Homogeneously staining chromosomal regions contain amplified copies of an abundantly expressed cellular oncogene (c-myc) in malignant neuroendocrine cells from a human colon carcinoma

An initiation zone of chromosomal DNA replication located upstream of the c-myc gene in proliferating HeLa cells

Studies on origins of DNA replication in mammalian cells have long been hampered by a lack of methods sensitive enough for the localization of such origins in chromosomal DNA. We have employed a new method for mapping origins, based on polymerase chain reaction amplification of nascent strand segments, to examine replication initiated in vivo near the c-myc gene in human cells. Nascent DNA, pulse-labeled in unsynchronized HeLa cells, was size fractionated and purified by immunoprecipitation with anti-bromodeoxyuridine antibodies. Lengths of the nascent strands that allow polymerase chain reaction amplification were determined by hybridization to probes homologous to amplified segments and used to calculate the position of the origin. We found that DNA replication through the c-myc gene initiates in a zone centered approximately 1.5 kilobases upstream of exon I. Replication proceeds bidirectionally from the origin, as indicated by comparison of hybridization patterns for three amplified segments. The initiation zone includes segments of the c-myc locus previously reported to drive autonomous replication of plasmids in human cells.

Coupling of early response gene expression to distinct regulatory pathways during alpha-interferon and phorbol ester-induced plasmacytoid differentiation of B chronic lymphocytic leukaemia cells

Phorbol esters (phorbol 12-myristate 13-acetate; PMA) and alpha-interferon (alpha-IFN) act through divergent signal transduction pathways to induce B chronic lymphocytic leukaemia cells (B-CLL) to undergo plasmacytoid differentiation in vitro. By using a panel of PMA-inducible early response gene probes we show that these two different effectors are coupled to second messenger pathways that do not converge on a common gene regulatory programme in differentiation of B-CLL cells. Moreover, using the calcium ionophore, A23187, four distinct regulatory classes of early response gene could be defined implying that multiple regulatory pathways may mediate the process of terminal differentiation in B lymphocytes.

Expression of the avian gag-myc oncogene in Saccharomyces cerevisiae

The gag-myc oncogenic sequence of the avian retrovirus MC29 was first inserted in a multicopy expression vector allowing its expression in Saccharomyces cerevisiae. The oncogene transcripts were detected in yeast by Northern blot hybridization and gag-myc proteins were revealed by immunoprecipitation. On solid medium, the average size of gag-myc transformant colonies was smaller than control. In liquid cultures, the gag-myc strains had a doubling time of 4.7 h compared with 3.1 h in the controls. In one of the recipient strains, and after an initial transient period of 5 days, the gag-myc transformants became physiologically indistinguishable from control. In another recipient strain, the slow-growth phenotype is permanent. Plasmid instability is increased in gag-myc transformants. When a single copy of the gag-myc gene was inserted in a yeast chromosome, no phenotype was observed, showing that slow growth is the consequence of plasmid loss.

AIDS-related B-cell non-Hodgkin's lymphomas in direct blood-stream HIV-infected patients: pathogenesis and differentiation features

Six AIDS-related NHLs from direct blood-stream HIV-infected patients were characterized for clonality, maturation cell characteristics, activation of c-myc proto-oncogene and presence of HIV and EBV genomes. Four out of the 6 AIDS-related NHLs were of immature B-cell origin, contrasting with the lower frequency (2 out of 31) of immature B-cell NHLs occurring in HIV-negative patients. Moreover, 3 out of the 4 AIDS-related pre-B-NHLs were extranodal lymphomas. C-myc translocations or rearrangements were not found in Italian AIDS-related NHLs, unlike c-myc activation which had a high prevalence in the American series of AIDS-related NHLs. HIV and EBV are not, or only occasionally, directly involved in AIDS-related NHL pathogenesis since HIV genome has never been found in the neoplastic clones and EBV genome was detected in only 1 out of the 6 lymphomas analyzed.

c-myc overexpression is a tumor-specific phenomenon in a subset of human colorectal carcinomas

The transcriptional activity of the c-myc proto-oncogene was examined in 25 primary human colorectal carcinomas and their corresponding normal mucosae. The purpose was to determine whether the elevated levels of c-myc expression, frequently detected in this type of tumor, might be the consequence of alterations in the cell growth rate or the effect of a real transcriptional deregulation of the gene. In about 44% of the tumors the elevated c-myc expression was consequent to the enhanced growth rate of the neoplastic tissue, as estimated by the expression of the S-phase-specific histone H3 gene. In the other 56%, c-myc overexpression did not entirely depend on the proliferative activity of the neoplastic population. In this latter group, c-myc deregulation did not reside in structural modifications of the putative regulatory regions of the gene. Therefore, c-myc overexpression, at least in a subset of colorectal cancer, seems to be consequent to alterations in transregulative phenomena exerted on the c-myc gene by other genetic loci.

Enhanced expression of the sis and c-myc oncogenes in human meningiomas

In 19 human meningiomas (14 primary and four recurrent tumors and one tumor transplanted into athymic nude mice), oncogene expression, amplification, and rearrangement, and loss of heterozygosity on chromosome 22 were examined. Compared to nontumor brain tissue, there was greater than a fivefold expression of the sis oncogene in six (40%) of 15 tumors studied and of the c-myc oncogene in 12 (63%) of the total 19 tumors. Expression of the sis gene was lower in the recurrent tumors than in the primary cases, and there was no detectable expression in anaplastic meningioma cells. Rearrangement of the sis gene was found in one meningioma. Loss of heterozygosity on chromosome 22 was detected in two of the five informative heterozygous cases. Expression of the c-myc gene was higher in cases with a loss of heterozygosity than in those without. These results suggest that the sis and c-myc oncogenes are associated with tumorigenicity and that c-myc may induce meningiomas through loss of the putative tumor suppressor gene.

