Platelet-derived growth factor-induced alterations in vinculin and actin distribution in BALB/c-3T3 cells

Platelet-derived growth factor induces rapid and sustained tyrosine phosphorylation of phospholipase C-gamma in quiescent BALB/c 3T3 cells

Platelet-derived growth factor (PDGF) stimulates the proliferation of quiescent fibroblasts through a series of events initiated by activation of tyrosine kinase activity of the PDGF receptor at the cell surface. Physiologically significant substrates for this or other growth factor receptor or oncogene tyrosine kinases have been difficult to identify. Phospholipase C (PLC), a key enzyme of the phosphoinositide pathway, is believed to be an important site for hormonal regulation of the hydrolysis of phosphatidylinositol 4,5-bisphosphate, which produces the intracellular second-messenger molecules inositol 1,4,5-trisphosphate and 1,2-diacylglycerol. Treatment of BALB/c 3T3 cells with PDGF led to a rapid (within 1 min) and significant (greater than 50-fold) increase in PLC activity, as detected in eluates of proteins from a phosphotyrosine immunoaffinity matrix. This PDGF-stimulated increase in phosphotyrosine-immunopurified PLC activity occurred for up to 12 h after addition of growth factor to quiescent cells. Interestingly, the PDGF stimulation occurred at 3 as well as 37 degrees C and in the absence or presence of extracellular Ca2+. Immunoprecipitation of cellular proteins with monoclonal antibodies specific for three distinct cytosolic PLC isozymes demonstrated the presence of a 145-kilodalton isozyme, PLC-gamma (formerly PLC-II), in BALB/c 3T3 cells. Furthermore, these immunoprecipitation studies showed that PLC-gamma is rapidly phosphorylated on tyrosine residues after PDGF stimulation. The results suggest that mitogenic signaling by PDGF is coincident with tyrosine phosphorylation of PLC-gamma.

The effect of platelet-derived growth factor on phagocytosis of cultured human trabecular cells

Platelet-derived growth factor (PDGF) enhanced the phagocytic activity of cultured human trabecular cells in a dose-dependent manner (5-40 ng ml-1). By transmission and scanning electron microscopy, microvilli on the cell surface were shown to make contact with latex particles. Subsequently the cell surface invaginated and engulfed them. By indirect immunofluorescence, actin was found to form stress fibers in PDGF-free cells. PDGF-treated cells were stained in thread-like patterns on the cell surface. In addition to this image, membrane ruffles and actin ribbons were also observed. These findings suggest that PDGF may serve to facilitate phagocytosis and migration of trabecular cells by modifying trabecular cell actin.

Fibroblasts that proliferate near denervated synaptic sites in skeletal muscle synthesize the adhesive molecules tenascin(J1), N-CAM, fibronectin, and a heparan sulfate proteoglycan

Four adhesive molecules, tenascin(J1), N-CAM, fibronectin, and a heparan sulfate proteoglycan, accumulate in interstitial spaces near synaptic sites after denervation of rat skeletal muscle (Sanes, J. R., M. Schachner, and J. Covault. 1986. J. Cell Biol. 102:420-431). We have now asked which cells synthesize these molecules, and how this synthesis is regulated. Electron microscopy revealed that mononucleated cells selectively accumulate in perisynaptic interstitial spaces beginning 2 d after denervation. These cells were identified as fibroblasts by ultrastructural and immunohistochemical criteria; [3H]thymidine autoradiography revealed that their accumulation results from local proliferation. Electron microscopic immunohistochemistry demonstrated that N-CAM is associated with the surface of the fibroblasts, while tenascin(J1) is associated with collagen fibers that abut fibroblasts. Using immunofluorescence and immunoprecipitation methods, we found that fibroblasts isolated from perisynaptic regions of denervated muscle synthesize N-CAM, tenascin(J1), fibronectin, and a heparan sulfate proteoglycan in vitro. Thus, fibroblasts that selectively proliferate in interstitial spaces near synaptic sites are likely to be the cellular source of the interstitial deposits of adhesive molecules in denervated muscle. To elucidate factors that might regulate the accumulation of these molecules in vivo, we analyzed the expression of tenascin(J1) and fibronectin by cultured fibroblasts. Fibroblasts from synapse-free regions of denervated muscle, as well as skin, lung, and 3T3 fibroblasts accumulate high levels of tenascin(J1) and fibronectin in culture, showing that perisynaptic fibroblasts are not unique in this regard. However, when they are first placed in culture, fibroblasts from denervated muscle bear more tenascin(J1) than fibroblasts from innervated muscle, indicating that expression of this molecule by fibroblasts is regulated by the muscle's state of innervation; this difference is no longer apparent after a few days in culture. In 3T3 cells, accumulation of tenascin(J1) is high in proliferating cultures, depressed in confluent cultures, and reactivated in cells stimulated to proliferate by replating at low density or by wounding a confluent monolayer. Thus, synthesis of tenascin(J1) is regulated in parallel with mitotic activity. In contrast, levels of fibronectin, which increase less dramatically after denervation in vivo, are similar in fibroblasts from innervated and denervated muscle and in proliferating and quiescent 3T3 cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship of cytosolic ion fluxes and protein kinase C activation to platelet-derived growth factor induced competence and growth in BALB/c-3T3 cells

