Efficacy and safety of topical WBI-1001 in patients with mild to severe atopic dermatitis: results from a 12-week, multicentre, randomized, placebo-controlled double-blind trial

BACKGROUND

There is a need for the development of novel nonsteroidal topical drugs for the treatment of atopic dermatitis (AD).

OBJECTIVES

The primary objective was to evaluate the efficacy of WBI-1001 over 6 weeks of treatment of mild to severe AD.

METHODS

  Patients with AD affecting 3-20% of their body surface area and with an Investigator's Global Assessment (IGA) of 2-4 were randomized (1 : 1 : 1) to receive placebo, WBI-1001 0·5% or WBI-1001 1·0% in a cream formulation applied twice daily for 6 weeks. At the end of this phase, patients receiving WBI-1001 continued the same treatment for an additional 6 weeks. Patients receiving placebo entered into a 6-week double-blind phase with re-randomization (1 : 1) to WBI-1001 0·5% or 1·0% cream. The primary objective was to evaluate the efficacy of WBI-1001 over 6 weeks of treatment of mild to severe AD. The primary endpoint was the mean change from baseline in IGA at day 42 (week 6).

RESULTS

In total, 148 patients were randomized and analysed in the placebo (51), WBI-1001 0·5% (50) and WBI-1001 1·0% (47) groups. There was a decrease of 1·3 [43%; P < 0·001; 95% confidence interval (CI) -1·2 to -0·5] and 1·8 (56·3%; P < 0·001; 95% CI -1·6 to -0·9) in IGA at day 42 in the WBI-1001 0·5% and 1·0% groups, respectively, as compared with a decrease of 0·5 (14·7%) in the placebo group. Adverse drug reactions included a few cases of folliculitis and contact dermatitis.

CONCLUSIONS

WBI-1001 is an efficacious novel topical anti-inflammatory molecule for the treatment of AD.

Images of asteroid 21 Lutetia: a remnant planetesimal from the early Solar System

Images obtained by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) cameras onboard the Rosetta spacecraft reveal that asteroid 21 Lutetia has a complex geology and one of the highest asteroid densities measured so far, 3.4 ± 0.3 grams per cubic centimeter. The north pole region is covered by a thick layer of regolith, which is seen to flow in major landslides associated with albedo variation. Its geologically complex surface, ancient surface age, and high density suggest that Lutetia is most likely a primordial planetesimal. This contrasts with smaller asteroids visited by previous spacecraft, which are probably shattered bodies, fragments of larger parents, or reaccumulated rubble piles.

Interaction between two isoforms of the NF2 tumor suppressor protein, merlin, and between merlin and ezrin, suggests modulation of ERM proteins by merlin

The product of the neurofibromatosis type II (NF2) tumor suppressor gene, merlin, is closely related to the ezrin-radixin-moesin (ERM) family, a group of proteins believed to link the cytoskeleton to the plasma membrane. Mutation in the NF2 locus is associated with Schwann cell tumors (schwannomas). The two predominant merlin isoforms, I and II, differ only in the carboxy-terminal 16 residues and only isoform I is anti-proliferative. Merlin lacks an actin-binding domain conserved among ezrin, radixin and moesin. Because merlin, ezrin and moesin are co-expressed in Schwann cells, and all homodimerize, we have examined whether merlin and ezrin dimerize with one another. We found by immunoprecipitation and yeast two-hybrid assays that both merlin isoforms interact with ezrin. The interaction occurs in a head-to-tail orientation, with the amino-terminal half of one protein interacting with the carboxy-terminal half of the other. The two merlin isoforms behave differently in their interaction with ezrin. Isoform I binds only ezrin whose carboxy-terminus is exposed, whereas isoform II binds ezrin regardless of whether ezrin is in the open or closed conformation. The heterodimerization of merlin is a much stronger interaction than the interaction between either merlin isoform and ezrin, and can inhibit merlin-ezrin binding. This suggests that, in vivo, merlin dimerization could regulate merlin-ERM protein interaction, and could thus indirectly regulate other interactions involving ERM proteins.

Interaction between two isoforms of the NF2 tumor suppressor protein, merlin, and between merlin and ezrin, suggests modulation of ERM proteins by merlin

The product of the neurofibromatosis type II (NF2) tumor suppressor gene, merlin, is closely related to the ezrin-radixin-moesin (ERM) family, a group of proteins believed to link the cytoskeleton to the plasma membrane. Mutation in the NF2 locus is associated with Schwann cell tumors (schwannomas). The two predominant merlin isoforms, I and II, differ only in the carboxy-terminal 16 residues and only isoform I is anti-proliferative. Merlin lacks an actin-binding domain conserved among ezrin, radixin and moesin. Because merlin, ezrin and moesin are co-expressed in Schwann cells, and all homodimerize, we have examined whether merlin and ezrin dimerize with one another. We found by immunoprecipitation and yeast two-hybrid assays that both merlin isoforms interact with ezrin. The interaction occurs in a head-to-tail orientation, with the amino-terminal half of one protein interacting with the carboxy-terminal half of the other. The two merlin isoforms behave differently in their interaction with ezrin. Isoform I binds only ezrin whose carboxy-terminus is exposed, whereas isoform II binds ezrin regardless of whether ezrin is in the open or closed conformation. The heterodimerization of merlin is a much stronger interaction than the interaction between either merlin isoform and ezrin, and can inhibit merlin-ezrin binding. This suggests that, in vivo, merlin dimerization could regulate merlin-ERM protein interaction, and could thus indirectly regulate other interactions involving ERM proteins.

