The characteristics of animal cells transformed in vitro

Derivation and osmotolerance characterization of three immortalized tilapia (Oreochromis mossambicus) cell lines

Fish cell cultures are becoming more widely used models for investigating molecular mechanisms of physiological response to environmental challenge. In this study, we derived two immortalized Mozambique tilapia (Oreochromis mossambicus) cell lines from brain (OmB) and lip epithelium (OmL), and compared them to a previously immortalized bulbus arteriosus (TmB) cell line. The OmB and OmL cell lines were generated without or with Rho-associated kinase (ROCK) inhibitor/3T3 feeder layer supplementation. Although both approaches were successful, ROCK inhibitor/feeder layer supplementation was found to offer the advantages of selecting for epithelial-like cell type and decreasing time to immortalization. After immortalization (≥ passage 5), we characterized the proteomes of the newly derived cell lines (OmB and OmL) using LCMS and identified several unique cell markers for each line. Subsequently, osmotolerance for each of the three cell lines following acute exposure to elevated sodium chloride was evaluated. The acute maximum osmotolerance of these tilapia cell lines (>700 mOsm/kg) was markedly higher than that of any other known vertebrate cell line, but was significantly higher in the epithelial-like OmL cell line. To validate the physiological relevance of these tilapia cell lines, we quantified the effects of acute hyperosmotic challenge (450 mOsm/kg and 700 mOsm/kg) on the transcriptional regulation of two enzymes involved in biosynthesis of the compatible organic osmolyte, myo-inositol. Both enzymes were found to be robustly upregulated in all three tilapia cell lines. Therefore, the newly established tilapia cells lines represent valuable tools for studying molecular mechanisms involved in the osmotic stress response of euryhaline fish.

Hyperproliferation and defects in epithelial polarity upon conditional ablation of alpha-catenin in skin

When surface epithelium was conditionally targeted for ablation of alpha-catenin, hair follicle development was blocked and epidermal morphogenesis was dramatically affected, with defects in adherens junction formation, intercellular adhesion, and epithelial polarity. Differentiation occurred, but epidermis displayed hyperproliferation, suprabasal mitoses, and multinucleated cells. In vitro, alpha-catenin null keratinocytes were poorly contact inhibited and grew rapidly. These differences were not dependent upon intercellular adhesion and were in marked contrast to keratinocytes conditionally null for another essential intercellular adhesion protein, desmoplakin (DP). KO keratinocytes exhibited sustained activation of the Ras-MAPK cascade due to aberrations in growth factor responses. Thus, remarkably, features of precancerous lesions often attributed to defects in cell cycle regulatory genes can be generated by compromising the function of alpha-catenin.

"Transformation" of human endothelial cells by SV40 virions

Human endothelial cells derived from the umbilical vein were transformed with SV40 virions. A cell line subcultured for over 60 serial passages was characterized in comparison with its untransformed counterpart which was culturable for less than five passages. The SV40-transformed human endothelial cells, designated SV-HUVEC, were positive not only for tumor (T) antigen specific to the SV40-transformed cell, but also for two markers of endothelial cells, Factor VIII-related antigen and a receptor for Ulex europaeus agglutinin I. By transformation the growth potential of the human endothelial cells was increased and their serum requirement was decreased. The SV40-transformed endothelial cells were, however, unable to form colonies in soft agar or to form tumors in athymic nude mice, although a small nodule was produced at the site of inoculation. Subcultivation of these cells up to the 62nd passage eventually resulted in crisis and loss of further cell division. Thus, the human endothelial cells were transformed by SV40 while retaining certain normal functions but without showing tumorigenicity.

