Identification of SV40 T-antigen mutants that alter T-antigen-induced chromosome damage in human fibroblasts

The SV40 T antigen causes numerical (aneuploidy) and structural (aberrations) chromosome damage when expressed in human diploid fibroblasts. This chromosome damage precedes the acquisition of neoplastic traits such as anchorage independence, colony formation in reduced serum growth factors, immortalization, or tumorigenicity. Therefore, chromosome damage may be important in acquiring these traits because it could provide a mutational mechanism. To determine how the T antigen causes chromosome damage, point mutations were constructed that altered previously defined biochemical functions of the T protein. Mutant T antigen constructs were introduced into human diploid fibroblasts and selected by using G418. Clones of G418r cells that expressed mutant T antigens were expanded and scored for chromosome damage. Most of these mutant T antigens caused [corrected] levels of chromosome damage similar to those caused by [corrected] the wild-type T antigen. However, some T-antigen mutants induced fewer chromosome changes. A subset of these clones that induced less chromosome damage than wild-type T were examined further. Mutant T-antigen protein levels from this subset were quantified with flow cytometry and compared with wild-type protein expression levels. Mutations of T antigen shown previously to form less stable complexes with p53 caused less chromosome damage. A mutation in the zinc finger domain of T antigen also caused less chromosome damage. Interestingly, a mutant that caused loss of the ATPase activity of T antigen caused an increase in endoreduplicated cells. Also, a correlation was noted between cells expressing very low levels of T antigen (below detection limits when using flow cytometry) and an undamaged karyotype. This correlation indicates that there is a threshold level of T-antigen expression that induces chromosome damage and that expression levels on a per-cell basis rather than on a population basis should be considered in subsequent studies.

Immortalization of human fibroblasts by SV40 large T antigen results in the reduction of cyclin D1 expression and subunit association with proliferating cell nuclear antigen and Waf1

Protein complexes containing cyclins and cyclin-dependent protein kinases (cdks) have been shown to be rearranged in both spontaneous and viral tumor antigen-transformed cells. We have examined G1- and S-phase cyclin/cdk complexes as a function of the neoplastic progression of human diploid fibroblasts transfected with the SV40 large T antigen. We find that the expression of cyclin D1 and its association with proliferating cell nuclear antigen (PCNA) and Waf1 remain unchanged in precrisis human fibroblasts transfected with SV40 large T antigen. However, in these same cells the association of cdk4 with cyclin D1, PCNA, and Waf1 is disrupted. Upon immortalization, cyclin D1 protein expression is decreased, and binding of both PCNA and Waf1 with the remaining cyclin D1 is reduced. In contrast, large T antigen increased the expression of cyclin A and cyclin E proteins in both precrisis and immortal cells and did not reduce the binding of PCNA or Waf1 to either cdk2 or cyclin A proteins. These results show that large T-antigen expression in human fibroblasts selectively uncouples cyclin D1 from cdk4, and subsequent immortalization of these cells results in additional changes to the cyclin D1-dependent cell cycle regulatory pathways.

Iterative chromosome mutation and selection as a mechanism of complete transformation of human diploid fibroblasts by SV40 T antigen

The acquisition of an extended lifespan and of neoplastic properties, including anchorage independence, ability to grow in low serum-containing media, morphological transformation, immortalization and tumorigenicity in nude mice were studied in 31 human fibroblast lineages transfected with plasmids containing the SV40 early genes. Plasmids were used that contained sequences for large T alone, or large T plus small t or large T plus small t plus the SV40 origin. Cells expressing large T antigen gradually acquired the ability to form colonies in low serum or to form anchorage-independent colonies. Large T antigen was sufficient to cause complete transformation to tumorigenicity if multi-step lineage evolution was obtained by prolonged serial passage and if in vivo progression was assisted by means of a gelatin sponge implantation technique. Cells derived from progressive tumors initiated in sponges showed enhanced tumorigenicity as measured by ability to obtain tumors without using sponges and with reduced latent period, higher incidence and with fewer cells inoculated. Multiple lineages of human fibroblasts have been converted to tumorigenicity without additional treatments such as transfection with activated oncogenes or exposure to carcinogens. These data, taken in conjunction with earlier studies showing that T antigen causes chromosome mutation preceding and accompanying the accumulation of the neoplastic phenotype, suggests that the T protein drives the transformation process by acting as a mutagen and cells with growth advantages were selected for in vitro and in vivo. With the possible exception of morphological transformation, the presence or absence of genes for small t and the SV40 origin were not critical for the process.

