Intermediate filaments: new proteins, some answers, more questions

Endosomal lipid accumulation in NPC1 leads to inhibition of PKC, hypophosphorylation of vimentin and Rab9 entrapment

BACKGROUND INFORMATION

Within the group of lysosomal storage diseases, NPC1 [NPC (Niemann-Pick type C) 1] disease is a lipidosis characterized by excessive accumulation of free cholesterol as well as gangliosides, glycosphingolipids and fatty acids in the late E/L (endosomal/lysosomal) system (Chen et al., 2005) due to a defect in late endosome lipid egress. We have previously demonstrated that expression of the small GTPase Rab9 in NPC1 cells can rescue the lipid transport block phenotype (Walter et al., 2003), albeit by an undefined mechanism.

RESULTS

To investigate further the mechanism by which Rab9 facilitates lipid movement from late endosomes we sought to identify novel Rab9 binding/interacting proteins. In the present study, we report that Rab9 interacts with the intermediate filament phosphoprotein vimentin and this interaction is altered by lipid accumulation in late endosomes, which results in inhibition of PKC (protein kinase C) and hypophosphorylation of vimentin, leading to late endosome dysfunction. Intermediate filament hypophosphorylation, aggregation and entrapment of Rab9 ultimately leads to transport defects and inhibition of lipid egress from late endosomes.

CONCLUSIONS

These results reveal a previously unappreciated interaction between Rab proteins and intermediate filaments in regulating intracellular lipid transport.

Morphological differences between the trabecular meshworks of zebrafish and mammals

PURPOSE

The zebrafish has been used as an animal model to study ocular development and diseases, including glaucoma. However, there are still many concerns about the morphological differences between zebrafish and mammals. Before using the zebrafish for glaucoma studies, we should understand the morphological differences in the trabecular meshworks (TMs) of zebrafish and other animal models. This study investigated and compared the histological morphologies and compositions of the extracellular matrices of the TMs of the zebrafish and some commonly used animal models, including the mouse, rat, rabbit, and cow.

METHODS

Sections of the angular portions from the studied species (mouse, rat, rabbit, cow, zebrafish, and human) were prepared for immunohistochemical and electron microscopic analyses. Antibodies directed against cytoskeletal and extracellular matrix components (AE1/AE3, vimentin, alpha-smooth muscle actin, keratocan, and lumican) were used for immunolocalization. Reverse transcription polymerase chain reaction (RT-PCR) for keratocan and lumican was also performed.

RESULTS

The TMs of the mouse, rat, and human consist of extracellular matrix organized into a network of beams covered in trabecular endothelial cells. However, no lamellate meshwork exists in the TMs of the rabbit, cow, or zebrafish. Instead, a reticular meshwork (rabbit and cow) and an annular ligament (zebrafish) develop. Immunohistological analysis revealed that vimentin is expressed in the TMs of the rat, rabbit, and human, and alpha-smooth muscle actin is expressed in the TMs of the mouse, rat, rabbit, and human. Only the annular ligament of the zebrafish stained positively with anti-AE1/AE3 antibody. The annular ligament of the zebrafish also expresses keratocan and lumican. The human TM showed weakly positive staining of lumican. A prominent distribution of mitochondria and intracellular vacuoles is observed in the trabecular cells of the mouse, rat, rabbit, and cow, but not the zebrafish. The analysis of RT-PCR shows the keratocan and lumican mRNAs are expressed in the annular ligament of zebrafish, but not in mouse, rat, rabbit, and cow.

CONCLUSIONS

We conclude that the zebrafish expresses different extracellular matrix proteins and has a distinctive ultrastructure in the TM. Therefore, zebrafish should be used with caution for glaucoma studies.

Molecular characterization, gene expression and dependence on thyroid hormones of two type I keratin genes (sseKer1 and sseKer2) in the flatfish Senegalese sole (Solea senegalensis Kaup)

BACKGROUND

Keratins make up the largest subgroup of intermediate filaments, and, in chordates, represent the most abundant proteins in epithelial cells. They have been associated with a wide range of functions in the cell, but little information is still available about their expression profile and regulation during flatfish metamorphosis. Senegalese sole (Solea senegalensis) is a commercially important flatfish in which no keratin gene has been described yet.

RESULTS

The development of large-scale genomics of Senegalese sole has facilitated the identification of two different type I keratin genes referred to as sseKer1 and sseKer2. Main characteristics and sequence identities with other fish and mammal keratins are described. Phylogenetic analyses grouped sseKer1 and sseKer2 in a significant clade with other teleost epidermal type I keratins, and have allowed for the identification of sseKer2 as a novel keratin. The expression profile of both genes was studied during larval development and in tissues using a real-time approach. sseKer1 and sseKer2 mRNA levels were significantly higher in skin than in other tissues examined. During metamorphosis, sseKer1 transcripts increased significantly at first stages, and reduced thereafter. In contrast, sseKer2 mRNA levels did not change during early metamorphosis although a significant drop at metamorphosis climax and late metamorphosis was also detected. To study the possible regulation of sseKer gene expressions by thyroid hormones (THs), larvae were exposed to the goitrogen thiourea (TU). TU-treated larvae exhibited higher sseKer1 and sseKer2 mRNA levels than untreated control at both 11 and 15 days after treatment. Moreover, addition of exogenous T4 hormone to TU-treated larvae restored or even reduced the steady-state levels with respect to the untreated control, demonstrating that expression of both genes is negatively regulated by THs.

CONCLUSION

We have identified two keratin genes, referred to as sseKer1 and sseKer2, in Senegalese sole. Phylogenetic analyses revealed sseKer2 as a novel keratin. Although they exhibit different expression patterns during larval development, both of them are negatively regulated by THs. The co-regulation by THs could explain the reduction of both keratin transcripts after the metamorphosis climax, suggesting their role in the tissue remodelling processes that occur during metamorphosis.

Epidermis-restricted expression of zebrafish cytokeratin II is controlled by a -141/+85 minimal promoter, and cassette -141/-111 is essential for driving the tissue specificity

We isolated a 2.3 kb DNA segment from the upstream region of the zebrafish cytokeratin II (zfCKII) gene. Transgenic embryos, produced by using a series of 5' deletions linked to the red fluorescent protein (RFP) reporter, showed that the -141/+85 segment of zfCKII directed RFP expression in epidermal cells, whereas the -111/+85 segment did not. When -141/-111 was deleted from -355/+85 and microinjected into one-celled embryos, no fluorescence was observed at later stages, indicating that the -141/-111 segment is required for green fluorescent protein expression in epidermal cells. Furthermore, when a putative KLF-binding site at -119/-117 was mutated, RFP expression rates and intensities were reduced dramatically, although still observed, suggesting that -119/-117 within -141/-111 is a key cis-element for controlling epidermis-specific expression of the zfCKII gene. Finally, we generated a zebrafish transgenic line, Tg(zfCKII(2.3):RFP), which carries an upstream 2.3 kb regulatory region of the zfCKII gene fused with RFP. The expression pattern in the epidermal cells of Tg(zfCKII(2.3):RFP) fish recapitulated that of the endogenous gene. F2 embryos derived from Tg(zfCKII(2.3):RFP) males crossed with wild-type females revealed that the earliest onset of RFP expression was at the sphere stage, indicating that this transgenic approach can be used for studying zygotic expression of maternally inherited genes.

