Identification of Dictyostelium discoideum plasma membrane proteins by cell surface labeling and quantitative two-dimensional gel electrophoresis

Analysis of two-dimensional protein patterns from developmental stages of the potato cyst-nematode,Globodera rostochiensis

Two-dimensional polyacrylamide gel electrophoresis was used to examine the differences in total protein composition between two motile stages and two sedentary stages of the potato cyst-nematode,Globodera rostochiensis. Using a sensitive silver stain, 542 reproducible protein spots were distinguished. A list of these spots is presented, showing their apparent molecular weights, estimated isoelectric points, and occurrences in the different developmental stages. When the protein patterns were compared, 401 spots were found to change their presence or size in one or more of the four developmental stages. It is therefore estimated that during the post-embryonic development ofG. rostochiensis, 74% of the polypeptides undergo modulation of their synthesis, or are affected by protein degradation or modification. In the motile stages several abundant proteins were present, which disappeared or decreased in concentration in the sedentary stages. Some of these proteins are presumably muscle proteins, and their modulation may illustrate the degeneration of body-wall musculature in the sedentary stages. It is concluded that the potato cyst-nematode has a very dynamic protein metabolism.

Phagosomal proteins of Dictyostelium discoideum

In recognizing food particles. Dictyostelium cell-surface molecules initiate cytoskeletal rearrangements that result in phagosome formation. After feeding D. discoideum cells latex beads, early phagosomes were isolated on sucrose step gradients. Protein analyses of these vesicles showed that they contained glycoproteins and surface-labeled species corresponding to integral plasma membrane proteins. Cytoskeletal proteins also were associated with phagosomes, including myosin II, actin and a 30 kDa-actin bundling protein. As seen by the acridine orange fluorescence of vesicles containing bacteria, phagosomes were acidified rapidly by a vacuolar H(+)-ATPase that was detected by immunoblotting. Except for the loss of cytoskeletal proteins, few other changes over time were noted in the protein profiles of phagosomes, suggesting that phagosome maturation was incomplete. The indigestibility of the beads possibly inhibited further endocytic processing, which has been observed by others. Since nascent phagosomes contained molecules of both the cytoskeleton and plasma membrane, they will be useful in studies aimed at identifying specific protein associations occurring between membrane proteins and the cytoskeleton during phagocytosis.

Peripheral and central vascular smooth muscle cells from rat lung exhibit different cytoskeletal protein profiles but similar growth factor requirements

In pulmonary vascular remodelling, the lining smooth muscle cells undergo various forms of growth involving cellular hypertrophy and hyperplasia. Differences in the growth pattern between central and peripheral regions suggested that cells from both should be obtained when investigating the cellular basis for the remodelling. Accordingly, we have obtained two smooth muscle cell types in culture: a cell from the central pulmonary artery (CC) and a cell morphologically similar to a pericyte (PC), from the periphery of the lung. Both cell types gave positive immunostaining for alpha-smooth muscle isoactin. In vivo, the alpha-isoactin was immunolocalized in the extracapillary vasculature. Quantitative two-dimensional gel electrophoresis of cell extracts showed that PC express more vimentin and gelsolin than CC. Despite the differences between PC and CC in the expression of cytoskeletal proteins, their response to growth factors was similar. Both cell types increased DNA synthesis when stimulated by exogenous PDGF-AB. This occurred in the absence of exogenous progression factors, but depended on a post-competence, suramin-sensitive mechanism that probably represents an autocrine progression factor. The cells were also stimulated by IGF-1 alone, in the absence of exogenous competence factors. At an IGF-1 concentration of 1 ng/ml, this response appeared specific for the IGF-1 receptor and was sensitive to pretreatment with pertussis toxin, thus implicating a role for a G protein.

