Interaction of stress proteins with misfolded keratins

Defining the Nature and Clinicopathologic Significance of Mallory-Denk-like Inclusions in Ovarian Fibromas: A Potential Degenerative Phenomenon Associated With Torsion

Mallory-Denk bodies (MBD), described in alcoholic hepatitis, are composed of intermediate filaments admixed with other proteins. These cytoplasmic inclusions are irregularly shaped and eosinophilic as seen under the light microscope. MBD-like inclusions have rarely been described outside the hepatobiliary tree. Though rare, intracytoplasmic inclusions have been reported in ovarian fibromas. This study evaluates a series of torsed ovarian fibromas with intracytoplasmic inclusions resembling MDBs. Forty-three ovarian fibromas were retrieved from the pathology archives. The H&E slides were evaluated for the presence of MBD-like inclusions and histologic evidence of torsion. The cases with histologic features of torsion were included in the study group while the nontorsed fibromas formed the control group. Among the 15 cases of fibromas with torsion, MBD-like intracytoplasmic inclusions were seen in 5 cases, predominantly in the interface between necrotic areas and viable stroma. None of the cases from the control group showed any inclusions. There was no significant difference in the size of the fibroma or patient demographics between cases with and without inclusions. The inclusions were positive for cytokeratin and ubiquitin while being negative for per acidic Schiff and periodic acid-Schiff with diastase reaction, in the 3 cases selected for immunohistochemistry and special stains. Electron microscopy of the index case revealed a predominance of type 3 Mallory hyaline. This is the first report describing MDB-like inclusions in ovarian fibromas. These MDB-like inclusions appear to be limited to a fraction of ovarian fibromas that underwent torsion, suggesting that these inclusions likely result from subacute hypoxic damage to the cells.

Roles of the Exosomes Derived From Myeloid-Derived Suppressor Cells in Tumor Immunity and Cancer Progression

Tumor immunity is involved in malignant tumor progression. Myeloid-derived suppressor cells (MDSCs) play an irreplaceable role in tumor immunity. MDSCs are composed of immature myeloid cells and exhibit obvious immunomodulatory functions. Exosomes released by MDSCs (MDSCs-Exos) have similar effects to parental MDSCs in regulating tumor immunity. In this review, we provided a comprehensive description of the characteristics, functions and mechanisms of exosomes. We analyzed the immunosuppressive, angiogenesis and metastatic effects of MDSCs-Exos in different tumors through multiple perspectives. Immunotherapy targeting MDSCs-Exos has demonstrated great potential in cancers and non-cancerous diseases.

Bone Cells Differentiation: How CFTR Mutations May Rule the Game of Stem Cells Commitment?

Cystic fibrosis (CF)-related bone disease has emerged as a significant comorbidity of CF and is characterized by decreased bone formation and increased bone resorption. Both osteoblast and osteoclast differentiations are impacted by cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The defect of CFTR chloride channel or the loss of CFTRs ability to interact with other proteins affect several signaling pathways involved in stem cell differentiation and the commitment of these cells toward bone lineages. Specifically, TGF-, nuclear factor-kappa B (NF-B), PI3K/AKT, and MAPK/ERK signaling are disturbed by CFTR mutations, thus perturbing stem cell differentiation. High inflammation in patients changes myeloid lineage secretion, affecting both myeloid and mesenchymal differentiation. In osteoblast, Wnt signaling is impacted, resulting in consequences for both bone formation and resorption. Finally, CFTR could also have a direct role in osteoclasts resorptive function. In this review, we summarize the existing literature on the role of CFTR mutations on the commitment of induced pluripotent stem cells to bone cells.

p62/Sequestosome-1 Is Indispensable for Maturation and Stabilization of Mallory-Denk Bodies

