Intermediate filaments in disease

Dynamic changes in protein concentrations of keratins in crop milk and related gene expression in pigeon crops during different incubation and chick rearing stages

1. The objective of this study was to examine the keratin composition of crop milk, the variation of epithelial thickness and keratin (K) gene expression in samples from young pigeon during incubation and chick rearing.2. Crop milk was collected from 1-, 3- and 5-day-old squab crops for keratin content analysis. Results showed that K4 accounted for the highest proportion of all detected keratins.3. In total, 42 pairs of adult pigeons were allocated to seven groups according to different stages to collect crop samples. Gene expression studies showed that the K3 gene expression was maximised at rearing Day 15 (15) and R1 in males and females, respectively. K6a gene level was the greatest at R15 in females, whereas it peaked at incubation Day 4 (I4) in males. The K12, K13, K23 and K80 gene levels were inhibited at the peak period of crop milk formation in comparison with I4. In females, K cochleal expression peaked at I10, whereas it was the greatest at R25 in males. K4 and K14 gene expression was the highest at I10 in females, while K4 and K14 were minimised at I17 and R7 in males, respectively. Gene expressions of K5, K8, K19 and K20 in males and K19 in females were maximised at R1. The K5, K20 and K75 gene levels in females peaked at R7. K75 and K8 expressions in males and females reached a maximum value at R25 and I17, respectively.4. The epithelial thickness of male and female crops reached their greatest levels at R1 and had the highest correlation with K19.5. These results emphasised the importance of keratinisation in crop milk formation, and different keratins probably play various roles during this period. The K19 was probably a marker for pigeon crop epithelium development. The sex of the parent pigeon affected keratin gene expression profiles.

Temporal and regulatory dynamics of the inner ear transcriptome during development in mice

The inner ear controls hearing and balance, while the temporal molecular signatures and transcriptional regulatory dynamics underlying its development are still unclear. In this study, we investigated time-series transcriptome in the mouse inner ear from embryonic day 11.5 (E11.5) to postnatal day 7 (P7) using bulk RNA-Seq. A total of 10,822 differentially expressed genes were identified between pairwise stages. We identified nine significant temporal expression profiles using time-series expression analysis. The constantly down-regulated profiles throughout the development are related to DNA activity and neurosensory development, while the constantly upregulated profiles are related to collagen and extracellular matrix. Further co-expression network analysis revealed that several hub genes, such as Pnoc, Cd9, and Krt27, are related to the neurosensory development, cell adhesion, and keratinization. We uncovered three important transcription regulatory paths during mice inner ear development. Transcription factors related to Hippo/TGFβ signaling induced decreased expressions of genes related to the neurosensory and inner ear development, while a series of INF genes activated the expressions of genes in immunoregulation. In addition to deepening our understanding of the temporal and regulatory mechanisms of inner ear development, our transcriptomic data could fuel future multi-species comparative studies and elucidate the evolutionary trajectory of auditory development.

The expression pattern of keratin 24 in tissue-engineered dermo-epidermal human skin substitutes in an in vivo model

AIMS AND OBJECTIVES

The use of autologous tissue-engineered skin substitutes is a promising approach to cover large skin defects in patients. Preclinical investigation is pivotal to test and improve the quality of these bio-engineered substitutes. In the skin, the epidermis, formed mainly by keratinocytes, provides the first physical barrier protecting from the environment. Proper keratinocyte differentiation and, thus, formation of a stratified epidermis is essential for this function. Keratins, the main structural support of keratinocytes, play a vital role regarding differentiation of keratinocytes. Here, we examined the expression pattern of a recently described keratinocyte differentiation marker, namely Keratin 24, in our skin substitutes.

MATERIALS AND METHODS

Human epidermal keratinocytes, melanocytes, dermal fibroblasts, palmar fibroblasts or sweat gland cells were used to prepare skin substitutes. Fibroblast-containing collagen hydrogels were prepared, and keratinocytes or sweat gland cells and melanocytes were seeded onto the hydrogels. The generated tissue-engineered dermo-epidermal skin analogs were transplanted onto full-thickness skin wounds created on the back of immuno-incompetent rats. The skin substitutes were excised at different time points and histologically examined with regard to Keratin 24 expression.

RESULTS

We observed the expression of Keratin 24 in keratinocytes of the upper stratum spinosum of the epidermis. In particular, we observed an intensified expression of Keratin 24 13 weeks after transplantation compared to 4 weeks after transplantation. Importantly, we noticed a markedly higher presence of Keratin 24 in more spinous layers if we used palmar fibroblasts or sweat gland cells in our skin substitutes compared non-palmar fibroblasts or epidermal keratinocytes.

CONCLUSION

Our observations prove that the keratinocyte differentiation marker Keratin 24 is expressed in our dermo-epidermal skin substitutes in a normal pattern. This highlights that our bio-engineered skin analogs mature and reach homeostasis in an in vivo assay. These findings harbor favorable implications regarding future clinical application.

Keratins Are Altered in Intestinal Disease-Related Stress Responses

Keratin (K) intermediate filaments can be divided into type I/type II proteins, which form obligate heteropolymers. Epithelial cells express type I-type II keratin pairs, and K7, K8 (type II) and K18, K19 and K20 (type I) are the primary keratins found in the single-layered intestinal epithelium. Keratins are upregulated during stress in liver, pancreas, lung, kidney and skin, however, little is known about their dynamics in the intestinal stress response. Here, keratin mRNA, protein and phosphorylation levels were studied in response to murine colonic stresses modeling human conditions, and in colorectal cancer HT29 cells. Dextran sulphate sodium (DSS)-colitis was used as a model for intestinal inflammatory stress, which elicited a strong upregulation and widened crypt distribution of K7 and K20. K8 levels were slightly downregulated in acute DSS, while stress-responsive K8 serine-74 phosphorylation (K8 pS74) was increased. By eliminating colonic microflora using antibiotics, K8 pS74 in proliferating cells was significantly increased, together with an upregulation of K8 and K19. In the aging mouse colon, most colonic keratins were upregulated. In vitro, K8, K19 and K8 pS74 levels were increased in response to lipopolysaccharide (LPS)-induced inflammation in HT29 cells. In conclusion, intestinal keratins are differentially and dynamically upregulated and post-translationally modified during stress and recovery.

