Cell configuration-related control of vimentin biosynthesis and phosphorylation in cultured mammalian cells

Targeted Modification of the Foot-And-Mouth Disease Virus Genome for Quick Cell Culture Adaptation

Foot-and-mouth disease virus (FMDV) causes the highly contagious foot-and-mouth disease, which is characterized by the appearance of vesicles in and around the mouth and feet of cloven-hoofed animals. BHK-21 cells are the cell line of choice for the propagation of FMDV for vaccine production worldwide but vary in their susceptibility for different FMDV strains. Previous studies showed that the FMDV resistance of a certain BHK cell line can be overcome by using a closely related but permissive cell line for the pre-adaptation of the virus, but the adapted strains were found to harbor several capsid mutations. In this study, these adaptive mutations were introduced into the original Asia-1 Shamir isolate individually or in combination to create a panel of 17 Asia-1 mutants by reverse genetics and examine the effects of the mutations on receptor usage, viral growth, immunogenicity and stability. A single amino acid exchange from glutamic acid to lysine at position 202 in VP1 turned out to be of major importance for productive infection of the suspension cell line BHK-2P. In consequence, two traditionally passage-derived strains and two recombinant viruses with a minimum set of mutations were tested in vivo. While the passaged-derived viruses showed a reduced particle stability, the genetically modified viruses were more stable but did not confer a protective immune response against the original virus isolate.

Adaption of FMDV Asia-1 to Suspension Culture: Cell Resistance Is Overcome by Virus Capsid Alterations

Foot-and-mouth disease virus (FMDV) causes a highly contagious disease with catastrophic economic impact for affected countries. BHK21 suspension cells are preferred for the industrial production of FMDV vaccine antigen, but not all virus strains can be successfully propagated in these cells. Serotype Asia-1 is often affected by this phenomenon. In this study, the Asia-1 strain Shamir was used to examine viral, cellular and environmental factors that contribute to resistance to cell culture infection. Cell media composition, pH and ammonium chloride concentration did not affect Asia-1 differently than other serotypes. Virus replication after transfection of viral genome was not impaired, but the adhesion to the cells was markedly reduced for Asia-1 in comparison to serotype A. The Asia-1 Shamir virus was successfully adapted to grow in the resistant cells by using a closely related but susceptible cell line. Sequence analysis of the adapted virus revealed two distinct mutations in the capsid protein VP1 that might mediate cell attachment and entry.

Comparative Proteomic Analysis of Three Chinese Hamster Ovary (CHO) Host Cells

Chinese hamster ovary (CHO) cells have been widely used to express heterologous genes and produce therapeutic proteins in biopharmaceutical industry. Different CHO host cells have distinct cell growth rates and protein expression characteristics. In this study, the expression of about 1,307 host proteins in three sublines, i.e. CHO K1, CHO S and CHO/dihydrofolate reductase (dhfr)^- , were investigated and compared using proteomic analysis. The proteins involved in cell growth, glycolysis, tricarboxylic acid cycle, transcription, translation and glycosylation were quantitated using Liquid chromatography tandem-mass spectrometry (LC-MS/MS). The key host cell proteins that regulate the kinetics of cell growth and the magnitude of protein expression levels were identified. Furthermore, several rational cell engineering strategies on how to combine the desired features of fast cell growth and efficient production of therapeutic proteins into one new super CHO host cell have been proposed.

Analysis of dermal papilla cell interactome using STRING database to profile the ex vivo hair growth inhibition effect of a vinca alkaloid drug, colchicine

Dermal papillae (DPs) control the formation of hair shafts. In clinical settings, colchicine (CLC) induces patients' hair shedding. Compared to the control, the ex vivo hair fiber elongation of organ cultured vibrissa hair follicles (HFs) declined significantly after seven days of CLC treatment. The cultured DP cells (DPCs) were used as the experimental model to study the influence of CLC on the protein dynamics of DPs. CLC could alter the morphology and down-regulate the expression of alkaline phosphatase (ALP), the marker of DPC activity, and induce IκBα phosphorylation of DPCs. The proteomic results showed that CLC modulated the expression patterns (fold>2) of 24 identified proteins, seven down-regulated and 17 up-regulated. Most of these proteins were presumably associated with protein turnover, metabolism, structure and signal transduction. Protein-protein interactions (PPI) among these proteins, established by Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, revealed that they participate in protein metabolic process, translation, and energy production. Furthermore, ubiquitin C (UbC) was predicted to be the controlling hub, suggesting the involvement of ubiquitin-proteasome system in modulating the pathogenic effect of CLC on DPC.

Fabrication of three-dimensional scaffolds using precision extrusion deposition with an assisted cooling device

In the field of biofabrication, tissue engineering and regenerative medicine, there are many methodologies to fabricate a building block (scaffold) which is unique to the target tissue or organ that facilitates cell growth, attachment, proliferation and/or differentiation. Currently, there are many techniques that fabricate three-dimensional scaffolds; however, there are advantages, limitations and specific tissue focuses of each fabrication technique. The focus of this initiative is to utilize an existing technique and expand the library of biomaterials which can be utilized to fabricate three-dimensional scaffolds rather than focusing on a new fabrication technique. An expanded library of biomaterials will enable the precision extrusion deposition (PED) device to construct three-dimensional scaffolds with enhanced biological, chemical and mechanical cues that will benefit tissue generation. Computer-aided motion and extrusion drive the PED to precisely fabricate micro-scaled scaffolds with biologically inspired, porosity, interconnectivity and internal and external architectures. The high printing resolution, precision and controllability of the PED allow for closer mimicry of tissues and organs. The PED expands its library of biopolymers by introducing an assisting cooling (AC) device which increases the working extrusion temperature from 120 to 250 °C. This paper investigates the PED with the integrated AC's capabilities to fabricate three-dimensional scaffolds that support cell growth, attachment and proliferation. Studies carried out in this paper utilized a biopolymer whose melting point is established to be 200 °C. This polymer was selected to illustrate the newly developed device's ability to fabricate three-dimensional scaffolds from a new library of biopolymers. Three-dimensional scaffolds fabricated with the integrated AC device should illustrate structural integrity and ability to support cell attachment and proliferation.

Equilibrium and non-equilibrium charge-dependent quantification of endothelial cell hydrogel scaffolds

Using equilibrium swelling and non-equilibrium membrane potential measurements, this study assesses the charge density in two representative series of polyelectrolyte hydrogels and examines the morphological and proliferative responses of endothelial cells as a function of the prepared charge offset. The neutral monomers 2-hydroxyethylmethacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (n = 1,000) (PEGDMA) were copolymerized with either the acidic monomer 2-sulfoethyl methacrylate (SEMA) or the basic monomer methacryloxy ethyltrimethylammonium chloride (MAETAC) to make membranes with pregelation charge offset concentrations varying from 0 to +/-200 mM. A thermodynamic analysis of swelling and membrane potential measurements quantified the hydrogel charge density state following equilibration at different ion strengths. Porcine pulmonary artery endothelial cells were seeded on samples of each HEMA and PEGDMA copolymer and the amount of cell coverage was measured over a 4-day period. Cellular attachment and proliferation increased with increasing proportions of charged monomers and showed a threshold pattern of attachment and growth on the positively charged HEMA-MAETAC copolymer hydrogels with increasing proportions of initially prepared charge. The series of PEGDMA copolymer hydrogels remained relatively resistant to cellular attachment and proliferation over the range of prepared charges considered in this study.

