Showing papers on "Carcinogenesis published in 1988"

Suppression of the neoplastic phenotype by replacement of the RB gene in human cancer cells

Abstract: Mutational inactivation of the retinoblastoma susceptibility (RB) gene has been proposed as a crucial step in the formation of retinoblastoma and other types of human cancer. This hypothesis was tested by introducing, via retroviral-mediated gene transfer, a cloned RB gene into retinoblastoma or osteosarcoma cells that had inactivated endogenous RB genes. Expression of the exogenous RB gene affected cell morphology, growth rate, soft agar colony formation, and tumorigenicity in nude mice. This demonstration of suppression of the neoplastic phenotype by a single gene provides direct evidence for an essential role of the RB gene in tumorigenesis.

The ras gene family and human carcinogenesis

Abstract: It has been well established that specific alterations in members of the ras gene family, H-ras, K-ras and N-ras, can convert them into active oncogenes. These alterations are either point mutations occurring in either codon 12, 13 or 61 or, alternatively, a 5- to 50-fold amplification of the wild-type gene. Activated ras oncogenes have been found in a significant proportion of all tumors but the incidence varies considerably with the tumor type: it is relatively frequent (20-40%) in colorectal cancer and acute myeloid leukemia, but absent or present only rarely in, for example, breast tumors and stomach cancer. No correlation has been found, yet, between the presence of absence of an activated ras gene and the clinical or biological features of the malignancy. The activation of ras oncogenes is only one step in the multistep process of tumor formation. The presence of mutated ras genes in benign polyps of the colon indicates that activation can be an early event, possibly even the initiating event. However, it can also occur later in the course of carcinogenesis to initiate for instance the transition of a benign polyp of the colon into a malignant carcinoma or to convert a primary melanoma into a metastatic tumor. Apparently, the activation of ras genes is not an obligatory event but when it occurs it can contribute to both early and advanced stages of human carcinogenesis.

Roles of cytochrome P-450 enzymes in chemical carcinogenesis and cancer chemotherapy.

Abstract: Studies involving the metabolism of chemical carcinogens were important in the discovery and initial characterization of the cytochrome P-450 enzyme system. The Millers and their associates identified NADPH-dependent microsomal enzymes involved in the biotransformation of azo dyes (1, 2). These reactions, reduction and mixed-function oxidation, were also found to be important in the processing of many other carcin ogens, as well as drugs and steroids. Subsequent work led to the identification of the hemoprotein P-4503 as the terminal oxidase involved in such microsomal mixed-function oxidations (3,4). Other early studies revealed that administration of many different chemicals to animals could alter the metabolism of carcinogens (5-7). As we know now, many forms of P-450 exist and the expression of these enzymes is influenced by the com pounds which are given to the animals. Administration of the carcinogenic polycyclic hydrocarbon 3-methylcholanthrene to rats and analysis of the liver microsomes provided some of the early evidence that multiple forms of P-450 exist (8, 9). Since that time, a great deal of effort has been concentrated upon understanding the biochemistry of these P-450 enzymes, in terms of how they catalyze reactions and how their expression is regulated. Although much of the focus regarding P-450 proteins has involved their contributions to the metabolism of steroids and drugs, considerable effort is still directed towards understanding the roles of P-450s in carcinogen metabolism. The characteristics of P-450 enzymes will not be reviewed at length here.4 The microsomal enzymes are found in most tissues but are concentrated in liver. All have characteristic ferrouscarbon monoxide complex Soret peaks near 450 nm, have montimene molecular weights of about 50,000, and accept electrons from the flavoprotein NADPH-P-450 reducÃ-ase. Nearly 20 different P-450 proteins have been isolated from rat liver and all appear to be distinct gene products. Levels of the individual proteins are altered by administration of or exposure to a wide variety of chemicals, many of which are carcinogens themselves (including tumor initiators such as the polycyclic hydrocarbons and tumor promoters such as phénobarbital). Mitochondrial P-450s accept electrons from ferridoxins and seem to be primarily involved in anabolic steroid metabolism, although some evidence for roles in carcinogen oxidation has been presented (14). Several reviews and monographs deal with various aspects of the catalytic mechanisms and regulation of the P-450 enzymes

Oncogene activation in chemical carcinogenesis.