Properties of the nonhelical end domains of vimentin suggest a role in maintaining intermediate filament network structure

To investigate the functional role of the nonhelical domains of the intermediate filament (IF) protein vimentin, we carried out transient transfection of constructs encoding fusion proteins of these domains with enhanced green fluorescent protein (EGFP). Expression of these fusion proteins did not have any effect on the endogenous IF networks of transfected cells. However, the head domain-EGFP fusion protein localized almost exclusively to the nucleus. This localization could be disrupted in a reversible fashion by chilling cells. Furthermore, the head domain was capable of targeting to the nucleus a strictly cytoplasmic protein, pyruvate kinase. Thus, the vimentin head domain contains information that specifically directs proteins into the nucleus. In contrast, the nonhelical tail domain of vimentin, when expressed as a fusion protein with EGFP, was retained in the cytoplasm. Cytoplasmic retention of tail domain-containing fusion proteins appeared to be dependent on the integrity of the microtubule network. Our results are consistent with a proposal that the nonhelical end domains of vimentin are involved in maintaining an extended IF network by exerting oppositely directed forces along the filaments. The head domains exert a nuclear-directed force while the tail domains extend the IF network toward the cell periphery via a microtubule-dependent mechanism.

Molecular characteristics and interactions of the intermediate filament protein synemin. Interactions with alpha-actinin may anchor synemin-containing heterofilaments

Synemin is a cytoskeletal protein originally identified as an intermediate filament (IF)-associated protein because of its colocalization and copurification with the IF proteins desmin and vimentin in muscle cells. Our sequencing studies have shown that synemin is an unusually large member (1,604 residues, 182,187 Da) of the IF protein superfamily, with the majority of the molecule consisting of a long C-terminal tail domain. Molecular interaction studies demonstrate that purified synemin interacts with desmin, the major IF protein in mature muscle cells, and with alpha-actinin, an integral myofibrillar Z-line protein. Furthermore, expressed synemin rod and tail domains interact, respectively, with desmin and alpha-actinin. Analysis of endogenous protein expression in SW13 clonal lines reveals that synemin is coexpressed and colocalized with vimentin IFs in SW13.C1 vim+ cells but is absent in SW13.C2 vim- cells. Transfection studies indicate that synemin requires the presence of another IF protein, such as vimentin, in order to assemble into IFs. Taken in toto, our results suggest synemin functions as a component of heteropolymeric IFs and plays an important cytoskeletal cross-linking role by linking these IFs to other components of the cytoskeleton. Synemin in striated muscle cells may enable these heterofilaments to help link Z-lines of adjacent myofibrils and, thereby, play an important role in cytoskeletal integrity.

Galileo imaging of atmospheric emissions from Io

The Galileo spacecraft has detected diffuse optical emissions from Io in high-resolution images acquired while the satellite was eclipsed by Jupiter. Three distinct components make up Io's visible emissions. Bright blue glows of more than 300 kilorayleighs emanate from volcanic plumes, probably due to electron impact on molecular sulfur dioxide. Weaker red emissions, possibly due to atomic oxygen, are seen along the limbs, brighter on the pole closest to the plasma torus. A faint green glow appears concentrated on the night side of Io, possibly produced by atomic sodium. Io's disk-averaged emission diminishes with time after entering eclipse, whereas the localized blue glows brighten instead.

Shwachman syndrome: phenotypic manifestations of sibling sets and isolated cases in a large patient cohort are similar

OBJECTIVES

With the use of clinical data from a large international cohort, we evaluated and compared affected siblings and isolated cases.

STUDY DESIGN

Data from 116 families were collected, and patients conforming to our predetermined diagnostic criteria were analyzed. Phenotypic manifestations of affected siblings and singletons were compared with the use of t tests, Wilcoxon scores, and chi2 analysis.

RESULTS

Eighty-eight patients (33 female, 55 male; median age 5.20 years) fulfilled our predetermined diagnostic criteria for Shwachman syndrome; 63 patients were isolated cases, and 25 affected siblings were from 12 multiplex families. Steatorrhea was present in 86% (57 of 66), and 91% (78 of 86) displayed a low serum trypsinogen concentration. Patients older than 4 years more often had pancreatic sufficiency. Neutropenia occurred in 98%, anemia in 42%, and thrombocytopenia in 34%. Myelodysplasia or cytogenetic abnormalities were reported in 7 patients. Short stature with normal nutritional status was a prominent feature.

CONCLUSIONS

Clinical features among patients with Shwachman syndrome varied between patients and with age. Similarities in phenotype between isolated cases and affected sibling sets support the hypothesis that Shwachman syndrome is a single disease entity.

