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PubMed1991

Identification of a cell surface component of Swiss 3T3 cells associated with an inhibition of cell division.

Polyclonal IgG, prepared to a purified bovine cell surface sialoglycopeptide (SGP) inhibitor of cell division, was used to identify an antigenically related molecule on the surface of Swiss 3T3 cells. SDS-PAGE and Western analyses showed that the anti-SGP antibody was monospecific and primarily recognized a 66-kDA protein of 3T3 cell membranes. Treatment of intact 3T3 cells or 3T3 cell membranes with either broad and phosphatidylinositol-specific phospholipase C enzymes suggested that the antigenic material most likely existed as an integral membrane molecule, or associated as a multimeric complex, and was not anchored at the cell surface by a phospholipid. The addition of anti-SGP IgG to 3T3 cell monolayer cultures was shown to promote cell division, suggesting a regulatory function for the membrane-associated molecule.

Animals↗
PubMed1978

Effect of interferon on the cell cycle of BALB/c 3T3 cells.

The effect of interferon on the exponential growth phase of BALB/c 3T3 cells was studied. Although interferon reduced the growth rate and the proportion of cells in both the M and S phases (mitotic index and labelling index), there were no appreciable differences in the duration of these phases between control and interferon-treated cells. Moreover, the shape of the first peak of the fraction of labelled mitoses (FLM) curve was not altered by treatment with interferon, which indicates that the duration of the S and G2 phases was not affected. However, the height of the second peak of the curve in interferon-treated cells was extremely reduced as compared to control culture. These results are compatible with the idea that the suppressive effect of interferon is exerted mainly in the G1 phase (A-state) of the cell cycle of BALB/c 3T3 cells.

Animals↗
PubMed1994

Bombesin, platelet-derived growth factor, and diacylglycerol induce selective membrane association and down-regulation of protein kinase C isotypes in Swiss 3T3 cells.

Swiss 3T3 cells contain protein kinase C (PKC) isotypes alpha, delta, epsilon and zeta (Olivier, A. R., and Parker, P. J. (1992) J. Cell. Physiol. 152, 240-244). Acute stimulation of quiescent cells with the neuropeptide bombesin decreases the mobility of PKC-delta and PKC-epsilon on SDS-polyacrylamide gels. These slower migrating forms of PKC-delta and PKC-epsilon rapidly (within 1 s) and selectively are found associated with the Triton X-100-soluble membrane fraction. No change in the mobility or distribution of PKC-alpha or PKC-zeta is detected. Long-term treatment of cells with bombesin induces selective membrane association and down-regulation of PKC-delta and PKC-epsilon (decreasing 70 and 65%, respectively). No change in the long-term distribution of PKC-alpha and PKC-zeta was detected. Bombesin did, however, increase PKC-alpha protein levels by 60% compared to control cells. PKC-zeta levels remained unchanged. Both the shift in mobility and down-regulation of PKC-delta and PKC-epsilon were only induced by mitogenic doses of bombesin. The potent mitogen platelet-derived growth factor induced similar effects on the PKC isotypes delta and epsilon. PKC-alpha and PKC-zeta levels were unaffected. Repeated doses of the synthetic diglyceride 1-oleoyl-2-acetyl-sn-glycerol induced PKC-delta and PKC-epsilon down-regulation and stimulated the cells to divide. Again PKC-alpha and PKC-zeta levels were unaffected. These results show a correlation between the membrane association and down-regulation of PKC-delta and PKC-epsilon and the entry of cells into S phase.

3T3 Cells↗
PubMed1997

Inhibition of phosphoinositide hydrolysis and cell growth of Swiss 3T3 cells by myristoylated phospholipase C inhibitor peptides.