The Wellcome Foundation lecture, 1986. The molecular control of normal and leukaemic granulocytes and macrophages

The development of semisolid culture methods supporting the clonal proliferation and maturation of granulocytes and macrophages led to the discovery of a group of specific glycoproteins, the colony-stimulating factors (CSFs), whose function it is to control the proliferation and functional activity of granulocytes, macrophages and associated blood cells. The four known CSFs in the mouse and man have been purified and complementary DNAs (cDNAs) for each have been cloned. The injection of bacterially synthesized recombinant CSF into mice has demonstrated that these CSFs can function in vivo to regulate granulocyte and macrophage formation. A major physiological role played by these CSFs is to control resistance to invading microorganisms through mechanisms capable of extremely rapid activation. Because the CSFs are the only known proliferative factors for these cells, the CSFs are involved in the initiation and the emergence of myeloid leukaemia but, conversely, at least one of the CSFs, G-CSF, is able to suppress myeloid leukaemic populations because of the ability of the CSFs to initiate differentiation commitment in responding granulocytic and macrophage populations. The CSFs are promising agents for clinical use in the treatment of infections in patients with depressed granulocyte-macrophage formation and possibly in the management of some types of myeloid leukaemia.

Cell aging in vitro: a historical perspective

This article describes the historical background to the demonstration by Hayflick and Moorhead that human diploid cell strains in culture have limited life-spans. I suggest that the recognition of cell aging in vitro is an example from the biological sciences of a Kuhnian scientific revolution.

Rat esophageal and epidermal keratinocytes: intrinsic differences in culture and derivation of continuous lines

Serially cultivated with 3T3 feeder layer support as colonies of stratified squamous epithelium, rat epidermal and esophageal epithelial cells were readily distinguishable by three criteria. First, the epidermal colonies, exhibiting extensive piling up of squames in the centers, were more stratified than esophageal colonies. Second, in sparse culture 70 to 90% of the esophageal cells but as few as 1 to 5% of the epidermal cells were competent in cross-linked envelope formation upon treatment with the ionophore X537A. After reaching confluence, up to 90% of the cells of both types formed envelopes upon ionophore treatment. Third, epidermal cells in suspension culture reached maximal levels of spontaneously cross-linked envelopes in 1 day or less, while esophageal cells required about 4 days in suspension to reach maximal levels. A reproducible finding with both cell types was that initial colony-forming efficiencies of less than 1% increased to about 40% upon serial passage with consequent derivation of continuous lines. Sparse cultures of esophageal cells with high colony-forming ability retained a high degree of envelope competence (70 to 90%), indicating these two properties are not mutually exclusive. The derived lines exhibited reduced dependence upon feeder layer support at clonal density, but in suspension culture the cells did not grow and lost colony-forming ability with a half-time of several hours. We conclude that cells from these keratinized rat epithelia exhibit intrinsic differences in culture and become continuous lines expressing characteristic regulation of envelope competence and loss of germinative capability in suspension.

Convergent differentiation in cultured rat cells from nonkeratinized epithelia: keratinocyte character and intrinsic differences

Epithelial cells derived from a variety of glandular and other nonkeratinized rat tissues (pituitary, thyroid, bladder, endometrium, trachea, seminal vesicle, prostate, and mammary epithelium) were serially cultivated using a feeder layer of lethally irradiated 3T3 cells. The epithelial cells grew as progressively expanding colonies, in some cases stratified, and were shown to form cornified envelopes upon ionophore-induced activation of cross-linking. Cultures derived from each tissue were distinguishable from the others by characteristic cellular appearance and colony morphology. Those examined in greater detail could be distinguished biochemically in three ways. (a) A majority of cells in sparse cultures of bladder, tracheal, endometrial, and vaginal epithelial cells were capable of envelope formation, whereas those from pituitary, thyroid, seminal vesicle, and mammary epithelia did not attain maximal envelope forming ability until after confluence. (b) Bladder, thyroid, and pituitary cells exhibited different electrophoretic profiles of keratins, which accounted for 20-50% of the cellular protein. (c) Bladder cells were distinguished from thyroid and pituitary cells by a greater suppression of envelope-forming ability by vitamin A. These observations showed that cells from many epithelia have the potential to express properties of keratinocytes in culture while maintaining morphological and physiological differences. Serial passage of these cells generated continuous lines.