Cytogenetics and DNA amplification in colorectal cancers

In vitro cultivated cells of 28 colorectal cancers were analyzed for chromosomal abnormalities that might signal amplification of DNA, either as double minutes (DMs) or homogeneously staining chromosomal regions (HSRs). Cells derived from 18 tumors showed DMs in 10 to 100% of all metaphases examined. Surveys that employed a panel of available oncogene probes failed to detect amplification of a known cellular oncogene with the exception of three cases where the ERBB2 gene was amplified. In one of these three cases neither DMs nor HSRs were detectable. Our studies show that from 28 lines established in culture, 19 (68%) show amplification of DNA, and indicate that DNA amplification is a frequent genetic alteration in colorectal cancers in addition to other genetic changes. Amplification is correlated with high Dukes stage, but not with histological grade. The identity of the amplified DNA remains to be established for most cases.

Alterations in the cellular phenotype induced by herpes simplex viruses

Numerous studies have shown that herpes simplex virus types 1 and 2 (HSV-1, HSV-2) are able to transform the morphological phenotype of rodent cells. Unlike other DNA tumor viruses the transformed cells did not consistently retain or express a given set of viral genes. In fact, transformation could be obtained using fragments of viral DNA that did not wholly encode viral proteins. Of interest within the transforming fragments were sequences which could assume a secondary structure like that of insertion elements. The failure to detect viral DNA in transformed cells led to the hit-and-run hypothesis of HSV transformation. The mechanism by which HSV induces transformation is not understood. Various lines of investigation have shown that HSV is able to cause mutations--both point mutations and gene rearrangements. HSV is also able to induce gene amplification, particularly of sequences harboring an origin of replication such as SV40 or papillomaviruses. Other experiments have shown that HSV can activate the expression of endogenous type C retroviruses. More broadly, HSV has been shown to activate cellular transcription or to switch on the synthesis of host cell proteins not normally expressed in untransformed cells. The failure to detect viral DNA in a high proportion of human anogenital tumors made it difficult to implicate HSV in the etiology of those neoplasias, but it is consistent, however, with the observations on the mode of HSV transformation in vitro, and suggests that HSV could be involved in a multistage process of oncogenic transformation.

N-myc gene is amplified in alveolar rhabdomyosarcomas (RMS) but not in embryonal RMS

DNA from 13 (6 alveolar and 7 embryonal) childhood rhabdomyosarcomas (RMS) was examined to determine the incidence and prognostic relevance of N- and c-myc genes. Southern analysis showed 5- to 20-fold amplification of N-myc gene in 4 of 6 alveolar but in none of 7 embryonal RMS (p less than 0.04; Fisher's exact test). The number of children who died with multiple- and single-copy N-myc gene was 4/4 and 5/9 respectively (p greater than 0.05; Chi-squared test). There was no statistically significant correlation between N-myc amplification and age, gender, site, stage or survival time. There was no amplification or gross rearrangement of c-myc in any of the 13 RMS.

Normal diploid human and rodent cells lack a detectable frequency of gene amplification

Gene amplification is frequently observed in tumors and transformed cell lines. This phenomenon is known to contribute to the generation of drug-resistant tumor cells and quantitation of the event is believed to have prognostic value in several types of neoplasias. To date, most studies of gene amplification have used immortalized cell lines and biopsied tumor samples. In this study I examine the amplification potentials of primary diploid cells, both human and rodent, and quantitatively compare them to the amplification potentials of their transformed counterparts. I have used a strictly defined protocol (i.e., selection at a stringency of 9 X LD50) to measure amplification potential at two loci, the gene for the multifunctional protein containing activities for carbamoyl phosphate synthase, aspartate transcarbamylase, and dihydroorotase (CAD) and the gene for dihydrofolate reductase (DHFR). I find that the frequency of amplification in transformed cells is at least four orders of magnitude greater than that in normal cells. Out of 29 cell populations studied, the 7 diploid normal cell populations exhibited no detectable amplification frequency (limit of detection at 10(-8) whereas the 22 transformed cell lines demonstrated amplification frequencies between 10(-3) and 10(-7). These results demonstrate that a dramatic difference exists between primary diploid cell populations and immortalized cell populations in their ability to amplify genomic sequences and suggests a significant difference in genetic stability between these two cell types.

Oncoprotein stability after tumour resection

The means by which oncogenes and their products activate malignant transformation are currently under intense investigation. However, published papers on experiments using human tumour material do not always report in detail their methods of collection or storage of the specimens. In order to assess the stability of oncogene encoded proteins following collection or storage of human tumour biopsies, we have examined the rate of decay of the c-myc, neu and EGF-receptor proteins. Solid tumours, containing amplified copies of each oncogene, were established in nude mice and the stability of the oncogene protein in portions of each tumour, left in phosphate buffered saline at room temperature for varying time intervals, was examined by immunoblotting. Intact EGF-receptor and neu oncoproteins were present even after 24 h under these conditions while the c-myc protein was apparently rapidly degraded after 20 min. These data demonstrate that oncogene products decay at different rates after tumour resection and that collection of human biopsies should take this into account in order to provide the basis for consistent measurements of protein expression.

Patterns of nuclear proto-oncogene expression during induced differentiation and proliferation of human B chronic lymphocytic leukaemia cells

Phorbol ester-induced differentiation of human B-chronic lymphocytic leukaemic cells was found to be preceded by a rapid transient induction in expression of the c-jun proto-oncogene, which paralleled that of c-fos. Induced expression of c-myc but not of c-fos/c-jun proto-oncogenes was markedly higher in a proliferating variant leukaemic cell population compared with that seen in typical lymphocytic leukaemia cells. These data suggest that the c-fos/c-jun nuclear oncogenes play a role in induced differentiation, whilst c-myc is more important in the proliferative response of B lymphocytes.

Modulation of c-myc expression by transforming growth factor beta 1 in human hepatoma cell lines

The effects of transforming growth factor beta 1 (TGF-beta 1) on cell proliferation of human hepatoma cell lines, PLC/PRF/5 and Mahlavu, were investigated under serum-free conditions. DNA synthesis was strongly inhibited in the PLC/PRF/5 cells by addition of TGF-beta 1 (0.5 to 4.0 ng/ml), but remained unchanged in the Mahlavu cells. Also the expression of c-myc mRNA was suppressed by the addition of TGF-beta 1 in the PLC/PRF/5 cells but not in the Mahlavu cells. These results indicate that TGF-beta 1 might regulate cell growth, in part, by modulating c-myc expression, although there is no direct proof that c-myc expression is really relevant to DNA synthesis mediated by TGF-beta 1.

