Activation of purified simian virus 40 virions by free amino-group containing phospholipid liposomes

The infectivity of the simian virus 40 (SV40) virions purified after treatment with sodium deoxycholate is activated by mixing, prior to infection, the virions with the liposomes composed of phosphatidylserine or a mixture of phosphatidylethanolamine and phosphatidylcholine (H. Shimura, and G. Kimura (1985), Virology 144, 268-272). The sucrose-CsCl cushion sedimentation analysis of the virions mixed with the liposomes revealed that the density of the radiolabeled virions became lower and that of the radiolabeled liposomes became higher to give a similar range, suggesting the binding of virions with the liposomes. Electron microscopy revealed the side-to-side association of virions with liposomes. The efficiency of adsorption of the virions to monkey kidney BSC-1 cells varied depending on phospholipid types mixed with virions and did not always become high. In the case of phosphatidylethanolamine liposomes, the free amino group in the phospholipid molecule was essential for the activation of the virion infectivity, because mono- and di-methylated phosphatidylethanolamine failed to activate the infectivity. Fluid nature of phospholipids seemed to be necessary also for the infectivity activation, because dipalmitoyl and distearoyl phospholipids did not activate virion infectivity at 37 degrees, the temperature at which the liposomes of these phospholipids are supposed to be in a solid state. Presence of free amino groups and difference in acyl groups of the phospholipids did not influence the adsorption of the virions to cells. These results suggest that events which occur after adsorption of virions to cells are responsible for the activation of the SV40 virion infectivity by the liposomes composed of free amino-group containing phospholipids.

Total body fluid volume determination based on urea kinetics in hemofiltration as an index of basal body weight in uremic patients

Assuming that urea is distributed uniformly within the total body water, urea-space or total body fluid volume was determined in six uremic patients based on urea kinetics in hemofiltration. The total body fluid volume before hemofiltration was 36.0 +/- 3.6 L (61.8 +/- 2.6% BW) and after hemofiltration 32.5 +/- 3.4 L (59.3 +/- 2.8% BW), suggesting that the total body fluid volume was nearly normalized by hemofiltration. It is concluded that urea-space, easily measurable based on urea kinetics during hemofiltration, is useful in evaluating the fluid balance in patients undergoing artificial kidney therapy.

Accumulation of cells with 4N DNA content at nonpermissive temperature in rat embryo diploid cells transformed by tsA mutant of simian virus 40

Primary rat embryo cells were transformed by a tsA mutant (tsA640) of simian virus 40 (SV40). Proliferation of all four independent diploid transformants was suppressed at a nonpermissive temperature (40.3 degrees C), being accompanied by a marked increase in the fraction of cells with a 4N DNA content (a 4N peak in the flow cytofluorogram). However, in this case, the fraction of cells with a 2N DNA content (a 2N peak in the flow cytofluorogram) was preserved. Both effects (suppression of proliferation and increase in the 4N peak) diminished when transformed cells were superinfected with wild-type SV40. The increased 4N peak was preserved, albeit not completely, for at least 24 hours, when cells were further incubated in the presence of hydroxyurea at the nonpermissive temperature. On the other hand, the preserved 2N peak all but disappeared within 24 hours, when cells were further incubated in the presence of colcemid at the nonpermissive temperature. These results suggest that the thermolabile large T antigen of SV40 directly or indirectly induces an accumulation of cells with a 4N DNA content, at the nonpermissive temperature, by prolonging the G2 (and/or late S) period.

Serum-dependent control of entry into S phase of next generation in rat 3Y1 fibroblasts. Effect of large T antigen of simian virus 40

When rat 3Y1 fibroblasts are deprived of serum in S phase and/or G2 phase in the first generation, the cells delay entry into S phase in the second generation for the duration of the serum deprivation. We can now show that when resting 3Y1 cells are infected with Simian virus 40 (SV40), the removal of serum through S and G2 phases in the first generation does not markedly delay entry into S phase in the second generation. These observations suggest that the serum-dependent control of entry into S phase of the second generation continues from the first generation, and that the abolition of this control by infection with SV40 in the first generation involves the mechanism operative when the resting cells are stimulated to enter S phase (of the first generation) by infection with SV40.

