of HSP47 in these cells. Methods and Results The deletion of HSP47 in mouse platelets or its inhibition in human platelets reduced their function in response to collagen and the GPVI agonist (CRP-XL), but responses to thrombin were unaltered. In the absence of functional HSP47, the interaction of collagen with platelets was reduced, and this was associated with reduced GPVI-collagen binding, signalling and platelet activation. Thrombus formation on collagen, under arterial flow conditions, was also decreased following the inhibition or deletion of HSP47, in the presence or absence of eptifibatide, consistent with a role for HSP47 in enhancing platelet adhesion to collagen. Platelet adhesion under flow to von Willebrand factor was unaltered following HSP47 inhibition. Laser-induced thrombosis in cremaster muscle arterioles was reduced and bleeding time was prolonged in HSP47-deficient mice or following inhibition of HSP47. Conclusions Our study demonstrates the presence of HSP47 on the platelet surface, where it interacts with collagen, stabilizes platelet adhesion and increases collagen-mediated signalling and therefore thrombus formation and hemostasis.

Biology of Hsp47 (Serpin H1), a collagen-specific molecular chaperone

Hsp47, a collagen-specific molecular chaperone that localizes in the endoplasmic reticulum (ER), is indispensable for molecular maturation of collagen. Hsp47, which is encoded by the SERPINH1 gene, belongs to the serpin family and has the serpin fold; however, it has no serine protease inhibitory activity. Hsp47 transiently binds to procollagen in the ER, dissociates in the cis-Golgi or ER-Golgi intermediate compartment (ERGIC) in a pH-dependent manner, and is then transported back to the ER via its RDEL retention sequence. Hsp47 recognizes collagenous (Gly-Xaa-Arg) repeats on triple-helical procollagen and can prevent local unfolding and/or aggregate formation of procollagen. Gene disruption of Hsp47 in mice causes embryonic lethality due to impairments in basement membrane and collagen fibril formation. In Hsp47-knockout cells, the type I collagen triple helix forms abnormally, resulting in thin and frequently branched fibrils. Secretion of type I collagens is slow and plausible in making aggregates of procollagens in the ER of hsp47-knocked out fibroblasts, which are ultimately degraded by autophagy. Mutations in Hsp47 are causally associated with osteogenesis imperfecta. Expression of Hsp47 is strongly correlated with expression of collagens in multiple types of cells and tissues. Therefore, Hsp47 represents a promising target for treatment of collagen-related disorders, including fibrosis of the liver, lung, and other organs.

Dissecting fibrosis: therapeutic insights from the small-molecule toolbox

Fibrosis, which leads to progressive loss of tissue function and eventual organ failure, has been estimated to contribute to ~45% of deaths in the developed world, and so new therapeutics to modulate fibrosis are urgently needed. Major advances in our understanding of the mechanisms underlying pathological fibrosis are supporting the search for such therapeutics, and the recent approval of two anti-fibrotic drugs for idiopathic pulmonary fibrosis has demonstrated the tractability of this area for drug discovery. This Review examines the pharmacology and structural information for small molecules being evaluated for lung, liver, kidney and skin fibrosis. In particular, we discuss the insights gained from the use of these pharmacological tools, and how these entities can inform, and probe, emerging insights into disease mechanisms, including the potential for future drug combinations.

The collagen chaperone HSP47 is a new interactor of APP that affects the levels of extracellular beta-amyloid peptides

Alzheimer disease (AD) is a neurodegenerative disorder characterized by progressive decline of cognitive function that represents one of the most dramatic medical challenges for the aging population. Aβ peptides, generated by processing of the Amyloid Precursor Protein (APP), are thought to play a central role in the pathogenesis of AD. However, the network of physical and functional interactions that may affect their production and deposition is still poorly understood. The use of a bioinformatic approach based on human/mouse conserved coexpression allowed us to identify a group of genes that display an expression profile strongly correlated with APP. Among the most prominent candidates, we investigated whether the collagen chaperone HSP47 could be functionally correlated with APP. We found that HSP47 accumulates in amyloid deposits of two different mouse models and of some AD patients, is capable to physically interact with APP and can be relocalized by APP overexpression. Notably, we found that it is possible to reduce the levels of secreted Aβ peptides by reducing the expression of HSP47 or by interfering with its activity via chemical inhibitors. Our data unveil HSP47 as a new functional interactor of APP and imply it as a potential target for preventing the formation and/or growth amyloid plaques.

