Membrane association of the hyaluronate stimulatory factor from LX-1 human lung carcinoma cells

LX-1 human lung carcinoma cells interact with human fibroblasts in culture to cause an increase in hyaluronate production (Knudson et al: Proceedings of the National Academy of Sciences of the United States of America 81:6767, 1984). It is shown here that a similar increase in hyaluronate production also occurs when membranes derived from LX-1 cells, or detergent extracts thereof, are added to cultures of the human fibroblasts. However, no stimulation occurs when membranes or extracts from fibroblasts are added to cultures of the LX-1 cells. The hyaluronate stimulatory factor present in the detergent extracts is a heat- and trypsin-sensitive protein, requires more than 12 h for its action on fibroblasts, causes an elevation in hyaluronate synthetase activity in membranes derived from the fibroblasts, and can be reconstituted into artificial lipid vesicles. Thus, it is concluded that the stimulatory factor is a membrane-bound protein present on the surface of the LX-1 cells and that it interacts with fibroblasts to induce increased hyaluronate synthesis.     

Matrix influence on the tumor cell stimulation of fibroblast collagenase production

Cocultures of rabbit fibroblasts and mouse B-16 melanoma cells produce increased levels of collagenase against type I collagen. This stimulatory effect was also found when fibroblasts were cultured in conditioned media from tumor cells. However, the level of the stimulatory factor in conditioned media was influenced by matrix deposited by fibroblasts. Thus, conditioned media collected from monolayers of B-16 plated on fibroblast matrix consistently showed high levels of the factor activity. The influence of the matrix on the level of the factor was not removed by treating the fibroblast matrix with collagenase or chondroitinase ABC and was not reproduced by collagen-coated dishes.     

Tumor cell stimulation of collagenase production by fibroblasts

Cocultures of rabbit fibroblasts with mouse tumor cells of epithelial origin showed increased collagenase production when compared to cultures of the individual cells. The stimulatory effect was observed when B-16 melanoma and A-10 adenocarcinoma cells, but not fibroblastic tumor cells or normal epithelial cells, were added to the fibroblasts. The effect was dependent on the cellular ratio between the normal fibroblasts and tumor cells and was mediated by a soluble factor produced by the tumor cells.     

Heparin and heparan sulfate binding sites on B-16 melanoma cells

We have reported previously that the production of a tumor cell factor that stimulates synthesis of fibroblast collagenase is influenced by a fibroblast-deposited matrix component, possibly heparan sulfate-proteoglycan. In this study, binding sites for heparin and heparan sulfate on mouse B-16 melanoma cells have been demonstrated. Binding of 3H-heparin and 35S-heparan sulfate has been shown to occur to whole cells, isolated membranes, and to a component(s) of detergent extracts of the membranes. Scatchard analysis of binding of 3H-heparin yielded a Kd of 2-5 x 10(-8) M and a Bmax of 0.5 x 10(7) heparin molecules bound per cell. Binding of 35S-heparan sulfate was of at least an order of magnitude lower affinity than heparin, but the Bmax was similar to that for heparin. Competition studies showed that 35S-heparan sulfate binding was inhibited totally by heparin and heparan sulfate and partially by dermatan sulfate, but no inhibition was obtained with hyaluronate or chondroitin sulfate. Binding of 3H-heparin was inhibited totally by heparin but to different extents by preparations of heparan sulfate from different tissue sources. The heparin/heparan sulfate binding activity is a protein(s) because it is destroyed by treatment with trypsin. Binding of 3H-heparin to transblots of the detergent extract of the B-16 cell membranes indicated that at least part of the binding activity is a 14,000-dalton protein.     

SecA protein, a peripheral protein of the Escherichia coli plasma membrane, is essential for the functional binding and translocation of proOmpA.