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.

Analysis of gene expression dynamics revealed delayed and abnormal epidermal repair process in aged compared to young skin

With aging, epidermal homeostasis and barrier function are disrupted. In a previous study, we analyzed the transcriptomic response of young skin epidermis after stratum corneum removal, and obtained a global kinetic view of the molecular processes involved in barrier function recovery. In the present study, the same analysis was performed in aged skin in order to better understand the defects which occur with aging. Thirty healthy male volunteers (67 ± 4 years old) were involved. Tape-strippings were carried out on the inner face of one forearm, the other unstripped forearm serving as control. At 2, 6, 18, 30 and 72 h after stripping, TEWL measurements were taken, and epidermis samples were collected. Total RNA was extracted and analyzed using DermArray^® cDNA microarrays. The results highlighted that barrier function recovery and overall kinetics of gene expression were delayed following stripping in aged skin. Indeed, the TEWL measurements showed that barrier recovery in the young group appeared to be dramatically significant during the overall kinetics, while there were no significant evolution in the aged group until 30 h. Moreover, gene expression analysis revealed that the number of modulated genes following tape stripping increased as a function of time and reached a peak at 6 h after tape stripping in young skin, while it was at 30 h in aged skin, showing that cellular activity linked to the repair process may be engaged earlier in young epidermis than in aged epidermis. A total of 370 genes were modulated in the young group. In the aged group, 382 genes were modulated, whose 184 were also modulated in the young group. Only eight genes that were modulated in both groups were significantly differently modulated. The characterization of these genes into 15 functional families helped to draw a scenario for the aging process affecting epidermal repair capacity.

Comparative proteomics analysis of differential proteins in respond to doxorubicin resistance in myelogenous leukemia cell lines

Background

Chemoresistance remains a significant challenge in chronic myelogenous leukemia (CML) management, which is one of the most critical prognostic factors. Elucidation the molecular mechanisms underlying the resistance to chemoresistance may lead to better clinical outcomes.

Results

In order to identify potential protein targets involved in the drug-resistant phenotype of leukemia, especially the chronic myelogenous leukemia (CML), we used a high-resolution “ultra-zoom” 2DE-based proteomics approach to characterize global protein expression patterns in doxorubicin-resistant myelogenous leukemia cells compared with parental control cells. Ultra-high resolution of 2DE was achieved by using a series of slightly overlapping narrow-range IPG strips during isoelectric focusing (IEF) separation. A total number of 44 proteins with altered abundances were detected and identified by MALDI-TOF or LC-MS/MS. Among these proteins, enolase, aldolase, HSP70 and sorcin were up-regulated in doxorubicin-resistant myelogenous leukemia cell line, whereas HSP27 was down-regulated. Some of the results have been validated by Western blotting. Both enolase and aldolase were first reported to be involved in chemoresistance, suggesting that process of glycolysis in doxorubicin-resistant myelogenous leukemia cells was accelerated to some extent to provide more energy to survive chemical stress. Possible roles of most of the identified proteins in development of chemoresistance in myelogenous leukemia cells were fully discussed. The results presented here could provide clues to further study for elucidating the mechanisms underlying drug resistance in leukemia.

Conclusions

As a whole, under the chemical stress, the doxorubicin-resistant myelogenous leukemia cells may employ various protective strategies to survive. These include: (i) pumping the cytotoxic drug out of the cells by P-glycoprotein, (ii) increased storage of fermentable fuel, (iii) sophisticated cellular protection by molecular chaperones, (iv) improved handling of intracellular calcium, (v) increased glucose utilization via increased rates of glycolysis. In the present study, proteomic analysis of leukemia cells and their drug resistant variants revealed multiple alterations in protein expression. Our results indicate that the development of drug resistance in doxorubicin-resistant myelogenous leukemia cells is a complex phenomenon undergoing several mechanisms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-014-0057-y) contains supplementary material, which is available to authorized users.

Unusual ultrastructures of the Branchiostoma IF protein C2 containing heptads in the tail

Branchiostoma intermediate filament (IF) protein C2 contains a long tail domain consisting of several degenerate repeats which display a heptad repeat pattern. This unique tail sequence is predicted to constitute a long coiled coil domain in C2, which is separated from the rod by a glycine-rich linker L3. The recombinant IF protein C2 shows, in electron microscopy (EM), parallel rodlike dimers of 66.7 nm decorated by a larger globule on one side and a smaller globule on the other side. In contrast, the length of the tailless C2 dimers, decorated by only one small globule, is about 26 nm shorter. These results indicate that both the rod domain and the newly predicted coiled coil segment 3 participate in the formation of a double-stranded coiled coil dimer. Moreover, the two to four C2 dimers are able to associate via their globular tail domain into multiarm oligomers, an ability not seen by the tailless C2 mutant or the other currently known protostomic and vertebrate IFs.