Platelet-derived growth factor (PDGF) and other agents that activate protein kinase C (PKC) rapidly alter cytosolic pH (pHi) and intracellular free calcium ([Ca++]i) in BALB/c-3T3 fibroblasts. To define whether changes in pHi or [Ca++]i are linked to PDGF-stimulated mitogenesis, these parameters were assessed in control and PKC depleted fibroblasts. PDGF addition to BALB/c-3T3 fibroblasts resulted in transient acidification of the cytoplasm followed by prolonged cytosolic alkalinization. Exposure of cells to 12-tetradecanoylphorbol-13-acetate (TPA), a phorbol ester that activates PKC, resulted in cytosolic alkalinization without prior acidification. Overnight incubation with 600 nM TPA decreased the total cell PKC histone phosphorylating activity in BALB/c-3T3 fibroblasts by greater than 90%. In PKC-deficient fibroblasts, TPA, and PDGF-induced alkalinization was abolished. In addition, the transient drop in pHi seen initially in control cells treated with PDGF is sustained to the point where pHi is fully 0.6-0.7 pH units below control cell values for up to 30 minutes. PDGF increased [Ca++]i threefold; this transient rise in [Ca++]i was only minimally affected (less than 15%) by lowering of the extracellular calcium level with ethylene glycol bis(b-aminoethyl ether)0 N,N,N' tetraacetic acid (EGTA) or blocking calcium influx with CoCl2. In contrast, 8-(diethylamine)-octyl-3,4,5-trimethoxybenzoate (TMB-8), an agent thought to inhibit calcium release from intracellular stores, substantially inhibited the rise in [Ca++]i caused by PDGF. TPA and 1-oleoyl-2-acetylglycerol (OAG) increased [Ca++]i but in contrast to PDGF this effect was blocked by pretreatment of cells with EGTA or CoCl2. In PKC-deficient fibroblasts, PDGF still increased [Ca++]i and stimulated DNA synthesis as effectively as in controls. TPA and OAG however, no longer increased [Ca++]i. The continued ability of PDGF to stimulate DNA synthesis in the face of sustained acidification and the absence of PKC activity suggests that cytosolic alkalinization and PKC activation are not essential for PDGF-induced competence in BALB/c-3T3 fibroblasts.

Relationship between organization of the actin cytoskeleton and the cell cycle in normal and adenovirus-infected rat cells

Flow cytometry and staining with 7-nitrobenz-2-oxa-1,3-diazole-phallacidin were used to investigate organization of the actin cytoskeleton in rat embryo cells at different stages of normal and adenovirus E1A-induced cell cycles. In uninfected cells in G0-G1 and S phases, actin was predominantly in the form of stress fibers. In G2, this organization changed to peripheral rings of thin filaments, while during mitosis, actin had a diffuse distribution. Infection of quiescent rat cells by adenovirus caused them to enter the cell cycle and replicate DNA and also caused disruption of stress fibers. Rapid disappearance of stress fibers and the appearance of peripheral rings of actin filaments began from 13 h after infection and closely followed synthesis of the E1A proteins. Infected cells began S phase at about 24 h after infection, and cells in G2 and mitosis were seen from 30 to 50 h. Thus, disruption of the actin cytoskeleton is an early effect of E1A and not an indirect consequence of the entry of infected cells into the cell cycle.

Nerve growth factor increases the cyclic GMP level and activates the cyclic GMP phosphodiesterase in PC12 cells

Nerve growth factor (NGF) rapidly increases the cyclic GMP (cGMP) level about 2-3-fold and enhances the cGMP phosphodiesterase (PDE) activity about 2-fold in rat pheochromocytoma PC12 cells. No changes in the level of cyclic AMP (cAMP) and in the activity of cAMP PDE were found. GTP and a nonhydrolysable analog of GTP, GMP-PCP, at 100 microM, were able to mimic the effect of NGF on the cGMP PDE activity. These results suggest that the cGMP system may be one of the second messengers of NGF action in PC12 cells.

cDNA-derived sequence of chicken embryo vinculin

We report the complete primary structure of chicken embryo vinculin. The amino acid sequence was derived from the nucleotide sequence of five overlapping cDNA clones isolated from a lambda gt11 phage library. Chicken embryo vinculin contains 1066 amino acids, has a calculated Mr of 116,990, a calculated pI of 5.9, and a hydropathy index of -4.22. A search of the National Biomedical Research Foundation protein sequence data base found no proteins with significant homology to vinculin. A striking feature of the linear sequence is a proline-rich region extending between residues 837 and 879. This region contains 45% proline and 19% aspartic plus glutamic acids; it is also the longest hydrophilic stretch in the molecule. The proline-rich region separates an amino-terminal domain with a calculated pI of 5.4 from a carboxyl-terminal domain with a calculated pI of 9.7. This feature suggests a structural basis for the specific interaction of vinculin with acidic phospholipids and a mechanism for the shuttling of vinculin between cytoplasm and membrane-associated junctional plaque.

The reorganization of microfilaments, centrosomes, and microtubules during in vitro small wound reendothelialization

The repair of small endothelial wounds is an important process by which endothelial cells maintain endothelial integrity. An in vitro wound model system was used in which precise wounds were made in a confluent endothelial monolayer. The repair process was observed by time-lapse cinemicrophotography. Using fluorescence and immunofluorescence microscopy, the cellular morphological events were correlated with the localization and distribution of actin microfilament bundles and vinculin plaques, and centrosomes and their associated microtubules. Single to four-cell wounds underwent closure by cell spreading while wounds seven to nine cells in size closed by initially spreading which was then followed at approximately 1 h after wounding by cell migration. These two processes showed different cytoskeletal patterns. Cell spreading occurred independent of centrosome location. However, centrosome redistribution to the front of the cell occurred as the cells began to elongate and migrate. While the peripheral actin microfilament bundles (i.e., the dense peripheral band) remained intact during cell spreading, they broke down during migration and were associated with a reduction in peripheral vinculin plaque staining. Thus, the major events characterizing the closure of endothelial wounds were precise in nature, followed a specific sequence, and were associated with specific cytoskeletal patterns which most likely were important in maintaining directionality of migration and reducing the adhesion of the cells to their neighbors within the monolayer.