We have reconstituted protein translocation across plasma membrane vesicles of Escherichia coli using purified proOmpA and trigger factor, a 63 kd soluble protein. Treatment of membrane vesicles with urea inactivates them for translocation unless a factor present in cytoplasmic extracts is added during the translocation reaction. Sedimentation analysis showed that the stimulatory activity is of distinctly higher mol. wt than trigger factor. Cytoplasmic extracts from a strain that greatly overproduces the SecA protein are highly enriched in the stimulatory activity for untreated membranes and restore translocation to urea-treated membranes, suggesting that this protein is the stimulatory factor. This assay was used to monitor the isolation of SecA protein from the overproducing strain. The purified protein is soluble, yet binds peripherally to membranes with high affinity and supports translocation. Using pure proOmpA, SecA protein, trigger factor and urea-treated membranes, the protein export process was resolved into binding and translocation steps. We find that proOmpA binds to membrane vesicles with or without SecA protein, but that translocation only occurs when SecA was bound prior to proOmpA.     

pH-dependent fusion induced by vesicular stomatitis virus glycoprotein reconstituted into phospholipid vesicles

Purified G-protein from vesicular stomatitis virus was reconstituted into egg phosphatidylcholine vesicles by detergent dialysis of octyl glucoside. A homogeneous population of reconstituted vesicles could be obtained, provided the protein to lipid ratio was high (about 0.3 mol % protein) and the detergent removal was slow. The reconstituted vesicles were assayed for fusion activity using electron microscopy and fluorescence energy transfer. The fusion activity mediated by the viral envelope protein was dependent upon pH, temperature, and target membrane lipid composition. Incubation of reconstituted vesicles at low pH with small unilamellar vesicles containing negatively charged lipids resulted in the appearance of large cochleate structures, as shown by electron microscopy using negative stain. This process did not cause leakage of a vesicle-encapsulated aqueous marker. The rate of fusion was pH-dependent with a pK of about 4 and the apparent energy of activation for the fusion was 16 +/- 1 kcal/mol. G-protein-mediated fusion showed a large preference for target membranes which contain phosphatidylserine or phosphatidic acid. Inclusion of 36% cholesterol in any of the lipid compositions had no effect on the rate of fusion. These reconstituted vesicles provide a system to study the mechanism of pH-dependent fusion induced by a viral spike protein.     

Reconstitution of ciliary membranes containing tubulin

Membranes from the gill cilia of the mollusc Aequipecten irradians may be solubilized readily with Nonidet P-40. When the detergent is removed from the solution by adsorption to polystyrene beads, the proteins of the extract remain soluble. However, when the solution is frozen and thawed, nearly all of the proteins reassociate to form membrane vesicles, recruiting lipids from the medium. The membranes equilibrate as a narrow band (d = 1.167 g/cm3) upon sucrose density gradient centrifugation. The lipid composition of reconstituted membranes (1:2 cholesterol:phospholipids) closely resembles that of the original extract, as does the protein content (45%). Ciliary calmodulin is the major extract protein that does not associate with the reconstituted membrane, even in the presence of 1 mM calcium ions, suggesting that it is a soluble matrix component. The major protein of reconstituted vesicles is membrane tubulin, shown previously to differ hydrophobically from axonemal tubulin. The tubulin is tightly associated with the membrane since extraction with 1 mM iodide or thiocyanate leaves a vesicle fraction whose protein composition and bouyant density are unchanged. Subjecting the detergent-free membrane extract to a freeze-thaw cycle in the presence of elasmobranch brain tubulin or forming membranes by warming the extract in the presence of polymerization-competent tubulin yields a membrane fraction with little incorporated brain tubulin. This suggests that ciliary membrane tubulin specifically associates with lipids, whereas brain tubulin preferentially forms microtubules.     

Lipid composition of isolated epiphyseal cartilage cells, membranes and matrix vesicles.

