F-actin in conifer roots

The distribution of F-actin in the complex tissues of a higher plant organ has been visualized by fluorescence labeling the roots of the conifers Chamaecyparis obtusa and Pseudotsuga menziesii with F-actin-specific fluorescent dye-conjugated phallicidin. F-actin is present in the parenchymatous cells of the vascular tissue. Some vascular parenchyma cells possess larger numbers of F-actin-containing structures (microfilament bundles) than are known to exist in any other higher plant cell. Tissue type appears to be an important determinant of the presence or absence of F-actin in a cell. For example, in contrast to vascular cells, cortical cells show no indication of fluorescence labeling of F-actin after incubation with fluorescent phallicidin. Cytoplasmic streaming is seen only in vascular cells and in a pattern that reflects the intracellular distribution of F-actin.

Ley/H: an endothelial-selective, cytokine-inducible, angiogenic mediator

Endothelial cells (ECs) are key participants in angiogenic processes that characterize tumor growth, wound repair, and inflammatory diseases, such as human rheumatoid arthritis (RA). We and others have shown that EC molecules, such as soluble E-selectin, mediate angiogenesis. Here we describe an EC molecule, Lewisy-6/H-5-2 glycoconjugate (Ley/H), that shares some structural features with the soluble E-selectin ligand, sialyl Lewisx (sialyl Lex). One of the main previously recognized functions of Lewisy is as a blood group glycoconjugate. Here we show that Ley/H is rapidly cytokine inducible, up-regulated in RA synovial tissue, where it is cell-bound, and up-regulated in the soluble form in angiogenic RA compared with nonangiogenic osteoarthritic joint fluid. Soluble Ley/H also has a novel function, for it is a potent angiogenic mediator in both in vitro and in vivo bioassays. These results suggest a novel paradigm of soluble blood group Ags as mediators of angiogenic responses and suggest new targets for therapy of diseases, such as RA, that are characterized by persistent neovascularization.

Cytokeratin expression and hyaluronic acid production in cultures of human synovial microvascular endothelial cells: influence of cytokines and growth factors

OBJECTIVES

To isolate and characterize human synovial endothelial cells and to determine the effects of cytokines and fibroblast growth factor on human synovial endothelial (HSE) cell hyaluronic acid production.

METHODS

Endothelial cells were isolated from primary cultures of human synovial cells by fluorescent activated cell sorting based on the incorporation of a fluorescent derivative of acetylated low-density lipoprotein (DiI-Ac-LDL). Identity of endothelial cells was confirmed by positive immunostaining for von Willebrand factor (vWf), cytokeratins, endoglin, and reactivity with the lectin ulex europeans agglutinin (UEA). Hyaluronic acid production was measured by a radioligand-binding assay.

RESULTS

HSE cells were isolated and maintained in long-term culture. The identity of the cultured cells as endothelial was based on uniform uptake of a (DiI-Ac-LDL), immunoreactivity for vWf, and endoglin and the binding of the lectin UEA. In addition, small blood vessels in the synovium were stained selectively with anticytokeratin antibodies K462 (cytokeratin 19 specific) and K8.13 (reactive for cytokines 1, 5, 6, 7, 8, 10, 11, and 18). Isolated HSE cells also demonstrated immunoreactivity with these cytokeratin antibodies. The cytokeratins identified by the monoclonal antibody clone K8.13 demonstrated a diffuse, fibrillar staining pattern. The cytokeratin distribution revealed with monoclonal antibody K4.62 (cytokeratin 19) was also fibrillar; however, the majority of cells also demonstrated numerous punctuate cytoplasmic vesicular structures. Treatment of HSE cells with interleukin-1 alpha (IL-1 alpha) or acidic fibroblasts growth factor (aFGF), but not tumor necrosis factor (TNF alpha), dramatically reduced the vesicular structures staining with the K4.62 antibody. HSE cells produced hyaluronic acid (HA) at a constitutive rate of 200-800 ng/10(5) cells/24 h, which could be upregulated when the cells were incubated with either IL-1 alpha or aFGF. HA production was not significantly increased when HSE cells were incubated with TNF alpha, IL-4 or interferon-gamma.

CONCLUSIONS

Synovial microvascular endothelial cells produce and secrete HA and endothelial HA secretion is upregulated by IL-1 and aFGF. IL-1 and aFGF also reduce the number of vesicular-like structures immunoreactive with a monoclonal antibody to cytokeratin 19. These studies suggest that cytokine stimulation of local endothelial secretion and/or accumulation of HA may influence leukocyte adhesion to the synovial endothelium.