Association of calponin with desmin intermediate filaments

Our previous immunoelectron microscopy studies of chicken gizzard smooth muscle cells showed that in certain areas the distribution of anti-calponin exhibits a high degree of overlap with beta-actin, filamin, and in particular, desmin, suggesting that in situ a fraction of calponin may be associated with intermediate filaments of the cytoskeleton. In this work we further explore this idea by studying the interaction between calponin and desmin. We found that at physiological salt concentrations, calponin bound only weakly to synthetic desmin intermediate filaments. On the other hand, calponin bound strongly to nonfilamentous desmin tetramers and was incorporated into intermediate filaments when the two proteins were mixed in a buffer containing 6 M urea and dialyzed into a buffer containing 0.15 M NaCl. Anti-calponin was found to label a portion of intermediate filaments and dense bodies isolated from gizzard tissues. Our findings suggest that in chicken gizzard smooth muscle cells, calponin may be an integral component of desmin intermediate filaments in the vicinity of dense bodies. Since calponin is also known to bind actin, we hypothesize that one of the functions of calponin might be to bridge intermediate filaments with actin in dense bodies.

Two-hybrid analysis reveals fundamental differences in direct interactions between desmoplakin and cell type-specific intermediate filaments

Desmosomes are cell junctions that act as sites of strong intercellular adhesion and also serve to anchor the intermediate filament (IF) cytoskeleton to the plasma membrane of a variety of cell types. Previous studies demonstrated that the COOH terminus of the desmosomal plaque protein, desmoplakin (DP), is required for the association of DP with IF networks in cultured cells and that this domain interacts directly with type II epidermal keratin polypeptides in vitro. However, these studies left open the question of how desmosomes might anchor other IF types known to associate with these junctions. In this report we used yeast two-hybrid and in vitro dot blot assays to further examine the requirements for direct interactions between desmoplakin and various IF types. Our results confirm the ability of the DP COOH terminus (DPCT) to interact with at least two regions of the head domain of the type II epidermal keratin K1 and also demonstrate that DPCT can interact with the type III IF family members, vimentin and desmin, as well as simple epithelial keratins. Unlike the situation for type II epidermal keratins, the interaction between DPCT and simple epithelial keratins appears to depend on heterodimerization of the type I and II keratin polypeptides, since both are required to detect an interaction. Furthermore, although the interaction between DPCT and K1 requires the keratin head domain, deletion of this domain from the simple epithelial keratins does not compromise interaction with DPCT. The interaction between DPCT and type III or simple epithelial keratins also appeared to be less robust than that between DPCT and K1. In the case of K8/K18, however, the interaction as assessed by yeast two-hybrid assays increased 9-fold when a serine located in a protein kinase A consensus phosphorylation site 23 residues from the end of DP was altered to a glycine. Taken together, these data indicate that DP interacts directly with different IF types in specific ways.

Is fibrosing colonopathy an immune mediated disease?

Fibrosing colonopathy, a recently described complication of patients with cystic fibrosis, manifests clinically approximately 7-12 months after starting high dose pancreatic enzyme treatment. Although the pathogenesis of fibrosing colonopathy is unknown, it is highly correlated with pancreatic enzyme dose. In this study, immune mediated factors which may be associated with fibrosing colonopathy were explored. Sera from 14 patients with cystic fibrosis and meconium ileus were collected at diagnosis and then longitudinally for four to five years after enzyme treatment. Sera were analysed for total IgG and antiporcine trypsin IgG using an ELISA assay. Before enzyme treatment, serum antiporcine trypsin IgG concentrations were negligible, at 2.9 (SD 0.3) micrograms/ml. Thirteen patients (93%) developed a significant antibody response to porcine trypsin after starting enzyme treatment, reaching a peak concentration of 69.4 (20.1) micrograms/ml 7-12 months after the introduction of enzymes. Since peak IgG concentrations coincided with published reports of time of onset of symptoms of fibrosing colonopathy, local injury by protease or by immune mediated mechanisms may be responsible for the pathological changes in this iatrogenic disease.

Galileo's First Images of Jupiter and the Galilean Satellites

The first images of Jupiter, Io, Europa, and Ganymede from the Galileo spacecraft reveal new information about Jupiter's Great Red Spot (GRS) and the surfaces of the Galilean satellites. Features similar to clusters of thunderstorms were found in the GRS. Nearby wave structures suggest that the GRS may be a shallow atmospheric feature. Changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on Io. Patchy emissions were seen while Io was in eclipse by Jupiter. The outer margins of prominent linear markings (triple bands) on Europa are diffuse, suggesting that material has been vented from fractures. Numerous small circular craters indicate localized areas of relatively old surface. Pervasive brittle deformation of an ice layer appears to have formed grooves on Ganymede. Dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution.

Neurofilament triplet protein interactions: evidence for the preferred formation of NF-L-containing dimers and a putative function for the end domains

In this report we examine the molecular interactions that lead to formation of neurofilaments, the intermediate filaments in neurons. Using the yeast two-hybrid system, we found that the rod domains of all three NF triplet proteins interacted strongly with one another and with rod domains of the Type III IF proteins, vimentin and desmin. A slight preference toward NF-L-containing dimers was observed over ones not containing NF-L. Interactions among the full length NF triplet proteins exhibited more specificity. Full length NF-L had only a relatively weak interaction with another full length NF-L molecule, but reacted more robustly with full length NF-M or NF-H lacking only part of the head domain. No homologous or heterologous dimerization of NF-M and NF-H was detectable. These results support the hypothesis that neurofilaments are obligate heteropolymers and that heterodimeric subunits are the preferred building blocks. They further suggest that the mechanism that specifies heterodimeric interaction among the NF triplet proteins resides in the end domains.

