Dependence of interfacial properties of normal and transformed 3T3 cell membranes on treatment with factors modifying proliferation

Interfacial properties of the outer cell membrane of normal and transformed in vitro cultures of mouse 3T3 cells have been investigated. The contact angles of sessile drops on dried cell preparations were measured and the interfacial tensions derived using the thermodynamic approach introduced by Neumann. Interfacial tensions were found to be within an order of magnitude of those determined for other cell and model membranes. Treatment of cells with calf serum, a stimulant to proliferation, resulted in a decrease in the interfacial tension of normal and transformed cells, whereas use of concanavalin A and its succinylated derivative lead to an increase of interfacial tensions of both cell types. These and further results show a detailed correlation between the growth-regulating effects and the effects on interfacial properties of these proliferation-modifying factors. An interpretation of the results of serum depression of the interfacial tension in terms of a binding equilibrium dependent on the concentration of humoral growth factors in the medium is attempted.     

Phosphoprotein phosphate activity at the outer surface of intact normal and transformed 3T3 fibroblasts

Using ³²P-labeled phosphocasein or phosphohistones as exogenous substrates it was possible to detect a phosphoprotein phosphate activity on the outer surface of intact normal and transformed 3T3 fibroblasts. Incubation of monolayers of intact cells in buffered salt solution with the radioactively labeled substrate resulted in the release of alkali-labile ³²P counts into the surrounding medium. The reaction was: (a) linear with time (at least up to 20 min); (b) proportional to the cell density; (c) dependent on the temperature and pH of the incubation medium; (d) stimulated by K⁺; and (e) inhibited by sodium fluoride, inorganic pyrophosphate, zinc chloride and relatively impermeant sulfhydryl reagents. Less than 2% of the externally located phosphoprotein phosphatase activity was detectable in pooled cell-free washings of the intact cell monolayer. Phosphocasein did not cause any detectable leakage of intracellular lactate dehydrogenase or soluble phosphoprotein phosphatase activity into the external medium; incubation of the cells with phosphohistones, on the other hand, resulted in appreaciable leakage of both these cytoplasmic activities. Neoplastic transformation was associated with a nearly two-fold decrease in the activity of the surface phosphoprotein phosphatase. Addition of serum to either non-transformed 3T3 or spontaneously transformed 3T6 cells resulted in a rapid and remarkable drop in the cell surface dephosphorylating activity. Acrylamide gel electrophoresis of the dephosphorylated casein or histone substrate revealed no proteolytic degradation or change in electrophoretic mobility. The intact cells showed no damage upon microscopic examination as a result of exposure to phosphocasein or phosphohistones.     

Effects of bovine platelet-poor plasma on the proliferation of normal and transformed BALB/c 3T3 cells

Summary Platelet-poor plasma, as well as autologous platelet-rich serum, was prepared from freshly-drawn bovine whole blood. Bovine platelet-poor plasma had properties similar to those previously decribed for human platelet-poor plasma; e. g., it would (a) support the growth of virally transformed but not normal BALB/ c 3T3 cells, (b) act synergistically with either partially purified platelet-derived growth factor or fibroblast growth factor to initiate cell replication in quiescent 3T3 cells, and (c) act sequentially with platelet-derived growth factor to initiate 3T3 replication. It appears that bovine serum contains both competence and progression factors and that stimulation of fibroblasts with bovine serum involves at least two sequential stages analogous to those described for stimulation with human serum.     

The role of calcium ions in the permeability changes produced by external ATP in transformed 3T3 cells