1. Intact cells, cell fragments (membranes) and matrix vesicles were isolated from the proliferating and calcifying layers of epiphyseal cartilage by sequential hyaluronidase and collagenase digestion and differential centrifugation. Lipids were extracted and analyzed for various lipid classes and their fatty acid composition by column, thin-layer, paper and gas-liquid chromatography. 2. On a protein basis the isolated matrix vesicles had more total lipid than either the membrane or cell fractions, the vesicles and membranes being richer in non-polar lipids and containing smaller quantities of phospholipids than whole cells. Expressed as a percentage of the total lipid, the cells were richer in triacylglycerols and lower in free fatty acids than in the membrane or vesicle fractions. The proportion of free cholesterol and the cholesterol/phospholipid ratio were nearly twice as high in the matrix vesicles as in the other tissue fractions. Choline and ethanolamine phosphoglycerides progressively declined in the membrane and matrix vesicle fractions, whereas serine phosphoglycerides and sphinogomyelin increased. Non-phosphorus-containing polar lipids were present in all fractions, the vesicles being richer in polyhexosyl ceramides, cerebrosides, glycosyldiacylglycerols and certain uncharacterized acidic polar lipids. 3. Fatty acid patterns of the matrix vesicles were distinctive from those of isolated cells, being generally richer in 18 : 0 and 18 : 2, and lower in 16 : 1 and 18 : 1 fatty acids. Monoacyl forms were similarly increased in 16 : 0 and/or 18 : 0, and reduced in 16 : 1, 18 : 1 or 20 : 2 fatty acids, depending on the lipid class. The fatty acid composition of diphosphatidylglycerol from cells and matrix vesicles was markedly different, providing evidence that the cardiolipin in the vesicles was not from mitochondrial components. 4. Based on the fact that the matrix vesicles were significantly enriched in free cholesterol, sphingomyelin, glycolipids and serine-phosphoglycerides, it is concluded that they are derived from the plasma membrane of the cell, supporting earlier conclusions based upon morphological and enzymological evidence.     

Partial sequencing and characterization of the tumor cell-derived collagenase stimulatory factor.

A tumor cell-derived, collagenase stimulatory factor (TCSF), previously isolated and purified from LX-1 human lung carcinoma cells and judged by immunoblotting and SDS-PAGE to contain a single protein of approximately 58 kDa, has been further analyzed for its biological activity and composition. Three significant new findings have been made. First, the biological activity of TCSF preparations was shown definitively to reside in the 58-kDa protein. This was achieved in two ways: (a) a polyclonal antibody was raised against the 58-kDa protein, after excision from an SDS-PAGE gel, and shown to inhibit the stimulation of fibroblast collagenase production by TCSF preparations; (b) the 58-kDa protein was eluted from a transblot of purified TCSF and shown to stimulate fibroblast collagenase production. Second, partial sequencing of the 58-kDa protein revealed no significant homologies with other known collagenase stimulatory factors. Third, purified TCSF was found, on transblotting to Immobilon, to contain a doublet of 58 kDa (TCSF1) and 54 kDa (TCSF2) proteins; the former was present in higher concentration than the latter. N-terminal amino acid sequencing of the two intact proteins and of four corresponding pairs of tryptic peptides derived from the two proteins showed identity in each case, indicating that TCSF1 and TCSF2 are very similar in composition. However, TCSF1 but not TCSF2 stimulated fibroblast collagenase production, confirming that the 58-kDa protein is the major active component of TCSF preparations.     

Induction of collagenase production in Vibrio B-30.

The inducible nature of an extracellular collagenase produced by a marine Vibrio (Vibrio B-30, ATCC 21250) was demonstrated by observing the increase in extracellular collagenase activity after the addition of collagen to cell cultures in the latter part of the exponential growth phase. When collagenase-hydrolyzed collagen was added, the lag time required before collagenase production was detected decreased significantly compared with cultures receiving collagen. Cells preinduced to synthesize collagenase did not produce the enzyme when collagen was removed from the culture medium. Incorporation of penicillin G had no effect on final collagenase activity levels in suspensions of Vibrio B-30 in complete medium supplemented with collagen. However, chloramphenicol and tetracycline inhibited collagenase production, indicating that de novo protein synthesis was necessary for the appearance of activity. Attempts to isolate the inducing substance(s) involved filtering hydrolyzed collagen through a series of ultrafiltration membranes. The lowest-molecular-weight fraction of collagen hydrolysate with inducing ability was between 1,000 and 10,000. Gel filtration of this fraction on Sephadex G-50 resulted in the appearance of three protein peaks, two of which were capable of inducing collagenase production. Results from amino acid composition and N-terminal amino acid analysis suggest that the inducing substance originates from the polar helical portion of the collagen molecule.     