DNase I-defined chromatin configuration of the human CD3 gene cluster

The three CD3 genes on human chromosome 11q23 encode proteins (gamma, delta and epsilon) which form part of the antigen receptor on T lymphocytes. All three genes are clustered within 50 kb and are activated approximately contemporaneously during the early stages of T cell ontogeny. In order to pinpoint potential regulatory sequences important for locus activation and tissue-specific gene expression, the chromatin structure of almost 90 kb of this region has been probed in five cell lines using the endonuclease pancreatic DNase I. A set of DNase I hypersensitive (HS) sites has been defined in T cell chromatin, five of which were strong and not found in non-T cells, with the exception of the erythroleukaemia cell line K562, in which three sites were weakly expressed, correlating with a low level of delta mRNA. The subset of five HS sites map close to the CD3 genes and lie in regions which contain elements of defined function: the gamma promoter; the delta promoter and its 3' enhancer; and the epsilon promoter and its 3' enhancer. Since no further major T cell-restricted HS sites lie within the 90kb of the CD3 locus analysed, these five regions may contain all the sequences important for CD3 gene expression.

Expression of the MyoD1 muscle determination gene defines differentiation capability but not tumorigenicity of human rhabdomyosarcomas

Several human rhabdomyosarcoma cell lines, cultured primary tumor explants, and biopsies of tumor and normal skeletal muscle tissue expressed a 2.0-kilobase transcript that hybridized to the mouse muscle determination gene MyoD1. This transcript was found in tumor cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines derived from other mesenchymal tumor cell types. Expression of the human homolog of MyoD1 therefore can define a tumor as a rhabdomyosarcoma. Transfection of the mouse MyoD1 gene into the human rhabdomyosarcoma cell line RD increased the ability of the tumor cells to differentiate into multinucleated myotubes and enhanced myosin heavy-chain gene expression but did not decrease tumorigenicity in nude mice.

Activation of proto-oncogenes: an immediate early event in human cytomegalovirus infection

A rapid increase in the RNA levels of the proto-oncogenes c-fos, c-jun, and c-myc was detected after human cytomegalovirus infection. Neither inactivation of viral infectivity with ultraviolet irradiation (with or without psoralen), nor inhibition of translation with cycloheximide or anisomycin adversely affected the enhanced expression of proto-oncogenes, even though these treatments substantially reduced or eliminated the detection of immediate early viral antigens. The increase in the RNA levels of the proto-oncogenes was prevented in the presence of alpha-amanitin or actinomycin D. Thus, expression of these oncogenes appears to be induced by events occurring before the onset of viral protein synthesis, perhaps by the interaction of viral particles with the cell surface.

Amplified N-myc in human neuroblastoma cells is often arranged as clustered tandem repeats of differently recombined DNA

Human neuroblastoma cells often carry amplified DNA encompassing the gene N-myc. Amplified N-myc has been found localized in "double minutes" in direct tumor cell preparations. In contrast, later passages carried amplified N-myc almost exclusively within a single homogeneously staining chromosomal region located at a chromosomal site different from the normal location of N-myc. We used pulsed field gel electrophoresis to define the structural arrangement of the amplified DNA. Long-range mapping was facilitated by the presence of several sites for rare cutting restriction endonucleases in the 5' region of N-myc. Amplified DNAs of different neuroblastoma cell lines were heterogeneous in size and had undergone recombination at various distances from N-myc. N-myc occupied a central position within the amplified DNA, and in no case was the coding region affected by recombination. Among neuroblastoma cells, varying proportions of amplified DNA (in some instances close to 100%) consisted of multiple tandem arrays of DNA segments ranging in size from 100 to 700 kilobase pairs. Tumor cells with low degrees of amplification revealed regions of amplified DNA in excess of 1,500 kilobase pairs without apparent rearrangement. Our observations, in concert with the cytogenetic findings, suggest a model of gene amplification which involves unscheduled DNA replication, recombination, and formation of extrachromosomal DNA followed by integration into a chromosome and subsequent in situ multiplication. The central position which N-myc occupies within the amplified sequences and the lack of recombination within the coding region of N-mc indicate that N-myc rather than other genetic information provides the selective advantage for retention of the amplified DNA.

P47 phosphoprotein of blood platelets (pleckstrin) is a major target for phorbol ester-induced protein phosphorylation in intact platelets, granulocytes, lymphocytes, monocytes and cultured leukaemic cells: absence of P47 in non-haematopoietic cells

Aggregating agents including phorbol esters which activate protein kinase C induce the rapid phosphorylation of a Mr = 47,000 cytosolic protein in blood platelets (P47 or pleckstrin). This protein is well resolved by analytical 16-BAC----SDS two-dimensional PAGE and was purified from platelets by preparative 16-BAC----SDS PAGE. Polyclonal antibodies were raised to the protein in mice and rabbits. These antisera detected a single protein with the migration of P47 on Western blots of platelet extracts, and the rabbit antisera immunoprecipitated 32P-labelled P47 from platelet cytosol. The presence of P47 in other haematopoietic cells was determined by prelabelling them with 32P and observing increased 32P incorporation into the location of P47 on autoradiographs of 16-BAC----SDS analytical PAGE of cells exposed to phorbol ester. The identity of the phosphoprotein found in this location was further established by probing Western blots of SDS PAGE gels of cultured cell lines with the P47 antisera. P47 was detected in peripheral blood lymphocytes, monocytes and granulocytes (including the granulocytes of two unrelated patients with X-linked chronic granulomatous disease). P47 was also found in HL-60 promyelocytes (especially after differentiation with retinoic acid), U937 histiocytes, HEL leukaemia cells, and Raji 'B' lymphoblasts. It was not detected in normal erythrocytes, K562 leukaemic cells, MOLT-3 'T' lymphoblasts, or in wide range of non-haematopoietic cell lines. We conclude that P47 is a major target for the action of phorbol ester induced phosphorylation in platelets, normal leucocytes and some haematopoietic cell lines. These cells have as their common feature the ability when stimulated to develop adhesive functions on their plasma membranes.

