The heparan sulfates of Swiss mouse 3T3 cells. The effect of transformation

Three major pools of heparan sulfate have been isolated from cultures of Swiss mouse 3T3 and SV40-transformed 3T3 cells: cell-surface, medium, and intracellular heparan sulfates. The cell-surface heparan sulfate is a high molecular weight proteogylcan which is partially degraded by pronase. Before pronase treatment, it has a peak molecular weight (as estimated by gel filtration) of appox. 7.2 · 10⁵ in contrast to only 2.4 · 10⁵ after pronase treatment. The medium heparan sulfate appears to be similar in structure to the cell-surface heparan sulfate, since they coelute on Bio-Gel A-15m and DEAE-cellulose, and are both proteoglycans. In contrast, the intracellular heparan sulfate has a low molecular weight (6.0 · 10³) and has little if any attached protein. Both the medium and intracellular heparan sulfate exhibit the transformation-associated change in structure reported earlier for cell-surface heparan sulfate (Underhill, C.B. and Keller, J.M. (1975) Biochem. Biophys. Res. Commun. 63, 448–454). This transformation-associated change, detected by DEAE-cellulose chromatography is not the result of changes in either molecular weight or protein core. Cellulose acetate electrophoresis of the cell-surface heparan sulfate at pH 1 suggests that the transformation-associated change in structure is due to a difference in sulfate content. Both types of heparan sulfate are produced in mixed cultures ot 3T3 and SV3T3 cells, indicating that neither serum factors in the culture medium nor secreted cell products are responsible for the transformation-associated change in heparan sulfate structure. The presented date are discussed with respect to the postulated role of heparan sulfate in cell social behavior.     

The heparan sulfates of Swiss mouse 3T3 cells. The effect of transformation.

Three major pools of heparan sulfate have been isolated from cultures of Swiss mouse 3T3 and SV40-transformed 3T3 cells: cell-surface, medium, and intracellular heparan sulfates. The cell-surface heparan sulfate is a high molecular weight proteoglycan which is partially degraded by pronase. Before pronase treatment, it has a peak molecular weight (as estimated by gel filtration) of approx. 7.2 . 10(5) in contrast to only 2.4 . 10(5) after pronase treatment. The medium heparan sulfate appears to be similar in structure to the cell-surface heparan sulfate, since they coelute on Bio-Gel A-15m and DEAE-cellulose, and are both proteoglycans. In contrast, the intracellular heparan sulfate has a low molecular weight (6.0 . 10(3)) and has little if any attached protein. Both the medium and intracellular heparan sulfate exhibit the transformation-associated change in structure reported earlier for cell-surface heparan sulfate (Underhill, C.B. and Keller, J.M. )1975) Biochem. Biophys. Res. Commun. 63, 448--454). This transformation-associated change, detected by DEAE-cellulose chromatography is not the result of changes in either molecular weight or protein core. Cellulose acetate electrophoresis of the cell-surface heparan sulfate at pH 1 suggests that the transformation-associated change in structure is due to a difference in sulfate content. Both types of heparan sulfate are produced in mixed cultures of 3T3 and SV3T3 cells, indicating that neither serum factors in the culture medium nor secreted cell products are responsible for the transformation-associated change in heparan sulfate structure. The presented data are discussed with respect to the postulated role of heparan sulfate in cell social behavior.     

Stimulation of synthesis of free chondroitin sulfate chains by beta-D-xylosides in cultured cells.

Beta-Xylosides stimulate 2- to 6-fold the synthesis of glycosaminoglycans by three types of nonconnective tissue cells (RG-C6, NB41A, and rat hepatoma cells, and normal and simian virus 40 (SV40)-transformed normal human skin fibroblasts. The effect, which is specific for the anomeric linkage and the glycone, is observed in the presence and absence of puromycin. Beta-Xylosides may substitute for xylosylated core protein as initiators of synthesis of chondroitin sulfate chains. No stimulation of synthesis of heparan sulfate was observed. With the use of a fluorogenic xyloside, 4-methylumbelliferyl-beta-D-xyloside, it was demonstrated that the free chondroitin sulfate chains secreted into the medium bear the xyloside at the reducing end, and have an average molecular weight of 16,500.     