Comparative study of the tyrosine phosphorylation of proteins in Swiss 3T3 fibroblasts stimulated by a variety of mitogenic agents

We have carried out a comparative study of the protein tyrosine phosphorylation induced by a wide range of mitogenic stimuli on a single cell type, Swiss 3T3 mouse fibroblasts. For this purpose we have used high-affinity antibodies directed to phosphotyrosine residues on proteins (Wang: Mol. Cell. Biol. 5:3640-3643, 1985) in immunoblotting and immunofluorescence microscopy experiments. Immunoblotting experiments showed that all of the mitogens tested, including epidermal growth factor, platelet-derived growth factor, basic fibroblast growth factor, insulin, fetal calf serum, trypsin, and 12-O-tetradecanoylphorbol-13-acetate, increased the phosphorylation on tyrosine of a number of proteins. Most of the increase in tyrosine phosphorylation induced by each factor involved a small set of proteins with apparent molecular weights (Mr) above 50,000. Following stimulation with epidermal growth factor, platelet-derived growth factor, and basic fibroblast growth factor, increased phosphotyrosine modification of proteins with molecular weights corresponding to those of the respective receptors was observed. A protein band of apparent Mr 160,000 contained substantially increased levels of phosphotyrosine following insulin treatment, but tyrosine phosphorylation of the insulin receptor was apparently below the level of detectability. The phosphotyrosine content of proteins with apparent Mr of 220,000, 120,000, and 70,000 was increased by all the agents tested. Phosphorylation on tyrosine of most of the proteins increased within a few minutes of the mitogenic stimulation, reached a peak, and returned more slowly to basal levels. Immunofluorescence labeling with the antibodies specific for phosphotyrosine showed a substantial increase in the amount of phosphotyrosine containing proteins only in the presence of platelet-derived growth factor and fetal calf serum. This finding suggests that most of the proteins phosphorylated on tyrosine in Swiss 3T3 fibroblasts are not concentrated in specific subcellular structures, but rather are diffusely distributed throughout the cell and are therefore not detectable by immunofluorescence microscopy.

Synthetic peptide GRGDS induces dissociation of alpha-actinin and vinculin from the sites of focal contacts

The synthetic peptide Gly-Arg-Gly-Asp-Ser (GRGDS) mimics the cellular binding site of many adhesive proteins in the extracellular matrix and causes rounding and detachment of spread cells. We have studied whether its binding affects the associations of two major components, alpha-actinin and vinculin, at the adhesion plaque. Living 3T3 cells were microinjected with fluorescently labeled alpha-actinin and/or vinculin and observed using video microscopy before and after the addition of 50 micrograms/ml GRGDS. As soon as 5 min after treatment, fluorescent alpha-actinin and vinculin became dissociated simultaneously from the sites of many focal contacts. The proteins either moved away as discrete structures or dispersed from adhesion plaques. As a result, the enrichment of alpha-actinin and vinculin at these focal contacts was no longer detected. The focal contacts then faded away slowly without showing detectable movement. These data suggest that the binding state of integrin has a transmembrane effect on the distribution of cytoskeletal components. The dissociation of alpha-actinin and vinculin from adhesion plaques may in turn weaken the contacts and result in rounding and detachment of cells.

Cell adhesion induces expression of growth-associated genes in suspension-arrested fibroblasts

A methylcellulose suspension system that prevents cell-surface contact with the substrate was used to study the role of cell adhesion in the regulation of proliferation. The nonadhesive conditions established by suspension culture cause BALB/c 3T3 (A31) cells to enter a G0 state of growth arrest within 48 hr as defined by an inhibition of DNA synthesis and a suppression of c-myc and histone mRNA expression. The adhesion of these suspension-arrested cells rapidly induces c-fos, c-myc, and actin gene expression. This stimulation did not depend on the presence of serum since the adhesion of suspension-arrested cells, in the absence of serum, also induced the expression of c-fos and c-myc mRNAs. In addition, adhesion onto fibronectin increased the number of cells able to respond to epidermal growth factor and insulin and progress into S phase. These results indicate that adhesion of suspension-arrested cells activates the G0/G1 transition independent of growth factors.

Nerve growth factor induces rapid redistribution of F-actin in PC12 cells

Nerve growth factor (NGF) induces the redistribution of F-actin in rat pheochromocytoma PC12 cells within 2-10 min, whereas epidermal growth factor (EGF) has no effect on microfilament organization. This redistribution of F-actin in PC12 cells is not protein synthesis dependent, but can be blocked by methyltransferase inhibitors.

Induction of circular membrane ruffling on human fibroblasts by platelet-derived growth factor

One of the earliest effects of platelet-derived growth factor (PDGF) on human fibroblasts in culture is an induction of membrane ruffling. The morphology of the ruffles induced by PDGF is unique in that they form circular arrangements on the dorsal side of the cells. Here we report that the induction of circular ruffle arrangements is an effect specific for PDGF, dose-dependent and inhibitable by anti-PDGF antibodies. We have attempted to utilize this effect to design a rapid and sensitive bioassay for PDGF. The "membrane ruffling assay" is compared with other methods to measure PDGF and its specificity with regard to the different dimeric forms of PDGF is discussed. Introduction of Ca2+ into the cells via the Ca2+ ionophore A23187 or the addition of the tumor-promor 12-O-tetradecanoylphorbol-13-acetate (TPA), which is a stimulator of protein kinase C, does not induce circular ruffle formations on human fibroblasts, neither does the addition of the combination of these two agents. However, addition of TPA almost completely inhibits PDGF-induced circular ruffle formations. Further, we find a shift in the time-course of the PDGF-induced circular ruffle formations by sodium orthovanadate, an inhibitor of protein tyrosine phosphatases. This may indicate the involvement of protein phosphorylation in the regulation of PDGF-induced membrane ruffling.