Different pattern of expression of cellular oncogenes in human non-small-cell lung cancer cell lines

Altered and deregulated cellular oncogenes were found in many human solid tumors. Except for a few types of tumors that consistently exhibited specific altered proto-oncogenes, the majority of tumors are associated with a number of transcriptionally activated cellular oncogenes. In the heterologous group of non-small-cell lung cancer (NSCLC), nothing about a specific pattern of proto-oncogene expression is known. Therefore, we investigated the expression of a panel of cellular oncogenes in NSCLC cell lines. DNA and RNA from 11 established NSCLC cell lines (4 adenocarcinoma cell lines, 3 squamous cell carcinoma cell lines, 3 large-cell carcinoma cell lines and 1 mesothelioma cell line) were isolated and analysed using the Southern, dot blot and Northern hybridization technique. c-myc RNA expression was found in all NSCLC cell line, L-myc expression only in 1 adenocarcinoma cell line, N-myc and c-myb expression in none of the 11 cell lines examined. No c-myc amplification could be detected in the DNAs. v-sis-related mRNA was observed in 5/11 cell lines without association to a specific NSCLC subtype. v-src-related mRNA, found in all tested cells, exhibited increased levels in 1 adenocarcinoma cell line (A-549) compared to the other cell lines. Binding sites for epidermal growth factor (EGF) had been described previously in NSCL, therefore we found erbB homologue transcripts coding for the EGF receptor in all NSCLC cell lines. Also, c-raf1-, N-ras-, Ki-ras-, and H-ras-related RNA expression was observed in all lines. We conclude that L-myc, N-myc, and c-myb expression does occur less frequently in NSCLC than in SCLC. Also amplification does not appear to be an important mechanism by which the c-myc proto-oncogene is activated in NSCLC. A specific pattern of oncogene expression could not be detected in NSCLC cells; each cell line examined showed its own pattern. However, transcriptional activation of a proto-oncogene like erbB, ras, raf, src, and c-myc, which are all involved in the progression pathway of EGF, may be a common feature of NSCLC.

Amplification of cellular oncogenes: a predictor of clinical outcome in human cancer

Increased dosage of cellular oncogenes resulting from amplification of DNA is a frequent genetic abnormality of tumor cells and the study of oncogene amplification has been paradigmatic for the usefulness of molecular genetic research in clinical oncology. Certain types of human tumors carry an amplified cellular oncogene at frequencies of up to 50-60%. Human neuroblastoma has been prototypic for the importance of oncogene amplification in tumorigenesis, and evidence is emerging that amplification may be an early event involved in a more malignant form of this cancer. It is unclear at which stage amplification plays a role in other cancers. Amplification of cellular oncogenes is a good predictor of clinical outcome in some human malignancies.

Activation of the pp60c-src protein kinase is an early event in colonic carcinogenesis

Colonic neoplasia provides an opportunity to study tumor progression because most carcinomas arise from adenomas (polyps), which, in turn, arise from normal epithelia. The malignant potential of adenomas varies with size, histology, and degree of dysplasia. Polyps that are less than 2 cm with villous architecture and severe dysplasia are most likely to contain carcinoma. Previous studies demonstrated that the in vitro protein-tyrosine kinase activity of pp60c-src from colon carcinomas is significantly higher than that from adjacent normal mucosa. Here we report that the protein kinase activity of pp60c-src is also elevated in colonic polyps. Activity is highest in malignant polyps and in greater than 2-cm benign polyps that contain villous structure and severe dysplasia. Thus, pp60c-src activation occurs in benign polyps that are at greatest risk for developing cancer. These data suggest that activation of the protooncogene product pp60c-src may be an important event in the genesis of human colon carcinoma.

Establishment of a human malignant meningioma cell line with amplified c-myc oncogene

A new cell line (KT21-MG1) has been established from a human malignant meningioma transplanted into nude mice. The cultured cells showed epithelial cell-like morphology and were positive immunohistochemically for vimentin as the original tumor. They have been grown continuously in vitro for more than 2 years. The population doubling time was about 24 hours at the 30th passage. The cells are capable of proliferating in soft agar medium and produced tumors in nude mice, the histologies of which were similar to the original patient-derived tumor. Analysis of cellular oncogenes showed that myc and fps were amplified approximately tenfold and threefold, respectively, in this cell line, whereas N-myc, L-myc, N-ras, K-ras, H-ras, abl, erbB2, Blym, src, raf-1, myb, and sis were not changed significantly. The amplification of myc was accompanied by an enhanced expression. Chromosome studies of cultured cells showed the monosomy of chromosome 22 that has been reported to be a specific abnormality in meningiomas.

Oncogene expression in cholangiocarcinoma and in normal hepatic development

The expression of the proteins encoded by the ras, myc, and erb B-2 oncogenes was examined in 63 paraffin-embedded human cholangiocarcinomas of Thai and English origin using immunohistochemistry. The observed distributions were compared with oncogene expression in a series of human hepatocellular carcinomas. In an attempt to relate expression of these three oncogenes to specific stages of normal tissue differentiation, tissue sections of normal fetal, infant, and adult human livers were also examined. Of 63 cholangiocarcinomas, 59 (95%) expressed p62 c-myc, 47 (75%) expressed p21 c-ras, and 46 (73%) expressed p190 c-erbB-2. The expression of c-myc and c-ras but not of c-erb B-2 correlated directly with tumor differentiation as judged by morphologic criteria. No difference was observed in oncogene expression between intrahepatic and extrahepatic cholangiocarcinomas. Twelve of 14 hepatocellular carcinomas (86%) stained positively for all three oncoproteins. During normal liver development, expression of c-myc and c-ras was shown to occur from 18 weeks' gestation until 5 years of age, but not thereafter. Expression of c-myc, c-ras, and c-erbB-2 oncogenes may be used as immunohistochemical markers to distinguish cholangiocarcinoma from nonneoplastic biliary tissues, and may provide useful information concerning the cell biology of tumor differentiation.