The decreased synthesis of chondroitin sulfate-containing extracellular proteoglycans by SV40 transformed Balb/c 3T3 cells.

Balb/c 3T3 cells synthesize 5--10 times more 35SO2/4- -labeled extracellular proteoglycan per cell than do Balb/c 3T3 cells transformed by SV40 (SV3T3). The extracellular 35SO2/4- -labeled proteoglycans of the Balb/c 3T3 and SV3T3 cells differ markedly in their acid mucopolysaccharide composition. Extracellular Balb/c 3T3 proteoglycans contain about 70--80% chondroitin sulfate, most of which is chondroitin 4-sulfate, and small amounts of heparan sulfate and/or heparin. On the other hand, extracellular SV3T3 proteoglycans contain 65-75% heparan sulfate and/or heparin and less than 15% chondroitin sulfate. Analysis of extracellular 35SO2/4- -labeled proteoglycan by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that Balb/c 3T3 alone synthesizes a class of proteoglycans capable of migrating in a 10% separating gel. This class of proteoglycans, designated as fraction C, accounts for up to 45% of the total extracellular Balb/c 3T3 35 SO2/4- -labeled proteoglycans and contains chondroitin sulfate extracellular SV3T3 proteoglycans. The absence of this and other classes of chondroitin sulfate-containing proteoglycans can account for the 5-10-fold decreased synthesis of 35SO2/4- -labeled proteoglycans by SV3T3 cells when compared to Balb/c 3T3 cells.     

Heparan sulfates from Swiss mouse 3T3 and SV3T3 cells: O-sulfate difference

A difference in the extent of sulfation between the heparan sulfate isolated from Swiss 3T3 mouse cells and that from Swiss 3T3 cells transformed by the DNA virus SV40 has been reported previously. This variance is manifested by different chromatographic and electrophoretic properties. Heparan sulfates from the two cell types were treated with nitrous acid under conditions that gave selective deaminative cleavage of glucosaminyl residues with sulfated amino groups in order to define the nature of the difference in sulfation further. The O-sulfate containing fragments from the heparan sulfates were compared by gel filtration and ion-exchange chromatography. The results showed that the 3T3 heparan sulfate contains 8% more O-sulfate than does the SV3T3 heparan sulfate. Analysis of uronic acids revealed that both types of heparan sulfates contain 45% L-iduronic acid and 55% D-glucuronic acid. These and other observations indicate that the primary difference in sulfation between the 3T3 and SV3T3 heparan sulfates lies in the extent of O-sulfation.     

A transformation-dependent difference in the heparan sulfate associated with the cell surface.

Glycosaminoglycans from the surface of cultured mouse cells (3T3, SV40-3T3, 3T6) were released by trypsin digestion and separated by ion-exchange chromatography into hyaluronic acid, heparan sulfate and chondroitin sulfate. Using a double label technique, the glycosaminoglycans from 3T3 cells were compared with those from SV40-3T3 and 3T6 cells. No differences were apparent in either the hyaluronic acid or chondroitin sulfate fractions, however, the heparan sulfate from 3T3 cells was found to elute from DEAE-cellulose at a higher ionic strength than that from transformed cells. This altered behavior implies a structural difference in the cell surface heparan sulfate which appears to be dependent upon transformation.     

The decreased synthesis of chondroitin sulfate-containing extracellular proteoglycans by SV40 transformed Balb/c 3T3 cells