Abstract: Publisher Summary This chapter discusses the advances made in understanding the mechanisms of action of chemical carcinogens in the light of the recent evidence that oncogenes are directly implicated in the process of tumor development. It discusses various model systems used to address the question of cell transformation in vivo. The process of carcinogenesis in cell culture is compared with the various stages of tumor development in vivo . It is noted that oncogenes provide potential targets for activation by carcinogens. Indeed, the full spectrum of changes that have been noted in the DNA of cells treated by chemical carcinogens— point mutations, translocations, and gene amplification—has been implicated in the activation of protooncogenes to an oncogenic state. It is, therefore, logical to expect that some oncogenes can be activated directly by the interaction between the target genes and chemical carcinogens. Others may be activated indirectly during the progression of tumorigenesis by nontargeted genetic events in somatic cells.

The origins of human cancer: molecular mechanisms of carcinogenesis and their implications for cancer prevention and treatment--twenty-seventh G.H.A. Clowes memorial award lecture.

Abstract: Epidemiological studies provide evidence that environmental factors (external agents such as chemicals, radiation, and viruses) play a major role in the causation of the majority of human tumors. This is a highly optimistic message, since it implies that cancer is largely a preventable disease. To meet this challenge we must, however, understand the mechanisms of cancer causation at the cellular and molecular levels and, in a parallel effort, develop new laboratory methods that can be used to identify specific causative agents in humans. The approach must be comprehensive since it is likely that human cancers are due to complex interactions between multiple factors, including the combined actions of chemical and viral agents. This paper reviews recent studies from our laboratory and studies by other investigators related to these themes. A major principle in studies on mechanisms of carcinogenesis is that the process proceeds through multiple discernible stages, including initiation, promotion, and progression. It is likely that the transition between these stages is driven by different environmental and endogenous factors and involves different biochemical mechanisms and genetic elements. Several types of chemicals initiate the carcinogenic process by yielding highly reactive species that bind covalently to cellular DNA. Our group has elucidated the details of this process with two groups of compounds, aromatic amines and polycyclic aromatic hydrocarbons, emphasizing how these agents distort the conformation of DNA and its functions during DNA replication and transcription. The implications of these findings with respect to oncogene activation, DNA amplification, gene transposition, and chromosome translocations are discussed. Our studies on tumor promotion have concentrated on the mechanisms of action of the potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate. Studies from several laboratories indicate that this agent and related compounds produce their effects by activating a specific cellular enzyme, protein kinase C (PKC). This produces a cascade of events which include alterations in the function of membrane-associated ion channels and receptors, alterations in gene expression and, ultimately, changes in cellular differentiation and proliferation. Recent studies on the isolation and stable overexpression of a cloned DNA sequence that encodes PKC are described. The results obtained provide direct evidence that PKC plays a critical role in growth control. The possible role of PKC, and other mediators of signal transduction pathways, in the origin of certain human cancers is also discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

c-fos promoter trans-activation by the tax1 protein of human T-cell leukemia virus type I

Abstract: To understand the mechanisms of oncogenesis by human T-cell leukemia virus type I, we have investigated the ability of the tax1, protein to modulate transcription of protooncogenes. By using a transient cotransfection assay, we report that the protooncogene fos promoter is transactivated by tax1 in a variety of cell types. Two regions containing upstream sequences between positions -362/-324 and -323/-276 of the c-fos promoter responded to this activation and also conferred tax1 responsiveness to the heterologous herpesvirus thymidine kinase promoter. These two sequences include elements mediating the induction by v-sis-conditioned medium and serum, phorbol ester, or epidermal growth factor, respectively. Furthermore, expression of the endogenous c-fos gene was activated by tax1 in human T-cell leukemia virus type I-infected cell lines. In contrast, no trans-activation of the c-myc or c-Ha-ras promoter was observed.