Coordinate increase in collagenase mRNA and enzyme levels in human fibroblasts treated with the tumor cell factor, TCSF

Cocultures of human fibroblasts and LX-1 human lung carcinoma cells expressed 8-10 fold higher levels of collagenase mRNA than the sum of the individual cells, in parallel with similar increases in collagenase activity. Addition of the tumor cell collagenase stimulatory factor, TCSF, purified from LX-1 cells, to these fibroblasts also gave a 3-4 times increase in collagenase mRNA level. However, various fibroblast cell lines differed in their response to TCSF stimulation. Thus one cell line, GM 1391, did not respond to TCSF but responded to another potent collagenase stimulator, tetradecanoyl phorbol ester. Another cell line 5383 did not respond significantly to either agent. In each case collagenase activity and mRNA levels responded in a parallel fashion.     

Effect of the purified (Mg2+ + Ca2+)-activated ATPase of sarcoplasmic reticulum upon the passive Ca2+ permeability and ultrastructure of phospholipid vesicles.

The passive Ca2+ permeability of fragmented sarcoplasmic reticulum membranes is 10(4) to 10(61 times greater than that of liposomes prepared from natural or synthetic phospholipids. The contribution of membrane proteins to the Ca2+ permeability was studied by incorporating the purified [Ca2+ + Mg2+]-activated ATPase into bilayer membranes prepared from different phospholipids. The incorporation of the Ca2+ transport ATPase into the lipid phase increased its Ca2+ permeability to levels approaching that of sarcoplasmic reticulum membranes. The permeability change may arise from a reordering of the structure of the lipid phase in the environment of the protein or could represent a specific property of the protein itself. The calcium-binding protein of sarcoplasmic reticulum did not produce a similar effect. The increased rate of Ca2+ release from reconstituted ATPase vesicles is not a carrier-mediated process as indicated by the linear dependence of the Ca2+ efflux upon the gradient of Ca2+ concentration and by the absence of competition and countertransport between Ca2+ and other divalent metal ions. The increased Ca2+ permeability upon incorporation of the transport ATPase into the lipid phase is accompanied by similar increase in the permeability of the vesicles for sucrose, Na+, choline, and SO42- indicating that the transport ATPase does not act as a specific Ca2+ channel. Native sarcoplasmic reticulum membranes are asymmetric structures and the 75-A particles seen by freeze-etch electron microscopy are located primarily in the outer fracture face. In reconstituted ATPase vesicles the distribution of the particles between the two fracture faces is even, indicating that complete structural reconstitution was not achieved. The Ca2+ transport activity of reconstituted ATPase vesicles is also much less than that of fragmented sarcoplasmic reticulum. The density of the 40-A surface particles visible after negative staining of native or reconstituted vesicles is greater than that of the intramembranous particles and the relationship between these two structures remains to be established.     

Stimulation of collagenase production by collagen in mammalian cell cultures.

In this study, we investigated the possible regulatory role of collagen in collagenase production by cultured human skin fibroblasts and human and rabbit synovial cells. Addition of types I, II or III collagen in solution to the culture media markedly stimulated trypsin-activable collagenase activity in these cultures. In the human cell cultures the stimulatory effect of collagen was further enhanced by a soluble factor isolated from human monocyte culture media (Dayer, Russell and Krane, 1977). Both native and denatured forms of collagen stimulated enzyme production; their relative efficacy varied among the different types. The native form of both types I and II collagen showed a greater effect on collagenase production than the corresponding denatured form, whereas with type III collagen the denatured form was more effective.     

Reconstitution of the purified calmodulin-dependent (Ca2+ + Mg2+)-ATPase from smooth muscle

The purified calmodulin dependent (Ca2+ + Mg2+)-ATPase (CaMg ATPase) from porcine antral smooth muscle transports Ca2+ after reconstitution in lipid vesicles indicating that this enzyme is indeed a Ca2+-transport ATPase. For CaMg ATPase reconstituted in asolectin vesicles a good correlation was found between the time course of Ca2+ accumulation and the corresponding changes in CaMg ATPase activity. The ATPase activity was stimulated 8-fold by A23187, which further indicates a tight coupling between ATP hydrolysis and Ca2+ transport. Asolectin vesicles with incorporated enzyme accumulated Ca2+ with a ratio approaching one Ca2+ ion transported for each ATP hydrolyzed. For CaMg ATPase reconstituted in phosphatidylcholine vesicles on the other hand, Ca2+ transport and CaMg ATPase were poorly coupled as is shown by the approximately 3.5 fold stimulation by A23187. The activity of the CaMg ATPase when reconstituted in asolectin vesicles was stimulated 1.25 fold by calmodulin while in phosphatidylcholine a value of 4.25 was obtained. The CaMg ATPase activity of the enzyme reconstituted either in asolectin or phosphatidylcholine was, after its stimulation by A23187, still further stimulated by detergent by a factor of 5.     