Reversible cAMP-dependent change in nuclear localization of microtubule-associated protein-1 analogues

Intranuclear immunofluorescent staining by monoclonal and polyclonal antibodies against microtubule-associated protein-1 (MAP-1) on SV-3Y1 cells disappeared when the cells were treated with 1 mM db-cAMP and 1 mM theophylline for 20-30 min at 37 degrees C. The nuclear dots of immunofluorescence disappeared and reappeared repeatedly on successive incubation of the cells with and without these drugs. The same phenomenon was induced by treatment of the cells with 6 mM theophylline or 6 mM papaverine which inhibits the cAMP-hydrolysing enzyme. The following results seem to support the hypothesis that cAMP-induced transfer of antigenic molecules from the nucleus to the cytoplasm is mediated by microtubules: Partial staining of the nucleus during the transitional period. Bright staining of the cytoplasm on treated cells in contrast to nuclear staining on control cells. Disappearance of the nuclear staining not only by the monoclonal antibody but also by the polyclonal antibody. Complete prevention of disappearance of nuclear dots induced by these drugs by pretreatment of the cells with colchicine (1 microgram/ml) or colcemid (1 microgram/ml).

Effects of sodium n-butyrate on entry into S phase in resting rat 3Y1 cells infected with simian virus 40

In quiescent rat 3Y1 fibroblasts infected with simian virus 40 (SV40), sodium butyrate elongated the time lag before entry into S phase in a concentration-dependent fashion. In spite of the elongated time lags, SV40-infected cells entered S phase in a very synchronous mode, irrespective of the butyrate concentrations. The elongated time lag seemed to be at least partially due to a delayed synthesis and a delayed accumulation of large T antigen caused by butyrate. The entry into S phase was also delayed even when butyrate was added to the cultures after expression of T antigen to an extent sufficient for untreated cells to enter S phase. This suggests that butyrate may also inhibit a cellular event(s) that is required for entry into S phase after expression of the T antigen. In contrast, serum-stimulated cells were more sensitive to butyrate with respect to entry into S phase than SV40-infected cells, and the distribution of the time lag among cell populations increased (i.e., asynchrony in entry into S phase increased) with an increase in the butyrate concentration.

Effect of sodium butyrate on actin distribution in rat 3Y1 fibroblasts in monolayer culture

We studied the effect of sodium butyrate, a potent G1/G2-arresting agent, on actin distribution in rat 3Y1 fibroblasts in monolayer culture by fluorescence microscopy of cells stained with 7-nitrobenz-2-oxa-1, 3-diazole phallacidine (NBD-Ph). When randomly proliferating cells were arrested mainly in G1 phase with butyrate, a reversible overaccumulation of cellular net protein occurred. In the G1-arrested cells, actin markedly accumulated at the margin of cells, and a network structure of actin stress fibers appeared. When density-arrested cells were replated sparsely and rearrested in the G1, early S, and G2 phases with butyrate or hydroxyurea, the actin network was observed extensively in the cells arrested in the G1 and G2 phases with butyrate. These results agree with our previous results indicating the existence of some physiological similarity between cells in the G1 and G2 phases and suggest that actin distribution somehow depends on the phases of the cell cycle. The actin profiles observed by the NBD-Ph staining were confirmed by transmission electronmicroscopy (TEM) of negatively stained whole cells. TEM further revealed that electron-dense amorphous materials were present at crossing points in the network but rarely present on interconnecting microfilament bundles.

Effect of dietary sodium on platelet alpha 2-adrenergic receptors in essential hypertension

To study the aggregation, adhesion, and specific binding of an alpha 2-antagonist, [3H]rauwolscine, to the platelet membrane fractions, platelets were obtained from 30 patients with essential hypertension and nine normotensive subjects fed a high sodium diet (NaCl, 16-18 g/day) for 7 days and thereafter a low sodium diet (NaCl, 1-3 g/day) for 7 days. The patients with essential hypertension were classified as either salt responders (all those who had greater than 7% decrease in mean arterial pressure from the high to low sodium period) or salt nonresponders (all others). In salt responders, the number of alpha 2-adrenergic receptors on platelet membrane fraction was increased from 523.4 +/- 55.4 fmol/mg of protein in the high sodium period to 669.4 +/- 84.0 fmol/mg of protein in the low sodium period (p less than 0.01), whereas it did not change in salt nonresponders. In contrast, the epinephrine-induced platelet aggregation through alpha 2-adrenergic receptors was decreased in nonresponders, from 47.3 +/- 7.4% in the high sodium period to 24.5 +/- 9.3% in the low sodium period (p less than 0.05), while it did not change in responders. No significant change in the number of alpha 2-adrenergic receptors or epinephrine-induced platelet aggregation was observed in the normotensive subjects.

