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

DNA tetraplex formation in the control region of c-myc

The c-myc oncogene is one of the most commonly malfunctioning genes in human cancers, and is an attractive target for anti-gene therapy. Although synthetic oligonucleotides designed to silence c-myc expression via one of its major control elements function well in vitro, their mode of action has been indefinite. Here we show that the targeted control element adopts an intrastrand fold-back DNA tetraplex, which requires potassium ions for stability in vitro. We believe formation of the tetraplex is important for c-myc activation in vivo, and propose a transcription initiation mechanism that explains how anti-gene therapy silence c-myc at the molecular level.

Comparative genomic hybridization: a comparison with molecular and cytogenetic analysis

Comparative genomic hybridization (CGH) is a powerful technique for detecting copy number changes throughout the genome. We describe the development of a versatile image analysis program for CGH studies. Several methods for the production of metaphases which give optimum hybridization signals have also been assessed. CGH analysis was performed on DNA samples from several different and clinically relevant specimens: amniotic fluid cells trisomic for a single chromosome, lymphoblastoid cell lines with abnormalities involving single chromosome bands, malignant cell lines and biopsy material from primary ovarian carcinomas. The results were compared with those derived from G-banding, chromosome painting, and molecular genetic techniques. Our data demonstrate that CGH was able to detect a wide range of quantitative genetic alterations including duplication or deletion of single chromosome bands. CGH analysis also indicated the presence of genetic abnormalities that were not detected by other cytogenetic or molecular approaches. Moreover, our CGH methodology allowed the ready comparison of CGH results from different tumors, a process which greatly facilitated identification of shared genetic changes.

The DNA content of chromosome division figures and interphase nuclei classifies ulcerative colitis

Long-standing ulcerative colitis is considered to be a precancerous condition. Therefore, a practical and reliable method is required for monitoring the progress of the disease. Liberation of the S-phase from karyokinesis occurs in DNA amplification and endoreplication, producing nuclei with more than 4 c DNA. The amount of Feulgen DNA was quantified with an image microphotometer in 8 microns sections for interphase nuclei and in 15 microns sections for chromosome division figures (CDFs). Development of ulcerative colitis was investigated in low grade dysplasia (n = 93 cases; score 3-7) and high grade dysplasia (n = 22; score 8-10). Bacterial colitis (n = 34) and invasive adenocarcinoma (n = 26) provided a basis for data interpretation in dysplasia. Lymphocyte nuclei served as an internal DNA standard. CDFs represent a novel type of aberrant 'mitoses'; they are different from and much more frequent than figures with multipolar spindles. Endoreplication began with low grade dysplasia in interphase nuclei as well as with CDFs; it was fully established in high grade dysplasia and carcinoma. Endoreplicated interphase nuclei and CDFs represent an early morphological mosaic of genomic instability. Both characteristics support a reproducible two-level classification of low and high grade dysplasia in ulcerative colitis.

Karyotypic evolution of cells in culture: a new concept

The Chapter summarizes peculiarities of karyotypic variability during establishment and long-term cultivation of permanent cell lines. A new concept on pathways of karyotypic evolution of cells in culture is put forward. A detailed description is presented of the author's original approach of cytogenetic analysis of cell lines provided for a principally new characteristic of the cell line: its generalized reconstructed karyotype (GRK). Its use as a criterion to evaluate authenticity, purity, and stability of cell lines is discussed. Based on analysis of the GRK, two stages of karyotype evolution of cell lines are revealed: establishment and stabilization, different in karyotypic variability of the cell population and in peculiarities of clone selection. Comparison of peculiarities of karyotypic variability of leukemic and tumor cells both in vitro and in vivo was made, and general regularities of their karyotypic evolution have been established, such as nonrandom changes in the number and structure of chromosomes and deletion of one of the sex chromosomes, as well as regularities characteristic only of cells in culture in most human and animal cell lines (at least 85%) of disomy on all autosomes. The rest of the cell lines, 15%, are characterized by either partial or total monosomies on certain autosomes during long-term cultivation. Three main compensatory mechanisms of maintaining viability of cell lines that have lost genetic material are discussed: polyploidization of the initial cell clone, amplification of oncogenes (predominantly of mys family), and extracopying of whole autosomes or of their fragments.