Faithful chaperones

This review describes the properties of some rare eukaryotic chaperones that each assist in the folding of only one target protein. In particular, we describe (1) the tubulin cofactors, (2) p47, which assists in the folding of collagen, (3) α-hemoglobin stabilizing protein (AHSP), (4) the adenovirus L4-100 K protein, which is a chaperone of the major structural viral protein, hexon, and (5) HYPK, the huntingtin-interacting protein. These various-sized proteins (102–1,190 amino acids long) are all involved in the folding of oligomeric polypeptides but are otherwise functionally unique, as they each assist only one particular client. This raises a question regarding the biosynthetic cost of the high-level production of such chaperones. As the clients of faithful chaperones are all abundant proteins that are essential cellular or viral components, it is conceivable that this necessary metabolic expenditure withstood evolutionary pressure to minimize biosynthetic costs. Nevertheless, the complexity of the folding pathways in which these chaperones are involved results in error-prone processes. Several human disorders associated with these chaperones are discussed.

Targeting collagen expression in alcoholic liver disease

Alcoholic liver disease (ALD) is a leading cause of liver disease and liver-related deaths globally, particularly in developed nations. Liver fibrosis is a consequence of ALD and other chronic liver insults, which can progress to cirrhosis and hepatocellular carcinoma if left untreated. Liver fibrosis is characterized by accumulation of excess extracellular matrix components, including type I collagen, which disrupts liver microcirculation and leads to injury. To date, there is no therapy for the treatment of liver fibrosis; thus treatments that either prevent the accumulation of type I collagen or hasten its degradation are desirable. The focus of this review is to examine the regulation of type I collagen in fibrogenic cells of the liver and to discuss current advances in therapeutics to eliminate excessive collagen deposition.

A missense mutation in the SERPINH1 gene in Dachshunds with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a hereditary disease occurring in humans and dogs. It is characterized by extremely fragile bones and teeth. Most human and some canine OI cases are caused by mutations in the COL1A1 and COL1A2 genes encoding the subunits of collagen I. Recently, mutations in the CRTAP and LEPRE1 genes were found to cause some rare forms of human OI. Many OI cases exist where the causative mutation has not yet been found. We investigated Dachshunds with an autosomal recessive form of OI. Genotyping only five affected dogs on the 50 k canine SNP chip allowed us to localize the causative mutation to a 5.82 Mb interval on chromosome 21 by homozygosity mapping. Haplotype analysis of five additional carriers narrowed the interval further down to 4.74 Mb. The SERPINH1 gene is located within this interval and encodes an essential chaperone involved in the correct folding of the collagen triple helix. Therefore, we considered SERPINH1 a positional and functional candidate gene and performed mutation analysis in affected and control Dachshunds. A missense mutation (c.977C>T, p.L326P) located in an evolutionary conserved domain was perfectly associated with the OI phenotype. We thus have identified a candidate causative mutation for OI in Dachshunds and identified a fifth OI gene.

Development of a high-throughput screening system for the compounds that inhibit collagen-protein interactions

Collagen-binding proteins (CBPs) play important roles in various physiological events. Some CBPs are regarded as targets for drug development; for example, platelet glycoprotein VI (GPVI) and heat shock protein 47 (HSP47) are promising targets for the development of novel antiplatelet and antifibrotic drugs, respectively. However, no systematic screening method to search compounds that inhibit collagen-CBP interactions have been developed, and only a few CBP inhibitors have been reported to date. In this study, a facile turbidimetric multiwell plate assay was developed to evaluate inhibitors of CBPs. The assay is based on the finding that CBPs retard spontaneous collagen fibril formation in vitro and that fibril formation is restored in the presence of compounds that interfere with the collagen-CBP interactions. Using the same platform, the assay was performed in various combinations of fibril-forming collagen types and CBPs. This homogeneous assay is simple, convenient, and suitable as an automated high-throughput screening system.

