An autoradiographic screening test for mycoplasmal contamination of mammalian cell cultures

Up-regulation of Ca2+ influx mediated by store-operated channels in HL60 cells induced to differentiate by 1 alpha,25-dihydroxyvitamin D3

The physiologically active form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 (1,25D3), induces promyelocytic HL60 cells to differentiate towards monocyte-like cells. During this differentiation increased cytosolic calcium (Cai2+) and expression of surface receptors for chemotactic factors "prime" the cell for the activation of monocyte functions and the triggering of the respiratory burst pathway. We examined whether the Ca2+ influx mediated by store-operated channels (SOC) contributed to the increased Cai2+ following exposure of HL60 cells to 10(-7) M 1,25D3. Cells treated with 1,25D3 for 72 hr demonstrated a rapid transient rise in Cai2+ followed by a second, phasic, increase in Cai2+ in response to the purinergic agonist ATP. This second Cai2+ transient was blocked by Ni2+, SKF 96365, or withdrawal of extracellular Ca2+. In cells suspended in Ca(2+)-free medium, peak changes (delta) in [Ca2+]i elicited by ATP-induced Ca2+ mobilization occurred with similar EC50 values in differentiated and vehicle (EtOH)-treated cells; however, peak [Ca2+]i was reduced by 55% in 1,25D3-treated cells. Decreased Ca2+ mobilization was associated with a 25-35% reduction in intracellular Ca2+ stores (determined with ionomycin). 1,25D3-treated cells exposed to ATP or thapsigargin (Tg) in Ca(2+)-free medium for 3 min with subsequent addition of 1 mM Ca2+ exhibited a respective 80% or 120% stimulation in peak [Ca2+]i compared to EtOH-treated cells. Enhanced Ca2+ influx mediated by SOC was also seen in these cells as an increase in the rate of Mn2+ entry after exposure to ATP or Tg. At 96 hr after addition of 1,25D3, when differentiated phenotype was established, basal Ca2+i and Ca2+ entry mediated by SOC returned to control values, but Ca2+ store size remained reduced. Up-regulation of Ca2+ influx via the SOC pathway during 1,25D3-induced differentiation may contribute to the functional properties of the maturing monocyte, or to the resetting of molecular programs responsible for the changing phenotype.

Vitamin D analog 25-(OH)-16,23E-Diene-26,27-hexafluoro-vitamin D3 induces differentiation of HL60 cells with minimal effects on cellular calcium homeostasis

Numerous vitamin D3 analogs (VDAs) can inhibit the proliferation of cells from several types of human malignancies. The physiologically active form of vitamin D3, 1,25-dihydroxyvitamin D3(1,25D3), is formed by successive hydroxylations of cholecalciferol at the 25 and 1 alpha positions. In this study we examined the effects of the absence of the 1 alpha (OH) group, introduction of a double bond in position 16, and further modifications at the 23, 26, and 27 positions in the side chain on the potency of the VDAs. The parameters studied were the rapidity of the induction of monocytic differentiation, the cell cycle traverse, and the effects of VDAs on intracellular calcium homeostasis in HL60 cells. The results show that (1) 1,25D3 derivatives which lace the 1 alpha (OH) group have little differentiation-inducing activity, (2) hexafluorination (6F) of the terminal methyl groups in the side chain partially restores the activity of 1 alpha-desoxy compounds and potentiates the activity of 1 alpha hydroxylated compounds, and (3) 25-(OH)-16,23E-diene-26,27-hexafluoro-vitamin D2 (Ro25-9887) alone among the twelve compounds tested induces differentiation with only minimal changes in the basal levels of intracellular calcium and store-dependent calcium influx in HL60 cells. Addition of 1 alpha (OH) group to this compound increases its differentiation-inducing activity but also elevates basal calcium level. The results suggest that altered calcium homeostasis is not an obligatory component of HL60 leukemia cell differentiation, and that Ro25-9887 and related VDAs may be suitable for testing as components of anti-leukemic therapy.