External ATP causes a rapid increase in passive permeability to nucleotides and phosphate esters in transformed cell lines, such as 3T6 mouse fibroblasts. However, untransformed lines, such as 3T3, do not show a similar sensitivity to external ATP. Ca²⁺ inhibits permeabilization, but only at concentrations approaching those of external ATP. In contrast, La³⁺ and Tb³⁺ inhibit ATP-dependent permeabilization at one-fifth the concentration of external ATP. Considering reports that lanthanides can substitute for calcium ion in many enzymatic reactions, often with a higher affinity, it would appear that Ca²⁺ plays a specific role in the maintenance of a passive membrane permeability barrier and in opposing the effects of external ATP.Other data suggest a regulatory role for the Ca²⁺-calmodulin complex in the permeabilization process. Trifluoperazine, chlorpromazine and W-7, compounds which inhibit cellular functions dependent on the Ca²⁺-calmodulin complex, are able to enhance the effect of external ATP. Thus, a dramatic stimulation of nucleotide permeability occurs with concentrations of external ATP and inhibitor that are ineffective when added alone. Calmodulin antagonists and low concentrations of external ATP increased membrane permeability to Na⁺ and K⁺ as was previously shown for permeabilization with ATP alone. Earlier studies have shown that energy inhibitors which reduce intracellular ATP levels greatly increase the sensitivity of transformed cells to external ATP. However, the Ca²⁺-calmodulin antagonists used in the present study exert their effects at concentrations which do not alter intracellular ATP levels.     

The different actions of normal and supranormal calcium concentrations on the proliferation of BALB/c 3T3 mouse cells

Summary In the presence of a normal (1.25 to 1.80 mM) calcium concentration, addition of fresh bovine calf serum or completely changing the medium induces proliferatively quiescent BALB/c 3T3 mouse cells in dense cultures to start a growth division cycle and initiate DNA synthesis about 12 hr later. Fresh, low-calcium (0.02 mM physiologically available) medium also causes cells to start a growth-division cycle. However, the development of such stimulated, calcium-deprived cells stops just before the expected time of initiation of DNA synthesis, which can then be rapidly induced by restoration of the normal calcium concentration. Simply raising the calcium concentration to nonphysiologically high levels (without otherwise altering the medium) can mimic the action of fresh serum or fresh whole medium by inducing some of the cells in proliferatively quiescent confluent cultures to start a growth-division cycle and initiate DNA synthesis 22 hr later. Issued as NRCC No. 15371.     

Biosynthesis in vitro of mono- and di-sialosylgangliosides from gangliotetraosylceramide by cultured cell lines and young rat brain. Structure of the products, and activity and specificity of sialosyltransferase

Incubations in vitro of GA1, labeled with 3H in the terminal D-galactopyranosyl group, with nonradioactive CMP-NeuNAc in the presence of homogenates of C21 rat brain glial cells, NIE mouse neuroblastoma cells, 3T3 mouse fibroblasts, SV 40-transformed 3T3 cells, chick embryo fibroblasts, Rous sarcoma virus-transformed chick embryo fibroblasts, and 9-day old rat brain resulted in all cases in the formation in high yield of GM1b, in which the neuraminidase-labile NeuNAc group is linked at O-3 of the terminal D-galactosyl residue, as shown by permethylation studies. No trace of the naturally occurring neuraminidase-stable GM1a was detected in any case. In addition, with NIE cells, and normal and RSV-transformed chick embryo fibroblasts, a disialosylganglioside (GD1) differing from GD1a and GD1b, and bearing only one substituent at O-3 of the terminal D-galactopyranosyl residue was formed. It was also biosynthesized from GM1b and CMP-NeuNAc by NIE and chick embryo cells but not by C21 cells, or rat brain. However, C21 cells and rat brain were capable of synthesizing GD1a from GM1a. Periodate oxidation degraded both NeuNAc groups in GD1 to a 7-carbon fragm:nt, indicating lack of substitution at O-8. GM1b could not be detected as a natural product in rat brain.     

Regulation of passive potassium transport of normal and transformed 3T3 mouse cell cultures by external calcium concentration and temperature

