Showing papers on "Carcinogenesis published in 1985"

Autocrine growth factors and cancer.

Abstract: The ability of cancer cells to produce and to respond to their own growth factors (autocrine secretion) has become a central concept linking oncogene and growth factor research. Oncogenes confer growth factor autonomy on cells not only by coding directly for autocrine peptide growth factors or their receptors, but also by amplifying the mitogenic signals generated by a growth factor at its receptor. Antagonists of positive autocrine growth factors can inhibit growth of cancer cells in experimental animals. Recently identified negative autocrine growth factors might themselves control aberrant cell growth.

The Molecular Basis of Cancer

Abstract: Malignant Transformation Growth and Spread of Cancer Molecular Abnormalities in Specific Malignancies, Molecular Basis of Cancer Therapy.

Phagocytes as carcinogens: malignant transformation produced by human neutrophils

Abstract: In a study of the relation between chronic inflammation and carcinogenesis, C3H mouse fibroblasts of the 10T 1/2 clone 8 line (10T 1/2 cells) were exposed to human neutrophils stimulated to synthesize reactive oxygen intermediates or to a cell-free enzymatic system generating superoxide (xanthine oxidase plus hypoxanthine). After exposure, the 10T 1/2 cells were either placed in tissue culture or immediately injected into athymic nude mice. Both malignant and benign tumors developed in the mice injected with treated cells, but not in those injected with control cells; in one instance cells grown from one of the benign tumors subsequently developed a malignant phenotype. Malignant transformation was also observed in treated cells in the experiments in vitro.

Reversal of oncogenesis by the expression of a major histocompatibility complex class I gene

Abstract: The classical transplantation antigens (the major histocompatibility complex class I antigens) play a key role in host defense against cells expressing foreign antigens. Several naturally occurring tumors and virally transformed cells show an overall suppression of these surface antigens. Since the class I molecules are required in the presentation of neoantigens on tumor cells to the cytotoxic T lymphocytes, their absence from the cell surface may lead to the escape of these tumors from immunosurveillance. To test this possibility, a functional class I gene was transfected into human adenovirus 12-transformed mouse cells that do not express detectable levels of class I antigens; the transformants were tested for expression of the transfected gene and for changes in oncogenicity. The expression of a single class I gene, introduced by DNA-mediated gene transfer into highly tumorigenic adenovirus 12-transformed cells, was sufficient to abrogate the oncogenicity of these cells. This finding has important implications for the regulation of the malignant phenotype in certain tumors and for the potential modulation of oncogenicity through derepression of the endogenous class I genes.

A method to detect and characterize point mutations in transcribed genes: amplification and overexpression of the mutant c-Ki-ras allele in human tumor cells

Abstract: A significant percentage of human tumors contain activated ras oncogenes that have acquired oncogenic potential as a result of somatic point mutations at codon 12 or 61 of the encoded ras gene product. We report here a method to detect and characterize mutations in ras genes that is based on the ability of pancreatic ribonuclease (RNase A; EC 3.1.27.5) to cleave RNA heteroduplexes containing single-base mismatches. Using this method, we show that certain human tumor cells contain mutant c-Ki-ras genes, and we define the nature and position of these mutations. At the same time, we describe the presence and estimate the expression of both normal and mutant c-Ki-ras alleles in the same tumor cells. This method should be useful for the diagnostic detection and characterization of single point mutations in expressed genes.