Changes in protein composition of epidermal mucus in turbot Scophthalmus maximus (L.) under high water temperature

To explore the skin mucous of juvenile turbot (Scophthalmus maximus) protein under thermo-treatment in different temperatures (20, 23, 25, and 27 °C), the corresponding proteome maps were constructed by two-dimensional gel electrophoresis (2-DE), from which the peptide mass map with MALDI-TOF-TOF was obtained, and a novel protein of polypeptide was identified by database retrieval. Results show that the proteome maps varied remarkably with temperature, indicating the increase or decrease in protein spot. Totally, 209 protein spots were matched in five maps in temperature using ImageMaster 2D Platinum 6.0. In addition, six unique protein spots were selected and identified with MALDI-TOF-TOF. By searching database for protein identification and function prediction, five proteins were confirmed, of which lectin and cytokeratin are highly potential as protein marker for further research. The information should be useful for better understanding the role of mucus as a component of innate immune system and for identifying genotypes that suit best to the aquiculture environment. These proteins could be used as potential biomarkers to environmental stressors in mucus for providing early warning when fish suffers in a dangerous situation.

Desmoplakin is important for proper cardiac cell-cell interactions

Normal cardiac function is maintained through dynamic interactions of cardiac cells with each other and with the extracellular matrix. These interactions are important for remodeling during cardiac growth and pathophysiological conditions. However, the precise mechanisms of these interactions remain unclear. In this study we examined the importance of desmoplakin (DSP) in cardiac cell-cell interactions. Cell-cell communication in the heart requires the formation and preservation of cell contacts by cell adhesion junctions called desmosome-like structures. A major protein component of this complex is DSP, which plays a role in linking the cytoskeletal network to the plasma membrane. Our laboratory previously generated a polyclonal antibody (1611) against the detergent soluble fraction of cardiac fibroblast plasma membrane. In attempting to define which proteins 1611 recognizes, we performed two-dimensional electrophoresis and identified DSP as one of the major proteins recognized by 1611. Immunoprecipitation studies demonstrated that 1611 was able to directly pulldown DSP. We also demonstrate that 1611 and anti-DSP antibodies co-localize in whole heart sections. Finally, using a three-dimensional in vitro cell-cell interaction assay, we demonstrate that 1611 can inhibit cell-cell interactions. These data indicate that DSP is an important protein for cell-cell interactions and affects a variety of cellular functions, including cytokine secretion.

Inroads into the structure and function of intermediate filament networks

Although intermediate filaments are one of three major cytoskeletal systems of vertebrate cells, they remain the least understood with respect to their structure and function. This is due in part to the fact that they are encoded by a large gene family which is developmentally regulated in a cell and tissue type specific fashion. This article is in honor of Ueli Aebi. It highlights the studies on IF that have been carried out by our laboratory for more than 40 years. Many of our advances in understanding IF are based on conversations with Ueli which have taken place during adventurous and sometimes dangerous hiking and biking trips throughout the world.

Keratin disorders: from gene to therapy

The term 'keratin' is generally accepted to refer to the epithelial keratins of soft and hard epithelial tissues such as: skin, cornea, hair and nail. Since their initial characterization, the total number of mammalian keratins has increased to 54, including 28 type I and 26 type II keratins. Inherited defects that weaken the keratin load-bearing cytoskeleton produce phenotypes characterized by fragility of specific subsets of epithelial tissues. The vast majority of mutations are either missense or small in-frame in-del mutations and disease severity often relates to the position of the mutation in relation to the rod domain. The most complex epithelial structure in humans, the hair follicle, contains trichocyte ('hard') keratin filaments and approximately half of the 54 functional human keratin genes are trichocyte keratins. So far, only four of these have been linked to human genetic disorders: monilethrix, hair-nail ectodermal dysplasia, pseudofolliculitis barbae and woolly hair, while the majority of the hair keratins remain unlinked to human phenotypes. Keratin disorders are a classical group of dominant-negative genetic disorders, representing a large healthcare burden, especially within dermatology. Recent advances in RNA interference therapeutics, particularly in the form of small-interfering RNAs, represent a potential therapy route for keratin disorders through selectively silencing the mutant allele. To date, mutant-specific siRNAs for epidermolysis bullosa simplex, pachyonychia congenita and Messmann epithelial corneal dystrophy-causing missense mutations have been developed and proven to have unprecedented specificity and potency. This could herald the dawn of a new era in translational medical research applied to genetics.

In vivo imaging of human and mouse skin with a handheld dual-axis confocal fluorescence microscope

Advancing molecular therapies for the treatment of skin diseases will require the development of new tools that can reveal spatiotemporal changes in the microanatomy of the skin and associate these changes with the presence of the therapeutic agent. For this purpose, we evaluated a handheld dual-axis confocal (DAC) microscope that is capable of in vivo fluorescence imaging of skin, using both mouse models and human skin. Individual keratinocytes in the epidermis were observed in three-dimensional image stacks after topical administration of near-infrared (NIR) dyes as contrast agents. This suggested that the DAC microscope may have utility in assessing the clinical effects of a small interfering RNA (siRNA)-based therapeutic (TD101) that targets the causative mutation in pachyonychia congenita (PC) patients. The data indicated that (1) formulated indocyanine green (ICG) readily penetrated hyperkeratotic PC skin and normal callused regions compared with nonaffected areas, and (2) TD101-treated PC skin revealed changes in tissue morphology, consistent with reversion to nonaffected skin compared with vehicle-treated skin. In addition, siRNA was conjugated to NIR dye and shown to penetrate through the stratum corneum barrier when topically applied to mouse skin. These results suggest that in vivo confocal microscopy may provide an informative clinical end point to evaluate the efficacy of experimental molecular therapeutics.

