The approaching era of the tumor suppressor genes

Chromosomal abnormalities and related events in prostate cancer

The amount of cytogenetic information on prostate cancer is relatively sparse when compared with that on other common adenocarcinomas. This is primarily due to frequent overgrowth in culture of the cancer cells by normal (diploid) cells. Although newly introduced techniques of in situ hybridization will undoubtedly reveal chromosome changes in a high percentage of primary and noncultured prostate cancers, such information is at present essentially limited to numeric changes, with structural changes (eg, translocations and deletions) not being readily or reliably ascertained with presently available in situ approaches. Future developments are likely to overcome these shortcomings and, thus, make possible detailed analysis of karyotypes in prostate cancer in a much higher proportion of these tumors than available up to now. The cytogenetic data on prostate cancer in the literature are reviewed in this article and, based on the frequent involvement of some chromosomes (nos. 2, 7, 8, 10, and 16) in and molecular data on prostate cancer, a suggested multistep process for the development of prostate cancer is presented. The steps in this process may not apply to all prostate cancers or in fact be the definitive ones, but the suggested scheme does indicate that a number of ordered genetic events are involved in the process of prostate cancer genesis. Epidemiologic and familial aspects of prostate cancer also have been discussed in this review as they might relate to the genetics of the disease.

Selection of appropriate cellular and molecular biologic diagnostic tests in the evaluation of cancer

In this article, the use of cellular and molecular markers to diagnose and stage tumors is discussed. Their role in the evaluation of tumor prognosis and tumor susceptibility also is covered. The immunologic, cytogenetic, and molecular phenotype is discussed. Traditional markers are compared with newer methodologic approaches including evaluation of oncogenes, tumor suppressor genes, and genes that predict tumor susceptibility. These discussions are presented in relation to specific tumors. Finally, statements one might use to decide which tests to perform are presented.

Constitutional translocation (8;13) in a patient with non-Hodgkin's lymphoma

We report a case of non-Hodgkin's lymphoma in a 16-year-old male, whose peripheral white blood cells have a t(8;13)(q24;q14). There are no previous reports that describe this association. Although the tumor cells were not studied, we discuss the possible link between this finding and the development of the malignant lymphoma.

The cell-cell channel in the control of growth

Several lines of evidence indicate that the cell-cell channels in gap junction are conduits for growth-regulating signals. Experimental upregulation of the channels by retinoids causes inhibition of cellular growth and, conversely, their downregulation by oncogenes, e.g. activated src, stimulates growth. In either direction, the extent of growth correlates tightly with the degree of communication. Cogent evidence of the channel's function in growth regulation is now on hand: incorporation of a channel-protein gene into the genome of a transformed communication-deficient cell line normalizes communication and growth. The current data conform to a model of growth control with discrete regulatory centers.

Oncogenes in gynecological tumors

Evidence is increasing that proto-oncogenes and cancer suppressor genes are involved in the development and/or progression of gynecological malignancies. While histopathologic examination remains an indispensable tool of the surgical pathologist in the diagnosis and evaluation of patients with gynecological malignancies, the advancement to technology and the development of new knowledge regarding neoplastic transformation are providing a basis for new opportunities to improve patients care. These new opportunities will depend on the use of the skills and reagents developed in the basic medical science laboratories. Thus, it is important for those in the field of diagnostic pathology to begin to acquire a knowledge of proto-oncogenes and cancer suppressor genes as well as a basic understanding of the techniques used to detect and evaluate them.

Flow cytometric measurements of somatic cell mutations in Thorotrast patients

Exposure to ionizing radiation has long been well-recognized as a risk factor for cancer development. Since ionizing radiation can induce mutations, an accurate way of measuring somatic mutation frequencies could be a useful tool for evaluating cancer risks. In the present study, we have examined in vivo somatic mutation frequencies at the erythrocyte glycophorin A (GPA) and T-cell receptor (TCR) loci in 18 Thorotrast patients who have been continuously irradiated with alpha-particles emitted from the internal deposition of thorium dioxide and who thus have increased risks of certain malignant tumors. When compared with controls, the results showed a significantly higher frequency of mutants at the lymphocyte TCR loci but not at the erythrocyte GPA loci in the Thorotrast patients. The discrepancy between the results of the two assays is discussed.