SV40 enhancer and large-T antigen are instrumental in development of choroid plexus tumours in transgenic mice

Abstract: We have shown recently that choroid plexus tumours frequently develop in transgenic mice which have developed from fertilized eggs injected with DNA molecules containing both simian virus 40 (SV40) early-region genes and metallothionein (MT) fusion genes1, and several lines of mice have now been established in which all of the offspring that inherit the foreign DNA succumb to these tumours at 3–5 months of age (ref. 1 and our unpublished data). Several other tissues, notably thymus and kidney, occasionally also show pathological changes. SV40 large-T antigen protein and messenger RNA are always present in affected tissues at much greater concentrations than in unaffected tissues, suggesting that SV40 early-region genes are preferentially activated in choroid plexus, thymus and kidney and that this activation frequently leads to tumorigenesis in the choroid plexus1. To determine which regions of the original constructs are important for this tumorigenesis, we have now tested several derivatives and report here that the large-T antigen is sufficient, that the MT fusion gene is dispensable and that the SV40 enhancer (72-base-pair repeat region) has an important role in directing tumours to the choroid plexus. Deletion of the SV40 enhancer region alone commonly leads to peripheral neuropathy, as well as liver and pancreatic tumours, which are the subject of the accompanying paper. Evidence is presented that these pathologies may result from an enhancing effect of the MT sequences on large-T antigen genes, made possible by removal of the otherwise dominant SV40 enhancer.

Estradiol 16 alpha-hydroxylation in the mouse correlates with mammary tumor incidence and presence of murine mammary tumor virus: a possible model for the hormonal etiology of breast cancer in humans.

Abstract: In this report, we describe our findings on the relationship between estradiol 16 alpha-hydroxylation and mammary tumor incidence. A close correlation between the two has been demonstrated with 16-hydroxylation being elevated in strains with a high incidence of tumors, such as RIII and C3H, and low in strains with a low incidence of cancer, such as C57BL. The extent of reaction is highly reproducible and unaffected by age or presence of overt mammary tumors. Studies on the inheritance of estradiol 16 alpha-hydroxylase showed that it is inherited as an autosomal dominant and is not correlated with estradiol 2-hydroxylase or androgen and progestin 16 alpha-hydroxylases. In addition, the reaction was shown to be markedly enhanced by the presence of murine mammary tumor virus and diminished in the absence of the virus. These studies establish a relationship between genetics, hormonal factors, and murine mammary tumor virus, the three key factors in mammary tumorigenesis.

Transformation of human bronchial epithelial cells transfected by Harvey ras oncogene

Abstract: Transfection of normal human bronchial epithelial (NHBE) cells with a plasmid carrying the ras oncogene of Harvey murine sarcoma virus (v-Ha ras) changed the growth requirements, terminal differentiation, and tumorigenicity of the recipient cells. One of the cell lines isolated after transfection (TBE-1) was studied extensively and shown to contain v-Ha ras DNA. Total cellular RNA from TBE-1 cells hybridized to v-Ha ras structural gene fragment probes five to eight times more than RNA from parental NHBE cells. The TBE-1 cells expressed phosphorylated v-Ha ras polypeptide p21, showed a reduced requirement for growth-factor supplements, and became aneuploid as an early cellular response to v-Ha ras expression. As the transfectants acquire an indefinite life-span and anchorage independence they became transplantable tumor cells and showed many phenotypic changes suggesting a pleiotropic mechanism for the role of Ha ras in human carcinogenesis.

Specific growth response of ras-transformed embryo fibroblasts to tumour promoters.

Abstract: Chemical carcinogenesis is a process involving multiple steps, as shown in several in vivo experimental systems. Two early steps have been well characterized: initiation, achieved by a single, subthreshold dose of a carcinogen, and promotion, induced by repetitive treatments with a non-carcinogenic tumour promoter. At the cellular level, establishment of the transformed phenotype is also a multi-step process and activation of several, independent genes appears to be required. Here we show that, like initiated cells, primary rat embryo fibroblasts (REFs) containing a ras but not a myc oncogene, are strongly and specifically stimulated to grow by tumour promoters. In the presence of these promoters, ras-containing REFs acquire the ability to overgrow normal cells in the monolayer and to form foci with 100% efficiency. Similar to the in vivo situation, promoter effects can be blocked by the concomitant application of retinoic acid.

Activated proto-onc genes: sufficient or necessary for cancer?