It has been demonstrated that the phospholipase C-gamma (PLC-gamma) molecule contains within it a phospholipase C inhibitor (PCI) region and that synthetic peptides based on the sequence of this region (PCI peptides) suppress the enzymatic activity of PLC isoforms [Y. Homma and T. Takenawa (1992) J. Biol. Chem. 267, 21884-21889]. In order to improve the permeability of the plasma membrane to PCI peptides, we synthesized myristoylated PCI peptides, myr-GLYRKAMRLRYPV [myr-PCI(Y)] and myr-GLFRKAMRLRFPV [myr-PCI(F)], which are identical except for the replacement of the two tyrosine residues in myr-PCI(Y) by phenylalanines in myr-PCI(F), and examined their inhibitory activity on PLC enzymes in vitro and in vivo. This fatty acid modification potentiated the inhibitory activity of the original PCI peptides and both myr-PCI(Y) and myr-PCI(F) suppressed the PIP2-hydrolyzing activity of purified PLC isoforms in vitro. The Ki values of myr-PCI(Y) and myr-PCI(F) for purified PLC-gamma1 were 3.5 and 55 microM, respectively. Myr-PCI(Y) at concentrations in the sub-micromolar range significantly suppressed IP3 formation induced by EGF, PDGF, bombesin, or serum in Swiss 3T3 cells. Furthermore, myr-PCI(Y) also strongly inhibited cell proliferation induced by these stimuli. The inhibitory effect on IP3 formation and proliferation of myr-PCI(F) was much less potent than that of myr-PCI(Y). These results suggest that myristoylated PCI peptides could be applied to living cells as specific inhibitors of PLC signaling pathways and that PLC pathways are at least in part required for growth in Swiss 3T3 cells.

3T3 Cells↗
PubMed1994

Daidzein inhibits insulin- or insulin-like growth factor-1-mediated signaling in cell cycle progression of Swiss 3T3 cells.

An isoflavone compound, daidzein, inhibits the cell proliferation of Swiss 3T3 cells. Analysis of entry in S phase of Swiss 3T3 cells reveals that daidzein blocked cell cycle G1 phase progression 4.6 h after stimulation by bombesin plus insulin. After removal of daidzein, insulin or insulin-like growth factors (IGFs) reinitiate cell cycle progression of daidzein-blocked cells without further addition of bombesin. The order in the mitogenic action of insulin or IGFs is as follows: IGF-1 (5 ng/ml) >> IGF-2 (0.5 microgram/ml) congruent to insulin (1 microgram/ml). Studies in vivo of protein kinase activation by mitogenic stimulation reveal that the treatment with daidzein decreased the activation of a MAP2 phosphorylating protein kinase (MAP2 kinase). In vitro kinase assays showed that daidzein inhibits casein kinase II activity, but does not inhibit MAP2 kinase activity. Activation of casein kinase II by polylysine augments the activity of MAP2 kinase in digitonin-permeabilized 3T3 cells. These results suggest that daidzein blocked G1 phase cell cycle progression of Swiss 3T3 by inhibiting the activity of casein kinase II which is required for the commitment of mitogenic signal by insulin or IGF-1 in G1 phase.

3T3 Cells↗
PubMed1998

Adhesion to fibronectin's EDb domain induces tyrosine phosphorylation of focal adhesion proteins in Balb/c 3T3 cells.

Balb/c 3T3 cell adhesion on substrata coated with fibronectin's (FN) alternatively-spliced EDb, implicated in some tumor cell systems, and its neighboring type III repeats (III7 and III8) induced intracellular signaling coincident with morphological responses. These events were analysed using minigene-expressed proteins containing various permutations of type III repeats of FN. Cells adherent to the tri-repeat protein 7-EDb-8 were compared to those attached to the tri-repeat 8-9-10 which can interact with integrins through RGD and its synergistic sequences. Cell adhesion to 7-EDb-8 generated rapid tyrosine phosphorylation of several intracellular proteins (particularly the complex at 120-130 kD), with the overall phosphorylation level and its sensitivity to tyrosine kinase inhibitors similar to responses on the 8-9-10 tri-repeat. This similarity contrasted with the differential morphological responses of cells mediated by these proteins. Further analysis of the kinetics of phosphorylation through immunoblotting of two focal adhesion proteins, p125FAK and pl30cas, revealed a profile for Balb/c 3T3 adhesion to 7-EDb-8 distinct from that on 8-9-10. EDb mono-repeat was also more potent for inducing both limited cell spreading and FAK tyrosine phosphorylation than its neighboring repeats III7 or III8. Examination of cellular localization of FAK and vinculin showed that cells spread on the 7-EDb-8 substratum displayed vinculin-positive focal complex-like structures at the cell periphery, in contrast to the classical focal adhesions seen in 8-9-10-adherent cells. These results suggest that EDb induces cell signaling events, leading to tyrosine phosphorylation of focal adhesion proteins, through a mechanism different from that mediated by integrins recognizing sequences in III8-9-10. EDb-dependent signaling may have special significance in some tumor systems.