Carnosine stimulates vimentin expression in cultured rat fibroblasts

Two-dimensional electrophoretic gel profiles were compared between rat 3Y1 fibroblasts cultured in the presence and absence of 30 mM L-carnosine (beta-alanyl-L-histidine) for one week without any replenishment of medium. While a number of cellular proteins changed their expression levels by the addition of carnosine, we identified one of the most prominently varied proteins as vimentin. Immunoblot analysis with anti-vimentin antibody demonstrated that the vimentin levels increased about 2-fold after one-week culture in the presence of carnosine. We also confirmed that the increase of vimentin expression was dependent on the concentration of carnosine added to the medium. Moreover, when cultured cells were stained with anti-vimentin antibody and observed by light microscopy, most cells grown in the presence of carnosine were found to have markedly developed vimentin filaments. The increase of vimentin expression was also observed by adding with carnosine related dipeptides, N-acetylcarnosine and anserine.

Altering the state of phosphorylation of rat liver keratin intermediate filaments by ethanol treatment in vivo changes their structure

Dephosphorylation of keratin intermediate filaments (IF) in livers from ethanol-fed rats relative to controls occurs concurrently with a reorganization of the distribution of IF in the cells. One possible molecular mechanism for this reorganization is a phosphorylation-induced conformational change in the keratin that propagates as a change in the polymerization of the keratin subunits. To test this hypothesis, the structure of liver keratin IF, from both control and alcohol-fed rats, was explored by circular dichroism (CD), tryptophan fluorescence quenching, and 13C nuclear magnetic resonance (NMR). Keratin IF were isolated from livers of control rats and from livers of rats that had ethanol included in their feed for 6-40 weeks. A significant decrease in the intensity of the CD spectrum of keratin IF from livers of ethanol-treated animals, relative to controls, was observed. These data suggested either that a change in conformation or an increase in conformational motility in the keratin IF from ethanol-treated animals occurred as a result of the ethanol-induced dephosphorylation. 13C NMR data were obtained to distinguish between these two possibilities. An increase in resonance intensity of some 13C NMR resonances was observed in the keratin IF from livers of ethanol-treated animals, relative to controls. The CD and NMR data were therefore consistent with an increase in conformational motility of the rod domain in these keratin IF. No significant change was observed in the quenching of tryptophan fluorescence by KI. The change in protein dynamics detected in these experiments could be the molecular basis for the alteration of keratin IF organization in alcoholic hepatitis.

Site-specificity of ethanol-induced dephosphorylation of rat hepatocyte keratins 8 and 18: A 31P NMR study

Chronic feeding of ethanol to rats results in disorganization of the keratin intermediate filament network within hepatocytes. Previous studies from this laboratory have shown that intermediate filament organization in cultured cells is related to the phosphorylation state of the proteins. Therefore, we have examined the phosphorylation state of hepatocyte keratins from control and ethanol-fed rats. Feeding ethanol to rats results in dephosphorylation of one site on keratin 8 and one site on keratin 18 at all time points beginning with 6 weeks of ethanol treatment. Dephosphorylation was detected by phosphate analysis and by two-dimensional electrophoresis in which a change in isoelectric point of keratins from ethanol-fed rats was observed. These observations indicate that dephosphorylation of keratins in ethanol-fed animals may be an early step in alcoholic hepatitis which has occurred by 6 weeks of ethanol treatment. To further characterize keratin dephosphorylation in ethanol-fed rats, we used 31P NMR spectroscopy to classify the dephosphorylation site(s). Hepatocyte keratins were purified and solubilized in 9.5 M urea, 10 mM Tris-Cl, pH 8.1. 31P NMR spectra were obtained at 109 MHz, in 10 mm tubes at 30 degrees C. Samples of hepatocyte keratins were phosphorylated with A-kinase, protein kinase C, casein kinase II or Ca/CAM kinase and these samples were analyzed by 31P NMR spectroscopy. The resulting spectra were used as standards to compare the 31P chemical shifts of the resonances produced by these kinases with the phosphorus resonances of control and experimental samples. The 31P NMR spectrum of control hepatocyte keratins shows three resonances at 0.7, 4 and 5 ppm. In vitro phosphorylation by A-kinase produces a resonance at 4 ppm which is distinctly different from the resonance produced by each of the other kinases. In hepatocyte keratins from ethanol-fed animals, the resonance at 4 ppm was missing from the spectrum. These observations indicate that the keratin site that is dephosphorylated in ethanol-fed rats is characterized by the same 31P chemical shift as the keratin site that is phosphorylated by A-kinase.

Ultrastructural co-localisation of vimentin and cytokeratin in visceral glomerular epithelial cells of dogs with glomerulonephritis

The expression of cytokeratin and vimentin was studied in the glomerular epithelial cells of canine kidneys with and without glomerular abnormalities. Using ultrastructural, immunogold single and double labelling techniques, cytokeratin and vimentin were found together in the visceral glomerular epithelial cells (vGECs) of abnormal kidneys. In normal kidneys, the vGECs expressed only vimentin, and cytokeratin was found exclusively in parietal glomerular epithelial cells (pGECs). These results confirm previous findings in the same animals, obtained by immunohistological staining techniques.

Tubular vimentin metaplasia in canine nephropathies

The expression of the intermediate filament vimentin was examined immunocytochemically in 17 cases of histologically confirmed primary canine nephropathy, and compared with its expression in normal canine kidney. In normal renal tissue, the expression of vimentin was restricted to glomerular elements, but in all cases of chronic interstitial nephritis it extended to the cortical tubular epithelia, and was correlated with the degree of tubulo-interstitial damage. Three of four cases of renal cell carcinoma had vimentin reactivity in neoplastic cells. In only one case of familial renal disease was vimentin expressed in scattered epithelial cells of the cortical tubules.

Evidence of cytokeratin expression in canine visceral glomerular epithelial cells in vivo

Visceral glomerular epithelial cells (vGECs) originate from a mesenchymal blastema and transiently express cytokeratin during embryogenesis. There are no reports of cytokeratin expression in vGECs of mature, normal or damaged, human or other mammalian kidneys in vivo, but in vitro studies have provided evidence of the synthesis of cytokeratin in cultured vGECs. Cytokeratin expression was observed in vGECs in the damaged kidneys of four dogs with spontaneous renal diseases and, by using monoclonal antibodies, type 18 cytokeratin was identified. vGECs are apparently able to (re-) activate in vivo a mechanism for switching on the synthesis of cytokeratin in damaged glomeruli.

Cloning of cDNAs with possible association with senescence and immortalization of human cells

Normal human diploid fibroblasts (HDF) have a finite life span in vitro and have been used as a model system for the study of in vivo aging. Little is known about how changes in gene expression may affect the immortalization of human fibroblasts. We looked for cDNA clones whose mRNAs were differentially expressed between mortal senescent SV40-transformed human fibroblasts (B-32) and the immortal counterparts (B-32F) derived from B-32 cells. We identified three cDNA isolates by subtractive differential hybridization with 32P-labeled cDNA probes from B-32 cells and B-32F cells. Nucleotide sequence analysis of these cDNA clones revealed that they were homologous to the human vimentin, a human mitochondrial gene and a human gene of unknown nature. Slot blot and Northern blot analyses demonstrated that the former two were preferentially expressed in senescent B-32 cells and the last one was less expressed in B-32F immortal cells.