Increased stringency of the 1,25-dihydroxyvitamin D3-induced G1 to S phase block in polyploid HL60 cells

Treatment of mammalian cells with 1,25-dihydroxyvitamin D3 (1,25D3) produces a G1 to S (G1/S) phase cell cycle block. In addition, it has been noted that a smaller proportion of cells accumulates in the G2/M compartment in 1,25D3-treated cultures. Since cyclins have a major influence on the regulation of cell cycle progression, we determined the expression of cyclins A and B as markers of the G2 phase and of cyclin E as the marker of G1/S transition. No increase in the steady-state levels of cyclin A or cyclin B mRNA was detected in the total cell population or in the cyclin B1 protein in the G2/M cell cycle compartment. In contrast, immunodetectable cyclin E protein was increased in cell cultures as a whole and specifically in the G2/M compartment cells. Determination of BrdU incorporation into DNA by flow cytometry showed marked inhibition of DNA replication in cells with DNA content higher than 4C, and autoradiography of 3H-TdR-pulsed cells showed that polynucleated cells did not replicate DNA after 96 h of treatment with 1,25D3 or analogs. Taken together, these experiments show that at least a portion of the G2/M compartment in 1,25D3-arrested cultures of HL60 cells represents G1 cells at a higher ploidy level, which are blocked from entering the high ploidy S phase.

Inhibition by 1,25 dihydroxyvitamin D3 of c-myc down-regulation and DNA fragmentation in cytosine arabinoside-induced erythroid differentiation of K562 cells

The effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on DNA fragmentation, altered expression of the heat shock protein (hsp) 70 gene, and protooncogenes c-myc and c-myb was studied during chemical induction of erythroid differentiation in K562 cells. Preincubation of K562 cells with 1,25(OH)2D3 did not alter the concentration of hemoglobin in cells which did differentiate, but led to a reduction in the accumulation of low molecular weight DNA generated by Ara-C administration. The extent of this reduction was similar to the degree of inhibition of hemoglobin formation in the culture as the whole. Preincubation with 1,25(OH)2D3 had no effect on the increase of hsp 70 gene expression induced by a 48-hr treatment with Ara-C, but prevented the Ara-C-induced down-regulation of the protooncogene c-myc. The protooncogene c-myb was down-regulated after 15 min of treatment with Ara-C, and exposure to 1,25(OH)2D3 prior to Ara-C caused a further down-regulation of its expression. The data suggest that the events associated with erythroid differentiation may be separable into at least two groups; one of these may have an influence on the kinetics of the cell cycle traverse, and the other may be related to the expression of the erythroid phenotype.

Association of c-myc protein with enzymes of DNA replication in high molecular weight fractions from mammalian cells

Oncoprotein c-myc is expressed in proliferating but not quiescent mammalian cells, and its overexpression or inappropriate expression is associated with malignant transformation. However, in spite of an intense interest, the normal function of this protein has remained elusive. As a step towards the elucidation of the function of c-myc protein, we studied its distribution within several types of cells, including HL 60, K 562, COLO 320, and CHEF/18 cells. In all of the cells studied, c-myc protein was detected in high molecular weight protein fractions, in 350-600 Kd range, in gel-exclusion chromatography and sucrose gradient centrifugation. This distribution of c-myc protein coincided with the distribution of DNA polymerase alpha and several other enzymes necessary for DNA replication. The data suggest that c-myc product may be a component of the replitase complex of enzymes involved in nuclear DNA replication.

Characterization of plasma membrane shedding from murine melanoma cells

Tumor cells release intact portions of their plasma membranes in the process of membrane fragment shedding. This released material has been shown to inhibit various synthetic functions of normal cells, which may play an important role in certain patho-physiological events occurring in advanced-stage cancer patients. Our studies on metastatic variants of the murine B16 melanoma, B16-F1 (low incidence of lung colonization) and B16-F10 (high incidence of lung colonization) indicate that the shed membrane fragment material is composed predominantly of vesicles, ranging in size from 20 to 100 nm in diameter. The release of membrane fragments represents a small percentage (approximately 16%) of the total shedding of plasma membrane components. Membrane fragments were shed at a higher rate from the highly "metastatic" (colonizing) B16-F10 cells than from poorly metastatic B16-F1 cells, resulting in a 2-fold greater accumulation of membrane fragment material by cultures of B16-F10 cells than by B16-F1 cultures during the 48-hr assay period. The study of various intracellu ar metabolic processes (protein and RNA synthesis, glycosylation, and generation of ATP) required for the shedding of membrane fragments indicated that the shedding event is only dependent on energy when inhibitors of the above processes are present for 2 hr. Treatment of cells with these inhibitors for 8 hr results in cessation of the shedding process, indicating both a limited pool of components to be shed and the requirement for further synthesis of the shed material. Glycoprotein components of the shed membrane fragments were analyzed by SDS-polyacrylamide gel electrophoresis. In addition to quantitative differences, 2 additional bands were present in fluorographs from SDS-PAGE gels from the B16-F10 membrane fragment material which were not present in fluorographs from B16-F1 fragments. The glycoprotein components of shed membrane fragments were shown to represent selected domains of the cell's plasma membranes, in that only certain plasma membrane glycoproteins are shed as part of membrane fragments. The glycoproteins released as non-particulate molecules into the extracellular environment failed to exhibit these quantitative and qualitative differences.