Interleukin 1 and the glomerular mesangium. III. IL-1-dependent stimulation of mesangial cell protein kinase activity

Interleukin 1 (IL-1) exerts a number of biologic actions upon cultured glomerular mesangial cells (MC). These include stimulation of cellular proliferation and induction of prostaglandin and type IV collagenase secretion. It was determined that this activity, as with other polypeptide growth factors, was associated with the activation of specific MC plasma membrane protein kinases. Plasma membranes from cycling MC were incubated with purified IL-1 and (32P) ATP in the absence of calcium and cyclic nucleotides. Macrophage IL-1 stimulated the rapid phosphorylation of several plasma membrane proteins, the most significant of which were 52-55 kd, 46 kd, and 20 kd in size. Macrophage IL-1 induced specific membrane phosphorylation in concentrations as low as 1.5 x 10(-12) M, an effect obtained with equivalent concentrations of purified MC IL-1. The 46 kd phosphoprotein, which was the most prominent, was alkali-resistant and contained phosphotyrosine when examined by phosphoamino acid analysis. The 52-55 kd and 20 kd phosphoproteins were alkali-labile and contained phosphoserine. The 46 kd phosphoprotein was the major phosphoprotein recovered from Con A-Sepharose and IL-1 affinity columns. Induction of plasma membrane-associated protein kinase activity may represent one mechanism whereby IL-1 initiates mesangial cellular activation.

Changes in fibroblast contractility, morphology, and adhesion in response to a phorbol ester tumor promoter

We have studied the effects of the phorbol ester tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the contractility, locomotion, morphology, and adhesion of two mammalian fibroblastic cell lines. Using the silicone rubber substratum technique, we have found that the first observable response to the tumor promoter is a rapid weakening of cell contractility (8-15 min). This is followed by gradual morphological changes, characterized by a hyperextension of the cells' leading lamellae, which stretch out to an unlimited degree, and occasionally even detach from the cell bodies. Treated cells also become able to crawl onto hydrophobic substrata which are insufficiently adhesive to support the spreading of untreated fibroblasts. We suggest that both the hyperextension and the ability to spread on nonadhesive surfaces can be explained as consequences of the reduced contractility, and that this reduced contractility may also help to explain the increased invasiveness and loss of anchorage dependence by transformed cells.

Inhibition of early platelet-derived growth factor responses in BALB/c-3T3 cells by interferon

Stimulation of total inositol phosphate production, alteration of cytosolic free calcium [( Ca++]i), vinculin disruption from adhesion plaques, and DNA synthesis caused by PDGF were examined in normal and INF pretreated density arrested BALB/c-3T3 fibroblasts. In normal cells, PDGF caused an increase in total inositol phosphates, a rapid, transient increase in [Ca++]i, disappearance of vinculin from adhesion plaques, and stimulation of DNA synthesis. Pretreatment of cells with INF inhibited PDGF-stimulated increases in [Ca++]i, vinculin disruption from adhesion plaques, and DNA synthesis, but had no effect on PDGF-induced increase in total inositol phosphate levels. These findings suggest that INF prevents entry of quiescent BALB/c-3T3 cells into G1 by inhibiting PDGF-induced release of Ca++ from intracellular stores.

Inhibitory effect of dimethyl sulfoxide on the proliferation of cultured arterial smooth muscle cells: relationship to the cytoplasmic microtubules

Our preliminary study has shown that dimethyl sulfoxide (DMSO) has an inhibitory effect on the proliferation of cultured arterial smooth muscle cells and promotes phenotypic modulation from the synthetic state to the contractile state. In the present study we have examined the effect of DMSO with special attention to relationship between cell growth and cytoplasmic microtubules. DMSO inhibited DNA synthesis and cell division, and concomitantly promoted microtubule assembly. Initiation of DNA synthesis and cell division of nonproliferating cells by platelet-derived growth factor (PDGF) was also inhibited in the presence of 1% DMSO. A 12-hr incubation with 10(-6) M colchicine caused disruption of microtubules; however, pretreatment with 1% DMSO for 24 hr prevented the disruption, indicating that DMSO has a stabilizing action on microtubules. A 24-hr exposure to PDGF resulted in microtubule depolymerization, while the addition of 1% DMSO prevented the depolymerization. These results suggest that DMSO inhibits DNA synthesis of cultured smooth muscle cells by stabilizing cytoplasmic microtubules.