Vmac: a novel protein associated with vimentin-type intermediate filament in podocytes of rat kidney

Vimentin-type intermediate filaments (IFs) play an important role in cytoskeletal organization and cell morphology. We identified here a novel protein associated with vimentin-type IFs and named it vimentin-type IF-associated coiled-coil protein (Vmac). Vmac consists of 171 amino acids with a calculated Mr of 18,844 and has a coiled-coil domain in its N-terminal region and the PDZ-binding tetrapeptide consensus motif in its C-terminal region. Northern blotting showed that the Vmac mRNA was expressed in many rat tissues examined but most abundantly expressed in the kidney. Immunofluorescence microscopy revealed that Vmac was highly concentrated at podocytes of renal glomeruli. Podocytes are highly specialized epithelial cells characterized by a large cell body and numerous foot processes, and express vimentin-type IFs that are distributed in the cell body and the major processes. Immunoelectron microscopy revealed that Vmac was associated with vimentin-type IFs of podocytes. These results indicate that Vmac is a novel protein associated with vimentin-type IF in podocytes of rat kidney.

Cell biology of laryngeal epithelial defenses in health and disease: further studies

This is the second annual report of an international collaborative research group that is examining the cellular impact of laryngopharyngeal reflux (LPR) on laryngeal epithelium. The results of clinical and experimental studies are presented. Carbonic anhydrase (CA), E-cadherin, and MUC gene expression were analyzed in patients with LPR, in controls, and in an in vitro model. In patients with LPR, we found decreased levels of CAIII in vocal fold epithelium and increased levels in posterior commissure epithelium. The experimental studies confirm that laryngeal CAIII is depleted in response to reflux. Also, cell damage does occur well above pH 4.0. In addition, E-cadherin (transmembrane cell surface molecules, which have a key function in epithelial cell adhesion) was not present in 37% of the LPR laryngeal specimens. In conclusion, the laryngeal epithelium lacks defenses comparable to those in esophageal epithelium, and these differences may contribute to the increased susceptibility of laryngeal epithelium to reflux-related injury.

Functional significance of the specific sites phosphorylated in desmin at cleavage furrow: Aurora-B may phosphorylate and regulate type III intermediate filaments during cytokinesis coordinatedly with Rho-kinase

Aurora-B is a protein kinase required for chromosome segregation and the progression of cytokinesis during the cell cycle. We report here that Aurora-B phosphorylates GFAP and desmin in vitro, and this phosphorylation leads to a reduction in filament forming ability. The sites phosphorylated by Aurora-B; Thr-7/Ser-13/Ser-38 of GFAP, and Thr-16 of desmin are common with those related to Rho-associated kinase (Rho-kinase), which has been reported to phosphorylate GFAP and desmin at cleavage furrow during cytokinesis. We identified Ser-59 of desmin to be a specific site phosphorylated by Aurora-B in vitro. Use of an antibody that specifically recognized desmin phosphorylated at Ser-59 led to the finding that the site is also phosphorylated specifically at the cleavage furrow during cytokinesis in Saos-2 cells. Desmin mutants, in which in vitro phosphorylation sites by Aurora-B and/or Rho-kinase are changed to Ala or Gly, cause dramatic defects in filament separation between daughter cells in cytokinesis. The results presented here suggest the possibility that Aurora-B may regulate cleavage furrow-specific phosphorylation and segregation of type III IFs coordinatedly with Rho-kinase during cytokinesis.

Vimentin affects localization and activity of sodium-glucose cotransporter SGLT1 in membrane rafts

It has been reported that vimentin, a cytoskeleton filament that is expressed only in mesenchymal cells after birth, is re-expressed in epithelial cells in vivo under pathological conditions and in vitro in primary culture. Whether vimentin re-expression is only a marker of cellular dedifferentiation or is instrumental in the maintenance of cell structure and/or function is a matter of debate. To address this issue, we used renal proximal tubular cells in primary culture from vimentin-null mice (Vim-/-) and from wild-type littermates (Vim+/+). The absence of vimentin did not affect cell morphology, proliferation and activity of hydrolases, but dramatically decreased Na-glucose cotransport activity. This phenotype was associated with a specific reduction of SGLT1 protein in the detergent-resistant membrane microdomains (DRM). In Vim+/+cells, disruption of these microdomains by methyl-β-cyclodextrin decreased SGLT1 protein abundance in DRM, a change that was paralleled by a decrease of Na-glucose transport activity. Importantly, we showed that vimentin is located to DRM, but it disappeared after methyl-β-cyclodextrin treatment. In Vim-/- cells,supplementation of cholesterol with cholesterol-methyl-β-cyclodextrin complexes completely restored Na-glucose transport activity. Interestingly,neither cholesterol content nor cholesterol metabolism changed in Vim-/- cells. Our results are consistent with the view that re-expression of vimentin in epithelial cells could be instrumental to maintain the physical state of rafts and, thus, the function of DRM-associated proteins.

DNA microarray analysis of gene expression markers of endometriosis

OBJECTIVE

To use DNA microarray technology to examine differential gene expression in uterine endometrium versus endometriosis implants.

DESIGN

Pilot study.

SETTING

Volunteers in an academic research environment.

PATIENT(S)

Premenopausal women scheduled for surgery for suspected endometriosis.

INTERVENTION(S)

Surgical excision of endometriosis tissue and uterine endometrial biopsy.

MAIN OUTCOME MEASURE(S)

Gene expression.

RESULT(S)

The expression of eight genes from a total of 4,133 genes on the DNA microarray was increased in endometriosis implants compared with uterine endometrium. The eight genes were beta-actin, alpha-2 actin, vimentin, 40S ribosomal protein S23, Ig-lambda light chain, Ig germline H chain G-E-A region gamma-2 constant region gene, major histocompatibility complex class 1,C, and complement component 1 S subcomponent.

CONCLUSION(S)

The data demonstrate that the DNA microarray is an effective tool for the identification of differentially expressed genes between uterine and ectopic endometrium; further study of the genes identified herein will expand our understanding of the nature of endometriosis and assist in the eventual development of new treatments for endometriosis.

Human synemin gene generates splice variants encoding two distinct intermediate filament proteins

Intermediate filament (IF) proteins are constituents of the cytoskeleton, conferring resistance to mechanical stress, and are encoded by a dispersed multigene family. In man we have identified two isoforms (180 and 150 kDa) of the IF protein synemin. Synemin alpha and beta have a very short N-terminal domain of 10 amino acids and a long C-terminal domain consisting of 1243 amino acids for the alpha isoform and 931 amino acids for the beta isoform. An intronic sequence of the synemin beta isoform is used as a coding sequence for synemin alpha. Both mRNA isoforms (6.5 and 7.5 kb) result from alternative splicing of the same gene, which has been assigned to human chromosome 15q26.3. Analyses by Northern and Western blot revealed that isoform beta is the predominant isoform in striated muscles, whereas both isoforms (alpha and beta) are present in almost equal quantities in smooth muscles. Co-transfection and immunolabeling experiments indicate that both synemin isoforms are incorporated with desmin to form heteropolymeric IFs. Furthermore synemin and desmin are found aggregated together in certain pathological situations.