Abrogation of a kinase-mediated G1 cell cycle arrest point is a late event in the neoplastic progression of human fibroblasts transfected with the SV40 large T antigen gene

Cell cycle arrest points that are sensitive to the kinase inhibitor staurosporine have been shown to have widely differing sensitivities for processes in G1 and G2. In addition, the exquisitely sensitive G1 arrest point has been reported to be abrogated in neoplastically transformed cells. Using a multistep model of the neoplastic process in human cells, we show here that abrogation of the G1 arrest point occurred in 5 of 11 tumorigenic cell populations. The abrogation, in those instances when it occurred, was a late step and associated with the acquisition of tumorigenicity, but apparently independent of conventional criteria for in vitro transformation.

SV40 T antigen induced chromosomal changes reflect a process that is both clastogenic and aneuploidogenic and is ongoing throughout neoplastic progression of human fibroblasts

In human fibroblasts, the expression of SV40 large T antigen is known to cause a variety of chromosomal aberrations and especially dicentric chromosomes. In some cases, the later aberrations have been reported to be reversible telomeric associations. We report here aberration and chromosome number studies of twenty-nine T antigen positive lineages, studied from their initiation by transfection of T antigen sequences into human diploid fibroblasts, until crisis or immortalization occurred or, in some cases until the lines became tumorigenic in nude mice. The data show that T antigen consistently produced chromosomal instability of both number and structure by an active process that began before transformation indicators were positive and continued throughout neoplastic progression. The most frequently observed aberrations were dicentric chromosomes, which were shown to be true dicentrics by examination by in situ hybridization with telomeric sequences. These data are consistent with the hypothesis that T antigen causes human fibroblasts to become neoplastically transformed by successive rounds of chromosomal mutation and lineage evolution.

Frequent deletions in nine newly immortal human cell lines

Nine newly immortal lines of human fibroblasts transfected with SV40 T antigen were examined for recurrent chromosome losses. In order of decreasing frequency, all nine lines had three or more of the following minimal deletions specifically associated with the immortalization event: del(6)(q21), del(3)(p24), del(1)(p34), del(4)(p25), del(5)(p14), del(11)(p11), del(11)(q14), del(12)(p12), and del(14)(p?). Many other chromosome changes were not clearly associated with immortalization, but were acquired during other stages of this multistep model of neoplastic transformation. We propose that these chromosome loci associated with immortalization are candidates for the location of genes involved in cellular senescence.

Karyotype evolution in a simian virus 40-transformed tumorigenic human cell line

Normal human foreskin fibroblasts (HSF4) were transfected using the pSV3-neo plasmid. A pool of 10 G418-resistant colonies, HSF4-T12, showed a progressive increase in the expression of a number of in vitro transformation markers with passage in culture and became immortalized. Although no tumors were formed when cells were injected subcutaneously into nude mice, this cell line produced progressive tumors when cells were injected into preimplanted Gelfoam sponges in the mice. When these tumors were cultured in vitro and subsequently injected subcutaneously, progressive tumors were produced with median latency periods as short as 4 weeks. Three phases of cytogenetic change could be distinguished. At early passages after transfection. HSF4-T12 exhibited many random chromosomal changes. At a time just after immortalization, both flow karyotype and G-banded analyses showed the appearance of balanced clonal rearrangements. These included t(2;4), t(2;14), t(3;?), 6p-, i(6p), 8p-, t(14;15), i(15), and t(18;?). These clonal rearrangements were stable with passage in culture, and less variability from cell to cell was noted. The only consistent chromosomal loss observed was -Y. Analysis of three independent tumors showed characteristic loss of chromosomal material rather than balanced chromosomal rearrangements. Frequent loss of 6q and chromosomes #13, 15, 20, and Y was noted.