Abstract: Proto-onc genes are normal cellular genes that are related to the transforming (onc) genes of retroviruses. Because of this relationship these genes are now widely believed to be potential cancer genes. In some tumors, proto-onc genes are mutated or expressed more than in normal cells. Under these conditions, proto-onc genes are hypothesized to be active cancer genes in one of two possible ways: The one gene-one cancer hypothesis suggests that one activated proto-onc gene is sufficient to cause cancer. The multigene-one cancer hypothesis suggests that an activated proto-onc gene is a necessary but not a sufficient cause of cancer. However, mutated or transcriptionally activated proto-onc genes are not consistently associated with the tumors in which they are occasionally found and do not transform primary cells. Further, no set of an activated proto-onc gene and a complementary cancer gene with transforming function has yet been isolated from a tumor. Thus, there is still no proof that activated proto-onc genes are sufficient or even necessary to cause cancer.

The ras oncogene product p21 is not a regulatory component of adenylate cyclase.

Abstract: Harvey (Ha-MSV) and Kirsten (Ki-MSV) murine sarcoma viruses induce tumours in animals and transform various cells in culture because of the expression of the ras oncogene product, p21 (ref. 1). Proto-oncogenes homologous with these genes are highly conserved evolutionarily and activated ras oncogenes have been detected in many human cancers. Whether c-ras oncogenes are directly responsible for human carcinogenesis is uncertain; however, it is clear that p21 mediates virus-induced transformation, although by an unknown mechanism. Epithelial and fibroblast cell lines transformed with Ha-MSV and Ki-MSV express p21 (ref. 8) and exhibit reduced adenylate cyclase activity. Like the guanine nucleotide regulatory proteins, Ns and Ni, which mediate stimulation and inhibition, respectively, of adenylate cyclase, p21 is a membrane-associated GTP binding protein, which exhibits GTPase activity. These similarities suggest that p21 and the adenylate cyclase regulatory proteins are related in cellular function, and that p21 depresses adenylate cyclase by inhibiting the activity of Ns or acting as Ni. We have therefore now examined the structural and functional similarities between p21 and Ns and Ni and find no evidence that p21 regulates adenylate cyclase activity by acting as one of these regulatory proteins.

Peripheral neuropathies, hepatocellular carcinomas and islet cell adenomas in transgenic mice

Abstract: The ability to introduce foreign DNA into the genome of mice offers unique opportunities to produce new models of disease processes. Recent experiments have shown that integration and expression of simian virus 40 (SV40) T antigen genes1 and the murine mammary tumour virus (MMTV)–myc genes2 in transgenic mice can lead to the development of neoplasia in a remarkably tissue-specific manner. In the case of SV40-bearing mice, tumours consistently develop in the choroid plexus1. In the accompanying paper, we show that the 72-base pair (bp) enhancer in the SV40 genome is instrumental in directing tumorigenesis to the choroid plexus3. However, when the enhancer is deleted from a construction also containing the metallothionein-human growth hormone fusion gene (SVΔe-MGH), an entirely new pattern of pathology results. The present report focuses on transgenic mice carrying this construct; they develop demyelinating peripheral neuropathies, hepatocellular carcinomas and islet cell adenomas.

Suppression of tropomyosin synthesis, a common biochemical feature of oncogenesis by structurally diverse retroviral oncogenes.