3T3 Cells↗
PubMed1991

Mitogens regulate the production of insulin-like growth factor-binding protein by Swiss 3T3 cells.

Quiescent Swiss 3T3 cells can be stimulated to reenter the cell cycle by various mitogens used in synergistic combinations with insulin-like growth factors (IGFs). The cells constitutively secrete an IGF-binding protein (IGFBP), which can modulate the interaction of IGFs with their receptors and could, therefore, alter cellular responsiveness to IGFs. We have now characterized the IGFBP secreted by Swiss 3T3 cells and tested whether its secretion is regulated by heterologous mitogens. Ligand blotting using [125I]IGF-I revealed a major IGFBP of 40,000 mol wt, and treatment of the cells with tunicamycin reduced the mol wt of this protein to about 32,000. mRNA from Swiss 3T3 cells hybridized to a 32P-labeled oligonucleotide (50-mer) complementary to rat IGFBP-3. Taken together, these results indicate that the principal IGFBP secreted by Swiss 3T3 cells is probably the N-glycosylated IGFBP-3. Production of this IGFBP by Swiss 3T3 cells was stimulated by 50-150% by the mitogens bombesin, vasopressin, platelet-derived growth factor, epidermal growth factor, and 12-O-tetradecanoylphorbol 13-acetate and also by IGF-I. The increased production of IGFBP was first detected after 4-6h of incubation and was then maintained for 48-72 h. Agents that elevate intracellular cAMP and the glucocorticoid dexamethasone reduced IGFBP output. In cells in which protein kinase-C had been down-modulated, the stimulation of IGFBP output by 12-O-tetradecanoylphorbol 13-acetate was abolished, but the stimulation induced by the other mitogens was not prevented. Thus, the production of IGFBP by Swiss 3T3 cells can be regulated by a number of different signalling pathways.

Animals↗
PubMed1984

Diacylglycerol stimulates DNA synthesis and cell division in mouse 3T3 cells: role of Ca2+-sensitive phospholipid-dependent protein kinase.

The synthetic diacylglycerol 1-oleoyl-2-acetylglycerol competes directly with [3H]phorbol 12,13-dibutyrate for common binding sites in monolayer cultures of Swiss 3T3 cells and rapidly stimulates the phosphorylation of a Mr 80,000 cellular protein that has recently been shown to reflect the activation of protein kinase C in intact cells. Thus, this diacylglycerol provided a useful tool to determine whether exogenously added diacylglycerols can mimic the potent tumor promoter phorbol ester in eliciting DNA synthesis and cell division in quiescent cells. We found that OAG acts synergistically with insulin and other growth factors to stimulate reinitiation of cell proliferation, and several lines of evidence indicate that OAG shares with phorbol esters a common pathway of mitogenic action via stimulation of protein kinase C activity in intact 3T3 cells. The findings support the hypothesis that diacylglycerols represent endogenous analogs of phorbol esters and raise the possibility that diacylglycerols generated in the plasma membrane could act as a mitogenic signal for quiescent cells.

Animals↗
PubMed1986

Immediate effects of serum depletion on dissociation between growth in size and cell division in proliferating 3T3 cells.

