'Hard' and 'soft' principles defining the structure, function and regulation of keratin intermediate filaments

Phosphorylation and Reorganization of Keratin Networks: Implications for Carcinogenesis and Epithelial Mesenchymal Transition

Metastasis is one of hallmarks of cancer and a major cause of cancer death. Combatting metastasis is highly challenging. To overcome these difficulties, researchers have focused on physical properties of metastatic cancer cells. Metastatic cancer cells from patients are softer than benign cancer or normal cells. Changes of viscoelasticity of cancer cells are related to the keratin network. Unexpectedly, keratin network is dynamic and regulation of keratin network is important to the metastasis of cancer. Keratin is composed of heteropolymer of type I and II. Keratin connects from the plasma membrane to nucleus. Several proteins including kinases, and protein phosphatases bind to keratin intermediate filaments. Several endogenous compounds or toxic compounds induce phosphorylation and reorganization of keratin network in cancer cells, leading to increased migration. Continuous phosphorylation of keratin results in loss of keratin, which is one of the features of epithelial mesenchymal transition (EMT). Therefore, several proteins involved in phosphorylation and reorganization of keratin also have a role in EMT. It is likely that compounds controlling phosphorylation and reorganization of keratin are potential candidates for combating EMT and metastasis.

A role for disulfide bonding in keratin intermediate filament organization and dynamics in skin keratinocytes

Disulfide bonds involving cysteine 367 in K14 play a crucial role in the assembly, dynamics, and organization of K14-containing filaments in epidermal keratinocytes.

We recently reported that a trans-dimer, homotypic disulfide bond involving Cys367 in keratin 14 (K14) occurs in an atomic-resolution structure of the interacting K5/K14 2B domains and in keratinocyte cell lines. Here we show that a sizable fraction of the K14 and K5 protein pools participates in interkeratin disulfide bonding in primary cultures of mouse skin keratinocytes. By comparing the properties of wild-type K14 with a completely cysteine-free variant thereof, we found that K14-dependent disulfide bonding limited filament elongation during polymerization in vitro but was necessary for the genesis of a perinuclear-concentrated network of keratin filaments, normal keratin cycling, and the sessile behavior of the nucleus and whole cell in keratinocytes studied by live imaging. Many of these phenotypes were rescued when analyzing a K14 variant harboring a single Cys residue at position 367. These findings establish disulfide bonding as a novel and important mechanism regulating the assembly, intracellular organization, and dynamics of K14-containing intermediate filaments in skin keratinocytes.

Mutations Affecting Keratin 10 Surface-Exposed Residues Highlight the Structural Basis of Phenotypic Variation in Epidermolytic Ichthyosis

Epidermolytic ichthyosis (EI) due to KRT10 mutations is a rare, typically autosomal dominant, disorder characterized by generalized erythema and cutaneous blistering at birth followed by hyperkeratosis and less frequent blistering later in life. We identified two KRT10 mutations p.Q434del and p.R441P in subjects presenting with a mild EI phenotype. Both occur within the mutational "hot spot" of the keratin 10 (K10) 2B rod domain, adjacent to severe EI-associated mutations. p.Q434del and p.R441P formed collapsed K10 fibers rather than aggregates characteristic of severe EI KRT10 mutations such as p.R156C. Upon differentiation, keratinocytes from p.Q434del showed significantly lower apoptosis (P-value<0.01) compared with p.R156C as assessed by the TUNEL assay. Conversely, the mitotic index of the p.Q434del epidermis was significantly higher compared with that of p.R156C (P-value<0.01) as estimated by the Ki67 assay. Structural basis of EI phenotype variation was investigated by homology-based modeling of wild-type and mutant K1-K10 dimers. Both mild EI mutations were found to affect the surface-exposed residues of the K10 alpha helix coiled-coil and caused localized disorganization of the K1-K10 heterodimer. In contrast, adjacent severe EI mutations disrupt key intermolecular dimer interactions. Our findings provide structural insights into phenotypic variation in EI due to KRT10 mutations.

Inflammation decreases keratin level in ulcerative colitis; inadequate restoration associates with increased risk of colitis-associated cancer

Background

Keratins are intermediate filament (IF) proteins, which form part of the epithelial cytoskeleton and which have been implicated pathology of inflammatory bowel diseases (IBD).

Methods

In this study biopsies were obtained from IBD patients grouped by disease duration and subtype into eight categories based on cancer risk and inflammatory status: quiescent recent onset (<5 years) UC (ROUC); UC with primary sclerosing cholangitis; quiescent long-standing pancolitis (20–40 years) (LSPC); active colitis and non-inflamed proximal colonic mucosa; pancolitis with dysplasia-both dysplastic lesions (DT) and distal rectal mucosa (DR); control group without pathology. Alterations in IF protein composition across the groups were determined by quantitative proteomics. Key protein changes were validated by western immunoblotting and immunohistochemical analysis.

Result

Acute inflammation resulted in reduced K8, K18, K19 and VIM (all p<0.05) compared to controls and non inflamed mucosa; reduced levels of if– associated proteins were also seen in DT and DR. Increased levels of keratins in LSPC was noted relative to controls or ROUC (K8, K18, K19 and VIM, p<0.05). Multiple K8 forms were noted on immunoblotting, with K8 phosphorylation reduced in progressive disease along with an increase in VIM:K8 ratio. K8 levels and phosphorylation are reduced in acute inflammation but appear restored or elevated in subjects with clinical and endoscopic remission (LSPC) but not apparent in subjects with elevated risk of cancer.

Conclusions

These data suggest that keratin regulation in remission may influence subsequent cancer risk.

Keratin 8 absence down-regulates colonocyte HMGCS2 and modulates colonic ketogenesis and energy metabolism

Absence of colonic keratin 8 causes intestinal inflammation and decreased levels of the ketogenic enzyme HMGCS2. Upstream, the butyrate transporter MCT1 is decreased, leading to increased luminal butyrate. Ketogenic conditions fail to induce HMGCS2 in the keratin 8–knockout colon, suggesting a role for keratins in colonocyte energy homeostasis.

Simple-type epithelial keratins are intermediate filament proteins important for mechanical stability and stress protection. Keratin mutations predispose to human liver disorders, whereas their roles in intestinal diseases are unclear. Absence of keratin 8 (K8) in mice leads to colitis, decreased Na/Cl uptake, protein mistargeting, and longer crypts, suggesting that keratins contribute to intestinal homeostasis. We describe the rate-limiting enzyme of the ketogenic energy metabolism pathway, mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), as a major down-regulated protein in the K8-knockout (K8^−/−) colon. K8 absence leads to decreased quantity and activity of HMGCS2, and the down-regulation is not dependent on the inflammatory state, since HMGCS2 is not decreased in dextran sulfate sodium-induced colitis. Peroxisome proliferator–activated receptor α, a transcriptional activator of HMGCS2, is similarly down-regulated. Ketogenic conditions—starvation or ketogenic diet—increase K8^+/+ HMGCS2, whereas this response is blunted in the K8^−/− colon. Microbiota-produced short-chain fatty acids (SCFAs), substrates in the colonic ketone body pathway, are increased in stool, which correlates with decreased levels of their main transporter, monocarboxylate transporter 1 (MCT1). Microbial populations, including the main SCFA-butyrate producers in the colon, were not altered in the K8^−/−. In summary, the regulation of the SCFA-MCT1-HMGCS2 axis is disrupted in K8^−/− colonocytes, suggesting a role for keratins in colonocyte energy metabolism and homeostasis.