Autocrine stimulation of WI38 cell proliferation in the presence of glucocorticoids. Characteristics of the stimulatory factor(s) involved in this response

Chronic exposure to hydrocortisone (HC) or dexamethasone (DEX) results in a 20-40% extension in the proliferative lifespan of WI38 cells. Within a single growth cycle, the addition of HC or DEX at seeding results in saturation densities 20-40% higher than in control cultures. We have recently reported that, within a single growth cycle, the proliferative response of WI38 cells to glucocorticoids is mediated by a stimulatory factor(s) present in medium conditioned by cells in the presence of the hormone. We report here that chronic exposure to medium conditioned in the presence of HC for the first 24 h after seeding (24-h HC-conditioned medium (24-h HC-CM)) results in a 25% extension in the proliferative lifespan of these cultures. The generation of the stimulatory factor(s) present in glucocorticoid-conditioned medium is apparently dependent upon undefined cellular alterations which result from the subcultivation-procedure; confluent or low-density quiescent cultures did not generate media stimulatory to cell growth in the presence of glucocorticoids. This response was not trypsin-dependent, since cultures subcultivated in the absence of proteolytic treatment generated media equally stimulatory to cell growth. A further characterization of this glucocorticoid-induced activity revealed the stimulatory factor(s) was of low MW (dialyzable and recoverable in the less than 10,000 MW fraction following ultrafiltration), heat-stable (95 degrees C), and resistant to treatment with trypsin, chymotrypsin, or protease (S. griseus).

Growth control of cultured rat calvarium cells by platelet-derived growth factor

Platelet-derived growth factor (PDGF), which is released during the "clotting cascade", has a mitogenic effect on a variety of mesenchymal cells including those of the periosteum. Cell culture provides a method of studying these effects. In the present study, PDGF was studied for its ability to stimulate quiescent calvarium periosteal cells to enter G1, indicated by new protein synthesis. After addition of platelet poor plasma, these cells later entered S phase, indicated by uptake of 3H-thymidine. Three hours after PDGF stimulation, there were quantitative increases of at least 18 protein bands as compared to cells left in serum starvation medium. Two of these new protein bands (31K and 45K) required transcription. These data suggest that PDGF in extravasated blood may stimulate appositional bone formation beneath intact periosteum at the site of injury.

Regulation of DNA repair in serum-stimulated xeroderma pigmentosum cells

The regulation of DNA repair during serum stimulation of quiescent cells was examined in normal human cells, in fibroblasts from three xeroderma pigmentosum complementation groups (A, C, and D), in xeroderma pigmentosum variant cells, and in ataxia telangiectasia cells. The regulation of nucleotide excision repair was examined by exposing cells to ultraviolet irradiation at discrete intervals after cell stimulation. Similarly, base excision repair was quantitated after exposure to methylmethane sulfonate. WI-38 normal human diploid fibroblasts, xeroderma pigmentosum variant cells, as well as ataxia telangiectasia cells enhanced their capacity for both nucleotide excision repair and for base excision repair prior to their enhancement of DNA synthesis. Further, in each cell strain, the base excision repair enzyme uracil DNA glycosylase was increased prior to the induction of DNA polymerase using the identical cells to quantitate each activity. In contrast, each of the three xeroderma complementation groups that were examined failed to increase their capacity for nucleotide excision repair above basal levels at any interval examined. This result was observed using either unscheduled DNA synthesis in the presence of 10 mM hydroxyurea or using repair replication in the absence of hydroxyurea to quantitate DNA repair. However, each of the three complementation groups normally regulated the enhancement of base excision repair after methylmethane sulfonate exposure and each induced the uracil DNA glycosylase prior to DNA synthesis. These results suggest that there may be a relationship between the sensitivity of xeroderma pigmentosum cells from each complementation group to specific DNA damaging agents and their inability to regulate nucleotide excision repair during cell stimulation.