Mallory-Denk bodies (MDBs) are hepatocytic protein aggregates found in steatohepatitis and several other chronic liver diseases as well as hepatocellular carcinoma. MDBs are mainly composed of phosphorylated keratins and stress protein p62/Sequestosome-1 (p62), which is a common component of cytoplasmic aggregates in a variety of protein aggregation diseases. In contrast to the well-established role of keratins, the role of p62 in MDB pathogenesis is still elusive. We have generated total and hepatocyte-specific p62 knockout mice, fed them with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) to induce MDBs and allowed the mice to recover from DDC intoxication on a standard diet to investigate the role of p62 in MDB formation and elimination. In the absence of p62, smaller, granular and less distinct MDBs appeared, which failed to mature to larger and compact inclusions. Moreover, p62 deficiency impaired the binding of other proteins such as NBR1 and Hsp25 to MDBs and altered the cellular defense mechanism by downregulation of Nrf2 target genes. Upon recovery from DDC intoxication on a standard diet, there was an enhanced reduction of p62-deficient MDBs, which was accompanied by a pronounced decrease in ubiquitinated proteins. Our data provide strong evidence that keratin aggregation is the initial step in MDB formation in steatohepatitis-related mouse models. Interaction of p62 with keratin aggregates then leads to maturation i.e., enlargement and stabilization of the MDBs as well as recruitment of other MDB-associated proteins.

Genetic deletion of keratin 8 corrects the altered bone formation and osteopenia in a mouse model of cystic fibrosis

Patients with cystic fibrosis (CF) display low bone mass and alterations in bone formation. Mice carrying the F508del genetic mutation in the cystic fibrosis conductance regulator (Cftr) gene display reduced bone formation and decreased bone mass. However, the underlying molecular mechanisms leading to these skeletal defects are unknown, which precludes the development of an efficient anti-osteoporotic therapeutic strategy. Here we report a key role for the intermediate filament protein keratin 8 (Krt8), in the osteoblast dysfunctions in F508del-Cftr mice. We found that murine and human osteoblasts express Cftr and Krt8 at low levels. Genetic studies showed that Krt8 deletion (Krt8(-/-)) in F508del-Cftr mice increased the levels of circulating markers of bone formation, corrected the expression of osteoblast phenotypic genes, promoted trabecular bone formation and improved bone mass and microarchitecture. Mechanistically, Krt8 deletion in F508del-Cftr mice corrected overactive NF-κB signaling and decreased Wnt-β-catenin signaling induced by the F508del-Cftr mutation in osteoblasts. In vitro, treatment with compound 407, which specifically disrupts the Krt8-F508del-Cftr interaction in epithelial cells, corrected the abnormal NF-κB and Wnt-β-catenin signaling and the altered phenotypic gene expression in F508del-Cftr osteoblasts. In vivo, short-term treatment with 407 corrected the altered Wnt-β-catenin signaling and bone formation in F508del-Cftr mice. Collectively, the results show that genetic or pharmacologic targeting of Krt8 leads to correction of osteoblast dysfunctions, altered bone formation and osteopenia in F508del-Cftr mice, providing a therapeutic strategy targeting the Krt8-F508del-CFTR interaction to correct the abnormal bone formation and bone loss in cystic fibrosis.

Functional Analysis of Keratin-Associated Proteins in Intestinal Epithelia: Heat-Shock Protein Chaperoning and Kinase Rescue

A growing body of evidence from several laboratories points at nonmechanical functions of keratin intermediate filaments (IF), such as control of apoptosis, modulation of signaling, or regulation of innate immunity, among others. While these functions are generally assigned to the ability of IF to scaffold other proteins, direct mechanistic causal relationships between filamentous keratins and the observed effects of keratin knockout or mutations are still missing. We have proposed that the scaffolding of chaperones such as Hsp70/40 may be key to understand some IF nonmechanical functions if unique features or specificity of the chaperoning activity in the IF scaffold can be demonstrated. The same criteria of uniqueness could be applied to other biochemical functions of the IF scaffold. Here, we describe a subcellular fractionation technique based on established methods of keratin purification. The resulting keratin-enriched fraction contains several proteins tightly associated with the IF scaffold, including Hsp70/40 chaperones. Being nondenaturing, this fractionation method enables direct testing of chaperoning and other enzymatic activities associated with IF, as well as supplementation experiments to determine the need for soluble (cytosolic) proteins. This method also permits to analyze inhibitory activity of cytosolic proteins at independently characterized physiological concentrations. When used as complementary approaches to knockout, knockdown, or site-directed mutagenesis, these techniques are expected to shed light on molecular mechanisms involved in the effects of IF loss of function.