PKC mediates 12(S)-HETE-induced cytoskeletal rearrangement in B16a melanoma cells

The fatty acid 12(S)-HETE may be a new second messenger capable of activating PKC. In tumor cells 12(S)-HETE stimulates cytoskeleton-dependent cellular responses such as adhesion and spreading. Analysis of 12(S)-HETE effects on B16a melanoma cell cytoskeleton revealed reversible rearrangement of microtubules, microfilaments, the actin-binding proteins, vinculin, myosin heavy (MHC) and light chains (MLC), as well as bundling of vimentin intermediate filaments. The alterations in microfilaments and intermediate filaments occurred very rapidly, i.e., 5 min after exposure of tumor cells to 12(S)-HETE. The 12(S)-HETE-induced cytoskeletal alterations were accompanied by centrifugal organelle-translocation. Interestingly, MLC exhibited clear association with the cytoplasmic organelles. Biochemical analysis of the 12(S)-HETE effect indicated a PKC-mediated reversible hyperphosphorylation of MLC, vimentin, and a 130 kD cytoskeletal-associated protein. Optimal effects were obtained after 5 min treatment with 12(S)-HETE at 0.1 microM concentration. 12(S)-HETE pretreatment induced tumor cell spreading on a fibronectin matrix which required the intactness of all three major cytoskeletal components. The spreading process was dependent upon the activity of PKC. Our data suggest that 12(S)-HETE is a physiological stimulant of PKC. Further, it induces rearrangement of the cytoskeleton of tumor cells in interphase resulting in the stimulation of cytoskeleton-dependent cell activity such as spreading.

The lipoxygenase metabolite 12(S)-HETE induces a cytoskeleton-dependent increase in surface expression of integrin alpha IIb beta 3 on melanoma cells

Integrin receptors are mediators of cell-extracellular matrix and cell-cell interactions. Biochemical and immunocytochemical evidence shows that the platelet integrin receptor alpha IIb beta 3 is present on the cell surface, at focal adhesion plaques and in the perinuclear region of metastatic B16a murine melanoma cells. Antibody to the fibronectin receptor alpha 5 beta i, inhibits basal adhesion by approx. 30%, whereas antibodies to alpha IIb beta 3 are ineffective. The surface immunoreactivity of tumor cells for alpha IIb beta 3 can be enhanced by pre-treatment (5 min) with a lipoxygenase metabolite of arachidonic acid [i.e. 12-(S)-HETE] in a dose-dependent manner (max. effect approx. 0.1 microM). Other lipoxygenase metabolites are ineffective. B16a cells possess a large intracellular pool of alpha IIb beta 3, from which the receptor complex translocates to the cell surface following 12-(S)-HETE pretreatment. This pre-treatment of tumor cells enhances their adhesion to fibronectin, which is mediated exclusively by alpha IIb beta 3 receptors. 12-(S)-HETE also facilitates the redistribution of alpha IIb beta 3 in the plasma membrane with localization at the focal adhesion plaques. The cytoskeleton of the B16a cell is characterized by an absence of distinct microtubules in interphase cells and the presence of prominent microfilaments and vimentin intermediate filaments. In B16a cells, the disruption of intermediate filaments and/or microfilaments prevents the 12-(S)-HETE-induced increase in plasma membrane alpha IIb beta 3 and enhanced tumor-cell adhesion to fibronectin. The microtubule-disrupting agent, colchicine, is ineffective in both respects. We conclude that the lipoxygenase metabolite of arachidonic acid, 12-(S)-HETE, regulates the surface expression and function of the alpha IIb beta 3 integrin in B16a cells. Further, these data support the hypothesis that microfilaments and intermediate filaments have a profound role in regulating the expression of a multifunctional integrin in B16a tumor cells.

Altered expression of keratin and vimentin in human retinal pigment epithelial cells in vivo and in vitro

Actively proliferating human retinal pigment epithelial (RPE) cells grown in tissue culture possess keratin-containing intermediate filaments that react with a combination of AE1 and AE3 anti-keratin monoclonal antibodies. Antibody reactivity is lost, however, from RPE cells as the cell population ceases to proliferate when it approaches confluence and attains morphological characteristics more similar to those in vivo. In contrast, clone 8.13 anti-keratin antibody stains all cells in the culture at all stages of the growth cycle and cell densities. These findings were reflected in vivo using retinal pigment epithelium taken directly from the eye. Normal non-proliferating RPE cells bound 8.13 antibody to cytoskeletal structures, as judged by indirect immunofluorescence, but did not bind AE1/AE3 antibodies. However, proliferating dedifferentiated RPE cells from the vitreous humor of patients with proliferative vitreoretinopathy possess filaments that bind both AE1/AE3 and 8.13 antibodies. Thus it appears that structures detected by AE1/AE3 antibodies only occur in actively growing RPE cells in vitro and in vivo. Keratins produced by RPE cells were identified using Western blotting. Species with molecular masses of 54 (keratin 7), 52 (keratin 8), 42 (keratin 18), and 40 (keratin 19) kiloDaltons were the most abundant in proliferating cultured cells, but cells isolated directly from the eye were found to lack keratin 7 and 19. Keratin 19 was, however, observed in proliferating RPE cells from some patients with proliferative vitreoretinopathy. The latter findings explain the differential staining observed with AE1/AE3 antibodies in cells in culture and isolated directly from the eye since these antibodies interact primarily with keratin 19 which is absent from non-proliferating RPE cells. In contrast to the presence of keratin-containing intermediate filaments in human RPE cells in vivo, there are apparently no detectable vimentin-containing cytoskeletal structures. However, all RPE cells cultured in vitro develop filaments composed of vimentin which persist in cells that have reached confluence.

Experimentally induced murine rhabdomyosarcomas--correlation between cellular contacts, matrix formation and cellular differentiation

Rhabdomyosarcomas (RMSs) consist of a mixture of primitive mesenchymal cells as well as cells showing various stages of rhabdomyomatous differentiation. The qualitative and quantitative degree of the rhabdomyomatous differentiation of the cells, evaluated by their morphology and expression of defined structural and functional proteins, is accepted as the basis of diagnosis and is considered to be related to the biological behaviour of RMSs. Therefore we investigated solid experimentally induced murine RMSs, adherent (subconfluent, confluent) cell cultures obtained therefrom, and also suspension cultures and studied the expression of muscular differentiation markers (vimentin, desmin, myoglobin) and the formation of extracellular matrix components (fibronectin, laminin). When we compared solid tumours with adherent cell cultures of decreasing cell densities (confluent up to single cells) and with cells grown in suspension, we found a gradual decline of differentiation ("dedifferentiation"). This decline paralleled the decrease of cell-cell and cell-substrate contacts. In suspension cultures, cells were prevented from interacting with each other and the substratum, no rhabdomyomatous differentiation of the cells took place. If restoration of cellular contacts was allowed, either by adherent growth or by reinoculation into nude mice, the process of dedifferentiation was completely reversible. Consequently, it was demonstrated that the increase of cell-cell and cell-substrate contacts was strongly associated with the appearance or increasing expression of the desmin intermediate filament cytoskeleton and with formation of the extracellular matrix components fibronectin and laminin. The microfilament (F-actin) system was modulated from an impressive stress-fiber system in subconfluent to a dense network in confluent monolayers. The extent of cell-substrate contacts, mediated by extracellular matrix components, and the number of cell-cell interactions are responsible for the capability of a malignant mesenchymal cell, which is able to undergo rhabdomyomatous differentiation, to achieve the various stages of maturation.