Altered temporal expression of DNA repair in hypermutable Bloom's syndrome cells

The temporal regulation of DNA repair during synchronous cell proliferation was examined in normal human skin fibroblasts and in Bloom's syndrome skin fibroblasts. Normal human cells regulated DNA repair in a defined temporal sequence prior to the induction of DNA replication. Nucleotide-excision repair was stimulated prior to the induction of base-excision repair, which itself was increased prior to the induction of DNA replication. This temporal sequence was observed (i) by quantitation of the induction of the base-excision repair enzyme uracil DNA glycosylase during cell proliferation in the absence of cellular insult and (ii) by quantitation of nucleotide-excision repair after UV irradiation or base-excision repair after exposure to methylmethane sulfonate. In contrast, Bloom's syndrome cells were characterized by specific alterations in this temporal sequence of gene regulation, such that DNA repair was not enhanced prior to the induction of DNA replication. Nucleotide-excision repair, base-excision repair, and the uracil DNA glycosylase were induced in a temporal sequence identical to that observed for DNA polymerase and for DNA replication. The inability of Bloom's syndrome cells to enhance DNA repair prior to DNA replication suggests that miscoding lesions remain in DNA and are replicated during cell proliferation.

Increased sensitivity of a xeroderma pigmentosum lymphoblastoid cell line to serum deprivation in vitro

Two human lymphoblastoid cell lines, GM 1989, from a normal individual, and GM 2345, from a patient with xeroderma pigmentosum, complementation group A, were selected for comparative biochemical studies because they both grow rapidly and at virtually identical rates in sealed flasks in RPMI 1640 medium buffered to physiological pH with HEPES buffer, supplemented with 12% heat-inactivated fetal bovine serum. Although the two cell lines showed no difference in growth parameters assayed by standard methods, further studies showed that the GM 2345 cell line was markedly more sensitive to diminution of the serum concentration of the culture medium than was the normal cell line. These results indicate that lymphoblastoid cell lines, particularly those from individuals with certain genetic or metabolic diseases, may be growing under marginal or limiting circumstances, different from those of control cell lines, which are not detected by standard techniques used to monitor mammalian cell cultures.

Nuclear deoxyribonuclease activities in human lymphoblastoid and mouse melanoma cells. A comparative study

Deoxyribonuclease activities were examined in isoelectric focusing fractions of non-histone, chromatin-associated and nucleoplasmic proteins of isolated normal human lymphoblastoid and mouse melanoma cell nuclei using parallel procedures. A very similar series of eight DNA endonucleases, each active on calf thymus DNA and containing no exonuclease activity, were found in the chromatin proteins of both cell lines. Several differences were observed: an activity in human cells at pI 6.6 was absent from murine cells, and there was an increased activity in mouse cells at pI 4.4 and a decreased activity at pI 7.3, as compared with corresponding human cell activities. Assay of these fractions against supercoiled, circular phage PM2 DNA showed greater activity among the fractions with acidic pI valves and slightly lower activities in the murine cells than in the human cells. Analysis of the nucleoplasmic fractions showed a series of DNA endonuclease and exonuclease activities which were again very similar between the two cell lines, although greater endonuclease activity at pI 4.4 occurred in mouse than in human nucleoplasm. These results demonstrate an entire series of deoxyribonuclease activities in both chromatin and nucleoplasm which are nearly identical in two very different mammalian cell lines, suggesting that many of these enzymes are ubiquitous in mammalian cell nuclei.

Effect of aminonucleoside on transcription, methylation, and maturation of ribosomal RNA in SV40-transformed human lung fibroblasts

The effects of puromycin aminonucleoside (AMS) have been studied in the nucleoli of SV40-transformed human lung fibroblasts with attention to the relationship between transcription, methylation, and maturation of ribosomal RNA (rRNA). Inhibition of the transcription of pre-rRNA became evident between 1 and 2 hr of exposure to AMS, and the degree of inhibition remained approximately constant throughout the remainder of the 18-hr period of study. Methylation of the ribose units of pre-rRNA was inhibited by AMS approximately as much as RNA transcription, but later, suggesting that the inhibition of methylation is a consequence of the lowered rate of RNA transcription. It was also noted that ribose methylation of nucleolar RNA occurs in the absence of concurrent RNA transcription, indicating that rRNA may be methylated post-transcriptionally. Exposure of the fibroblasts to fresh serum had the capacity to increase the rate of nucleolar RNA transcription if the fibroblasts were treated with AMS for periods of less than 2 hr but was ineffective thereafter, confirming that the inhibitory effect of AMS on pre-rRNA transcription is established in approximately 2 hr. On the other hand, processing of the primary transcript (45 S RNA) to the mature rRNA species (28 and 18 S) was inhibited more gradually, with a complete inhibition of rRNA maturation being noted after 18 hr of AMS treatment. These data are consistent with the view that the primary effect of AMS is on the rate of rRNA transcription, with a later effect on its maturation, while RNA methylation is reduced only because of the diminished availability of the RNA substrate.