Enhancing spot detection and reducing noise from digitized electrophoretic gel images using area processing filters

Twenty area processing filters and filter combinations were evaluated in an effort to optimize presentation of two-dimensional electrophoretic profiles to the Laplacian spot finder for maximal spot detection sensitivity. Images of electrophoresis gels were obtained by digitizing polyacrylamide gels at 1024 x 1024 picture elements (pixels) resolution with 256 grey scale levels using the charge coupled device (CCD) camera of the Millipore Bio Image 110S computerized imaging system. The images were imported into an Apple Macintosh microcomputer and selectively enhanced by applying various area processing filters. Previously described least squares fit, low-pass, Gaussian and median filters were used to reduce noise in the digitized images. These filters differ in that during the summation process the least squares template weighs the immediately adjacent pixels more heavily than the Gaussian template. The low-pass filters weigh all neighboring pixels equally. Median filters replace the pixel of interest with the middle (median) value of the pixel neighborhood. An analysis of convolution filter sizes indicated that a 7 x 7 matrix was optimal for 22 cm x 22 cm gels. When using the median area processing procedure, however, the 3 x 3 filter was found to be superior to the 7 x 7 filter. The 7 x 7 least squares filter significantly improved detection of low abundance polypeptides while having only minimal effects on the high abundance polypeptides. The 7 x 7 Gaussian and 3 x 3 median filters also improved detection of low abundance polypeptides but reduced the integrated areas of the high abundance polypeptides and thus their integrated optical densities as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in mucins from human whole saliva

The predominant mucins in human whole saliva, MG1 and MG2, serve to protect and to lubricate the oral cavity. In this study, both unstimulated and stimulated whole salivas were collected from two groups of subjects: young (18-35 years of age) and aged (65-83 years of age). The subjects were in apparent good health. Saliva samples from each subject were analyzed by SDS-PAGE. The gels were stained with Stains-all, and both MG1 and MG2 were quantitated by video-image densitometry. The protocol gave reproducible values for each mucin. The stimulated and unstimulated salivas from aged subjects showed significant reductions in concentrations of both MG1 and MG2, as quantitated in mucin dye-binding units. Possible associations of these reductions with the aging process are discussed.

Mercury-arc photolysis: a method for examining second messenger regulation of endothelial cell monolayer integrity

Cell-cell apposition in bovine pulmonary endothelial cell monolayers was modulated by inducing transient increases in intracellular adenosine 3':5'-cyclic monophosphate (cAMP) and 1,4,5-inositol triphosphate (IP3). This was accomplished by mercury-arc flash photolysis of o-nitrobenzyl derivatives of the second messengers (caged compounds). Second messenger release by the mercury-arc lamp was determined by radioimmunoassay of cAMP to have a t1/2 of approximately 8 min. Each second messenger induced the phosphorylation of a distinct subset of cytoskeletal proteins; however, both IP3 and cAMP increased vimentin phosphorylation. Actin isoform patterns were not altered by the second messengers. Intracellular pulses of IP3 in pulmonary endothelial cells caused disruption of endothelial monolayer integrity as determined by phase-contrast microscopy and by visualization of actin stress fibers with rhodamine-phalloidin. Intracellular pulses of cAMP increased cell-cell contact, cell surface area, and apposition. IP3 appeared to have its greatest effect on the actin peripheral band. In silicone rubber contractility assays this agent caused contraction of pulmonary microvascular endothelial cells as visualized by an increase in wrinkles beneath the cells. On the other hand, cAMP appeared to effect both the peripheral band and centralized actin domains. Caged cAMP caused relaxation of endothelial cells as visualized by a disappearance of wrinkles beneath the cells.

Macro- and microvascular endothelial cells in vitro: maintenance of biochemical heterogeneity despite loss of ultrastructural characteristics