Clostridium difficile toxin B induces reorganization of actin, vinculin, and talin in cultured cells

Clostridium difficile toxin B is a powerful cytopathic agent which causes animal cells in culture to become rounded and arborized, an effect similar to that induced by the cytochalasins. In this study, we demonstrated that the morphological effects of the toxin are directed specifically against the actin and related components of the cytoskeleton. Dramatic disruption and reorganization of the actin stress fibers were detectable prior to significant changes in cell shape and alterations in the microtubular and intermediate filament networks. Along with F-actin, the adhesion plaque proteins, vinculin and talin were localized in intoxicated cells in a patchy pattern reminiscent of that seen in cells treated with phorbol esters or transformed by oncogenic viruses. A quantitative fluorescence assay for cellular F-actin showed that these morphological changes were accompanied by a modest net depolymerization of only 15 to 20% of the actin filaments in the cell, and that depolymerization was closely correlated with changes in cell shape. In complementary studies on cells spreading on a substrate, we found that the toxin affected the actin content and the shape of the processes extended from the cell body. As in cells treated with cytochalasin, there was a differential response between normal and virally transformed cells spreading in the presence of the toxin. The results of this study support the view that C. difficile toxin B affects one or more cellular components that regulate the structure and function of the actin cytoskeleton, and that its predominant effect is to cause a dramatic disruption of stress fibers and relocalization of the F-actin.+

Colocalization of calcium-dependent protease II and one of its substrates at sites of cell adhesion

Adhesion plaques, specialized regions of the plasma membrane where a cell contacts its substratum, are dynamic structures. However, little is known about how the protein-protein interactions that occur at adhesion plaques are controlled. One mechanism by which a cell might modulate its associations with the substratum is by selective, regulated proteolysis of an adhesion plaque component. Here we show that the catalytic subunit of the calcium-dependent protease type II (CDP-II) is localized in adhesion plaques of several cell types (BS-C-1, EBTr, and MDBK). We have compared the susceptibility of the adhesion plaque constituents vinculin, talin, and alpha-actinin to calcium-dependent proteolysis in vitro and have found talin to be the preferred substrate for CDP-II. The colocalization of a calcium-requiring proteolytic enzyme and talin in adhesion plaques raises the possibility that calcium-dependent proteolytic activity provides a mechanism for regulating some aspect of adhesion plaque physiology and function via cleavage of talin.

Transforming growth factor type beta can act as a potent competence factor for AKR-2B cells

Transforming growth factor type beta (TGF beta) is a pleiotropic regulator of cell growth with specific high-affinity cell-surface receptors on a large number of cells; its mechanism of action, however, is poorly defined. In this report, we utilized the mouse fibroblast line AKR-2B to explore the question of the temporal requirements during the cell cycle in regard to both the growth inhibitory and the growth stimulatory action of TGF beta. The results indicate that AKR-2B cells are most sensitive to the inhibitory action of TGF beta during early to mid-G1. In addition, TGF beta need be present only briefly (as little as 1 min) in order to exert its inhibitory effect on EGF-induced DNA synthesis. Likewise, the stimulatory effect of TGF beta in the absence of EGF requires only an equally brief exposure to TGF beta. Use of homogeneous 125I-labeled TGF beta in a cell-binding assay demonstrates that TGF beta bound to cell-surface receptors can readily exchange into the culture medium T1/2 = 120 min), helping to rule out the possibility that persistent receptor-bound TGF beta is the source of a continuous stimulus. The data indicate that TGF beta exposure induces a stable state in the cell (T1/2 = 20 h) similar to but distinct from the state of "competence" induced by platelet-derived growth factor (PDGF).

Calcium-induced assembly of adherens junctions in keratinocytes

Extracellular calcium concentration has been shown to control the stratification of cultured keratinocytes, presumably by regulation of formation of desmosomes. Previous studies have shown that keratinocytes cultured in medium containing 0.1 mM Ca++ form loose colonies without desmosomes. If the Ca++ is raised to 1 mM, desmosomes are assembled and the distribution of keratin filaments is altered. We have examined the disposition of vinculin and actin in keratinocytes under similar conditions. Using immunofluorescence microscopy we show that raising [Ca++] in the medium dramatically alters the distribution of vinculin and actin and results in the formation of adherens-type junctions within 15 min after switching to high calcium medium. Borders of cells at the edge of colonies, which are not proximal to other cells, are not affected, while cells in the interior of the colony form junctions around their periphery. Attachment plaques in keratinocytes grown in low calcium medium are located at the ventral plane of the cell, but junctions formed after switching to high calcium are not, as demonstrated by interference reflection microscopy. In cells colabeled with antibodies against vinculin and desmoplakin, vinculin-containing adherens junctions were visible before desmosomal junctions when cells were switched to high calcium. Although newly formed vinculin-containing structures in high calcium cells, like desmosomes, colocalize with phase-dense structures, superimposition of video fluorescence images using digitized fluorescence microscopy indicates that adherens junctions and desmosomes are discrete structures. Adherens junctions, like desmosomes, may play an essential role in controlling stratification of keratinocytes.

Isolation and characterization of a vinculin cDNA from chick-embryo fibroblasts

A chick-embryo fibroblast lambda gt11 cDNA library was screened with affinity-purified antibodies to chick gizzard vinculin. One recombinant was purified to homogeneity and the fusion protein expressed in Escherichia coli strain C600. The fusion protein was unstable, but polypeptides that reacted with vinculin antibodies, but not non-immune immunoglobulin, were detected by Western blotting. The recombinant contained a single EcoRI fragment of 2891 bp with a single open reading frame. The deduced protein sequence could be aligned with that of six CNBr-cleavage peptides and two tryptic peptides derived from chicken gizzard vinculin. AUG-247 has tentatively been identified as the initiation codon, as it is contained within the consensus sequence for initiation sites of higher eukaryotes. The cDNA lacks 3' sequence and encodes 74% of the vinculin sequence, presuming the molecular mass of vinculin to be 130,000 Da. Analysis of the deduced sequence showed no homologies with other protein sequences, but it does display a triple internal repeat of 112 amino acid residues covering residues 259-589. The sequences surrounding the seven tyrosine residues in the available sequence were aligned with the tyrosine autophosphorylation consensus sequence found in protein tyrosine kinases. Tyr-822 showed a good match to this consensus, and may represent one of the two major sites of tyrosine phosphorylation by pp60v-sre. Northern blots showed that the 2.89 kb vinculin cDNA hybridized to one size of mRNA (approx. 7 kb) in chick-embryo fibroblasts, chick smooth muscle and chick skeletal muscle. Southern blots revealed multiple hybridizing bands in genomic DNA.