Cytoskeletal organization and synthesis in substrate-independent and -dependent myogenesis in chick embryos

Chick embryo myoblasts were fused in suspension culture to form myoballs by modification of previous procedures that excluded the use of divalent ion chelators and antimitotic drugs and included the continuous presence of serum in order to analyze the organized appearance and synthesis of major cytoskeletal proteins during cell attachment and spreading. The organization of the major cytoskeletal proteins actin, tubulin, and vimentin was assessed by fluorescence microscopy under these conditions as well as under conditions in which the myoballs were allowed to attach and spread on a collagen-coated substrate. Actin, detected by fluorescence microscopy, stained myoballs diffusely and was reorganized to form stress fibers in the attached and spreading myoball. Nuclei were segregated to a centrally located lattice of microtubules. The microtubule-specific drugs nocodazole and taxol prevented myoball spreading and the establishment of myotube polarity, respectively. Vimentin appeared as wavy ribbons in a perinuclear position around attached and spreading myoballs. In parallel studies, the synthesis of these cytoskeletal proteins was analyzed by radioisotopic labeling and polyacrylamide gel electrophoresis. These studies showed that myoballs possess altered ratios of actin and tubulin isoforms and of phosphorylated and nonphosphorylated vimentin compared to myotubes. These ratios rapidly change to the myotube pattern when myoballs are allowed to attach to solid substrata. Thus, although both myoballs and myotubes undergo muscle-specific differentiation, their cytoskeletal proteins are morphologically and biochemically distinct.

Application of two-dimensional gel electrophoresis in the study of cytoskeletal protein regulation during growth activation and differentiation

Two-dimensional gel electrophoresis was used to study the regulation of cytoskeletal protein synthesis during growth activation and development of the differentiated phenotype. We demonstrated a correlation between the state of organization and the expression of the respective cytoskeletal protein by showing that depolymerization of microtubules leads to a rapid decrease in new tubulin synthesis. We found that the synthesis of vimentin in both fibroblasts and epithelial cells correlates with extensive cell spreading on the substrate, while cytokeratin synthesis is maximal when cell to cell contacts are abundant. The analysis of cytoskeletal elements, involved directly in the formation of cell contacts, revealed that the level of vinculin synthesis is dependent on the extent of adherent type of cell contacts formed. Moreover, we found that the transient disappearance of vinculin from adhesion plaques of quiescent fibroblasts in response to serum factors was followed by an induction of vinculin mRNA and protein synthesis. The morphological changes associated with establishment of the differentiated phenotype were also found to include changes in the expression of the cytoskeletal-extracellular matrix complex. This was demonstrated in several differentiating systems: in 3T3 preadipocytes which change their shape from a fibroblastic to a spherical shape when stimulated to differentiate with adipogenic medium, we observed a decrease in mRNA levels and in the synthesis of fibronectin, beta-integrin, and the microfilament proteins, vinculin, alpha-actinin, tropomyosin and actin. The culturing of these cells on a certain extracellular matrix prevented the morphological changes occurring in the presence of adipogenic medium and blocked the shifts in cytoskeletal- and differentiation-related gene expression. Similar changes in the organization and expression of cytoskeletal proteins were identified during maturation of primary ovarian granulosa cell cultures, stimulated with gonadotropic hormones to form highly steroidogenic cells. The cell rounding and aggregation occurring during this process were associated with a decreased synthesis of vinculin, alpha-actinin, actin and the nonmuscle tropomyosins. The physiological relevance of these changes was suggested by the observation that the level of tropomyosin mRNA was lower in follicles of animals at late stages of granulosa cell maturation when compared to earlier stages. The expression of tissue-specific and cytoskeletal proteins was also determined in primary cultures of liver hepatocytes, maintained under conditions either favorable for growth or for expression of liver-specific functions. When DNA synthesis was elevated, cytoskeletal protein synthesis was high and that of liver-specific proteins was low.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of fibronectin, integrin and cytoskeleton expression in differentiating adipocytes: inhibition by extracellular matrix and polylysine

The differentiation of 3T3 preadipocytes into adipocytes is characterized by major changes in cell morphology from a fibroblastic to a rounded shape and by the induction of gene expression related to lipid metabolism. We have studied the synthesis and mRNA levels of proteins involved in the formation of cell-matrix contacts and in defining cell shape to determine the role and molecular basis of these morphological changes during adipose conversion. When confluent preadipocyte cultures were stimulated with adipogenic medium there was a gradual decrease in the expression of fibronectin, beta-integrin, actin and in the microfilament-associated proteins vinculin, alpha-actinin and tropomyosin. The changes in extracellular matrix and cytoskeletal mRNA levels were apparent before the accumulation of glycerophosphate dehydrogenase (GPD) mRNA and continued during the massive increase in GPD mRNA level. The culturing of preadipocytes on an extracellular matrix deposited on the dish by corneal endothelial cells, or on substrata coated with polylysine, prevented the morphological changes, the decrease in the level of assembled actin, the accumulation of lipid and the shifts in the expression of integrin, cytoskeletal proteins and GPD. In cells cultured on malleable hydrated collagen gels, adipocyte differentiation proceeded at normal rates. The results suggest that the regulated expression of proteins involved in the formation of the transmembrane linkage between the extracellular matrix and the microfilaments are programmed regulatory events that affect cell adhesion and thereby cell shape during adipocyte differentiation.

Expression of vimentin by cultured astroglia and oligodendroglia

The objective of this study was to determine whether vimentin expression by process-bearing astroglia and oligodendroglia cultured from neonatal rat cerebral cortex resembled that in brain where vimentin is common in immature astroglia and a few subpopulations of mature astroglia, but is absent in oligodendroglia. Vimentin expression was detected by immunofluorescence microscopy using a monoclonal antibody (V9) against porcine lens vimentin in combination with either antiserum against the astroglial marker, glial fibrillary acidic protein (GFAP), or with antiserum against the oligodendroglial marker, galactocerebroside (GC). Specificity of the antivimentin antibody was indicated on immunoblots of process-bearing cell proteins separated by two-dimensional polyacrylamide gel electrophoresis. Enrichment of cultures for either GFAP+ astroglia or GC+ oligodendroglia was achieved by supplementation of the culture medium with fetal calf serum at 10% or 0.5%, respectively. Process-bearing cells maintained in 10% serum exhibited heterogeneity in their expression of GFAP and vimentin. Approximately half of the cells were GFAP+/vimentin+ throughout the 2-week culture period examined. GFAP+/vimentin- cells were a minor population at early times (3-4 days) in culture, but accounted for 40% of process-bearing cells after 2 weeks. Cultures maintained in reduced (0.5%) serum and stained for GC and vimentin also exhibited heterogeneity. Both GC+/vimentin+ and GC+/vimentin- cells were observed, with vimentin+ cells composing two-thirds and one-half of the GC+ population after 3 and 6 days, respectively, in reduced serum. The high incidence of vimentin expression by process-bearing astroglia and oligodendroglia suggests that these cultures contain glia in a relatively early stage of development.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of vimentin in the reverse transformation reaction