Balb/c 3T3 cells synthesize 5–10 times more ³⁵SO₄^2?-labeled extracellular proteoglycan per cell than do Balb/c 3T3 cells transformed by SV40 (SV3T3). The extracellular ³⁵SO₄^2?-labeled proteoglycans of the Balb/c 3T3 and SV3T3 cells differ markedly in their acid mucopolysaccharide composition. Extracellular Balb/c 3T3 proteoglycans contain about 70–80% chondroitin sulfate, most of which is chondroitin 4-sulfate, and small amounts of heparan sulfate and/or heparin. On the other hand, extracellular SV3T3 proteoglycans contain 65–75% heparan sulfate and/or heparin and less than 15% chondroitin sulfate. Analysis of extracellular ³⁵SO₄^2?-labeled proteoglycan by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that Balb/c 3T3 alone synthesizes a class of proteoglycans capable of migrating in a 10% separating gel. This class of proteoglycans, designated as fraction C, accounts for up to 45% of the total extracellular Balb/c 3T3 ³⁵SO₄^2?-labeled proteoglycans and contains chondroitin sulfate exclusively. It is altogether absent in the extracellular SV3T3 proteoglycans. The absence of this and other classes of chondroitin sulfate-containing proteoglycans can account for the 5–10-fold decreased synthesis of ³⁵SO₄^2?-labeled proteoglycans by SV3T3 cells when compared to Balb/c 3T3 cells.     

Heparan sulfates of mouse cells. Analysis of parent and transformed 3T3 cell lines.

Heparan sulfate from the surface of a variety of mouse cells at different cell densities was examined by ion-exchange chromatography. The results of this analysis show that: (1) The heparan sulfate from new isolates of Swiss 3T3 cells transformed by SV40 virus (a DNA tumor virus) elutes from DEAE-cellulose at a lower ionic strength than that from the parent cell type. This finding confirms our earlier observation with an established SV40-transformed cell line (Underhill and Keller, '75) and eliminates the possibility that this change is caused by extended passage in culture. (2) For both parent and transformed 3T3 cells, the heparan sulfates from low and high density cultures were the same as judged by chromatography on DEAE-cellulose. This result demonstrates that the transformation-dependent change which we have observed is independent of cell density. (3) The heparan sulfate from Balb/c 3T3 cells transformed with Kirsten murine sarcoma virus (an RNA tumor virus) elutes from DEAE-cellulose prior to that from parent Balb/c 3T3 cells. This result extends the transformation dependent change in heparan sulfate to the Balb/c 3T3 cell line and to cells transformed with an RNA virus.     

Turnover, change of composition with rate of cell growth and effect of phenylxyloside on synthesis and structure of cell surface sulfated glycosaminoglycans of normal and transformed cells

The synthesis of sulfated glycosaminoglycans was analysed in mouse fibroblasts during the transition from exponential growth to quiescent monolayers. 'Normal' Swiss 3T3 fibroblasts were compared with SV40 transformed 3T3, C6, ST1 and HeLa cells. p-Nitrophenyl-beta-D-xyloside, an artificial acceptor for glycosaminoglycans synthesis, was used as a probe. Exponentially growing 'normal' 3T3 cells synthesized both dermatan sulfate and chondroitin 4-sulfate, retaining the latter and releasing the former to the medium. Upon reaching quiescence these cells switched to retention of dermatan sulfate and release of chondroitin 4-sulfate. SV3T3 cells synthesized several fold less sulfated glycosaminoglycans than 'normal' 3T3. Even though SV3T3 cells are able to synthesize dermatan sulfate, they only retained chondroitin 4-sulfate, never switching to retention of dermatan sulfate. These results indicated that the transition from rapidly proliferating to resting G0 state in normal cells is accompanied by a switch from chondroitin-sulfate rich to dermatan-sulfate-rich cells. This switching was not observed with transformed cells, which are unable to enter the G0 state. Phenylxyloside caused a several fold increase in glycosaminoglycans released to the medium in both cell types, but it did not interfere with either growth rate or cell morphology. Particularly the phenylxyloside treatment led to an increase of more than 10-fold in production of dermatan and chondroitin sulfate by SV3T3, C6, ST1 and HeLa cells. This demonstrated that transformed cells have a high capacity for glycosaminoglycan synthesis. Analysis of enzymatic degradation products of glycosaminoglycans, synthesized in the presence of phenylxyloside, by normal and transformed cells, led to the finding of 4- and 6-sulfated iduronic and glucuronic acid-containing disaccharides. This result indicated that the xyloside causes the synthesis of a peculiar chondroitin sulfate/dermatan sulfate, in both normal and transformed cells.     