Molecular genetic analysis of lymphoid tumors arising after organ transplantation

A variety of gene analyses were performed on lymphoid tumors from transplant patients who received cyclosporine A for immunosuppression. Epstein-Barr virus DNA was detected in the tumors, and the structure of circular episomal virus DNA was used as a measure of cell clonality. This analysis was correlated with clonality determined by study of immunoglobulin gene rearrangement. Some of the tumors had DNA rearrangements near the c-myc gene. Analysis suggested the pathogenesis of the tumors and indicated four categories of lymphoproliferation, three neoplastic and one reactive.

Amplified N-myc in human neuroblastoma cells is often arranged as clustered tandem repeats of differently recombined DNA

Human neuroblastoma cells often carry amplified DNA encompassing the gene N-myc. Amplified N-myc has been found localized in "double minutes" in direct tumor cell preparations. In contrast, later passages carried amplified N-myc almost exclusively within a single homogeneously staining chromosomal region located at a chromosomal site different from the normal location of N-myc. We used pulsed field gel electrophoresis to define the structural arrangement of the amplified DNA. Long-range mapping was facilitated by the presence of several sites for rare cutting restriction endonucleases in the 5' region of N-myc. Amplified DNAs of different neuroblastoma cell lines were heterogeneous in size and had undergone recombination at various distances from N-myc. N-myc occupied a central position within the amplified DNA, and in no case was the coding region affected by recombination. Among neuroblastoma cells, varying proportions of amplified DNA (in some instances close to 100%) consisted of multiple tandem arrays of DNA segments ranging in size from 100 to 700 kilobase pairs. Tumor cells with low degrees of amplification revealed regions of amplified DNA in excess of 1,500 kilobase pairs without apparent rearrangement. Our observations, in concert with the cytogenetic findings, suggest a model of gene amplification which involves unscheduled DNA replication, recombination, and formation of extrachromosomal DNA followed by integration into a chromosome and subsequent in situ multiplication. The central position which N-myc occupies within the amplified sequences and the lack of recombination within the coding region of N-mc indicate that N-myc rather than other genetic information provides the selective advantage for retention of the amplified DNA.

Expression of the MyoD1 muscle determination gene defines differentiation capability but not tumorigenicity of human rhabdomyosarcomas

Several human rhabdomyosarcoma cell lines, cultured primary tumor explants, and biopsies of tumor and normal skeletal muscle tissue expressed a 2.0-kilobase transcript that hybridized to the mouse muscle determination gene MyoD1. This transcript was found in tumor cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines and primary explants that developed multinucleated myotubes but was absent in Wilms' tumors or cell lines derived from other mesenchymal tumor cell types. Expression of the human homolog of MyoD1 therefore can define a tumor as a rhabdomyosarcoma. Transfection of the mouse MyoD1 gene into the human rhabdomyosarcoma cell line RD increased the ability of the tumor cells to differentiate into multinucleated myotubes and enhanced myosin heavy-chain gene expression but did not decrease tumorigenicity in nude mice.

Establishment of a human glioma cell line bearing a homogeneously staining chromosomal region and releasing alpha- and beta-type transforming growth factors

A human glioma cell line (YKG1), which was positively identified for glial fibrillary acidic (GFA) and S-100 proteins, was established from a surgical specimen of a patient with glioblastoma. Chromosome analysis of the cells revealed a homogeneously staining region (HSR) on a marker chromosome. The assay for transforming growth factors (TGFs) in the conditioned medium of the cell line revealed that it contained high levels of alpha- and beta-type TGFs, which might regulate the growth of glioblastoma and influence on the peritumoral tissues.

Loss of the MYC gene amplified in human HL-60 cells after treatment with inhibitors of poly(ADP-ribose) polymerase or with dimethyl sulfoxide

In HL-60 cells, a human promyelocytic leukemia cell line, the human c-myc gene, designated MYC, is amplified about 16-fold. On differentiation of the HL-60 cells into granulocytes induced by several inhibitors of poly(ADP-ribose) polymerase [NAD+ poly(adenosine diphosphate D-ribose)ADP-D-ribosyltransferase, EC 2.4.2.30] including benzamide, nicotinamide, coumarin, and 4-hydroxyquinazoline or dimethyl sulfoxide, some MYC loss was observed. In contrast, benzoic acid, a noninhibitory analogue of benzamide, did not induce either granulocytic differentiation or loss of MYC. Loss of MYC seems to be associated with granulocytic differentiation because the time course of its loss was similar to that of appearance of nitroblue tetrazolium-positive cells, mature granulocytes, and its loss was not observed on differentiation of HL-60 cells into macrophages induced by phorbol 12-myristate 13-acetate or teleocidin. The loss of MYC is not the reason for the down regulation of MYC expression observed within 1 hr after addition of inducers, since the loss of MYC was not detected by 1-day treatment with inducers.

Co-amplification of c-myc and c-erbB-2 oncogenes in a poorly differentiated human gastric cancer

c-erbB-2 oncogene has been reported to be frequently amplified in differentiated, tubular type of gastric cancer. Here we report a human gastric cancer which bore co-amplified c-myc and c-erbB-2 oncogenes: a portion of the amplified c-erbB-2 oncogene was found to be rearranged. Furthermore, c-myc and c-erbB-2 oncogenes were over-expressed in the tumor cells. In contrast to the previous reports, this gastric adenocarcinoma was classified as a poorly differentiated type, and was highly tumorigenic in nude mice. These results might suggest that activated c-myc and c-erbB-2 oncogenes co-operate and influence the malignant state of some gastric carcinomas.