An organized cytoskeleton is required for the cAMP-induced reverse transformation reaction in CHO-K1 cells. In the course of the reaction a considerable fraction of the genome changes its nuclease sensitivity. The current paper presents the following evidence that cAMP-induced phosphorylation of vimentin is an early step in this reaction complex. (i) Vimentin is only slightly phosphorylated in transformed CHO-K1 cells but is heavily phosphorylated in normal fibroblasts. (ii) cAMP addition almost triples the vimentin phosphorylation of CHO-K1 cells but does not change that of normal cells. (iii) Vimentin phosphorylation is one of the earliest phenomena to occur after addition of cAMP to CHO-K1 cells, preceding the cell-stretching reaction and other manifestations of reverse transformation. (iv) Indirect immunofluorescence experiments demonstrate that vimentin appears as a condensed mass in transformed CHO-K1 cells but cAMP addition restores the filamentous structure characteristic of the normal fibroblast. (v) Other transformed cells unresponsive to reverse transformation by cAMP failed to demonstrate increased phosphorylation of vimentin on treatment with cAMP. These results support the proposed scheme that phosphorylation of cytoskeletal elements initiates a large-scale genetic regulatory action in which a substantial change in the spectrum of genome exposure and sequestration occurs. A function for intermediate filaments in reverse transformation is implied.

Alterations in intermediate filament proteins in rat kidney proximal tubule epithelial cells

Changes in the intermediate filament composition of rat kidney proximal tubule cells in culture have been investigated. The data suggest that differentiated tubular epithelial cells do not express vimentin, but vimentin expression is induced when the cells begin to proliferate in culture. The cultured cells are positive for both cytokeratins and vimentin by immunofluorescence microscopy. The data support the concept that the intermediate filament composition of proximal tubule epithelial cells can be altered during proliferation induced by nephrotoxic chemicals or by neoplastic transformation.

Vimentin and glial fibrillary acidic protein filaments in radial glia of the adult urodele spinal cord

This work, based on Golgi impregnations, transmission electron microscopy and immunocytochemistry, demonstrates that the intermediate filaments found in the radial gliocytes of the adult newt spinal cord are both vimentin and glial fibrillary acidic protein (GFAP) structures. Gliocytes appeared as large, arboreous cells, with appendages extending peripherally. They were extensively immunolabelled with both anti-vimentin and anti-GFAP monoclonal antibody conjugates. Outstanding correspondence in cell configuration was found when Golgi-impregnated specimens were compared to the distribution of immunolabels. Electron micrographs showed cytoplasmic bundles of anti-vimentin decorated intermediate filaments occupying the radial projections. The presence of GFAP confirms the astroglial character of the radial glia in urodeles; the existence of vimentin suggests that the spinal cord of the adult animal retains immature astroglia, which should express enlarged capabilities of adaptation.

Differential immunoreactivity and Ca2+-dependent degradation of vimentin in human fibroblasts and fibrosarcoma cells

Immunostaining of normal human fibroblasts with a monoclonal antibody (MAb) (V22AC12) revealed typical cytoplasmic arrays of vimentin filaments in both mitotic and interphase cells. In human A8387 fibrosarcoma cells and SV40-virus-transformed human fibroblasts, the same antibody showed positivity only in mitotic cells and in interphase cells only after treatment of the fixed cells with alkaline phosphatase. Upon immunoblotting with the MAb, an Mr 57,000 vimentin polypeptide was seen in normal fibroblasts. In fibrosarcoma cells the same polypeptide was revealed by this antibody only after treatment with alkaline phosphatase. The Mr 57,000 vimentin polypeptide was a major cytoskeletal protein in both fibroblasts and fibrosarcoma cells. Inclusion of Ca2+ into the cytoskeleton extraction medium brought about a somewhat increased degradation of vimentin in fibroblasts. In fibrosarcoma cells, such treatment caused a quantitative disappearance of the Mr 57,000 protein with a concomitant appearance of 3 distinct, low-molecular-weight degradation products in the detergent-soluble fraction. Another Ca2+-induced change in the polypeptide profile of fibrosarcoma cells was the disappearance of the Mr 240,000 non-erythroid alpha-spectrin and the concomitant appearance of a prominent Mr 140,000 degradation product. Inclusion of proteolysis inhibitors in the Ca2+-supplemented extraction medium inhibited degradation of both vimentin and alpha-spectrin polypeptides. The results suggest differences in the composition of the cytoskeletons of normal fibroblasts and fibrosarcoma cells, manifested in the differential Ca2+-susceptibility of vimentin and non-erythroid alpha-spectrin. Results with MAb V22AC12 suggest that differential phosphorylation of vimentin could account for at least part of this difference.

Cell-cell and cell-matrix interactions differentially regulate the expression of hepatic and cytoskeletal genes in primary cultures of rat hepatocytes

Freshly isolated adult rat hepatocytes exhibit a flat, extended morphology when cultured on dried rat tail collagen in the presence of growth factors; they actively synthesize DNA and express high levels of cytoskeletal mRNAs and proteins (actin, tubulin, cytokeratins, vinculin, alpha-actinin, and desmoplakin), while exhibiting low levels of liver-specific mRNAs (albumin, alpha 1-inhibitor III, and alpha 1-antitrypsin) and limited synthesis and secretion of albumin. Hepatocytes cultured on hydrated gel matrix from the Engelbreth-Holm-Swarm (EHS) mouse tumor form small spherical aggregates and exhibit low DNA, cytoskeletal mRNA, and protein synthesis, while at the same time exhibiting elevated liver-specific mRNAs and albumin production; these cells, therefore, more nearly conform to the program of gene expression seen within the normal animal. Hepatocytes on hydrated rat tail collagen resemble those on dry collagen when cultured at low density, but at high density they form compact trabecular aggregates, synthesize negligible amounts of DNA, and maintain a pattern of gene expression resembling that of hepatocytes seeded on the EHS matrix. If cell morphology is compact, as on EHS or on hydrated rat tail collagen when densely populated, DNA synthesis and expression of cytoskeletal genes are low, while liver-specific mRNAs are abundant. When cells are extended the opposite is the case. Without the growth supplement DNA synthesis is low throughout but gene expression is little affected. These studies point to the importance of cell-cell and cell-matrix interactions in determining the differentiated phenotype of hepatocytes, and they reveal an inverse relationship between cytoskeletal and liver-specific protein expression.