Differential DNA replication origin activities in human normal skin fibroblast and HeLa cell lines

A modification of the extrusion method for the isolation of nascent DNA from mammalian cells and a PCR-based assay has been used in order to compare the in vivo activities of DNA replication origins in different cell lines. Conventional PCR was firstly applied to detect the chromosomal activities of several known (origins associated with c-myc, hsp70, beta-globin, immunoglobulin mu-chain enhancer) and putative DNA replication origins (autonomously replicating sequences obtained from enriched libraries of human origins of DNA replication from normal and transformed cells) in four human cell lines (HeLa, NSF, WI-38 and SK-MG-1). Then, in nascent DNA samples from normal skin fibroblast (NSF) and HeLa cells, abundance of DNA sequences in the regions of five of these origins was determined by competitive PCR. Our results suggest that autonomously replicating sequences NOA3, S14, S3 and F15 are associated with functional chromosomal origins of replication. Quantitative comparison of origin activities demonstrates that origins associated with c-myc and NOA3 are approximately twice as active in HeLa cells as in NSF cells. The described approach can facilitate the identification of origins which may be differentially active in normal cells and transformed cells or in different cell types.

Cytogenetic abnormalities related to histopathologic grade of astrocytic tumors

Cytogenetic analysis was performed on 7 low-grade astrocytomas, 10 anaplastic astrocytomas, and 14 glioblastomas. Abnormal chromosome numbers were noted in all cases of high-grade astrocytomas but were rarely noted in low-grade astrocytomas (28%). The most consistent changes in high-grade astrocytomas were complete loss of chromosome 10 (61%), gain of chromosome 7 (56%), and loss of chromosome 17 (28%). Certain structural abnormalities, such as marker chromosomes and double minutes (33%), and the deletion and translocation of chromosomes 1 (33%) and 17 (17%), were also noted. These results indicate that changes in the number and/or structure of chromosomes with related inactivation of tumor suppressor gene or oncogene activation might play a critical role in the formation and anaplastic progression of astrocytic tumors.

Topographic genotyping of colorectal carcinoma: from a molecular carcinogenesis model to clinical relevance

BACKGROUND

In recent years, as a result of refinement in molecular biology techniques, significant progress has been made in the understanding of colorectal carcinogenesis. Particular attention has been drawn to identification of genetic mutation that may predispose to colorectal carcinoma (familial syndromes) and may affect tumor behavior and prognosis (sporadic cases).

CONCLUSIONS

Our method of topographic genotyping of human colonic carcinomas has shown a correlation between K-ras-2 and p53 mutations and stage at diagnosis as well as long-term survival. Data from other investigators in this field confirm the importance of genetic analysis of human colorectal tumors. These findings are likely to impact management by allowing a more individualized therapeutic approach.

Expression of HGF, its receptor c-met, c-myc, and albumin in cirrhotic and neoplastic human liver tissue

Hepatocellular carcinoma (HCC) is a common type of cancer, with approximately 260,000 new cases each year, and liver cirrhosis is generally considered a major predisposing factor for HCC. However, specific changes of gene expression in liver cirrhosis and HCC remain obscure. The expression of genes for hepatocyte growth factor (HGF), its receptor c-met proto-oncogene, c-myc proto-oncogene, and albumin was analyzed. Gene expression was studied by PCR in seven normal human livers, nine cases of hepatitis C cirrhosis, 12 cases of alcoholic cirrhosis, two cases of liver adenoma, and 12 cases of HCC. HGF and c-met protein were revealed by immunofluorescent staining. HGF mRNA was not expressed in normal livers but was detected in adenomas, in 80% of HCC, and in some cirrhoses. Paraffin-embedded and fresh-frozen tissue samples yielded similar results. Immunohistochemical data correlated with PCR results regarding the overexpression of the HGF/c-met system in HCC. Albumin gene expression was decreased in HCC vs normal livers, consistent with altered function of tumor hepatocytes. The elevated expression of the HGF/c-met system in HCC may play a role in tumor development and/or progression. Tissue localization studies of HGF and its receptor c-met protein support the existence of both autocrine and paracrine mechanisms of action of HGF in HCC vs only a paracrine mechanism in normal liver.