Trans-acting factors in chromosomal instability

The hypothesis that trans-acting factors affect chromosome stability was explored using human X Chinese hamster somatic cell hybrids. Two types of hybrids were examined. In either case, the human parent consisted of human diploid fibroblasts, the chromosomes of which tended to be lost from the hybrid cell. Comparisons were made between hybrid clones in which the hamster parent had a very stable karyotype (line CHO) and clones from a hamster parent with an unusual ongoing unstable karyotype (line CHX). Chinese hamster-human hybrid cell clones were expanded, and metaphase spreads were analyzed with an in situ hybridization procedure that uses biotin-labeled human genomic DNA as probe. Analyses of chromosome numbers and interspecies translocations were made after 20, 60, and 100 population doublings. Throughout the experiments, the generation of human-hamster-translocated chromosomes was more frequent in the hybrid cells with the CHX background. In addition, these cells also generated human acentric fragments, which were rare in cells with the CHO background. These results favor explanations for the instability of the CHX line that involve ongoing production of a diffusible clastogenic factor.

A new multi-locus DNA fingerprinting probe: pV47-2

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SV40 T antigen alone drives karyotype instability that precedes neoplastic transformation of human diploid fibroblasts

To define the role of SV40 large T antigen in the transformation and immortalization of human cells, we have constructed a plasmid lacking most of the unique coding sequences of small t antigen as well as the SV40 origin of replication. The promoter for T antigen, which lies within the origin of replication, was deleted and replaced by the Rous sarcoma virus promoter. This minimal construct was co-electroporated into normal human fibroblasts of neonatal origin along with a plasmid containing the neomycin resistance gene (neo). Three G418-resistant, T antigen-positive clones were expanded and compared to three T antigen-positive clones that received the pSV3neo plasmid (capable of expressing large and small T proteins and having two origins of replication). Autonomous replication of plasmid DNA was observed in all three clones that received pSV3neo but not in any of the three origin minus clones. Immediately after clonal expansion, several parameters of neoplastic transformation were assayed. Low percentages of cells in T antigen-positive populations were anchorage independent or capable of forming colonies in 1% fetal bovine serum. The T antigen-positive clones generally exhibited an extended lifespan in culture but rarely became immortalized. Large numbers of dead cells were continually generated in all T antigen-positive, pre-crisis populations. Ninety-nine percent of all T antigen-positive cells had numerical or structural chromosome aberrations. Control cells that received the neo gene did not have an extended life span, did not have noticeable numbers of dead cells, and did not exhibit karyotype instability. We suggest that the role of T antigen protein in the transformation process is to generate genetic hypervariability, leading to various consequences including neoplastic transformation and cell death.

Spontaneous in vitro neoplastic evolution of cultured Chinese hamster cells. Nucleolus organizing region activity

Silver staining to demonstrate active nucleolus organizing regions (NORs) was performed at four different stages of the spontaneous tumorigenic progression in vitro of Chinese hamster WCHE/5 cells. The number of active NORs increased for fully transformed, highly tumorigenic, late passage cells. The increase of NOR material was due to additional NOR-bearing chromosomes or chromosome arms, i.e., trisomy 5, trisomy 8, and the marker chromosome i(3q). Intermediate stages of the neoplastic evolution showed changing patterns of NOR activity, but not an overall increase. We postulate that the increase of active rDNA enhances cell growth and provides undefined selective advantage, and that this supports our previous conclusion that selectable karyotype changes provide competitive advantages rather than being essential for neoplastic evolution in vitro.

Clonal diversity of the Kirsten-ras oncogene during tumor progression in athymic nude mice: mechanisms of amplification and rearrangement