Regulation of gene expression in adult rat hepatocytes cultured on a basement membrane matrix

Freshly isolated adult rat hepatocytes, when cultured on type I collagen (commercially available as Vitrogen), assume a polygonal shape, form a stable monolayer within 24 hours, but lose the capacity to express some liver-specific functions over time in culture. We incubated hepatocytes in a serum-free medium on a reconstituted basement membrane gel, "matrigel" (prepared from an extract of extracellular matrix of the murine Engelbreth-Holm-Swarm sarcoma), and observed that the cells adhered firmly, remained rounded as single cells or clusters, and maintained liver-specific gene expression for more than 1 week in vitro. Hepatocytes on matrigel secreted substantially higher amounts of albumin, transferrin, haptoglobin, and hemopexin, Northern blot analyses of extracted cellular RNA, expressed increased amounts of mRNA for the liver-specific protein albumin (as compared with cells on vitrogen). In cultures treated with phenobarbital, cytochrome P-450b, and cytochrome P-450e, mRNAs and proteins were barely detectable in cells on Vitrogen but were induced to levels similar to those in the liver in vivo in matrigel cultures. Likewise, the use of matrigel greatly enhanced the induction of mRNA and protein for P-450c by 3-methylcholanthrene and for P-450p by steroidal and nonsteroidal inducers. However, neither substratum permitted induction of P-450d by 3-methylcholanthrene, suggesting that the effects of matrigel are selective even for expression in liver of members of the superfamily of cytochrome P-450 genes. Within 5 days in cultures on Vitrogen, hepatocytes expressed detectable amounts of fetal liver aldolase activity and also mRNA for vimentin and type I collagen, each considered a phenotypic change reflecting hepatocyte "dedifferentiation." None of these was present in cells on matrigel. Responsiveness to mitogenic stimuli, as judged by incorporation of 3H-thymidine into DNA, was also decreased in hepatocytes cultured on matrigel. Finally, there was a remarkable increase in the levels of both matrices during the first 2 days in culture. However, the continuously cytoskeleton mRNA over time in culture than did the rounded cells on matrigel. We conclude that hepatocytes cultured on matrigel, as opposed to the standard collagen, exhibit remarkably enhanced expression of many liver-specific functions.

Participation of cytoskeletal intermediate filaments in the infectious cycle of human respiratory syncytial virus (RSV)

RSV infection of Hep-2 or HeLa cells leads to biochemical and morphological changes of cytoskeletal intermediate filaments (IF). Thus, human cytokeratin 18 is modified to generate a more acidic polypeptide of slightly larger apparent molecular weight. In addition, the amounts of vimentin and other cytokeratins are reduced, probably as a consequence of proteolytic degradation. These changes are reflected in a decrease of immunofluorescence with specific antibodies in RSV-induced syncytia and a more disorganized arrangement of IF arrays. About 50% of virus nucleoprotein (NP) is extracted with the high salt and detergent-insoluble intermediate filament fraction. Pulse-chase experiments indicate that NP needs a maturation period after synthesis to associate with IF. It is suggested that RSV needs to interact with IF during its life cycle and that association of NP, and/or other viral components, with IF might then lead to cytoskeletal structures becoming unstable in RSV-infected cells.

Regulation of human mesothelial cell differentiation: opposing roles of retinoids and epidermal growth factor in the expression of intermediate filament proteins

We report here the discovery that retinoids are potent regulators of epithelial morphology and keratin expression in cultured human mesothelial cells. When LP-9 cells are cultured in medium supplemented with vitamin A-depleted serum, they grow with an extreme spindle-shaped morphology and synthesize abundant levels of vimentin, but very little keratin. When retinoic acid is added to the medium at 1 X 10(-8) to 1 X 10(-6) M, keratin synthesis is increased, vimentin synthesis is decreased, and the cells assume an epithelioid morphology. Keratin synthesis, but not epithelioid morphology, seems to be dependent on cell density as well: even when vitamin A is present, sparse cultures cannot fully maintain keratin synthesis. In contrast, epidermal growth factor (EGF) acts in an antagonistic fashion to suppress both keratin synthesis and epithelial morphology. The effects of vitamin A, EGF, and cell shape on intermediate filament (IF) expression seem to occur in a growth-independent manner, and they appear to be at the level of transcription or mRNA stability. Even so, their effects on IF expression do not appear to be rapid ones, and hence it is unlikely that these agents interact directly at the gene level to cause changes in IF gene expression.

Coexpression of keratin and vimentin in damaged and regenerating tubular epithelia of the kidney

Most renal cell carcinomas coexpress vimentin and keratin, while renal tubular epithelia express only keratin. Investigation of the intermediate filament composition of tubular epithelia in diseased rat and human kidneys now shows that altered tubular epithelia unequivocally coexpress keratin and vimentin. In rats, pronounced coexpression of vimentin and keratin was observed in chronic nephrosis induced by daunomycin, and the extent of coexpression seemed to increase with the incidence of altered collapsed and cystically dilated tubules and with the degree of tubular epithelial proliferation. It was also seen during tubular regeneration after acute tubulotoxic injury induced by mercury chloride poisoning, with vimentin expression being lost in fully regenerated tubular epithelium. In man, expression was seen in chronically and irreversibly damaged kidneys. Thus, vimentin can be expressed temporarily in acutely and reversibly damaged kidneys and chronically in irreversibly damaged kidneys. Vimentin could perhaps be regarded as an indicator of the regenerating and proliferating activity of tubular lesions.

Gonadotropin-induced differentiation of granulosa cells is associated with the co-ordinated regulation of cytoskeletal proteins involved in cell-contact formation

The gonadotropin-induced differentiation of granulosa cells in culture was studied, with particular attention being given to the organization and expression of cytoskeletal proteins involved in the formation of cell contacts, as well as to progesterone production. Gonadotropin-treated granulosa cells formed clusters of spherical cells containing few vinculin-containing focal contacts, exhibited a diffuse distribution of actin, and had few adherens junctions but more gap junctions than cells grown without the hormone. In gonadotropin-treated cells, the levels of synthesis of the cytoskeletal proteins, vinculin, alpha-actinin, and actin, were dramatically reduced, but the synthesis of the tubulins and vimentin was unaffected. Decreased levels of synthesis of these cytoskeletal proteins were also observed in an in vitro translation assay using poly(A)+ RNA from gonadotropin-treated cells. The hybridization of cytoplasmic RNA with cloned actin and vimentin cDNAs revealed a marked decrease in actin-RNA levels, but no change in vimentin-RNA levels in these cells. Such alterations in cytoskeletal-protein expression were also observed in cells treated with compounds that cause elevated cellular cAMP levels by acting at a stage beyond gonadotropin receptor stimulation. Furthermore, by keeping the cells in a spherical configuration in suspension culture, or by treating the cells with cytochalasin B, similar changes in the synthesis of these cytoskeletal proteins were observed. During this process, there was a concomitant increased in the production of progesterone (although to a much lesser extent in suspension culture) that occurred in parallel with the appearance of large mitochondria with lamellar-tubular cristae and a well-developed smooth endoplasmic reticulum, these features being characteristic of granulosa-lutein cells in vivo. Our results suggest that changes in cell shape and contact, together with the regulation of cytoskeletal elements that determine cellular morphogenesis, are part of the gonadotropin-controlled differentiation program in granulosa cells and may also occur during the maturation of these cells in vivo.

Modulation of fibronectin gene expression in chondrocytes by viral transformation and substrate attachment

Chicken vertebral chondrocytes, which normally grow in suspension, synthesize large amounts of cartilage extracellular matrix proteins, but little fibronectin. We have analyzed the effects of both substrate attachment and transformation with a temperature-sensitive mutant of Rous sarcoma virus on fibronectin gene expression in these cells. Our experiments show that viral transformation increases fibronectin synthesis to a greater extent than substrate attachment. Furthermore, transformed chondrocytes have lost the ability to decrease fibronectin synthesis in response to suspension culture, suggesting that transformation alters the normal attachment-responsive control of fibronectin gene expression. Finally, infected substrate-attached chondrocytes shifted to the nonpermissive temperature for transformation use fibronectin RNA more efficiently in protein synthesis than cells grown under the other conditions, suggesting for the first time a role for translational control of fibronectin gene expression.