Cell cycle-dependent changes in localization of a 210-kDa microtubule-interacting protein in Leishmania

Using the monoclonal antibody MA-01, a new 210-kDa microtubule-interacting protein was identified in Leishmania promastigotes by immunoblotting and by immunoprecipitation. The protein was thermostable and was located on microtubules prepared by taxol-driven polymerization in vitro. On fixed cells the antibody gave specific staining of flagellum, flagellar pocket, and mitotic spindle. Subpellicular microtubules were basically not decorated but posterior poles of the cells were labeled in a cell-cycle-dependent manner. In anterior and posterior poles of cells the 210-kDa protein codistributed with the 57-kDa protein, immunodetected with anti-vimentin antibody, that was located only on cell poles. Immunolocalization of the 57-kDa protein was most prominent in dividing cells. The presented data suggest that the 210-kDa protein is a newly identified microtubule-interacting protein of Leishmania that could be involved in anchoring the microtubules in posterior poles of these cells. The striking codistribution of the microtubule-interacting protein and the 57-kDa protein in protozoa is described for the first time.

Phosphorylation of vimentin head domain inhibits interaction with the carboxyl-terminal end of alpha-helical rod domain studied by surface plasmon resonance measurements

The amino-terminal head domain of vimentin is the target site for several protein kinases and phosphorylation induces disassembly of the vimentin intermediate filaments in vivo and in vitro. To better understand molecular mechanisms involved in phosphorylation-dependent disassembly, we examined domain interactions involving the head domain and the effect of phosphorylation on the interaction, using surface plasmon resonance. We observed that the head domain binds to the carboxyl-terminal helix 2B in the rod domain, under physiological ionic strength. This interaction was interfered with by A-kinase phosphorylation of the head domain. Deletion of the carboxyl-terminal 20 amino acids of helix 2B resulted in loss of the interaction. Furthermore, peptide representing the carboxyl-terminal 20 residues of helix 2B had a substantial affinity with the head domain but not with the phosphorylated one. These findings support the idea that the interaction between the head domain and the last 20 residues of helix 2B is essential for association of vimentin tetramers into the intermediate filaments and that the phosphorylation-dependent disassembly is the result of loss of the interaction.

Coexpression of cytokeratin and vimentin in mice trophoblastic giant cells

Trophoblastic giant cells reach their maximum size and exhibit a conspicuous synthetic and invasive activity during mouse placentation. The cytoskeleton, given the complex functions of the cells, shows a well-developed network of intermediate filament proteins. Immunohistochemistry combined with confocal and conventional immunofluorescence studies of intermediate filaments proteins cytokeratin and vimentin were performed in mice trophoblastic giant cells on days 9-11 of pregnancy. Specimens were fixed in phosphate-buffered formaldehyde and tissues were processed for routine paraffin embedding. Trophoblastic giant cells from antimesometrial, lateral or mesometrial uterine regions, through days 9-11 of pregnancy, expressed the same staining with both immunoperoxidase and immunofluorescent techniques. Cytokeratin filamentous structures were intensely immunoreactive and were detected throughout the cells cytoplasm; a few cells exhibited strongest fluorescence in the peripheral cytoplasm. Vimentin-positive staining was often distributed throughout the cells cytoplasm, most frequently and more intensely in the peripheral region; in some cells, it was present only in the peripheral regions. It is probable that expression of vimentin in midpregnancy trophoblastic giant cells may be associated with the rapid and conspicuous increase in size and synthetic activity of the cells and also with phagocytosis of degraded materials and invasion of decidual tissue.

The Raf-1 kinase associates with vimentin kinases and regulates the structure of vimentin filaments

Using immobilized GST-Raf-1 as bait, we have isolated the intermediate filament protein vimentin as a Raf-1-associated protein. Vimentin coimmunoprecipitated and colocalized with Raf-1 in fibroblasts. Vimentin was not a Raf-1 substrate, but was phosphorylated by Raf-1-associated vimentin kinases. We provide evidence for at least two Raf-1-associated vimentin kinases and identified one as casein kinase 2. They are regulated by Raf-1, since the activation status of Raf-1 correlated with the phosphorylation of vimentin. Vimentin phosphorylation by Raf-1 preparations interfered with its polymerization in vitro. A subset of tryptic vimentin phosphopeptides induced by Raf-1 in vitro matched the vimentin phosphopeptides isolated from v-raf-transfected cells labeled with orthophosphoric acid, indicating that Raf-1 also induces vimentin phosphorylation in intact cells. In NIH 3T3 fibroblasts, the selective activation of an estrogen-regulated Raf-1 mutant induced a rearrangement and depolymerization of the reticular vimentin scaffold similar to the changes elicited by serum treatment. The rearrangement of the vimentin network occurred independently of the MEK/ERK pathway. These data identify a new branch point in Raf-1 signaling, which links Raf-1 to changes in the cytoskeletal architecture.

Calyculin A-induced vimentin phosphorylation sequesters 14-3-3 and displaces other 14-3-3 partners in vivo

14-3-3 proteins bind their targets through a specific serine/threonine-phosphorylated motif present on the target protein. This binding is a crucial step in the phosphorylation-dependent regulation of various key proteins involved in signal transduction and cell cycle control. We report that treatment of COS-7 cells with the phosphatase inhibitor calyculin A induces association of 14-3-3 with a 55-kDa protein, identified as the intermediate filament protein vimentin. Association of vimentin with 14-3-3 depends on vimentin phosphorylation and requires the phosphopeptide-binding domain of 14-3-3. The region necessary for binding to 14-3-3 is confined to the vimentin amino-terminal head domain (amino acids 1-96). Monomeric forms of 14-3-3 do not bind vimentin in vivo or in vitro, indicating that a stable complex requires the binding of a 14-3-3 dimer to two sites on a single vimentin polypeptide. The calyculin A-induced association of vimentin with 14-3-3 in vivo results in the displacement of most other 14-3-3 partners, including the protooncogene Raf, which nevertheless remain capable of binding 14-3-3 in vitro. Concomitant with 14-3-3 displacement, calyculin A treatment blocks Raf activation by EGF; however, this inhibition is completely overcome by 14-3-3 overexpression in vivo or by the addition of prokaryotic recombinant 14-3-3 in vitro. Thus, phosphovimentin, by sequestering 14-3-3 and limiting its availability to other target proteins can affect intracellular signaling processes that require 14-3-3.

GFAP is expressed as a major soluble pool associated with glucagon secretory granules in A-cells of mouse pancreas

To elucidate the role of intermediate filament proteins in endocrine cells, we investigated the expression and subcellular distribution of GFAP in mouse islets of Langerhans. For this purpose, combined immunocytochemical and biochemical analysis with a panel of antibodies was carried out to identify GFAP-immunoreactive cells in mouse endocrine pancreas. Cell fractionation into NP-40-soluble and detergent/high salt-insoluble components was performed to assess whether GFAP was located in the cytosolic and/or cytoskeletal compartments of immunoreactive cells. Immunoelectron microscopic analysis was carried out to determine the subcellular distribution of the protein. Peripheral islet cells were stained with anti-GFAP antiserum. These cells were identified as glucagon-secreting cells by immunocytochemical staining of consecutive sections with anti-somatostatin, anti-GFAP, and anti-glucagon antisera. Western blotting analysis of both NP-40-soluble and detergent/high-salt insoluble fractions of isolated islets of Langerhans allowed detection of GFAP in both cytosolic and cytoskeletal compartments. Interestingly, however, the former location was highly predominant. In addition, immunoelectron microscopy localized GFAP associated with the periphery of secretory granules. On the basis of these results, an intriguing role for GFAP in secretory events should be strongly suspected.(J Histochem Cytochem 48:1233-1242, 2000)