Abstract: To identify proteins whose production may be altered as a common event in the expression of structurally diverse oncogenes, we compared two-dimensional electropherograms of newly synthesized proteins from NIH/3T3 cell lines transformed by a variety of retroviral oncogenes, from cellular revertant lines, and from a line (433.3) which expresses the v-ras oncogene in response to corticosteroids. Most alterations in the synthesis of specific proteins detected by this approach appeared to be the result of selection during prolonged cultivation and were probably unrelated to the transformation process. However, we detected seven proteins whose synthesis was strongly suppressed in cell lines transformed by each of the six retroviral oncogenes we studied and whose production was fully or partially restored in two cellular revertant lines. Suppression of two of these proteins was also correlated with the initial appearance of morphological alteration during corticosteroid-induced oncogene expression in 433.3 cells. These proteins (p37/4.78 and p41/4.75) were identified as tropomyosins, a group of at least five cytoskeletal proteins. Transformation by the papovaviruses simian virus 40 and polyomavirus caused no suppression of synthesis of these tropomyosins. This indicates that suppression of tropomyosin synthesis is not a nonspecific response by cells to being forced to grow with the transformed phenotype but is specifically associated with oncogenesis by diverse retroviral oncogenes. The results are consistent with the hypothesis that the different biochemical processes initiated by expression of structurally diverse retroviral oncogenes may converge on a limited number of common targets, one of which is the mechanism which regulates the synthesis of tropomyosins.

Induction by asbestos fibers of anaphase abnormalities: mechanism for aneuploidy induction and possibly carcinogenesis.

Abstract: Syrian hamster embryo cells were treated with crocidolite asbestos at a dose (1 microgram/cm2) which was shown in previous studies to induce cell transformation and aneuploidy in these cells. Treatment of cells with asbestos induced a greater than 20-fold increase in the incidence of cells in anaphase with abnormalities, including lagging chromosomes, bridges, and sticky chromosomes. Asbestos fibers were observed in mitotic cells and appeared, in some cases, to be interacting directly with the chromosomes. From these studies, we propose that the physical interaction of the asbestos fibers with the chromosomes or structural proteins of the spindle apparatus causes missegregation of chromosomes during mitosis resulting in aneuploidy. These findings provide a mechanism, at the chromosomal level, by which asbestos and other mineral fibers might induce cell transformation and cancer.

The nude mouse in cancer research

Abstract: Publisher Summary The nude mouse is considered a marvel as a laboratory animal and in many respects is uniquely qualified for in vivo model studies of human cancer. Most human tumors have been transplanted to nude mice and tumor lines are established with varying degrees of ease. It is noted that the additional immunosuppression of the mice or the use of very young animals can increase tumor growth and malignant expression. Other variables that affect tumor transplantation include the health of the mice, site of injection of the transplant, and specific properties or requirements of the human tumor cells. Hormone-dependent human tumors are grown in nude mice, either in special sites or after hormonal supplement. It is observed that the tumor growth rates differ in nude mice and in cancer patient and this tumor heterogeneity occasionally result in the growth of selected tumor components. These differences do not necessarily demean the human tumor-nude mouse model, but is well in line with the changes occurring with time in the human patient tumors. Many tumor characteristics appear to be stable in the nude mouse, and it has been shown that tumor markers and secretion of certain hormones may be maintained in the xenografts.

Smooth muscle α-actin is a transformation-sensitive marker for mouse NIH 3T3 and Rat-2 cells

Abstract: Heteroploid mouse NIH 3T3 fibroblasts and several rat fibroblast strains (Rat-1, Rat-2 and REF-52) are cell lines of special interest in the field of carcinogenesis because of their extensive use as normal cells in transformation assays for putative cancer-causing genes. Exposure of these cells to carcinogenic chemicals or oncogenic DNA produces anchorage-independent cells with retracted cytoplasms that lack actin cables1–7. All human fibroblast strains, normal and transformed, synthesize two electrophoretic forms of actin (β- and γ-actin)8–10. In contrast, we discovered that early-passage mouse and rat strains synthesize abundant amounts of each of the three electrophoretic forms of actin (α-, β- and γ-actin) but mouse and rat cancer cells express only β- and γ-actins. We now show that in NIH 3T3 and Rat-2 fibroblasts a third actin, the smooth muscle α isoform, is abundantly co-expressed with β-and γ-actin. In every instance tested following transformation to tumorigenicity, the accumulation of a-actin messenger RNA and α-actin synthesis was greatly inhibited. Shutdown of α-actin expression thus appears to be a reproducible transformation-sensitive marker in rodent fibroblasts.