Glial filament protein expression in astroglia in the mouse visual pathway

We have studied the onset of expression of glial filament protein (GFP) in astrocytes along a single axon trajectory, the mouse retinal axon pathway, and the relationship of GFP expression to maturation of astroglial morphology. In fetal optic nerve from embryonic day (E) 12 to E16, primitive glia (neuroepithelial cells) lack GFP, but express vimentin and contain intermediate filaments. GFP is expressed at E17 in two gradients: cells in the optic nerve become GFP-positive first in the borders of the nerve, then in the central nerve by postnatal day (P)0. The second gradient is a distoproximal one, with GFP appearing in the optic nerve at E17, in the optic chiasm by PO, and in the optic tract by P3. The expression of GFP in the optic nerve marks the transformation of radial neuroepithelial cells to multipolar astroglia, accomplished by outgrowth of filament-rich glial processes tipped by a growth cone. Several days after the onset of GFP expression in each portion of the pathway astrocytes exhibit a transient increase in staining, and resemble reactive astrocytes after injury. During this period, filaments are arranged in densely packed bundles, and appear coalesced at points. Thus, primitive glial cells in optic nerve express vimentin. In the retinofugal pathway, GFP is expressed in a distinct spatiotemporal sequence from optic nerve to optic tract. Finally, in contrast to neurons, the extension of astroglial processes is accompanied by the increased expression and assembly of intermediate filaments.

Coordinate regulation of stromelysin and collagenase genes determined with cDNA probes

Secreted proteinases are required for tumor metastasis, angiogenesis, and tissue remodeling during wound healing and embryonic growth. Thus, the regulation of the genes of secreted proteinases may serve as an interesting model for growth-controlled genes in general. We studied the genes of the secreted proteinases stromelysin and collagenase by using molecularly cloned cDNAs from each proteinase. Stromelysin cDNA was cloned by differential screening of a total cDNA library from rabbit synovial cells treated with phorbol 12-myristate 13-acetate, which yielded a clone of 1.2 kilobase pairs; collagenase cDNA was obtained by cloning reverse transcripts of anti-collagenase-immunoadsorbed polysomal mRNA, which yielded a clone of 0.8 kilobase pairs. Stromelysin and collagenase mRNA species of 2.2 and 2.4 kilobases, respectively, were detected on hybridization blots of RNA from phorbol 12-myristate 13-acetate-treated but not untreated rabbit synovial cells. Expression of stromelysin mRNA was also induced in rabbit alveolar macrophages and rabbit brain capillary endothelial cells treated with phorbol 12-myristate 13-acetate. Stromelysin and collagenase mRNA were both induced by phorbol 12-myristate 13-acetate and cytochalasin B at a constant ratio of the two gene products; this suggests coordinate regulation. The fact that induction was blocked after inhibition of protein synthesis by cycloheximide implicates an indirect signal transduction pathway that requires new protein synthesis.

Vimentin: an evaluation of its role as a tumour marker

In this study we examined 198 sarcomas, 38 carcinomas, 13 'tumours with a spindle cell component' and 22 malignant melanomas with a commercial monoclonal vimentin antibody. All histopathological material was formalin fixed and paraffin embedded. The results show this antibody to be a sensitive and specific marker of mesenchymal derivation or differentiation. It is a useful tool in separating sarcomas from most carcinomas, and in separating malignant melanomas from carcinomas. When used in combination with a cytokeratin antibody it identifies carcinosarcomas and synovial sarcomas.

Cell-contact and -architecture of malignant cells and their relationship to metastasis

The interaction of metastatic cells with the host environment occurs, to a large extent, through the cell surface, and the cell cytoskeletal system controls the distribution and motility of cell surface receptors. During metastasis, tumor cells migrate from one organ to another, and the dynamic properties and mechanochemical deformability of disseminated cells play a central role in the process. The studies described here under suggest an interrelationship between the cytoskeleton and cell adhesion, which can control and augment the expression of the metastatic phenotype of neoplastic cells.

Cleavage of vimentin in dense cell cultures. Inhibition upon transformation by type 5 adenovirus

The analysis on two-dimensional isoelectric focusing and SDS polyacrylamide gels (2D gels) of the Triton X-100 and high salt-insoluble fraction of fibroblast cell lines, certain epithelial cell lines and granulosa cells revealed various amounts of a vimetin cleavage product, with a more basic pI and with a MW (1,500-2,000) lower than that of intact vimentin. This cleavage product of vimentin which constituted as much as 30% of the total vimentin in an established rat embryo fibroblast cell line (CREF), was detected by a monoclonal antivimentin antibody in whole cell and Triton-insoluble extracts, and it has a phosphorylated variant which can be degraded to form the "staircase pattern" on 2D gels similarly to intact vimentin. This processing of vimentin occurred mainly in dense cell cultures and it could not be induced in sparse cell cultures by inhibiting DNA synthesis with ara C, or by arresting cell growth in medium containing 0.1% serum. Transformation of CREF cells with intact wild-type (H5wt) and host-range cold-sensitive mutants (H5hr1 or H5d1101) of type 5 adenovirus (Ad5), or transformation of CREF cells by Ca2+-mediated DNA transfection with the transforming E1a (0-4.5 map units) or E1a + E1b (0-11.5 map units) region of Ad5 inhibits the cleavage of vimentin in dense cultures only at temperatures which are permissive for expression of the transformed phenotype. The transformation of cells with bovine papilloma virus type 1, with T24 ras oncogene, or with RSV does not interfere with the cleavage of vimentin. The organization of the vimentin network in dense cultures, where the vimentin cleavage occurs, is very different from that of sparse untransformed and sparse or dense Ad5-transformed cells. The possibility that the acidic amino acid-rich C-terminus of vimentin is cleaved in dense cell cultures in conjunction with the reorganization of the vimentin network and the inhibition of this cleavage by transformation with Ad5, are discussed.

Tumor promoter-induced disruption of junctional complexes in cultured epithelial cells is followed by the inhibition of cytokeratin and desmoplakin synthesis

The organization and synthesis of proteins involved in the formation and stabilization of desmosome-type junctions was investigated in cultured epithelial cells treated with a tumor promoter (12-O-tetradecanoyl-phorbol-13-acetate (TPA]. In Madin-Darby bovine (MDBK) and canine (MDCK) kidney cell colonies, TPA induced a rapid disruption of desmosomes and marked alterations in cell morphology. Within 4-6 h after TPA treatment, cell shape changed from cuboidal to highly irregular, with some very long extensions that contained cytokeratin fibrils, and many flat lamellar protrusions which were devoid of cytokeratin fibrils. These morphological changes in both MDBK and MDCK cells were followed by a dramatic and coordinated inhibition in the synthesis of all cytokeratins, 14-24 h after the addition of TPA, but without a similar effect on the synthesis of vimentin, which is coexpressed in these cells. In contrast, in dense cultures of MDBK and MDCK cells the synthesis of cytokeratins and the organization of desmosomal contacts were not affected by TPA. In an epithelial cell line derived from the bovine mammary gland (BMGE-H) the synthesis of an acidic cytokeratin of 45 kD, which was previously shown to be synthesized at high levels only in dense cultures, was dramatically inhibited by TPA treatment. Cell-free in vitro translation assays with mRNA from control and TPA-treated cells also demonstrated a decrease in the synthesis of cytokeratins in response to TPA. The inhibition of cytokeratin synthesis after TPA treatment was paralleled by a decrease in the synthesis of a high molecular weight (HMW) desmoplakin protein, which was abundant in dense MDBK and BMGE-H cells. The results with TPA-treated cells are suggestive of a coordinated down-regulation in the synthesis of only those cytokeratins and of a desmoplakin which were shown to be regulated by the extent of cell-cell contact. Cytokeratin phosphorylation in TPA-treated cells was low and reflected the decrease in their total mass, suggesting that it was not altered by TPA treatment. The possible linkage between the regulation of synthesis and organization of proteins involved in desmosome formation is discussed.