The identification and localization of two intermediate filament proteins in the tunic of Styela plicata (Tunicata, Styelidae)

The intermediate filament (IF) proteins Styela C and Styela D from the tunicate Styela (Urochordata) are co-expressed in all epidermal cells and they are thought to behave as type I and type II keratins. These two IF proteins, Styela C and Styela D, were identified in immunoblots of proteins isolated from the tunic of Styela plicata. The occurrence and distribution of these proteins within the tunic of this ascidian was examined by means of immunofluorescence and immunoperoxidase techniques, using anti-Styela C and anti-Styela D antibodies. In addition, immuno-electron microscopy of the tunic showed that the two proteins are located in the cuticle layer and in the tunic matrix. These results represent the first data about the presence of IF proteins in the tunic of adult ascidian S. plicata. The possible involvement of these IF proteins in reinforcing the integrity of the tunic, that represents the interface between the animal body and the external environment, is discussed.

Vimentin isoform expression in the human retina characterized with the monoclonal antibody 3CB2

The antigen recognized by the monoclonal antibody 3CB2 (3CB2-Ag and 3CB2 mAb) is expressed by radial glia and astrocytes in the developing and adult vertebrate central nervous system (CNS) of vertebrates as well as in neural stem cells. Here we identified the 3CB2-Ag as vimentin by proteomic analysis of human glial cell line U-87 extracts (derived from a malignant astrocytoma). Indeed, the 3CB2 mAb recognized three vimentin isoforms in glial cell lines. In the human retina, 3CB2-Ag was expressed in Müller cells, astrocytes, some blood vessels, and cells in the horizontal cell layer, as determined by immunoprecipitation and immunofluorescence. Three populations of astrocytes were distinguishable by double-labeling immunohistochemistry: vimentin+/GFAP+, vimentin-/GFAP+, and vimentin+/GFAP-. Hence, we conclude that 1) the 3CB2-Ag is vimentin; 2) vimentin isoforms are differentially expressed in normal and transformed astrocytes; 3) human retinal astrocytes display molecular heterogeneity; and 4) the 3CB2 mAb is a valuable tool to study vimentin expression and its function in the human retina.

Dual roles of intermediate filaments in apoptosis

New roles have emerged recently for intermediate filaments (IFs), namely in modulating cell adhesion and growth, and providing resistance to various forms of stress and to apoptosis. In this context, we first summarize findings on the IF association with the cell response to mechanical stress and growth stimulation, in light of growth-related signaling events that are relevant to death-receptor engagement. We then address the molecular mechanisms by which IFs can provide cell resistance to apoptosis initiated by death-receptor stimulation and to necrosis triggered by excessive oxidative stress. In the same way, we examine IF involvement, along with cytolinker participation, in sequential caspase-mediated protein cleavages that are part of the overall cell death execution, particularly those that generate new functional IF protein fragments and uncover neoantigen markers. Finally, we report on the usefulness of these markers as diagnostic tools for disease-related aspects of apoptosis in humans. Clearly, the data accumulated in recent years provide new and significant insights into the multiple functions of IFs, particularly their dual roles in cell response to apoptotic insults.

Hair follicle-specific keratins and their diseases

The human keratin family comprises 54 members, 28 type I and 26 type II. Out of the 28 type I keratins, 17 are epithelial and 11 are hair keratins. Similarly, the 26 type II members comprise 20 epithelial and 6 hair keratins. As, however, 9 out of the 37 epithelial keratins are specifically expressed in the hair follicle, the total number of hair follicle-specific keratins (26) almost equals that of those expressed in the various forms of epithelia (28). Up to now, more than half of the latter have been found to be involved in inherited diseases, with mutated type I and type II members being roughly equally causal. In contrast, out of the 26 hair follicle-specific keratins only 5 have, at present, been associated with inherited hair disorders, while one keratin merely acts as a risk factor. In addition, all hair follicle-specific keratins involved in pathologies are type II keratins. Here we provide a detailed description of the respective hair diseases which are either due to mutations in hair keratins (monilethrix, ectodermal dysplasia of hair and nail type) or hair follicle-specific epithelial keratins (two mouse models, RCO3 and Ca(Rin) as well as pseudofolliculitis barbae).

Interleukin-6 induces keratin expression in intestinal epithelial cells: potential role of keratin-8 in interleukin-6-induced barrier function alterations

Keratin 8 (K8) and keratin-18 (K18) are the major intermediate filament proteins in the intestinal epithelia. The regulation and function of keratin in the intestinal epithelia is largely unknown. In this study we addressed the role and regulation of K8 and K18 expression by interleukin 6 (IL-6). Caco2-BBE cell line and IL-6 null mice were used to study the effect of IL-6 on keratin expression. Keratin expression was studied by Northern blot, Western blot, and confocal microscopy. Paracellular permeability was assessed by apical-to-basal transport of a fluorescein isothiocyanate dextran probe (FD-4). K8 was silenced using the small interfering RNA approach. IL-6 significantly up-regulated mRNA and protein levels of K8 and K18. Confocal microscopy showed a reticular pattern of intracellular keratin localized to the subapical region after IL-6 treatment. IL-6 also induced serine phosphorylation of K8. IL-6 decreased paracellular flux of FD-4 compared with vehicle-treated monolayers. K8 silencing abolished the decrease in paracellular permeability induced by IL-6. Administration of dextran sodium sulfate (DSS) significantly increased intestinal permeability in IL-6-/- mice compared with wild type mice given DSS. Collectively, our data demonstrate that IL-6 regulates the colonic expression of K8 and K18, and K8/K18 mediates barrier protection by IL-6 under conditions where intestinal barrier is compromised. Thus, our data uncover a novel function of these abundant cytoskeletal proteins, which may have implications in intestinal disorders such as inflammatory bowel disease wherein barrier dysfunction underlies the inflammatory response.