Cell growth and differentiation in vitro in mouse macrophages transformed by a tsA mutant of simian virus 40. III. Large T antigen level and cell proliferation and survival in an SV40 tsA640-transformed macrophage line

The levels of simian virus 40 (SV40) large T antigen in a tsA-transformed mouse macrophage line at the permissive (33 degrees C) and the nonpermissive (39 degrees C) temperature were examined by immunofluorescence, sodium dodecylsulfate-polyacrylamide gel electrophoresis, complement fixation, and enzyme-linked immunosorbent assay. When the cells were confluent and rested at 33 degrees C, and then were shifted to 39 degrees C, the amount of large T antigen per cell decreased, and most cells survived and remained phagocytic. When the cells were proliferating at 33 degrees C, and then were shifted to 39 degrees C, the cells died with only a small reduction in the amount of large T antigen. Therefore, the physiological state of the cells may determine the survival of cells by affecting the level of large T antigen after exposure to 39 degrees. The confluent cells may be rested with a concomitant decrease of large T antigen. The proliferating cells may not survive in the presence of a relatively high level of functionally defective large T antigen at 39 degrees C.

Prolongation of duration of G2 arrest delays and finally blocks entry into M phase in contrast to stable and reversible G1 arrest: study of a G1/G2 temperature-sensitive mutant of rat 3Y1 fibroblasts

Proliferation of 3Y1tsF121 cells was arrested in G1 and G2 phases after a shift up to 39.8 degrees C (restrictive temperature). Both arrests were reversible: after a shift down to 33.8 degrees C (permissive temperature), these cells effectively entered the next phases. However, the entry into M phase of the G2-arrested cells was delayed depending on the time in arrest. The G2-arrested cells finally became incapable of entering M phase with a prolonged incubation at 39.8 degrees C. Under the same condition, G1-arrested cells did not lose their ability to proliferate, and their delay of entry into S phase was slight. Therefore, cells in G2 phase are, in a sense, more unstable than the cells in G1 phase. These results also suggest that the time required for entry into M phase may depend on the preparedness for the initiation of M phase and, that it may be prolonged under the condition where the preparedness for entry into M phase is diminished.

Phospholipid liposomes enhance the infectivity of purified simian virus 40 virions

When simian virus 40 virions purified after treatment with sodium deoxycholate were incubated with the extract of monkey kidney CV-1 cells, infectivity of the virions was enhanced. The infectivity-enhancing activity was recovered from the phospholipid fraction of CV-1 cells. The constructed liposomes composed of phosphatidylserine were able to enhance the infectivity of the purified virions, but those composed either of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, or phosphatidylinositol could not. The liposomes constructed with a mixture of phosphatidylethanolamine and phosphatidylcholine at a ratio of 1:1 (w:w) also enhanced the infectivity of the purified virions. Pretreatment of cells with liposomes either of phosphatidylserine or of phosphatidylethanolamine did not enhance susceptibility of the cells to infection with the purified virions. These observations suggest that the major phospholipids of the cellular membrane, when associated with virions, play a vital role in activation of purified virions.

Serum-independent regulation of initiation of DNA synthesis relating to temperature-sensitive defect in rat 3Y1tsD123 fibroblasts and its compensation by simian virus 40