Human prostate tumor growth in athymic mice: inhibition by androgens and stimulation by finasteride

When the human prostate cancer cell line, LNCaP 104-S, the growth of which is stimulated by physiological levels of androgen, is cultured in androgen-depleted medium for > 100 passages, the cells, now called LNCaP 104-R2, are proliferatively repressed by low concentrations of androgens. LNCaP 104-R2 cells formed tumors in castrated male athymic nude mice. Testosterone propionate (TP) treatment prevented LNCaP 104-R2 tumor growth and caused regression of established tumors in these mice. Such a tumor-suppressive effect was not observed with tumors derived from LNCaP 104-S cells or androgen receptor-negative human prostate cancer PC-3 cells. 5 alpha-Dihydrotestosterone, but not 5 beta-dihydrotestosterone, 17 beta-estradiol, or medroxyprogesterone acetate, also inhibited LNCaP 104-R2 tumor growth. Removal of TP or implantation of finasteride, a 5 alpha-reductase inhibitor, in nude mice bearing TP implants resulted in the regrowth of LNCaP 104-R2 tumors. Within 1 week after TP implantation, LNCaP 104-R2 tumors exhibited massive necrosis with severe hemorrhage. Three weeks later, these tumors showed fibrosis with infiltration of chronic inflammatory cells and scattered carcinoma cells exhibiting degeneration. TP treatment of mice with LNCaP 104-R2 tumors reduced tumor androgen receptor and c-myc mRNA levels but increased prostate-specific antigen in serum- and prostate-specific antigen mRNA in tumors. Although androgen ablation has been the standard treatment for metastatic prostate cancer for > 50 years, our study shows that androgen supplementation therapy may be beneficial for treatment of certain types of human prostate cancer and that the use of 5 alpha-reductase inhibitors, such as finasteride or anti-androgens, in the general treatment of metastatic prostate cancer may require careful assessment.

Initial expression of phosphoenolpyruvate carboxykinase gene in fetal hepatocytes: role of transcription factors

BACKGROUND/AIMS

Hepatic phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) gene is absent in fetal liver. However, this gene can be initially expressed in 20-day-old fetal hepatocyte primary cultures under specific hormonal stimulation. The role of transcriptional factors involved is also studied.

METHODS

Primary 20-day-old fetal hepatocytes have been cultured and Northern-blot and nuclear run-on transcription assays have been performed.

RESULTS

Fetal hepatocytes in culture initially expressed PEPCK gene by dibutyryl cAMP, in the presence of dexamethasone. Dibutyryl cAMP increased by 8-fold the rate of transcription of PEPCK gene at 30 min, and produced a 50-fold increase in its mRNA content at 3 h. This induction of PEPCK expression by cAMP occurred in the presence of sustained levels of CCAAT/enhancer binding protein (C/EBP) alpha-delta mRNAs, and was accompanied by an increase in the rate of transcription and mRNA content of C/EBP beta gene, and a decrease in the expression of c-myc, in the absence of c-fos expression. In addition, insulin or phorbol esters decreased by 50% the PEPCK rate of transcription and its mRNA accumulation induced by dibutyryl cAMP. This inhibitory effect of insulin or phorbol esters on PEPCK gene expression was accompanied by an increase in the rate of transcription and mRNA content of nuclear factors such as c-fos and c-myc, the expression of C/EBPs remaining essentially unmodified.

Early response gene signalling in bryostatin-stimulated primary B chronic lymphocytic leukaemia cells in vitro

The protein kinase C activator bryostatin induces differentiation and antagonizes the effects of tumour-promoting phorbol esters in a number of different cell types. We show here that bryostatin preferentially inhibits phorbol 12-myristate 13-acetate (PMA)-induced proliferation compared with differentiation in a number of different B chronic lymphocytic leukaemia (BCLL) cell populations examined. By using a panel of 11 early-response gene probes in Northern hybridization analysis, we found that the profile of genes induced in response to bryostatin and PMA was qualitatively similar and displayed comparable sensitivities to inhibition with the serine-threonine kinase inhibitor 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine hydrochloride (H7), consistent with common signalling through protein kinase C. However, the nuclear oncogene. c-myc, which was induced strongly in response to PMA treatment, was only marginally up-regulated by bryostatin. In addition, bryostatin selectively inhibited the magnitude of PMA-responsive induction of c-myc, to a degree commensurate with its antagonistic effects seen at the biological level. Finally, an anti-sense oligonucleotide blockade of c-myc inhibited PMA-induced proliferation but not the differentiation of BCLL cells, implicating this nuclear oncogene as an important determinant distinguishing PMA from bryostatin-coupled biological responses and also as a candidate third-messenger effector target for the anti-tumour effects of bryostatin.