An autoradiographic method of detecting A. laidlawii and M. hyorhinis in cell cultures

The autoradiographic investigation of L cells and chinese hamster cells for the presence of mycoplasmas (A. laidlawii and M. hyorhinis) using uridine/uracil (UdR/U) testing is a rapid and reliable method suitable for the serial checking of even a small number of cells. It depends on a reduced incorporation of [3H]uridine and an increased uptake of [3H]uracil into the RNA of mycoplasma-infected cells, shown in autoradiograms by the density of the grains and their distribution. Results obtained by the autoradiographic technique correspond approximately to specific activity values of RNA-infected cells after the incorporation of [3H]uridine and [3H]uracil.

Cell cycle regulation of DNA repair in normal and repair deficient human cells

The regulation of nucleotide excision repair and base excision repair by normal and repair deficient human cells was determined. Synchronous cultures of WI-38 normal diploid fibroblasts and Xeroderma pigmentosum fibroblasts (complementation group D) (XP-D) were used to investigate whether DNA repair pathways were modulated during the cell cycle. Two criteria were used: (1) unscheduled DNA synthesis (UDS) in the presence of hydroxyurea (HU) after exposure to UV light or after exposure to N-acetoxy-acetylaminofluorene (N-AcO-AAF) to quantitate nucleotide excision repair or UDS after exposure to methylethane sulfonate (MMS) to measure base excision repair; (2) repair replication into parental DNA in the absence of HU after exposure to UV light. Nucleotide excision repair after UV irradiation was induced in WI-38 fibroblasts during the cell cycle reaching a maximum in cultures exposed 14--15 h after cell stimulation. Similar results were observed after exposure to N-AcO-AAF. DNA repair was increased 2--4-fold after UV exposure and was increased 3-fold after N-AcO-AAF exposure. In either instance nucleotide excision repair was sequentially stimulated prior to the enhancement of base excision repair which was stimulated prior to the induction of DNA replication. In contrast XP-D failed to induce nucleotide excision repair after UV irradiation at any interval in the cell cycle. However, base excision repair and DNA replication were stimulated comparable to that enhancement observed in WI-38 cells. The distinctive induction of nucleotide excision repair and base excision repair prior to the onset of DNA replication suggests that separate DNA repair complexes may be formed during the eucaryotic cell cycle.

Cytological evidence for DNA chain elongation after UV irradiation in the S phase

Human cells irradiated with UV light synthesize lower molecular weight DNA than unirradiated cells. This reduction in molecular weight is greater in xeroderma pigmentosum (XP) cells than in normal cells. The molecular weight of DNA is further reduced by the addition of caffeine to XP cells. By several hours after irradiation, DNA fragments are barely detectable. Cells from excision-proficient and excision-deficient XP patients were studied autoradiographically to produce cytological evidence of DNA chain elongation. Replicate cultures with and without caffeine were synchronized and irradiated with UV light during the S phase. Caffeine was removed in G2, and the cells were labeled with 3H-thymidine. Results showed significantly increased labeling during G2 of excision-deficient XP cells. Labeling was dependent on the time of irradiation and presence of caffeine. The XP variant cells had no increase in labeling for any irradiation time.

A comparison of the proliferative and replicative life span kinetics of cell cultures derived from monozygotic twins

We have compared the growth rates, kinetics of cell aging, and replicative life spans of skin fibroblasts cell cultures derived from three pairs of monozygotic twins of similar ages. The results of these studies indicated no significant differences in the cell densities 7 days after inoculation or replicative life spans within each twin pair but highly significant differences among each twin pair. The kinetics by which each culture aged ([3H]thymidine-labeled nuclei) were compared within and among the twin cell cultures. Although the slopes of each regression line were not significantly different, comparisons of the elevations of each line supported the conclusion that the aging of monozygotic twin cell cultures is similar within the twin pairs but differs among the twin pairs.