Summary Regulation of passive potassium ion transport by the external calcium concentration and temperature was studied on cell cultures of 3T3 mouse cells and their DNA-virus transformed derivatives. Upon lowering of external calcium concentration, passive potassium efflux generally exhibits a sharp increase at about 0.1mm. The fraction of calcium-regulated potassium efflux is largely independent of temperature in the cases of the transformed cells, but shows a sharp increase for 3T3 cells upon increasing temperature above 32°C. In the same range of temperature, the 3T3 cells exhibit the phenomenon of high-temperature inactivation of the residual potassium efflux at 1mm external calcium. At comparable cellular growth densities, the transformed cell lines do not show high-temperature inactivation of residual potassium efflux. These results are consistent with the notion of a decisive role of the internal K⁺ concentration in the cell-density dependent regulation of cell proliferation. In particular, the growth-inhibiting effect of lowering the external Ca²⁺ concentrations is considered as largely due to a rise of passive K⁺ efflux and a subsequent decrease of internal K⁺ concentration. The experimental data on the Ca²⁺ dependence of passive K⁺ flux are quantitatively described by a theoretical model based on the constant field relations including negative surface charges on the external face of the membrane, which cooperatively bind Ca²⁺ ions and may concomitantly undergo a lateral redistribution. The present evidence is consistent with acidic phospholipids as representing these negative surface charges.This work is dedicated to the memory of Max Delbrück (deceased March 10, 1981), in whose laboratory in 1966 the earlier version of the present theoretical model was developed by one of the authors.     

Tissue inhibitor of metalloproteinase-1 promotes NIH3T3 fibroblast proliferation by activating p-Akt and cell cycle progression

Tissue inhibitor of metalloproteinase-1 (TIMP-1) plays various roles in cell growth in different cell types. However, few studies have focused on TIMP-1’s effect on fibroblast cells. In this study, we investigated the effects of TIMP-1 overexpression on NIH3T3 fibroblast proliferation and potential transduction signaling pathways involved. Overexpression of TIMP-1, by transfection of the pLenti6/V5-DESTTIMP-1 plasmid, significantly promoted NIH3T3 proliferation as determined by the BrdU array. Neither 5 nor 15 nM GM6001 (matrix metalloproteinase system inhibitor) affected NIH3T3 proliferation, but 45 nM GM6001 inhibited proliferation. TIMP-1 overexpression activated the p-Akt pathway, but not the p-ERK or p-p38 pathway. In TIMP-1-transfected cells, cyclinD1 was upregulated and p21CIP1 and p27^KIP1 were downregulated, which promoted cell entry into the S and G2/M phases. The PI3-K inhibitor LY294002 abolished the TIMP-1-induced effects. Overexpression of intracellular TIMP-1 stimulated NIH3T3 fibroblast proliferation in a matrix metalloproteinase (MMP)-independent manner by activating the p-Akt pathway and related cell cycle progression.     

The effect of selenium on cell proliferation in liver and colon

Epidemiologic and experimental evidence support a chemoprotective role for selenium (Se) in malignancy. Many mechanisms have been proposed to explain this phenomenon. In this study, the effect of Se intake on proliferation of hepatocytes and normal colonic epithelial cells in rats was determined using autoradiographic analysis of thymidine incorporation into DNA. Hepatocyte proliferation was measured 24 h after partial hepatectomy. Selenium-dosed animals demonstrated a significant reduction in hepatocyte labeling compared to the control group (6.1±2.6 vs 29.2±15.6,p=0.003). However, Se dosing did not affect the thymidine-labeling indices or distribution of labeling in colonic epithelium. Selenium may inhibit cell proliferation when it is the result of an unusually intense stimulus. This finding could explain in part the inhibitory effect of Se in some experimental cancer models. Dr. Tempero is a recipient of a Junior Clinical Faculty Fellowship from the American Cancer Society.     

Quantitation of cell proliferation,colony formation,and carcinogen induced cytotoxicity of rat tracheal epithelial cells grown in culture on 3T3 feeder layers