Flavonoids inhibit cytokine-induced endothelial cell adhesion protein gene expression

Treatment of human endothelial cells with cytokines such as interleukin-1, tumor necrosis factor-alpha (TNF-alpha) or interferon-gamma induces the expression of specific leukocyte adhesion molecules on the endothelial cell surface. Interfering with either leukocyte adhesion or adhesion protein upregulation is an important therapeutic target as evidenced by the potent anti-inflammatory actions of neutralizing antibodies to these ligands in various animal models and in patients. In the present study we report that cotreatment of human endothelial cells with certain hydroxyflavones and flavanols blocks cytokine-induced ICAM-1, VCAM-1, and E-selectin expression on human endothelial cells. One of the most potent flavones, apigenin, exhibited a dose- and time-dependent, reversible effect on adhesion protein expression as well as inhibiting adhesion protein upregulation at the transcriptional level. Apigenin also inhibited IL-1 alpha-induced prostaglandin synthesis and TNF-alpha-induced IL-6 and IL-8 production, suggesting that the hydroxyflavones may act as general inhibitors of cytokine-induced gene expression. Although apigenin did not inhibit TNF-alpha-induced nuclear translocation of NF-kappa B(p50(NFKB1)/p65(RelA)) we found this flavonoid did inhibit TNF-alpha induced beta-galactosidase activity in SW480 cells stably transfected with a beta-galactosidase reporter construct driven by four NF-kappa B elements, suggesting an action on NF-kappa B transcriptional activation. Adhesion of leukocytes to cytokine-treated endothelial cells was blocked in endothelial cells cotreated with apigenin. Finally, apigenin demonstrated potent anti-inflammatory activity in carrageenan induced rat paw edema and delayed type hypersensitivity in the mouse. We conclude that flavonoids offer important therapeutic potential for the treatment of a variety of inflammatory diseases involving an increase in leukocyte adhesion and trafficking.

Chemokine gene expression and secretion by cytokine-activated human microvascular endothelial cells. Differential regulation of monocyte chemoattractant protein-1 and interleukin-8 in response to interferon-gamma

The elicitation of leukocytes from the circulation to inflamed tissue depends on the activation of both the leukocyte and endothelial cell. In this study we determined the gene expression and secretion patterns for the chemokines interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) in cytokine- and lipopolysaccharide (LPS)-treated cultured human lung microvascular endothelial cells (HLE). HLE constitutively expressed low levels of MCP-1 and IL-8. Treatment of HLE with a variety of cytokines and LPS up-regulated both IL-8 mRNA expression and release of immunoreactive IL-8 with an order of potency tumor necrosis factor-alpha (TNF-alpha) >> IL-1 alpha > LPS, whereas interferon-gamma (IFN-gamma) had no effect on IL-8 mRNA or antigenic levels. However, IFN-gamma, in combination with high doses of IL-1 alpha, resulted in a synergistic increase in IL-8 generation. MCP-1 gene expression and secretion was induced in a dose-dependent manner after IL-1 alpha, TNF-alpha, IFN-gamma, and LPS activation of HLE. IL-1 alpha was the most potent inducer of MCP-1 generation and LPS was relatively ineffective. IFN-gamma, in combination with low doses of IL-1 alpha, resulted in a synergistic increase in MCP-1 generation by HLE. These results demonstrate that although IL-8 and MCP-1 generation by HLE occurs on cytokine treatment, the relative ability of a given cytokine to elicit IL-8 generation is not directly parallel to effects on MCP-1 generation. These data suggest that the regulation of IL-8 and MCP-1 expression exhibit significant differences in their mechanisms. Such differences in the expression of specific chemokines may explain the specific appearance of various leukocytes at sites of inflammation and injury. These data also directly demonstrate that the lung microvascular endothelium contribute to the cytokine network of the lung, with the ability to respond to locally generated cytokines and to produce potent mediators of the local inflammatory response.

Induction of cyclooxygenase II in human synovial microvessel endothelial cells by interleukin-1. Inhibition by glucocorticoids

OBJECTIVE

To characterize the effects of interleukin-1 alpha (IL-1) on prostanoid biosynthesis by human rheumatoid synovium microvessel endothelium (HSE).