Single-cell clones from primary and lung metastatic tumors have been evaluated for the state of the viral-Kirsten-ras oncogene (v-Ki-ras) by Southern blot analysis after injection of Kirsten sarcoma virus-transformed BALB/c 3T3 cells (KiMSV, with a replication-defective provirus) into athymic nude mice by four different injection routes. While all clones of early-passage KiMSV cells contained an EcoRI-generated 5.3-kilobase DNA fragment at high dosage level, most clones of late-passage cells had lost this v-Ki-ras fragment or had greatly diminished levels. However, all clones of all tumors (greater than 90 tested) obtained after injection of these late-passage cells contained a dosage of the 5.3-kilobase v-Ki-ras band similar to that of the early-passage KiMSV cells, suggesting either a very strong selection for v-Ki-ras-bearing cells of the early-passage type in tumor formation and/or the ability of a subset of late-passage cells to amplify this gene to some minimal dosage level. Both flow cytometric analyses for DNA content and quantitation of chromosomes showed that all primary and lung metastatic tumors had more than twice the number of chromosomes as the late-passage KiMSV cells; however, four of 80 late-passage cells had a chromosome count in the range of tumors, consistent with their importance in tumor generation and possibly amplification of the v-Ki-ras-bearing chromosome. Clonal analyses of lung micrometastatic tumors revealed a v-Ki-ras blot pattern identical to that of the s.c. primary tumors. However, two of five lung metastases from the footpad (as large rapidly growing nodules) and i.v. routes had multiple copies of v-Ki-ras in new sites; a second injection round led to even greater complexity in v-Ki-ras patterns in clones of lung tumors. Two assays were used to demonstrate that these new v-Ki-ras integrations were generated by superinfection with a "helper" retrovirus, not sarcomagenic by itself in the nude mice, that led to rescue/reinfection of tumor cells with the defective Kirsten sarcoma proviral genome--cellular transformation of 3T3 or C3H10T1/2 cells and RNA dot blot analyses for medium-secreted retrovirus specific for LTR or v-Ki-ras sequences. This "helper" retrovirus could not be detected in early- or late-passage KiMSV cells used for inoculation but could be detected in certain tissues of normal nude mice, demonstrating its in vivo origin.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and reactivity of host effectors associated with the manifestation of concomitant tumor immunity

In this study, we have measured the specific tumoricidal activity of tumor-infiltrating lymphocytes that prevent the growth of secondary tumors in animals harboring progressing primary tumors (concomitant immunity). Since no tumor grows at the challenge site when concomitant immunity is established, tumor cells were inoculated into a preimplanted gelatin sponge whose subsequent solubilization in collagenase permitted the retrieval of leukocytes after tumor challenge. Primary progressing EMT6 tumors were established in normal BALB/c mice and 10 days later they were challenged with a secondary tumor inoculum introduced through a preimplanted gelatin sponge. At 3, 7, and 10 days after the administration of the tumor inoculum challenge, a monodispersed suspension of infiltrating leukocytes was recovered by collagenase digestion of the sponge matrix and tested for cytotoxicity toward EMT6 tumor targets. Cytotoxic T-lymphocytes with tumoricidal activity accumulated at the site of the secondary tumor challenge by 3 days. This antitumor activity was maximal 7 days following challenge and decayed thereafter. Splenic lymphocytes from these animals showed little cytotoxicity. In animals harboring a primary tumor, lymphocytes found in sponges that were not inoculated with tumor cells were not cytotoxic. We interpret these data to indicate that cytotoxic lymphocytes migrate to, and accumulate at the site of the tumor but not at other sites and that peripheral sources of lymphocytes in tumor-bearing animals such as the spleen may not be the best source of effector cells for evaluating the host's immune response to its tumor. The approach described here may also be useful in studying the mechanisms for host control of metastatic disease.

Amplification and rearrangement of the Kirsten ras oncogene in virus-transformed BALB/c 3T3 cells during malignant tumor progression

Analyses of the cellular and viral Kirsten ras genes (c-Ki-ras and v-Ki-ras, respectively) during malignant tumor progression were performed by using Kirsten murine sarcoma virus-transformed BALB/c 3T3 cells that harbor a replication-defective provirus. After injection into athymic nude mice by four different routes, primary tumors and secondary lung metastases were isolated, adapted to in vitro growth, and analyzed for DNA levels and mRNA expression of both genes for comparison with the originally injected transformed cells and untransformed 3T3 cells. For all tumors (primary or secondary), the v-Ki-ras gene was amplified and v-Ki-ras mRNA expression was highly elevated above that observed in the original transformed cell population. In two of five lung metastases from the i.v. and footpad injection routes, rearranged Ki-ras DNA sequences were observed. Micrometastases from the s.c. route of injection did not display these alterations. Injection of footpad lung tumor cells with rearrangements into a second group of animals led to multiple lung metastases with even further rearrangements correlating with more effective lung colonization/growth ability (overt lung tumors in five of eight animals less than 20 days after injection). However, reinjection of an i.v. lung tumor with rearranged Ki-ras led to no further rearrangements in the lung microfoci tumors isolated greater than 40 days after injection. These data suggest (i) the significance of amplification and elevated expression of v-Ki-ras in tumor formation, (ii) correlation of this amplification with more effective tumor progression, and (iii) the selective advantage that cells with Ki-ras DNA sequence additions have in the formation of overt lung tumors.