Intermediate filament protein domain interactions as revealed by two-hybrid screens

All intermediate filament proteins possess three distinct domains: heads, rod and tail, and subdomains within the rod called helices 1A, 1B, 2A, and 2B. Subunit packing within a filament is a consequence of interactions among these domains. Several such interactions are known, but probably many more contribute to stabilizing filament structure. We examined a number of such potential interactions using the yeast two-hybrid system. Domains or subdomains of murine vimentin, a Type III intermediate filament protein, were fused with either the DNA-binding or trans-activating domain of GAL4, a transcription factor. Interaction between the vimentin domains/subdomains functionally reconstituted GAL4, thereby activating transcription of a GAL1-LacZ reporter gene. The oligomeric state at which the interactions took place, i.e. whether the domains/subdomains were dimeric or tetrameric as they interacted, was also determined. These studies revealed a number of interesting interactions, among which was a strong homotypic binding to helix 2B to form tetramers. They also demonstrated a lack of interaction among others expected to do so based on current structural models. From these results we deduced which of the candidates for interactions, suggested by current models, were true protein-protein interactions and which represented nearest-neighbors only. Thus, the A11 and A22 modes of molecular alignment identified by Steinert et al. (Steinert, P. M., Marekov, L. N., Fraser, R. D. B., and Parry, D. A. D. (1993) J. Mol. Biol. 230, 436-452) are probably true interactions, whereas the A12 and ACN modes may describe adjacent but non-interacting molecules.

Cell orientation response to cyclically deformed substrates: experimental validation of a cell model

We have developed a stochastic model that describes the orientation response of bipolar cells grown on a cyclically deformed substrate. The model was based on the following hypotheses regarding the behavior of individual cells: (a) the mechanical signal responsible for cell reorientation is the peak to peak surface strain along the cell's major axis (p-p axial strain); (b) each cell has an axial strain threshold and the threshold is normally distributed in the cell population; (c) the cell will avoid any direction where the p-p axial strain is above its threshold; and (d) the cell will randomly orient within the range of directions where the p-p axial strains are less than the cell's threshold. These hypotheses were tested by comparing model predictions with experimental observations from stretch experiments conducted with human melanocytes. The cells were grown on elastic rectangular culture dishes subjected to unidirectional cyclic (1 Hz) stretching with amplitudes of 0, 4, 8, and 12%. After 24 h of stimulation, the distribution of cell orientations was determined by measuring the orientations of 300-400 randomly selected cells. The 12% stretch experiment was used to determine the mean, 3.5%, and the standard deviation, 1.0% of the strain threshold for the cell population. The Kolmogorov-Smirnov test was then used to determine if the orientation distributions predicted by the model were different from experimentally measured distributions for the 4 and 8% stretches. No significant differences were found between the predicted and experimental distributions (4%: p = 0.70; and 8%: p = 0.71). These results support the hypothesis that cells randomly orient, but avoid directions where the p-p axial strains are above their thresholds.

Yeast two-hybrid system demonstrates that estrogen receptor dimerization is ligand-dependent in vivo

Previous studies using in vitro procedures have not clearly established whether the estrogen receptor (ER) acts as a monomer or dimer in the cell. We have used the yeast two-hybrid system as an in vivo approach to investigate the dimerization of the estrogen receptor in the absence and presence of estrogen and anti-estrogens. This system is independent of ER binding to the estrogen response element. Two vectors, expressing GAL4 DNA binding domain-human ER and GAL4 transactivation domain-human ER, were constructed. Control experiments showed that each fusion protein had a high affinity binding site for estradiol-17 beta and could transactivate an ERE-LacZ reporter gene in yeast similar to the wild type ER. The two fusion proteins, GAL4 DB-hER and GAL 4 TA-hER, were expressed in the yeast strain, PCY2, which carries a GAL1 promoter-lacZ reporter. ER dimerization was measured via reconstitution of GAL4 through interaction of the fusion proteins, which transactivates LacZ through the GAL1 promoter. When both ER fusion proteins were expressed, beta-galactosidase activity was estradiol-17 beta-inducible. Furthermore, we showed that both tamoxifen and ICI 182,780 also induced beta-galactosidase activity, albeit lower than that induced by estradiol-17 beta. These results strongly argue that ER dimerization is ligand-dependent and the dimer can be induced by estradiol-17 beta, tamoxifen, or ICI 182,780. We also treated the yeast containing the two fusion proteins with estradiol-17 beta and tamoxifen or ICI 182,780 simultaneously to determine the effects on ER dimerization. beta-Galactosidase activity was lower when the yeast was treated with a higher ratio of tamoxifen or ICI 182,780 to estrogen than estradiol-17 beta alone. Taken together, we conclude that ER dimerization is ligand (estradiol-17 beta, tamoxifen, or ICI 182, 780)-dependent, and we suggest that estradiol-17 beta-induced dimers are destabilized when estradiol-17 beta is used with tamoxifen or ICI 182,780 simultaneously.

HST far-ultraviolet imaging of Jupiter during the impacts of comet Shoemaker-Levy 9

Hubble Space Telescope far-ultraviolet images of Jupiter during the Shoemaker-Levy 9 impacts show the impact regions darkening over the 2 to 3 hours after the impact, becoming darker and more extended than at longer wavelengths, which indicates that ultraviolet-absorbing gases or aerosols are more extended, more absorbing, and at higher altitudes than the absorbers of visible light. Transient auroral emissions were observed near the magnetic conjugate point of the K impact site just after that impact. The global auroral activity was fainter than average during the impacts, and a variable auroral emission feature was observed inside the southern auroral oval preceding the impacts of fragments Q1 and Q2.