Randomly proliferating 3Y1tsD123 cells are arrested in G1 phase within 24 h after a shift up to 39.8 degrees C (temperature arrest), yet the density-arrested cells (prepared at 33.8 degrees C) enter S phase at 39.8 degrees C with serum stimulation, with or without preexposure to 39.8 degrees C for 24 h (Zaitsu and Kimura 1984a). When the density-arrested 3Y1tsD123 cells were preexposed to 39.8 degrees C for 96 h, they lost the ability to enter S phase at 39.8 degrees C by serum stimulation and required a longer lag time to enter S phase at 33.8 degrees C by serum stimulation than did the cells not preexposed to 39.8 degrees C. Simian virus 40 induced cellular DNA synthesis at 39.8 degrees C in the density-arrested 3Y1tsD123 preexposed to 39.8 degrees C for 96 h. In the absence of serum after a shift down to 33.8 degrees C, the temperature-arrested 3Y1tsD123 cells entered S phase and then divided once. We postulate from these results that (1) the ts defect in 3Y1tsD123 is involved in a serum-independent process. Once this process is accomplished, its accomplishment is invalidated slowly with preexposure to 39.8 degrees C. This and the serum-dependent processes occur in parallel but not necessarily simultaneously. The accomplishment of both (all) processes is required for the initiation of S phase. The density-arrested 3Y1tsD123 cells have accomplished the serum-independent process related to the ts defect, but have not accomplished serum-dependent processes. In case of the temperature-arrested 3Y1tsD123 cells, the reverse holds true. The lag time for entry into S phase depends on the preparedness for the initiation of DNA synthesis (on the extent of accomplishment of each of all processes required for entry into S phase). (2) To induce cellular DNA synthesis, simian virus 40 stimulates directly the serum-independent process. However, we do not rule out the possibility that simian virus 40 stimulates serum-dependent processes simultaneously.

Abortive transformation of temperature-sensitive mutants of rat 3Y1 cells by simian virus 40: effect of cellular arrest states on entry into S phase and cellular proliferation

Four temperature-sensitive (ts) mutants of rat 3Y1 fibroblasts, representing independent complementation groups, cease to proliferate predominantly with a 2n DNA content, at the restrictive temperature (39.8 degrees C) (temperature arrest) or at the permissive temperature (33.8 degrees C) at a confluent cell density (density arrest) (Ohno et al., 1984). We studied the temperature- or the density-arrested cells of these mutants infected with simian virus 40 (SV40) or its mutants affecting large T or small t antigen with respect to kinetics at 39.8 degrees C of entry into S phase and cellular proliferation. Three mutants, 3Y1tsD123, 3Y1tsF121 and 3Y1tsG125, expressed T antigen and entered S phase at 39.8 degrees C from both the arrested states after infection with either wild-type, tsA mutants, or a .54/.59 deletion mutant of SV40, whereas in the density-arrested 3Y1tsH203, expression of T antigen and entry into S phase were inefficient and ts. Following the WT-SV40 induced entry into S phase, the temperature-arrested 3Y1tsD123 detached from the substratum with no detectable increase in cell number, whereas the density-arrested ones completed a round of the cell cycle and then detached. 3Y1tsF121 and 3Y1tsG125 in the both arrested states proliferated through more than one generation. 3Y1tsF121 and 3Y1tsG125 in the density-arrested state infected with tsA mutants once proliferated and then ceased to increase in number as the percentage of T-antigen positive population decreased. These results suggest that wild-type and tsA-mutated large T antigens are able to overcome the cellular ts blocks of entry into S phase in the 3 ts mutants of 3Y1 cells in both the arrested states, and that small t antigen is not required to overcome the blocks. It is also suggested that cellular behaviors subsequent to S phase (viability, mitosis, and proliferation in the following generations) depend on cellular arrest states, on traits of cellular ts defects, and on the duration of large T antigen expression.

Induction of endoreduplication in temperature-sensitive mutants of rat 3Y1 fibroblasts

Four temperature-sensitive mutants of rat 3Y1 fibroblasts belonging to separate complementation groups (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) are arrested mainly with a 2C DNA content, when cells proliferating at 33.8 degrees C are shifted up to 39.8 degrees C (Ohno et al., 1984). Zaitsu and Kimura (submitted for publication) showed that 3Y1tsF121 cells synchronized in the early S phase were arrested with a 4C DNA content at 39.8 degrees C. We studied the traverse through the S and G2 phases at 39.8 degrees C in the four ts mutants synchronized at the early S phase and found that 3Y1tsG125 and 3Y1tsH203 cells were arrested with a 4C DNA content as 3Y1tsF121, while 3Y1tsD123 cells went through S and G2 phases and underwent mitosis. When 3Y1tsF121 and 3Y1tsG125 mutants arrested at 39.8 degrees C were shifted down to 33.8 degrees C, a substantial fraction of the cells with a 4C DNA content started, with a certain lag period, DNA synthesis without intervening mitosis and underwent the first mitosis with a lag period similar to that in the cells arrested with a 2C DNA content. The tetraploid cells thus generated had a proliferating ability lower than that of diploid cells.