Induction of DNA double-strand breaks by ionizing radiation at the c-myc locus compared with the whole genome: a study using pulsed-field gel electrophoresis and gene probing

Ionizing radiation-induced double-strand breaks (dsb) in a human colon carcinoma-derived cell line COLO320HSR were determined from the fragment size distribution of non-specifically labelled DNA and Sfi I restriction enzyme-digested DNA uniformly labelled with a c-myc probe. The dose-effect relation for the induction of DNA dsb was linear with no significant difference between slopes for the curves in the whole genome (7.2 +/- 0.3 x 10(-9) dsb/bp/Gy) and in the 130 kbp restriction fragments containing c-myc (6.5 +/- 0.5 x 10(-9) dsb/bp/Gy). The size distribution of the c-myc fragments showed deviations from the random-breakage model, indicating heterogeneity of dsb induction at this locus.

B cell early response gene expression coupled to B cell receptor, CD40 and interleukin-4 receptor co-stimulation: evidence for a role of the egr-2/krox 20 transcription factor in B cell proliferation

B lymphocytes are activated following antigen stimulation of the B cell receptor but require co-stimulation with accessory molecules provided by interleukin (IL)-4/CD40 ligand for cell cycle progression and proliferation. By analyzing a panel of 11 early response genes induced by cross-linking of surface immunoglobulin, we show that CD40 signaling alone induces only 2 genes, c-myc together with an anonymous gene, 3L3, and that these are distinct from the set of genes induced in response to IL-4. Co-stimulation with the proliferative combination of anti-mu, IL-4 + CD40 signaling led to a fourfold enhancement of egr-2/krox 20 expression over that seen with anti-mu alone. Egr-2 expression/activity was selectively inhibited by the immunosuppressive drug cyclosporin A, and antisense oligonucleotide blockade of Egr-2 activity elicited a dose-dependent inhibition of B cell proliferation. Taken together, these observations show that the early gene regulatory programs coupled to different surface receptors on B cells are largely distinct from each other, but that certain genes, exemplified by egr-2, may represent a point of convergence in the integration of different signaling pathways into the B cell proliferative response.

A highly amplified mouse gene is homologous to the human interferon-responsive Sp100 gene encoding an autoantigen associated with nuclear dots

In human cells, three proteins are currently known to colocalize in di screte nuclear domains (designated nuclear dots): Sp100, a transcription-activating protein autoantigenic primarily in patients with primary biliary cirrhosis; PML, a tumor suppressor protein involved in development of acute promyelocytic leukemia; and NDP52, a protein of unknown function. Here we report sequence similarities between the Sp100 protein and a putative protein encoded by a highly amplified mouse gene which is visible as an inherited homogeneously staining region (HSR) on chromosome 1 of some mouse populations. By in situ hybridization, the Sp100 gene was mapped to locus 2q37, the syntenic region of the HSR on mouse chromosome 1. Unlike the highly amplified mouse gene, Sp100 was found to be a single-copy gene and showed no restriction fragment length polymorphisms. Sequence similarities in the promoter regions and similar exon-intron organizations of the two genes were revealed. As for Sp100, steady-state levels of the mRNAs of the HSR-encoded genes could be greatly increased by interferon (IFN) treatment. As in human cells, IFN treatment led to an enlargement in both size and number of nuclear dots in mouse cells as visualized by immunofluorescence staining with autoimmune sera from patients with primary biliary cirrhosis. These data indicate that a gene located in the inherited HSR of mice, designated mSp100, is homologous to the human Sp100 gene, has a similar gene organization, and responds similarly to IFN treatment.

Transforming growth factor beta 1 induces mitogenesis in fetal rat brown adipocytes

The presence of transforming growth factor beta 1 (TGF-beta 1) for 24 or 48 h stimulated DNA synthesis, the percentage of cells in the S + G2/M phases of the cell cycle, and cell number, as compared to quiescent cells. The mitogenic capacity of TGF-beta 1 (1 pM) was similar to that shown by 10% fetal calf serum (FCS). TGF-beta 1 for 48 h increased by 5-fold the percentage of cells containing (3H)thymidine-labeled nuclei as compared to quiescent cels. In addition, single fetal brown adipocytes, showing their typical multilocular fat droplets phenotype, become positive for (3H)thymidine-labeled nuclei in response to TGF-beta 1. Moreover, TGF-beta 1 induced the mRNA expression of a complete set of proliferation-related genes, such as c-fos (30 min), c-myc and beta-actin (2 h), and H-ras, cdc2 kinase, and glucose 6-phosphate dehydrogenase (G6PD) at 4 and 8 h, as compared to quiescent cells. Concurrently, TGF-beta 1 for 12 h increased the protein content of proliferating cellular nuclear antigen (PCNA) by 6-fold and p21-ras by 2-fold. Although our results demonstrate that TGF-beta 1 induces the expression of very early genes related to cell proliferation, TGF-beta 1 could be acting either as a mitogen or as a survival factor in induce proliferation to fetal brown adipocytes.