Heparin induces changes in the synthesis of porcine aortic endothelial cell heparan sulfate proteoglycans

Heparin is known to bind to cultured endothelial cells. This report documents that addition of heparin to endothelial cells results in an alteration of the heparan sulfate proteoglycan synthetic pattern. Specifically, the addition of saturating amounts of heparin to confluent cultures of porcine aortic endothelial cells results in an increase in the amount of radiolabeled heparan sulfate proteoglycan secreted into the growth medium. The increase is apparent as early as 8 h after heparin administration. Although there is often a decrease in the amount of cell surface heparan sulfate proteoglycan produced, it is not sufficient to account for the increase in the secreted form. Of the other glycosaminoglycans tested, only dextran sulfate and commercial heparan sulfate induce changes in heparan sulfate proteoglycan synthesis and secretion. Chondroitin sulfate glycosaminoglycans do not elicit this synthetic change. These data indicate that endothelial cells can alter the synthesis of heparan sulfate proteoglycans in response to extracellular signals including heparin and related glycosaminoglycans.     

Estradiol beta-D-xyloside, an efficient primer for heparan sulfate biosynthesis

Animal cells utilize beta-D-xylosides as primers for glycosaminoglycan synthesis. However, most xylosides preferentially stimulate chondroitin sulfate synthesis and only weakly prime heparan sulfate synthesis. To test if the structure of the aglycone determines the type of glycosaminoglycan made, the priming activity of methyl, n-octyl, p-nitrophenyl, 4-methylumbelliferyl, trans,trans-farnesyl, cholesteryl, and estradiol beta-D-xylosides was compared. Their potency was tested in pgsA-745 cells, a Chinese hamster ovary cell mutant unable to initiate glycosaminoglycan synthesis due to a defect in xylosyltransferase. All of the xylosides stimulated chondroitin sulfate synthesis in the mutant, but only estradiol beta-D-xyloside primed heparan sulfate synthesis efficiently. When incubated with 30 microM estradiol beta-D-xyloside, mutant cells made about 3-fold more glycosaminoglycan than untreated wild-type cells and as much as 50% was heparan sulfate. Estradiol beta-D-xyloside also induced heparan sulfate synthesis in cycloheximide-treated wild-type Chinese hamster ovary cells, bovine aortic endothelial cells, baby hamster kidney cells, and Balb/c 3T3 fibroblasts. In addition to stimulating heparan sulfate synthesis, low concentrations of estradiol beta-D-xyloside inhibited the formation of endogenous heparan sulfate proteoglycans.     

Density-dependent changes in the amount of sulfated glycosaminoglycans associated with mouse 3T3 cells.

The relative amount of sulfated glycosaminoglycans associated with the cell layer of parent and SV40-transformed Swiss mouse 3T3 cells was determined from the incorporation of labeled sulfate (35SO4) into macromolecular material. In cultures of SV40-transformed cells, the glycosaminoglycan content per cell was constant over a wide range of densities. In cultures of parent 3T3 cells, the glycosaminoglycan content per cell increased directly with density, the highest values being found in contact-inhibited cultures. At high cell densities, the glycosaminoglycan content of 3T3 cells was several-fold higher than that for SV40-transformed cells. Most of the density-dependent increase in glycosaminoglycans of 3T3 cells was accounted for by chondroitin sulfate (dermatan sulfate) which was over 6-fold higher in confluent cultures than in low density cultures.     

Relationship of transformation, cell density, and growth control to the cellular distribution of newly synthesized glycosaminoglycan