Charge interactions in the rod domain drive formation of tetramers during intermediate filament assembly

The purpose of this study was to test a long standing hypothesis regarding the forces that drive the assembly of intermediate filaments (IFs). The initial step of IF assembly is the formation of dimeric, alpha-helical coiled coils. On the outside of the coiled coils, charged amino acids are distributed periodically such that positively and negatively charged residues are arranged in alternating zones, 9.5/2 residues wide (Parry et al., 1977; McLachlan and Stewart, 1982). This structural feature has given rise to the hypothesis that, if neighboring coiled coils were staggered axially by an odd multiple of a charged zone, electrostatic interactions between them could provide the driving force for the assembly of higher order oligomers or filaments (Fraser et al., 1986; Parry and Steinert, 1992). Using the IF protein vimentin as a model system, we carried out deletion mutagenesis experiments to test this hypothesis. We generated mutant vimentin proteins lacking 14, 21, and 28 residues in Helix 1B of the rod domain, and analyzed their assembly properties by DNA transfection into IF null cells, in vitro assembly, and chemical cross-linking. Results from these experiments are consistent with, and support, the hypothesis that charge complementation plays a key role in the assembly and stabilization of intermediate filaments.

A conserved region in the tail domain of vimentin is involved in its assembly into intermediate filaments

Although the head and rod domains of intermediate filament (IF) proteins are known to play significant roles in filament assembly, the role of the tail domain in this function is unclear and the available information supports contradictory conclusions. We examined this question by comparing transfection of the same cDNA constructs, encoding vimentins with modified tail domains, into cell lines that do and do not contain endogenous IF proteins. By this approach, we were able to distinguish between the ability of a mutant IF protein to initiate assembly de novo, from that of incorporating into existing filament networks. Vimentins with modifications at or near a highly conserved tripeptide, arg-asp-gly (RDG), of the tail domain incorporated into existing IF networks in vimentin-expressing (vim+) cells, but were assembly-incompetent in cells that did not express IF proteins (vim-). The failure of the RDG mutant vimentins to assemble into filament arrays in vim- cells was reversible by re-introducing a wild-type vimentin cDNA, whereupon both wild-type and mutant vimentins coassembled into one and the same IF network. We conclude that the function of the tail domain of type III IF proteins, and possibly of keratins K8 and K18, in IF assembly is distinct from those of other domains; a region encompassing the RDG tripeptide appears to be important in the assembly process.

Nuclear proteins of the bovine esophageal epithelium. I. Monoclonal antibody W2 specifically reacts with condensed nuclei of differentiated superficial cells

Cells from three layers of the bovine esophageal epithelium, representing different stages of differentiation, were dissociated and separated by Percoll gradient centrifugation into fractions of small, medium and large sizes. A majority of the large cells possessed condensed nuclei, a characteristic feature of terminal differentiation of the superficial epithelium. The small cells resembled the proliferate cells of the basal layer. In vitro culture of the esophageal epithelial cells resulted in proliferation of the small cells, colony formation, and, in some cases, differentiation into cells with condensed nuclei. Nuclei, or nuclear subfractions derived from cells of the different layers, were used as immunogens for the generation of hybridomas secreting monoclonal antibodies that bound specifically to different regions of the esophageal tissue. One such antibody, designated W2, labeled the condensed nuclei from the superficial layer of stratified esophageal and corneal epithelia in situ, as well as the large cells from esophageal culture in vitro. Thus, the expression of the W2 antigen may be associated with the process of nuclear condensation during epithelial differentiation. Immunoisolation of the target antigen of W2 from extracts of large cells of the bovine esophagus yielded a band of M(r) approximately 33,000 on nonreducing polyacrylamide gels. This band dissociated into two polypeptides, of M(r) approximately 22,000 and approximately 11,000, upon treatment with dithiothreitol. Amino acid sequence analysis of the larger polypeptide showed extensive homology to a group of small calcium-binding proteins, including two helix-turn-helix motifs designated as the EF-hand, characteristic of the configuration of the metal-ion coordinating ligands of the calcium-binding site. Similarly, the sequence at the amino terminus of the polypeptide of approximately 11,000 indicated that it was the light chain counterpart of the same calcium-binding protein complex.