The surface character of separated prostatic cells and cultured fibroblasts of prostatic tissue as determined by concanavalin-A hemadsorption

Con-A-coated human type O red blood cells (indicator RBC) were used for ConA reactivity assay of separated epithelial cells and cultured fibroblasts of human prostatic tissue. The epithelial cells of carcinoma showed higher reactivity than those of normal tissue or hyperplastic tissue. Although both cultured fibroblasts of PC and BPH are considered to be non-malignant, it is clearly demonstrated that the PC fibroblasts have a malignant surface character in terms of ConA reactivity, whereas the BPH fibroblasts have a quite low ConA reactivity. ConA-mediated HAD appeared to be a useful tool to distinguish malignant epithelial cells of human prostate from non-malignant ones. It still remains unknown whether the alteration of PC fibroblasts is the cause or the result of carcinogenic transformation of prostatic tissue.

Characterization of the presumptive sarcoma cells in primary MSV tumors

Presumptive sarcoma cells have been isolated from primary MSV tumors induced in normal, immunosuppressed (ALG) and athymic nude mice. These cells were atypical in appearance, induced tumors in secondary hosts and expressed the viral antigens gp70, p30 and p12. In vitro growth characteristics of the MSV cells were tested in a variety of assays defining cell transformation. None of these indicated that the virus-positive cells were transformed. Sex chromosome marker studies were carried out to determine if secondary tumor arose solely from proliferation of donor cells or through infection of host tissue. Tumors from female irradiated mice induced by injections of tumor cells derived from male mice contained a high proportion of metaphases of non-donor origin, indicating that infection is an important but not the sole mechanism involved in tumor transfer. These data also demonstrated that many of the sarcoma cells are damaged as a result of infection as shown by the presence of chromosome breaks and aneuploid metaphases. Histologic sections of both regressor and progressor tumors showed that the virus-positive cells were scattered as single cells surrounded by inflammatory cells, rather than as masses of dividing virus-positive cells found in the MSV-induced transplanted tumor. Collectively, these data support the contention that the MSV tumor is the manifestation of a response to a highly noxious virus infection rather than a tumor of dividing, transformed malignant cells.

Pactamycin resistance in CHO cells: morphological changes induced by the drug in the wild-type and mutant cells

Stable mutants resistant to pactamycin (PacR), a polypeptide chain initiation inhibitor, have been selected in a single step in Chinese hamster ovary (CHO) cells. The sensitivity of protein synthesis in mutant cell extracts to pactamycin indicates that resistance involves an alteration in the permeability of this drug. The failure of PacR mutants to show cross-resistance to other compounds provides further indication that the lesion is presumably specific for pactamycin. Cell hybrids formed between PacR X PacS lines show intermediate sensitivity towards pactamycin, suggesting that the PacR lesion behaves codominantly under these conditions. In the presence of subinhibitory concentrations of pactamycin, CHO cells, which are normally short, polygonal and disoriented, became greatly elongated and aligned themselves in parallel fashion to produce highly oriented colony morphologies, reminiscent of normal diploid fibroblasts. This effect of pactamycin on cellular morphology was seen much more clearly with the PacR mutants, although somewhat higher concentrations of the drug were required to produce this change.

Experimental carcinogenesis: induction of multiple tumors by viruses

Many viruses are able to cause the development of tumors when inoculated into suitable vertebrate hosts. Among them, polyoma virus can induce tumors in several mammalian species: not only many different kinds of tumor, but a large number of tumors within a single individual. Tissue culture studies employing cells from mice and hamsters, as well as observations of the manner of tumor development following polyoma virus injection in these species in vivo, suggest that some, or all, of the tumors so induced are multiple primaries. Because of the availability of mice of different genetic constitutions, the relative ease with which mouse cells from both normal and malignant tissue can cultivate in vitro, the known responses of mice to many carcinogenic agents, as well as the availability of transplantable, metastasizing mouse tumors, it is believed the polyoma virus/mouse host system would provide a highly suitable model in which an experimental approach to the elucidation of mechanisms for the origin of multiple tumors would be possible.