Summary A cell culture system is described for the growth of rat tracheal epithelial (RTE) cells at clonal density. The system uses normal, early passage RTE cells grown on feeder layers of lethally irradiated 3T3 cells. The RTE cells have a high colony forming efficiency (5 to 10%) in culture, can be passaged up to 5 times, and are capable of more than 20 cumulative doublings per colony forming cell. The epithelial nature of the cells was confirmed by cell and colony morphology, immunoperoxidase staining of intracellular keratin, and cellular ultrastructural studies. The cytotoxic response of RTE cells to a variety of carcinogens, including a direct acting chemical carcinogen, a physical carcinogen, and a series of polycyclic aromatic hydrocarbons, was quantitated. A linear decrease in the logarithm of survival was observed with increasing doses ofN-methyl-N′-nitro-N-nitrosoguanidine (MNNG), γ-irradiation, 7,12-dimethylbenz(a)anthracene, and a diol-epoxide of benzo(a)pyrene. No toxicity was observed after treatment with benzo(a)pyrene or 3-methylcholanthrene over the concentration range examined. In contrast, phorbol ester tumor promoters stimulated cell growth markedly. Based on these and other studies, the RTE cell culture system represents a model system that will be useful for quantitative studies of epithelial cell growth, differentiation, and carcinogenesis.     

ORAI-mediated calcium influx in T cell proliferation, apoptosis and tolerance

Ca²⁺ homeostasis controls a diversity of cellular processes including proliferation and apoptosis. A very important aspect of Ca²⁺ signaling is how different Ca²⁺ signals are translated into specific cell functions. In T cells, Ca²⁺ signals are induced following the recognition of antigen by the T cell receptor and depend mainly on Ca²⁺ influx through store-operated CRAC channels, which are mediated by ORAI proteins following their activation by STIM proteins. The complete absence of Ca²⁺ influx caused by mutations in Stim1 and Orai1 leads to severe immunodeficiency. Here we summarize how Ca²⁺ signals are tuned to regulate important T cell functions as proliferation, apoptosis and tolerance, the latter one being a special state of immune cells in which they can no longer respond properly to an otherwise activating stimulus. Perturbations of Ca²⁺ signaling may be linked to immune suppressive diseases and autoimmune diseases.     

Differential effects of Cbl and 70Z/3 Cbl on T cell receptor-induced phospholipase Cγ-1 activity

We demonstrate that the differential effects Cbl and oncogenic 70Z/3 Cbl have on Ca²⁺/Ras-sensitive NF-AT reporters is partially due to their opposing ability to regulate phospholipase Cγ1 (PLCγ1) activation as demonstrated by analysis of the activation of an NF-AT reporter construct and PLCγ1-mediated inositol phospholipid (PI) hydrolysis. Cbl over-expression resulted in reduced T cell receptor-induced PI hydrolysis, in the absence of any effect on PLCγ1 tyrosine phosphorylation. In contrast, expression of 70Z/3 Cbl led to an increase in basal and OKT3-induced PLCγ1 phosphorylation and PI hydrolysis. These data indicate that Cbl and 70Z/3 Cbl differentially regulate PLCγ1 phosphorylation and activation. The implications of these data on the mechanism of Cbl-mediated signaling regulation are discussed.     

The novel mTORC1/2 dual inhibitor INK-128 suppresses survival and proliferation of primary and transformed human pancreatic cancer cells

Pancreatic cancer has one of worst prognosis among all human malignancies around the world, the development of novel and more efficient anti-cancer agents against this disease is urgent. In the current study, we tested the potential effect of INK-128, a novel mammalian target of rapamycin (mTOR) complex 1 and 2 (mTORC1/2) dual inhibitor, against pancreatic cancer cells in vitro. Our results demonstrated that INK-128 concentration- and time-dependently inhibited the survival and growth of pancreatic cancer cells (both primary cells and transformed cells). INK-128 induced pancreatic cancer cell apoptosis and necrosis simultaneously. Further, INK-128 dramatically inhibited phosphorylation of 4E-binding protein 1 (4E-BP1), ribosomal S6 kinase 1 (S6K1) and Akt at Ser 473 in pancreatic cancer cells. Meanwhile, it downregulated cyclin D1 expression and caused cell cycle arrest. Finally, we found that a low concentration of INK-128 significantly increased the sensitivity of pancreatic cancer cells to gemcitabine. Together, our in vitro results suggest that INK-128 might be further investigated as a novel anti-cancer agent or chemo-adjuvant for pancreatic cancer treatment.     