METHODS

HSE cells were treated with cytokines, metabolic inhibitors, and steroids under various conditions, and prostaglandin biosynthesis was determined by radioimmunoassay. Newly synthesized cyclooxygenase (COX) was quantitated by immunoprecipitation of metabolically labeled HSE cell lysates. The effects of IL-1 on levels of messenger RNA (mRNA) for COX II were also determined.

RESULTS

IL-1 induced an increase in COX activity (as assessed by prostaglandin E2 release) that was dose- and time-dependent and was blocked by cycloheximide, actinomycin D, and dexamethasone. IL-1 induced a selective increase in COX II mRNA and biosynthesis of COX II protein that was blocked by dexamethasone.

CONCLUSION

IL-1 treatment of HSE cells induces COX II, as demonstrated by both Northern blotting and immunoprecipitation. The induction of COX II expression provides, at least in part, a mechanism for the pronounced increase in prostanoid synthesis observed in HSE cells following incubation with IL-1. The selective up-regulation of HSE COX II by inflammatory cytokines such as IL-1 suggests that development of specific pharmaceutical inhibitors for this novel isozyme may provide significant new therapeutic advantages in the treatment of RA.

Regulation of the expression of intercellular adhesion molecule 1 in cultured human endothelial cells derived from rheumatoid synovium

OBJECTIVE

To examine the regulation of intercellular adhesion molecule 1 (ICAM-1) in human synovial microvascular endothelial cells (HSE) and human umbilical vein endothelial cells (HUVE) upon exposure to a variety of agents.

METHODS

Cultured endothelial cells were treated with various cytokines alone and in combination. The expression of ICAM-1 was evaluated at several levels, including an investigation of messenger RNA (mRNA) and surface protein expression.

RESULTS

Treatment of HSE with interleukin-1 alpha (IL-1 alpha) or tumor necrosis factor alpha (TNF alpha) resulted in minimal increases in ICAM-1 expression, in contrast to findings with HUVE. Incubation of HUVE or HSE with IL-1 or TNF in combination with interferon-gamma (IFN gamma) greatly potentiated the increase in ICAM-1 surface expression. The synergistic effect of IFN gamma and TNF was confirmed by several methods, including a cell-based enzyme-linked immunosorbent assay, fluorescence-activated cell sorting, immunofluorescence staining, and determination of mRNA levels. IFN gamma also augmented the actions of several other agonists on HSE, i.e., IL-4, lipopolysaccharide, and TNF beta/lymphotoxin. Immunoprecipitation of TNF alpha + IFN gamma-stimulated, 125I-labeled HSE cells with anti-ICAM-1 revealed a single 90-kd band, similar in size to ICAM-1 from HUVE treated in an identical manner. Unexpectedly, IFN gamma alone was a potent stimulus for HSE ICAM-1 mRNA synthesis, but was relatively ineffective in HUVE.

CONCLUSION

These studies indicate that IFN gamma plays a critical synergistic role in the regulation of ICAM-1 expression in human synovial endothelial cells.

Isolation and characterization of human and rat cardiac microvascular endothelial cells

Although reciprocal intercellular signaling may occur between endocardial or microvascular endothelium and cardiac myocytes, suitable in vitro models have not been well characterized. In this report, we describe the isolation and primary culture of cardiac microvascular endothelial cells (CMEC) from both adult rat and human ventricular tissue. Differential uptake of fluorescently labeled acetylated low-density lipoprotein (Ac-LDL) indicated that primary isolates of rat CMEC were quite homogeneous, unlike primary isolates of human ventricular tissue, which required cell sorting based on Ac-LDL uptake to create endothelial cell-enriched primary cultures. The endothelial phenotype of both primary isolates and postsort subcultured CMEC and their microvascular origin were determined by characteristic histochemical staining for a number of endothelial cell-specific markers, by the absence of cells with fibroblast or pericyte-specific cell surface antigens, and by rapid tube formation on purified basement membrane preparations. Importantly, [3H]-thymidine uptake was increased 2.3-fold in subconfluent rat microvascular endothelial cells 3 days after coculture with adult rat ventricular myocytes because of release of an endothelial cell mitogen(s) into the extracellular matrix, resulting in a 68% increase in cell number compared with CMEC in monoculture. Thus biologically relevant cell-to-cell interactions can be modeled with this in vitro system.