Are cell number and cell proliferation risk factors for cancer

Abstract: Relatively little is known about the mechanisms underlying carcinogenesis in humans. Caloric restriction strongly inhibits the development of neoplasia in rodents, and there is evidence of a positive relationship between cancer and body weight in humans. Caloric restriction early in life is also known to permanently diminish organ cellularity. A recent link between adult stature and cancer incidence similarly implicates a lasting effect for growth and possibly for early nutrition in carcinogenesis. It is postulated that cancer risk is proportional to the number of proliferating cells, which in turn depends on both the number of cells and the rate of cell division within the tissue. This hypothesis is consistent with several aspects of human carcinogenesis, including multistage models and the epithelial origin of most cancers.

Localized production of TGF-β mRNA in tumour promoter-stimulated mouse epidermis

Abstract: Tumour promoters induce a wide spectrum of morphological and biochemical alterations when applied to mouse epidermis in vivo. These include the induction of RNA, DNA and protein synthesis during discrete phases of proliferation and differentiation. This constitutes an ideal model for studying molecular events underlying the disruption of epidermal homeostasis by TPA, and its subsequent re-establishment. Transforming growth factor-beta (TGF-beta) can induce either growth stimulation, inhibition, or differentiation, depending on the target cell. A function has been proposed for TGF-beta in wound healing and in tumour promotion, but the main source of TGF-beta is generally thought to be platelets, macrophages or lymphocytes, and a direct role for this growth factor in regulating tissue homeostasis in vivo has not been demonstrated. We show here that when the tumour promoter 12-tetradecanoyl-phorbol-13-acetate (TPA) is applied to the skin of mice, very high levels of TGF-beta messenger RNA are induced in the epidermal cells. In situ hybridization techniques show that the main site of TGF-beta synthesis is in the suprabasal differentiating epidermal cells. These results suggest that TGF-beta may be a natural regulator of epidermal homeostasis which is important in tumour promotion.

Analysis of RAS oncogene mutations in human lymphoid malignancies

Abstract: We investigated the frequency of mutations activating RAS oncogenes in human lymphoid malignancies, including B- and T-cell-derived acute lymphoblastic leukemia, chronic lymphocytic leukemia, and non-Hodgkin lymphoma. By the polymerase chain reaction/oligonucleotide hybridization method, DNA from 178 cases was analyzed for activating mutations involving codons 12 and 61 of the HRAS, KRAS and NRAS genes and codon 13 of the NRAS gene. Mutations involving codons 12 or 13 of the NRAS gene were detected in 6 of 33 cases of acute lymphoblastic leukemia (6/33, 18%), whereas no mutations were found in non-Hodgkin lymphoma or chronic lymphocytic leukemia. Direct nucleotide sequence analysis of polymerase chain reaction products showed that the mutations involved a G----A transition in five of the six cases of acute lymphocytic leukemia. In four cases the mutations seemed to occur in only a fraction of the neoplastic cells, and one case displayed two distinct NRAS mutations, most likely present in two distinct cell populations. These results indicate the following: (i) RAS oncogenes are not found in all types of human malignancies, (ii) significant differences in the frequency of RAS mutations can be found among subtypes of neoplasms derived from the same tissue, (iii) in lymphoid neoplasms the NRAS mutation correlates with the most undifferentiated acute lymphocytic leukemia phenotype, and (iv) NRAS mutations present in only a fraction of malignant cells may result from either the selective loss or the acquisition of mutated alleles during tumor development.

Stromal involvement in malignant growth.