Absence of keratins 8 and 18 in rodent epithelial cell lines associates with keratin gene mutation and DNA methylation: Cell line selective effects on cell invasion

Epithelial-mesenchymal transition (EMT) in carcinoma is associated with dramatic up-regulation of vimentin and down-regulation of the simple-type keratins 8 and 18 (K8/K18), but the mechanisms of these changes are poorly understood. We demonstrate that two commonly-studied murine (CT26) and rat (IEC-6) intestinal cell lines have negligible K8/K18 but high vimentin protein expression. Proteasome inhibition led to a limited increase in K18 but not K8 stabilization, thereby indicating that K8/K18 absence is not due, in large part, to increased protein turnover. CT26 and IEC-6 cells had <10% of normal K8/K18 mRNA and exhibited decreased mRNA stability, with K8 mRNA levels being higher in IEC-6 versus CT26 and K18 being higher in CT26 versus IEC-6 cells. Keratin gene sequencing showed that KRT8 in CT26 cells had a 21-nucleotide deletion while K18 in IEC-6 cells had a 9-amino acid in-frame insertion. Furthermore, the KRT8 promoter in CT26 and the KRT18 promoter in IEC-6 are hypermethylated. Inhibition of DNA methylation using 5-azacytidine increased K8 or K18 in some but all the tested rodent epithelial cell lines. Restoring K8 and K18 by lentiviral transduction reduced CT26 but not IEC-6 cell matrigel invasion. K8/K18 re-introduction also decreased E-cadherin expression in IEC-6 but not CT26 cells, suggesting that the effect of keratin expression on epithelial to mesenchymal transition is cell-line dependent. Therefore, some commonly utilized rodent epithelial cell lines, unexpectedly, manifest barely detectable keratin expression but have high levels of vimentin. In the CT26 and IEC-6 intestinal cell lines, keratin expression correlates with keratin gene insertion or deletion and with promoter methylation, which likely suppress keratin transcription and mRNA or protein stability.

Cleavage of host cytokeratin-6 by lysine-specific gingipain induces gingival inflammation in periodontitis patients

BACKGROUND/PURPOSE

Lysine-specific gingipain (Kgp) is a virulence factor secreted from Porphyromonas gingivalis (P. gingivalis), a major etiological bacterium of periodontal disease. Keratin intermediate filaments maintain the structural integrity of gingival epithelial cells, but are targeted by Kgp to produce a novel cytokeratin 6 fragment (K6F). We investigated the release of K6F and its induction of cytokine secretion.

METHODS

K6F present in the gingival crevicular fluid of periodontal disease patients and in gingipain-treated rat gingival epithelial cell culture supernatants was measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometer-based rapid quantitative peptide analysis using BLOTCHIP. K6F in gingival tissues was immunostained, and cytokeratin 6 protein was analyzed by immunofluorescence staining and flow cytometry. Activation of MAPK in gingival epithelial cells was evaluated by immunoblotting. ELISA was used to measure K6F and the cytokines release induced by K6F. Human gingival fibroblast migration was assessed using a Matrigel invasion chamber assay.

RESULTS

We identified K6F, corresponding to the C-terminus region of human cytokeratin 6 (amino acids 359-378), in the gingival crevicular fluid of periodontal disease patients and in the supernatant from gingival epithelial cells cultured with Kgp. K6F antigen was distributed from the basal to the spinous epithelial layers in gingivae from periodontal disease patients. Cytokeratin 6 on gingival epithelial cells was degraded by Kgp, but not by Arg-gingipain, P. gingivalis lipopolysaccharide or Actinobacillus actinomycetemcomitans lipopolysaccharide. K6F, but not a scrambled K6F peptide, induced human gingival fibroblast migration and secretion of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein-1. These effects of K6F were mediated by activation of p38 MAPK and Jun N-terminal kinase, but not p42/44 MAPK or p-Akt.

CONCLUSION

Kgp degrades gingival epithelial cell cytokeratin 6 to K6F that, on release, induces invasion and cytokine secretion by human gingival fibroblasts. Thus, Kgp may contribute to the development of periodontal disease.

H3K9 histone methyltransferase, KMT1E/SETDB1, cooperates with the SMAD2/3 pathway to suppress lung cancer metastasis

Aberrant histone methylation is a frequent event during tumor development and progression. KMT1E (also known as SETDB1) is a histone H3K9 methyltransferase that contributes to epigenetic silencing of both oncogenes and tumor suppressor genes in cancer cells. In this report, we demonstrate that KMT1E acts as a metastasis suppressor that is strongly downregulated in highly metastatic lung cancer cells. Restoring KMT1E expression in this setting suppressed filopodia formation, migration, and invasive behavior. Conversely, loss of KMT1E in lung cancer cells with limited metastatic potential promoted migration in vitro and restored metastatic prowess in vivo. Mechanistic investigations indicated that KMT1E cooperates with the TGFβ-regulated complex SMAD2/3 to repress metastasis through ANXA2. Together, our findings defined an essential role for the KMT1E/SMAD2/3 repressor complex in TGFβ-mediated lung cancer metastasis.

Characterization of myeloid-specific peroxidase, keratin 8, and dual specificity phosphatase 1 as innate immune genes involved in the resistance of crucian carp (Carassius auratus gibelio) to Cyprinid herpesvirus 2 infection

Myeloid-specific peroxidase (MPO), keratin 8 (KRT-8), and dual specificity phosphatase 1 (DUSP-1) are believed to play essential roles in innate immunity. Through suppression subtractive hybridization (SSH) analysis, we previously identified MPO, KRT-8, and DUSP-1 as the three genes that were the most significantly upregulated in crucian carp (Carassius auratus gibelio) that survived Cyprinid herpesvirus 2 (CyHV-2) infection. Here, we have further characterized these three genes and their response to pathogen challenge. The open reading frames (ORF) of MPO, KRT-8, and DUSP-1 were cloned by RACE technique and sequenced. The full-length cDNAs of the three genes contained ORFs of 2289, 1575 and 1083 bp respectively. The polypeptides from each ORF were projected to contain 762 (MPO), 524 (KRT-8), and 360 (DUSP-1) amino acids. Phylogenetic analysis showed that the three genes were most closely related to zebrafish. We found that MPO, KRT-8, and DUSP-1 were expressed at low levels in all of the tissues examined in healthy crucian carp. Quantitative real-time RT-PCR analysis indicated that MPO, KRT-8, and DUSP-1 mRNA expression was significantly upregulated within 72 h of CyHV-2 infection compared to mock infected controls. Maximum expression of MPO was detected at 24 hpi (2.71-fold, P < 0.05). While, 12 hpi (3.80-fold, P < 0.01) and 6 hpi (8.70-fold, P < 0.01) were the highest expression time points for KRT-8 and DUSP-1, respectively. In contrast, after Aeromonas hydrophila challenge, the transcripts of these three genes remained unchanged or slightly down-regulated. For the fish survived from viral infection, expression levels of MPO and KRT-8 were 2.72 fold and 2.47 fold higher than those of fish died from acute infection, and similar level of DUSP-1 was observed in samples of survived fish. These data suggested MPO, KRT-8 and DUSP-1 might be involved in the antiviral, but not antibacterial innate immune response in crucian carp. These findings also support the use of MPO and KRT-8 as immunological markers for a response to viral infection in crucian carp.