Isolation, cultivation, and partial characterization of microvascular endothelium derived from human lung

Primary cultures of peripheral lung lobes were grown in a highly supplemented medium. Human lung endothelial cells (HLE) were isolated from the mixed population by FACS. The cells proliferated rapidly and were serially cultivated for at least 16 passages. Both early and late passage cells were positive for the standard endothelial markers. Factor VIII related-antigen (Factor VIII R-Ag), angiotensin-converting enzyme, acetylated low-density lipoprotein labeled with 1,1'-dioctadecyl-1,3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI-Ac-LDL) uptake, and bound the lectin Ulex europaeus agglutinin (UEA). Prostaglandin E2 was the major cyclooxygenase product of HLE, in contrast to human umbilical vein endothelial cells (HUVE), which synthesized PGI2 in excess of PGE2. Factor VIII R-Ag exhibited a diffuse cytoplasmic as well as an extracellular fibrillar distribution in HLE, in contrast to a vesicular (Weibel-Palade body) cytoplasmic distribution in HUVE. The HUVE did demonstrate some extracellular fibrillar Factor VIII R-Ag as well. Urokinase was the predominant plasminogen activator (PA) secreted by HLE, whereas tissue PA was predominant in HUVE cultures. HLE formed tube-like structures within 2 h of plating on a Matrigel matrix whereas HUVE formed larger tube-like structures only after 1 or more days. The properties described here indicate that human lung microvessel endothelium can be isolated and continuously grown from small tissue segments and express a number of properties that differ from those of HUVE. These studies provide further support for the concept that endothelial cells from different sources can exhibit considerable heterogeneity relating to their phenotypic and biochemical properties.

Endotoxin-induced exposure of pulmonary glycoproteins in an intact animal

A method has been developed to radioiodinate luminally disposed endothelial proteins in an in situ perfused lung system without causing obvious vascular changes. The spectrum of endothelial cell proteins labeled in control animals and those treated with endotoxin for 45 min were compared. No changes in gross tissue morphology or in the distribution of radiolabel (125I-s-SHPP) were detected in control or treated lungs. Lectin affinity purification was applied to a lung membrane fraction to isolate labeled proteins, which were in turn resolved by gel electrophoresis and autoradiography. Comparisons of gel autoradiographs from control and treated lungs identified eight glycoproteins, the labeling of which was enhanced in endotoxin-treated animals. A similar lectin affinity analysis of radiolabeled effluent blood cells from the lungs identified only two proteins, neither of which were consistently changed by endotoxin pretreatment. A glycoprotein response can, therefore, be measured at the pulmonary endothelial surface on endotoxin administration to the whole animal without causing obvious lung injury.

Molecular mapping of pulmonary endothelial membrane glycoproteins of the intact rabbit lung

To study the biochemical characteristics of endothelium in vivo, we radioiodinated endothelial membrane proteins of the perfused rabbit lung using a water soluble analog of the Bolton-Hunter reagent, 125I-sulfosuccinimidyl (hydroxyphenyl) propionate (125I-s-SHPP). This technique led to a 10-fold increase in specific activity of radioiodinated lung membrane protein compared with our previously reported method using lactoperoxidase and glucose oxidase-catalyzed radioiodination. Tissue autoradiography confirmed that radioiodination was largely confined to the endothelium. Perfusion pressure, wet-to-dry weight ratios, and the morphological appearance of the lungs were within normal limits, indicating that the procedure does not cause apparent lung injury. Lectin binding to a crude membrane fraction of 125I-s-SHPP labeled lung led to isolation of several putative endothelial membrane proteins. Immunoprecipitation studies with appropriate antibodies enabled the identification of radioiodinated angiotensin-converting enzyme and beta 2-microglobulin associated major histocompatibility complex class I molecules in the membrane fraction. This technique will be useful for studying biochemical responses of the endothelium in vivo to a variety of pharmacological and physiology stimuli.

Isolation of rabbit pulmonary microvascular endothelial cells and characterization of their angiotensin converting enzyme activity

An in vitro model using cultured rabbit pulmonary endothelial cells of microvascular origin was developed to define the luminal surface membrane characteristics of microvascular endothelium. Endothelial cells were isolated from peripheral lung segments and sorted after preferential uptake of a fluorescent derivative, diiodoindocarbo cyanine acetylated-LDL. Cells were further characterized by demonstrating angiotensin converting enzyme (ACE) on their surface by means of indirect immunofluorescence. ACE activity and its pharmacologic modification were then studied as functional assays of cell activity. Hydrolysis of Benz-phe-ala-pro (BPAP), a synthetic substrate for ACE was saturable over a concentration range of 1 to 100 microns. Thus, BPAP hydrolysis in cultured microvascular endothelial cells behaves overall in a manner similar to that seen in large resistance vessels except that a portion of the hydrolysis is not inhibited by captopril, an ACE-specific inhibitor, indicating the presence of another protease capable of BPAP hydrolysis. Accordingly, this system can be used to compare ACE and other protease kinetics in microvessel cells with those of large vessel endothelium or perfused lungs.