Genes associated with tumor suppression and growth control in the human nervous system

Cancer, the uncontrolled proliferation of a population of somatic cells, is fundamentally a genetic disorder. Although the specific array of genetic changes causing individual tumor types remains largely obscure, the past two decades have witnessed a tremendous increase in our understanding of the specific genes regulating cell differentiation, proliferation, and senescence. There appear to be two distinct fundamental genetic mechanisms of tumorigenesis. One mechanism is associated with the activation of growth-promoting factors such as proto-oncogenes. Alternatively, tumor formation may be induced as the result of the loss or inactivation of genes which normally regulate or suppress cell growth. These genes have been termed 'tumor suppressor' genes or 'anti-oncogenes'. This review focuses on the role of 'tumor suppressor' genes in tumor formation and growth control of the human nervous system.

Tumor suppressor genes

For the past decade, cellular oncogenes have attracted the attention of biologists intent on understanding the molecular origins of cancer. As the present decade unfolds, oncogenes are yielding their place at center stage to a second group of actors, the tumor suppressor genes, which promise to teach us equally important lessons about the molecular mechanisms of cancer pathogenesis.

Short-term treatment with gamma interferon induces stable reversion of ras-transformed mouse fibroblasts

Persistent revertants have been generated from NIH 3T3 cells transformed by an activated human Ha-ras gene after short-term gamma interferon treatment in the presence of the cardiac aminoglycoside ouabain. Normal fibroblastlike morphology and anchorage dependence are restored in revertants. Tumorigenicity in nude mice is abolished. The revertants continue to express high steady-state levels of the ras oncogene. Partial retransformation of reverted cells is induced after 5-azacytidine treatment or after infection with retrovirus vectors carrying the v-abl, v-fes, v-myc, or v-src oncogene. The revertants resist the transforming activities of the v-Ha-ras and v-mos oncogenes.

Allelotyping of human prostatic adenocarcinoma

Allelotyping (using at least one probe detecting a restriction fragment length polymorphism on each chromosomal arm, with the exception of the short arms of the acrocentric chromosomes), showed loss of genetic information in 11 of 18 prostate adenocarcinoma specimens analyzed (61%). Frequent allelic deletions were detected on the long arm of chromosome 16 (6 of 10 informative cases, 60%), on the short arm of chromosome 8 (3 of 6 informative cases, 50%), and on the short and/or the long arms of chromosome 10 (6 of 11 informative cases (10p), 55% and 4 of 13 informative cases (10q), 30%, respectively). No losses of alleles were detected in any case unless at least one of the chromosomes 8, 10, or 16 also showed deletions. The long arm of chromosome 18 also showed a high frequency of allelic deletions (3 of 7 informative cases, 43%). Allelic deletions on the following chromosomes were detected at lower frequencies: chromosomes 2, 3, 7, 12, 13, 17, 22, and XY. Tumors with allelic deletions on more than one chromosome had a higher histological malignancy grade. Tumors from patients with advanced disease all showed allelic deletions.

Classification of carcinogens: polemics, pedantics, or progress?

Rodent carcinogens may, for physiological or other reasons, induce cancer by a variety of mechanisms which vary in their ability to affect humans. While the current approach of some regulatory agencies to carcinogen risk assessment and regulation may possibly be justified with most genotoxic carcinogens, this is not true with all nongenotoxic carcinogens. Mechanisms attributable to high dose toxicity occasioned by misuse of the maximum tolerated dose concept, imbalancing of homeostasis, unphysiological conditions, and induced cellular proliferation are reviewed. The greatest present need for meaningful regulation of carcinogens is to obtain public acceptance of the fact that some carcinogens are species specific and probably will not exert their effects in humans.