Suppression of MYC by high expression of NMYC in human neuroblastoma cells

Members of the MYC gene family, including MYC, NMYC, and LYMC, have been found amplified and expressed at high level in various human cancers. We have analysed the expression of two members of the MYC gene family, NMYC and MYC, in human and murine neuroblastoma cells. Whenever NMYC and MYC are co-expressed, MYC expression predominates. Cells carrying high expression of NMYC as result of amplification lack MYC expression. The same is ture for neuroblastoma cells in which expression of a single-copy NMYC is upregulated or into which a vector forcing high expression of an exogenous NMYC had been introduced by transfection. Our studies indicate a regulatory interaction between MYC and NMYC in neuroblastoma cells.

A reversible selection system for UMP synthase gene amplification and deamplification

The bifunctional enzyme UMP synthase provides a unique reversible selection system whereby cells that have amplified the UMP synthase gene can be isolated from a wild-type population and cells that have deleted the extra genes can be selected from a population with amplified copies of the gene. UMP synthase catalyzes the conversion of orotic acid to orotidine 5'-monophosphate (OMP) and then OMP to UMP. In the amplification step, Chinese hamster lung cells are selected for resistance to pyrazofurin and 6-azauridine, two inhibitors of the orotidine 5'-decarboxylase activity that converts OMP to UMP. The resistant cells have increased levels of both activities of UMP synthase as a result of a stable amplification of the UMP synthase gene. The deamplification step depends on 5-fluorouracil (5FU), which is converted to its monophosphate form by the orotate phosphoribosyltransferase activity of UMP synthase. Thus cells with increases in this activity are more sensitive to 5FU cytotoxicity, permitting single-step selection of revertants that have lost their amplified UMP synthase genes. These 5FU-selected cells are similar to the parental cell line in their level of UMP synthase activity and number of UMP synthase gene copies. Reselection in increasing concentrations of pyrazofurin and 6-azauridine allows one to isolate cells that have reamplified the UMP synthase gene. The ability to cycle cells of a single lineage through states of amplification and deamplification will facilitate study of the gene amplification process and the factors that influence the composition and stability of amplified regions.

Analysis of polyadenylation site usage of the c-myc oncogene

The c-myc gene contains 2 well conserved polyadenylation (pA) sites. In all human and rat cell lines from various differentiation stages and tissue types the amount of mRNA terminating at the second pA site is 6-fold higher than the amount ending at the upstream site. This is not due to a difference in stability of the two mRNA types and therefore must be due to preferential usage of the downstream site. The usage of the pA sites is not altered during growth factor induction of quiescent cells. We have not been able to detect differences in behavior between mRNAs ending at either pA site. Both types of mRNA are induced upon treatment of cells with cycloheximide. Furthermore, we have shown that the poly(A) tail of c-myc mRNA is lost during degradation of the messenger, as was described previously for c-myc mRNA in an in vitro system. The time required for the loss of the poly(A) tail is similar to the half-life of c-myc mRNA.

RNA polymerase II transcripts as targets for 5-fluorouridine cytotoxicity: antagonism of 5-fluorouridine actions by alpha-amanitin

The cytotoxicity of 5-fluorouridine (FUrd) results from actions directed at the synthesis of both DNA and RNA. The role of mRNA as a target for FUrd was investigated by selectively decreasing the incorporation of FUrd into RNA polymerase II transcripts of K-562 erythroleukemia cells, which was accomplished by the addition of alpha-amanitin to cultures of K-562 cells permeabilized with lysolecithin. In these cells alpha-amanitin at concentrations of 1-5 micrograms/ml inhibited the incorporation of [3H]-uridine into polyadenylated RNA by up to 45% and decreased the steady-state levels of two specific mRNAs but had no effect on poly A- RNA synthesis. alpha-Amanitin decreased the incorporation of FUrd into poly A+ RNA by up to 60%. The decrease in FUrd incorporation produced by alpha-amanitin was accompanied by an antagonism of the growth inhibitory effects of the fluorinated pyrimidine nucleoside by the mycotoxin, as measured by both growth in suspension culture and colony formation in 0.12% agar. Antagonism between these agents increased as the concentration of alpha-amanitin was elevated; furthermore, it was sequence-dependent, occurring only when alpha-amanitin preceded FUrd. These findings provide evidence that the actions of FUrd directed against mRNA are antagonized when FUrd incorporation into mRNA transcripts is decreased and that the effects of FUrd on mRNA produce cytotoxic consequences.

Transformation of mouse mammary epithelial cells with the Ha-ras but not with the neu oncogene results in a gene dosage-dependent increase in transforming growth factor-alpha production

An enhanced expression of transforming growth factor-alpha (TGF alpha) was demonstrated in two clones of NOG-8 mouse mammary epithelial cells, NOG-8 SR1 and NOG-8 SR2, that have been transformed by a v-Ha-ras oncogene. The amount of TGF alpha production in NOG-8 SR1 and NOG-8 SR2 cells was dependent on the level of p21ras expression in these clones, which directly correlated with their cloning efficiency in soft agar. There was also a decrease in the number of epidermal growth factor (EGF) receptors on the NOG-8 SR1 and NOG-8 SR2 cells that is proportional to the amount of TGF alpha secreted. These effects were specific for ras because neu-transformed NOG-8 cells grew in soft agar at a comparable level to NOG-8 SR2 cells yet did not show any increase in TGF alpha production or change in EGF receptor expression.

Animal models of human disease. Pathology and molecular biology of spontaneous neoplasms occurring in transgenic mice carrying and expressing activated cellular oncogenes

This present review focuses on spontaneous neoplasms occurring in transgenic mice carrying and expressing activated cellular oncogenes. The historical development of transgenic mice as in vivo disease models is briefly traced, followed by a brief description of the actual technology in such systems. Additional emphasis is placed on the concept of targeting activated cellular oncogenes to specific tissues in transgenic mice. Cumulative experience with activated (Vmyc, ras, and neu (erb-B2] oncogenes in transgenic mice is considered in detail, with particular attention paid to the observed pathology, as well as to the kinetics of disease occurrence. It is concluded that transgenic mice offer the interested investigator(s) an excellent prospective, in vivo model of oncogenesis.