Response to oral acitretin in lichen amyloidosis

We report the therapeutically challenging case of a patient with severe and extensive lichen amyloidosis (LA) who responded to oral acitretin and topical corticosteroids. Colloid milia and terra firma-forme dermatoses were noted post healing of the lesions of LA. There has been no recurrence of lesions post 8 months of follow-up. We recommend that acitretin should be used more often in severe and recalcitrant cases of LA.

Ubiquitinated proteins in exosomes secreted by myeloid-derived suppressor cells

We provide evidence at the molecular level that ubiquitinated proteins are present in exosomes shed by myeloid-derived suppressor cells (MDSC). Ubiquitin was selected as a post-translational modification of interest because it is known to play a determinant role in the endosomal trafficking that culminates in exosome release. Enrichment was achieved by two immunoprecipitations, first at the protein level and subsequently at the peptide level. Fifty ubiquitinated proteins were identified by tandem mass spectrometry filtering at a 5% spectral false discovery rate and using the conservative requirement that glycinylglycine-modified lysine residues were observed in tryptic peptides. Thirty five of these proteins have not previously been reported to be ubiquitinated. The ubiquitinated cohort spans a range of protein sizes and favors basic pI values and hydrophobicity. Five proteins associated with endosomal trafficking were identified as ubiquitinated, along with pro-inflammatory high mobility group protein B1 and proinflammatory histones.

Inhibition of intracellular clusterin attenuates cell death in nephropathic cystinosis

Nephropathic cystinosis, characterized by accumulation of cystine in the lysosomes, is caused by mutations in CTNS. The molecular and cellular mechanisms underlying proximal tubular dysfunction and progressive renal failure in nephropathic cystinosis are largely unclear, and increasing evidence supports the notion that cystine accumulation alone is not responsible for the end organ injury in cystinosis. We previously identified clusterin as potentially involved in nephropathic cystinosis. Here, we studied the expression of clusterin in renal proximal tubular epithelial cells obtained from patients with nephropathic cystinosis. The cytoprotective secretory form of clusterin, as evaluated by Western blot analysis, was low or absent in cystinosis cells compared with normal primary cells. Confocal microscopy revealed elevated levels of intracellular clusterin in cystinosis cells. Clusterin in cystinosis cells localized to the nucleus and cytoplasm and showed a filamentous and punctate aggresome-like pattern compared with diffuse cytoplasmic staining in normal cells. In kidney biopsy samples from patients with nephropathic cystinosis, clusterin protein expression was mainly limited to the proximal tubular cells. Furthermore, expression of clusterin overlapped with the expression of apoptotic proteins (apoptosis-inducing factor and cleaved caspase-3) and autophagy proteins (LC3 II and p62). Silencing of the clusterin gene resulted in a significant increase in cell viability and attenuation of apoptosis in cystinosis cells. Results of this study identify clusterin as a pivotal factor in the cell injury mechanism of nephropathic cystinosis and provide evidence linking cellular stress and injury to Fanconi syndrome and progressive renal injury in nephropathic cystinosis.

Cytoskeleton and CFTR

Cystic Fibrosis Transmembrane conductance Regulator, CFTR, is a membrane protein expressed in epithelia. A protein kinase A (PKA)-regulated Cl(-) channel, it is a rate-limiting factor in fluid transport. Mutations in CFTR are responsible for cystic fibrosis, CF, an autosomal recessive disease. The most frequent mutation is deletion of phenylalanine at position 508, ΔF508. The regulation of trafficking and degradation of CFTR/ΔF508CFTR as well as its function(s) is a complex process which involves a number of proteins including chaperones and adaptors. It is now known that cytoskeletal proteins, previously considered only as structural proteins, are also important factors in the regulation of cellular processes and functions. The aim of the present review is to focus on how microfilaments, microtubules and intermediary filaments form a dynamic interactome with CFTR to participate in the regulation of CFTR-dependent transepithelial ion transport, CFTR trafficking and degradation.