Proliferating nonconfluent 3T3 cells become committed to proceed through the cell cycle or to enter G0 during the first post-mitotic part of G1 (G1pm). The decision to proceed through G1pm is dependent on the presence of serum growth factors in the culture medium. Cells that have passed this particular growth-factor-dependent cell cycle stage are independent of serum growth factors and undergo mitosis on schedule. We report here that G1ps, S, and G2 cells cease to increase in size when serum is withdrawn. As a result the mitotic cell size after 8 hours serum starvation is reduced to approximately 60% of the normal mitotic cell. This reduced growth in cell size is due to a rapid decrease in protein synthesis and some increase in protein degradation. This dissociation between growth in size and cell-cycle progression within a single cell cycle provides a new approach to study the two processes separately.

Animals↗
PubMed1994

Modulation of alpha-actinin levels affects cell motility and confers tumorigenicity on 3T3 cells.

alpha-Actinin is an abundant actin crosslinking protein, also localized at adherens type junctions. In adhesion plaques, alpha-actinin can link the actin filaments to integrin via vinculin and talin, or directly by binding to the cytoplasmic domain of beta 1-integrin. The expression of alpha-actinin is rapidly elevated in growth-activated quiescent cells, and is reduced in SV40-transformed 3T3 cells and various differentiating cell types (reviewed by Glück, U., Kwiatkowski, D. J. and Ben-Ze'ev, A. Proc. Nat. Acad. Sci. USA 90, 383-387, 1993). To study the effect of changes in alpha-actinin levels on cell behavior, alpha-actinin expression was elevated in 3T3 cells by transfection with a full-length human nonmuscle alpha-actinin cDNA. To suppress alpha-actinin levels, 3T3 cells were transfected with an antisense alpha-actinin cDNA construct. Cells overexpressing alpha-actinin by 40-60% displayed a significant reduction in cell motility, as demonstrated by their slower locomotion into an artificial wound, and by forming shorter phagokinetic tracks on colloidal gold-coated substrata. 3T3 cells in which the expression of alpha-actinin was reduced to 25-60% of control levels, after antisense alpha-actinin transfection, had an increased cell motility. Moreover, such alpha-actinin-deficient 3T3 cells formed tumors upon injection into nude mice. The results demonstrate that modulations in alpha-actinin expression can affect, in a major way, the motile and tumorigenic properties of cells, and support the view that decreased alpha-actinin expression could be a common regulatory pathway to malignant transformation of 3T3 cells.

3T3 Cells↗
PubMed1992

Overexpression of vinculin suppresses cell motility in BALB/c 3T3 cells.

The content of vinculin, a cytoplasmic protein found in focal contacts and cell-cell junctions, was increased in BALB/c 3T3 cells by gene transfection. The vinculin expressed from the full length chicken cDNA, incorporated into focal contacts and its pattern was identical to that of the endogenous protein. Cells stably expressing vinculin by 20% over the endogenous level had altered locomotory properties. In these cells, the ability to migrate into a wound formed in a confluent monolayer and the locomotion of individual cells were drastically reduced. The results provide direct evidence that cell locomotion can be regulated by modulating vinculin expression.

3T3 Cells↗
PubMed1994

Variations in signal-mediated nuclear transport during the cell cycle in BALB/c 3T3 cells.

Signal-mediated nuclear import was investigated in proliferating BALB/c 3T3 cells 1, 2, 4, 6, 8, 12, 18, and 21 h after the onset of anaphase. Using nucleoplasmin-coated colloidal gold particles to assay transport capacity, it was found that import was greatest at 1 h postanaphase (after complete reformation of the nuclear envelope). At this time, both the relative rate of gold uptake and the functional size of the transport channels were significantly greater than in control cells, which were randomly selected from nonsynchronized cultures. At 21 h, there was a decrease in the size of the transport channel, but not the rate of nuclear import. This suggests that these two factors are regulated independently. No changes in transport capacity, compared to controls, were detected at other times in the cell cycle.

3T3 Cells↗
PubMed1995

NGF-producing transfected 3T3 cells: behavioral and histological assessment of transplants in nigral lesioned rats.