Type I and type II cytokeratin cDNAs from the zebrafish (Danio rerio) and expression patterns during early development

Full-length cDNAs of a type I (zfCKI), and a type II (zfCKII) cytokeratin from the adult zebrafish, Danio rerio, were characterized and their expressions studied during early development and in the adult. The 1,426 bp long zfCKI cDNA encodes a 46.7 kD protein, whereas the 2,398 bp zfCKII cDNA encodes a protein of 58.6 kD. zfCKI and zfCKII each have a central rod domain that is characteristic of intermediate filaments and which share 73%-91% and 87%-93% similarity, respectively, with those of type I and type II cytokeratins from zebrafish, goldfish, and the rainbow trout. The central rod domains of zfCKI and zfCKII also contain the IF signature motif, IA[T/E]YR[K/R]LL[D/E]. zfCKI has, in addition, a leucine-zipper motif at a.a. residues 184-205 and 191-212. Both zfCKI and zfCKII mRNAs are expressed in the epidermis of the zebrafish. zfCKII mRNA was both maternally inherited and zygotically transcribed and was detected from the one-cell embryo to adult stages. zfCKII was also strongly expressed specifically during the 20-somites, protruding-mouth, and adult stages. In the adult, it was uniformly expressed in the skin, fins and scale epidermis. In contrast, zfCKI mRNA was undetectable in the oocyte but was zygotically transcribed from the epiboly stage onwards. Its expression in the skin was strong only up to the swimming larva stage and was weak and patchy in the adult. Both zfCKI and zfCKII were expressed in the neurons and glial cells of the brain and spinal cord. In the adult eye, zfCKI and zfCKII were expressed in the ganglion cell layer and the retina, but zfCKII was also strongly expressed in the cornea as well as in chondrocytes in the skull.

Localizing the adhesive and signaling functions of plakoglobin

Plakoglobin (PKG) is a major component of cell-cell adhesive junctions. It is also closely related to the Drosophila segment polarity gene product armadillo and can induce a WNT-like neural axis duplication (NAD) phenotype in Xenopus [Kamovsky and Klymkowsky, 1995.] To define the regions of PKG involved in cell adhesion and inductive signaling, we examined the behavior of mutated forms of PKG in Xenopus. Deletion of amino acids 22 through 39 (in the Xenopus PKG sequence increased the apparent stability of the polypeptide within the embryo and increased its ability to induce a WNT-like, NAD phenotype when expressed in the vegetal hemisphere. The N-terminal "head" and first 6 "ARM" repeats of PKG, or the C-terminal "tail" and the last 3 "ARM" repeats, could be removed without destroying the remaining polypeptide's ability to induce a NAD phenotype. The nuclear localization of mutant PKGs, however, was not strictly correlated with the ability to induce a NAD phenotype, i.e., some inactive polypeptides still accumulate in nuclei. Removal of PKG's head and first ARM repeat, which includes its alpha-catenin binding site, resulted in a polypeptide that, when expressed in the embryo, generated alpha dramatic cell adhesion defect. Removal of the next three ARM repeats abolished this adhesion defect, suggesting that the polypeptide no longer competes effectively with endogenous catenins for binding to cadherins. Expression of a form of PKG truncated after the 5th ARM repeat produced a milder cell adhesion defect, whereas expression of a polypeptide truncated after the 8th ARM repeat had little apparent effect on cellular adhesion. Based on these observations, we conclude that functions related to stability and cellular adhesion reside in the N-terminal region of the polypeptide, whereas the ability to induce a NAD phenotype lies within repeats 6-10 of the central region. The function(s) of the C-terminal domain of PKG remain uncertain at this time.

Preliminary report of the clinical performance of a new urinary bladder cancer antigen test: comparison to voided urine cytology in the detection of transitional cell carcinoma of the bladder

We compared the ability of a new urinary bladder cancer antigen (UBC) test with conventional cytology for the detection of transitional cell carcinoma of the bladder using voided urine samples. The UBC was measured and corrected for the creatinine concentration in the urine of 61 patients with transitional cell carcinoma of the bladder (group 1), 23 patients without recurrent bladder tumors during follow-up (group 2), 28 patients with benign prostatic hyperplasia (group 3), nine patients with prostate cancer (group 4), and 90 healthy volunteers free of urological diseases (group 5). The UBC concentrations were 408.8+/-578.5, 18.8+/-26.6, 23.9+/-32.7, 17.5+/-18.6 and 4.6+/-6.7 ngmg(-1) creatinine (mean+/-S. D.) for groups 1-5, respectively. The level for group 1 was significantly higher than for any other group. The sensitivity and specificity, which were optimized using receiver-operating characteristic curves for groups 1 and 2 were 82.0% and 82.6%, respectively, at a threshold value of 39 ngmg(-1) creatinine. The sensitivity and specificity of cytology for these same groups were 60.7% and 86.9%, respectively. The sensitivity of the UBC was significantly higher than that of cytology, not only for total bladder tumors (82.0% vs. 60.7%, P<0.02) but also for grade I transitional cell carcinoma of the bladder (76.5% vs. 11.8%, P<0. 001). While offering a similarly high specificity, the UBC test might have an advantage over cytology in terms of superior sensitivity, particularly for low-grade tumors.

Vimentin expression in human squamous carcinoma cells: relationship with phenotypic changes and cadherin-based cell adhesion

Phenotypic changes resembling an epithelial-to-mesenchymal transition often occur as epithelial cells become tumorigenic. Two proteins that have been implicated in this process are vimentin and N-cadherin. In this study, we sought to establish a link between expression of vimentin and N-cadherin as oral squamous epithelial cells undergo a morphologic change resembling an epithelial-to-mesenchymal transition. We found that N-cadherin and vimentin did not influence the expression of one another.

Localization of transitin mRNA, a nestin-like intermediate filament family member, in chicken radial glia processes

We have examined the gene expression of two radial glia intermediate filament proteins, transitin and vimentin, in the developing chick CNS. Despite global similarities in their mRNA distributions, marked regional differences are observed. Most notably, we show that transitin mRNA is localized along radial glial processes and is localized to radial glia endfeet, whereas vimentin mRNA is not localized in radial glia. Localization of transitin mRNA is best shown in the diencephalic radial glia, as well as cerebellar Bergmann glia. In addition, in the early embryonic optic tectum, telencephalon, and retina, transitin mRNA is highly localized to radial glia endfeet, which is suggestive of its transport in these cells. These in vivo demonstrations of transitin mRNA localization are confirmed by in situ hybridization analysis of cultured chick brain radial glia, which demonstrates the presence of granular staining for transitin mRNA in glial processes. Transitin mRNA distribution in developing muscle also shows a highly regulated expression pattern, especially along the Z-lines of myofibrils. As further support for the transport and localization of transitin mRNA in radial glia and muscle, we have identified a consensus RNA transport signal in transitin mRNA that is absent from vimentin. These data suggest that the local regulation of transitin protein synthesis may contribute to its function as an intermediate filament protein in radial glia.

Glial fibrillary acidic protein (GFAP)-like immunoreactivity in rat endocrine pancreas

The study of intermediate filament expression in the pancreatic epithelium has been previously focused almost exclusively on cytokeratins. Transient vimentin immunoreactivity has also been detected in duct cells of rat fetal pancreas. Here we report that, in rat pancreas, intense GFAP-like immunoreactivity is detectable in a subpopulation of endocrine cells located in the periphery of the islet of Langerhans. In addition, staining appeared to be preferentially localized to the apical pole of the cells. Two different polyclonal antibodies were employed in this study, with analogous results. Staining of consecutive sections with anti-GFAP, anti-glucagon, and anti-somatostatin antibodies demonstrates that GFAP-like immunoreactivity is present in glucagon-secreting cells. The relevance of this finding is discussed. (J Histochem Cytochem 48:259-265, 2000)

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.