Contribution of proteomics to the study of the role of cytokeratins in disease and physiopathology

Cytokeratins (CKs), the most abundant group of cytoskeletal intermediate filaments, and proteomics are strongly connected. On the one hand, proteomics has been extremely useful to uncover new features and functions of CKs, on the other, the highly abundant CKs serve as an exceptional tool to test new technological developments in proteomics. As a result, proteomics has contributed to finding valuable associations of CKs with diseases as diverse as cancer, cystic fibrosis, steatohepatitis, viral and bacterial infection, keratoconus, vitreoretinopathy, preeclampsia or the chronic fatigue syndrome, as well as to characterizing their participation in a number of physiopathological processes, including drug resistance, response to toxicants, inflammation, stem cell differentiation, embryo development, and tissue repair. In some cases, like in cystic fibrosis, CKs have been described as potential therapeutic targets. The development of a specific field of proteomics where CKs become the main subject of research aims and hypotheses is suggested.

Cross β-sheet conformation of keratin 8 is a specific feature of Mallory-Denk bodies compared with other hepatocyte inclusions

BACKGROUND & AIMS

Mallory-Denk bodies (MDBs) are cytoplasmic protein aggregates in hepatocytes in steatohepatitis and other liver diseases. We investigated the molecular structure of keratin 8 (K8) and 18 (K18), sequestosome 1/p62, and ubiquitin, which are the major constituents of MDBs, to investigate their formation and role in disease pathogenesis.

METHODS

Luminescent conjugated oligothiophenes (LCOs), h-HTAA, and p-FTAA are fluorescent amyloid ligands that specifically bind proteins with cross β-sheet conformation. We used LCOs to investigate conformational changes in MDBs in situ in human and murine livers as well as in transfection studies.

RESULTS

LCO analysis showed cross β-sheet conformation in human MDBs from patients with alcoholic and nonalcoholic steatohepatitis or hepatocellular carcinoma, but not in intracellular hyaline bodies, α₁-antitrypsin deficiency, or ground-glass inclusions. LCOs bound to MDBs induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine feeding of mice at all developmental stages. CHO-K1 cells transfected with various combinations of SQSTM1/p62, ubi, and Krt8/Krt18 showed that K8 was more likely to have cross β-sheet conformation than K18, whereas p62 never had cross β-sheet conformation. The different conformational properties of K8 and K18 were also shown by circular dichroism analysis.

CONCLUSIONS

K8 can undergo conformational changes from predominantly α-helical to cross β-sheet, which would allow it to form MDBs. These findings might account for the observation that krt8⁻/⁻ mice do not form MDBs, whereas its excess facilitates MDB formation. LCOs might be used in diagnosis of liver disorders; they can be applied to formalin-fixed, paraffin-embedded tissues to characterize protein aggregates in liver cells.

Peroxiredoxin 2: a potential biomarker for early diagnosis of hepatitis B virus related liver fibrosis identified by proteomic analysis of the plasma

Background

Liver fibrosis is a middle stage in the course of chronic Hepatitis B virus (HBV) infection, which will develop into cirrhosis and eventually hepatocellular carcinoma (HCC) if not treated at the early stage. Considering the limitations and patients' reluctance to undergo liver biopsy, a reliable, noninvasive diagnostic system to predict and assess treatment and prognosis of liver fibrosis is needed. The aim of this study was to identify biomarkers for early diagnosis of HBV related liver fibrosis.

Method

Plasma samples from 7 healthy volunteers and 27 HBV infected patients with different stages of fibrosis were selected for 2-DIGE proteomic screening. One-way ANOVA analysis was used to assess differences in protein expression among all groups. The alteration was further confirmed by western blotting. Plasma levels of 25 serological variables in 42 healthy volunteers and 68 patients were measured to establish a decision tree for the detection of various stages fibrosis.