Establishment and characterization of a cell line derived from a spontaneous murine lung carcinoma (M109)

The Madison lung (M109) tumor cell line, initiated from a "spontaneous", anaplastic murine lung carcinoma, has been propagated continuously in vitro for more than 300 cell generations. Cytogenetic analysis revealed a mouse karyotype with a mode of 78 chromosomes (2n = 40). Three distinct marker chromosomes were identified by trypsin-giemsa banding. The cells piled up in culture and had a short generation time and high plating efficiency. Electron microscopy revealed highly undifferentiated cells with little rough endoplasmic reticulum, an abundance of free polysomes, the presence of few and often odd-shaped mitochondria, lipid bodies and phagocytic vacuoles. Virus particles of the C-type were found frequently. The subcutaneous transplantation of M109 cultured cells at a relatively low cell inoculum produced highly metastatic tumors in syngeneic BALG/c mice.

Markers to distinguish normal and neoplastic mammary epithelial cells in vitro: comparison of saturation density, morphology and concanavalin A reactivity

Normal and premalignant mouse mammary epithelial cells can be prepared in high yields by collagenase dissociation of minced glands followed by a brief, differential centrifugation to remove contaminating fibroblasts and fat cells. The major difficulties in preparing pure cultures in quantity are 1) incomplete dissociation of gland material, and 2) cell death during enzymatic digestion. These problems are eliminated by careful selection of collagenases for dissociation. Normal and premalignant mammary epithelial cells are morphologically indistinguishable from malignant mouse mammary epithelial cells in primary monolayer cultures. In addition, the growth rates and saturation densities achieved by normal mammary epithelial cells are indistinguishable from those of malignant mammary epithelial cells in primary culture. In both cases, a monolayer of cells is preserved with no evidence of focal overgrowth. Malignant adenocarcinoma mammary cells can however be distinguished from normal mammary epithelial cells by virtue of differences in their surface interactions with concanavalin A. A hemadsorption assay using Con-A-coated erythrocytes was the most sensitive indicator for these differences. In hemadsorption assays malignant mammary epithelial cells were half-maximally reactive with 2.5 mug/ml concanavalin A, while normal cells were completely unreactive even at concanavalin A concentrations five-times higher. Premalignant mammary epithelial cells were as reactive as malignant mammary epithelial cells in the hemadsorption assays. Hemadsorption of malignant cells was observed in primary and secondary cultures of epithelium as well as in cell lines. Malignant cells forming mammary adenocarcinomas were as highly reactive as malignant cells forming scirrhous carcinomas. Malignant cells not releasing mammary tumor virus (MuMTV) were as reactive as cells releasing that virus. Adsorption of concanavalin-A-coated erythrocytes to normal mammary epithelial cells could be induced by brief treatment of cell monolayers with hyaluronidase. Exposure of active sites was not affected with either trypsin or collagenase. Our results show that while the growth of malignant cells does not serve to distinguish them from normal cells in monolayer culture, surface changes do exist which can be identified by differences in concanavalin A reactivity. Since the earliest transformants identifiable in vivo (premalignant) have undergone conversion of the surface marker, concanavalin-A-mediated hemadsorption provides a sensitive measure for mammary epithelial cell transformants in vitro.