Freedom from wholism in multicellular organisms: a possible role of tumor suppressor genes

Wholism, known as 'homeostasis' in multicellular organisms, is fundamentally expressed in the regulation of cell proliferation and of the metabolism of individual cells. Control mechanisms represent an overriding control of the autonomy of cells in multicellular organisms. Negative regulation by suppressor genes including tumor suppressor genes is essential to maintain homeostasis in these organisms. Without wholistic regulation, the cellular society of multicellular organisms would progress from bad to worse, with eventual destruction of the whole system. The enhancement of division and differentiation of cells transduced by water-soluble factors may be considered as the controlling structure on the tumor suppressor genes. In microevolution, cell killing by the immunosurveillance systems directed at the external environments has been avoided for the 'self' cells in general, since the multicellular organism may not be considered as only a crowd of single cells.

Loss of heterozygosity on chromosome 1p in thyroid adenoma and medullary carcinoma, but not in papillary carcinoma

We analyzed 53 loci on 21 chromosomes other than chromosome 4 to detect possible loss of heterozygosity in 31 thyroid tumors using polymorphic DNA markers that detect allelic deletions at specific chromosomal loci. Loss of heterozygosity on chromosomes 1, 7 and 12 was detected in one follicular thyroid adenoma, and on chromosome 1 in two medullary thyroid carcinomas. However, no loss of heterozygosity was detected at any of the loci examined in papillary thyroid carcinomas. These results suggest that chromosomal loss detected in thyroid adenoma is one of the signals for risk of premalignant transformation, and that inactivation of unknown genes on chromosome 1p contributes to tumorigenesis of medullary thyroid carcinoma. Some genetic changes other than chromosomal losses may participate in the tumorigenesis of papillary thyroid carcinoma.

Assignment of the human prohibitin gene (PHB) to chromosome 17 and identification of a DNA polymorphism

Prohibition is a recently identified antiproliferative protein whose exact role in the cell is under investigation. To determine the human chromosomal location of the prohibition gene (PHB) and whether this site corresponds to that of any suspected tumor suppressor gene, we have analyzed DNA from three sources by hybridization analysis: mouse--human hybrid cell lines, hybrid cell lines containing portions of human chromosomes, and human metaphase chromosomes in situ. All three techniques confirm a location in the region 17q21-q22, a region genetically linked to early-onset human breast cancer. Further analysis will be required to establish the significance of this relationship; Southern hybridizations show a polymorphic EcoRI site that may be useful for this purpose.

Cytogenetic analysis of hepatic cell lines derived from SV40-T antigen gene-harboring transgenic mice

A total of five hepatic cell lines were established from SV40-T transgenic mice at different stages of development. Karyotype analysis performed on these cell lines revealed 1) chromosomal instability manifested by numerous karyotypic alterations, 2) non-random numerical changes of chromosome number 18 and 3) frequent occurrence of marker chromosomes in four of the five lines. These findings indicate that genetic abnormalities occur very frequently in hepatocytes of the transgenic mice, most probably caused by the mutagenic action of T-antigen, raising the possibility that they play essential roles in initiation and progression in this model of murine hepatocarcinogenesis.