Formation of proliferative tetraploid cells after treatment of diploid cells with sodium butyrate in rat 3Y1 fibroblasts

When randomly proliferating rat 3Y1 fibroblasts were treated with sodium butyrate, more than 90% of their cells were arrested reversibly with a 2C DNA content at least 12 h before the G1/S boundary. When cells synchronized in the early S phase were treated with butyrate, approximately 70% of all cells were arrested with a 4C DNA content. The arrests in both G1 and G2 phases by the single inhibitor suggest that the two phases share a common mechanism. The ability of cells to undergo mitosis on time was quickly lost with time of arrest in the G2 phase. Upon removal of the inhibitor, the cells arrested with a 4C DNA content entered a new S phase without intervening mitosis. The tetraploid cells thus produced kept proliferating as fast as diploid cells. These results suggest that the inhibition of the normal G2 traverse is somehow responsible for the formation of the proliferative polyploid cells.

Model prediction of plasma volume change induced by hemodialysis

We simulated the change in plasma volume by hemodialysis by combining two models for transcapillary and transcellular fluid exchange. Model predictions of the plasma volume change were found to be in good agreement with the measured values in five patients who were studied during 4-hour hemodialysis at a constant ultrafiltration rate of 0.5 L/hr using three different dialysate sodium concentrations: 7% below, 7% above, and equal to the predialytic serum concentration. The measurements and model predictions indicate that the decrease in plasma volume is smaller in high sodium dialysis than in normal and low sodium dialyses. Because model predictions were consistent with measurements, this model should be useful in clinical practice to quantitatively analyze the change in plasma volume during hemodialysis and to relate it with hypovolemic hypotension.

Decline in infectivity of simian virus 40 by sodium deoxycholate and its restoration with the extract of monkey kidney cells

Plaque-forming activity and T-antigen-synthesizing activity in the crude preparation of simian virus 40 (SV40) decreased to 1/20-27 after treatment with 0.5% sodium deoxycholate (DOC) for 30 min at 37 degrees C. A full restoration of the activity occurred after incubation of DOC-treated virions with the extract of monkey CV-1 cells, host cells for productive infection with SV40. Analysis by sedimentation through 15% sucrose to CsCl cushion (rho = 1.327 g/cm3) revealed that virions in the [35S]methionine-labeled crude virus preparation sedimented to the interface between CsCl and sucrose, and that treatment with DOC resulted in the loss of infectivity and the appearance of virions sedimentable into CsCl cushion. The [35S]methionine-labeled purified virions (prepared after treatment with DOC and sedimentable into CsCl cushion) sedimented to the CsCl-sucrose interface after incubation with the cell extract, with restoration of infectivity. The infectivity-restoring activity of the cell extract was sensitive to ethyl ether, partially sensitive to heating at 75 degrees-97 degrees for 30 min, but resistant to treatment with DNase (50 micrograms/ml), RNase (40 micrograms/ml), or trypsin (0.05%) for 30 min at 37 degrees. These results suggest that lipid-related cellular components bind stably to virions of SV40 and facilitate an efficient infection.

Control in previous and present generations of preparation for entry into S phase and the relationship to resting state in 3Y1 rat fibroblastic cells

In both the presence and absence of serum, 3Y1 rat fibroblastic cells synchronized at early S phase by aphidicolin entered M phase 6 h after removal of aphidicolin. However, in the second generation their entry into S phase in the presence of serum was delayed due to the deprivation of serum in the first generation. A similar delaying effect in the second generation was observed when the resting cells were stimulated by serum and then deprived of serum during a period of 8 h preceding mitosis. In both cases, the interval between mitosis and entry into S phase in the second generation was almost equal to that required for the resting cells to enter S phase when stimulated by serum. A similar delaying effect was also observed when the cells, synchronized at early S phase, were kept in suspension culture in the presence of serum for a period in the first generation. Results of a similar type of experiments using various combinations of growth factors showed that, when the G1 period in the second generation was shortened by exposure to growth factors in the first generation, and when the resting cells were stimulated to enter S phase, the same combination of growth factors was required. These and previous results suggest that the preparation for entry into S phase is controlled in both previous and present generations of 3Y1 cells.