The role of adenosine 3',5'-monophosphate in the transformation of Cloudman mouse melanoma cells

The role of adenosine 3',5'-monophosphate (cyclic AMP) in the regulation of mouse melanoma cell growth and differentiation was investigated. A variant melanoma (Cloudman S91-F) which displays a greater degree of transformation than the parental cell (Cloudman S91) was isolated. A correlation between cyclic AMP metabolism and transformation was made. Dibutyryl cyclic AMP depressed cell growth and increased pigmentation in both parental and variant cell lines. The parental cell line, however, was more responsive to melanocyte-stimulating hormone (MSH) which was found to affect cell growth and pigmentation by increasing cyclic AMP levels. The more transformed S91-F cell line contained lower levels of cyclic AMP than the parental cell line, and this fact correlated well with the higher degree of growth and lesser degree of pigmentation in the variant. Enzymatic analysis revealed that the hydrolysis of cyclic AMP in both cell lines was similar, while the adenylate cyclase activity of the variant cell line was lower than that of the parental cell line. Lineweaver-Burk plots demonstrated that the Km's for the enzymes in the two cell lines were the same but that the Vmax of the S91-F cell line was significantly less that that of the S91 cell line. Thus, the lesion in the S91-F cell which is responsible for its more transformed characteristics seems to be one which affects adenylate cyclase at the level of the cell membrane.

Oxygen toxicity in normal and neoplastic hamster cells in culture

The effects of different partial pressures of oxygen on the growth of hamster embryo and hamster tumor cells in culture were studied. Hamster embryo cells grown in medium with calf serum became established as continous cell lines in 1 to 3% O2 but degenerated in 20, 50, or 97% O2. The same cells grown in medium with fetal calf serum became established in 1 to 3 or 20% O2 and degenerated in 50 or 97% O2. Hamster embryo cells grown in medium with fetal calf serum in 20% O2 were less sensitive to O2 toxicity after 119 than after 46 culture days. Treatment of secondary or tertiary cultures of hamster embryo cells grown in medium with calf serum in 20% O2 with chemical carcinogens facilitated their establishment and increased their resistance to O2 toxicity. Cells that developed into established lines and cells that died became heteroploid during the first few weeks of their growth in culture. Lines of carcinogen-treated and untreated cells became tumorigenic in hamsters. Cells from tumors grew permanently in medium with fetal calf or calf serum in 1 to 3 or 20% O2, and were very resistant to higher O2 concentrations. Differences in growth rate and O2 consumption of hamster embryo and hamster tumor cells changed the concentration of O2 calculated to occur at the cell-fluid interface for a given concentration in the gas phase. Such changes may have been partly responsible for the observed differences in O2 toxicity.

Polypeptide composition of cell membranes from chick embryo fibroblasts transformed by rous sarcoma virus

Chick embryo fibroblasts were transformed by the Bryan high-titer strain of Rous sarcoma virus (RSV-BH), or a mutant (RSV-BH-Ta) inducing temperature-dependent transformation. Surface membranes from normal and transformed cells were isolated as membrane vesicles by differential centrifugation, and as cell ghosts after ZnCl2 treatment and separation in an aqueous two-phase system. These preparations were analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate or phenol/urea/acetic acid. In general a greater resolution of individual bands was found in gels containing phenol/urea/acetic acid, which separates polypeptides on the bases of size and charge. Electrophoresis of preparations from nontransformed cells showed that two polypeptides (molecular weights 200 000 and 250 000) found in cell ghosts were missing in membrane vesicles. In cell ghosts, transformation by RSV-BH resulted in a significant decrease of the 250 000 molecular weight complex. Also a polypeptide (molecular weight 73 000) prominent in membrane vesicles from nontransformed cells was decreased in transformed cells. Surfaces from cells transformed by RSV-BH-Ta at 37 degrees C presented patterns similar to those for RSV-BH infected cells. Shifting these cells to 41 degrees C resulted in an increase in the 250 000 molecular weight complex, although the amount of this protein(s) never reached that found in noninfected cells. Inhibitors of RNA and protein synthesis failed to block the morphological changes occurring in RSV-BH-Ta cells after temperature shifts from 41 degrees C to 37 degrees C or vice-versa. The same inhibitors caused a reduction in the levels of the 250 000 molecular weight complex at both temperatures. These data indicate that these large membrane-associated polypeptides play little or no role in the morphological changes associated with transformation and its reversal.