Spontaneous in vitro neoplastic evolution: selection of specific karyotypes in Chinese hamster cells

Recurrent cytogenetic changes occurred reproducibly in vitro during the spontaneous neoplastic evolution of cultured Chinese hamster cells. In particular, excess 3q material appeared shortly after immortalization in numerous independent trials. By contrast, when clones were isolated at the earliest possible time after immortalization, a wide spectrum of types of cytogenetic evolution followed, which also resulted in transformed and tumorigenic cells. Clones with stable distinct colonial morphologies were used to demonstrate growth rate interactions when subpopulations compete. We conclude that specific recurring karyotypes are associated with specific stem lines with transient growth advantage during the early stages of in vitro carcinogenesis. Stem lines with other karyotypic change or no detectable karyotypic change are almost equally capable of undergoing the entire spontaneous neoplastic process in vitro.

A gelatin sponge model for studying tumor growth: quantitation of tumor cells and leukocytes in the CHO tumor

A gelatin sponge model system for tumor cell inoculation and retrieval of tumor-associated leukocytes is described. Gelatin sponges pre-implanted in nude mice harboring tumorigenic Chinese hamster ovary cells (line CHO) were examined at 2 and 11 days after injection of tumor cells for tumor cell content and leukocyte accumulation after digesting the sponge matrix in collagenase solution. The data indicate a progressive influx of host cells consisting primarily of macrophages, neutrophils and lymphocytes. The total number of viable tumor cells as well as the fraction of surviving tumor cells with clonogenic potential also increased with tumor age. Blank sponges not harboring tumor cells elicited an inflammatory response in the animals which did not change appreciably with length of sponge residence. However, when the sponges were harboring tumor cells, the accumulation of host leukocytes far exceeded that which occurred in blank sponges. This observation suggests a host response directed toward the tumor which is absent in animals bearing blank sponges. Apart from providing anchorage for injected cells, the gelatin sponge, by virtue of its digestibility in collagenase, makes possible the easy retrieval and precise quantitation of tumor-associated host cells.

Cultured Bloom's syndrome substrains: a relationship between growth in low serum and the expression of double minute chromosomes

Four Bloom's syndrome fibroblast strains were examined for chromosome changes, immortalization, tumorigenicity, anchorage independent growth, and the ability to grow in low serum. Only one strain (GM 1492) exhibited some of these characteristics, which are generally associated with neoplastic cells. Strain GM 1492 also exhibited a low frequency of cells that contained double minute chromosomes. Substrains from GM 1492 were cloned, and showed that some of the above characteristics were expressed as a heritable trait. Karyotype instability (heteroploidy) was seen in all clones studied, with modal chromosome numbers ranging from near-diploid to near-tetraploid, as confirmed by DNA content distributions. Although no clones studied were tumorigenic in nude mice or immortalized, some showed an increased cellular proliferative capacity. Several clones were isolated after growth in 1% fetal bovine serum, and these all showed an increased expression of double minute chromosomes. Two of these 1% serum-isolated clones, (1492/clone 3-1% and clone 8-1%) were further studied by G-banding analysis, and found to show specific chromosomal anomalies. Clone 3 showed monosomy for chromosomes #4, #13, and #19, along with the absence of both copies of chromosome #7 but with both i(7p) and i(7q) chromosomes consistently seen. Clone 8 showed monosomy for chromosome #13. Preliminary experiments using DNA slot blots indicated that erb a and b, v-fes, v-mos, c-myc, n-myc, v-src, and v-sis showed no sequence amplification in GM 1492 cells or subclones.

Karyotype instability of Chinese hamster cells during in vivo tumor progression

The extent of karyotype instability in spontaneously transformed Chinese hamster cells was determined after tumor formation by cytogenetic analysis of karyotype heterogeneity. The degree of karyotype heterogeneity among tumors formed in nude mice correlated with tumor latent period. The karyotypes of tumors formed after a short latent period by cells of high tumorigenic potential were similar to each other and to the injected cells. The karyotypes of tumors from cells of low tumorigenic potential and long latents periods were diverse, however. No chromosome aberration was common to every tumor. These results suggest that preneoplastic cells whose phenotypes are not directly capable of tumor formation can progress in vivo and that karyotype instability plays an important role in providing cell variants for tumor progression.