Heterologous regulation of EGF receptors in fibroblastic cells

Platelet-derived growth factor (PDGF) increases the mitogenic activity of epidermal growth factor (EGF) in several cells lines, including BALB/C-3T3. PDGF-treated BALB/C-3T3 cells manifest a reduced capacity to bind 125I-labeled EGF due to a loss of high affinity EGF receptors. Cholera toxin potentiates the ability of PDGF to both decrease EGF binding and initiate mitogenesis. Whether PDGF increases EGF sensitivity via its effects on EGF receptors is not known and requires a more complete understanding of the mechanism by which PDGF decreases EGF binding. 12-O-tetradecanoylphorbol 13-acetate (TPA) also reduces EGF binding in BALB/C-3T3 and other cells, presumably by activating protein kinase C and, consequently, inducing the phosphorylation of EGF receptors at threonine-654. PDGF indirectly activates protein kinase C, and EGF receptors in PDGF-treated WI-38 cells are phosphorylated at threonine-654. Thus, the effects of PDGF on EGF binding may also be mediated by protein kinase C. We investigated this hypothesis by comparing the actions of PDGF and TPA on EGF binding in density-arrested BALB/C-3T3 cells. Both PDGF and TPA caused a rapid, transient, cycloheximide-independent loss of 125I-EGF binding capacity. The actions of both agents were potentiated by cholera toxin. However, whereas TPA allowed EGF binding to recover, PDGF induced a secondary and cycloheximide-dependent loss of binding capacity. Most importantly, PDGF effectively reduced binding in cells refractory to TPA and devoid of detectable protein kinase C activity. These findings indicate that PDGF decreases EGF binding by a mechanism that involves protein synthesis and is distinct from that of TPA.

The cytoskeletal protein vinculin is acylated by myristic acid

In non-muscle cells the mechanism by which microfilament bundles interact with the plasma membrane is unclear. Vinculin, a 130 kDa protein found in adhesion plaques, has been postulated to have a role as a membrane anchor for microfilaments and we have investigated the biochemistry of this molecule in more detail. We report that a fraction of vinculin in chick embryo fibroblasts is acylated by myristic acid. This modification was present in both membrane-bound, cytoskeletal and cytosolic vinculin and thus did not determine preferential subcellular localisation. Myristic acid was also present in vinculin from cells transformed by Rous sarcoma virus.

Platelet-derived growth factor-induced alterations in vinculin distribution in porcine vascular smooth muscle cells

Exposure of porcine vascular smooth muscle cells to platelet-derived growth factor (PDGF; 18-180 ng/ml) but not epidermal growth factor (EGF; 30 ng/ml), somatomedin C (SmC; 30 ng/ml), or insulin (10 microM), results in a rapid, reversible, time- and concentration-dependent disappearance of vinculin staining in adhesion plaques; actin-containing stress fibers also become disrupted following exposure of cells to PDGF. Disappearance of vinculin staining from adhesion plaques is also caused by 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 200-400 nM), though the time course of the disappearance of vinculin staining under these conditions takes longer than in cells exposed to PDGF. The PDGF-induced removal of vinculin from adhesion plaques was inhibited in a concentration-dependent fashion by 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate (TMB-8; 0.25-4 microM) and leupepetin (2-300 microM), and by n-alpha-tosyl-L-lysine chloromethylketone (TLCK; 100 microM) and trifluoperazine (TFP; 2.5 microM). Addition of PDGF to vascular smooth muscle cells caused a rapid, transient increase in cytosolic free calcium, from a basal resting level of 146 +/- 6.9 nM (SEM, n = 62) to 414 +/- 34 nM (SEM, n = 22) as determined using the calcium-sensitive indicator Fura-2 and Digitized Video Microscopy. This increase in cellular calcium preceded the disappearance of vinculin from adhesion plaques and was partially blocked by pretreatment of cells with TMB-8 but not leupeptin. This rise in cytosolic free calcium was found to occur in approximately 80% of the sample population and displayed both spatial and temporal subcellular heterogeneity. Exposure of cells to TPA (100 nM) did not result in a change in cytosolic free calcium. Both PDGF (20 ng/ml) and TPA (100 nM) caused cytosolic alkalinization which occurred after PDGF-induced disruption of vinculin from adhesion plaques, as determined using the pH-sensitive indicator BCECF and Digitized Video Microscopy. PDGF stimulated DNA synthesis and vinculin disruption in a similar dose-dependent fashion. Both could be inhibited by leupeptin or TMB-8. These results suggest that 1) exposure of vascular smooth muscle cells to PDGF is associated with the disruption of vinculin from adhesion plaques, 2) PDGF-induced vinculin disruption is regulated by an increase in cytosolic calcium (but not cytosolic alkalinization), and involves proteolysis; 3) activation of protein kinase C also causes vinculin removal from adhesion plaques but by a calcium-independent mechanism, and 4) the cellular response to PDGF-stimulated increases in cytosolic free calcium is heterogeneous.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet-derived growth factor stimulation of [3H]-glucosamine incorporation in density-arrested BALB/c-3T3 cells