Establishment and characterization of immortalized gingival epithelial and fibroblastic cell lines for the development of organotypic cultures

In vitro studies using 3D co-cultures of gingival cells can resemble their in vivo counterparts much better than 2D models that typically only utilize monolayer cultures with short-living primary cells. However, the use of 3D gingival models is still limited through lack of appropriate cell lines. We aimed to establish immortalized cell line models of primary human gingival epithelium keratinocytes (HGEK) and gingival fibroblasts (GFB). Immortalized cell lines (HGEK-16 and GFB-16) were induced by E6 and E7 oncoproteins of human papillomavirus. In addition, 3D multilayered organotypic cultures were formed by embedding GFB-16 cells within a collagen (Col) matrix and seeding of HGEK-16 cells on the upper surfaces. Cell growth was analyzed in both immortalized cell lines and their parental primary cells. The expression levels of cell type-specific markers, i.e. cytokeratin (CK) 10, CK13, CK16, CK18, CK19 for HGEK-16 and Col I and Col II for GFB-16, were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR). Expansion of the primary cultures was impeded at early passages, while the transformed immortalized cell lines could be expanded for more than 30 passages. In 3D cultures, immortalized HGEK formed a multilayer of epithelial cells. qRT-PCR showed that cell-specific marker expression in the 3D cultures was qualitatively and quantitatively closer to that in human gingival tissue than to monolayer cultures. These results indicate that immortalized gingival fibroblastic and epithelial cell lines can successfully form organotypic multilayered cultures and, therefore, may be useful tools for studying gingival tissue in vitro.

Keratin 76 is required for tight junction function and maintenance of the skin barrier

Keratins are cytoskeletal intermediate filament proteins that are increasingly being recognised for their diverse cellular functions. Here we report the consequences of germ line inactivation of Keratin 76 (Krt76) in mice. Homozygous disruption of this epidermally expressed gene causes neonatal skin flaking, hyperpigmentation, inflammation, impaired wound healing, and death prior to 12 weeks of age. We show that this phenotype is associated with functionally defective tight junctions that are characterised by mislocalization of the integral protein CLDN1. We further demonstrate that KRT76 interacts with CLDN1 and propose that this interaction is necessary to correctly position CLDN1 in tight junctions. The mislocalization of CLDN1 has been associated in various dermopathies, including the inflammatory disease, psoriasis. These observations establish a previously unknown connection between the intermediate filament cytoskeleton network and tight junctions and showcase Krt76 null mice as a possible model to study aberrant tight junction driven skin diseases.

Central role of Snail1 in the regulation of EMT and resistance in cancer: a target for therapeutic intervention

Snail1 is the founding member of the Snail superfamily of zinc-finger transcription factors, which also includes Snail2 (Slug) and Snail3 (Smuc). The superfamily is involved in cell differentiation and survival, two processes central in cancer research. Encoded by the SNAI1 gene located on human chromosome 20q13.2, Snail1 is composed of 264 amino acids and usually acts as a transcriptional repressor. Phosphorylation and nuclear localization of Snail1, governed by PI3K and Wnt signaling pathways crosstalk, are critical in Snail1’s regulation. Snail1 has a pivotal role in the regulation of epithelial-mesenchymal transition (EMT), the process by which epithelial cells acquire a migratory, mesenchymal phenotype, as a result of its repression of E-cadherin. Snail1-induced EMT involves the loss of E-cadherin and claudins with concomitant upregulation of vimentin and fibronectin, among other biomarkers. While essential to normal developmental processes such as gastrulation, EMT is associated with metastasis, the cancer stem cell phenotype, and the regulation of chemo and immune resistance in cancer. Snail1 expression is a common sign of poor prognosis in metastatic cancer, and tumors with elevated Snail1 expression are disproportionately difficult to eradicate by current therapeutic treatments. The significance of Snail1 as a prognostic indicator, its involvement in the regulation of EMT and metastasis, and its roles in both drug and immune resistance point out that Snail1 is an attractive target for tumor growth inhibition and a target for sensitization to cytotoxic drugs.

Immunolocalization of alpha-keratins and associated beta-proteins in lizard epidermis shows that acidic keratins mix with basic keratin-associated beta-proteins

The differentiation of the corneous layers of lizard epidermis has been analyzed by ultrastructural immunocytochemistry using specific antibodies against alpha-keratins and keratin associated beta-proteins (KAbetaPs, formerly indicated as beta-keratins). Both beta-cells and alpha-cells of the corneous layer derive from the same germinal layer. An acidic type I alpha-keratin is present in basal and suprabasal layers, early differentiating clear, oberhautchen, and beta-cells. Type I keratin apparently disappears in differentiated beta- and alpha-layers of the mature corneous layers. Conversely, a basic type II alpha-keratin rich in glycine is absent or very scarce in basal and suprabasal layers and this keratin likely does not pair with type I keratin to form intermediate filaments but is weakly detected in the pre-corneous and corneous alpha-layer. Single and double labeling experiments show that in differentiating beta-cells, basic KAbetaPs are added and replace type-I keratin to form the hard beta-layer. Epidermal alpha-keratins contain scarce cysteine (0.2-1.4 %) that instead represents 4-19 % of amino acids present in KAbetaPs. Possible chemical bonds formed between alpha-keratins and KAbetaPs may derive from electrostatic interactions in addition to cross-linking through disulphide bonds. Both the high content in glycine of keratins and KAbetaPs may also contribute to increase the hydrophobicy of the beta- and alpha-layers and the resistance of the corneous layer. The increase of gly-rich KAbetaPs amount and the bonds to the framework of alpha-keratins give rise to the inflexible beta-layer while the cys-rich KAbetaPs produce a pliable alpha-layer.

Healing effect of a two-herb recipe (NF3) on foot ulcers in Chinese patients with diabetes: a randomized double-blind placebo-controlled study

BACKGROUND

In the present study, we examined the effect of a two-herb traditional Chinese medicine (NF3), comprised of Astragali Radix and Radix Rehmanniae, on the healing of diabetic foot ulcer and the possible molecular mechanisms involved.

METHODS

This was a prospective randomized double-blind placebo-controlled study. Sixteen diabetic patients were randomized to receive either placebo or NF3 for 6 months. Ulcer healing and sensory changes were examined. Molecular studies included measurement of serum tumor necrosis factor (TNF)-α and RNA microarray investigation.

RESULTS

The daily rate of reduction in ulcer area was 3.55% in the NF3 group and 1.52% in the placebo group (P = 0.062). In the index limb, the number of negative tests for sensory neuropathy using monofilament was reduced from 27% to 7% in the NF3 group and from 37% to 35% in the placebo group (P < 0.001). In addition, NF3 significantly decreased serum TNF-α levels (P = 0.034). Microarray studies revealed concerted changes following NF3 treatment in the expression of genes implicated in fibroblast regeneration, angiogenesis, and anti-inflammation.

CONCLUSIONS

In this proof-of-concept study, 6-month treatment with NF3 was associated with improved wound healing and sensation accompanied by concerted changes in gene expression.