Result

The up-regulated proteins along with fibrosis progress included fibrinogen, collagen, macroglobulin, hemopexin, antitrypsin, prealbumin and thioredoxin peroxidase. The down-regulated proteins included haptoglobin, serotransferrin, CD5 antigen like protein, clusterin, apolipoprotein and leucine-rich alpha-2-glycoprotein. For the discrimination of milder stage fibrosis, the area under curve for Prx II was the highest. Four variables (PT, Pre, HA and Prx II) were selected from the 25 variables to construct the decision tree. In a training group, the correct prediction percentage for normal control, milder fibrosis, significant fibrosis and early cirrhosis was 100%, 88.9%, 95.2% and 100%, respectively, with an overall correct percent of 95.9%.

Conclusion

This study showed that 2-D DIGE-based proteomic analysis of the plasma was helpful in screening for new plasma biomarkers for liver disease. The significant up-expression of Prx II could be used in the early diagnosis of HBV related liver fibrosis.

Serum fragmented cytokeratin 18 levels reflect the histologic activity score of nonalcoholic fatty liver disease more accurately than serum alanine aminotransferase levels

BACKGROUND AND GOALS

Reliable noninvasive biomarkers to assess the histologic activity of nonalcoholic fatty liver disease (NAFLD) have not been established. As the frequency of Mallory bodies is known to be closely associated with the disease severity, we hypothesized that serum levels of Mallory body-related proteins were correlated with NAFLD histologic activity and evaluated this possibility.

STUDY

Serum levels of total and fragmented cytokeratin (CK) 18, heat shock protein (Hsp) 70, Hsp90alpha, ubiquitin+1, and p38alpha at the time of liver biopsy were measured in 118 NAFLD patients and their association with histologic findings and NAFLD histologic activity score (NAS) was investigated.

RESULTS

Serum levels of both forms of CK18 and Hsp90alpha were markedly higher in patients having nonalcoholic steatohepatitis (NASH) compared with non-NASH ones. Both forms of CK18 significantly correlated with degree of steatosis, lobular inflammation, and ballooning, and showed stronger positive correlations with NAS than serum aspartate and alanine aminotransferase (AST and ALT). Multiple regression analysis further revealed that fragmented CK18 and AST were effective predictors of NAS, with the former being the more definitive of the two (P<0.001 vs. 0.005). In 20 NAFLD patients who received a follow-up biopsy, changes in fragmented CK18 levels, but not AST or ALT levels, closely paralleled those in NAS.

CONCLUSIONS

These results establish the usefulness of fragmented CK18 measurement for assessing and monitoring the histologic activity of NAFLD.

Clusterin: a forgotten player in Alzheimer's disease

Clusterin, also known as apolipoprotein J, is a versatile chaperone molecule which contains several amphipathic and coiled-coil alpha-helices, typical characteristics of small heat shock proteins. In addition, clusterin has three large intrinsic disordered regions, so-called molten globule domains, which can stabilize stressed protein structures. Twenty years ago, it was demonstrated that the expression of clusterin was clearly increased in Alzheimer's disease (AD). Later it was observed that clusterin can bind amyloid-beta peptides and prevent their fibrillization. Clusterin is also involved in the clearance of amyloid-beta peptides and fibrils by binding to megalin receptors and enhancing their endocytosis within glial cells. Clusterin is a complement inhibitor and can suppress complement activation observed in AD. Clusterin is also present in lipoprotein particles and regulates cholesterol and lipid metabolism of brain which is disturbed in AD. Clusterin is a stress-induced chaperone which is normally secreted but in conditions of cellular stress, it can be transported to cytoplasm where it can bind to Bax protein and inhibit neuronal apoptosis. Clusterin can also bind to Smad2/3 proteins and potentiate the neuroprotective TGFbeta signaling. An alternative splicing can produce a variant isoform of clusterin which can be translocated to nuclei where it induces apoptosis. The role of nuclear clusterin in AD needs to be elucidated. We will review here the extensive literature linking clusterin to AD and examine the recent progress in clusterin research with the respect to AD pathology. Though clusterin can be viewed as a multipotent guardian of brain, it is unable to prevent the progressive neuropathology in chronic AD.