In situ iodination of angiotensin-converting enzyme and other pulmonary endothelial membrane proteins

Biochemical responses of endothelial cells in culture to pharmacological or physiological stimuli are often extrapolated to define the behavior of the vascular endothelium in vivo. However, culture conditions cannot recreate the environment of endothelial cells in vivo. To compare cell functions in vivo and in vitro, we iodinated endothelial membrane proteins of both the perfused rabbit lung and cultured rabbit lung endothelial cells. Endothelial cell protein 125I-labeling in the perfused intact lung was catalyzed by lactoperoxidase and glucose oxidase immobilized on 3-10 microns polyacrylamide beads (Enzymobeads, Bio-Rad). Changes in 5-hydroxytryptamine uptake, angiotensin converting enzyme activity and perfusion pressure made before, during and/or after iodination were small, suggesting that the procedure does not grossly injury the lung. As confirmed by tissue autoradiography, iodination was confined to the vascular space. A subcellular "membrane" fraction of the whole homogenate was enriched for several iodinated proteins. Lectin binding further purified a library of putative iodinated endothelial membranes proteins, one of which was angiotensin-converting enzyme as shown by immunoprecipitation with goat anti-rabbit antibody to angiotensin-converting enzyme. Iodinated proteins of similar molecular weights were also isolated from cultured rabbit lung endothelium iodinated under the same conditions, thus confirming the endothelial lineage of proteins iodinated in the intact lung. We conclude that this technique labels endothelial surface proteins in the intact lung without causing observable tissue injury and thus should be valuable in the study of the physiology and pathophysiology of the vascular lining in vivo.

Attachment of plasma membranes of cultured cells to silicon chips for high magnification imaging in scanning electron microscopy

In the membrane preparation method described in this paper, a polylysine-coated silicon chip is adsorbed to the exposed apical surface of a cell monolayer. Upon removal, the adsorbed chip separates the plasmalemma from the residual bodies of the cultured cells. This sandwich-membrane separation approach simplifies access to the cytoplasmic aspects of both the apical and the basal plasmalemma which remains on the culture substrate and is covered to a varied extent by cytoplasmic infrastructures. To stabilize the attached membranes, small crosslinking agents are used in a controlled osmium impregnation. Large crosslinkers are avoided since they induce thickening of fine structures. Optimal conditions for attachment of plasmalemma of cultured adrenal endothelial cells to the cationic chip are defined. Effective cleaning procedures of the chips and useful molecular weights of polylysine are determined by quantitating colloidal gold adherence to the surface of the chips. The specimens are examined by high resolution scanning electron microscopy.

Extracellular matrix specificity for the differentiation of capillary endothelial cells

Capillary endothelial cells in a fenestrated vasculature contain openings in attenuated areas of the cytoplasm which are often covered with one or two diaphragms. However, due to endothelial cell dedifferentiation upon culturing, such indicative membrane structure are often not expressed. The expression of a more differentiated phenotype can be regulated by the extracellular matrix to which the cells attach. In addition, during angiogenesis endothelial cell migration enables their interaction with other cell types and matrices which may directly affect endothelial cell growth and function. We report the ability to modify the expression of diaphragmed fenestrations and transcapillary channels in capillary endothelial cells by specific extracellular matrices. When the number of membrane openings is measured, growth of the cells on Madin--Darby canine kidney cell matrix results in the greatest number while other matrices or isolated matrix components are only partially active. Production of such a biologically active matrix not only allows an avenue to identify fenestrae-associated proteins but also provides an easy culture method to more closely mimic the in vivo phenotype of endothelial cells.