Antibody labeling of bovine neurofilaments: implications on the structure of neurofilament sidearms

We carried out immunolabeling studies of purified bovine spinal cord neurofilaments (NFs) and filaments reconstituted from several combinations of the NF triplet polypeptides, NF-H, NF-M, and NF-L. Six antibodies with known epitopes in either the rod domains or the tailpiece extensions of the NF triplet were used in these studies, and the immune complexes were visualized directly by the glycerol-spray, rotary shadowing technique, which permitted unambiguous identification of the NF sidearms. Antibodies directed against the tailpiece extensions of NF-H and NF-M labeled the sidearms of native NFs and reconstituted filaments containing those two polypeptides, but not the backbone of the filaments. Combining these two antibodies in the same labeling experiment resulted in more intense labeling than either of the antibodies alone, indicating that both NF-H and NF-M are capable of forming sidearms. The anti-NF-L tailpiece antibody recognized only a limited number of sites along native NFs, but labeled reconstituted NF-L homopolymers uniformly and heavily. This suggests that the NF-L tailpiece extension is relatively inaccessible in native filaments, but is accessible in reconstituted homopolymers. One possible explanation is that, in native NFs, the NF-H- and NF-M-containing sidearms curtailed antibody access to NF-L. A second possibility that is not mutually exclusive with the first is that, when both NF-L and another triplet polypeptide are present, they preferentially form heterodimers such that the NF-L tailpiece epitope becomes hidden. Taken collectively, and in combination with published structural information, our data are consistent with a subunit packing scheme in which an NF-L-containing dimer serves as the fundamental building block of most mammalian NFs, such that their sidearms consist of pairs of NF-H/NF-L, NF-M/NF-L, or NF-L/NF-L tailpiece extensions.

Site-specific antibodies block kinase A phosphorylation of desmin in vitro and inhibit incorporation of myoblasts into myotubes

Desmin and vimentin are two type III intermediate filament (IF) proteins, which can be phosphorylated in vitro by cAMP-dependent kinase (kinase A) and protein kinase C, and the in vitro phosphorylation of these proteins appears to favor the disassembled state. The sites of phosphorylation for desmin and vimentin have been mapped to their amino-terminal headpiece domains; in chicken smooth muscle desmin the most kinase A-reactive residues are ser-29 and ser-35. In this study we have examined the phosphorylation of desmin by the catalytic subunit of kinase A by using anti-peptide antibodies directed against residues 26-36. The antibodies, which we call anti-D26, recognize both native and denatured desmin and can discriminate between intact desmin and those derivatives that do not possess residues 26-36. Pre-incubation of desmin with affinity purified anti-D26 blocks total kinase A catalyzed incorporation of 32P into desmin by 75-80%. When antibody-treated IFs are subjected to phosphorylation, no filament break-down is observed after 3 hours. Thus anti-D26 antibodies block phosphorylation of IF in vitro. We have also explored the role of desmin phosphorylation in skeletal muscle cell differentiation using these antibodies. Quail embryo cells, induced to differentiate along the myogenic pathway by infection with avian SKV retroviruses expressing the ski oncogene, were microinjected with affinity purified anti-D26 at the mononucleated, myoblast stage. By 24 h post-injection, the vast majority of uninjected cells had fused into multinucleated myotubes, but all microinjected cells were arrested in the process of incorporating into myotubes and remained mononucleated. This observation suggests that kinase A phosphorylation-induced dynamic behavior of the desmin/vimentin IF cytoskeleton may be one of the many cytoskeletal restructuring events that must take place during myoblast fusion.

Desmin-binding specificities of two desmin CNBr fragments that correspond to the headpiece domain and Helix 1B

D88 and D109, two cyanogen bromide fragments of desmin which essentially correspond to the amino terminal headpiece domain and Helix 1B, respectively, bind to intact desmin with different topological specificities. D88, the headpiece domain fragment, binds only to the headpiece of intact desmin. In contrast, D109, which encompasses Helix 1B and most of the linker L10 binds to desmin even when its headpiece is removed. Additionally, these fragments only bind desmin if they are present during filament assembly; they do not bind pre-assembled desmin IF or tetramers. These observations suggest that, while alpha-helical coiled-coil interaction between rod domains provides the major driving force behind IF protein dimer formation, homophilic binding of head domains of these proteins may provide an additional stabilizing force and/or specify axial registration in certain IF proteins.

Properties of the desmin tail domain: studies using synthetic peptides and antipeptide antibodies

Intermediate filament (IF) proteins have a common structural motif consisting of an alpha-helical rod domain flanked by non-alpha-helical amino-terminal head and carboxy-terminal tail domains. Coiled-coil interaction between neighboring rod domains is though to generate the backbone of the 10-nm filament. There must also be other interactions between subunits to bring them into alignment and to effect elongation of the filament, but these are poorly understood. To examine the involvement of the tail domain in filament structure and stabilization, we have studied the interaction between a synthetic peptide corresponding to residues 442-450 of avian desmin, and authentic desmin protein. The potential importance of this region lies in its hydrophilic nature and its high degree of homology among the Type III IF proteins and cytokeratins 8 and 18. The peptide, D442-450, binds to a 27-residue region between lys-436 and leu-463, the carboxy terminus. The presence of the peptide during assembly causes the filaments to appear much more loosely packed than normal desmin IF. We have also generated polyclonal antibodies against this peptide and attempted to localize this portion of the tailpiece along desmin IFs by immunological procedures. By immunoblotting, we found that anti-D442-450 antibodies recognize desmin and only those proteolytic fragments that contain the tailpiece. In contrast, the antibodies do not label any structure in adult gizzard smooth muscle and skeletal muscle myofibrils in immunofluorescence experiments during which conventional antidesmin antibodies do. At the ultrastructural level, anti-D442-450 antibodies label free desmin tetramers but not desmin IFs. These results show that, as part of an assembled IF, the epitope of anti-D442-450 is inaccessible to the antibodies, and suggest that either the tailpiece of an IF protein may not be entirely peripheral to the filament backbone, or the interaction between end domains during assembly masks this particular region of the IF molecule.