Use of epithelial cell cultures for studies on the mechanism of transformation by chemical carcinogens

Evidence is reviewed for and against four major theories of chemical carcinogenesis. The development of several normal and transformed epithelial cell lines which should be useful for the analysis of this problem is described. The detection of RNA viral particles in cells transformed with chemical carcinogens is a recurrent finding in studies from our own and other laboratories, but the significance of these particles in terms of the mechanism of chemical carcinogenesis remains to be determined. Finally, we have described the first mutants of chemically transformed epithelial cells which are temperature sensitive in the maintenance of the transformed phenotype. These mutants should be particularly useful for detecting the critical biochemical changes that distinguish a chemically induced tumor cell from its normal counterpart.

Temperature-sensitive mutants of chemically transformed epithelial cells

The first temperature-sensitive mutants of epithelial cells transformed with chemical carcinogens have been isolated. Like the wild-type transformed parental cells, the mutants readily grow in agar suspension at 36 degrees, but in contrast to the wild type, they do not do so at 40 degrees. Detailed studies of one of these mutants, TS-223, indicate that at high temperature it also has reduced cloning efficiency in monolayer culture and a lower saturation density. Scanning electron microscopy revealed that at 40 degrees confluent cultures of TS-223 consist of a monolayer of generally flat polygonal cells, whereas 36 degrees cultures contain many patches of piled-up cells that are spherical and have rougher surface membranes. All of these cellular changes are reversible with upward or downward temperature shifts. The temperature-sensitive lesion appears to reside in a host cell gene which modulates expression of the transformed cell phenotype. These mutants may provide a useful system for elucidating the minimal biochemical changes required for expression of the transformed phenotype in epithelial cells.

Relationship between organization of mammary tumors and the ability of tumor cells to replicate mammary tumor virus and to recognize growth-inhibitory contact signals in vitro

Mammary tumor virus (MTV) replication was confined primarily to cells organized as acini in intact mouse mammary glands. Primary mammary tumors maintained a high degree of acinar organization and cells therein continued to replicate MTV vegetatively. Nonacinar mammary cells, derived by serial transplantation of acinar tumor cells, no longer actively replicated MTV. This suggests that phenotypic differences exist among mammary epithelial cells in their ability to support virus replication, that a fundamental relationship exists between the organization of epithelium for secretion and active virus replication, and that this relationship is not altered as a primary consequence of neoplastic transformation. Mammary epithelial cells from pregnant, non-tumor-bearing, MTV-infected BALB/cfC3H mice or from acinar mammary tumors from a number of mouse strains were grown in primary monolayer cultures. Such cell cultures under the influence of insulin and cortisol exhibited the ability to organize into discrete three-dimensional structures called "domes." MTV replication in such cultures took place primarily in cells within the organized domes. Cells cultured from nonacinar tumors did not exhibit any propensity to organize into domes, nor did they replicate MTV in primary culture. This suggests that the cell organizational requirement for MTV replication observed in vivo is conserved in primary culture. Dome formation is not an effect of virus replication, as cells from uninfected BALB/c animals organized into domes in culture without concomitant MTV replication. Growth-regulating signals, exerted between contiguous cells in cultures of non-MTV-infected mammary epithelium, were not modified by the occurrence of active virus replication nor as a direct consequence of neoplastic transformation. Cells derived from nontumor BALB/cfC3H glands and from spontaneous tumors exhibited cell growth kinetics, saturation densities, and deoxyribonucleic acid synthesis kinetics nearly identical to those of noninfected normal mammary epithelium in primary culture. Cell to cell growth regulatory signals were modified in cultures of nonalveolar tumor cells wherein evidence of overgrowth is documented.