The PVT gene frequently amplifies with MYC in tumor cells

The line of human colon carcinoma cells known as COLO320-DM contains an amplified and abnormal allele of the proto-oncogene MYC (DMMYC). Exon 1 and most of intron 1 of MYC have been displaced from DMMYC by a rearrangement of DNA. The RNA transcribed from DMMYC is a chimera that begins with an ectopic sequence of 176 nucleotides and then continues with exons 2 and 3 of MYC. The template for the ectopic sequence represents exon 1 of a gene known as PVT, which lies 50 kilobase pairs downstream of MYC. We encountered three abnormal configurations of MYC and PVT in the cell lines analyzed here: (i) amplification of the genes, accompanied by insertion of exon 1 and an undetermined additional portion of PVT within intron 1 of MYC to create DMMYC; (ii) selective deletion of exon 1 of PVT from amplified DNA that contains downstream portions of PVT and an intact allele of MYC; and (iii) coamplification of MYC and exon 1 of PVT, but not of downstream portions of PVT. We conclude that part or all of PVT is frequently amplified with MYC and that intron 1 of PVT represents a preferred boundary for amplification affecting MYC.

The interleukin-1 receptor in Raji human B-lymphoma cells. Molecular characterization and evidence for receptor-mediated activation of gene expression

In a previous paper [Horuk, Huang, Covington & Newton (1987) J. Biol. Chem. 262, 16275-16278] we reported that there were fundamental differences in the biochemical properties of the interleukin-1 (IL-1) receptor between Raji and EL4 cell lines. In the present study we have investigated the basis for these differences. Kinetic studies measuring the on and off rates of IL-1 receptor binding revealed that the low-affinity IL-1-binding sites observed in Raji cells, compared with EL4 cells, result from a combination of a lower association rate and a higher dissociation rate in the Raji cells. The turnover of the Raji IL-1 receptor, measured by inhibiting protein synthesis with cycloheximide, was much faster than that of the EL4 IL-1 receptor, with a half-time of 2 h as against 5 h. Treatment of 125I-IL-1-labelled IL-1 receptors in Raji and EL4 cells with neuraminidase decreased their molecular mass by approx. 2-5 kDa as assessed by SDS/polyacrylamide-gel electrophoresis (PAGE). The covalently labelled IL-1 receptors in both cell types were sensitive to treatment with endoglycosidase F, which decreased their molecular mass on SDS/PAGE by 12-13 kDa. Incubation of Raji cells with maximally stimulating doses of IL-1 resulted in an increase in the nascent RNA levels of several genes, including the IL-2 receptor and the proto-oncogenes c-Ha-ras and c-myc.

c-myc oncogene expression and clinical outcome in carcinoma of the cervix

The expression of the c-myc oncogene was studied in paraffin-embedded specimens of cervical biopsies using a monoclonal antibody which binds to the 62,000 Dalton protein encoded by the c-myc gene. A range of cervical cancers from intraepithelial neoplasia to advanced grade IV tumours were studied together with normal cervical biopsies; c-myc status was correlated to clinical progress. There was no correlation seen between the clinical stage of the disease at presentation and c-myc expression. The 15 patients with c-myc negative cervical cancers were shown to have better disease free (mean--95.4 mos) and total survival (mean 118.0--mos) compared to the 16 patients that were c-myc positive 28.4 and 48.4 mos respectively). The pattern of recurrence differed between the two groups with c-myc positive tumours more likely to develop extra pelvic metastatic disease. The c-myc status of cervical cancer offers a prognostic indicator that could be useful in guiding treatment decisions.

pp60c-src activation in human colon carcinoma

We measured the in vitro protein-tyrosine kinase activity of pp60c-src from human colon carcinoma cell lines and tumors. The activity of pp60c-src from six of nine carcinoma cell lines was higher (on average, fivefold as measured by enolase phosphorylation, or eightfold as measured by autophosphorylation) than that of pp60c-src from normal colonic mucosal cells, or human or rodent fibroblasts. Similarly, the activity of pp60c-src from 13 of 21 primary colon carcinomas was five- or sevenfold higher than that of pp60c-src from normal colonic mucosa adjacent to the tumor. The increased pp60c-src activity did not result solely from an increase in the level of pp60c-src protein, suggesting the specific activity of the pp60c-src kinase is elevated in the tumor cells. pp60c-src from colon carcinoma cells and normal colonic mucosal cells was phosphorylated at similar sites. We used immunoblotting with antibodies to phosphotyrosine to identify substrates of protein-tyrosine kinases in colonic cells. Three phosphotyrosine-containing proteins were detected at significantly higher levels in most colon carcinoma cell lines than in normal colonic mucosal cells or human or rat fibroblasts. All colon carcinoma cell lines with elevated pp60c-src in vitro kinase activity, showed increased phosphorylation of proteins on tyrosine in vivo, suggesting the presence of an activated protein-tyrosine kinase(s).

Evidence that the familial adenomatous polyposis gene is involved in a subset of colon cancers with a complementable defect in c-myc regulation

Human colorectal carcinomas frequently express elevated levels of c-myc mRNA in the absence of a gross genetic change at the c-myc locus. To test the hypothesis that these tumors are defective in a gene function necessary for the regulation of c-myc expression, we fused an osteosarcoma cell line that exhibits normal c-myc regulation with two colon carcinoma cell lines that express deregulated levels of c-myc mRNA. The levels of c-myc transcripts in all of the hybrid clones examined were normal and were induced normally by a mitogenic stimulus. Since rates of c-myc mRNA turnover in the colon carcinoma cells were found to be comparable to those in normal cells, increased message stability cannot account for the increased steady-state levels of transcripts. Our findings suggest that loss of function of a trans-acting regulator is responsible for the deregulation of c-myc expression in a major fraction of colorectal carcinomas. Analysis of restriction fragment length polymorphisms in tumor/normal tissue pairs from patients with primary colorectal lesions indicated that deregulation of c-myc expression in the tumors is correlated with frequent loss of alleles of syntenic markers on chromosome 5q; allele loss on 5q could be detected in 9 of 19 tumors expressing deregulated levels of c-myc mRNA, but not in any of 8 tumors expressing normal levels of c-myc RNA. Chromosome 5q is the region known to contain the gene for familial adenomatous polyposis, an inherited predisposition to colon cancer. These findings, together with the earlier finding that the colonic distribution of tumors exhibiting deregulated c-myc expression is similar to that reported for familial polyposis, provide evidence that loss of function of the familial adenomatous polyposis gene is involved in a subset of colorectal cancers in which c-myc expression is deregulated.