Tau regulates the attachment/detachment but not the speed of motors in microtubule-dependent transport of single vesicles and organelles

We have performed a real time analysis of fluorescence-tagged vesicle and mitochondria movement in living CHO cells transfected with microtubule-associated protein tau or its microtubule-binding domain. tau does not alter the speed of moving vesicles, but it affects the frequencies of attachment and detachment to the microtubule tracks. Thus, tau decreases the run lengths both for plus-end and minus-end directed motion to an equal extent. Reversals from minus-end to plus-end directed movement of single vesicles are strongly reduced by tau, but reversals in the opposite direction (plus to minus) are not. Analogous effects are observed with the transport of mitochondria and even with that of vimentin intermediate filaments. The net effect is a directional bias in the minus-end direction of microtubules which leads to the retraction of mitochondria or vimentin IFs towards the cell center. The data suggest that tau can control intracellular trafficking by affecting the attachment and detachment cycle of the motors, in particular by reducing the attachment of kinesin to microtubules, whereas the movement itself is unaffected.

Characterization of the chicken transitin gene reveals a strong relationship to the nestin intermediate filament class

Our laboratory previously reported that transitin is a radial glial intermediate filament protein sharing the basic structural features common to all intermediate filament (IF) proteins. It contains an alpha-helical core domain flanked by a short nonhelical head and a long COOH-terminal tail. The core sequence of transitin shows the greatest similarity to Xenopus tanabin and to rat and human nestin. We also reported that transitin has multiple splice variants derived from the deletion or inclusion of a leucine-zipper heptad repeat domain in the COOH-terminal tail. In the present study, we provide new evidence to support the classification of nestin and transitin in the same group of IF proteins based on the number and position of its introns. In addition, we suggest that the different isoforms of transitin are produced by a splicing mechanism that recognizes consensus 5' and 3' splice sites contained within the coding sequence of the leucine-zipper heptad repeat domain.

Alterations in temporal/spatial distribution of GFAP- and vimentin-positive astrocytes after spinal cord contusion with the New York University spinal cord injury device

Astrocytes become reactive as a result of various types of lesions and upregulate 2 intermediate filaments, glial fibrillary acidic protein (GFAP), and the developmentally regulated protein vimentin. Young female Sprague-Dawley rats were subjected to a spinal cord contusion at segment T10 using the New York University injury device. Animals were killed at 1, 2, 7, 14, and 30 days postinjury. Horizontal spinal cord sections spanning segments T7-T13 were assessed with antibodies to both intermediate filament proteins. The number of gray matter GFAP-positive astrocytes increased by 2 days postinjury, with segments adjacent (proximal) to the injury site showing greater responses than areas several segments away (distal). By 30 days following injury, astroglial cell numbers returned to normal levels. Vimentin-positive astrocytes also showed a graded proximal/distal response by 2 days following injury. Proximal regions remained significantly higher at 30 days following injury than control animals. Rostral/caudal changes were also evident, with regions caudal to the injury showing significantly higher numbers of vimentin positive astrocytes than those rostral, indicating that gray matter areas caudal to spinal cord injury may undergo more stress following spinal cord injury.

The cytoskeleton of the vertebrate smooth muscle cell

Smooth muscle cells possess a structural lattice composed of two primary parts: the 'cytoskeleton' that pervades the cytoplasm and the 'membrane skeleton' that provides anchorage for the cytoskeleton and contractile apparatus at the cell surface. The cytoskeleton contains two major components: first, a complement of actin filaments that links the cytoplasmic dense bodies at equispaced intervals in longitudinal fibrils; and second, a network of desmin intermediate filaments that co-distributes with the cytoskeletal actin. The actin filaments of the contractile apparatus are presumed to interface with the cytoskeleton at the cytoplasmic dense bodies and with the longitudinal rib-like arrays of dense plaques of the membrane skeleton that couple to the extracellular matrix. The present report focuses attention on the functional role of intermediate filaments and on the molecular domain structure of the protein calponin, which is found both in the cytoskeleton and the contractile apparatus. New information about the role of intermediate filaments in smooth muscle has come from studies of transgenic mice in which desmin expression has been ablated. These have shown that while desmin is dispensable for normal development and viability its absence has significant consequences for the mechanical properties of muscle tissue. Thus, the visceral smooth muscles develop only 40% of the normal contractile force and the maximal shortening velocity is reduced by 25-40%. Intermediate filaments therefore play an active role in force transmission and do not contribute solely to cell shape maintenance, as has hitherto been presumed. Recent studies on calponin have revealed a second actin binding domain at the C-terminus of the molecule and have also pinpointed an N-terminal domain that shares homology with a growing family of actin binding and signalling molecules. How these newly identified features of calponin relate to its function in vivo remains to be established.

Image processing and analysis of fluorescent labelled cytoskeleton

Cytoskeleton elements play an important role in cellular processes including normal and pathological conditions or even cell death. Although immunofluorescence microscopy techniques have proved useful to study the cytoskeleton, description and comparative results commonly rely on the direct visual analysis of the targeted cells. We report here an objective and quantitative method to analyze the cytoskeletal pattern of cultured HeLa cells based on image processing and analysis (IPA) of fluorescent labelled cytoskeleton components. Different structural quantifiable characteristics using IPA facilities (densitometric profile, number of branched points, Euler number, convexity, orientation value) allow accurate characterization and differentiation of the three types of fibre nets studied (microtubules, actin microfilament, and cytokeratin intermediate filaments). The application of the analytical methods presented here provides information concerning the organization and modification of cytoskeleton components, and could aid in the further understanding of structural and functional aspects of the cytoskeleton under normal and pathological conditions.

Transforming growth factor beta 1 induces squamous carcinoma cell variants with increased metastatic abilities and a disorganized cytoskeleton

Previous studies indicated that mouse transformed keratinocytes undergo an epithelial-fibroblastic conversion when cultured in the presence of TGF-beta1. This conversion is associated in vivo with a squamous-spindle carcinoma transition. We derived epithelioid (A6, FPA6) and spindle (B5) clonal cell variants from a squamous carcinoma cell line (PDV) after treatment with TGF-beta1. FPA6 cells were isolated from the ascites fluid of an A6-tumor-bearing mouse. FPA6 and A6 cell lines produced in nude mice mixed carcinomas with a squamous and poorly differentiated component. Both cell lines coexpressed keratins and vimentin and synthesized E-cadherin protein, although FPA6 cells cultured at early passages (FPA6-ep) had reduced levels of E-cadherin mRNA and increased synthesis of keratin K8, a marker of malignant progression. Immunofluorescence analysis revealed that FPA6-ep cells exhibited a disorganized cytoskeleton with keratins forming focal juxtanuclear aggregates and loss of F-actin stress fibers and cortical bundles, and E-cadherin was localized in the cytoplasm out of cell-cell contact areas. Sporadic cells in A6 and PDV cultures also presented those anomalous keratin structures, suggesting that FPA6 cells originated from a subpopulation of A6 tumor cells that metastasized into the peritoneal cavity. The analysis of the spontaneous and experimental metastatic potentials of the cell lines showed that epithelioid and fibroblastic cell variants had acquired metastatic abilities compared to PDV which was nonmetastatic. The FPA6-ep cell line exhibited a highly aggressive behavior, killing the animals at about 17 days after intravenous injection of the cells into athymic mice. The phenotype of FPA6-ep cells was unstable and reverted at later passages in which the normal organization of keratin and F-actin in filaments and the localization of E-cadherin at cell-cell contacts were restored. This phenotypic reversion occurred concomitantly with a reduction of the experimental metastatic potential of FPA6 cells.