Proteomic analysis of human ovaries from normal and polycystic ovarian syndrome

Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility, affecting 5-10% of females of reproductive age. Currently, little is known about the changes in whole proteins between PCOS and normal ovaries. In the present study, a proteomic approach comprised two-dimensional gel electrophoresis (2DE) analysis and mass spectroscopy was used to identify proteins and examine expression patterns in three PCOS and normal ovaries. One hundred and ten protein spots were separated and showed different intensities between PCOS and normal ovaries. Sixty-nine proteins associated with cellular metabolism and physiological process were identified from 72 spots. Fifty-four proteins were up-regulated in PCOS ovaries and 15 other proteins were up-regulated in normal ovaries. These data demonstrate, for the first time, the complexity in the regulation of ovarian protein expression in human PCOS, and will provide important insight for a better understanding of the pathogenetic mechanisms underlying this clinical disorder.

The collagen-specific molecular chaperone HSP47: is there a role in fibrosis?

Heat shock protein 47 (HSP47) is a collagen-specific molecular chaperone that is required for molecular maturation of various types of collagens. Recent studies have shown a close association between increased expression of HSP47 and excessive accumulation of collagens in scar tissues of various human and experimental fibrotic diseases. It is presumed that the increased levels of HSP47 in fibrotic diseases assist in excessive assembly and intracellular processing of procollagen molecules and, thereby, contribute to the formation of fibrotic lesions. Studies have also shown that suppression of HSP47 expression can reduce accumulation of collagens to delay the progression of fibrotic diseases in experimental animal models. Because HSP47 is a specific chaperone for collagen synthesis, it provides a selective target to manipulate collagen production, a phenomenon that might have enormous clinical impact in controlling a wide range of fibrotic diseases. Here, we outline the fibrogenic role of HSP47 and discuss the potential usefulness of HSP47 as an anti-fibrotic therapeutic target.

Specific recognition of the collagen triple helix by chaperone HSP47. II. The HSP47-binding structural motif in collagens and related proteins

The endoplasmic reticulum-resident chaperone heat-shock protein 47 (HSP47) plays an essential role in procollagen biosynthesis. The function of HSP47 relies on its specific interaction with correctly folded triple-helical regions comprised of Gly-Xaa-Yaa repeats, and Arg residues at Yaa positions have been shown to be important for this interaction. The amino acid at the Yaa position (Yaa(-3)) in the N-terminal-adjoining triplet containing the critical Arg (defined as Arg(0)) was also suggested to be directly recognized by HSP47 (Koide, T., Asada, S., Takahara, Y., Nishikawa, Y., Nagata, K., and Kitagawa, K. (2006) J. Biol. Chem. 281, 3432-3438). Based on this finding, we examined the relationship between the structure of Yaa(-3) and HSP47 binding using synthetic collagenous peptides. The results obtained indicated that the structure of Yaa(-3) determined the binding affinity for HSP47. Maximal binding was observed when Yaa(-3) was Thr. Moreover, the required relative spatial arrangement of these key residues in the triple helix was analyzed by taking advantage of heterotrimeric collagen-model peptides, each of which contains one Thr(-3) and one Arg(0). The results revealed that HSP47 recognizes the Yaa(-3) and Arg(0) residues only when they are on the same peptide strand. Taken together, the data obtained led us to define the HSP47-binding structural epitope in the collagen triple helix and also define the HSP47-binding motif in the primary structure. A motif search against human protein database predicted candidate clients for this molecular chaperone. The search result indicated that not all collagen family proteins require the chaperoning by HSP47.