Advanced technologies for studying circulating tumor cells at the protein level

Metastasis is the main cause of cancer death. As the tumor progresses, cells from the primary tumor site are shed into the bloodstream as circulating tumor cells (CTCs). Eventually, these cells colonize other organs and form distant metastases. It is therefore imperative that we gain a better understanding of the biological characteristics of CTCs for development of novel treatment modalities to minimize metastasis-associated cancer deaths. In recent years, rapid developments in technologies for the study of CTCs have taken place. We now have a variety of tools for the isolation and examination of CTCs which were not available before. This review introduces some commonly used protein markers in CTC investigations and summarizes a few advanced technologies which have been successfully applied for studying CTC biology at the protein level.

Interaction of plectin with keratins 5 and 14: dependence on several plectin domains and keratin quaternary structure

Plectin, a cytolinker of the plakin family, anchors the intermediate filament (IF) network formed by keratins 5 and 14 (K5/K14) to hemidesmosomes, junctional adhesion complexes in basal keratinocytes. Genetic alterations of these proteins cause epidermolysis bullosa simplex (EBS) characterized by disturbed cytoarchitecture and cell fragility. The mechanisms through which mutations located after the documented plectin IF-binding site, composed of the plakin-repeat domain (PRD) B5 and the linker, as well as mutations in K5 or K14, lead to EBS remain unclear. We investigated the interaction of plectin C terminus, encompassing four domains, the PRD B5, the linker, the PRD C, and the C extremity, with K5/K14 using different approaches, including a rapid and sensitive fluorescent protein-binding assay, based on enhanced green fluorescent protein-tagged proteins (FluoBACE). Our results demonstrate that all four plectin C-terminal domains contribute to its association with K5/K14 and act synergistically to ensure efficient IF binding. The plectin C terminus predominantly interacted with the K5/K14 coil 1 domain and bound more extensively to K5/K14 filaments compared with monomeric keratins or IF assembly intermediates. These findings indicate a multimodular association of plectin with K5/K14 filaments and give insights into the molecular basis of EBS associated with pathogenic mutations in plectin, K5, or K14 genes.

The small heat shock protein Hsp27 affects assembly dynamics and structure of keratin intermediate filament networks

The mechanical properties of living cells are essential for many processes. They are defined by the cytoskeleton, a composite network of protein fibers. Thus, the precise control of its architecture is of paramount importance. Our knowledge about the molecular and physical mechanisms defining the network structure remains scarce, especially for the intermediate filament cytoskeleton. Here, we investigate the effect of small heat shock proteins on the keratin 8/18 intermediate filament cytoskeleton using a well-controlled model system of reconstituted keratin networks. We demonstrate that Hsp27 severely alters the structure of such networks by changing their assembly dynamics. Furthermore, the C-terminal tail domain of keratin 8 is shown to be essential for this effect. Combining results from fluorescence and electron microscopy with data from analytical ultracentrifugation reveals the crucial role of kinetic trapping in keratin network formation.

Autosomal recessive transmission of a rare KRT74 variant causes hair and nail ectodermal dysplasia: allelism with dominant woolly hair/hypotrichosis

Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T>C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.

Coiling and maturation of a high-performance fibre in hagfish slime gland thread cells

The defensive slime of hagfishes contains thousands of intermediate filament protein threads that are manufactured within specialized gland thread cells. The material properties of these threads rival those of spider dragline silks, which makes them an ideal model for biomimetic efforts to produce sustainable protein materials, yet how the thread is produced and organized within the cell is not well understood. Here we show how changes in nuclear morphology, size and position can explain the three-dimensional pattern of thread coiling in gland thread cells, and how the ultrastructure of the thread changes as very young thread cells develop into large cells with fully mature coiled threads. Our model provides an explanation for the complex process of thread assembly and organization that has fascinated and perplexed biologists for over a century, and provides valuable insights for the quest to manufacture high-performance biomimetic protein materials.

Attractive interactions among intermediate filaments determine network mechanics in vitro

Mechanical and structural properties of K8/K18 and vimentin intermediate filament (IF) networks have been investigated using bulk mechanical rheometry and optical microrheology including diffusing wave spectroscopy and multiple particle tracking. A high elastic modulus G₀ at low protein concentration c, a weak concentration dependency of G₀ (G₀∼c^0.5±0.1) and pronounced strain stiffening are found for these systems even without external crossbridgers. Strong attractive interactions among filaments are required to maintain these characteristic mechanical features, which have also been reported for various other IF networks. Filament assembly, the persistence length of the filaments and the network mesh size remain essentially unaffected when a nonionic surfactant is added, but strain stiffening is completely suppressed, G₀ drops by orders of magnitude and exhibits a scaling G₀∼c^1.9±0.2 in agreement with microrheological measurements and as expected for entangled networks of semi-flexible polymers. Tailless K8Δ/K18ΔT and various other tailless filament networks do not exhibit strain stiffening, but still show high G₀ values. Therefore, two binding sites are proposed to exist in IF networks. A weaker one mediated by hydrophobic amino acid clusters in the central rod prevents stretched filaments between adjacent cross-links from thermal equilibration and thus provides the high G₀ values. Another strong one facilitating strain stiffening is located in the tail domain with its high fraction of hydrophobic amino acid sequences. Strain stiffening is less pronounced for vimentin than for K8/K18 due to electrostatic repulsion forces partly compensating the strong attraction at filament contact points.

Cytokeratin localization in toe pads of the anuran amphibian Philautus annandalii (Boulenger, 1906)

We have examined cytokeratin distribution and their nature in toe pads of the Himalayan tree-frog Philautus annandalii. Toe pads are expanded tips of digits and show modifications of their ventral epidermis for adhesion. The toe pad epidermal cells, being organized into 3-4 rows, possess keratin bundles, especially in surface nanostructures that are involved in adhesion. Immunohistochemical localization using a pan-cytokeratin antibody revealed that cytokeratin immunoreactivity is the strongest in the mid- to basal cell rows of the epidermis, which parallels our previous ultrastructural observation of dense keratin bundles present in this part of the epidermis. The remainder of the epidermis (i.e., the superficial cell layer) showed little immunoreactivity. Immunoblot analysis revealed that toe-pads possessed keratins prominently in the molecular mass of 50 kDa. Possible presence of keratin 5 in toe pad epidermis has been correlated with its usual distribution pattern in mammalian epidermis.

Protective role of the mitochondrial Lon protease 1 in ochratoxin A-induced cytotoxicity in HEK293 cells

Ochratoxin A (OTA) is a common kind of mycotoxin and food contaminant, which has various toxicological effects, especially nephrotoxicity. Our previous work about OTA-induced renal cytotoxicity indicated that mitochondrial Lon Protease 1 (Lonp1) might play a protective role. Lonp1 is a multifunctional ATP-dependent protease which mainly participates in mitochondrial proteolysis and protein quality control. The study aimed at probing how Lonp1 functioned in OTA-induced renal cytotoxicity. By means of RNA interference, we down-regulated the expression of Lonp1 in HEK293 cells. Cell viability results revealed that cells with Lonp1 deficiency were more vulnerable to OTA. Then we identified differentially expressed proteins between Lonp1 knock-down cells and scrambled control both in the absence and presence of OTA, using iTRAQ-based quantitative proteomics approach. Thirty-four proteins were differentially expressed as a result of Lonp1 deficiency, while forty-four proteins were differentially expressed in response to both Lonp1 deficiency and OTA treatment. By function summary and pathway analysis, we presumed that Lonp1 realized its protective function in the resistance to OTA-induced renal cytotoxicity via 4 processes: defensing against OTA-induced oxidative stress in the mitochondria; regulating protein synthesis, modification and repair; maintaining the balance of carbohydrate metabolism; and assisting in mtDNA maintenance.