Abstract: Publisher Summary This chapter describes various modes of interaction between malignant cells and stroma. Malignant cells are shown to produce various lytic enzymes, which attack the stroma or to induce fibroblasts to synthesize collagenolytic, elastolytic, and glycosaminoglycan-degrading enzymes. In some cancers tumor cells stimulate fibroblasts to produce stromal components—collagen, elastin, and glycosaminoglycans. Migration of tumor cells is partly determined by versatile adhesive glycoproteins in the stroma. Wound healing and especially fibrosis (scars) appear to be possible auxiliary factors in carcinogenesis. Stromal cells (local or generalized) may exhibit subtle alterations similar to transformed cells. Stromal alterations preceding manifest malignancy contribute to carcinogenesis. In vitro data point to intricate interdependencies between cancer cells and fibroblasts resulting in synthesis of collagenolytic enzymes. Normal ontogenesis depends on a complex of interactions between various tissues among which the stroma plays an essential role. Epithelial–stromal interactions are also important in the adult organism. In cancer growth, the microenvironmental signals constitute an essential category of influences contributing to malignancy.

Dissecting Multistep Tumorigenesis in Transgenic Mice

Abstract: Article de synthese sur les tumeurs associees aux oncogenes transgeniques et utilisation des souris transgeniques en vue d'etudier les etapes de la tumorigenese

Oncogenes and tumor-suppressing genes.

Abstract: THE past decade has witnessed great changes in our understanding of the molecular origins of cancer. Much of this progress stems from the discovery of specific genes, the oncogenes, which are carri...

The short arm of chromosome 11 is a "hot spot" for hypermethylation in human neoplasia.

Abstract: Inactivation of normally expressed genes may play a role in the formation and/or progression of human cancers. Methylation of cytosine in DNA could potentially participate in such alterations of gene expression. Abnormalities in DNA methylation are a consistent feature of human neoplasms, and we now show that these include not only previously recognized widespread genomic hypomethylation, but also regional increases in gene methylation. A hot spot for abnormal methylation of C + G-rich areas has been detected on the short arm of chromosome 11 in an area known to harbor tumor suppressor genes. This change occurs consistently in common forms of human cancer and appears early during the transformation of cells with viruses including members of the human T-cell leukemia (HTLV) family. Furthermore, in one chromosome 11 gene examined, calcitonin, the increased methylation in somatic tumor cells coincides with the presence of an "inactive" chromatin pattern in the transcriptional regulatory area. The increased regional DNA methylation demonstrated may then participate in or mark chromosomal changes associated with gene inactivation events that are central to the genesis and/or progression of human cancers.

Role of antioxidant enzymes in cell immortalization and transformation

Abstract: The role of antioxidant enzymes, particularly superoxide dismutase (SOD), in immortalization and malignant transformation is discussed. SOD (generally MnSOD) has been found to be lowered in a wide variety of tumor types when compared to an appropriate normal cell control. Levels of immunoreactive MnSOD protein and mRNA for MnSOD also appear to be lowered in tumor cells. Tumor cells have the capacity to produce superoxide radical, the substrate for SOD. This suggests that superoxide production coupled with diminished amounts of MnSOD may be a general characteristic of tumor cells. The levels of MnSOD in certain cells correlates with their degree of differentiation; non-differentiating cells, whether normal or malignant, appear to have lost the ability to undergo MnSOD induction. These observations are used to elucidate a two-step model of cancer. This model involves not only the antioxidant enzymes, but also organelle (particularly mitochondria and peroxisomes) function as a dominant theme in carcinogenesis.

RAS mutations in myelodysplasia detected by amplification, oligonucleotide hybridization, and transformation.

Abstract: Members of the RAS gene family have been implicated in many neoplasms with activating mutations around amino acid positions 12 and 61. We have assessed the mutational activation of H, K, and NRAS in myelodysplasia (MDS) by polymerase chain reaction and hybridization with synthetic oligonucleotide probes. Using this method, point mutations in codons 12/13 and 61 of these RAS genes were detected in 20 of 50 patients including two with refractory anemia with ringed sideroblasts (RARS). Ten normal individuals had no detectable RAS mutations. In 11 instances, DNA from patients with detectable RAS mutations were shown to register in either NIH3T3 focus-forming or nude mouse tumorigenicity assays. In addition, one patient (RARS) was shown to have an activated NRAS gene detected by a tumorigenicity assay and Southern blot analyses. Two MDS patients had mutations detected in two different RAS genes. DNA from one of these patients was observed to give rise to transformants with activated N and HRAS. Two patients with detectable NRAS mutations in the MDS stage progressed to AML and DNA from the AML stage registered positively in a transformation assay with NRAS activation. These results show that RAS mutations can occur at early, as well as late, stages of leukemic progression. The incidence of RAS mutations appears to be significantly higher in CMML than in the other subgroups (p = 0.02).