Albumin interacts specifically with a 60-kDa microvascular endothelial glycoprotein

Confluent monolayers of microvascular endothelial cells, derived from the rat epididymal fat pad and grown in culture, were radioiodinated by using the lactoper-oxidase method. Their radioiodinated surface polypeptides were detected by NaDodSO4/PAGE (followed by autoradiography) and were characterized by both lectin affinity chromatography and protease digestion to identify the proteins involved in albumin binding. All detected polypeptides were sensitive to Pronase digestion, whereas several polypeptides were resistant to trypsin. Pronase treatment of the cell monolayer significantly reduced the specific binding of radioiodinated rat serum albumin, but trypsin digestion did not. Limax flavus, Ricinus communis, and Triticum vulgaris agglutinins competed significantly with radioiodinated rat serum albumin binding, whereas other lectins did not. A single 60-kDa glyco-protein was precipitated in common by these three lectins and was trypsin-resistant and Pronase-sensitive. Rat serum albumin affinity chromatography columns weakly but specifically bound a 60-kDa polypeptide from cell lysates derived from radioiodinated cell monolayers. These findings indicate that the 60-kDa glycoprotein is directly involved in a specific interaction of albumin with the cultured microvascular endothelial cells used in these experiments.

Specific albumin binding to microvascular endothelium in culture

The specific binding of rat serum albumin (RSA) to confluent microvascular endothelial cells in culture derived from the vasculature of the rat epididymal fat pad was studied at 4 degrees C by radioassay and immunocytochemistry. Radioiodinated RSA (125I-RSA) binding to the cells reached equilibrium at approximately 20 min incubation. Albumin binding was a slowly saturating function over concentrations ranging from 0.01 to 50 mg/ml. Specific RSA binding with a moderate apparent affinity constant of 1.0 mg/ml and with a maximum binding concentration of 90 ng/cm2 was immunolocalized with anti-RSA antibody to the outer (free) side of the endothelium. Scatchard analysis of the binding yielded a nonlinear binding curve with a concave-upward shape. Dissociation rate analysis supports negative cooperativity of albumin binding, but multiple binding sites may also be present. Albumin binding fulfilled many requirements for ligand specificity including saturability, reversibility, competibility, and dependence on both cell type and cell number. The results are discussed in terms of past in situ investigations on the localization of albumin binding to vascular endothelium and its effect on transendothelial molecular transport.

Fluorescence light microscopy of F-actin in retinal rods and glial cells

The actin cytoskeleton of rod photoreceptors and glial cells in toad retina has been directly viewed using fluorescence microscopy of cells labeled with a potent phallotoxin that specifically binds to F-actin. The three-dimensional organization of this cytoskeletal protein consists of actin filaments, which course through the inner segment and end at the tips of the calycal processes surrounding the base of the outer segment. A transverse layer of actin staining is also observed at the base of rod outer segments in the region where new discs are formed. At the level of the external limiting membrane, evidence has been found for rings of actin within the glial cells that surround the photoreceptors. These actin rings form a structural meshwork in which photoreceptor cells are embedded.

F-actin aggregates in transformed cells contain alpha-actinin and fimbrin but apparently lack tropomyosin

Transformation-specific F-actin structures are examined in tumor cells after in vitro tumor cell growth alone or on an untransformed cell monolayer. In transformed cells F-actin aggregates near the ventral plasma membrane in close substrate adhesion areas contain the cytoskeletal proteins alpha-actinin and fimbrin but, unlike microfilament bundles, are not labeled with antibody against tropomyosin. By electron microscopy the dense ventral aggregates in transformed cells resemble stress fiber termini found at the membrane in normal cells. These transformed-cell cytoskeletal structures are not limited solely to substrate adhesion areas; they are also expressed at cell-cell contacts about 48 h after transformed cells are plated on untransformed cells. These specialized F-actin aggregates appear to be implicated in the processes of penetration of these transformed cells between adjoining untransformed cells in vitro.

Endothelial plasmalemmal vesicles have a characteristic striped bipolar surface structure