Regulation of cytoskeletal proteins involved in cell contact formation during differentiation of granulosa cells on extracellular matrix

The organization and the expression of cytoskeletal proteins involved in determining cell contact and shape were analyzed in granulosa cells during their differentiation on extracellular matrix (ECM)-coated culture plates. Rat granulosa cells from preovulatory follicles displayed an epithelial shape on ECM and formed multilayered aggregates with numerous gap junctions between neighboring cells. These cells had few actin cables and often only a diffuse pattern of actin and a low amount of vinculin in very thin focal adhesion sites. In contrast, cells grown on plastic formed a monolayer of flat cells with a reduced number of gap junctions but with numerous stress fibers and abundant large vinculin-containing focal contacts. On ECM, the cells were stimulated to produce high levels of progesterone, while only trace amounts of the steroid accumulated in cells on plastic dishes. Two-dimensional gel electrophoretic analysis of [35S]methionine-labeled cells revealed a dramatic decrease in vinculin, alpha-actinin, and actin synthesis in cells grown on ECM, as compared to cells grown on plastic, while the synthesis of the tubulins and of the intermediate filament protein vimentin remained unchanged. RNA blot analysis showed a marked decrease in actin mRNA levels in cells from ECM plates, while the level of tubulin mRNA remained essentially unchanged. It is concluded that the differentiation of granulosa cells on ECM in vitro is associated with changes in cell shape and cell contacts and that such changes in cell morphology are accompanied by simultaneous alterations in the organization and expression of cytoskeletal proteins that are involved in determining these cellular structures.

Cytochalasin D alters the rate of synthesis of some HEp-2 cytoskeletal proteins. Examination by two-dimensional gel electrophoresis

The most abundant proteins of HEp-2 cells were resolved by two-dimensional gel electrophoresis. The protein spots corresponding to several cytoskeletal proteins (vimentin, alpha-tubulin, beta-tubulin, alpha-actinin, tropomyosins, and cytokeratins) were identified by comigration with protein markers or by immunological techniques. After treatment of HEp-2 cells with 0.2 microM or 2.0 microM cytochalasin D for 20 h, radioautograms of two-dimensional gel patterns of lysates from cells pulse-labeled with [35S]methionine indicated that the drug altered the rate of synthesis of some proteins. The relative rate of synthesis of the identified cytoskeletal proteins was measured. Synthesis of alpha-actinin, the higher-molecular-mass pair of tropomyosins and actin were similarly increased with cytochalasin D treatment, suggesting coordinate induction. Vimentin and tubulin synthesis was depressed. One cytokeratin exhibited an increase in synthesis comparable to actin, another was increased to a lesser extent and one was decreased.

Cell contact- and shape-dependent regulation of vinculin synthesis in cultured fibroblasts

Recent studies have demonstrated the fundamental role of cell-substrate contacts and changes in cell shape in the regulation of cell growth, motility and differentiation, but the molecular basis for these phenomena is poorly understood. Because of the involvement of cytoskeletal networks in cell morphogenesis and contact formation, it is of interest that the expression of genes encoding several cytoskeletal proteins is markedly affected by changes in cell contacts and configuration. Because most of these phenomena involve changes in the form, extent or topology of cell contacts, we sought to determine whether the expression of components directly involved in the formation of cell-cell or cell-substrate contacts is affected by the respective cellular interactions. A suitable candidate for such analysis is vinculin, a cytoskeletal protein of relative molecular mass (Mr) 130,000 (130K), which is localized in focal contacts and intercellular adherens junctions. The assembly of vinculin into a membrane-bound junctional plaque seems to be one of the earliest cellular responses to contact with exogenous substrates, leading to the subsequent local assembly of the actin-rich microfilament bundles. Here we report on the regulation of vinculin synthesis in response to environmental conditions that affect cell shape and contacts.

Early expression of vimentin in human mammary cultures

The intermediate filaments of most epithelial cells in vivo consist solely of cytokeratins. Using monoclonal antibodies to vimentin or keratin, we have examined the expression of vimentin in homologous specimens of frozen tissue sections and primary cultures of normal human mammary epithelium. In frozen sections, only epithelial cells reacted with the antikeratin antibody, whereas antivimentin reactivity was associated with stromal cells. All epithelial cultures were positive for cytokeratin and in addition coexpressed vimentin as strongly as cultured fibroblasts and as early as the 4th d after initiation of the culture. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of cytoskeletal preparations of secondary cultures of normal mammary epithelium have also demonstrated the appearance of a moiety identical to the vimentin found in cultured fibroblasts. Our observations are consistent with the hypothesis that vimentin expression is induced, possibly as a result of changes in cell shape or growth rate, when cells are freed from three-dimensional restrictions imposed by the tissue of origin.

Cell density and cell shape-related regulation of vimentin and cytokeratin synthesis. Inhibition of vimentin synthesis and appearance of a new 45 kD cytokeratin in dense epithelial cell cultures

The pattern of the intermediate type filament protein synthesis was examined in cultured bovine mammary gland epithelial (BMGE) cells under conditions of varied cell shape and cell-cell contact. In dense monolayer and suspension cultures BMGE cells expressed a new cytokeratin of 45 kD identified as a member of the acidic subfamily of cytokeratins. This polypeptide has a phosphorylated component and is dissociated from the cytokeratins complex in the presence of 6.5 M urea. The mRNA of the new cytokeratin accumulated in dense cell cultures, as revealed by in vitro translation in a cell-free system. In BMGE-H cells that express also vimentin, the synthesis of vimentin decreased dramatically in dense cell cultures, while the synthesis of the 45 kD cytokeratin was maximal under these conditions. The results suggest that the expression of certain cytokeratins and that of vimentin can be coordinately regulated by factors in the cellular environment that effect cell shape and cell surface contacts.

Isoelectric focusing and two-dimensional electrophoresis of tubulin using immobilized pH gradients under denaturing conditions

Modifications of the LKB Immobiline isoelectric focusing (IEF) technique are described for use under conditions that solubilize and denature most proteins (8 M urea and 2% Nonidet-P40). This procedure permits pH gradients that are four- to fivefold shallower than previously available with conventional ampholine-IEF procedures. It can also be used as a first dimension in two-dimensional gel electrophoresis. The advantage of the stable ultranarrow pH gradient is demonstrated by directly comparing the resolution of vertebrate brain tubulins using (i) denaturing conventional ampholine-IEF and (ii) denaturing Immobiline-IEF. Analysis of tubulin on the Immobiline-IEF gel increases the separation distance between the individual tubulins and distinguishes differences among tubulin samples that could not be resolved by conventional ampholine isoelectric focusing.