Loss of allelic heterozygosity at the harvey ras locus in human oral carcinomas

The Harvey ras locus was examined for restriction fragment polymorphism and loss of allelic heterozygosity in 62 oral cancer patients. Southern blot analysis on BamHI digests of the tumour tissue DNA, revealed 23 patients with H-ras-1 heterozygosity. The probes used to study the polymorphism were the BamHI 6.6-kb fragment encoding the complete H-ras-1 sequence plus the variable tandem repeat (VTR) region, and the 1-kb MspI fragment encoding the VTR region. The allelic heterozygosity was better resolved by PvuII and further confirmed by TaqI. In addition, TaqI digestion demonstrated a unique VTR rearrangement indicated by 2.1-kb, 0.9-kb and 0.6-kb fragments, implying additional TaqI sites, in three of the patients. Further analysis of matched tumor tissue and peripheral blood cell DNA from the same patient demonstrated tumor-associated loss of one of the allelic fragments in 7/23 (30%) of the patients with H-ras-1 heterozygosity. However, the loss was not significantly correlated to clinicopathological parameters staging the disease. Thus, our data showing loss of H-ras-1 alleles and VTR rearrangement, with relatively high incidence (9/23; 39%) in the oral cancer patients at various stages of the disease, implies H-ras-1 involvement as an early event in the process of oral carcinogenesis.

Synthetic androgens suppress the transformed phenotype in the human prostate carcinoma cell line LNCaP

Experiments have been designed to investigate hormonal effects on the human prostatic carcinoma cell line LNCaP in the presence of complete foetal calf serum. At physiological concentrations (3.3 x 10(-9)M), several derivatives of 17 alpha-methyl-testosterone led to a significant reduction of cell proliferation, inhibition of colony formation in soft agar, change of morphology, induction of a prostate specific mRNA and down-regulation of c-myc RNA. Two different antiandrogens, hydroxyflutamide and cyproterone acetate, were capable of reversing the effects exerted by the synthetic androgens on growth properties. The proliferation rate of control cells devoid of androgen receptor was not inhibited by synthetic androgens. Our results indicate that the cellular androgen response mechanism of LNCaP cells is intact and that synthetic androgens elicit androgen receptor mediated suppression of the transformed phenotype. Rare cases of remission of prostatic cancer on androgen treatment have been reported. LNCaP cells may be a model of an uncommon class of prostatic cancer which responds favourably to androgen treatment.

Transformation effector and suppressor genes

Much has been learned about the molecular basis of cancer from the study of the dominantly acting viral and cellular oncogenes and their normal progenitors, the proto-oncogenes. More recent studies have resulted in the isolation and characterization of several genes prototypic of a second class of cancer genes. Whereas oncogenes act to promote the growth of cells, members of this latter class of genes act to inhibit cellular growth and are believed to contribute to the tumorigenic phenotype only when their activities are absent. This new class of cancer genes is referred to by a number of different names including; anti-oncogenes, recessive oncogenes, growth suppressor genes, tumor suppressor genes and emerogenes. Although only a few of these cancer genes have been identified, to date, it is likely that many additional genes of this class await identification. A third class of genes, necessary for the development of the cancer phenotype, is comprised of the transformation effector genes. These are normal cellular genes that encode proteins that cooperate with or activate oncogene functions and thereby induce the development of the neoplastic phenotype. The inactivation of transformation effector functions would therefore inhibit the ability of certain dominantly acting oncogenes to transform cells. The approaches outlined here describe functional assays for the isolation and molecular characterization of transformation effector and suppressor genes.

Suppression of the translocated myc gene and expression of intracisternal A-particle genes in tumorigenic and non-tumorigenic hybrids between murine myeloma and normal fibroblasts

We have studied the tumorigenic potential of a series of independent intraspecies hybrid clones derived from fusion of murine myeloma (BALB/c) and normal fibroblasts (C3H). All of these hybrids grew as adherent cells and thus resembled the fibroblast phenotype. As judged by chromosome enumeration, these hybrids appear to retain the full complement of their parental cells. Three out of 4 hybrids tested were able to form colonies in soft agar and to grow as tumors in either nude or (BALB/c x C3H) F1 mice, albeit at a reduced rate. The 4th hybrid did not grow in agar, was non-tumorigenic and may have had a 2:1 fibroblast to myeloma genomic equivalence ratio. In contrast to the parental myeloma cells, all the hybrids exhibited restricted growth rates in serum-free medium. As in our previous sets of hybrids formed between myeloma and L-cells, expression of the Ig genes was inhibited in the new hybrids and the derived tumors. The constitutive expression of the translocated myc gene in the myeloma parental cells was decreased in the hybrids and in all their derived tumors. In contrast, all of the hybrid cell lines and the tumors express high levels of the intracisternal A particle mRNAs. Our results show that the tumorigenic phenotype of myeloma cells is either fully or partially suppressed in myeloma x fibroblast hybrids and that this may be due to the fact that expression of the translocated c-myc is suppressed. We suggest that, in addition to the translocated myc gene, myeloma cells contain other activated oncogene(s), and that the latter are responsible for the residual tumorigenic potential of the myeloma x fibroblast hybrids.