The rodent fibroblast clonal cell line, 3T3, was retrovirally transfected with the rat nerve growth factor (NGF) gene and selected for NGF synthesis. This study tested the hypothesis that transplanted 3T3 cells, transfected to secrete nerve growth factor (3T3NGF+), change motor behavioral indices created by striatal denervation in a dose-dependent fashion. 3T3NGF+ cells were transplanted into the lateral ventricle of rats following ipsilateral lesions of the substantia nigra pars compacta by stereotaxic injections of 6-hydroxydopamine (10 micrograms), an established lesion model. Control groups included vehicle injections and transplanted untransfected cells. The extent of the lesions was measured by determining rotational behavior before and two weeks after transplantation. Immediately prior to transplantation, cells were incubated with the fluorescent dye marker, Dil. To assess cell viability, whole brains were cryosectioned and examined for Dil-labeled 3T3 cells using fluorescent microscopy. The number of Dil-labeled profiles in five animals per group were counted in at least five noncontiguous sections per animal. From these data a statistically derived estimate of viable, transplanted 3T3 cells was obtained. The number of surviving transplanted cells correlated with the behavioral changes measured. The 3T3NGF+ transplants reduced rotational behavior, while control 3T3 transplants exacerbated rotational behavior. Thus, while NGF delivery was found to be beneficial, it was apparent that naive 3T3 had detrimental effects. These results underscore the importance of making dose-response measurements when attempting transplant-based modifications of CNS behavior.

3T3 Cells↗
PubMed1977

Division of BALB/c mouse 3T3 and simian virus 40-transformed 3T3 cells in cellular aggregates.

BALB/c mouse 3T3 cells and 3T3 cells transformed by simian virus 40 (SV40) were cultured as aggregates in agitated liquid medium. When maintained with daily medium changes, 3T3 cells incorporated [(3)H]thymidine into acid-insoluble material at a rate (1/4) that of 3T3 cells in logarithmic-phase flat cultures but 16 times that of the same cells in stationary-phase flat cultures. Similarly, SV40-transformed 3T3 cells in aggregates incorporated [(3)H]thymidine at (1/3) the rate of SV40-3T3 cells in logarithimic-phase flat culture and 14 times that of these cells in stationary-phase flat culture. Autoradiographs of aggregates of 3T3 and SV40-3T3 cells incubated for 2 hr in the presence of [(3)H]uridine and [(3)H]thymidine indicated that penetration of the nucleosides into aggregates during this period was limited to the outer four to six cell layers. Aggregates were also incubated in the presence of radiolabeled thymidine and uridine continuously for 4 days. Under these conditions, where nucleoside penetration was not limiting, 100% of the SV40-3T3 cells and 56% of the 3T3 cells incorporated [(3)H]thymidine into acid-insoluble material. The rates of cell division, cell loss, and net cell accumulation in aggregates of 3T3 and SV40-3T3 cells were measured by techniques not influenced by possible alterations in transport, pool size, or penetration. SV40-3T3 cells divided with a doubling time for the total population of 26.0 hr. The total cell number increased more slowly (doubling time of 48.3 hr) because of cell loss, which occurred with a half-time (time for 50% of the cells to be lost) of 53.3 hr. 3T3 cells in aggregates began to divide only after 3 days, then did so with a doubling time for the total population of 76.4 hr. Total cell number decreased (half-time of 26.3 hr) because this rate of cell division was exceeded by the rate of cell loss, which was constant with a half-time of 22.9 hr. The results suggest that 3T3 and SV40-3T3 cells display growth properties in aggregates consistent with their previously reported behavior in conventional flat culture: SV40-transformed 3T3 cells can proliferate under conditions of high cell density to a much greater extent than 3T3 cells can. Both cell lines, however, display an increased capacity to divide in aggregates relative to confluent flat culture, despite conditions of high cell density and absence of anchorage to an artificial solid substrate.

Cell Aggregation↗
PubMed1978

Cell adhesion and cell surface topography in aggregates of 3T3 and SV40-virus-transformed 3T3 cells. Visualization of interior cells by scanning electron microscopy.