Altered growth of a human neuroendocrine carcinoma line after transfection of a major histocompatibility complex class I gene

The major histocompatibility complex (MHC) class I molecules are known to serve as recognition elements for cytotoxic T cells in mediating the rejection of transplanted tumors. We demonstrate that MHC molecules may have nonimmune functions in modulating tumor cell growth in addition to their classical role in antitumor immunity. A human neuroendocrine carcinoma cell line, COLO 320, with low levels of endogenous class I expression was transfected with the murine H-2Ld gene. Eleven independent stable clones were established, four containing only pRSV-neo and seven also containing varying copy numbers of the transfected Ld gene. The ability of the different clones to grow as colonies in soft agar correlated strongly with the relative amounts of Ld antigen expression (r = 0.89; P less than 0.001). There was a weaker correlation between increased clonogenic ability and higher levels of Ld mRNA (r = 0.67; P less than 0.05). There was no correlation between clonogenic ability and relative expression of amplified c-myc gene or of integrated pRSV-neo. Furthermore, in nude mice, Ld antigen expression was associated with increased formation of metastatic lung colonies 6 weeks after intravenous injection of 10(5) cells. These observations are consistent with the concept that MHC class I antigens may have a role in modulating the growth potential of certain tumor cells independent of their involvement in immune responses.

The dihydrofolate reductase amplicons in different methotrexate-resistant Chinese hamster cell lines share at least a 273-kilobase core sequence, but the amplicons in some cell lines are much larger and are remarkably uniform in structure

We have previously cloned and characterized two different dihydrofolate reductase amplicon types from a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400). The largest of these (the type I amplicon) is 273 kilobases (kb) in length. In the present study, we utilized clones from the type I amplicon as probes to analyze the size and variability of the amplified DNA sequences in five other independently isolated methotrexate-resistant Chinese hamster cell lines. Our data indicated that the predominant amplicon types in all but one of these cell lines are larger than the 273-kb type I sequence. In-gel renaturation experiments as well as hybridization analysis of large SfiI fragments separated by pulse-field gradient gel electrophoresis showed that two highly resistant cell lines (A3 and MK42) have amplified very homogeneous core sequences that are estimated to be at least 583 and 653 kb in length, respectively. Thus, the sizes of the major amplicon types can be different in different drug-resistant Chinese hamster cell lines. However, there appears to be less heterogeneity in size and sequence arrangement within a given methotrexate-resistant Chinese hamster cell line than has been reported for several other examples of DNA sequence amplification in mammalian systems.

Establishment and characterization of a human neuroblastoma cell line

A continuous human cell line RN-GA was established from a stage-III primary neuroblastoma prior to therapy. Light and electron microscopic analysis of the biopsy showed morphological features typical of neuroectodermal origin. Relative cellular DNA content and N-myc oncogene copy number were also analyzed in the biopsy tissue: the tumor cells presented a near-diploid genome with N-myc amplification. The derived tumor cell line expressed distinctive ultrastructural, cytogenetic and immunological markers of neuroblastoma. Moreover, cells from the culture could be serially transplanted into splenectomized-irradiated nude mice, where they formed a progressively growing solid tumor. Surprisingly, the cells in culture did not show any N-myc amplification, while they retained a near-diploid DNA content. We propose that several techniques (electron microscopy, oncogene analysis, flow cytometry, cytogenetics, tissue culture, cell antigen immunodetection) should be used to establish a firm diagnosis and a correct clinical grading of this tumor. The establishment of this continuous cell line should be valuable as an experimental in vitro system for further studies of neuroblastoma biology and morphology.

Recessive mutations and chromosome deletions leading to cancer

This review examines the effect that a small chromosome deletion affecting a specific DNA sequence may have in producing a state of 'hemizygosity' for a gene or genes, and so triggering malignancy of the cells concerned. The association between such deletions and a variety of cancers will be considered and the implications for clinical practice will be outlined.

Human neuroblastoma cell lines as models for the in vitro study of neoplastic and neuronal cell differentiation

Neuroblastoma is a childhood solid tumor composed of primitive cells derived from precursors of the autonomic nervous system. This neoplasm has the highest rate of spontaneous regression of all cancer types and has been noted to undergo spontaneous and chemically induced differentiation into elements resembling mature nervous tissue. As such, neuroblastoma has been a prime model system for the study of neuronal differentiation and the process of cancer cell maturation. In this paper we review those agents that have been described to induce the differentiation of neuroblastoma, with an emphasis on the effects and possible mechanisms of action of a group of related compounds, the retinoids. With this model system and the availability of subclones that are both responsive and resistant to chemically induced differentiation, fundamental questions regarding the mechanisms and processes underlying cell maturation have become more amenable to in vitro study.

Overexpression and amplification of the c-myc gene in mouse tumors induced by chemicals and radiations

We examined expression of the c-myc gene by the dot blot hybridization of total cellular RNA from mouse primary tumors induced by chemicals and radiations. Expression of the c-myc gene was found to be elevated in 69 cases among 177 independently induced tumors of 12 different types. DNA from tumors overexpressing the myc gene was analyzed by Southern blotting. No case of rearrangement was detected. However, amplification of the c-myc gene was found in 7 cases of primary sarcomas. These included 4 cases out of 24 methylcholanthrene-induced sarcomas and 3 cases out of 7 alpha-tocopherol-induced sarcomas. We also analyzed 8 cases of sarcomas induced by radiations, but could not find changes in the gene structure of the c-myc gene. Thus, our data indicate tumor type specificity and agent specificity of c-myc gene amplification.