Capillary endothelial cells have a large population of small (65-80 nm diameter in transmission electron microscopy) vesicles of which a large fraction is associated with the plasmalemma of the luminal and abluminal side. We studied the fine structure and distribution of these plasmalemmal vesicles by high resolution scanning electron microscopy in cultured endothelial cells obtained from bovine adrenal cortical capillaries. Cell monolayers were covered with polylysine-coated silicon chips, split in high potassium buffer, fixed in aldehyde mixtures, and then treated with OsO4 and thiocarbohydrazide. After critical point drying, the specimens were coated with a thin (less than 2 nm) continuous film of chromium. On the cytoplasmic aspect of the dorsal plasmalemmal fragments seen in such specimens, plasmalemmal vesicles appear as uniform vesicular protrusions approximately 70-90 nm in diameter, preferentially concentrated in distinct large fields in which they occur primarily as single units. Individual plasmalemmal vesicles exhibit a striped surface fine structure which consists of ridges approximately 10 nm in diameter, separated by furrows and oriented as meridians, often ending at two poles on opposite sides of the vesicles in a plane parallel to the plasmalemma. This striped surface structure is clearly distinct from the cage structure of coated pits found, at low surface density, on the same specimens. The cytoplasmic aspect of the plasmalemma proper is covered by a fibrillar infrastructure which does not extend over plasmalemmal vesicles but on which the latter appear to be anchored by fine filaments.

The formation of fenestrations and channels by capillary endothelium in vitro

Microvascular endothelial cells isolated from fenestrated capillaries have been shown to form tubes in vitro, thereby demonstrating that they retain the ability to express some degree of their in vivo differentiated phenotype. However, some of their physiologically important structural features, such as transendothelial openings (i. e., diaphragmed fenestrations and transendothelial channels) are lost or are greatly reduced in number. In this study, cloned bovine adrenal cortex endothelial cells were cultured on plastic or on a basal lamina produced by Madin-Darby canine kidney (MDCK) cells for up to 17 days postconfluence. All cultures were then routinely fixed and processed for electron microscopic morphometry. For cells grown on plastic for 17 days postconfluence, the linear density of transendothelial openings in endothelial profiles less than 400 nm thick was found to be 0.007 openings per micron. On MDCK matrix, however, the linear density of transendothelial openings in endothelial profiles less than 400 nm thick was found to be 0.157 per micron. Occasionally some cells formed "tube-like" structures that also contained diaphragmed fenestrations and transendothelial channels on both sides of the tubes. These findings suggest that the substrate on which endothelial cells are grown can affect their differentiation.

Fluorescent erythrosin B is preferable to trypan blue as a vital exclusion dye for mammalian cells in monolayer culture

Erythrosin B and trypan blue are tested and compared for their effectiveness as vital exclusion stains for mammalian cells in monolayer culture. Both stains are supposed to mark cells that have lost membrane integrity. Fluorescein diacetate (FDA), an efficient vital inclusion stain, is used as a control, as it marks cells retaining membrane integrity. Erythrosin B and FDA are used as fluorescent dyes, whereas trypan blue colors via light absorption. The effectiveness of both vital exclusion stains is assayed by their ability to stain a high percentage of monolayer cells exposed to treatments lethal to an entire cell population. Two types of lethal treatment, severe heat and metabolic poison, are employed. Erythrosin B stains all monolayer cells immediately after complete lethal treatment. Trypan blue optimally stains only about 60% of monolayer cells. Cell staining by erythrosin B and by FDA are found to be mutually exclusive. This result demonstrates the coincidence of viability indications by erythrosin B and FDA and thus confirms the reliability of both viability stains as they probe membrane permeability via independent mechanisms. This study shows that erythrosin B is an effective, nontoxic, and convenient fluorescent vital exclusion dye for three mammalian cell lines in monolayer culture, but tends to disqualify trypan blue for this application.

Regulation and drug insensitivity of F-actin association with adhesion areas of transformed cells

F-actin aggregates have been found near the substrate attachments in a variety of transformed cells (Carley et al., 1981). Interference reflection microscopy shows that these aggregates are present in central close adhesion areas in Rous sarcoma virus (RSV)-transformed rat kidney cells. If these transformed cells are incubated with N6, O2-dibutyryl 3':5'-cyclic monophosphoric acid (db-cAMP), adenosine 5'-monophosphoric acid (5'-AMP) or adenosine, the F-actin aggregates and their associated close adhesion areas disappear, and the cells flatten out. Treatment of untransformed cells with db-cAMP spreads their focal adhesion plaques and thickens microfilament bundles. Furthermore, F-actin aggregates are substantially more resistant to cytochalasin B and the Ca2+ ionophore A23187 than microfilament bundles in untransformed cells. These differences between F-actin complexes in untransformed and in RSV-transformed cells, with respect to morphology and sensitivities to db-cAMP and cytoskeleton-disrupting drugs, define properties of the change in F-actin regulation and association with the plasma membrane due to transformation.