Distribution and organization of desmin in cultured adult cardiac muscle cells: reflection on function

The cell-culture model for the study of desmin in adult cardiac muscle cells has provided insight into the function of desmin based on its distribution and structural organization. Initially, desmin emerged as a filamentous network from the existing amorphous form in the growing adult cardiac myocytes in vitro. Later, desmin became organized in various forms. In addition to the presence of a periodic array of desmin in the Z-line regions as observed in cardiac myocytes in vivo, longitudinally and transversely oriented strands of desmin were observed along the length of myofibrils in cardiac myocytes in vitro. These desmin strands and transverse perodicities formed a complex interwoven network, interlacing myofibrils of cells. Desmin and alpha-actinin were organized in ribbon- or aponeuroses-like structures that appeared as sheet-like, supportive structures for the cell body. The cellular cytoplasmic processes containing myofibrils were supported by desmin bars. The complex desmin network, desmin bars, transverse strands and ribbons or aponeuroses were observed in in vitro cardiac myocytes in contrast to in vivo cardiac myocytes. The functional implication of desmin, as indicated by in vivo studies, required more information concerning the organization of desmin for its supportive function, and is addressed in the present study. The elaborate organization of desmin provides evidence for its supportive function for the maintenance of the structural integrity and function of cardiac muscle cells.

Homologues of vertebrate type I, II and III intermediate filament (IF) proteins in an invertebrate: the IF multigene family of the cephalochordate Branchiostoma

We searched for functional homologues of the four subfamilies of vertebrate cytoplasmic intermediate filament (IF) proteins in the cephalochordate Branchiostoma. The epidermis contains in addition to IF proteins C2 and D1 two novel IF proteins E1 and E2. Both sequence comparisons as well as the obligatory heteropolymer formation by the recombinant proteins identify E1 as a type I keratin and E2 and D1 as type II keratins. In contrast the non-epidermal B1 forms as type III homologue homopolymeric IF. We propose that type I-III diversification of IF proteins is a property of the chordate branch of metazoa and discuss a possible origin of type IV neurofilaments.

The developmentally regulated avian protein IFAPa-400 is transitin

Transitin and IFAPa-400 are developmentally regulated high M(r) proteins expressed transiently in early chick embryogenesis. Both are associated with radially oriented fibers in the developing CNS and with various neural and myogenic tissues before their down-regulation at later stages. Previous studies have shown that IFAPa-400 colocalized and copurified with intermediate filament proteins and recent molecular cloning has indicated that transitin is a member of this family of cytoskeletal proteins. Here, we provide evidence that IFAPa-400 and transitin are the same protein. The sequence of a composite cDNA corresponding to more than 700 amino acids of IFAPa-400 carboxy-terminal extremity is identical to that of transitin. Both proteins exhibit identical apparent M(r) and isoelectric point. Immunopurified IFAPa-400 reacts with different antibodies to transitin and vice-versa. The patterns of expression of both proteins show a perfect coincidence at the tissue level. At the subcellular level, most antibodies to IFAPa-400/transitin decorate a typical intermediate filament network. However, monoclonal antibody A2B11, at the origin of transitin identification, exhibits a staining more typical of a cortical component, suggesting that different populations of transitin exist within the cell.

Properties of the novel intermediate filament protein synemin and its identification in mammalian muscle

We examined specific properties of highly purified synemin (230 kDa), recently identified as a novel intermediate filament (IF) protein, from avian smooth muscle. Soluble synemin in 10 mM Tris-HCl, pH 8.5, appears as approximately 11-nm-diameter globular structures by negative-stain and low-angle shadow electron microscopy. Chemical crosslinking and SDS-PAGE analysis indicate that soluble synemin molecules contain two 230-kDa subunits. The pH- and ionic strength-dependent solubility properties of synemin are similar to those of the type III IF protein desmin, but under physiological-like conditions in which desmin self-assembles into long approximately 10-nm-diameter IFs, synemin self-associates into complex, approx 15- to 25-nm-diameter globular structures. Calpain digestion demonstrated that synemin is extremely proteolytically labile. Western blot analysis, with monospecific polyclonal antibodies against avian synemin, shows the presence of the reactive 230-kDa synemin band in samples of adult avian skeletal, cardiac, and smooth muscle and of two reactive bands at approximately 225 kDa (major) and approximately 195 kDa in adult porcine skeletal, cardiac, and smooth muscle. Partial purification of synemin from porcine smooth muscle also resulted in fractions highly enriched in the approximately 225- and approximately 195-kDa polypeptides. Conventional immunofluorescence and immunoconfocal microscopy of isolated myofibrils and of frozen sections also demonstrated, for the first time, that synemin is present in all three adult porcine muscle cell types and is colocalized with desmin in skeletal and cardiac muscle cells at the myofibrillar Z-lines.

Protein-protein interactions between keratin polypeptides expressed in the yeast two-hybrid system

Keratin filaments are obligatory heteropolymers of type I and type II keratin polypeptides. Specific type I/type II pairs are coexpressed in vivo. In contrast, all type I/type II pairs assemble into filaments in vitro, but the different pairs have different stabilities as demonstrated by treatment with increasing concentrations of urea. We have used the yeast two-hybrid system to analyse type I/type II interactions in a cellular context. We measured interactions between two different keratin pairs and we confirm the findings that K6+K17 form very stable heterodimers whereas K8+K18 interactions were weaker. The deletion of head domains did not reduce the strength of type I/type II interactions. Rather, the affinities were increased and the differences between the two pairs were retained in headless mutants. These findings argue against a major role of the head domains in directing heterodimer interactions and in defining heterodimer stabilities.

Ligand-independent role of the beta 4 integrin subunit in the formation of hemidesmosomes

Recently, we have shown that a region within the beta4 cytoplasmic domain, encompassing the second fibronectin type III (FNIII) repeat and the first 27 amino acids of the connecting segment, is critical for the localization of alpha6 beta4 in hemidesmosomes. In addition, this region was shown to regulate the distribution of HD1/plectin in transfected cells. In order to investigate the function of the beta4 extracellular and cytoplasmic domains in the assembly and integrity of hemidesmosomes, we have constructed chimeric receptors consisting of the extracellular and transmembrane domains of the interleukin 2 receptor (IL2R), fused to different parts of the beta4 cytoplasmic domain. These chimeras are expressed as single subunits at the plasma membrane. The results show that the first and the second FNIII repeat, together with the first part of the connecting segment (in total a stretch of 241 amino acids spanning amino acids 1,115 to 1,356) are both essential and sufficient for the localization of beta4 in pre-existing hemidesmosomes. Moreover, expression of the IL2R/beta4 chimeric constructs in COS-7 and CHO cells, which do not express alpha6 beta4 or the bullous pemphigoid (BP) antigens but do express HD1/plectin, revealed that the stretch of 241 amino acids is sufficient for inducing the formation of type II hemidesmosomes. Expression of the IL2R/beta4 chimeras in a keratinocyte cell line derived from a patient lacking beta4 expression, showed that amino acids 1,115 to 1,356 can also induce the formation of type I hemidesmosomes. We further demonstrate that type I and II hemidesmosomes can also be formed upon adhesion of alpha6 beta4-expressing cells to fibronectin. These findings establish that the beta4 extracellular domain is not essential for the induction of hemidesmosome assembly. Moreover, they demonstrate that binding of alpha6 beta4 to ligand, and heterodimerization of alpha6 with beta4, are not required for hemidesmosome formation. This indicates that the assembly of hemidesmosomes can be regulated from within the cell.