Mouse 3T3 cells and their Simian Virus 40-transformed derivatives (3T3SV) were used to assess the relationship of transfromation, cell density, and growth control to the cellular distribution of newly synthesized glycosaminoglycan (GAG). Glucosamine- and galactosamine- containing GAG were labeled equivalently by [3H=A1-glucose regardless of culture type, allowing incorporation into the various GAG to be compared under all conditions studied. Three components of each culture type were examined: the cells, which contain the bulk of newly synthesized GAG and are enriched in chondroitin sulfate and heparan sulfate; cell surface materials released by trypsin, which contain predominantly hyaluronic acid; and the media , which contain predominantly hyaluronic acid and undersulfated chondroitin sulfate. Increased cell density and viral transformation reduce incorporation into GAG relative to the incorporation into other polysaccharides. Transformation, however, does not substantially alter the type or distribution of newly synthesized GAG; the relative amounts and cellular distributions were very similar in 3T3 and 3T3SV cultures growing at similar rates at low densities. On the other hand, increased cell density as well as density-dependent growth inhibition modified the type and distribution of newly synthesized GAG. At high cell densities both cell types showed reduced incorporation into hyaluronate and an increase in cellular GAG due to enhanced labeling of chondroitin sulfate and heparan sulfate. These changes were more marked in confluent 3T3 cultures which also differed in showing substantially more GAG label in the medium and in chondroitin-6-sulfate and heparan sulfate at the cell surface. Since cell density and possibly density- dependent inhibition of growth but not viral transformation are major factors controlling the cellular distribution and type of newly synthesized GAG, differences due to GAG's in the culture behavior of normal and transformed cells may occur only at high cell density. The density-induced GAG alterations most likely involved are increased condroitin-6-sulfate and heparan sulfate and decreased hyaluronic acid at the cell surface.     

Heparan sulfate modulates kinin release by Trypanosoma cruzi through the activity of cruzipain.

Trypanosoma cruzi activates the kinin pathway through the activity of its major cysteine proteinase, cruzipain. Because kininogen molecules may be displayed on cell surfaces by binding to glycosaminoglycans, we examined whether the ability of cruzipain to release kinins from high molecular weight kininogen (HK) is modulated by heparan sulfate (HS). Kinetic assays show that HS reduces the cysteine proteinase inhibitory activity (K(i app)) of HK about 10-fold. Conversely, the catalytic efficiency of cruzipain on kinin-related synthetic fluorogenic substrates is enhanced up to 6-fold in the presence of HS. Analysis of the HK breakdown products generated by cruzipain indicated that HS changes the pattern of HK cleavage products. Direct measurements of bradykinin demonstrated an up to 35-fold increase in cruzipain-mediated kinin liberation in the presence of HS. Similarly, kinin release by living trypomastigotes increased up to 10-fold in the presence of HS. These studies suggest that the efficiency of T. cruzi to initiate kinin release is potently enhanced by the mutual interactions between cruzipain, HK, and heparan sulfate proteoglycans.     

Turnover of heparan sulfate proteoglycans from substratum adhesion sites of murine fibroblasts

Substratum adhesion sites from murine Balb/c SVT2 fibroblasts are enriched in heparan sulfate proteoglycans which have been implicated in mediating adhesion of these cells to a fibronectin-adsorbed tissue culture substratum. Most of the heparan sulfate isolated from newly formed adhesion sites is found covalently attached to protein as proteoglycan while a significant portion of heparan sulfate from older sites has been identified as a single-chain species. This observation suggests that there may be catabolism of the heparan sulfate proteoglycan during the "maturation" of these adhesion sites at the cell's undersurface. Zwittergent 3-12 selectively extracts the single-chain class of heparan sulfate from either newly formed or "mature" adhesion sites while leaving the proteoglycan firmly bound in these sites. In an effort to further characterize the metabolism of these proteoglycans, substratum adhesion sites were isolated at various times after the cells had been pulse-radiolabeled using radioactive sulfate and subsequently chased. Greater than 80% of the sulfate-radiolabeled material is lost from the substratum-attached material within 24-48 h. Characterization of both the Zwittergent-soluble and -resistant heparan sulfate indicated that there was an initial accumulation followed by a rapid loss of a portion of the radiolabeled heparan sulfate as the single-chain Zwittergent-soluble class. However, most of the heparan sulfate proteoglycan was lost from the adhesion sites following approximately a 4-h time lag during the chase period without going through a smaller molecular weight intermediate. The turnover properties of the heparan sulfate proteoglycan in the EGTA-detachable cells were different from those in the substratum-attached fraction of the cell. The significance of these two different mechanisms of turnover of heparan sulfate proteoglycan in adhesion sites is discussed in relation to the role of this proteoglycan in mediating adhesion processes.     