Serum sodium concentration and body fluid distribution during interdialysis: importance of sodium to fluid intake ratio in hemodialysis patients

Changes in the serum Na+ concentration and transcellular body fluid distribution during the interdialytic period were simulated as functions of body weight gain assuming that the effective extracellular osmolality consists only of sodium. Our model shows that these changes are mainly determined by the relative ratio between sodium intake and weight gain in this period. If the sodium intake-to-net fluid intake ratio is equal to the postdialytic serum [Na+], neither changes in serum [Na+] nor transcellular fluid shifts occur. When sodium intake is relatively greater than the net water intake, serum [Na+] is increased and transcellular fluid shifts will occur out of the cells. On the other hand, when the net water intake is relatively greater than the sodium intake, serum [Na+] is decreased and fluid is distributed to both the intracellular and extracellular compartments. The combined application of our models for both the intradialytic interval described previously and the interdialytic interval described here is very useful in quantitatively analyzing the overall sodium and water metabolism in dialyzed patients.

Advance toward S phase and retreat toward deeper "G0" states in resting 3Y1 cells with environmental changes

To elucidate conditions which affect the lag time for resting cells to enter S phase after serum stimulation, we used a wild-type 3Y1 rat fibroblast line and four temperature-sensitive mutants of 3Y1 (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203). Among these five lines, in only tsG125 cells was there an obviously prolonged lag time with increase in time in resting state at 33.8 degrees C. The resting wild-type 3Y1 cells, preexposed to 39.8 degrees C, also showed a prolongation of lag time. The prolongation in tsG125 had a certain limit. Preexposure to 39.8 degrees C before serum stimulation accelerated such prolongation in tsG125 to its limit, but did not change the limit, per se. Resting tsG125 cells stimulated by serum at 39.8 degrees C, did not enter S phase, yet they did advance toward S phase. When they were kept at 39.8 degrees C, they retreated toward a deeper resting state ("G0") with time. These retreats correlated with the decrease in stimulating activity in the culture media. About 20% of the resting tsG125 cells stimulated by serum at 39.8 degrees C were committed to enter S phase, when the extent of commitment was examined at 33.8 degrees C. Most of the tsG125 cells committed at 33.8 degrees C did not enter S phase, when the extent of commitment was examined at 39.8 degrees C. More cells were committed after stimulation at 33.8 degrees C than at 39.8 degrees C, when the test was done at 33.8 degrees C. We suggest that resting cells may be reversibly changed within range of resting states, in either direction, that is, advance toward S phase or retreat toward deeper "G0." These changes may be determined by alterations in the balance between synthesis and decay of the preparedness for the initiation of DNA synthesis caused by cellular response to environmental changes (e.g., medium activity, temperature, etc.). The ts defect in tsG125 may affect the cell cycle progression, both before and after commitment by serum.

Cell growth and differentiation in vitro in mouse macrophages transformed by a tsA mutant of simian virus 40. II. Changes in the distribution of DNA content during the reversible transition between macrophage and nonmacrophage states in the cultures of tsA640-transformed macrophages

Cultures of mouse macrophage cell lines transformed by wild-type or the tsA640 mutant of simian virus 40 (SV40) show a reversible phenotypic transition between the nonmacrophage (proliferating phase) and the macrophage (stationary phase) states (Takayama, 1980; Tanigawa et al., 1983). Distribution of DNA content in the cultures of the tsA640-transformed macrophage lines in the process of the phenotypic transition was determined by flow cytometry. Taking the mean DNA content of mouse peritoneal macrophages as 1 unit in the scale of fluorescence intensity in the flow cytogram, the transformed macrophages showed, at 33 degrees C, two peaks, one located around the 1.0-unit position (peak 1.0) and the other around the 1.6-unit position (peak 1.6), and a plateau distribution continuing to 3.2 units. Peak 1.0 was predominant in the stationary-phase culture, whereas peak 1.6 was predominant in the proliferating-phase culture. Almost the entire population of the strictly resting culture, which was obtained by culturing the stationary-phase culture for a further 5 days at nonpermissive temperature (39 degrees C), was phagocytic, and had accumulated at peak 1.0. Cells in peak 1.0 moved to peak 1.6 and to higher positions, after the strictly resting culture was sparsely reseeded and incubated at 33 degrees C. In contrast, the DNA content distribution of the successively proliferating cells, which were obtained by repeated passage of an extensively proliferating culture and none of which were phagocytic, was similar to that of proliferating hypotetraploid BALB/c3T3 fibroblasts with a G1 peak at 1.6 unit followed by a plateau containing S- and G2-phase cells. The peak 1.0 cell population appeared from the recloned population of the successively proliferating cells in company with the restoration of the culture condition-dependent phagocytic ability when cocultured with primary macrophages. Each peak in the flow cytogram reflected fairly well DNA content per cell as determined by other methods.