A technique for exposing the interior of aggregates of cultured cells has been developed and is described in this report. Using this technique, we have examined for the first time, by scanning electron microscopy, cell morphology and cell contact ultrastructure in the interior of aggregates of BALB/c 3T3 and SV40-transformed 3T3 cells. The 3T3 cells make initial intercellular contact by means of microvillar processes. Over a period of 3-8 h, some of these microvillar contacts are replaced by broader projections. In contrast, the SV40-transformed cells make initial intercellular contact by means of blebs or blunt projections which are also broadened and extended over a period of 3-8 h. For both 3T3 and SV40-3T3 cells, the surfaces of the cells which form the outer layer of the aggregate resemble the surfaces of single cells fixed in suspension, regardless of how long the aggregates have been cultured. Thse cells are covered with many cellular processes and are roughly hemispherical in profile. The surfaces of the internal cells of the aggregates, however, lose many of their cellular processes, develop smooth patches, and many become irregular in shape. This smooth morphology was also observed on the interior surfaces of the peripheral cell layer. From these observations we conclude that: (a) the stabilization of adhesive contacts is a slow process which takes at least 3-8 h; (b) the outer surfaces of peripheral cells differ significantly from the surfaces of interior cells; and (c) clear differences in surface topography exist between nonmalignant 3T3 cells and their malignant SV40 transformants.

Cell Adhesion↗
PubMed1981

Dissociation of tumour-promoter-induced effects on prostaglandin release, polyamine synthesis and cell proliferation of 3T3 cells.

The phorbol ester 12-O-tetradecanoylphorbol 13-acetate induces tumour promotion, inflammation, cell proliferation and prostaglandin release. Recent reports suggest that the prostaglandins released by 12-O-tetradecanoylphorbol 13-acetate (TPA) initiate a cascade of events leading to polyamine synthesis and cell proliferation. In experiments designed to test this contention, it was found that addition of TPA (1 microM to 1 nM) to confluent mouse 3T3 fibroblasts successively caused the release of prostaglandins E2 and I2, induction of the enzyme ornithine decarboxylase (EC 4.1.1.17), stimulation of [3H]thymidine incorporation into DNA, and cell proliferation. Pretreatment of the cells with the anti-inflammatory steroid dexamethasone (1 microM) or the non-steroidal anti-inflammatory drug indomethacin (1 microM) inhibited TPA-induced prostaglandin release. However, dexamethasone enhanced the other effects of TPA, whereas indomethacin was ineffective. Addition of prostaglandin E2 to the cultures did not induce ornithine decarboxylase activity and cell proliferation. Pretreatment of the cells with 1,3-diaminopropane (1 mM) or alpha-methylornithine (5 mM), inhibitors of polyamine synthesis, decreased TPA-induced ornithine decarboxylase activity without affecting DNA synthesis. TPA stimulated [3H]thymidine incorporation into DNA, even when the ornithine decarboxylase activity was completely blocked. These data suggest that the proliferative effect of TPA on 3T3 cells is independent of prostaglandin release and polyamine synthesis.

Animals↗
PubMed1985

Coupling of a loop diuretic-sensitive Na+ influx with the net loop diuretic-sensitive K+ efflux in mouse NIH 3T3 cells.

Mouse 3T3 fibroblasts have a loop diuretic sensitive Na+ transport system, responsible for more than 50% of the total Na+ influx. This transport system is dependent on the simultaneous presence of all three ions; Na+, K+, (Rb+) and Cl- in the extracellular medium. The same requirement for these three ions was also found for the loop diuretic-sensitive K+ efflux. In addition, the sensitivities of Na+ influx and Rb+ efflux for the two loop diuretics, furosemide and bumetanide were found to be similar. The similar ionic requirement and sensitivity towards loop diuretics of the two fluxes, support the hypothesis, that this loop diuretic-sensitive Na+ influx in mouse 3T3 cells, is accompanied by the net loop diuretic-sensitive K+ efflux.

Animals↗