Keratin 8 modulation of desmoplakin deposition at desmosomes in hepatocytes

Keratins, the intermediate filament proteins of epithelial cells, connect to desmosomes, the cell-cell adhesion structures at the surface membrane. The building elements of desmosomes include desmoglein and desmocollin, which provide the actual cell adhesive properties, and desmoplakins, which anchor the keratin intermediate filaments to desmosomes. In the work reported here, we address the role of keratin 8 in modulating desmoplakin deposition at surface membrane in mouse hepatocytes. The experimental approach is based on the use of keratin 8- and keratin 18-null mouse hepatocytes as cell models. In wild-type mouse hepatocytes, desmoplakin is aligned with desmoglein and keratin 8 at the surface membrane. In keratin 8-null hepatocytes, the intermediate filament loss leads to alterations in desmoplakin distribution at the surface membrane, but not of desmoglein. Intriguingly, a significant proportion of keratin 18-null hepatocytes express keratin 8 at the surface membrane, associated with a proper desmoplakin alignment with desmoglein at desmosomes. A Triton treatment of the monolayer reveals that most of the desmoplakin present in either wild-type, keratin 8- or keratin 18-null hepatocytes is insoluble. Deletion analysis of keratin 8 further suggests that the recovery of desmoplakin alignment requires the keratin 8 rod domain. In addition, similarly to other works revealing a key role of desmoplakin phosphorylation on its interaction with intermediate filaments, we find that the phosphorylation status of the keratin 8 head domain affects desmoplakin distribution at desmosomes. Together, the data indicate that a proper alignment/deposition of desmoplakin with keratins and desmoglein in hepatocytes requires keratin 8, through a reciprocal phosphoserine-dependent process.

The genetic basis of pachyonychia congenita

In 1994, the molecular basis of pachyonychia congenita (PC) was elucidated. Four keratin genes are associated with the major subtypes of PC: K6a or K16 defects cause PC-1; and mutations in K6b or K17 cause PC-2. Mutations in keratins, the epithelial-specific intermediate filament proteins, result in aberrant cytoskeletal networks which present clinically as a variety of epithelial fragility phenotypes. To date, mutations in 20 keratin genes are associated with human disorders. Here, we review the genetic basis of PC and report 30 new PC mutations. Of these, 25 mutations were found in PC-1 families and five mutations were identified in PC-2 kindreds. All mutations identified were heterozygous amino acid substitutions or small in-frame deletion mutations with the exception of an unusual mutation in a sporadic case of PC-1. The latter carried a 117 bp duplication resulting in a 39 amino acid insertion in the 2B domain of K6a. Also of note was mutation L388P in K17, which is the first genetic defect identified in the helix termination motif of this protein. Understanding the genetic basis of these disorders allows better counseling for patients and paves the way for therapy development.

Type II keratins precede type I keratins during early embryonic development

We and others have recently demonstrated that the keratin (K) gene family in mammals is even more complex than previously thought [Eur. J. Cell Biol. 83, 19-26]. To address the function of keratins during early development, precise information on their spatio-temporal expression is required. Here, we examined the expression of selected mouse keratins from pre-implantation to mid-gestational embryonic stages using RT-PCR and immunofluorescence. At E0.5, transcripts encoding K5, K6, K7, K8, K14, K15, K18, and K19 are apparently absent. We report on a post-transcriptional regulation of type I keratins, preventing filament formation in 8- to 16-cell stage embryos. In these embryos, mRNAs coding for K7, K8, K18, and K19 are present, but only K7 and K8 are translated into protein which is deposited in aggregates. Following the accumulation of K18 protein at E3.5, keratin filaments are formed. Delayed onset of type I keratin protein expression was additionally observed in later embryonic stages for K5 and K14. K5 protein expression starts in the forelimb surface ectoderm as early as E9.25, while the expression of its partner, K14, begins at E9.75. From E9.25 to E9.75, K5 forms atypical filaments with K18. Remarkably, in embryonic K5-/- mice, K14 formed normal filaments until E12.5 despite the absence of its partner K5, due to the presence of K8. Following periderm formation, K14-containing filaments disappeared and K14 became localized in aggregates in basal keratinocytes. Despite the absence of a keratin cytoskeleton, there was no cytolysis. We suggest that the formation of the first embryonic cytoskeleton from soluble keratins is regulated by unknown mechanisms. Whether the premature expression of type II keratins relates to their proposed role in TNF- and Fas-mediated signalling is presently unknown.

Cytokeratins and dermatology

Cytokeratins are fibrous intermediate-filament protein polymers present in almost all animal cells. Their function is related to epithelium structural maintenance, protection from mechanical trauma, and possibly communication between adjacent cells or cytoplasm components. Today there are 20 known cytokeratins, classified according to their molecular weight and pH as type I or acidic (cytokeratins 9-20) and type II or neutral-basic (cytokeratins 1-8). Cytokeratins are always expressed in specific pairs for each type of tissue, composed of one unit of type I and one unit of type II. Primary structural defects of cytokeratins are associated with various keratinization impairments. Two of the better characterized defects are bullous epidermolysis and epidermolytic hyperkeratosis. Anti-cytokeratin monoclonal antibodies are being used for diagnostic purposes to characterize the origin of poorly differentiated tumors and metastatic solid tumors.

Insights into genotype-phenotype correlation in pachyonychia congenita from the human intermediate filament mutation database

Keratins are the intermediate filament proteins specifically expressed by epithelial cells. The Human Genome Project has uncovered a total of 54 functional keratin genes that are differentially expressed in specific epithelial structures of the body, many of which involve the epidermis and its appendages. Pachyonychia congenita (PC) is a group of autosomal dominant genodermatoses affecting the nails, thick skin and other ectodermal structures, according to specific sub-type. The major clinical variants of the disorder (PC-1 and PC-2) are known to be caused by dominant-negative mutations in one of four differentiation-specific keratins: K6a, K6b, K16, and K17. A total of 20 human keratin genes are currently linked to single-gene disorders or are predisposing factors in complex traits. In addition, a further six intermediate filament genes have been linked to other non-epithelial genetic disorders. We have established a comprehensive mutation database that catalogs all published independent occurrences of intermediate filament mutations (http://www.interfil.org), with details of phenotypes, published papers, patient support groups and other information. Here, we review the genotype-phenotype trends emerging from the spectrum of mutations in these genes and apply these correlations to make predictions about PC phenotypes based on the site of mutation and keratin pair involved.