Expression and interactions of human adenovirus oncoproteins

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A genetic tool used to identify thioredoxin as a mediator of a growth inhibitory signal

Loss of sensitivity to growth inhibitory polypeptides is likely to be one of the events that participates in the formation of some tumors and might be caused by inactivation or loss of the genetic elements that transduce these extracellular signals. The isolation of such a gene was achieved by randomly inactivating genes by an anti-sense complementary DNA expression library followed by direct selection for growth in the presence of an inhibitory polypeptide. Thus, a gene whose inactivation conveyed growth resistance to interferon-gamma (IFN-gamma) was isolated. Sequence analysis showed complete identity with human thioredoxin, a dithiol reducing agent, implicated here in the IFN-gamma-mediated growth arrest of HeLa cells.

A case of pheochromocytoma associated with meningioma

We have recently observed a rare case of pheochromocytoma associated with meningioma. To determine the mechanism of such a coexistence in this particular case, we compared the constitutional and pheochromocytoma genotypes of the patient using polymorphic four DNA markers, and we found a loss of heterozygosity at the D1S7 locus. A loss of heterozygosity at this locus has previously been reported by Mathew et al. in pheochromocytoma patients, and our results were in agreement with that study. Therefore the allelic deletion at the D1S7 locus may be an important step in the tumorigenesis of pheochromocytoma in this case.

Overview: genes that predispose to cancer

Heredity and environment both operate in the origin of cancer. Dominantly heritable cancer is caused by 'cancer' genes that impart high relative risks but account for only a small part of the incidence of cancer; they are usually recessive in oncogenesis, mutation or loss of the second allele being necessary. Non-hereditary forms of cancer may involve the same genes. Other genes interact with environment in carcinogenesis; these may impart relatively small relative risks, but because their frequencies may be high, the attributable risks can be great, as probably is the case with lung cancer. The process of carcinogenesis is thought to involve 2 or more somatic genetic events in most cases. The genes whose germline mutations cause dominantly inherited cancer can also be mutated somatically to cause non-hereditary cancer. Other genes may influence the numbers of target cells, or the proliferation of once-hit stem cells, without being critical events on the path to cancer. However, such genes could greatly influence the incidence of a cancer. Other genes, such as that for Bloom's syndrome, may affect the rates at which first and second events occur. Finally, other genes may influence the occurrence of events critical for progression and metastasis, such as vascularization of a small tumor.

Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells

Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development.

Detection of somatic DNA alterations in ovarian cancer by DNA fingerprint analysis

The M13 phage single-strand DNA probe which recognizes highly polymorphic loci was applied to HinfI-digested DNA isolated from tumor tissue and peripheral leukocytes from 20 patients with ovarian cancer. An average of 22 minisatellite-containing DNA fragments were observed per individual. DNA fingerprint analysis revealed a change in restriction-fragment-length patterns in the DNA from 12 of 20 (60%) tumors compared with the patient's constitutional DNA. Deletion of one or more bands from the tumor was recognized by the probe in seven cases, new bands were identified in two, and intensity shift was demonstrated in eight. The authors conclude that the unmapped M13 minisatellite probe is a useful method for identifying cancer-related somatic DNA alterations.