Spontaneous immortalization rate of cultured Chinese hamster cells

Chinese hamster cell cultures derived from either fetal cell suspensions or adult ear clippings invariably became permanent cell lines during conventional subcultivation. The immortal cell cultures arose from rare spontaneous cellular events during the in vitro cultivation of cells with limited proliferative capacity. Immortality was not related to rare, precommitted cells from the animals. The expansion of clones of cells with limited life-span to form permanent cell lines was routinely successful only when the initial, unsubdivided culture achieved a total number in excess of 10(6) cells. On the basis of this observation, a serial clonogenicity assay was developed for determining the life-span of the cells with limited proliferative capacity and for determining whether a cell population is immortal. In addition, the technique of clonal expansion was used for a fluctuation analysis to determine the rate of immortalization. This analysis yielded a rate of 1.9 X 10(6) per cell per generation.

Spontaneous in vitro neoplastic evolution: recurrent chromosome changes of newly immortalized Chinese hamster cells

Spontaneous neoplastic progression in cultured Chinese hamster cells was studied at the earliest stage possible. Eighteen independent newly immortalized cell populations (from six individual Chinese hamsters) were characterized for karyotype instability. Colonies were selected from initial sparse platings of adult or fetal cells and were expanded for study. The chromosomes from these newly established cell lines were studied using a combination of G-banding and flow karyotype analysis. At a slightly later passage, the 18 cell lines were tested for tumorigenicity in nude mice. Frequent recurring chromosome changes were observed in the karyotypes. The most frequent changes were either total or partial trisomy of chromosome #3 (83%) and trisomy of chromosome #5 (61%). Only 4 of 18 clones (22%) were tumorigenic at the time of testing, and these had long latent periods. The presence of recurrent chromosome changes did not obligate these cell lines to become tumorigenic, but the karyotype instability appeared to be an indicator of the ongoing process of neoplasia.

Preneoplastic phenotype and chromosome changes of cultured human Bloom syndrome fibroblasts (strain GM 1492)

The Bloom syndrome fibroblast strain, GM 1492, was examined for phenotypic properties generally associated with neoplastic cells. A serial clonogenicity assay indicated that these cells can proliferate in culture, achieving approximately twice the number of population doublings as compared to normal human skin fibroblasts. Strain GM 1492 appeared to be partially transformed in that these cells showed a slight degree of anchorage independence when grown in methylcellulose, and also appeared to have relaxed growth requirements compared to normal fibroblasts. GM 1492 cells are heteroploid, with 20 to 80 chromosomes/cell and a modal chromosome number of 44. Cytogenetic analysis of G-banded metaphase chromosomes indicated that most cells contained at least one copy of each normal human chromosome, and many cells exhibited only aneuploidies with no detectable chromosomal rearrangements. Minute chromosomes were seen in a few of the metaphase cells examined. GM 1492 cells did not form tumors in athymic nude mice. Since many of the characteristics of GM 1492 cells are similar to those seen only in tumor cells, but the strain is nontumorigenic, we suggest that GM 1492 cells are preneoplastic and thus represent an ideal system for the in vitro study of human neoplastic progression.

Multistep change in epidermal growth factor receptors during spontaneous neoplastic progression in Chinese hamster embryo fibroblasts

Whole Chinese hamster embryo lineages have been shown to undergo multistep spontaneous neoplastic progression during serial passage in culture. We have studied the binding, internalization, and degradation of 125I-labeled epidermal growth factor at four different stages of transformation. The whole Chinese hamster embryo cells lost cell surface epidermal growth factor receptors gradually during the course of neoplastic progression until only 10% of the receptor number present in the early-passage cells (precrisis) were retained in the late-passage cells (tumorigenic). No differences in internalization rates, chloroquine sensitivity, or ability to degrade hormone between the various passage levels were seen. No evidence for the presence in conditioned medium of transforming growth factors which might mask or down-regulate epidermal growth factor receptor was obtained. These results suggest that a reduction in cell surface epidermal growth factor receptor might be an early event during spontaneous transformation in whole Chinese hamster embryo cells.