Amplified expression of the HER2/ERBB2 oncogene induces resistance to tumor necrosis factor alpha in NIH 3T3 cells.

Abstract: Functional characterization of oncogene products that induce cellular transformation has progressed rapidly in recent years. However, less is known about the mechanism(s) by which the transformed cells may escape destruction by host immune defenses and form tumors. A recently described oncogene that has an important association with aggressive human breast carcinoma is "HER2," for human epidermal growth factor receptor 2. The oncogene has also been called NGL and human c-erbB-2 (ERBB2). In this paper we show that amplification of HER2 oncogene expression can induce resistance of NIH 3T3 cells to the cytotoxic effects of recombinant tumor necrosis factor alpha (rTNF-alpha) or macrophages. Resistance is accompanied by an increased dissociation constant for rTNF-alpha binding to high-affinity receptors on the HER2-transformed NIH 3T3 cells. The resistance phenotype is independent of transformation since NIH 3T3 cells transformed by the activated human homologue of the Harvey-ras oncogene (HRAS) retain high-affinity binding sites for rTNF-alpha as well as sensitivity to its cytotoxic effects. These results suggest that HER2 may potentiate tumorigenesis by inducing tumor cell resistance to host defense mechanisms.

Transforming genes in chronic myelogenous leukemia

Abstract: Chronic myelogenous leukemia (CML) is a hematopoietic malignancy characterized by an indolent chronic phase that invariably leads to a "blast crisis" indistinguishable from acute leukemia. Using a sensitive assay based on gene transfer and tumorigenesis, we sought evidence that damage to protooncogenes might figure in the progression from the chronic to the blast phase of CML. Seven of the 12 patients with CML examined in this manner harbored transforming genes. Mutations in RAS protooncogenes were detected in the leukemic cells from 1 of 6 chronic-phase patients, and 3 of 6 blast-crisis patients. In addition, a presently unidentified transforming gene (neither RAS nor RAF) was detected in 1 patient with chronic phase and 1 with blast crisis. Our data indicate that mutations in RAS genes may play diverse roles in the pathogenesis of CML.

Transgenic mice bearing the human c-myc gene activated by an immunoglobulin enhancer: a pre-B-cell lymphoma model

Abstract: Transgenic mice carrying a fusion gene in which the mouse immunoglobulin enhancer has been inserted into an otherwise normal human c-myc gene develop a narrow spectrum of pre-B-cell lymphomas. Tumor occurrence is correlated with expression of the transgene in organs in which large numbers of pre-B cells predominate. These tumors, which arise stochastically, are virtually all lymphoblastic lymphomas of the pre-B-cell type. Evidently the isolated enhancer targets oncogene expression and tumorigenesis to the early B-cell population in preference to more mature B-cell populations. The transgene also confers enhanced in vitro growth properties on nontransformed pre-B cells as observed in bone marrow cultures derived from transgenic animals. These cultured cells represent a population in which the activating function of c-myc can be uncoupled from secondary oncogenic events occurring in vivo.

Expression of Growth Factors and Oncogenes in Normal and Tumor-derived Human Mammary Epithelial Cells