Selective capture of acentric fragments by micronuclei provides a rapid method for purifying extrachromosomally amplified DNA

The amplification and overexpression of a number of oncogenes is strongly associated with the progression of a variety of different cancers. We now present a strategy to purify amplified DNA on double minute chromosomes (DMs) to enable analysis of their prevalence and contribution to tumourigenesis. Using cell lines derived from four different tumour types, we have developed a general and rapid method to purify micronuclei that are known to entrap extrachromosomal elements. The isolated DNA is highly enriched in DM sequences and can be used to prepare probes to localize the progenitor single copy chromosomal regions. The capture of DMs by micronuclei appears to be dependent on their lack of a centromere rather than their small size.

Biology of colorectal and gastric cancer cell lines

Cell lines established from the human colorectal and gastric cancers may provide very useful tools to the study of the disease and to develop and test new therapeutic approaches, and a large bank of well-characterized cell lines should reflect the diversity of tumor phenotypes and provide adequate models for the study of tumor heterogeneity. Colorectal lines are relatively easy to establish, while gastric cancer cell lines remain extremely difficult to propagate in long-term culture, and the number of cell lines is very limited. In this paper, we describe the up-to-date results of the characteristics of our nine colorectal cancer cell lines and four gastric cancer cell lines. Based on culture, xenograft, and ultrastructural morphologies, these cell lines could be subtyped into well-differentiated, moderately differentiated, poorly differentiated, and mucinous carcinomas. Basic properties concerning expression and secretion of antigens, neuroendocrine features, receptor binding of various gastrointestinal hormones and neurotransmitters, cytogenetic studies, gene amplification and expression, and chemosensitivity profiles are described. In particular, a greater number of receptors for hormones and neurotransmitters are expressed on human colorectal cancer cell lines compared to gastric cancer cell lines, raising the possibility that gastrointestinal hormones may have a greater autocrine effect on colon cancer cell growth. Despite major differences in the biology of colorectal cancer and gastric cancer as indicated by clinical studies, the multiple properties that we examined reveals marked similarities between the colorectal and gastric cancer cell lines. However, in vitro chemosensitivity patterns to cytotoxic drugs are very different in colorectal and gastric cell lines. Some of these observations may be due to the relatively low expression of the multidrug-resistance-associated (MDR1) gene in gastric cancer cell lines. In addition, colorectal cancer cell lines express receptors for peptide hormones more frequently.

Transforming growth factor beta modulates growth and differentiation of fetal hepatocytes in primary culture

Fetal hepatocytes in primary culture are cells capable to carry out both proliferation and differentiation processes simultaneously. Previous studies have shown that these cells respond to mitogens, such as hepatocyte growth factor (HGF) or epidermal growth factor (EGF), inducing the expression of early genes, such as fos and myc. The transforming growth factor-beta (TGF-beta) family is one of the most influential groups of growth and differentiation factors. In this report, we show that TGF-beta 1 inhibits fetal hepatocyte proliferation, arresting these cells at G1 phase of the cell cycle. In addition, TGF-beta down-regulates the mitogen-induced myc early expression. However, TGF-beta has no effect on the expression of other protooncogenes, such as fos and H-ras. In addition to its inhibitory role on fetal hepatocyte growth, TGF-beta increases the mRNA levels of fibronectin, an extracellular matrix protein, and maintains the expression of some liver specific genes, such as albumin and alfafetoprotein, above control values. The analysis of the expression of some hepatocyte transcriptional factors has shown that TGF-beta increases HNF1 alpha and HNF1 beta mRNA levels. We conclude that TGF-beta may modulate liver growth and differentiation throughout fetal development.