A cellular protein that competes with SV40 T antigen for binding to the retinoblastoma gene product

Tumour-suppressor genes, such as the human retinoblastoma susceptibility gene (Rb), are widely recognized as being vital in the control of cell growth and tumour formation. This role is indicated, in part, by the suppression of tumorigenicity of human tumour cells after retrovirus-mediated Rb replacement. How Rb acts to bring about this suppression is not clear but one clue is that the Rb protein forms complexes with the transforming oncoproteins of several DNA tumour viruses, and that two regions of Rb essential for such binding frequently contain mutations in tumour cells. These observations suggest that endogenous cellular proteins might exist that bind to the same regions of Rb and thereby mediate its function. We report here the identification of one such human cellular Rb-associated protein of relative molecular mass 46,000 (46K) (RbAP46). Two lines of evidence support the notion that RbAP46 and simian virus 40 T antigen have homologous Rb-binding properties: first, several mutated Rb proteins that failed to bind to T also did not associate with RbAP46; and second, both T antigen and T peptide (amino acids 101-118) were able to compete with RbAP46 for binding to Rb. The apparent targeting of the RbAP46-Rb interaction by oncoproteins of DNA tumour viruses strongly suggests that formation of this complex is functionally important.

Genetic basis of limited cell proliferation

Knowledge about the changes that occur as cells traverse their replicative lifespans grows apace, as evidenced by the articles in this issue. Controversy over the interpretation of this knowledge continues, however, and is indeed fuelled by new discoveries (e.g., see Cristofalo, 1990; Holliday, 1990; Smith, 1990). This paper makes a brief commentary on the problems of cellular ageing, with particular emphasis on the unfolding picture of the genetic control of ageing and longevity which derives from evolutionary theory (Kirkwood and Rose, 1991). The case is argued for a synthetic view which recognizes that the immediate causes of limited cell proliferation probably involve some form of active genetic control, but that the ultimate reason for cell ageing is found in evolutionary theories which suggest that the ageing process is not actively programmed and that senescence may be due to the accumulation of damage.

A comparison of induced mutation at homologous alleles of the tk locus in human cells

Using a restriction fragment length polymorphism which can distinguish the two copies of the thymidine kinase (tk) gene in the TK6 human lymphoblastoid cell line, we have identified heterozygous subclones with alternate active alleles. Quantitative mutagenesis studies with X-rays revealed a markedly different response, depending on which homolog carried the active allele. The slopes of the dose-response curves differed by approximately 10-fold for mutation of the two alleles and this relationship held true for several independently isolated cell lines. Only one of the cell lines showed a different response to ethyl methanesulfonate. There were no differences among any of the cell lines at the X-linked hprt locus. Analyses of TK- mutants recovered from these cell lines indicated that the reduced yield of mutants from the one allele may be due, at least in part, to a lack of a specific class of TK- mutant, that is, the slow-growing mutants which have been associated with large-scale mutagenic events.

Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells

Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development.

Amplification of oncogenes in mammary carcinoma shown by fine-needle biopsy

A procedure that measures the amplification of oncogenes in human cancer cells is described. The cells were obtained by fine-needle biopsy to allow repeated sampling from individual metastases. A drawback was the low number of cells obtained, but this could be overcome by using a slot-blot hybridization technique to measure gene amplification. Two patients with mammary cancer (primary tumors or metastases), analyzed for the levels of amplification of the oncogene erb-B2, are described in detail. This technique is suitable for analyzing alterations occurring during cancer progression and for identifying subgroups of mammary cancer with different characteristics.

1990 Richardson Lecture. Challenges for neurology in the nineties: will we survive?

It is a great honor for me to present the Richardson Lecture this year. Although I was not personally acquainted with Dr. Richardson, his contributions to Canadian neurology are legendary, not the least of which is immortalized in the disease he and his colleagues first described in 1964: Steele-Richardson-Olszewski syndrome.