In vitro effects of growth factors and hormones on three Perkinsus species and increased proliferation of P. marinus during cloning

Clonal cultures are essential for the genotypic and phenotypic characterization of Perkinsus species but their cloning, especially of P. marinus, can be tedious. The use of a growth factor and hormone supplement to facilitate cloning was, therefore, investigated. Many of the 16 supplements tested significantly increased P. marinus and P. olseni proliferation but only two significantly increased P. chesapeaki proliferation. The concentration of the most effective supplement for all three Perkinsus species (i.e., endothelial cell growth supplement, ECGS) and medium dilution were then optimized for P. marinus cultured at low densities. Finally, the advantage of using conditioned culture medium, a feeder layer, and ECGS alone and in different combinations to improve cloning of P. marinus were compared. Using conditioned culture medium, a feeder layer and ECGS in combination, each cell (N = 7) seeded singly yielded clonal cultures with 253 ± 167 cells after 21 days. In contrast, only 4 out of 7 cells seeded singly in culture medium yielded clonal cultures with 5 ± 4 cells after 21 days.     

Cord blood CD4CD25 regulatory T cells fail to inhibit cord blood NK cell functions due to insufficient production and expression of TGF-beta1

Although CD4⁺CD25⁺ Treg (Treg) cells are known to modulate NK cell functions, the modulation mechanism of these cells in cord blood has not been fully clarified. The purpose of this study was to clarify the mechanism whereby cord blood Treg cells modulate cord NK cells. By performing various cultures of purified NK cells with or without autologous Treg cells, diminished inhibitory effects of cord Treg cells towards cord NK cell functions, including activation, cytokine production, and cytotoxicity, were observed. We also observed lower secretion of sTGF-beta1 and lower expression of mTGF-beta1 by cord Treg cells than by adult Treg cells. These data revealed the capability of adult Treg cells to suppress rhIL-2-stimulated NK cell function by TGF-beta1, both membrane-bound and soluble types. The reduced inhibitory capabilities of cord Treg cells compared with adult Treg cells is thought to be due to insufficient expression of TGF-beta1.     

Concanavalin A-mediated agglutinability of Balbc3T3 cells grown in media supplemented with different phosphatidylcholines

$\text{Balb}\text{c3T3}$ cells were grown near confluency in media supplemented with 10% fetal calf serum and than exposed for 24 hours to media containing different phosphatidylcholines bound to delipidated fetal calf serum. Compared to cells grown in regular media, 3T3 cells exposed to media containing dioleoyl-phosphatidylcholine dramatically increased their agglutinability by Concanavalin A. Exposure to several other phosphatidylcholines had no effect.     

A novel interaction of CLN3 with nonmuscle myosin-IIB and defects in cell motility of Cln3 cells

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a pediatric lysosomal storage disorder characterized by accumulation of autofluorescent storage material and neurodegeneration, which result from mutations in CLN3. The function of CLN3, a lysosomal membrane protein, is currently unknown. We report that CLN3 interacts with cytoskeleton-associated nonmuscle myosin-IIB. Both CLN3 and myosin-IIB are ubiquitously expressed, yet mutations in either produce dramatic consequences in the CNS such as neurodegeneration in JNCL patients and Cln3^−/− mouse models, or developmental deficiencies in Myh10^−/− mice, respectively. A scratch assay revealed a migration defect associated with Cln3^−/− cells. Inhibition of nonmuscle myosin-II with blebbistatin in WT cells resulted in a phenotype that mimics the Cln3^−/− migration defect. Moreover, inhibiting lysosome function by treating cells with chloroquine exacerbated the migration defect in Cln3^−/−. Cln3^−/− cells traversing a transwell filter under gradient trophic factor conditions displayed altered migration, further linking lysosomal function and cell migration. The myosin-IIB distribution in Cln3^−/− cells is elongated, indicating a cytoskeleton defect caused by the loss of CLN3. In summary, cells lacking CLN3 have defects that suggest altered myosin-IIB activity, supporting a functional and physical interaction between CLN3 and myosin-IIB. We propose that the migration defect in Cln3^−/− results, in part, from the loss of the CLN3–myosin-IIB interaction.