Selective induction of cell cycle regulatory genes cdk1 (p34cdc2), cyclins A/B, and the tumor suppressor gene Rb in transformed cells by okadaic acid

Genes encoding cdk1 (p34cdc2), cyclin A, cyclin B, and the tumor suppressor gene Rb are fundamental regulators of cell cycle progression which associate as a complex with the transcription factor E2F. Expression of many of these proteins has previously been shown to be repressed by okadaic acid, a specific inhibitor of protein phosphatases 1/2A (PP1/PP2A), resulting in growth arrest in nontransformed but immortalized cells. We have investigated levels of mRNA encoding cdk1 (p34cdc2), cyclin A, cyclin B, Rb, GAPDH, c-myc, and histone H4 genes for sensitivity to okadaic acid in HeLa cells to determine if transformation altered their regulation. Serum starvation slowed growth and diminished mRNA levels for all genes tested except c-myc and GAPDH. When starved cells were subsequently exposed to 19 nM okadaic acid or refed 10% serum, mRNA levels of cyclin A, cyclin B, cdk1, and Rb dramatically increased while mRNA levels for c-myc and GAPDH were largely unaffected. Histone H4 mRNA levels and the rate of DNA synthesis were greatly enhanced by serum addition but not affected appreciably by okadaic acid. Okadaic acid was also effective in blocking proliferation of exponentially growing HeLa cells at G2/M and S phase. Despite the cell cycle phase-specific block, elevated mRNA levels for cdk1, cyclin A, cyclin B, Rb, and suppression of H4 mRNA levels were detected and persisted for at least 12 hr following okadaic acid removal. The results demonstrate that cell cycle progression is blocked and several cell cycle regulatory genes, encoding transcription factor E2F-associated proteins, experience elevation of mRNA levels through mechanisms sensitive to okadaic acid likely through a PP1/PP2A-sensitive mechanism. Data from transformed cells contrast with data from immortalized but nontransformed cells in which okadaic acid also blocks cell cycle progression during G2/M phase but suppresses expression of these genes. Such contrasts may be correlated with reduced growth factor dependence and transformation.

Glyceraldehyde-3-phosphate dehydrogenase selectively binds AU-rich RNA in the NAD(+)-binding region (Rossmann fold)

A 36-kDa protein that binds AU-rich RNA was purified from human spleen and identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH). GAPDH has been previously demonstrated to bind tRNA with high affinity. Competition studies suggested that cytoplasmic GAPDH binds the AU-rich elements (AREs) of lymphokine mRNA 3'-untranslated regions with higher affinity than tRNA. The AUUUA-specific RNA binding activity of GAPDH was inhibited by NAD+, NADH, and ATP in a concentration-dependent manner, suggesting that RNA binding of GAPDH might involve the NAD(+)-binding region, or dinucleotide-binding (Rossmann) fold. This hypothesis was supported by experiments that localized RNA binding to the predicted N-terminal 6.8-kDa peptide, known to be involved in the formation of the NAD(+)-binding domain. The direct demonstration of ARE-specific binding protein activity localized to the NAD(+)-binding region of GAPDH supports the general concept that enzymes containing this domain may exhibit specific RNA binding activity and play additional roles in nucleic acid metabolism. Finally, cytoplasmic GAPDH was found in the polysomal fraction of T lymphocytes. Thus, the RNA binding specificity of GAPDH as well as its localization within the cell merit its strong consideration as a protein important in the regulation of ARE-dependent mRNA turnover and translation in addition to its well described role in glycolysis.

Correlation of C-myc and HER-2/neu amplification and expression with histopathologic variables in uterine corpus cancer

OBJECTIVE

Initial studies of protooncogenes in uterine corpus cancer have focused on a single aspect of the gene in question (deoxyribonucleic acid, ribonucleic acid, protein) or have studied a small number of patients. Therefore we evaluated c-myc and HER-2/neu gene amplification and ribonucleic acid overexpression in such malignancies and correlated these molecular changes with known pathologic risk factors.

STUDY DESIGN

Quantitative Southern blot analysis for oncogene deoxyribonucleic acid was used to examine 37 tumors from patients with primary untreated uterine corpus cancer referred to the City of Hope National Medical Center. Six normal endometrial specimens were controls. Seventeen tumors were also examined by Northern blotting to assess increased ribonucleic expression.