A direct comparison of procedures for the detection of mycoplasma in tissue culture

Mycoplasma contamination of cell cultures has been shown to perturb a number of immunologic parameters. Because such contamination is almost always introduced in the laboratory, the immunologist requires a procedure to screen his cell lines frequently for mycoplasma. Two procedures recently described for the detection of mycoplasma in cell cultures, the uridine-uracil incorporation procedure and a direct fluorescent assay, were compared with the standard procedures of agar culture and transmission electron microscopy. The results with uridine-uracil incorporation were totally non-concordant with those of any of the other 3 procedures and, moreover, were inconsistent through serial assays on the same cell culture. In contrast, the direct fluorescent assay, using the fluorochrome Hoechst 33258, yielded consistent results in full agreement with the agar culture data. Since the fluorescent assay is rapid and has discriminatory capability at least equivalent to that of agar culture, it would appear to be the method of choice for routine screening of cell cultures for mycoplasma.

Changes in the properties of human fibroblasts in culture after treatment with vitamin A palmitate

The behaviour of subcultures of vitamin A-treated human embryo fibroblasts was studied from the point of view of morphology, growth characteristics, karyology and agglutinability at subsequent passages after treatment. Evidence was obtained that vitamin A-induced rupture of lysosomes may lead to transient alterations in the pattern of growth, structure of the membranes and morphology in cell generations deriving from the cells injured by the action of the vitamin.

Arrest and metastasis of blood-borne tumor cells are modified by fusion of plasma membrane vesicles from highly metastatic cells

B16 mouse melanoma sublines in culture spontaneously shed intact plasma membrane vesicles. These vesicles can be fused with the plasma membrane of cells from homologous and heterologous B16 sublines by using polyethylene glycol and phytohemagglutinin-P. Fusion of vesicles from a highly metastatic subline (F10) that localizes exclusively in the lung with cells from a poorly metastatic subline (F1) significantly increased the ability of F1 cells to become arrested in the lung and form metastases in this organ. In contrast, fusion of F1 vesicles with F10 cells did not alter the ability of vesicle-modified cells to localize in the lung or form lung metastases. F10 vesicle-modified F1 cells reverted to their original arrest behavior and metastatic capacity after removal of F10 vesicle components from the plasma membrane. The changes in the arrest and metastatic behavior of F10 vesicle-modified F1 cells were highly highly specific. Vesicles from other B16 sublines that are poorly metastatic and show limited localization in the lung (F1, FLLr, and F10Lr) did not modify the arrest behavior and metastatic capacity of FU cells. These results suggest that the differences in the abilities of the F1 and F10 sublines to localize in the lung are determined by differences in cell surface properties.

Comparative studies on cell lines established from normal and radiation-exposed miniature swine

Cloned cell lines were established from two swine with radiation-induced myeloproliferative disorders, including one cell culture from an animal with myelogenous leukemia and one from an animal with myeloid metaplasia. A third cloned cell line with similar morphology was established from pooled normal fetal swine cornea to compare the growth characteristics of cells from normal and irradiated swine. All three cell lines grew as foci of aggregated cells and were able to form macroscopic colonies in semisolid agar medium. The lack of normal mechanisms of contact inhibition and the observed aneuploidy indicated that these cells were morphologically transformed. Further, the cloned cells caused tumors in nude mice, clearly indicating that these cells were also malignantly transformed. A major difference between these cell lines was that type C viruses were observed only in the cells derived from swine with myeloproliferative disorders.

Effect of cell density and senescence of WI-38 cells on cytochemically demonstrable phosphatases

Exponentially growing and stationary phase young and old cultures of the human cell line WI-38 were studied using cytochemistry at the ultrastructural level. 5'-Nucleotidase activity was present in the plasma membrane of all cells examined; in exponentially growing cultures the reaction was more intense in mitotic cells than in interphase cells. An increase in the amount of the reaction product was observed at confluencey, especially in older cells. The reaction of Mg2+-activated adenosine 5'-triphosphatase was absent or very weak in exponentially growing cells and increased at confluency, especially in older cells. Alkaline phosphatase was detectable only in the cell membranes and in intercellular spaces of young cells at confluency. Acid phosphatase activity was increased in old cells, especially at confluency. In these old cells, positive reactions appeared in numerous small lysosomes, autophagic vacuoles and in some flattened sacs of the Golgi apparatus. The obtained results confirm and extend previous biochemical observations and indicate that changes in phosphatase activity are associated with proliferative activity and senescence of cells growing in vitro.