Microvascular endothelial cells from bovine adrenal medulla and brain and macrovessel endothelial cells from bovine aorta were isolated and cultured under similar conditions in order to determine morphologic and biochemical heterogeneity in vitro. All three cell types exhibited nearly identical ultrastructural morphology and two-dimensional gel protein patterns of 35S-methionine-labeled whole cells. Two-dimensional gel analysis of 35S-methionine-labeled plasma membrane proteins however, revealed two-dimensional gel protein patterns unique to the tissue type from which the endothelial cells were isolated. This suggests that the functional significance of these specific endothelial cell types is manifested primarily in surface-associated proteins and that many of the differences are sustained in culture. To determine the potential of aorta, brain, and adrenal medulla endothelial cell (EC) cultures to respond to developmentally significant signals, morphology, growth pattern, and cell surface proteins were monitored in the presence and absence of growth factors. A 17 to 26% increase in cell density as well as an increase in the number of elongated and overlapping cells resulted when all three EC types were exposed to a mitogenic medium. Additionally, expression of specific glycoprotein profiles, as determined by Concanavalin A Western blotting of two-dimensional gels, was dependent on the presence or absence of growth factors in the medium. The ability to induce this morphologic and biochemical variation in the three endothelial cell types was maintained into later passage. Taken together, these data imply that endothelial cells isolated from different tissues exhibit and maintain biochemical heterogeneity and do not completely dedifferentiate into a common endothelial cell type in culture. Furthermore, expression of specific subsets of cell surface proteins is dependent on environmental conditions, and in some cases is both cell-type and media-type dependent. Thus, even though endothelial cells are considered terminally differentiated cells, there exists additional or "latent" heterogeneity in the ability of these different cells to respond to "developmental signals" (i.e. mitogenic medium) in vitro.

Cytokeratin filament modulation in pulmonary microvessel endothelial cells by vasoactive agents and culture confluency

Recently, bovine pulmonary microvascular endothelial cells (PMV) were shown to contain cytokeratin 8 and 19 intermediate filaments (Patton et al., 1990). In this study, we examine the effect of culture contiguity and vasoactive agents on the content and assembly of cytokeratins in PMV. Immunofluorescent staining of PMV cultures show a progressive increase in cytokeratin filament assembly. In freshly plated PMV, keratin appears as hazy staining (less than 4 hr) and later organizes into keratin 'plaques' (4 days) associated with cell-cell contacts; post confluent (greater than 7 days) PMV cultures contain fully assembled cytokeratin filaments which extend to the cell periphery and approach filaments in apposed cells. Vimentin filaments are also present in freshly plated PMV cultures but unlike cytokeratins, become less filamentous at confluency. This cell density-dependent modulation of cytokeratins is also demonstrated by densitometric analysis of autoradiographs of 35S-methionine labeled keratins in which PMV keratin content is elevated at high cell densities, while vimentin content remains constant. Desmoplakins I and II, components of desmosomes, could not be demonstrated in PMV by immunoblotting. PMV treated with permeability modulating agents (4 x 10(-3) M EGTA, 1 microM cytochalasin B, 1 microM bradykinin, 1 microM A23187, and 1 microM PMA) exhibit border retraction and altered keratin filament staining. From these studies we conclude: 1) cytokeratin 8 and 19 containing intermediate filaments are present in confluent PMV cultures with vimentin but without desmosomes, 2) the state of assembly of PMV cytokeratin and vimentin filaments appears to be oppositely affected by culture contiguity, and 3) treatment of monolayers with vasoactive agents alters the state of assembly of cytokeratin filaments. We speculate that modulation of cytokeratin assembly in PMV may be involved in regulation of pulmonary microvascular structure and function.

Expression of simple epithelial cytokeratins in bovine pulmonary microvascular endothelial cells

Polypeptides of bovine aortic, pulmonary artery, and pulmonary microvascular endothelial cells, as well as vascular smooth muscle cells and retinal pericytes were evaluated by two-dimensional gel electrophoresis. The principal cytoskeletal proteins in all of these cell types were actin, vimentin, tropomyosin, and tubulin. Cultured pulmonary microvascular endothelial cells also expressed 12 unique polypeptides including a 41 kd acidic type I and two isoforms of a 52 kd basic type II simple epithelial cytokeratin microvascular endothelial cell expression of the simple epithelial cytokeratins was maintained in cultured in the presence or absence of retinal-derived growth factor, and regardless of whether cells were cultured on gelatin, fibronectin, collagen I, collagen IV, laminin, basement membrane proteins, or plastic. Cytokeratin expression was maintained through at least 50 population doublings in culture. The expression of cytokeratins was found to be regulated by cell density. Pulmonary microvascular endothelial cells seeded at 2.5 X 10(5) cell/cm2 (confluent seeding) expressed 3.5 times more cytokeratins than cells seeded at 1.25 X 10(4) cells/cm2 (sparse seeding). Vimentin expression was not altered by cell density. By indirect immunofluorescence microscopy it was determined that the cytokeratins were distributed cytoplasmically at subconfluent cell densities but that cytokeratin 19 sometimes localized at regions of cell-cell contact after cells reached confluence. Vimentin had a cytoplasmic distribution regardless of cell density. These results suggest that pulmonary microvascular endothelial cell have a distinctive cytoskeleton that may provide them with functionally unique properties when compared with endothelial cells derived from the macrovasculature. In conjunction with conventional endothelial cell markers, the presence of simple epithelial cytokeratins may be an important biochemical criterion for identifying pulmonary microvascular endothelial cells.