Clusterin expression in cholestasis, hepatocellular carcinoma and liver fibrosis

AIMS

Clusterin shares functional properties with small heat shock proteins. In contrast to other heat shock proteins, it is present in the extracellular space. Its expression is altered in various diseases. The aim was to evaluate the presence and distribution of clusterin in liver diseases associated with cholestasis, in fibrosis and in hepatocellular carcinoma.

METHODS AND RESULTS

Tissue microarrays and biopsy materials were used to evaluate immunohistochemically the expression of clusterin in hepatocellular carcinoma, primary sclerosing cholangitis, primary biliary cirrhosis, mechanical cholestasis, drug-induced cholestasis, liver fibrosis and cirrhosis. The presence of clusterin in human bile was assessed by Western blotting. Furthermore, real-time reverse transcriptase-polymerase chain reaction was performed on liver tissue with mechanical cholestasis. Clusterin colocalized with elastic fibres, but not with collagen, hepatocytes or bile duct epithelia. It was detected in bile plugs in cholestasis and hepatocellular carcinomas with pseudoglandular features within the lumina. Clusterin was demonstrated in bile by Western blotting and its mRNA was expressed in normal and cholestatic livers.

CONCLUSIONS

Clusterin may protect bile duct epithelium against offensive biliary components or inhibit precipitation of biliary proteins. The association of clusterin with elastic fibres could reflect an extracellular chaperone function by either protecting elastic fibres or shielding abnormal elastic material.

Epidermolysis bullosa simplex: a paradigm for disorders of tissue fragility

Epidermolysis bullosa (EB) simplex is a rare genetic condition typified by superficial bullous lesions that result from frictional trauma to the skin. Most cases are due to dominantly acting mutations in either keratin 14 (K14) or K5, the type I and II intermediate filament (IF) proteins tasked with forming a pancytoplasmic network of 10-nm filaments in basal keratinocytes of the epidermis and in other stratified epithelia. Defects in K5/K14 filament network architecture cause basal keratinocytes to become fragile and account for their trauma-induced rupture. Here we review how laboratory investigations centered on keratin biology have deepened our understanding of the etiology and pathophysiology of EB simplex and revealed novel avenues for its therapy.

The HCV serum proteome: a search for fibrosis protein markers

Liver fibrosis/cirrhosis is a serious health issue in hepatitis C virus (HCV-) infected patients and is currently diagnosed by the invasive liver biopsy. The aim of this study was to find useful fibrosis markers in HCV-patients' sera of different fibrosis degrees (METAVIR F0-F4) based on proteomics. Serum proteome profiles were created by two-dimensional gel electrophoresis. Profiles were analysed between different degrees of fibrosis (F0-F4) and between early (F0F1) and late (F2F3F4) fibrosis by univariate analyses (P <or= 0.05). Differentially expressed proteins were subsequently identified by mass spectrometry. Mac-2-binding protein, alpha-2-macroglobulin and hemopexin were increased in F4 opposite F0/F1. A-1-antitrypsin, leucine-rich alpha-2-glycoprotein and fetuin-A were decreased in F4 opposite F0/F1. Late fibrosis was characterized by an increase in Mac-2-binding protein, alpha-2-macroglobulin and alpha-1B-glycoprotein expression and a decrease in haptoglobin expression. Mac-2-binding protein expression was confirmed by dot blot assay and enzyme-linked immunosorbent assay in a secondary population. In conclusion, serum proteome analysis enabled the detection/identification of existing and new candidate markers in line with fibrosis progression in HCV-patients.