BIOLOGICAL SIGNIFICANCE

OTA is a kind of mycotoxin that seriously threatens human health and has various toxicological effects. However, the mechanisms of its toxicity have not been exactly elucidated yet. The method of combination of RNAi and iTRAQ-based quantitative proteomics paves the way to gain a better understanding of the toxicity mechanisms of OTA. The present study, for the first time, verified the protective role of Lonp1 in OTA-induced renal cytotoxicity and clarified the defensive mechanism. Proteomic changes in Lonp1 deficient cells induced by OTA added new knowledge to OTA cytotoxicity.

Relationship of CK8/18 expression pattern to breast cancer immunohistochemical subtyping in Egyptian patients

The immunohistochemical (IHC) subtyping of breast cancer can be a useful substitute for gene expression analysis. The aim of this study was to investigate the relationship of CK8/18 to the biology of breast carcinoma (BC) represented by its IHC subtypes. The IHC expression of CK8/18 was correlated with IHC subtypes of BC using ER, PR, HER2/neu, and Ki67 LI (with cutoff 14%). All cases showed CK 8/18 expression in tumour cells with varying degree of intensities; 49/70 cases (70%) showed diffuse cytoplasmic expression (loss of membranous pattern), while 21/70 cases (30%) showed membrano-cytoplasmic pattern. Adjacent non-neoplastic breast lobules showed membrano-cytoplasmic pattern in 58% of cases, which was significantly different from the pattern in invasive cancer (P = 0.002). A loss of membranous pattern in malignant tumours was significantly associated with higher tumour grade (P = 0.02), higher mitotic count (P = 0.03), and negative HER2/neu status (P = 0.04). CK 8/18 H score ranged between 1 and 290 with mean ± SD was 181 ± 70.54. Tumours with lower CK 8/18 H score were in the advanced stage group (P = 0.04). Low CK8/18 H score and loss of membranous pattern were significantly associated with triple negative (TN) subtype as compared with luminal subtype (P = 0.006 and P = 0.026, respectively). In addition, CK8/18 with lost membranous pattern was significantly associated with TN subtype compared with HER2/neu positive subtype (P = 0.001). However, there was no significant difference between luminal A and B subtypes regarding CK8/18 H score or pattern of expression. This study concluded that low CK8/18 H score and loss of membranous pattern of CK8/18 are associated with worse prognostic features and TN subtype.

A miR-SNP of the KRT81 gene is associated with the prognosis of non-Hodgkin's lymphoma

MicroRNA (miRNA), which plays an important role in tumorigenesis, can regulate post-transcriptional gene expression by binding to the 3' untranslated regions (3'-UTRs) of messenger RNAs and repressing its translation. Several single nucleotide polymorphisms (SNPs) are considered to have significant impacts on susceptibility of the role these genetic polymorphisms in development of carcinogenesis through that mechanism. But few of them focus their impact on non-Hodgkin's lymphoma (NHL). Therefore, we conducted this study to investigate the associations between the genetic variants and cancer risk or cancer outcome. MiRNA-related single nucleotide polymorphism (miR-SNP) sites rs3660 of KRT81, rs1044129 of RYR3, rs4901706 of f101, and rs1053667 of KIAA0423 were selected and analyzed in 210 patients in NHL to evaluate their association with cancer risk and prognosis. The results indicated that none of them is associated with the cancer risk in NHL. Otherwise KRT81 rs3660 GG type is associated with a shorter survival time (p=0.012), after being assessed by multivariate Cox analyses, its effect on prognosis was verified (p=0.003). It suggests that KRT81 rs3660 GG type is an independent prognostic marker in NHL.

Biodegradation of hard keratins by two bacillus strains

Background:

Extensive quantities of keratinic by-products are disposed annually by animal-processing industry, causing a mounting ecological problem due to extreme resilience of these materials to enzymatic breakdown. There is a growing trend to apply cheap and environment-friendly methods to recycle keratinic wastes. Soil bacteria of profound keratinolytic potential, especially spore-forming rods from the genus Bacillus, play a significant role in keratinase-mediated biodegradation of keratins, therefore could be effective in hastening their biodegradation. Keratin hydrolysis in microbial cultures is one of the most promising techniques not only to utilize this protein but also to obtain valuable by products.

Objectives:

The study was undertaken to investigate the biodegradation process of various keratinic materials by two Bacillus strains.

Materials and Methods:

Two keratinolytic strains, Bacillus cereus and B. polymyxa, were subject to cultures in the presence of several keratinic appendages, like chicken feathers, barbs and rachea of ostrich feathers, pig bristle, lamb wool, human hair and stratum corneum of epidermis, as main nutrient sources. Bacterial ability to decompose these waste materials was evaluated, at the background of keratinase and protease biosynthesis, in brief four-day cultures. Keratinolytic activity was measured on soluble keratin preparation and proteases were assayed on casein. Additionally, amounts of liberated proteins, amino acids and thiols were evaluated. Residual keratin weight was tested afterwards.

Results:

Both tested strains proved to be more adapted for fast biodegradation of feather β-keratins than hair-type α-keratins. B. cereus revealed its significant proteolytic potential, especially on whole chicken feathers (230 PU) and stratum corneum (180 PU), but also on separated barbs and rachea, which appeared to be moderate protease inducers. Keratinolytic activity of B. cereus was comparable on most substrates and maximum level obtained was 11 KU. B. polymyxa was found to be a better producer of keratinases, up to 32 KU on chicken feathers and 14 KU on both fractions of ostrich feathers. Its proteolytic activity was mostly revealed on stratum corneum and human hair. Stratum corneum was extensively degraded by both bacterial strains up to 99% - 87%, chicken feathers 47-56%, ostrich barbs and rachea, 28% and 35% at maximum, respectively. Keratin fibres of structures like human hair, lamb wool and pig bristle remained highly resilient to this short microbiological treatment, however certain extent of keratinase induction was also observed.

Conclusions:

The obtained results prove that keratinolytic potential of both tested bacterial strains could be applied mainly in biodegradation of feathers, however, B. cereus and B. polymyxa differed in terms of keratinase and protease production on each of the substrates. Biodegradation of highly resilient structures like hair or pig bristle requires further analysis of process conditions.