Concomitant alterations in distribution of 70 kDa heat shock proteins, cytoskeleton and organelles in heat shocked 9L cells

Maintenance of cell architecture and positioning of organelles are major functions of the cytoskeleton. On the other hand, induction of heat shock proteins (HSPs) and reorganization of the cytoskeleton are the most significant changes in heat-shocked mammalian cells. We examine the alterations in HSP70 and its constitutively expressed cognate, HSC70, as well as the cytoskeleton and organelles in 9L rat brain tumor cells upon heat shock. We employed fluorescence microscopy and scanning electron microscopy to follow these changes. Levels of HSP70s were quantified by Western blotting. Accumulation of HSC70 was more transient and the protein translocated to and subsequently exited from the nucleus more rapidly than HSP70. Changes in actin microfilaments include the nuclear localization of actin fraction and disappearance of cytoplasmic microfilament bundles, while the cortical actin microfilaments were almost unaffected. Furthermore, microtubules retracted slightly from the cell periphery but remained largely unchanged. In contrast, the intermediate filaments collapsed into the perinuclear region. The mitochondria converted from filamentous into granular forms and clustered in a region overlapping with the collapsed intermediate filaments. All of the above alterations are reversible and largely reverted after 8 h of recovery. The effect on Golgi organization was very transient and the apparatus assumed a normal appearance within 4 h after the heat treatment. The ER, on the other hand, was totally unaffected by the heat treatment. These observations help correlate the sequential events following a stress like heat shock and suggest possible physiological functions of these essential constituents of a cell under stress.

The role of keratin filaments during nuclear envelope reassembly in Xenopus egg extracts

We report here a new structure, named 'strings-of-pearls', which are seen to form in Xenopus egg extracts after incubation, as 200 nm membrane vesicles attach to 10 nm filaments. These membrane vesicles fuse together along the filaments to form annulate lamellae (AL) or attach to demembranated sperm chromatin to initiate assembly of a nuclear envelope. Immunoassay with anti-keratin antibodies AE3 showed that the filaments were mainly composed of a 56 kDa keratin-like protein. Addition of AE3 to the extracts resulted in inhibition of AL formation and defective assembly of NE. These results suggest a function of keratins in the assembly of nuclear envelopes during Xenopus development.

Molecular characteristics of the novel intermediate filament protein paranemin. Sequence reveals EAP-300 and IFAPa-400 are highly homologous to paranemin

Paranemin was initially found to copurify with the intermediate filament (IF) proteins vimentin and desmin from embryonic chick skeletal muscle and was described as an IF-associated protein (IFAP). We have purified paranemin from embryonic chick skeletal muscle, prepared antibodies, and demonstrated that they label at the Z-lines of both adult avian and porcine cardiac and skeletal muscle myofibrils. We determined the cDNA sequence of paranemin by immunoscreening a lambdagt22A cDNA library from embryonic chick skeletal muscle. Northern blot analysis revealed a single transcript of 5.3 kilobases, which is much smaller than predicted from the size of paranemin (280 kDa) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The derived amino acid sequence of paranemin (1,606 residues; 178,161 kDa) contains the conserved IF rod domain (308 amino acids), which has highest homology to the rod domains of nestin and tanabin. Thus, paranemin is an IF protein rather than an IFAP. Sequence analysis also revealed that the partial cDNA sequences of two proteins, namely EAP-300 and IFAPa-400, are almost identical to regions of the cDNA sequence of paranemin. The complete paranemin cDNA was expressed in a cell line (SW13) with, and without, detectable cytoplasmic IFs. Antibody labeling of these cells suggests that paranemin does not form IFs by itself, but rather is incorporated into heteropolymeric IFs with vimentin.

Molecular cloning of a new intermediate filament protein expressed by radial glia and demonstration of alternative splicing in a novel heptad repeat region located in the carboxy-terminal tail domain

In the present study we describe the molecular cloning of transitin, formerly named EAP-300. We show that transitin is an intermediate filament protein with a core domain most closely resembling nestin and tanabin. Transitin also contains a novel heptad amino acid repeat domain, comprising multiple leucine zipper repeats, located in its tail region. Based on these structural motifs we propose that a novel intermediate filament protein that is transiently expressed by radial glia during CNS development has been identified. We also show the existence of splice variants of transitin with splicing occurring in the novel heptad repeat domain to give rise to transitin isoforms that lack this heptad repeat. By in situ hybridization analysis we show that transitin mRNA is expressed by midline radial glial structures, by several axon commissures, and by Bergmann glia of the developing cerebelium. Based on the structural properties of the transitin protein, and expression of its mRNA, we suggest that transitin is a new member of the intermediate filament gene superfamily that is transiently expressed by radial glia.

In vitro efficacy of anti-glial fibrillary acidic protein monoclonal antibodies against human malignant glioma cell lines

Our studies have confirmed the presence of large concentrations of various intermediate filament proteins (IFPs) in glioma tissue compared to normal brain. This avenue of research was extended to assess the anti-proliferative activity of anti-intermediate filament protein monoclonal antibodies (anti-IFP mAbs) against human glioma cells. In this study, anti-proliferative activity of glial fibrillary acidic protein monoclonal antibodies (anti-GFAP mAbs) has been tested in vitro, using glioma cell lines prepared and established from freshly resected brain tumors. One anaplastic astrocytoma (AA), two glioblastoma multiforme (GB1 and GB2) cell lines and three anti-GFAP mAbs (B12C4, B12B4 and B6C6, all IgG1, kappa) were used. Immunofluorescence study indicated the ability of anti-GFAP mAbs to recognize the cell surface of glioma cells and the inhibition study showed that mAb B12B4 inhibited the proliferation of GB1 (96%), GB2 (85%) and AA (93%) at a concentration of 3.2 x 10(-10) M. mAb B12C4 inhibited the proliferation of GB1 (95%), GB2 (86%) and AA (94%) at a concentration of 3.26 x 10(-10) M and mAb B6C6 inhibited the proliferation of GB1 (75%), GB2 (75%) and AA (91%) at a concentration of 2.074 x 10(-10) M. Thymidine release assay demonstrated the cytolytic activities of anti-GFAP mAbs towards these glioma cell lines, and this observation was confirmed by dye exclusion, which indicated the lysis of glioma cells after anti-GFAP mAbs treatment. Anti-GFAP mAbs had little effect (< or = 20%) on normal human lymphocyte, liver and intestine cell lines. These results look promising for radioimaging and immunotherapy of human gliomas.