Gene Expression During Normal and Malignant Differentiation

Abstract: This book contains 18 selections. Some of the titles are: Exploring Carcinogenesis with Retroviral and Cellular Oncogenes; Retroviruses, Oncogenes and Evolution; HTLV and Human Neoplasi; Modes of Activation of cMyc Oncogene in B and T Lymphoid Tumors; The Structure and Function of the Epidermal Growth Factor Receptor: Its Relationship to the Protein Product of the V-ERB-B Oncogene; and Expression of Human Retrovirus Genes in Normal and Neoplastic Epithelial Cells.

Genetic suppression of tumor formation.

Abstract: Publisher Summary Genomic changes of all kinds, ranging from base substitutions, deletions, duplications, amplifications, and rearrangements, are characteristic of malignant cells. With respect to genetic suppression of tumor formation, genomic changes can play a crucial role in eliminating or silencing suppressor genes during tumorigenesis. The chapter provides one avenue for the loss of suppression that states that the loss of specific chromosomes from cell hybrids result in the re-emergence of tumor-forming ability that is initially suppressed. Another avenue—namely, the same process of chromosome re-arrangement that generates oncogene activity is also considered as a source of suppressor loss. In this context, cancer can be viewed as a disease of the genome in which chromosome instability lies at the heart of the process, generating the genotypic and phenotypic changes that typify the malignant disease. To assess the potential of tumor suppressor genes and gene products, it is often useful to re-examine the record of past studies as well as consider the application of novel molecular approaches.

Keratinocytes blocked in phorbol ester-responsive early stage of terminal differentiation by sarcoma viruses.

Abstract: It has been suggested that the initiation step in mouse skin carcinogenesis involves an alteration in epidermal-differentiation, as mouse basal keratinocytes exposed to initiators resist the arrest of cell growth that is normally associated with the induction of terminal differentiation by calcium ions. The growth of epidermal basal cells infected by Kirsten (Ki) or Harvey (Ha) sarcoma viruses is, however, arrested in response to calcium ions, although the cells do not progress through their entire maturation programme when a functioning ras gene of those viruses is expressed. If continuous proliferation in the differentiating cell layers is a requirement for tumour formation in skin, the response of sarcoma virus-infected cells seems inconsistent with the suggestion that an activated ras gene is sufficient to initiate skin carcinogenesis. We now show that sarcoma virus-infected keratinocytes, when induced to differentiate, are blocked at an early, reversible stage of maturation. Furthermore, the cells respond to phorbol ester tumour promoters by undergoing a phenotypic reversion to a less mature stage. These results suggest that activation of a ras gene can produce conditionally initiated cells, in which the full expression of tumorigenicity depends on exposure to tumour promoters.

Loss of polymorphic restriction fragments in malignant melanoma: implications for tumor heterogeneity

Abstract: Loss of genetic material at certain chromosomal sites is implicated in the etiology of retinoblastoma and Wilms tumor. Whether specific chromosomal deletions are associated with other types of human cancer needs to be explored. We have examined 24 melanoma cell lines, derived from 21 patients with nonfamilial malignant melanoma, for evidence of somatically induced hemizygosity or homozygosity. Twelve DNA probes, recognizing single-copy restriction fragment length polymorphisms (RFLP) determined by loci on 11 different chromosomes, were used to screen autologous combinations of melanoma cells and either B cells or fibroblasts. Loss of heterozygosity in melanoma cells was identified at 27 of 100 informative loci. These losses occurred at loci on 8 different chromosomes, and the frequency of loss at individual loci varied between 8% and 67%. We conclude that somatic mutations resulting in homozygosity or hemizygosity are common in melanoma and evidently not restricted to specific chromosomes.

Nonrandom loss of chromosome 15 in Syrian hamster tumours induced by v-Ha-ras plus v-myc oncogenes.