"Toxic memory" via chaperone modification is a potential mechanism for rapid Mallory-Denk body reinduction

The cytoplasmic hepatocyte inclusions, Mallory-Denk bodies (MDBs), are characteristic of several liver disorders, including alcoholic and nonalcoholic steatohepatitis. In mice, MDBs can be induced by long-term feeding with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) for 3 to 4 months or rapidly reformed in DDC-induced then recovered mice by DDC refeeding or exposure to a wide range of toxins for only 5 to 7 days. The molecular basis for such a rapid reinduction of MDBs is unknown. We hypothesized that protein changes retained after DDC priming contribute to the rapid MDB reappearance and associate with MDB formation in general terms. Two-dimensional differential-in-gel-electrophoresis coupled with mass spectrometry were used to characterize protein changes in livers from the various treatment groups. The alterations were assessed by real-time reverse-transcription polymerase chain reaction and confirmed by immunoblotting. DDC treatment led to pronounced charged isoform changes in several chaperone families, including Hsp25, 60, 70, GRP58, GRP75, and GRP78, which lasted at least for 1 month after discontinuation of DDC feeding, whereas changes in other proteins normalized during recovery. DDC feeding also resulted in altered expression of Hsp72, GRP75, and Hsp25 and in functional impairment of Hsp60 and Hsp70 as determined using a protein complex formation and release assay. The priming toward rapid MDB reinduction lasts for at least 3 months after DDC discontinuation, but becomes weaker after prolonged recovery. MDB reinduction parallels the rapid increase in p62 and Hsp25 levels as well as keratin 8 cross-linking that is normally associated with MDB formation.

CONCLUSION

Persistent posttranslational modifications in chaperone proteins, coupled with protein cross-linking and altered chaperone expression and function likely contribute to the "toxic memory" of DDC-primed mice. We hypothesize that similar changes are important contributors to inclusion body formation in several diseases.

Dual-specificity phosphatases in the hypo-osmotic stress response of keratin-defective epithelial cell lines

Although mutations in intermediate filament proteins cause many human disorders, the detailed pathogenic mechanisms and the way these mutations affect cell metabolism are unclear. In this study, selected keratin mutations were analysed for their effect on the epidermal stress response. Expression profiles of two keratin-mutant cell lines from epidermolysis bullosa simplex patients (one severe and one mild) were compared to a control keratinocyte line before and after challenge with hypo-osmotic shock, a common physiological stress that transiently distorts cell shape. Fewer changes in gene expression were found in cells with the severely disruptive mutation (55 genes altered) than with the mild mutation (174 genes) or the wild type cells (261 genes) possibly due to stress response pre-activation in these cells. We identified 16 immediate-early genes contributing to a general cell response to hypo-osmotic shock, and 20 genes with an altered expression pattern in the mutant keratin lines only. A number of dual-specificity phosphatases (MKP-1, MKP-2, MKP-3, MKP-5 and hVH3) are differentially regulated in these cells, and their downstream targets p-ERK and p-p38 are significantly up-regulated in the mutant keratin lines. Our findings strengthen the case for the expression of mutant keratin proteins inducing physiological stress, and this intrinsic stress may affect the cell responses to secondary stresses in patients' skin.

How a cell deals with abnormal proteins. Pathogenetic mechanisms in protein aggregation diseases

Defective protein folding is responsible for many diseases. Although these diseases seem to be quite diverse at the first glance, there is evidence for common pathogenetic principles. The basis of the pathological changes is the cell's inability to prevent protein misfolding, to revert misfolded proteins to normal or to eliminate misfolded proteins by degradation. This could result in deposition of potentially cytotoxic protein aggregates (protein aggregation diseases). Chronic degenerative diseases of the central nervous system (e.g. Alzheimer's and Parkinson's disease), the amyloidoses, but also chronic liver diseases, for example alcoholic and nonalcoholic steatohepatitis, belong to this category of disorders. This review highlights general pathogenic principles of protein aggregation diseases based on immunohistochemical and biochemical studies as well as observations in a mouse model for protein aggregation in the context of alcoholic and nonalcoholic steatohepatitis. The cellular defense mechanisms involved in protein quality control as well as the pathogenesis of protein aggregation diseases will be discussed.