Imaging the microstructural abnormalities of meesmann corneal dystrophy by in vivo confocal microscopy

PURPOSE

To delineate the microstructural features of Meesmann corneal dystrophy using in vivo confocal microscopy.

METHOD

Three subjects with clinically diagnosed Meesmann corneal dystrophy were examined by slit-lamp biomicroscopy and slit-scanning in vivo confocal microscopy.

RESULTS

On slit-lamp biomicroscopy, all subjects demonstrated large bilateral multiple epithelial cystic lesions extending to the midperiphery. On in vivo confocal microscopy, these lesions appeared as hyporeflective areas in the basal epithelial layer. The majority were circular, oval or teardrop shaped and ranged between 48 mum and 145 mum in diameter. Large elongated intraepithelial clefts were also seen. Reflective spots were visible within most of the lesions and these may represent the fibrillogranular material (termed peculiar substance) and tonofilament bundles observed in electron microscopy studies. An additional finding was the fragmented appearance of the subbasal nerve plexus.

CONCLUSION

We present the first case series of Meesmann corneal dystrophy imaged by in vivo confocal microscopy and describe the associated microstructural features. Delineation of these features facilitates the use of the confocal microscope to aid diagnosis and management of corneal dystrophies.

Genetics of Corneal Disease for the Ocular Surface Clinician

Advances in the understanding of inherited corneal and external diseases may allow interventions that prevent the substantial vision impairment currently caused by these diseases. The observant clinician may first recognize inherited corneal and external diseases based on clinical examination and a careful family history. Researchers using positional cloning and candidate gene techniques have identified several disease-causing genes. Identification of the genes responsible for inherited corneal and external diseases will lead to more definitive diagnoses and represent the first step in development of effective therapies. Future endeavors are directed toward identifying additional inherited corneal and external diseases, the genes that cause them, and possible gene therapies to improve visual outcomes.

Requirement for ERK activation in acetone extract identified from Bupleurum scorzonerifolium induced A549 tumor cell apoptosis and keratin 8 phosphorylation

We previously demonstrated that the crude acetone extract of Bupleurum scorzonerifolium (AE-BS) 60 microg/ml has anti-proliferation activity and apoptosis effects to A549 human lung cancer cells. They can also cause tumor cell arrest in G2/M phase. To better understand its target protein in A549 cell, two-dimensional electrophoresis and liquid chromatography-tandem mass spectrometry were applied. The modification of keratin 8 was identified. By immunoblot, the expression of phosphorylated keratin 8 at Ser-73 was increased from 2.0 to 3.0-fold after AE-BS treatment 24 to 48 hr respectively as compared with untreated A549 control cells. Furthermore, the A549 cells were pretreated with 50 microM PD98059, a specific inhibitor of the upstream regulator of ERK1/2, or with the p38 kinase inhibitor 20 microM SB203580 or JNK inhibitor 20 microM SP600125 for 30 min, followed by 24 h of incubation with AE-BS, PD98059 can inhibit K8-Ser-73 hyperphosphorylation and prevented cell apoptosis which was induced by AE-BS significantly. By immunoblot, AE-BS also can induce ERK 1/2 phosphorylation. In conclusion, our data indicate that the AE-BS induced tumor apoptosis in A549 cells was related to ERK 1/2 activation. The molecular mechanism of hyperphosphorylation of K8 on Ser-73 was associated with ERK 1/2 activation rather than JNK and p38 kinase. The apoptosis induced by AE-BS may be related to K8 phosphorylation.

Absence of glial fibrillary acidic protein and vimentin prevents hypertrophy of astrocytic processes and improves post-traumatic regeneration

The regenerative capacity of the CNS is extremely limited. The reason for this is unclear, but glial cell involvement has been suspected, and oligodendrocytes have been implicated as inhibitors of neuroregeneration (Chen et al., 2000, GrandPre et al., 2000; Fournier et al., 2001). The role of astrocytes in this process was proposed but remains incompletely understood (Silver and Miller, 2004). Astrocyte activation (reactive gliosis) accompanies neurotrauma, stroke, neurodegenerative diseases, or tumors. Two prominent hallmarks of reactive gliosis are hypertrophy of astrocytic processes and upregulation of intermediate filaments. Using the entorhinal cortex lesion model in mice, we found that reactive astrocytes devoid of the intermediate filament proteins glial fibrillary acidic protein and vimentin (GFAP-/-Vim-/-), and consequently lacking intermediate filaments (Colucci-Guyon et al., 1994; Pekny et al., 1995; Eliasson et al., 1999), showed only a limited hypertrophy of cell processes. Instead, many processes were shorter and not straight, albeit the volume of neuropil reached by a single astrocyte was the same as in wild-type mice. This was accompanied by remarkable synaptic regeneration in the hippocampus. On a molecular level, GFAP-/-Vim-/- reactive astrocytes could not upregulate endothelin B receptors, suggesting that the upregulation is intermediate filament dependent. These findings show a novel role for intermediate filaments in astrocytes and implicate reactive astrocytes as potent inhibitors of neuroregeneration.