Heparan sulfate and control of endothelial cell proliferation: increased synthesis during the S phase of the cell cycle and inhibition of thymidine incorporation induced by ortho-nitrophenyl-beta-D-xylose

The effect of xylosides on the synthesis of [35S]-sulfated glycosaminoglycans by endothelial cells in culture was investigated. Ortho-nitrophenyl-beta-D-xylose (10(-3)M) produces a dramatic enhancement on the synthesis of heparan sulfate and chondroitin sulfate secreted to the medium (20- and 100-fold, respectively). Para-nitrophenylxyloside, at the same concentration, produces an enhancement of only 37- and 3-fold of chondroitin sulfate and heparan sulfate, respectively. These differences of action seem to be related with the higher lipophilic character of ortho-nitrophenyl-xyloside. A lower enhancement of the synthesis of the two glycosaminoglycans is also observed with 2-naphtol beta-D-xylose and cis/trans-decahydro-2-naphtol beta-D-xylose. Besides stimulating the synthesis, O-nitrophenyl-beta-D-xylose as PMA [J. Cell. Biochem. 70 (1998) 563] also inhibits [3H]-thymidine incorporation by quiescent endothelial cells stimulated for growth by fetal calf serum (FCS). The combination of xylosides with PMA produced some cumulative effect. PMA stimulates the synthesis of heparan sulfate mainly at G1 phase whereas the highest enhancement of synthesis produced by the xylosides is in the S phase of the endothelial cell cycle.     

Altered expression of glycosaminoglycans in metastatic 13762NF rat mamma adenocarcinoma cells

A difference in the expression and metabolism of sulfated glycosaminoglycans between rat mammary tumor cells derived from a primary tumor and those from its metastatic lesions has been observed. Cells from the primary tumor possessed about equal quantities of chondroitin sulfate and heparan sulfate on their cell surfaces but released fourfold more chondroitin sulfate than heparan sulfate into their medium. In contrast, cells from distal metastatic lesions expressed approximately 5 times more heparan sulfate than chondroitin sulfate in both medium and cell surface fractions. This was observed to be the result of differential synthesis of the glycosaminoglycans and not of major structural alterations of the individual glycosaminoglycans. The degree of sulfation and size of heparan sulfate were similar for all cells examined. However, chondroitin sulfate, observed to be only chondroitin 4-sulfate, from the metastases-derived cells had a smaller average molecular weight on gel filtration chromatography and showed a decreased quantity of sulfated disaccharides upon degradation with chondroitin ABC lyase compared to the primary tumor derived cells. Major qualitative or quantitative alterations were not observed for hyaluronic acid among the various 13762NF cells. The metabolism of newly synthesized sulfated glycosaminoglycans was also different between cells from primary tumor and metastases. Cells from the primary tumor continued to accumulate glycosaminoglycans in their medium over a 72-h period, while the accumulation of sulfated glycosaminoglycans in the medium of metastases-derived cells showed a plateau after 18-24 h. A pulse-chase kinetics study demonstrated that both heparan sulfate and chondroitin sulfate were degraded by the metastases-derived cells, whereas the primary tumor derived cells degraded only heparan sulfate and degraded it at a slower rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biosynthesis and modification of Golgi mannosidase II in HeLa and 3T3 cells