G0/G1 traverse in density-arrested BALB/c-3T3 cells is controlled by multiple serum-derived growth factors. Platelet-derived growth factor (PDGF) initiates a proliferative response, whereas factors present in plasma facilitate progression through G0/G1. In the absence of competence formation, progression factors are unable to stimulate cell cycle traverse. We have identified the stimulation of a biochemical process specific to competence formation in BALB/c-3T3 cells. PDGF treated BALB/c-3T3 cells incorporated 5-10-fold more [3H]-glucosamine (GlcN) into acid-insoluble material as compared to platelet-poor plasma (PPP) treated cultures. Increased GlcN incorporation occurred in density-arrested BALB/c-3T3 cells in response to treatment with other competence factors, fibroblast growth factor, and Ca3 (PO4)2 and was not due to cell-cycle traverse. Stimulation of [3H]-GlcN incorporation by PDGF was time dependent, and increased incorporation of [3H]-GlcN into protein required de novo protein synthesis. Several mechanisms through which PDGF could increase GlcN incorporation into cellular material were examined. Results of these studies suggest an increase in the cellular capacity to glycosylate proteins is a response to or a part of competence formation.

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.

Stimulation of the chemotactic migration of human fibroblasts by transforming growth factor beta

Transforming growth factor beta (TGF-beta) is a potent chemoattractant in vitro for human dermal fibroblasts. Intact disulfide and perhaps the dimeric structure of TGF-beta is essential for its ability to stimulate chemotactic migration of fibroblasts, since reduction with 2-ME results in a marked loss of its potency as a chemoattractant. Although epidermal growth factor (EGF) appears to be capable of modulating some effects of TGF-beta, it does not alter the chemotactic response of fibroblasts to TGF-beta. Specific polyvalent rabbit antibodies to homogeneously pure TGF-beta block its chemotactic activity but has no effect on the other chemoattractants tested (platelet-derived growth factor, fibronectin, and denatured type I collagen). Since TGF-beta is secreted by a variety of neoplastic and normal cells including platelets, monocytes/macrophages, and lymphocytes, it may play a critical role in vivo in embryogenesis, host response to tumors, and the repair response that follows damage to tissues by immune and nonimmune reactions.

Scanning microfluorometric measurement of immunofluorescently labelled microtubules in cultured cells. Dependence of microtubule content on cell density

A method for evaluation of microtubule content in cultured cells has been developed. The method is based on scanning microfluorometric measurement of immunofluorescently labelled microtubules. The method has been applied to the comparison of microtubule content in epithelial XTH-2 cells grown in culture at various cell densities. The results have shown that the microtubule content in the cells is not dependent on their proliferative state rather than it depends on cellular contacts.

Spatial and temporal relationships between vinculin and talin in the developing chicken gizzard smooth muscle

The spatiotemporal relationships between vinculin and talin in developing chicken gizzard smooth muscle were investigated. Immunofluorescence and immunoelectron-microscopic labeling revealed that both proteins are associated with membrane-bound dense plaques in muscle cells; however, the most intense labeling for vinculin was located rather closer to the membrane than that for talin. The localization of vinculin and talin in embryonic chicken gizzards indicated that both are primarily cytoplasmic during the first 2 embryonic weeks. Only around days 16-18 does talin apparently become associated with the plasma membrane, this being concomitant with the appearance of distinct myofilament-bound dense plaques. Vinculin, on the other hand, remains primarily cytoplasmic and appears in the plaques only 1-3 days after hatching. It is thus proposed that the interactions of the dense plaque with myofilaments or with the membrane do not depend on the presence of vinculin in the plaque. Electrophoretic analyses indicated that, during development, there is no major change in the differential expression of specific vinculin isoforms. Quantitative immunoblotting analysis indicated that the vinculin content (relative to total extracted protein) is virtually constant during the last week of embryonic life. However, within 3 days of hatching, the vinculin concentration increases remarkably to over twice the embryonic level, and then slowly increases until it reaches the adult levels, which are three to four times higher than the embryonic level. The concentration of metavinculin (a 160-Kd vinculin-related protein) showed only a limited increase after hatching. We discuss the possible roles of vinculin and talin in the assembly of membrane-bound dense plaques during the different phases of smooth-muscle development.

Interferon inhibits the establishment of competence in Go/S-phase transition

Addition of mouse interferon-alpha/beta (IFN) to confluent, quiescent BALB/c 3T3 (clone A31) mouse fibroblasts resulted in a block or delay in serum-induced activation of the cell cycle. It was necessary to add IFN within 6 hours after serum stimulation to inhibit nuclear labeling with [3H]thymidine. This is consistent with the time required for platelet-derived growth factor (PDGF) to induce cells to become competent to respond to additional growth factors present in platelet-poor plasma. Simultaneous addition of IFN with PDGF inhibited the PDGF-induced synthesis of a 29-kilodalton and a 35-kilodalton protein that normally occurs within 1 hour after PDGF addition. IFN also suppressed the general increase in protein synthesis that occurs by the fifth hour after PDGF addition. These results show that IFN antagonizes the action of PDGF, thereby interfering with the activation of Go cells for G1 traverse and S-phase entry.