Analysis of plasma membrane protein changes in Dictyostelium discoideum during concanavalin A induced receptor redistribution using two-dimensional gel electrophoresis

The 127 major polypeptides obtained from the purified plasma membrane of Dictyostelium discoideum were examined using two-dimensional gel electrophoresis and a microcomputer-based videodensitometer. Plasma membrane proteins were analyzed at four discrete stages of concanavalin A induced cell surface capping; (i) the cell surface in the absence of ligand (unbound), (ii) the surface immediately after ligand binding (bound), (iii) the cell surface after receptors had patched (patched) and (iv) the cell surface after receptors had capped (capped). Plasma membranes were obtained at various stages of capping by using a colloidal silica density perturbation technique which immediately immobilized the proteins, preserving their lateral distribution in the bilayer during the isolation. Proteins were characterized with respect to post-translational modification changes resulting from the capping process as well as changes in their association with the plasma membrane fraction. Posttranslational changes of plasma membrane proteins, such as phosphorylation, methylation and proteolytic cleavage, were not observed during the four stages of capping. Myosin heavy chain phosphorylation, however, decreased almost twofold during patching and capping. Actin, which is known to colocalize directly underneath capped receptors did not appear to be recruited to the cap from the cytoplasm.

Phenotypic comparison between mesothelial and microvascular endothelial cell lineages using conventional endothelial cell markers, cytoskeletal protein markers and in vitro assays of angiogenic potential

Endothelial and mesothelial cells are mesodermally derived simple squamous epithelial cells. A controversy concerning the ontogenetic origin of neoplasms derived from these cell types, commonly cited in the literature, is whether Kaposi's sarcoma is a mesothelioma or an angioma. To assess the similarities and differences between these cell types, pulmonary microvascular endothelial cells (PMVEC) and pericardial mesothelial cells (PMC) were cultured in vitro. PMVEC and PMC were found to be difficult to distinguish from one another by histological criteria alone. Both cell types formed contact-inhibited, and 'cobblestone', monolayers typical of simple epithelial cells. PMVEC and PMC demonstrated positive immunoreactivity to Factor VIII-related antigen and angiotensin-converting enzyme (ACE) antigen. They also showed uptake of 1,1'-dioctacecyl-1,3,3,3',3-tetramethyl-indocarbocyanine perchlorate acetylated low density lipoprotein (DiI-Ac-LDL) in 4 h. Both PMVEC and PMC expressed low ACE activities when compared to macrovessel endothelial cells. PMVEC and PMC shared similar isoform profiles for vimentin and actin. Both cell types expressed the simple epithelial keratins, cytokeratins 8 and 19, though PMC contained 50% more cytokeratins than PMVEC. Additionally, PMC contained cytokeratin 18, an intermediate filament protein not detectable in PMVEC. PMC formed 15 times as many epithelial ringlets or "stomata" as PMVEC. PMVEC but not PMC could be induced in vitro to differentiate into branching tube-like structures in response to their culture environment. Reorganization of PMVEC into vessel-like structures was more rapid and complete than PMC when embedded in three-dimensional collagen I lattices, cultured on Matrigel or exposed to a shaped-pulsed electromagnetic field. The angiogenic response of PMVEC to specialized culture conditions in vitro may reflect their phenotypic differentiation state characterized by anastomosing vascular structures in vivo, whereas PMC remain differentiated into monolayer sheet-like structures.