I have entitled my talk “Challenges for Neurology in the 90s: Will We Survive?”, to highlight some of the issues that I believe are important for us to consider as we embark upon our academic enterprise during the last decade of the 20th century. There are a number of opportunities as well as, potentially, major difficulties that we face, and I wish to focus attention on some of them.

Progress in cancer

Definite progress has been made against cancer since the National Cancer Act was passed in 1971. Physicians are giving increased attention to cancer prevention. The exciting changes in molecular biology provide increased knowledge about basic mechanisms in tumor growth and metastases. Detailed discussions of two common solid cancers--breast and colorectal--attest to continuing advances in cancer diagnosis and treatment. All of these augur well for further progress in oncology. Continued research, basic and clinical, is mandatory.

Contributions of the Gordon-Kosswig melanoma system to the present concept of neoplasia

Modern cancerology is based on the oncogene concept. This is rather new. The idea of the oncogene, however, is old, and can be traced back to two sources, namely to "cancer families," reported in 1866 by P. Broka, and to "virus induced" neoplasia, detected by P. Rous in 1911. A gene which is--to my knowledge--the first reported oncogene by definition was detected in the little ornamental Mexican fish Xiphophorus by Myron Gordon, Curt Kosswig, and Georg Häussler in 1928 when they observed the terrible hereditary melanomas that we are now coming to understand and to compare with other kinds of neoplasms in Xiphophorus and in mammals, including humans. Although the Xiphophorus model was always modest in its claims, it has--sometimes too early in its history--contributed many facts to the present concept of neoplasia.

MC29-immortalized clonal avian heart cell lines can partially differentiate in vitro

We established quail clonal heart muscle cell lines from cardiac rhabdomyosarcomas developed in embryos injected in ovo with the MC29 virus containing the v-myc oncogene. These clones were characterized by means of antibodies detecting markers of striated muscle cells. Two clones were selected for further characterization on the basis of a distribution of myogenic markers similar to that in normal early embryonic cardiac muscle cells. However, these muscle markers progressively disappeared with time in culture. Cardiomyocytic differentiation could be reinduced in culture, by associating the avain cardiac cells with 3T3 cells in a defined synthetic medium. Muscle markers were then reexpressed in all cardiac cells as soon as Day 1 after coculture. Multiplication of cardiac cells continued at the same time. This is characteristic of cardiac clones since MC29-infected quail myoblasts and MC29-infected quail fibroblasts exhibited a split response to 3T3 association, i.e., decreased growth and enhanced differentiation. The cardiac clones were maintained in vitro for more than 60 generations (6 months) without morphological changes. To our knowledge, this is the first description of clonal embryonic avian heart cell lines.

Normal human chromosome 5, on which a familial adenomatous polyposis gene is located, has tumor suppressive activity

The suppressive activity of normal human chromosome 5 was detected by means of the chromosomal transfer technique using DT cells as recipients. A hybrid clone, which exhibited reduced tumorigenicity, contained chromosomal regions such as 5pter-p15, q21 and q33-qter. Since a familial adenomatous polyposis gene has been reported to be located at 5q21-q22, the suppressive activity of chromosome 5 might be due to this gene.

An appreciation of the maximum tolerated dose: an inadequately precise decision point in designing a carcinogenesis bioassay?

Cancers arise in specific tissues. One difficulty with the present definitions of the Maximum Tolerated Dose (MTD), as they pertain to the rodent cancer bioassay, is that they base MTD on relatively crude parameters associated with the well-being of the entire animal rather than with the lack of specific tissue toxicity. Additional factors that could be included in the MTD definition, or could be separately determined, are addressed. Many of these factors refer to toxic behavior in one or a few tissues and, if used in setting the MTD, may mask more relevant events occurring at higher dose levels in other tissues. Reducing the MTD to a level that fails to take into account pesticide or drug-related toxicity may lead to the loss of relevant information in the bioassay. It is concluded, therefore, that there are two possible approaches to a more appropriate use of the MTD. The highest dose of the test agent (MTD) may be chosen (i) to lie below the thresholds of carcinogenicity-related non-genotoxic toxicity or (ii) the present high level MTD may continue to be used and tumors that arise may be classified as being irrelvant to humans at some or all exposure levels. The latter approach is to be preferred. It has the potential to avoid missing high level effects of the test agent that may be relevant to the human population.