Keratins of the Human Hair Follicle

Substantial progress has been made regarding the elucidation of differentiation processes of the human hair follicle. This review first describes the genomic organization of the human hair keratin gene family and the complex expression characteristics of hair keratins in the hair-forming compartment. Sections describe the role and fate of hair keratins in the diseased hair follicle, particularly hereditary disorders and hair follicle-derived tumors. Also included is a report on the actual state of knowledge concerning the regulation of hair keratin expression. In the second part of this review, essentially the same principles are applied to outline more recent and, thus, occasionally fewer data on specialized epithelial keratins expressed in various tissue constituents of the external sheaths and the companion layer of the follicle. A closing outlook highlights issues that need to be explored further to deepen our insight into the biology and genetics of the hair follicle.

Astrocyte intermediate filaments in CNS pathologies and regeneration

Astroglial cells are the most abundant cells in the mammalian central nervous system (CNS), yet our knowledge about their function in health and disease has been limited. This review focuses on the recent work addressing the function of intermediate filaments in astroglial cells under severe mechanical or osmotic stress, in hypoxia, and in brain and spinal cord injury. Recent data show that when astrocyte intermediate filaments are genetically ablated in mice, reactive gliosis is attenuated and the course of several CNS pathologies is altered, while the signs of CNS regeneration become more prominent. GFAP is the principal astrocyte intermediate filament protein and dominant mutations in the GFAP gene have been shown to lead to Alexander disease, a fatal neurodegenerative condition in humans.

Keratins and skin disorders

The association of keratin mutations with genetic skin fragility disorders is now one of the best-established examples of cytoskeleton disorders. It has served as a paradigm for many other diseases and has been highly informative for the study of intermediate filaments and their associated components, in helping to understand the functions of this large family of structural proteins. The keratin diseases have shown unequivocally that, at least in the case of the epidermal keratins, a major function of intermediate filaments is to provide physical resilience for epithelial cells. This review article reflects on the variety of phenotypes arising from mutations in keratins and the reasons for this variation.

In vivo alteration of the keratin 17 gene in hair follicles by oligonucleotide-directed gene targeting

Using intradermal injection of a chimeric RNA-DNA oligonucleotide (RDO) or a single-stranded oligonucleotide (ssODN) into murine skin, we attempted to make a dominant mutation (R94p) in the conserve alpha-helical domain of keratin 17 (K17), the same mutation found in pachyononychia congenichia type 2 (PC-2) patients with phenotypes ranging from twisted hair and multiple pilosebaceous cysts. Both K17A-RDO and -ssODN contained a single base mismatch (CGC to CCC) to alter the normal K17 sequence to cause an amino acid substitution (R94P). The complexes consisting of oligonucleotides and cationic liposomes were injected to C57B1/6 murine skin at 2 and 5 day after birth. Histological examination of skin biopsies at postnatal day 8 from several mice showed consistent twisted hair shafts or broken hair follicles at the sebaceous gland level and occasional rupture of the hair bulb or epidermal cyst-like changes. In the injected area, the number of full anagen hair follicles decrease by 50%. Injection of the control oligonucleotide, identical to K17A-RDO but containing no mismatch to the normal sequence, did not result in any detectable abnormality. The frequency of gene alteration was lower than 3%, according to the restriction fragment length polymorphism (RFLP) analysis of the genomic DNA isolated by dissection of hair follicles from slides. Although intradermal injection of K17A-RDO or K17-ssODN caused a dominant mutation in K17 affecting hair growth and morphology, these phenotypic changes were transient either due to the compensation of K17 by other keratins or the replacement of the mutated cells by normal surrounding cells during hair growth.

Under stress, the absence of intermediate filaments from Müller cells in the retina has structural and functional consequences

In epithelial and muscle cells, intermediate filaments (IFs) are important for resistance to mechanical stress. The aim of this study was to elucidate whether IFs are also important for providing resistance to mechanical stress in the Müller cells of the retina and whether this has any pathophysiological consequences. We used mice deficient in IF proteins glial fibrillary acidic protein and/or vimentin (GFAP(-/-), Vim(-/-) and GFAP(-/-) Vim(-/-)), and stress on the retina was applied by excision of the eyes immediately post mortem (compared with in situ fixation) or by inducing a neovascular response to oxygen-induced retinopathy (OIR). The structure of unchallenged retinas was normal, but mechanical stress caused local separation of the inner limiting membrane (ILM) and adjacent tissue from the rest of the retina in GFAP(-/-) Vim(-/-) mice and, to a lesser extent, in Vim(-/-) mice. This detachment occurred within the endfeet of Müller cells, structures normally rich in IFs but IF-free in GFAP(-/-) Vim(-/-) mice. Hypoxia-induced neovascularization was comparable in all groups of mice with respect to the retinal surface area occupied by new vessels. However, the vessels traversed the ILM and penetrated the vitreous body less frequently than in wild-type retinas (31-55% in Vim(-/-), 66-79% in GFAP(-/-) Vim(-/-)). We conclude that IFs are important for maintaining the mechanical integrity of Müller-cell endfeet and the inner retinal layers under a mechanical challenge. Furthermore, the absence of IFs in Müller cells leads to an abnormal response of the vascular system to ischemia, specifically decreased ability of newly formed blood vessels to traverse the ILM.

A novel arginine substitution mutation in 1A domain and a novel 27 bp insertion mutation in 2B domain of keratin 12 gene associated with Meesmann's corneal dystrophy

AIM

To determine the disease causing gene defects in two patients with Meesmann's corneal dystrophy.

METHODS

Mutational analysis of domains 1A and 2B of the keratin 3 (K3) and keratin 12 (K12) genes from two patients with Meesmann's corneal dystrophy was performed by polymerase chain reaction amplification and direct sequencing.