Abstract: The expression of genes which may be involved in the regulation of human mammary epithelial cell growth [transforming growth factors α and β] and tumorigenesis [c- myc, erb B2, epidermal growth factor receptor (EGFR), Ha- ras, pS2 ] has been compared in similarly cultured normal cell strains and tumor cell lines. We have found that the normal breast cells produce high levels of EGFR mRNA, which are translated into nearly 105 low affinity epidermal growth factor-binding molecules/cell. In the estrogen receptor-negative lines examined, the EGFR gene was expressed at levels comparable to those in the normal cells. In contrast, EGFR and transforming growth factor α mRNAs were reduced in estrogen receptor-positive tumor lines compared to estrogen receptor-negative lines and normal cells. Steady state mRNA levels for transforming growth factor β, erb B2, c- myc , and Ha- ras in the normal cells were greater than or comparable to those in all of the breast tumor lines. Furthermore, in the absence of gene amplification, only one of the genes examined ( i.e., pS2 ) was overexpressed in a subset of the tumor cells compared to their normal counterparts. Several reports by other investigators have described overexpression of some of these genes in breast biopsies and in tumor lines in studies lacking normal controls. Thus, our results, in which the same genes were not overexpressed compared to normal cells unless amplified, underscore the importance of including appropriate normal controls in studies aimed at defining aberrant patterns of gene expression in tumor cells.

c-H-ras and c-K-ras gene hypomethylation in the livers and hepatomas of rats fed methyl-deficient, amino acid-defined diets.

Abstract: The extent of methylation of the c-H-ras and c-K-ras oncogenes was compared in neoplastic and preneoplastic livers of rats fed one of several methyl-deficient, amino acid-defined diets for 18 months, with or without a preceding initiating dose of diethylnitrosamine (DEN). The restriction endonucleases MspI, HpaII, HhaI, PaeR71 and XhoI were used for studying the extent and pattern of DNA methylation. The results indicated that both c-H-ras and c-K-ras oncogenes were hypomethylated in all DNA samples derived from both neoplastic and preneoplastic livers of rats fed any of the methyl-deficient diets used, regardless of whether or not the rats had received an initiating dose of DEN. It thus appears that dietary methyl deficiency does indeed lead to hypomethylation of ras genes in the DNAs of the resulting tumors. However, the significance of this hypomethylation in the tumorigenic process is not clearly understood.

Requirement for the simian virus 40 small tumor antigen in tumorigenesis in transgenic mice.

Abstract: To examine the role of simian virus 40 (SV40) large T and small t antigens in tumorigenesis in animals, we generated transgenic mice which expressed either both the SV40 large T and small t antigens or the SV40 large T antigen alone under the control of the mouse mammary tumor virus long terminal repeat. The mouse mammary tumor virus long terminal repeat directs the expression of transgenes in ductal epithelial cells of several organs, including the mammary gland, lung, and kidney, and in lymphoid cells. The mice which expressed both the T and t tumor antigens developed lung and kidney adenocarcinomas, while those which expressed large T alone did not. Both types of mice developed malignant lymphomas with similar frequencies and latency periods. Our results show that the SV40 small t antigen cooperates with the large T antigen in inducing tumors in slowly dividing epithelial cells in the lung and kidney.

Heart and bone tumors in transgenic mice

Abstract: Tissue-specific tumorigenesis can be induced in transgenic mice by the directed expression of simian virus 40 (SV40) large tumor (T) antigen. In an attempt to determine the susceptibility of haploid, round spermatids to neoplastic transformation by this oncogene, transgenic mice were generated that harbored a chimeric gene composed of the SV40 T-antigen genes fused to the 5' and 3' flanking sequences of the mouse protamine 1 gene. The transgene was expressed in round spermatids and, surprisingly, in the heart and temporal bone as well. Expression in the heart resulted in rhabdomyosarcomas that always appeared in the right atrium. Bilateral osteosarcomas developed within the petrous portion of the temporal bone. No testicular pathology was observed. T-antigen immunostaining was readily detected in tumor tissue but not in the testis. In addition, SV40 transcripts were processed differently in testis and tumor tissue. Transgenic mouse lines were established that routinely develop these tumors, and they should provide a valuable resource for studies involving cardiac and bone physiology and neoplasia. The atrial tumor cells can be maintained in vitro and some continue to display a cardiac muscle phenotype.