Identification of RB and p53 mutations in mouse lymphoma cell lines

We analyzed the genomic structure and mRNA of the RB and p53 genes in four mouse lymphoid leukemia cell lines (DL-1, DL-5, DL-8, and DL-12). Although no gross structural alteration of the RB gene was observed in any cell line, abnormalities of RB mRNA were detected in at least two cell lines. RB mRNA expression was greatly reduced in DL-12. In addition, cloning and sequencing analysis of the RB cDNA revealed that the RB mRNA in DL-8 had a 276-nucleotide deletion presumably consisting of exons 10, 11, and 12, suggesting that altered splicing resulted in the loss of these exons. Analysis of the p53 gene indicated that DL-5 had a deletion in both alleles and expressed a smaller mRNA. These results suggest that mutations of the RB or p53 genes, or both, are associated with lymphoid leukemogenesis in mice.

Two prostate carcinoma cell lines demonstrate abnormalities in tumor suppressor genes

Two prostate carcinoma cell lines, DU-145 and PC-3, were examined for abnormalities in the retinoblastoma (Rb) and the p53 putative tumor suppressor genes. We found an abnormal Rb gene product in DU-145 using Western blot analysis. Polymerase chain reaction amplification followed by direct DNA sequencing demonstrated a base substitution mutation that generates a stop codon in exon 21. On Northern, Southern, and Western blot analysis, the p53 gene and its product appear to be normal in DU-145. PC-3, however, failed to demonstrate expression of either the p53 transcript on Northern blot analysis or the p53 protein on Western blot analysis, while the Rb gene products appeared to be normal on both Northern and Western blot analysis. This work extends the correlation between abnormal expression of putative tumor suppressor genes and human malignancies.

Altered oncogenes in UV-transformed C3H 10T1/2 mouse cells: identification of mutated H-ras allele(s)

Ultraviolet (UV) light will transform mammalian cells in culture to a phenotype which is characteristic of in vivo neoplasia. The UV-transformed C3H 10T1/2 mouse cell lines, TU-2 and TU-3, were analysed to determine the molecular mechanisms which may account for their phenotype, and to determine the types of mutations induced by UV light. DNA-transfection assays indicated that the transformed phenotype of TU-2 could not be transferred to non-transformed recipient cells. Therefore, studies were initiated to determine the mutagenic effects of UV light with respect to cellular oncogenes. Northern blot analysis indicated that five of the oncogenes analysed (erb-A, erb-B, mos, myb, and N-ras) were not expressed at detectable levels. The steady-state mRNA levels of fos, K-ras, abl, sis, and src oncogenes were similar in the C3H 10T1/2 and TU-2 cells. The mRNA levels of three oncogenes, raf, myc and H-ras, were 1.5-2.0-fold greater in the TU-2 cells compared to C3H 10T1/2. Southern blot analysis of HpaII restriction digested TU-2 DNA indicated that the H-ras oncogene has undergone methylation changes. More extensive analyses of the H-ras locus in TU-2 demonstrated a deletion of the 3' end of the gene, that may involve two separate mutated alleles. This type of damage is consistent with the lesions associated with sister chromatid exchange. While the H-ras locus in the other UV-transformed line, TU-3, showed methylation changes, there were no large genetic mutations detected by Southern blot analysis. These results suggest that UV-irradiation in vitro induces endogenous DNA damage that includes methylation changes and large genomic alterations. Further analysis will be necessary to determine the extent to which each may be involved in cell transformation.