Mutation of caspase-digestion sites in keratin 18 interferes with filament reorganization, and predisposes to hepatocyte necrosis and loss of membrane integrity

Keratin 18 (K18 or KRT18) undergoes caspase-mediated cleavage during apoptosis, the significance of which is poorly understood. Here, we mutated the two caspase-cleavage sites (D238E and D397E) in K18 (K18-DE), followed by transgenic overexpression of the resulting mutant. We found that K18-DE mice develop extensive Fas-mediated liver damage compared to wild-type mice overexpressing K18 (K18-WT). Fas-stimulation of K18-WT mice or isolated hepatocytes caused K18 degradation. By contrast, K18-DE livers or hepatocytes maintained intact keratins following Fas-stimulation, but showed hypo-phosphorylation at a major stress-kinase-related keratin 8 (K8) phosphorylation site. Although K18-WT and K18-DE hepatocytes showed similar Fas-mediated caspase activation, K18-DE hepatocytes were more 'leaky' after a mild hypoosmotic challenge and were more susceptible to necrosis after Fas-stimulation or severe hypoosmotic stress. K8 hypophosphorylation was not due to the inhibition of kinase binding to the keratin but was due to mutation-induced inaccessibility to the kinase that phosphorylates K8. A stress-modulated keratin phospho-mutant expressed in hepatocytes phenocopied the hepatocyte susceptibility to necrosis but was found to undergo keratin filament reorganization during apoptosis. Therefore, the caspase cleavage of keratins might promote keratin filament reorganization during apoptosis. Interference with keratin caspase cleavage shunts hepatocytes towards necrosis and increases liver injury through the inhibition of keratin phosphorylation. These findings might extend to other intermediate filament proteins that undergo proteolysis during apoptosis.

In vitro assembly properties of human type I and II hair keratins

Multiple type I and II hair keratins are expressed in hair-forming cells but the role of each protein in hair fiber formation remains obscure. In this study, recombinant proteins of human type I hair keratins (K35, K36 and K38) and type II hair keratins (K81 and K85) were prepared using bacterial expression systems. The heterotypic subunit interactions between the type I and II hair keratins were characterized using two-dimensional gel electrophoresis and surface plasmon resonance (SPR). Gel electrophoresis showed that the heterotypic complex-forming urea concentrations differ depending on the combination of keratins. K35-K85 and K36-K81 formed relatively stable heterotypic complexes. SPR revealed that soluble K35 bound to immobilized K85 with a higher affinity than to immobilized K81. The in vitro intermediate filament (IF) assembly of the hair keratins was explored by negative-staining electron microscopy. While K35-K81, K36-K81 and K35-K36-K81 formed IFs, K35-K85 afforded tight bundles of short IFs and large paracrystalline assemblies, and K36-K85 formed IF tangles. K85 promotes lateral association rather than elongation of short IFs. The in vitro assembly properties of hair keratins depended on the combination of type I and II hair keratins. Our data suggest the functional significance of K35-K85 and K36-K81 with distinct assembly properties in the formation of macrofibrils.

Cytokeratin 18 is not required for morphogenesis of developing prostates but contributes to adult prostate regeneration

Cytokeratin 18 (CK18) is a key component of keratin-containing intermediate filaments and has long been used as a classic luminal cell marker in prostatic tissue. However, the in vivo function of CK18 in prostate is not known so far. We reported in this study, unexpectedly, that deletion of CK18 in a mouse model did not affect the morphological or the histological structures of adult prostate, as the CK18 knockout prostate displayed a normal glandular ductal structure, branching pattern, and composition of both luminal and basal cells. However, CK18 loss compromised the regenerative tubular branching in dorsolateral prostate after castration and androgen replacement. Therefore, in contrast to its importance as luminal cell marker, CK18 is dispensable for the prostate morphogenesis but contributes to adult prostate regeneration.

Krtap11-1, a hair keratin-associated protein, as a possible crucial element for the physical properties of hair shafts

BACKGROUND

The physical properties of the hair are predominantly determined by the assembly of keratin bundles. The keratin-associated proteins (Krtaps) are thought to be involved in keratin bundle assembly, however, the functional role of the individual member still remains largely unknown.

OBJECTIVE

The aim of this study is to clarify the role of a unique class of Krtaps, Krtap11-1, in the development and physical properties of the hair.

METHODS

The expression regulation of Krtap11-1 was analyzed and its binding partners in the hair cortex were determined. Also, the effects of the forcible expression of this protein on the hair follicle development were analyzed in culture.

RESULTS

The expression pattern of Krtap11-1 was concentrically asymmetric in the faulty hair that develops in Foxn1nu mice. In cultured keratinocytes, the expression of Krtap11-1 transgene product was strictly regulated by the keratinization process and proteasome-dependent protein elimination. While the association with keratin as well as the cohesive self-assembly of Krtap11-1 appeared to be stabilized by disulfide cross-links, the biotinylated Krtap11-1 probe enabled the adherence to certain type I keratins in the hair cortex, including K31, 33 and 34, in the absence of disulfide formation. When embryonic upper lip rudiments were forcibly introduced with Krtap11-1, the hair follicles formed irregularly arranged globular hair keratin-clumps surrounded by multilayered epithelial cells in culture.

CONCLUSION

Krtap11-1 may play an important role on keratin-bundle assembly in the hair cortex and this study provides insight into the physical properties of the hair shaft.

Keratins significantly contribute to cell stiffness and impact invasive behavior

Cell motility and cell shape adaptations are crucial during wound healing, inflammation, and malignant progression. These processes require the remodeling of the keratin cytoskeleton to facilitate cell-cell and cell-matrix adhesion. However, the role of keratins for biomechanical properties and invasion of epithelial cells is only partially understood. In this study, we address this issue in murine keratinocytes lacking all keratins on genome engineering. In contrast to predictions, keratin-free cells show about 60% higher cell deformability even for small deformations. This response is compared with the less pronounced softening effects for actin depolymerization induced via latrunculin A. To relate these findings with functional consequences, we use invasion and 3D growth assays. These experiments reveal higher invasiveness of keratin-free cells. Reexpression of a small amount of the keratin pair K5/K14 in keratin-free cells reverses the above phenotype for the invasion but does not with respect to cell deformability. Our data show a unique role of keratins as major players of cell stiffness, influencing invasion with implications for epidermal homeostasis and pathogenesis. This study supports the view that down-regulation of keratins observed during epithelial-mesenchymal transition directly contributes to the migratory and invasive behavior of tumor cells.

Keratin 8 modulates β-cell stress responses and normoglycaemia

Keratin intermediate filament (IF) proteins are epithelial cell cytoskeletal components that provide structural stability and protection from cell stress, among other cellular and tissue-specific functions. Numerous human diseases are associated with IF gene mutations, but the function of keratins in the endocrine pancreas and their potential significance for glycaemic control are unknown. The impact of keratins on β-cell organisation and systemic glucose control was assessed using keratin 8 (K8) wild-type (K8(+/+)) and K8 knockout (K8(-/-)) mice. Islet β-cell keratins were characterised under basal conditions, in streptozotocin (STZ)-induced diabetes and in non-obese diabetic (NOD) mice. STZ-induced diabetes incidence and islet damage was assessed in K8(+/+) and K8(-/-) mice. K8 and K18 were the predominant keratins in islet β-cells and K8(-/-) mice expressed only remnant K18 and K7. K8 deletion resulted in lower fasting glucose levels, increased glucose tolerance and insulin sensitivity, reduced glucose-stimulated insulin secretion and decreased pancreatic insulin content. GLUT2 localisation and insulin vesicle morphology were disrupted in K8(-/-) β-cells. The increased levels of cytoplasmic GLUT2 correlated with resistance to high-dose STZ-induced injury in K8(-/-) mice. However, K8 deletion conferred no long-term protection from STZ-induced diabetes and prolonged STZ-induced stress caused increased exocrine damage in K8(-/-) mice. β-cell keratin upregulation occurred 2 weeks after treatments with low-dose STZ in K8(+/+) mice and in diabetic NOD mice, suggesting a role for keratins, particularly in non-acute islet stress responses. These results demonstrate previously unrecognised functions for keratins in β-cell intracellular organisation, as well as for systemic blood glucose control under basal conditions and in diabetes-induced stress.