Expression of insulin-like growth factor I (IGF-I) and IGF-II mRNA during hepatic development, proliferation and carcinogenesis in the rat

Abstract: Insulin-like growth factor I (IGF-I) and IGF-II are peptides that presumably are required for normal fetal and postpubertal growth The production of IGFs is developmentally regulated and the liver appears to be a major site of production By analysing mRNA levels for IGF-I and IGF-II in the rat liver we have attempted to further study the expression of these growth factors during development and regeneration as well as during the course of hepatic carcinogenesis Fetal livers are characterized by a high level of IGF-II mRNA and a low level of IGF-I mRNA, while in adult livers the opposite situations occur, ie a high level of IGF-I mRNA and a non-measurable level of IGF-II mRNA During the course of experimentally induced hepatic cancer, IGF-I mRNA was consistently reduced and in a majority of cancers analysed (6/9) IGF-II mRNA was increased, ie a fetal type of IGF expression can be switched on in some experimentally induced hepatocellular carcinomas The onset of IGF-II production during hepatic carcinogenesis appears to be a late phenomenon since liver nodules, preceding the development of hepatocellular cancer, were found not to contain IGF-II mRNA Furthermore, during hepatic regeneration following partial hepatectomy no marked change in IGF-I or IGF-II mRNA levels was noted The above results suggest that the fetal growth factor IGF-II could have a role in hepatic cancer

Tumor Necrosis Factor and Lymphotoxin Gene Expression in Human Tumor Cell Lines

Abstract: In this paper we show that eight of 17 tumor cell lines of various tissue origin constitutively express tumor necrosis factor (TNF) mRNA. Five of these eight cell lines concomitantly contained lymphotoxin (LT) mRNA. Of the remaining nine cell lines that lacked detectable TNF or LT gene expression, five could be induced by phorbol ester and/or cytokines to accumulate the respective mRNAs. While TNF mRNA was found not only in neoplastic hematopoietic cells, but also in cell lines derived from carcinomas, LT gene expression seemed to be restricted to lymphoid tumor cells. Tumor cells that expressed LT mRNA also secreted LT protein and proved to be resistant to the cytostatic/cytotoxic effects of their own protein product as well as to exogenous recombinant TNF and recombinant LT. In contrast, most of the cell lines containing TNF mRNA did not release TNF protein into the supernatants, indicating that TNF gene expression may be controlled predominantly at a post-transcriptional level. Thus, the presence of TNF mRNA does not necessarily reflect a TNF-resistant phenotype. Our findings demonstrate that TNF and/or LT mRNA expression is a rather common phenomenon in long-term cultured tumor cell lines and reveal that ectopic TNF and/or LT production by tumor cells may be involved in certain paraneoplastic syndromes as well as in tumorigenesis.

Neoplastic transformation of a human bronchial epithelial cell line by a recombinant retrovirus encoding viral harvey ras

Abstract: Activated ras oncogenes have previously been implicated in the pathogenesis of human lung carcinomas. A v-Ha-ras-containing retrovirus, Zip-ras, was generated by inserting the coding region of the v-Ha-ras oncogene into the Zip-NeoSV(X) [Cepko et al., Cell 37:1053-1062, 1984] retroviral vector. Amphotrophic Zip-ras retrovirus was used to infect an SV40 large T antigen-positive immortalized cell line, BEAS-2B, derived from normal bronchial epithelial cells, the predominant progenitor cells of human lung carcinomas. Zip-ras-infected BEAS-2B cells selected for G418 resistance formed anaplastic carcinomas in 12 of 15 athymic nude mice (latency 3 wk), whereas Zip-NeoSV(X)-infected BEAS-2B control cultures inoculated into 12 nude mice formed no tumors after a minimum of 7 mo. Tumor cell lines were established and demonstrated to be of human epithelial origin and to express v-Ha-ras p21 protein. A common feature of the tumor cell lines was an increase in ploidy. The increased efficiency of neoplastic transformation by v-Ha-ras of cell lines as compared with our previous results with normal bronchial epithelial cells [Yoakum et al., Science 227:1174-1179, 1985] is consistent with the hypothesis that the "immortalization" step is rate-limiting in in vitro human epithelial cell carcinogenesis.