Dye-release assay for investigation of antimicrobial peptide activity in a competitive lipid environment

A dye-release method for investigating the effect of a competitive lipid environment on the activity of two membrane-disrupting antimicrobial peptides (AMP), maculatin 1.1 and aurein 1.2, is presented. The results support the general conclusion that AMP have greater affinity for negatively charged membranes, for example bacterial membranes, than for the neutral membrane surface found in eukaryotic cells, but only within a competitive lipid environment. Indeed, in a single-model membrane environment, both peptides were more potent against neutral vesicles than against charged vesicles. The approach was also used to investigate the effect of pre-incubating the peptides in a neutral lipid environment then introducing charged lipid vesicles. Maculatin was shown to migrate from the neutral lipid bilayers, where pores had already formed, to the charged membrane bilayers. This result was also observed for charged-to-charged bilayers but, interestingly, not for neutral-to-neutral lipid interfaces. Aurein was able to migrate from either lipid environment, indicating weaker binding to lipid membranes, and a different molecular mechanism for lysis of lipid bilayers. Competitive lipid environments could be used to assess other critical conditions that modulate the activity of membrane peptides or proteins.     

Shedding of membrane vesicles mediates fibroblast growth factor-2 release from cells

Fibroblast growth factor-2 (FGF-2), a polypeptide with regulatory activity on cell growth and differentiation, lacks a conventional secretory signal sequence, and its mechanism of release from cells remains unclear. We characterized the role of extracellular vesicle shedding in FGF-2 release. Viable cells released membrane vesicles in the presence of serum. However, in serum-free medium vesicle shedding was dramatically down-regulated, and the cells did not release FGF-2 activity into their conditioned medium. Addition of serum to serum-starved cells rapidly induced intracellular FGF-2 clustering under the plasma membrane and into granules that colocalized with patches of the cell membrane with typical features of shed vesicle membranes. Shed vesicles carried three FGF-2 isoforms (18, 22, 24 kDa). Addition of vesicles to endothelial cells stimulated chemotaxis and urokinase plasminogen activator production, which were blocked by anti-FGF-2 antibodies. Treatment of intact vesicles with 2.0 m NaCl or heparinase, which release FGF-2 from membrane-bound proteoglycans, did not abolish their stimulatory effect on endothelial cells, indicating that FGF-2 is carried inside vesicles. The comparison of the stimulatory effects of shed vesicles and vesicle-free conditioned medium showed that vesicles represent a major reservoir of FGF-2. Thus, FGF-2 can be released from cells through vesicle shedding.     

Differential expression of platelet-derived growth factor alpha- and beta- receptors on fat-storing cells and endothelial cells of rat liver.

Fat-storing cells and endothelial cells of the liver sinusoids play important roles in the biosynthesis and degradation of hyaluronan (HYA). These cells were isolated from rat liver by a simple and rapid procedure involving: (1) cell separation by centrifugation on a Nycodenz gradient, after dispersion of the liver cells by collagenase perfusion; (2) further purification of the cells by centrifugation on a discontinuous Percoll gradient; and (3) culturing of the cells, taking advantage of the different time that seeded cells need for attachment to plastic surfaces. We have determined the effects of two isoforms of platelet-derived growth factor (PDGF), PDGF-BB and PDGF-AA, on HYA production by the original fat-storing cells, as well as by fat-storing cells which had changed in vitro to myofibroblast-like cells. PDGF-BB was found to stimulate HYA synthesis in both types of cells with a maximal response equal to that obtained with 10% fetal calf serum. PDGF-AA had no stimulatory effect on HYA production. Fat-storing cells and their modified myofibroblast-like phenotype bound specifically to 125I-PDGF-BB, but not to 125I-PDGF-AA, indicating that they had PDGF beta-receptors, but not alpha-receptors. In contrast, liver endothelial cells were found to have PDGF alpha-receptors, but not beta-receptors.     