Flow karyology of serially cultured Chinese hamster cell lineages

Flow karyology of serially cultured Chinese hamster cell lineages has been observed to be influenced by the degree of cellular heterogeneity in culture. The minimum coefficient of variation (CV) and debris fraction obtainable vary as a cell lineage evolves from a primary cell culture to an established cell line. The cell lineages pass through a stage of decreased cellular heterogeneity from which flow karyotypes can be obtained with lower CV and debris fraction. The influence of cellular heterogeneity on flow karyology is observed with constant preparative protocol and constant instrument performance, and can be an additional source of variability.

Chromosome polymorphism involving heterochromatic blocks in Chinese hamster chromosome 9

A chromosome polymorphism was detected between two early passage euploid Chinese hamster cell strains when a fluorescence shift of the small metacentric No. 9 chromosome was resolved by flow cytometry. The characteristics of the polymorphism were studied using cultures established from ear clippings taken from 16 additional hamsters from our breeding colony. Additional variants of chromosome 9 were detected using flow cytometry, and a subset of these variants were analyzed by G- and C-banding. An increase of fluorescence recorded by flow cytometry correlated with an increase of centromeric heterochromatin. Autosomal normalization of the flow karyotype from 18 different animals indicated three distinct peak positions for chromosome 9. The results indicate that a discrete block of constitutive heterochromatin may be present in one or two extra copies within the small inbred colony of hamsters studied. To determine the inheritance patterns, hamsters with known polymorphic No. 9 chromosomes were bred. The flow karyotypes derived from the offspring of these matings provide strong evidence that chromosomal polymorphisms are inherited in Mendelian fashion.

Spontaneous neoplastic evolution of Chinese hamster cells in culture: multistep progression of phenotype

Chinese hamster cell strains, each initiated from a separate fetus, were carried in culture and tested for tumorigenicity and in vitro indicators of neoplasia at various passage levels. In the absence of any treatment, all 20 such lineages yielded permanent cell lines and showed other indications of neoplastic progression. A preimplanted gelatin sponge assay method was used to monitor tumorigenicity in nude mice. The process of spontaneous neoplastic progression in vitro could be divided into four stages. The rate of progression through these stages, as measured by passage level, was extremely variable between independent lineages. Detailed studies of one lineage showed that transformation indicators, in general, correlated with tumorigenicity but did not indicate whether or not a preneoplastic, permanent lineage would rapidly progress.

Spontaneous neoplastic evolution of Chinese hamster cells in culture: multistep progression of karyotype

Chromosomes from successive passages of a Chinese hamster cell strain (WCHE/5) that spontaneously progressed from a euploid primary cell culture to a heteroploid tumorigenic cell line were isolated and analyzed by Giemsa banding and high-resolution flow karyotype analysis. The frequency and identification of aneuploid and marker chromosomes were determined at both pre- and postcrisis culture stages and pre- and posttumorigenic stages. The combination of Giemsa banding and flow karyotypes provided detailed analysis of karyotype instability at each stage of cell culture progression. Aneuploidy (trisomy of chromosome 5) preceded the appearance of tumorigenicity in nude mice as well as in vitro indicators of neoplasia. The four stages of neoplastic progression defined in the previous paper correlated with a steady progression in karyotypic instability, including, in sequence: trisomy of chromosome 5; an 8q marker chromosome; a 3q+ insertion; and trisomy of chromosome 8. Additional changes continued to appear as the cells acquired classical properties of in vitro transformation.

In vivo and in vitro properties of malignant variants of RAW117 metastatic murine lymphoma/lymphosarcoma

Using the RAW117 lymphoma/lymphosarcoma system syngeneic to Balb/c strain mice, variant sublines have been selected for enhanced blood-borne liver colonization in vivo or for lack of binding to immobilized lectins in vitro. The kinetic organ distributions of intravenously injected, 3H-thymidine-labelled RAW117 parental cells and a subline sequentially selected ten times for enhanced liver colonization were similar, suggesting that the differences in malignancy between these two cell lines were not due to dramatic differences in organ localization properties. Examination of the malignant properties of the selected sublines and cell clones derived from these in immune-impaired animals indicated that host immune status was important in determining the quantity of experimental metastases in this system. Although impairment of T-cell or NK-mediated anti-tumor responses by using 400 R 60Co-irradiated or Balb/c nude (nu/nu) mice suggested that certain immunologic responses were not effective in preventing experimental metastasis, impairment of macrophage function with chlorine, silica, trypan blue, carrageenan, cyclophosphamide or pristane were effective and resulted in enhanced malignancy of the parental RAW117 line. In contrast, impairment of macrophage function had little or no effect on the experimental metastatic properties of highly malignant RAW117 sublines or clones. In vitro humoral responses or cell-mediated immunologic assays using lymphoid cells from normal or tumor-bearing hosts failed to demonstrate antibody-mediated or antibody-dependent cell-mediated cytotoxicity (ADCC), T-cell or NK-cell responses against RAW117 cells. However, poly I: C activated macrophages were more effective against parental RAW117 cells than against a highly metastatic subline in cytolysis and cytostasis assays suggesting that the highly metastatic RAW117 cells can more readily escape macrophage-mediated host defenses.