Fluorescent measurement of desmin intermediate filament assembly

Intermediate filaments (IF) are cytoskeletal elements that are believed to play a major role in the specification and maintenance of cell form. Although previously thought to be stable and static because of their relative insolubility in physiological solvents, IF have recently been shown to have dynamic properties not unlike those of other cytoskeletal elements. The methodology for measuring this dynamic behavior, however, has been mostly borrowed from studies of other filament proteins and are poorly suited to IF because of their unusual physicochemical properties. In this report we introduce a fluorescence assay for quantifying in vitro IF assembly. Desmin subunits labeled with iodoacetamidofluorescein (IAF) to approximately 0.4 mol/mol retain the ability to polymerize into filaments indistinguishable from unlabeled IF in the electron microscope. By spectrophotometry, however, up to 90% of the starting fluorescence is quenched upon maximal IF assembly from IAF-desmin subunits. This quench is proportional to the total concentration of desmin subunits and is a sensitive measure of the assembly process. The critical concentration of assembly, measured at 170 mM NaCl, 1 mM MgCl2, 10 mM Tris-HCl, pH 7.0, is 0.2 microM. This indicates that a significant level of unpolymerized desmin exists in steady-state equilibrium with polymerized filaments under these conditions and suggests that IF subunit-filament equilibria may play a role in cytoskeletal dynamics.

Assembly properties of two CNBr fragments of avian desmin that correspond to the headpiece domain and helix 1B

To study how different domains of the muscle-specific intermediate filament protein, desmin, contribute to its polymerization, two of its CNBr fragments were examined as to their oligomeric structure under assembly conditions. One of these, D88, covers residues 1-88 and represents almost the entire headpiece; the other, D109, covers residues 145-254, and includes the entire Helix 1B and part of linker L12 of the intact molecule. Chemical cross-linking followed by SDS-PAGE, and analytical gel filtration, revealed that in 10 mM Tris-HCl, pH 8.5, conditions that favor tetramerization of intact desmin D88 formed only dimers. D109, on the other hand, formed primarily a dimeric species but low levels of trimeric and tetrameric species were also detectable. These data are consistent with the proposal that, during assembly of intact protein molecules into IF, the headpiece and Helix 1 contribute to dimerization of two polypeptides into a parallel, in-register coiled-coil. However, additional interactions, including headpiece-to-rod binding and hydrophobic interaction along the entire rod domain, are required to stabilize the tetramers and full-size IF.

Modulation of desmin intermediate filament assembly by a monoclonal antibody

We have used a monoclonal antibody against desmin to examine the assembly of intermediate filaments (IF) from their building blocks, the tetrameric protofilaments. The antibody, designated D76, does not cross react with any other IF proteins (Danto, S.I., and D.A. Fischman. 1984. J. Cell Biol. 98:2179-2191). It binds to a region amino-terminal to cys-324 of avian desmin that is resistant to chymotrypsin and trypsin digestion, and in the electron microscope appears to bind to the ends of tetrameric protofilaments. In combination, these findings suggest that the epitope of the antibody resides at the amino-terminal end of the alpha-helical rod domain. Preincubation of desmin protofilaments with an excess of D76 antibodies blocks their subsequent assembly into IF. In the presence of sub-stoichiometric amounts of antibodies, IF are assembled from protofilaments but they are morphologically aberrant in that (a) they are capped by IgG molecules at one or both ends; (b) they are unraveled to varying degree, revealing a characteristic right-handed helical arrangement of sub-filamentous strands of different diameters. The antibody binds only to the ends but not along the length of desmin IF. The most straightforward explanation for this is that the epitope resides in a part of the desmin molecule that becomes buried within the core of the filament upon polymerization and is therefore inaccessible to the antibody.

Rigor crossbridges are double-headed in fast muscle from crayfish

The structure of rigor crossbridges was examined by comparing rigor crossbridges in fast muscle fibers from glycerol-extracted abdominal flexor muscle of crayfish with those in "natively decorated" thin filaments from the same muscle. Natively decorated thin filaments were obtained by dissociating the backbone of the myosin filaments of rigor myofibrils in 0.6 M KCl. Intact fibers were freeze-fractured, deep-etched, and rotary shadowed; isolated filaments were either negatively stained or freeze dried and rotary shadowed. The crossbridges on the natively decorated actin maintain the original spacing and the disposition in chevrons and double chevrons for several hours, indicating that no rearrangement of the actomyosin interactions occurs. Thus the crossbridges of the natively decorated filaments were formed within the geometrical constraints of the intact myofibril. The majority of crossbridges in the intact muscle have a triangular shape indicative of double-headed crossbridge. The triangular shape is maintained in the isolated filaments and negative staining resolves two heads in a single crossbridge. In the isolated filaments, crossbridges are attached at uniform acute angles. Unlike those in insect flight muscle (Taylor et al., 1984), lead and rear elements of the double chevron may be both double-headed. Deep-etched images reveal a twisted arrangement of subfilaments in the backbone of the thick filament.