Biochemical and molecular characterization of a serine keratinase from Brevibacillus brevis US575 with promising keratin-biodegradation and hide-dehairing activities

Dehairing is one of the highly polluting operations in the leather industry. The conventional lime-sulfide process used for dehairing produces large amounts of sulfide, which poses serious toxicity and disposal problems. This operation also involves hair destruction, a process that leads to increased chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspended solid (TSS) loads in the effluent. With these concerns in mind, enzyme-assisted dehairing has often been proposed as an alternative method. The main enzyme preparations so far used involved keratinases. The present paper reports on the purification of an extracellular keratinase (KERUS) newly isolated from Brevibacillus brevis strain US575. Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) analysis revealed that the purified enzyme was a monomer with a molecular mass of 29121.11 Da. The sequence of the 27 N-terminal residues of KERUS showed high homology with those of Bacillus keratinases. Optimal activity was achieved at pH 8 and 40°C. Its thermoactivity and thermostability were upgraded in the presence of 5 mM Ca²⁺. The enzyme was completely inhibited by phenylmethanesulfonyl fluoride (PMSF) and diiodopropyl fluorophosphates (DFP), which suggests that it belongs to the serine protease family. KERUS displayed higher levels of hydrolysis, substrate specificity, and catalytic efficiency than NUE 12 MG and KOROPON® MK EG keratinases. The enzyme also exhibited powerful keratinolytic activity that made it able to accomplish the entire feather-biodegradation process on its own. The kerUS gene encoding KERUS was cloned, sequenced, and expressed in Escherichia coli. The biochemical properties of the extracellular purified recombinant enzyme (rKERUS) were similar to those of native KERUS. Overall, the findings provide strong support for the potential candidacy of this enzyme as an effective and eco-friendly alternative to the conventional chemicals used for the dehairing of rabbit, goat, sheep and bovine hides in the leather processing industry.

Keratin 8 is required for the maintenance of architectural structure in thymus epithelium

Keratins (Ks), the intermediate filament (IF) proteins of epithelia, are coordinately expressed as pairs in a cell-lineage and differentiation manner. Cortical thymic epithelial cells (cTECs) predominantly express the simple epithelium keratin 8/18 (K8/K18) pair, whereas medullary thymic epithelial cells (mTECs) express the stratified epithelium K5/K14 pair, with TECs exhibiting K5 and K8 at the cortico-medullary junction in mature thymus. In the work reported here, we used wild-type (WT) and K8-knockout (K8-null) mice to address the contribution of K8/K18 IFs in the maintenance of the thymic epithelial structure. K8-null thymus maintained the differential cell segregation at the cortex versus the medulla observed in WT thymus, and the distribution of immature thymocytes at the cortex. The K8/K18 loss did not affect thymocyte development. However, it massively perturbed the TEC morphology both at the cortex and the medulla, along with a prominent depletion of cTECs. Such tissue alterations coincided with an increase in apoptosis and a reduced expression of Albatross (Fas-binding factor-1), also known for its capacity to bind K8/18 IFs. In addition, the K8/K18 loss affected the distribution of K5/K14-positive mTECs, but not their differentiation status. Together, the results indicate that K8/K18 IFs constitute key promoters of the thymic epithelium integrity.

Downregulation of keratin 76 expression during oral carcinogenesis of human, hamster and mouse

Background

Keratins are structural marker proteins with tissue specific expression; however, recent reports indicate their involvement in cancer progression. Previous study from our lab revealed deregulation of many genes related to structural molecular integrity including KRT76. Here we evaluate the role of KRT76 downregulation in oral precancer and cancer development.

Methods

We evaluated KRT76 expression by qRT-PCR in normal and tumor tissues of the oral cavity. We also analyzed K76 expression by immunohistochemistry in normal, oral precancerous lesion (OPL), oral squamous cell carcinoma (OSCC) and in hamster model of oral carcinogenesis. Further, functional implication of KRT76 loss was confirmed using KRT76-knockout (KO) mice.

Results

We observed a strong association of reduced K76 expression with increased risk of OPL and OSCC development. The buccal epithelium of DMBA treated hamsters showed a similar trend. Oral cavity of KRT76-KO mice showed preneoplastic changes in the gingivobuccal epithelium while no pathological changes were observed in KRT76 negative tissues such as tongue.

Conclusion

The present study demonstrates loss of KRT76 in oral carcinogenesis. The KRT76-KO mice data underlines the potential of KRT76 being an early event although this loss is not sufficient to drive the development of oral cancers. Thus, future studies to investigate the contributing role of KRT76 in light of other tumor driving events are warranted.

Proteomic profile of keratins in cancer of the gingivo buccal complex: consolidating insights for clinical applications

Keratins play a major role in several cellular functions. Each tissue type expresses a specific set of keratins. The immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. Oral cancer is the fifteenth most common cancer worldwide. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. A few recent proteomic studies have reported the identification of keratins in head and neck cancer. Majority of the studies have used tissues from the head and neck region without specifying subsites. This study reports the analysis of enriched preparations of keratins from cancer of the gingivo buccal complex (GBC) using MS, 2DE, WB, silver staining of 2DE gels and IHC. Our study reveals the absence of K4 and K13 and presence of K14, K16, and K17, in cancers of the GBC and combination of these expression patterns in the cut margins. This report also shows that K13 is glycosylated. This well characterized profile of keratins may have potential to be used in clinics.

BIOLOGICAL SIGNIFICANCE

In recent years the immense potential of keratins as diagnostic and prognostic markers for different cancers is emerging. However, comprehensive information on the profile of keratins in the oral cavity is not available. Several independent reports have identified keratins using only antibody based techniques which have pitfalls due to the cross reactivity of the antibodies to this set of very homologous proteins. This study reports the analysis of enriched preparations of keratins from a subsite of the oral cavity, the gingivo buccal complex (GBC) using mass spectrometry, 2DE, western blotting, silver staining of 2DE gels and IHC. The proteomic analysis shows the absence of K4 and K13 and presence of K14, K16, and K17 in cancers of the GBC and combination of these expression patterns in the cut margins. This well characterized profile of keratins from the gingivo buccal complex provides defined markers which may have potential to be used in the clinics.