The biosynthesis and post-translational modification of mannosidase II, an enzyme required in the maturation of asparagine-linked oligosaccharides in the Golgi complex, has been investigated. Antibody raised against this enzyme purified from rat liver Golgi membranes was used to immunoprecipitate mannosidase II from rat liver, 3T3 cells, or HeLa cells. Mannosidase II immunoprecipitated from rat liver Golgi membranes, when analyzed by polyacrylamide gel electrophoresis, migrated with an apparent molecular weight of approximately 124,000. In contrast, the enzyme purified from rat liver Golgi membranes was shown to contain both the 124,000-dalton component and a 110,000-dalton polypeptide believed to result from degradation of intact mannosidase II during purification. Mannosidase II from 3T3 and HeLa cells migrated on polyacrylamide gels with apparent molecular weights of approximately 124,000 and 134,000-136,000, respectively. When immunoprecipitated from radiolabeled cultures, mannosidase II from both cell types was similar in the following respects: (a) the initial synthesis product had an apparent molecular weight of approximately 124,000; (b) in cultures treated with tunicamycin the initial synthesis product had an apparent molecular weight of approximately 117,000; (c) endoglycosidase H digestion of the initial synthesis product gave an apparent molecular weight similar to the tunicamycin-induced polypeptide; (d) the mature enzyme was mostly (HeLa) or entirely (3T3) resistant to digestion by endoglycosidase H. Loss of [35S]methionine from intracellular mannosidase II occurred with a half-life of approximately 20 h; there was no appreciable accumulation of labeled immuno-reactive material in the medium. HeLa mannosidase II, but not the 3T3 enzyme, was additionally modified 1-3 h after synthesis, the initial synthesis product being converted to a doublet with an apparent molecular weight of approximately 134,000-136,000. Evidence is presented that this mobility shift may result from O-glycosylation. Mannosidase II from both cell types could be labeled with [32P]phosphate or [35S]sulfate. The latter is apparently attached to oligosaccharide as indicated by inhibition of labeling by tunicamycin; the former was shown with the HeLa enzyme to be present as serine phosphate moieties. In addition, [3H]palmitate could be incorporated into the enzyme in 3T3 cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Transforming growth factor beta 1 stimulates the production of basic fibroblast growth factor binding proteoglycans in Balb/c3T3 cells.

Basic fibroblast growth factor (bFGF) binds to cell surface receptors and to heparin sulfate proteoglycans. Heparan sulfate binding may limit bFGF degradation and be an obligatory step for bFGF cell interaction. Transforming growth factor-beta 1 (TGF-beta 1) is a potent regulator of proteoglycan production and composition. The possibility that TGF-beta 1 synergistically regulates bFGF activity by altering bFGF-proteoglycan interactions was investigated. TGF-beta 1 increased 125I-bFGF binding to the extracellular matrix (ECM) of Balb/c3T3 cells 2-4-fold by increasing the number of bFGF binding sites. Increased bFGF binding correlated with a 2-5-fold increase in the production of sulfated proteoglycans, including heparan sulfate proteoglycans. TGF-beta 1 selectively stimulated production of high molecular mass proteoglycans (190-300 kDa) in conditioned medium and stimulated all proteoglycans in ECM. 125I-bFGF bound to TGF-beta 1 induced proteoglycans immobilized onto cationic nylon filters. Furthermore, ECM isolated from TGF-beta 1-treated cells incorporated more mitogenically active bFGF than native ECM. The mitogenic potential of the ECM was significantly reduced by treatment with heparinase. These results suggest that the ability of TGF-beta 1 to stimulate binding of bFGF to ECM, increase ECM heparan sulfate proteoglycan, and potentiate the mitogenic activity of bFGF are linked. Thus one aspect of TGF-beta 1/bFGF synergy may involve modulation of the ECM.     

Protein synthesis in 3T3 and SV40-transformed 3T3 cells. Activity of ribosomes and cytosol proteins in cell-free protein synthesis.

The activity of specific components involved in protein synthesis in 3T3 cells and its SV40-transformed derivative, SV3T3, were examined in a cell-free protein synthetic system, and the results correlated with previous studies, indicating that a decreasing rate of protein synthesis does not accompany the stationary phase of growth. We found that 3T3 and SV3T3 polysome preparations containing endogenous mRNA were equally efficient in supporting cell-free protein synthesis in this system. Further, the net protein synthesis observed was not altered by an increase in the population density of the cellular polysome source. The activity of the aminoacyl-tRNA synthetase enzymes from 3T3 and SV3T3 cells was examined in vitro after isolation by pH 5 precipitation and by ammonium sulfate fractionation. The activity of these preparations from stationary phase 3T3 and nonexponential phase SV3T3 cells was found to be approximately 3 times higher than the activity of fractions from the homologous exponential phase cell. However, at both growth stages, the SV3T3 preparations were 30 to 40 times more active than the 3T3 preparations. These findings may have implications for the different growth properties observed in the two cell types.