Assembly of vimentin in vitro and its implications concerning the structure of intermediate filaments

After dialysis against 10 mM-Tris-acetate (pH 8.5), vimentin that has been purified in the presence of urea is present in the form of tetrameric 2 to 3 nm X 48 nm rods known as protofilaments. These building blocks in turn polymerize into intermediate filaments (10 to 12 nm diameter) when they are dialyzed against a solution of physiological ionic strength and pH. By varying the ionic conditions under which polymerization takes place, we have identified two classes of assembly intermediates whose structures provide clues as to how an intermediate filament may be constructed. The structure of the first class, seen when assembly takes place at 10 to 20 mM-salt at pH 8.5, strongly suggests that one of the initial steps of filament assembly is the association of protofilaments into pairs with a half-unit axial stagger. Increasing the ionic strength of the assembly buffer leads to the emergence of short, full-width intermediate filaments at approximately 50 mM-salt at pH 8.5. In the presence of additional protofilaments, these short filaments elongate to many micrometers when the ionic strength and pH are further adjusted to physiological levels. The electron microscope images of the assembly intermediates suggest that vimentin-containing intermediate filaments are made up of eight protofilaments, assembled such that there is an approximately 22 nm axial stagger between neighboring protofilaments. We propose that this half-unit staggering of protofilaments is a fundamental feature of intermediate filament structure and assembly, and that it could account for the 20 to 22 nm axial repeat seen in all intermediate filaments examined so far.

Arrest of pigment granule motion in erythrophores by quick-freezing

We report the use of quick-freezing, as an alternative to conventional chemical fixation, to arrest the movement of pigment granules at various stages of the dispersion-aggregation cycle in Holocentrus erythrophores. During pigment aggregation, the granules in these cells move at up to 20 microns/sec, hence the structural changes underlying the movement are likely to be too fleeting to be captured faithfully by conventional aldehyde fixation. On the other hand, quick-frozen cells, when examined by freeze-etch electron microscopy, provide novel views of certain cytoplasmic components which appear to be involved in pigment granule movement, namely, fine (2- to 6-nm diameter) fibrils which link the granules to each other and to the radial array of microtubules. These fine crosslinking fibrils can be distinguished from thicker (8- to 15-nm diameter) strands of coherent granular material which pervade the cytoplasm of pigment-dispersed as well as pigment-aggregated cells. This granular matrix is removed by detergent permeabilization, after which it becomes apparent that the fine fibrils are insoluble and are distributed both within and distal to the aggregated pigment mass. The diameter of the specific fibrils does not change during pigment motion, which indicates that they are not contractile.

Direct visualization of the myosin crossbridge helices on relaxed rabbit psoas thick filaments

Thick filaments in relaxed, quick-frozen and freeze-etched psoas myofibrils display a prominent helical pattern of projections repeating at 43 +/- 1 nm. These helices are right-handed, and measurement of the pitch angle indicates that the thick filaments are three-stranded. Each half-turn of a helix is composed of three to five projections, 11 to 12 nm in diameter. These projections probably represent individual myosin crossbridges. This is the first direct visualization of the crossbridge helices in vertebrate striated muscle filaments whose three-dimensional structure is preserved without chemical fixation.

Detection of desmin-containing intermediate filaments in cultured muscle and nonmuscle cells by immunoelectron microscopy

Antibodies raised against chicken gizzard smooth muscle desmin were shown to be specific by immunofluorescence cytochemistry and immunoautoradiography after two-dimensional polyacrylamide gel electrophoresis. Embryonic chick heart cell cultures (permeabilized with Triton X-100) and enucleated adult chicken erythrocyte ghosts (Granger, B. L., E. A. Rapasky, and E. Lazarides, 1982, J. Cell Biol. 92:299-312) were then used for immunoelectronmicroscopic localization of desmin. As expected, all intermediate filaments (IF) of the cardiac myocytes were labeled heavily and uniformly with the desmin antibodies. No periodicity or helicity was detectable along the labeled IF. Of interest was the intermittent but clear labeling of the IF of the nonmuscle, fibroblastic cells in the identical cultures. These antibodies did not bind vimentin from embryonic chick heart homogenates; furthermore, they did not label IF of avian erythrocytes known to contain vimentin but not desmin. We conclude that IF of cardiac fibroblastic cells contain low, but significant, concentrations of desmin and that this protein probably forms a copolymer with vimentin in these cells.

High resolution scanning electron microscopy of isolated and in situ cytoskeletal elements

Evidence is presented that cytoskeletal structures (actin filaments, intermediate filaments, and microtubules) can be resolved by scanning electron microscopy after osmium impregnation of biological material, using thiocarbohydrazide as a ligand, followed by critical-point drying. These different classes of filaments or tubules can be identified both as purified protein polymers and as structured organelles within cryofractured or detergent-extracted cells.

Polymerization polarity of actin

The actin polymer, like the thin filaments of muscle, is known to be polarized as demonstrated by the well known "HMM decoration" technique to give a "herringbone" pattern pointing in one direction. The question "Does polymer formation proceed unidirectionally, or bidirectionally?" was raised and tested experimentally. Short fragments of actin polymers were prepared, fully decorated with HMM and these decorated fragments were used as initiation centers for further actin polymerization without HMM. The resultant polymers showing both decorated and undecorated portions were examined and found to consist of a large majority of "spears" i.e., the added undecorated polymer extended in the direction opposite to that direction pointed by the "herringbone" pattern. However, a few cases of polymers indicating the opposite direction of polymerization were also found. Analysis leads to the conclusion that actin polymerization is unidirectional, although further experimentation is necessary to establish this completely.