Inhibition of cellular transition from G1-resting to G1-prereplicative phase by aminonucleoside of puromycin

Human embryonic lung fibroblasts (IMR-90 and WI-38) were arrested in the G1 phase of the cell cycle by serum deprivation and high population density. Within 1 hr after the addition of medium containing fresh serum, these cells showed an increase in rRNA synthesis. The inclusion of 100 micrograms per ml aminonucleoside of puromycin (AMS) in the fresh medium eliminated the serum stimulation of rRNA synthesis and prevented the cells from making the G1-resting phase to G1-prereplicative phase transition. AMS also prevented the synthesis of HnRNA normally found within 10 hr after serum stimulation. Serum-stimulated RNA synthesis in starved, SV-40 transformed fibroblasts (WI-38-VA-13 cells) was inhibited, but not completely prevented, by AMS indicating that transformed cells may produce specific RNA's that are not AMS-sensitive and that may be responsible for the failure of transformed cells to be arrested in G1.

Selective inhibition of preribosomal RNA synthesis by puromycin aminonucleoside in transformed human fibroblasts: studies of the nature of the inhibition in isolated nuclei and nucleoli

Puromycin aminonucleoside selectively inhibits the synthesis of ribosomal RNA in human lung fibroblasts transformed by the oncogenic virus SV40. The mechanism of this inhibition was studied utilizing nuclei and nucleoli isolated from cells treated for 18 hours with 100 micrograms/ml of this compound. It was established that for a limited period of time nuclei and nucleoli isolated from the fibroblasts continue synthesis of RNA of size classes seen in intact cells, and that the inhibitory effect of aminonucleoside persists after isolation of these organelles. The inhibition was shown to be directed primarily to the activity of RNA polymerase I. Studies of the mechanism of this inhibition have indicated that the decreased rate of the polymerase reaction is not due to the impairment of the template function of nucleolar chromatin, and that unbound, as well as chromatin-bound, RNA polymerase I is present in both control and treated nucleoli. Analysis of the size distribution of the products of cell-free RNA synthesis showed that aminonucleoside pretreatment results in marked reduction in the synthesis of preribosomal 45S RNA, abnormal accumulation of 32S RNA, and reduced formation of mature ribosomal RNA species in the in vitro system. The data suggest that the inhibitory effect of aminonucleoside on ribosomal synthesis is due in part to a lower rate of transcription by RNA polymerase I of preribosomal RNA, and in part to its impaired maturation.

Hydrocortisone: a specific modulator of in vitro cell proliferation and aging

The effects of hydrocortisone on the proliferative activity of various vertebrate fibroblast-like cell lines have been measured. The proliferative activity of human fetal lung-derived cell lines, such as WI-38, and those of human fetal foreskin origin were always enhanced by the hormone. The addition of hydrocortisone to a number of other vertebrate cell lines grown under identical conditions showed growth inhibition. We also determined that the stimulation of WI-38 cell growth by hydrocortisone was a specific steroid-cell interaction by testing the growth promoting activity of several steroids with molecular structures similar to that of hydrocortisone. This observation was further supported by the presence of high effinity glucocorticoid binding sites in WI-38 cells whose concentration per cell was found to decrease with increased in vitro age. The results suggest that the proliferative response to hydrocortisone shows a cell-type specificity as well as a steroid-molecular structure specificity. The response appears to be mediated by high affinity glucocorticoid binding sites.

Factors influencing microbiological assay of cell-culture mycoplasma

A total of 6432 cell cultures was assayed for mycoplasmas over a 6-year period by aerobic and anaerobic incubation of agar and broth media. Mycoplasmas were detected in 375 cultures (5.8%). M. orale and A. laidlawii accounted for 61.3% of the isolates. Anaerobic incubation detected 98.1% of the isolates; aeorbic incubation detected 45.8%. Of factors studied to determine their effect on mycoplasma assay, only two, anaerobic incubation and presence of mycoplasmacidal/static antibiotics, were significant. In separate studies, 86 of 2656 cell cultures (3.2%) were infected with strains of M. hyorhinis that did not grow on cell-free media. Recommendations are given for microbiological assay of cell-culture mycoplasmas.