Clusterin associates with altered elastic fibers in human photoaged skin and prevents elastin from ultraviolet-induced aggregation in vitro

Clusterin is a secreted glycoprotein with stress-induced expression in various diseased and aged tissues. It shares basic features with small heat shock proteins because it may stabilize proteins in a folding-competent state. Besides its presence in all human body fluids, clusterin associates with altered extracellular matrix proteins, such as beta-amyloid in Alzheimer senile plaques in the brain. Because dermal connective tissue alterations occur because of aging and UV radiation, we explored the occurrence of clusterin in young, aged, and sun-exposed human skin. Immunohistochemical analysis showed that clusterin is constantly associated with altered elastic fibers in aged human skin. Elastotic material of sun-damaged skin (solar elastosis), in particular, revealed a strong staining for clusterin. Because of the striking co-localization of clusterin with abnormal elastic material, we investigated the interaction of clusterin with elastin in vitro. A chaperone assay was established in which elastin was denatured by UV irradiation in the absence or presence of clusterin. This assay demonstrated that clusterin exerted a chaperone-like activity and effectively inhibited UV-induced aggregation of elastin. The interaction of both proteins was further analyzed by electron microscopy, size exclusion chromatography, and mass spectrometry, in which clusterin was found in a stable complex with elastin after UV exposure.

From Mallory to Mallory–Denk bodies: What, how and why?

Frank B. Mallory described cytoplasmic hyaline inclusions in hepatocytes of patients with alcoholic hepatitis in 1911. These inclusions became known as Mallory bodies (MBs) and have since been associated with a variety of other liver diseases including non-alcoholic fatty liver disease. Helmut Denk and colleagues described the first animal model of MBs in 1975 that involves feeding mice griseofulvin. Since then, mouse models have been instrumental in helping understand the pathogenesis of MBs. Given the tremendous contributions made by Denk to the field, we propose renaming MBs as Mallory-Denk bodies (MDBs). The major constituents of MDBs include keratins 8 and 18 (K8/18), ubiquitin, and p62. The relevant proteins and cellular processes that contribute to MDB formation and accumulation include the type of chronic stress, the extent of stress-induced protein misfolding and consequent proteasome overload, a K8-greater-than-K18 ratio, transamidation of K8 and other proteins, presence of p62 and autophagy. Although it remains unclear whether MDBs serve a bystander, protective or injury promoting function, they do serve an important role as histological and potential progression markers in several liver diseases.

Immunoreactivities of p62, an ubiqutin-binding protein, in the spinal anterior horn cells of patients with amyotrophic lateral sclerosis

An ubiquitin-binding protein, p62, is one of the components of the ubiquitin-containing inclusions in several human neurodegenerative diseases. Amyotrophic lateral sclerosis (ALS) is characterized by the presence of skein-like inclusions, Lewy body-like inclusions, and basophilic inclusions in the remaining anterior horn cells, in which these inclusions contain ubiquitin, while the other characteristic inclusions of Bunina type are ubiquitin-negative. We examined the spinal cord from 28 ALS cases including two ALS with dementia and two ALS with basophilic inclusions, using antibody to p62. The results demonstrated that p62 localized in skein-like inclusions, Lewy body-like inclusions and basophilic inclusions. The number of p62-positive inclusions observed in the remaining anterior horn cells of each section was variable among the ALS cases. In contrast, Bunina bodies, that do not contain ubiquitin, were negative for p62. As far as we examined, the 11 non-ALS cases did not show any p62 immunoreactivities in the anterior horn cells. Our results suggested that p62 plays important roles in forming the inclusions and may be associated with the protection of the neurons from degenerative processes involving ubiquitin.

Predicting alternate structure attainment and amyloidogenesis: a nonlinear signal analysis approach

Chain hydrophobicity values have been used in prediction of alternate structure attainment by a polypeptide. Nonlinear signal analysis on the hydrophobicity values gives important clues about the propensities of particular stretches of a protein to form local or nonlocal contacts. These contacts determine the folding behavior of a polypeptide and helps in predicting the final structure that can be attained. A nonlinear signal analysis called the recurrent quantification analysis has been carried out using the hydrophobicity values on a wide range of proteins obtained from human, plant, and fungal sources. Here, we show that such an analysis gives us an easy handle in determining sequences within the proteins that may be important in beta-sheet formation leading to amyloidosis.