Abstract: Nonrandom chromosome rearrangements, observed in a variety of human and animal tumours1,2, are associated in some cases with enhanced expression or deregulation of cellular oncogenes3,4. Recently, it was shown that normal, diploid rodent cells are neoplastically transformed following transfection with two cooperating oncogenes, for example myc plus ras5–7. However, the number of steps necessary to convert a normal cell into a malignant cell is unknown. If activation of two oncogenes is sufficient for tumorigenicity, tumours derived from diploid cells tranformed by the transfected oncogenes may remain diploid or have only random chromosome alterations. We have performed cytogenetic analyses of tumours formed after transfection of Syrian hamster embryo cells with either v-Ha-ras plus v-myc DNAs or polyoma DNA alone. Whereas polyoma-induced, tumour-derived cells were diploid, tumours induced by v-Ha-ras plus v-myc oncogenes were monoclonal and had a nonrandom chromosome change, monosomy of chromosome 15. Thus, an additional change, loss of chromosome 15, is required for or is advantageous for tumorigenicity induced by v-Ha-ras plus v-myc oncogenes. These results suggest that the neoplastic progression of normal, diploid cells requires more than two steps under certain conditions.

Loss of the normal N-ras allele in a mouse thymic lymphoma induced by a chemical carcinogen

Abstract: Young mice injected with the carcinogen N-nitroso-N-methylurea develop thymic lymphomas 2-4 months later. We previously have shown that these tumors frequently contain an activated N-ras gene that can transform rodent fibroblasts in vitro. We report here the intron/exon structure of such an activated N-ras gene and the sequence of its four coding exons. A single nucleotide change is responsible for the transforming alteration, a C----A transversion in the first base of codon 61. Through the use of synthetic oligonucleotides as hybridization probes, we show that this tumor lacks the normal allele of the N-ras gene. The implications of this finding for oncogene dominance are discussed.

Immunocytochemical demonstration of p21 ras family oncogene product in normal mucosa and in premalignant and malignant tumours of the colorectum.

Abstract: Study of the distribution of the p21 ras oncogene product as demonstrated by monoclonal antibody Y13-259 shows this protein to be apparently present in all epithelial populations of both premalignant and malignant tumours and throughout the normal foetal and adult epithelial crypt population in the colorectum. Metastatic tumour in liver shows a similar staining pattern which is less intense however than in the surrounding normal hepatocytes. Our results suggest that the presence of this protein is a widespread feature of normal cellular metabolism in certain cell types and is not restricted to those actively involved in cellular proliferation. It appears, furthermore, that neither cells at different stages of carcinogenesis nor those representing variants of a malignant phenotype can be identified using this particular antibody.

Modulation of cell communication and carcinogenesis.

Abstract: In this paper, recent studies on the role of cell communication in cancer induction, particularly in two-stage carcinogenesis, were reviewed. Cell communication has been proposed to play an important role in cell growth and differentiation since its discovery. The recent finding that tumor promoters inhibit cell communication supports this possibility. The inhibition of cell communication by phorbol ester tumor promoters was also shown to correlate with enhancement of in vitro carcinogenesis in Balb/c 3T3 cells. This strongly suggests that the blocked cell communication may play a crucial causative role in the process of carcinogenesis.Accumulated evidence indicates that phorbol ester may induce blockage of cell communication through binding to its membrane receptor which is presumably Ca2+/phospholipid-dependent kinase. cAMP enhances cell communication and protects its inhibition by phorbol ester, presumably through activating cAMP-dependent kinase. This indicates the possibility that the two kinases may be key elements for physiological regulation of cell communication. It is proposed that the disturbance of the kinase systems by endogenous and exogenous factors may be responsible for the promotion phase of cancer induction.However, the true physiological role of cell communication in carcinogenesis remains to be demonstrated more directly. Especially, what kinds of molecules can pass through the gap junction and regulate cell functions in a cell community must be challenged in future. Some such molecules were speculatively described in this review.