Stimulation of the clonal growth and differentiation of feeder layer dependent mouse embryonal carcinoma cells by beta-mercaptoethanol

Embryonal carcinoma cells are the undetermined stem cells of teratocarcinomas. Supplementation of culture medium with beta-mercaptoethanol permits the feeder layer independent clonal growth and differentiation of normally feeder layer dependent embryonal carcinoma cell lines. Differentiated cells within the clones appeared less than 6 days after plating and were distinguished from embryonal carcinoma cells by their morphology, lack of histochemically detectable alkaline phosphatase activity, and secretion of plasminogen activator. Over 70% of the colonies secreted plasminogen activator after 6 days. In comparison, a different embryonal carcinoma cell line which has lost the potential for substantial differentiation, either in vitro or in vivo forms very few clones (less than 1%) which secrete plasminogen activator. Embryonal carcinoma cells derived from the rare clones which secrete plasminogen activator have the same frequency of production of plasminogen activator secreting colonies as the parental cell line.

Differences in incorporation of nucleic acid bases and nucleosides by various Mycoplasma and Acholeplasma species

Eight species representative of the serological diversity of the Mycoplasmatales were tested for their ability to incorporate radiolabeled nucleic acid precursors into acid-insoluble material. Cultures in complex growth medium were centrifuged and resuspended in minimal essential medium (Eagle). For Acholeplasma laidlawii, labeling occurred mainly during the first 4 h of incubation, with substrate saturation at 20 micron. All organisms tested incorporated uracil, adenine, and guanine; none incorporated cytosine. Thymine was incorporated only by bovine group 7, Mycoplasma putrefaciens, and Mycoplasma pneumoniae (strain 3546), but deoxynucleosides enhanced thymine incorporation in A. laidlawii, Mycoplasma gallisepticum, M. pneumoniae (strain AP-164), and Mycoplasma hyorhinis. Nucleoside incorporation (adenosine, guanosine, uridine, cytidine, and thymidine) was not observed for the arginine-utilizing species, Mycoplasma hominis and Mycoplasma arginini, whereas all other organisms tested incorporated nucleosides. The incorporation pattern provides additional metabolic evidence to support the biochemical and antigenic diversity of these organisms. The recognition of differences in incorporation of nucleic acid precursors is important not only to the specific labeling of these organisms, but also to the study of metabolism and transport.

Target cell - substratum interaction. I. Effect of primed lymphocytes on a rat mammary adenocarcinoma tumor cell line

The differential effects of normal and immunologically primed lymphocytes on the adherence of trypsinized rat mammary adenocarcinoma tumor cells (DMBA"8) to their substratum are described, utilizing both allogeneically and syngeneically primed lymphoid cells as effectors. This observation may illustrate an important immunological phenomenon, and may result in a simplified assay procedure for the detection of cell-mediated immunity.

Responses of protein synthesis and degradation in growth control of WI-38 cells

The overall rates of protein synthesis and degradation in perfusion-grown WI-38 cells were followed in the three days after a stepdown in the serum concentration of the culture medium, from 10% to 0.3%. Within three hours after the stepdown, the rate of protein synthesis had decreased and the rate of protein degradation had increased, the combined result being the cessation of protein accumulation. The degradation rate returned over the next three days to its original value, but a zero rate of accumulation was retained because the synthesis rate continued to decline. The rate of DNA synthesis remained constant for six hours after the stepdown. It then declined steadily until reaching a minimum about eight hours later. The results show that extracellular control of protein accumulation depends on adjustments in both protein synthesis and protein degradation, and that the adjustments take place rapidly. This behavior suggests that the cell cycle is arrested after a stepdown because post-mitotic cells are unable to accumulate additional protein. However, an alternative interpretation of the data is that at least part of the changed accumulation is the result, rather than the cause, of the cycle arrest, and that the arrest is caused by other, more specific, reactions than those of general protein metabolism.

Prostaglandin E2 production in 3T3 cells transformed by polyoma virus raises the intracellular adenosine 3':5'-monophosphate levels

High cellular adenosine 3':5'-monophosphate (cyclic AMP) were found in a polyoma-virus-transformed 3T3 fibroblast line, which produces comparatively high prostaglandin E2 concentrations. Prostaglandin E2 and cyclic AMP increased with time during 6 days of growth. Both effects were prevented by three different cyclo-oxygenase inhibitors. Addition of prostaglandin E2, at a concentration which would been synthesized in the absence of inhibitor, reversed the effect of indomethacin, one of the cyclo-oxygenase inhibitors, on cyclic AMP. It is concluded that endogenous prostaglandin E2 production in these transformed cells influences their cellular cyclic AMP levels.