Immunocytochemical localization of a novel radial glial intermediate filament protein

We have examined by immunocytochemistry the subcellular localization of a chick radial glial protein, named transitin, that by molecular cloning has been shown to be a novel member of the intermediate filament protein superfamily. In astrocytes cultured from E10 chick brain, transitin is localized to the intermediate filament network in accordance with its structural properties. Using confocal microscopy we examined the expression of transitin, vimentin and glial fibrillary acidic protein (GFAP) in cultured astrocytes, and show that transitin co-distributes with these other glial intermediate filament proteins. The expression of transitin, vimentin and GFAP was also compared in embryonic chick spinal cord and brain radial glia, with these studies showing that these intermediate filament proteins display distinct expression patterns during CNS development. Of particular note is the absence of vimentin and GFAP in spinal cord midline radial glia that express transitin protein, and a transient expression of transitin in brain midline radial glia that continue to express vimentin. Our studies presented here therefore indicate that transitin, a novel radial glial intermediate filament protein, may have functions that are unrelated to GFAP or vimentin during CNS development, since transitin is localized to the processes of midline radial glia and is transiently expressed during chick CNS development.

Regulation of vimentin expression and protease-mediated vimentin degradation during differentiation of human monocytic leukemia cells

Terminal differentiation of human monocytic leukemia THP-1 cells is induced in vitro by 12-O-tetradecanoylphorbol-13-acetate (TPA). We investigated the effects of TPA on the expression of vimentin during the differentiation of THP-1 cells at both the mRNA and the protein level. On northern blotting analysis, a 2.1 kb vimentin mRNA was up-regulated by TPA. On western blotting, small vimentin molecules with a molecular mass of approximately 40 kDa were observed in the soluble fraction and increased with TPA-induction of cellular differentiation. Since larger, including intact, vimentin molecules were detectable at a high TPA dose, we assessed the possible existence of protease activity directed against vimentin in THP-1 cells. With incubation of the cellular lysates of THP-1 cells, the endogenous vimentin became increasingly smaller over time, suggesting the presence of a vimentin-degrading protease. Phenylmethylsulfonyl fluoride inhibited this apparent protease activity against vimentin, suggesting the enzyme involved to be a serine protease. Interestingly, the protease activity was down-regulated by TPA treatment. TPA-treated THP-1 cells were found to express a vimentin-filament network based on immunocytochemical analysis using an anti-vimentin monoclonal antibody, V9. Taken together, these observations suggest that post-translational mechanisms work in cooperation with transcriptional regulation to maintain the vimentin-intermediate filament structure in differentiated THP-1 cells.

Association of influenza virus NP and M1 proteins with cellular cytoskeletal elements in influenza virus-infected cells

We have investigated the association of the influenza virus matrix (M1) and nucleoprotein (NP) with the host cell cytoskeletal elements in influenza virus-infected MDCK and MDBK cells. At 6.5 h postinfection, the newly synthesized M1 was Triton X-100 (TX-100) extractable but became resistant to TX-100 extraction during the chase with a t1/2 of 20 min. NP, on the other hand, acquired TX-100 resistance immediately after synthesis. Significant fractions of both M1 and NP remained resistant to differential detergent (Triton X-114, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate [CHAPS], octylglucoside) extraction, suggesting that M1 and NP were interacting with the cytoskeletal elements. However, the high-molecular-weight form of the viral transmembrane protein hemagglutinin (HA), which had undergone complex glycosylation, also became resistant to TX-100 extraction but was sensitive to octylglucoside detergent extraction, indicating that HA, unlike M1 or NP, was interacting with TX-100-insoluble lipids and not with cytoskeletal elements. Morphological analysis with cytoskeletal disrupting agents demonstrated that M1 and NP were associated with microfilaments in virus-infected cells. However, M1, expressed alone in MDCK or HeLa cells from cloned cDNA or coexpressed with NP, did not become resistant to TX-100 extraction even after a long chase. NP, on the other hand, became TX-100 insoluble as in the virus-infected cells. M1 also did not acquire TX-100 insolubility in ts 56 (a temperature-sensitive mutant with a defect in NP protein)-infected cells at the nonpermissive temperature. Furthermore, early in the infectious cycle in WSN-infected cells, M1 acquired TX-100 resistance very slowly after a long chase and did not acquire TX-100 resistance at all when chased in the presence of cycloheximide. On the other hand, late in the infectious cycle, M1 acquired TX-100 resistance when chased in either the presence or absence of cycloheximide. Taken together, these results demonstrate that M1 and NP interact with host microfilaments in virus-infected cells and that M1 requires other viral proteins or subviral components (possibly viral ribonucleoprotein) for interaction with host cytoskeletal components. The implication of these results for viral morphogenesis is discussed.

Keratin pattern in hyperkeratotic and ulcerated gastric pars oesophagea in pigs

Ulceration of the gastric pars oesophagea is a serious problem in the pig industry, and in spite of numerous studies the underlying mechanisms of the development of such ulcers remains largely unknown. The present study was designed first to test the hypothesis that the epithelium of the pars oesophagea of affected pigs would be more susceptible to the irritating action of acidic gastric content owing to a change in the pattern of expression of keratin, and second to look for a member of the keratin family that could be a suitable indicator of early lesions. Samples were collected from the gastric pars oesophagea of slaughter pigs with and without grossly visible mucosal changes, and the keratin patterns of normal and hyperkeratotic and ulcerated epithelium were compared immunohistochemically. The keratin pairs K 4/K 13, and K 5/K 14 were present in both normal and affected epithelia, and had a similar pattern of expression in both conditions. K 4 and K 13 were expressed in all the suprabasal layers, and K 5 and K 14 were expressed only in the basal and epibasal cells. Immunological reactivity with the monoclonal antibodies LL020 and LHK6-markers for hyperproliferative conditions-was present in the suprabasal layers of the epithelium of the hyperkeratotic and the ulcerated pars oesophagea but not in the normal epithelium. These results indicate that K 6 is expressed in association with the mucosal changes. The pattern of the intermediate filaments of keratin suggests that in basic to gastric ulcers in pigs there is an epithelial proliferation leading to visible hyperkeratosis.

Role of intermediate filaments in migration, invasion and metastasis

The expression of intermediate filament proteins is remarkably tissue-specific which suggests that the intermediate filament (IF) type(s) present in cells is somehow related to their biological function. However, in some cancers-particularly malignant melanoma and breast carcinoma, there is a strong indication that vimentin and keratin IFs are coexpressed, thus presenting as a dedifferentiated or interconverted (between epithelial and mesenchymal) phenotype. In this review, two in vitro models are presented which recapitulate the interconverted phenotype in human melanoma and breast carcinoma, and allow, for the first time, unique observations to be made with respect to the role of IFs in cancer progression. These studies have provided direct evidence linking overexpression of keratin IFs in human melanoma with increased migratory and invasive activity in vitro, which can be down-regulated by substituting dominant-negative keratin mutants. Overexpression of vimentin IFs in the breast carcinoma model leads to augmentation of motility and invasiveness in vitro, which can be transiently down-regulated by treatment with antisense oligonucleotides to vimentin. Additional experimental evidence suggests that the mechanism(s) responsible for the differential expression of metastatic properties associated with the interconverted phenotype rest(s) in the unique interaction, either direct or indirect, of IFs with specific integrins interacting with the extracellular matrix. In this review, we discuss the observations derived from the human melanoma and breast carcinoma models to address the hypothesis that the ability to coexpress vimentin and keratins confers a selective advantage to tumor cells in their interpretation of and response to signaling cues from the extracellular matrix. The ramifications of these observations are discussed with respect to the patholophysiology of the respective in situ tumors.