Cyclic AMP-dependent protein kinase activation of cystic fibrosis transmembrane conductance regulator chloride channels in planar lipid bilayers.

Membrane vesicles, prepared from mouse NIH-3T3 fibroblasts and Chinese hamster ovary cells expressing high levels of cystic fibrosis transmembrane conductance regulator (CFTR), were fused with Mueller-Rudin planar lipid bilayers. Upon addition of the catalytic subunit of cAMP-dependent protein kinase and ATP, low conductance Cl(-)-selective ion channels were observed in 10 of 16 experiments. The channels had a linear current-voltage relationship and a unitary conductance of approximately 6.5 pS. The channels were more permeable to Cl- than to I- and showed no appreciable time-dependent voltage activation. In contrast, addition of cAMP-dependent protein kinase and ATP to lipid bilayers fused with vesicles prepared from mock transfected (n = 14) cells failed to activate Cl- channels. These data support the conclusion that CFTR is a Cl- channel. They indicate that it can be reconstituted in a planar lipid bilayer and that the biophysical and regulatory properties are very similar to those observed in the native cell membrane. These data also argue against the requirement for loosely associated factors for regulation or function of the channel.     

Distinctive regulation of the functional linkage between the human cation-independent mannose 6-phosphate receptor and GTP-binding proteins by insulin-like growth factor II and mannose 6-phosphate

The rat insulin-like growth factor II (IGF-II) receptor develops transmembrane signaling functions by directly coupling to a guanine nucleotide-binding protein (G protein) having a 40-kDa alpha subunit, Gi-2, whereas recent studies have indicated that the IGF-II receptor is a molecule identical to the cation-independent mannose 6-phosphate receptor (CI-MPR), a receptor implicated in lysosomal enzyme sorting. In this study, by using vesicles reconstituted with the clonal human CI-MPR and G proteins, we indicated that the CI-MPR could stimulate guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding and GTPase activities of Gi proteins in response to IGF-II. The stimulatory effect of IGF-II on Gi-2 depended on the reconstituted amount of the CI-MPR; it could not be found in vesicles reconstituted with Gi-2 alone; and it was also observed on Gi-1 reconstituted with the CI-MPR in phospholipid vesicles. Of interest, such stimulatory effect was not reproduced by Man-6-P in CI-MPR vesicles reconstituted with either G protein. Furthermore, the affinity for Man-6-P-mediated beta-glucuronidase binding to several kinds of native cell membranes was not reduced by 100 microM GTP gamma S. Instead, however, Man-6-P dose-dependently inhibited IGF-II-induced Gi-2 activation with an IC50 of 6 microM in vesicles reconstituted with the CI-MPR and Gi-2. The action of 100 nM IGF-II was completely abolished by 1 mM Man-6-P. Such an inhibitory effect of Man-6-P was reproduced by 4000 times lower concentrations of beta-glucuronidase or similar concentrations of fructose 1-phosphate, but not by mannose or glucose 6-phosphate. These results indicate that the human CI-MPR has two distinct signaling functions that positively or negatively regulate the activity of Gi-2 in response to the binding of IGF-II or Man-6-P.     

Uptake of amino acids in reconstituted vesicles derived from plasma membranes of Ehrlich ascites cells.

To obtain a clearer concept of the mechanism of organic solute transport in mammalian cells, we have attempted to reconstitute a functional transport system for amino acids from plasma membranes of Ehrlich ascites cells. Purified plasma membranes were dissolved in 2% Na cholate--4 M urea, a mixture which brought over 85% of the membrane proteins into solution. After centrifugation of the solubilized material for 2 hrs at 100,000 x g, the supernatant was dialyzed in the cold for 20 hrs with additional lipid. The reformed vesicles were tested for the ability to transport amino acids. The preliminary results obtained show that the uptake of alpha-aminoisobutyric acid can be inhibited by L-methionine and much less by L-leucine as would be predicted from the known properties of alpha-aminoisobutyric transport in the intact cells. In addition, it has been possible to show accelerated efflux of intravesicular phenylalanine when phenylalanine is added to the trans side (medium side). The data are consistent with the conclusion that there is carrier mediated transport in the reconstituted vesicles.