Role of anchorage in the expression of tumorigenicity of untransformed mouse cell lines

Cultured mouse cells were tested for tumorigenicity in nude mice with both a conventional assay (injection of cell suspensions) and a new test involving implantation of cells grown on gelatin sponges. Sublines of Balb/3T3 cells, obtained from different sources, varied in their tumorigenic potential with either assay. One subline (A) formed distinctive precancerous nodules only in the sponge assay; these nodules often became progressive after a latent period of 3-4 months. However, suspensions of cells of this subline also caused tumors after a similar latent period, but no nodular phase preceded tumor formation. Another subline of Balb/3T3 (M) has failed to form tumors in either assay. The Balb/3T3 sublines did not differ in vitro properties, such as low saturation density, failure to grow in methylcellulose, and monolayer morphology. A second experimental approach involved tests on nude BALB/c mouse-embryo fibroblasts at various passage levels. The cells were passaged from primary culture, through crisis, to heteroploid, established cell lines. Tumorigenicity was demonstrable earlier in the sponge assay, at which time in vitro parameters putatively associated with malignant behavior were unchanged. Possible relationships with the in vivo phenomenon of solid-surface sarcomagenesis are discussed.

Growth and biochemical characteristics of a detachment variant of CHO cells

A variant subline of Chinese hamster cells (line CHO) was isolated that had increased resistance to detachment from the substratum. Comparisons between parental and variant cells of the complex carbohydrates liberated during trypsin detachment showed that the variant cells synthesized little or no hyaluronic acid. These cells also had reduced amounts of other complex carbohydrates in the cell periphery. However, parental and variant cells did not differ in morphology, growth control, or cyclic AMP concentration. Profound changes in the physical nature of the cell periphery, in themselves, evidently are insufficient to cause changes in many aspects of cell behavior.

A method for comparing effects of different synchronizing protocols on mammalian cell cycle traverse. The traverse perturbation index

After treatment of Chinese hamster cells (line CHO) with various protocols for synchrony induction, the subsequent ability of cells to traverse the cell cycle (i e., to perform, an essential cell cycle process) has been determined by measurement of the DNA distribution pattern among cells in large populations with the Los Alamos flow microfluorometer In the cultures prepared by the various synchronizing techniques the vast majority of cells traversed the cell cycle in a normal fashion; however, in all cultures examined there remained small subpopulations which, though remaining viable for several days, could not carry out normal traverse. After reversible inhibition of DNA synthesis by means of a double-thymidine blockade, approximately 17% of the cells were unable to complete genome replication. After reversal of G(1) arrest resulting from cultivation of cells in isoleucine-deficient medium, 12 4% of the cells commenced synthesis of DNA but were unable to complete the S phase. Cells prepared by mitotic selection yielded a subpopulation (5 5% of the total cells) with a G(1) DNA content which remained viable but noncycling for at least 5 days. We propose a term "traverse perturbation index" which is defined as the fraction of cells converted to a noncycle-traversing state as the result of experimental manipulation. A knowledge of the perturbation index will allow direct comparison of effects on cell cycle traverse of various synchrony-induction protocols

DNA constancy in heteroploidy and the stem line theory of tumors

Cellular DNA was measured by high-speed flow microfluorometry in mammalian diploid and heteroploid cell populations stained by the fluorescent Feulgen procedure. Heteroploid cells with elevated modal chromosome number showed the expected increase in modal DNA content. However, the variability of DNA content was the same in diploid and heteroploid cell populations despite the large variability of chromosome number in the latter populations. This suggests that heteroploidy may include defects in the chromosomal condensation and kinetochore development systems.