Platelet-derived growth factor modulates epidermal growth factor receptors by a mechanism distinct from that of phorbol esters

Platelet-derived growth factor (PDGF) and phorbol 12-myristate 13-acetate (PMA) decrease high affinity binding of 125I-labeled epidermal growth factor (EGF) and potentiate mitogenesis in BALB/c 3T3 cells, and both have been shown to induce the phosphorylation of the EGF receptor at threonine residues. These similarities suggest that the actions of PDGF on EGF binding may be mediated by protein kinase C, the cellular effector of PMA. We show that in density-arrested BALB/c 3T3 cells PDGF and PMA induce a rapid, transient, cycloheximide-independent loss of EGF binding activity. As has been previously shown for PDGF, the ability of PMA to reduce EGF binding was enhanced by cholera toxin, a potent activator of adenylate cyclase. In contrast to PMA, however, PDGF induced a further reduction in EGF binding that was strictly dependent upon continued protein synthesis. Furthermore, PDGF effectively reduced EGF binding in cells refractory to PMA. Cells desensitized to PMA, presumably due to the loss of protein kinase C activity, also remained mitogenically responsive to PDGF. These data suggest that the mechanism by which PDGF modulates EGF binding differs from that of PMA and thus, at least in part, is independent of protein kinase C.

Reorganization of alpha-actinin and vinculin induced by a phorbol ester in living cells

We have used fluorescent analogue cytochemistry, image intensification, and digital image processing to examine the redistribution of alpha-actinin and vinculin in living cultured African green monkey kidney (BSC-1) cells treated with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Before treatment, microinjected alpha-actinin shows characteristic distribution along stress fibers and at adhesion plaques; vinculin is localized predominantly at adhesion plaques. Soon after the addition of TPA, highly dynamic membrane ruffles begin to form. These incorporate a large amount of alpha-actinin but little vinculin. Alpha-actinin is subsequently depleted, more or less uniformly, from stress fibers. Disrupted stress fibers often fragment into aggregates and move into the perinuclear region. Careful analyses of fluorescence intensity distribution indicate that alpha-actinin is depleted more rapidly from adhesion plaques than from stress fibers. Furthermore, the depletion of alpha-actinin from adhesion plaques is also faster than either the depletion of vinculin or the disappearance of focal contacts. These observations indicate that TPA may initiate disruption of stress fibers by interfering with a link between alpha-actinin and vinculin, causing alpha-actinin to be preferentially depleted from adhesion plaques.

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.

Identification of the cellular mechanisms responsible for platelet-derived growth factor induced alterations in cytoplasmic vinculin distribution

Exposure of quiescent density arrested BALB/c-3T3 cells (clone A31) to platelet-derived growth factor (PDGF; 6-12 ng/ml) results in a rapid, reversible, time- and dose-dependent removal of vinculin from adhesion plaques (Herman and Pledger, 1985). Potential cellular mechanisms involved in PDGF-induced removal of vinculin from adhesion plaques were examined. Removal of vinculin from adhesion plaques following exposure of cells to PDGF was temperature dependent, occurred in many fibroblast cell lines, and could be mimicked by 12-tetradecanoyl phorbol-13-acetate (TPA; 5-125 nM) or melittin (0.35 microM). Unlike the effect of PDGF, TPA- or melittin-induced vinculin disruption was not reversible. The removal of vinculin from adhesion plaques was inhibited by trifluoroperazine (TFP; 2.5 microM). 8-(N,N-diethylamino) octyl-3,4,5-trimethoxy benzoate (TMB-8; 1.0 microM), mepacrine (220 microM), n-alpha-p-tosyl-L-lysine chloromethylketone (TLCK; 100 microM), phenylmethoxysulphonylfluoride (PMSF; 500 microM), and epsilon-aminocaproic acid (epsilon-ACA; 100 microM); however, amiloride (100 microM), A23187 (20 microM), and chloroquine (1 mM) were unable to inhibit this effect. Melittin disruption of vinculin was inhibited by (in order of decreasing effectiveness) mepacrine greater than TMB-8 greater than TFP greater than leupeptin greater than PMSF, whereas A23187 and amiloride had no effect. The return of vinculin to adhesion plaques following PDGF treatment required de novo mRNA transcription and protein synthesis and was associated with PDGF-stimulated synthesis of vinculin. The observation that both PDGF- and melittin-induced removal of vinculin from adhesion plaques is inhibited by mepacrine suggests that phospholipase activation may be an early and important step in PDGF-induced disruption of vinculin from adhesion plaques. In addition, TFP, TMB-8 and protease inhibitor inhibition of both the PDGF and melittin effects on vinculin distribution, coupled with the finding that TPA can mimic the PDGF or melittin response, suggests that Ca2+, calmodulin, protein kinase C, and/or proteolysis may play an important role(s) in the removal of vinculin from adhesion plaques following PDGF addition. The lack of effect of A23187 addition on vinculin distribution suggests that alterations in cellular Ca2+ is necessary but not sufficient for vinculin removal from adhesion plaques.

Phosphotyrosine-containing proteins are concentrated in focal adhesions and intercellular junctions in normal cells

We have used a high-affinity polyclonal antibody directed against phosphotyrosine (P-Tyr) to localize P-Tyr-containing proteins in normal and transformed cells in culture by immunofluorescence microscopy experiments. The distribution of the proteins with modified tyrosine was compared with that of F-actin in these cells. Cells infected with Abelson murine leukemia virus were found to contain elevated levels of P-Tyr, as expected. Various permanent lines of fibroblastic and epithelial cells exhibited lower, but easily detectable, levels of P-Tyr. The P-Tyr in fibroblasts was concentrated at the focal contacts at the termini of actin-containing microfilament bundles and, in the epithelial cells examined, at the intercellular junctions. Early passages of primary cultures of chicken embryo fibroblasts and chicken embryo heart cells also showed detectable levels of P-Tyr in focal contacts and cell-cell junctions. However, P-Tyr was not detectable in later passages of chicken embryo fibroblasts. The concentration of P-Tyr-containing proteins in intercellular junctions in normal cells suggests that these are sites of significant biochemical regulatory activities which may be important in the control of normal cell adhesivity, motility, and shape.