RESULTS

Novel mutations of the K12 gene were identified in both patients. In one patient a heterozygous point mutation (429A-->C = Arg135Ser) was found in the 1A domain of the K12 gene. This mutation was confirmed by restriction digestion. In the second patient a heterozygous 27 bp duplication was found inserted in the 2B domain at nucleotide position 1222 (1222ins27) of the K12 gene. This mutation was confirmed by gel electrophoresis. The mutations were not present in unaffected controls.

CONCLUSION

Novel K12 mutations were linked to Meesmann's corneal dystrophy in two different patients. A missense mutation replacing a highly conserved arginine residue in the beginning of the helix initiation motif was found in one patient, and an insertion mutation, consisting of a duplication of 27 nucleotides, was found before the helix termination motif in the other.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49' and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Desmin aggregate formation by R120G alphaB-crystallin is caused by altered filament interactions and is dependent upon network status in cells

The R120G mutation in alphaB-crystallin causes desmin-related myopathy. There have been a number of mechanisms proposed to explain the disease process, from altered protein processing to loss of chaperone function. Here, we show that the mutation alters the in vitro binding characteristics of alphaB-crystallin for desmin filaments. The apparent dissociation constant of R120G alphaB-crystallin was decreased while the binding capacity was increased significantly and as a result, desmin filaments aggregated. These data suggest that the characteristic desmin aggregates seen as part of the disease histopathology can be caused by a direct, but altered interaction of R120G alphaB-crystallin with desmin filaments. Transfection studies show that desmin networks in different cell backgrounds are not equally affected. Desmin networks are most vulnerable when they are being made de novo and not when they are already established. Our data also clearly demonstrate the beneficial role of wild-type alphaB-crystallin in the formation of desmin filament networks. Collectively, our data suggest that R120G alphaB-crystallin directly promotes desmin filament aggregation, although this gain of a function can be repressed by some cell situations. Such circumstances in muscle could explain the late onset characteristic of the myopathies caused by mutations in alphaB-crystallin.

Mutation Report. Novel keratin 14 gene mutations in patients from Hungary with epidermolysis bullosa simplex

Mutations in genes keratin 5 (KRT5) and 14 (KRT14) encoding the basal type keratin intermediate filaments have been identified in epidermolysis bullosa simplex (EBS) families and are likely to cause skin fragility. Three novel keratin 14 mutations in cases from the Hungarian Epidermolysis Bullosa Centre are reported. In a 7-year-old boy with Dowling-Meara type EBS (DM-EBS), who had severe skin symptoms with extended herpetiform blisters, a novel amino acid substitution N123K in keratin 14 had been detected. A 26-year-old woman with mild DM-EBS with prominent palmoplantar hyperkeratosis and without active blister formation had a novel R125G mutation in keratin 14. In a 6-year-old girl, with Weber-Cockayne type EBS (WC-EBS) with palmoplantar blisters and moderate mental retardation, a novel V133L substitution was detected. Her pedigree showed autosomal dominant mode of inheritance; in the two other families, only the index patients were affected. The N123K and R125G mutations causing DM-EBS phenotypes are located within the helix initiation motif of the rod domain, whereas the very close V133L mutation underlying the WC-EBS phenotype is outside of this region. These novel amino acid substitutions provide further information for genotype-phenotype correlation in KRT14 mutations, and demonstrate the first molecular genetic data in EBS patients from Hungary.

Bfsp2 mutation found in mouse 129 strains causes the loss of CP49 and induces vimentin-dependent changes in the lens fibre cell cytoskeleton

Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.

Functional complexity of intermediate filament cytoskeletons: from structure to assembly to gene ablation

The cell biology of intermediate filament (IF) proteins and their filaments is complicated by the fact that the members of the gene family, which in humans amount to at least 65, are differentially expressed in very complex patterns during embryonic development. Thus, different tissues and cells express entirely different sets and amounts of IF proteins, the only exception being the nuclear B-type lamins, which are found in every cell. Moreover, in the course of evolution the individual members of this family have, within one species, diverged so much from each other with regard to sequence and thus molecular properties that it is hard to envision a unifying kind of function for them. The known epidermolytic diseases, caused by single point mutations in keratins, have been used as an argument for a role of IFs in mechanical "stress resistance," something one would not have easily ascribed to the beaded chain filaments, a special type of IF in the eye lens, or to nuclear lamins. Therefore, the power of plastic dish cell biology may be limited in revealing functional clues for these structural elements, and it may therefore be of interest to go to the extreme ends of the life sciences, i.e., from the molecular properties of individual molecules including their structure at the atomic level to targeted inactivation of their genes in living animals, mouse, and worm to define their role more precisely in metazoan cell physiology.

A usual frameshift and delayed termination codon mutation in keratin 5 causes a novel type of epidermolysis bullosa simplex with migratory circinate erythema

We report here two unrelated families in Japan and Korea having patients with a unique type of epidermolysis bullosa simplex and a novel mutation in the keratin gene KRT5, i.e., a frameshift and delayed stop codon inconsistent with any subtype described before. The patients showed migratory circinate erythema and multiple vesicles on the circular belt-like areas affected by erythema. Electron microscopy of skin biopsies showed a reduction in the number of keratin intermediate filaments in the basal cells without tonofilament clumping. We identified a novel heterozygous deletion mutation (1649delG of KRT5) in both cases. This deletion is predicted to produce a mutant keratin 5 protein with a frameshift of its terminal 41 amino acids and 35 amino acids longer than the wild-type keratin 5 protein due to a delayed termination codon. As the same abnormal elongated mutant KRT5 gene was found in the independent families, the predicted abnormal elongated keratin protein is likely to lead to an atypical clinical phenotype that has never been reported, possibly by interfering with the functional interaction between keratin and its associated proteins.