F-actin aggregates may activate transformed cell surfaces

Observations on the role of transformation-specific F-actin aggregates [Carley et al, 1981] in altering morphology, adhesion and intercellular interaction in transformed cells are reported here. The appearance and disappearance of membrane- and substrate-associated F-actin aggregates (MAG and SAG, respectively) are followed in a cell line temperature-sensitive for transformation. Since MAG structures also appear near the membrane in suspension cultures of transformed cells and in transformed cells in coculture with untransformed cells, they appear to function at cell-cell contacts. Unlike microfilament bundles in untransformed cells, MAG and SAG do not contain the F-actin regulatory protein tropomyosin. The lack of tropomyosin in these structures near the membrane is reminiscent of areas of an exceptionally active actin cytoskeleton usually associated with motile processes of the normal cell membrane. Such areas of membrane-cytoskeletal interaction may be involved in the aberrant cell-cell communication as well as the aggressive behavior often seen in transformed cells.

ATP-dependent phosphate transport in sarcoplasmic reticulum and reconstituted proteoliposomes

During uptake of Ca2+ by rabbit sarcoplasmic reticulum, about 1 mumol of 32Pi was taken up per mumol 45Ca2+ transported. The uptake of Pi was dependent on external Ca2+, Mg2+ and ATP. Intravesicular Ca2+ did not substitute for external Ca2+. In contrast to the accumulation of Ca2+ which was abolished by the ionophore A23187, the uptake of Pi continued to take place provided sufficient Ca2+ was present in the medium. Thus, a Ca2+ gradient did not seem to be required. Similar observations were made with proteoliposomes reconstituted with membrane preparations of sarcoplasmic reticulum and soybean phospholipids. However, when purified Ca2+ -ATPase was used for reconstitution, there was ATP-dependent Ca2+ uptake but no ATP-dependent Pi transport was observed. These data show that the mechanism of Pi transport cannot be a passive movement in response to a Ca2+ gradient but appears to be catalyzed by a specific protein, which is inactivated during purification of the Ca2+ -ATPase. A protein that catalyzes Pi transport in reconstituted vesicles has been solubilized by extraction of sarcoplasmic reticulum with sodium cholate.

F-actin aggregates in transformed cells

Polymerized actin has been found aggregated into distinctive patches inside transformed cells in culture. The F-actin-specific fluorescent probe, nitrobenzoxadiazole-phallacidin, labels these F-actin aggregates near the ventral cell surface of cells transformed by RNA or DNA tumor viruses, or by chemical mutagens, or spontaneously. Their appearance in all eight transformed cell types studied suggests their ubiquity and involvement in transformation morphology. Actin patches developed in normal rat kidney (NRK) cells transformed by a temperature-sensitive mutant of Rous sarcoma virus (LA23-NRK) within 30 min after a shift from the nonpermissive (39 degrees C) to the permissive temperature (32 degrees C). Patch appearance paralleling viral src gene expression tends to implicate pp60src kinase activity in destabilizing the cytoskeleton. However, appearance of the actin aggregates in cells not transformed by retrovirus calls for alternative mechanisms, perhaps involving an endogenous kinase, for this apparently common trait.

The correlation of plasma membrane microvilli and intracellular cyclic AMP content in a rat epitheloid kidney cell line

Modulation of the intracellular concentration of cyclic AMP has been associated with a regulatory role in cell division, cell morphology, and physical properties of the plasma membrane. Untransformed rat kidney cells in culture exhibit epitheloid morphology, high intracellular cyclic AMP levels, and contact inhibition of growth. Untransformed rat kidney cells transformed with the Kirsten murine sarcoma virus exhibit a low cyclic AMP content, rapid growth rate, and a loss of contact inhibition. Scanning electron microscopy reveals a distinctive difference in the surface structure of the two cell types during Gl of the cell cycle. The surface of the transformed cell is covered with microvilli while its untransformed counterpart is devoid of microvilli. The presence of microvilli can be controlled as a function of temperature by two temperature-sensitive mutants of the Kirsten sarcoma virus (ts6t6 and ts371 cl 5). In the ts6t6 mutant, growth at 32 degrees C results in a low cyclic AMP content and the presence of microville, while growth at 39 degrees C results in a high cyclic AMP content and a decrease in microvilli. The opposite effect is seen with the ts371 cl 5 mutant. Correlation of cyclic AMP content with the presence of microvilli suggests that this surface phenomenon is a function of cyclic AMP concentration.