Sorafenib enhances proteasome inhibitor-mediated cytotoxicity via inhibition of unfolded protein response and keratin phosphorylation

Hepatocellular carcinoma (HCC) is highly resistant to conventional systemic therapies and prognosis for advanced HCC patients remains poor. Recent studies of the molecular mechanisms responsible for tumor initiation and progression have identified several potential molecular targets in HCC. Sorafenib is a multi-kinase inhibitor shown to have survival benefits in advanced HCC. It acts by inhibiting the serine/threonine kinases and the receptor type tyrosine kinases. In preclinical experiments sorafenib had anti-proliferative activity in hepatoma cells and it reduced tumor angiogenesis and increased apoptosis. Here, we demonstrate for the first time that the cytotoxic mechanisms of sorafenib include its inhibitory effects on protein ubiquitination, unfolded protein response (UPR) and keratin phosphorylation in response to endoplasmic reticulum (ER) stress. Moreover, we show that combined treatment with sorafenib and proteasome inhibitors (PIs) synergistically induced a marked increase in cell death in hepatoma- and hepatocyte-derived cells. These observations may open the way to potentially interesting treatment combinations that may augment the effect of sorafenib, possibly including drugs that promote ER stress. Because sorafenib blocked the cellular defense mechanisms against hepatotoxic injury not only in hepatoma cells but also in hepatocyte-derived cells, we must be careful to avoid severe liver injury.

Differentially expressed proteins in the skin mucus of Atlantic cod (Gadus morhua) upon natural infection with Vibrio anguillarum

Background

Vibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces (gut, skin and gills) of fish. Therefore it is necessary to investigate the role of different mucosal components in fish upon V. anguillarum infection. The present study has two parts; in the first part we analyzed the differential expression of skin mucus proteins from Atlantic cod naturally infected with V. anguillarum using two dimensional gel electrophoresis coupled with mass spectrometry. In the second part, a separate bath challenge experiment with V. anguillarum was conducted to assess the mRNA levels of the genes in skin tissue, corresponding to the selected proteins identified in the first part.

Results

Comparative proteome analysis of skin mucus of cod upon natural infection with V. anguillarum revealed key immune relevant proteins like calpain small subunit 1, glutathione-S-transferase omega 1, proteasome 26S subunit, 14-kDa apolipoprotein, beta 2-tubulin, cold inducible RNA binding protein, malate dehydrogenase 2 (mitochondrial) and type II keratin that exhibited significant differential expression. Additionally a number of protein spots which showed large variability amongst individual fish were also identified. Some of the proteins identified were mapped to the immunologically relevant JNK (c-Jun N-terminal kinases) signalling pathway that is connected to cellular events associated with pathogenesis. A bath challenge experiment with V. anguillarum showed differential expression of beta 2-tubulin, calpain small subunit 1, cold inducible RNA binding protein, flotillin1, and glutathione S-transferase omega 1 transcripts in the skin tissue of cod during early stages of infection.

Conclusions

Differentially expressed proteins identified in the cod skin mucus point towards their possible involvement in V. anguillarum pathogenesis. The role of some of these proteins in vibriosis in cod described in this paper can be considered unconventional with respect to their established functions in higher vertebrates. Based on the differential expression of these proteins they are possibly important components of fish defence against bacteria and innate immunity at large. The feasibility of utilizing these proteins/genes as markers of bacterial infection or stress in cod needs to be explored further.

The HER2 amplicon in breast cancer: Topoisomerase IIA and beyond

HER2 gene amplification is observed in about 15% of breast cancers. The subgroup of HER2-positive breast cancers appears to be heterogeneous and presents complex patterns of gene amplification at the locus on chromosome 17q12-21. The molecular variations within the chromosome 17q amplicon and their clinical implications remain largely unknown. Besides the well-known TOP2A gene encoding Topoisomerase IIA, other genes might also be amplified and could play functional roles in breast cancer development and progression. This review will focus on the current knowledge concerning the HER2 amplicon heterogeneity, its clinical and biological impact and the pitfalls associated with the evaluation of gene amplifications at this locus, with particular attention to TOP2A and the link between TOP2A and anthracycline benefit. In addition it will discuss the clinical and biological implications of the amplification of ten other genes at this locus (MED1, STARD3, GRB7, THRA, RARA, IGFPB4, CCR7, KRT20, KRT19 and GAST) in breast cancer.

Depolymerization of cytokeratin intermediate filaments facilitates intracellular infection of HeLa cells by Bartonella henselae

Bartonella henselae is capable of invading epithelial and endothelial cells by modulating the function of actin-dependent cytoskeleton proteins. Although understanding of the pathogenesis has been increased by the development of an in vitro infection model involving endothelial cells, little is known about the mechanism of interaction between B. henselae and epithelial cells. This study aims to identify the binding candidates of B. henselae in epithelial cells and explores their effect on B. henselae infection. Pull-down assays and mass spectrometry analysis confirmed that some of the binding proteins (keratin 14, keratin 6, and F-actin) are cytoskeleton associated. B. henselae infection significantly induces the expression of the cytokeratin genes. Chemical disruption of the keratin network by using ethylene glycol tetraacetic acid promotes the intracellular persistence of B. henselae in HeLa cells. However, cytochalasin B and phalloidin treatment inhibits B. henselae invasion. Immunofluorescent staining demonstrates that B. henselae infection induces an F-actin-dependent rearrangement of the cytoskeleton. However, we demonstrated via immunofluorescent staining and whole-mount cell electron microscopy that keratin intermediate filaments are depolymerized by B. henselae. The results indicate that B. henselae achieves an intracellular persistence in epithelial cells through the depolymerization of cytokeratin intermediate filaments that are protective against B. henselae invasion.

Keratin 71 mutations: from water dogs to woolly hair

The study of rare genetic disorders of the hair follicle has resulted in the identification of many causative genes, leading to the potential for the development of novel therapeutic approaches for both inherited and acquired hair disorders. In this issue, Fujimoto et al. identify a missense mutation within the keratin 71 (KRT71) gene as the cause for autosomal dominant woolly hair/hypotrichosis in a Japanese family. This represents the first human mutation in KRT71 to be linked to a hair disorder, establishing this gene as an important determinant of mammalian hair texture. Moreover, this finding provides new insight into the relationship between similar phenotypes resulting from mutations in distinct regulatory pathways and underscores the role of the inner root sheath in human hair growth.

Understanding the role of keratins 8 and 18 in neoplastic potential of breast cancer derived cell lines

Background

Breast cancer is a complex disease which cannot be defined merely by clinical parameters like lymph node involvement and histological grade, or by routinely used biomarkers like estrogen receptor (ER), progesterone receptor (PGR) and epidermal growth factor receptor 2 (HER2) in diagnosis and prognosis. Breast cancer originates from the epithelial cells. Keratins (K) are cytoplasmic intermediate filament proteins of epithelial cells and changes in the expression pattern of keratins have been seen during malignant transformation in the breast. Expression of the K8/18 pair is seen in the luminal cells of the breast epithelium, and its role in prognostication of breast cancer is not well understood.

Methodology/Principal Findings

In this study, we have modulated K8 expression to understand the role of the K8/18 pair in three different breast epithelium derived cell lines: non-transformed MCF10A, transformed but poorly invasive MDA MB 468 and highly invasive MDA MB 435. The up-regulation of K8 in the invasive MDA MB 435 cell line resulted in a significant decrease in proliferation, motility, in-vitro invasion, tumor volume and lung metastasis. The down-regulation of K8 in MDA MB 468 resulted in a significant increase in transformation potential, motility and invasion in-vitro, while MCF10A did not show any changes in cell transformation assays.

Conclusions/Significance

These results indicate the role of K8/18 in modulating invasion in breast cancer -its presence correlating with less invasive phenotype and absence correlating with highly invasive, dedifferentiated phenotype. These data may have important implications for prognostication of breast cancer.