Imidazole-resistant phenotype and virus transformation in cultured rat cells

Compared to an untransformed rat cell line, 3Y1, adenovirus 12-transformed cell lines of 3Y1 were highly sensitive to the cytotoxic action of an imidazole antibiotic, clotrimazole. In contrast, SV40-transformed rat cell lines derived from the 3Y1 cell line showed no appreciable difference in the response to clotrimazole when compared to 3Y1 cells. Clotrimazole-resistant clones, WCT-1 and WCT-2, which were spontaneously isolated from the adenovirus 12-transformed cell line W5, showed 5- to 10-fold higher resistance than did W5; the dose-response curves of clotrimazole-resistant clones were similar to those of the untransformed 3Y1 cells. The growth of 3Y1 cells was blocked in the presence of 1% serum, whereas those of W5, WCT-1, and WCT-2 cells were only slightly affected by the same dose of serum in the medium. The membrane fractions of 3Y1, W5, and WCT-1 cells were found to contain similar cholesterol:phospholipid ratios. The phospholipid composition in the membrane fraction of line WCT-1 was similar to that of line W5 but not to that of line 3Y1. By contrast, the fatty acid composition was specifically altered in clotrimazole-resistant clones; cellular contents and some species of fatty acid such as 16:1, 18:2, and 20:4 in WCT-1 and WCT-2 cells were similar to those of 3Y1 but not to those of W5 cells. Differential sensitivities of various cell lines to clotrimazole are discussed in relation to the lipid composition.

Arrest states in a set of mutants of rat 3Y1 cells temperature-sensitive for entering S phase

Four temperature-sensitive (ts) mutants of rat 3Y1 cells (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) are arrested at 39.8 degrees C mainly with a 2N DNA content (temperature-arrested cells). The states of these cells were compared with findings in case of cells arrested at 33.8 degrees C at saturation density (density-arrested cells), with regard to the ability to enter S phase after release from arrest or after serum stimulation at 39.8 degrees C. With the 3Y1tsD123, the ts defect is an event which seems essential for the initiation of S phase and occurs after mitosis but not after release from the density arrest. The defect in 3Y1tsF121 related to the efficiency of utilization of serum component(s). In case of 3Y1tsG125, the state of temperature arrest appeared to locate between the state of density arrest and the beginning of S phase. There was no significant difference between the density- and the temperature-arrested cells, in case of 3Y1tsH203.

Abortive transformation of rat 3Y1 cells by simian virus 40: viral function overcoming inhibition of cellular proliferation under various conditions of culture

Resting cultures of nonpermissive rat 3Y1 cells were infected with simian and T antigen expression and entry into S phase were examined under various conditions of culture. In the complete absence of serum from the medium or at an extremely high cell density, the cells delayed T antigen expression and entry into S phase, leaving the interval between the two events constant. Results using the viral mutants deleted in the coding region for the small t antigen ruled out the role of this antigen in induction of S phase. From these and other results presented, we conclude that the large T antigen induces S phase with the same efficiency under different conditions of cultures. We also present the evidence that the large T antigen function is required and is sufficient for entry into S phase in the second as well as in the first generation.

Genetic analysis of control of proliferation in fibroblastic cells in culture. I. Isolation and characterization of mutants temperature-sensitive for proliferation or survival of untransformed diploid rat cell line 3Y1

Mutants temperature sensitive for proliferation or survival were isolated from an untransformed diploid clone of fibroblastic rat cells (3Y1), according to an isolation protocol that selected for mutants defective at 38.5 degrees C (selection temperature) in undergoing the transition from quiescent to proliferating state while maintaining viability at 38.5 degrees C. Of the 108 temperature-sensitive clones isolated, 32 were examined for survival in sparse cultures at 39.8 degrees C (nonpermissive temperature) and classified into four classes. Results of temperature shift-up experiments suggest that functions defective in 11 of the 32 mutants are necessary not only for changing from the quiescent to proliferating state but also for maintenance of the proliferating state. Of the 32 mutants, 17 were assigned to eight complementation groups. Results of the physiological characterization of the representative mutants of each of the eight complementation groups are presented.