RESULTS

Histologic types included adenocarcinoma (n = 30), papillary serous adenocarcinoma (n = 2), adenosquamous carcinoma (n = 2), mixed mullerian sarcoma (n = 2), and leiomyosarcoma (n = 1). Carcinomas were stage I (n = 10), II (n = 18), or III (n = 6). Twenty-three had myometrial invasion of less than one third, six one third to two thirds, and eight deeper invasion (greater than two thirds). According to the criteria of the International Federation of Gynecology and Obstetrics stage was as follows: I (n = 22), II (n = 3), III (n = 7), and IV (n = 5). Ten (27%) and four (11%) tumors showed gene amplification of c-myc and HER-2/neu, respectively. Six demonstrated overexpression of either the c-myc or HER-2/neu gene. HER-2/neu gene amplification was associated more closely with overexpression. Stepwise logistic analysis demonstrated c-myc amplification to be associated with higher grade (p = 0.01).

CONCLUSION

In this referral population, c-myc activation is more common than HER-2/neu activation in uterine corpus cancer and is associated with tumors of higher grade.

Analysis of gene amplification and overexpression in human esophageal-carcinoma cell lines

Gene amplification/overexpression was analyzed in 23 cell lines derived from human esophageal squamous-cell-carcinoma tissues by Southern and Northern hybridizations to c-myc, c-erbB, hst-1 and cyclin-D1 probes. Amplification of the c-myc gene was observed in 5 cell lines derived from well-differentiated carcinomas and all of them were accompanied by co-amplification of other examined oncogenes. The c-erbB gene was amplified in 3 cell lines. Co-amplification of hst-1 and cyclin D1, both of which are located in chromosome 11q13, was found in 9 cell lines. Without exception their amplification was simultaneous and the magnitudes were similar. Their amplification, but not their overexpression, was significantly correlated with poor prognosis in patients from whom the cell lines were established. While hst-1-gene expression was not detected, at least 1 of the genes analyzed was overexpressed in 20 cell lines vs. its expression in normal esophageal mucosal tissues. However, gene amplification was not necessarily accompanied by overexpression of the corresponding genes. Expression of the cyclin D1 gene, which has been assumed to be a target gene for 11q13 amplification, was not detected in one particular cell line with amplification of 11q13. These results suggest that the amplification/overexpression of more than I oncogene is involved in the carcinogenic process of esophageal carcinoma and that c-myc-gene amplification is associated with a well-differentiated subtype. There remains a possibility that key oncogenes other than cyclin D1 are involved in 11q13 amplification.

Astrocyte growth is regulated by neuropeptides through Tis 8 and basic fibroblast growth factor

The important intracellular mechanisms of astrocyte growth are not well defined. Using an inhibitor of astrocyte proliferation, atrial natriuretic peptide (ANP), and the glial mitogen endothelin (ET-3), we sought a common pathway for growth regulation in these neural cells. In cultured fetal rat diencephalic astrocytes, ANP selectively and rapidly inhibited the Tis 8 immediate early gene and protein. After 4 h, ANP selectively inhibited the basic fibroblast growth factor (bFGF) gene and protein. ET-3 significantly stimulated both Tis 8 and bFGF mRNAs and protein, but also stimulated several other immediate early and growth factor/receptor genes. An antisense oligonucleotide to Tis 8 strongly prevented ET-stimulated thymidine incorporation, while the inhibitory action of ANP was enhanced. The Tis 8 antisense oligonucleotide also significantly reversed ET-stimulated bFGF transcription and enhanced the bFGF inhibition caused by ANP. In addition, an antisense oligonucleotide to bFGF significantly reversed the ET-stimulated thymidine incorporation and enhanced the ANP inhibition of DNA synthesis. The sequential modulation of Tis 8, followed by bFGF, provides a novel mechanism for both positive and negative regulation of astrocyte growth by endogenous neuropeptides.

Varicella-zoster virus open reading frame 4 encodes a transcriptional activator that is functionally distinct from that of herpes simplex virus homology ICP27

Varicella-zoster virus is the etiological agent of chickenpox and zoster in humans and belongs to the Alphaherpesvirinae subfamily within the family Herpesviridae. Much of the current understanding of gene regulation in alphaherpesviruses has been derived from studies of the prototype herpes simplex virus (HSV). In HSV, two virus-encoded, trans-regulatory proteins, ICP4 and ICP27, are essential for the replicative cycle of the virus. ICP4 is important in modulating HSV genes of all three kinetic classes, whereas the trans-regulatory effects of ICP27 are primarily associated with the expression of late genes. Recent evidence indicates that the trans-regulatory effects of ICP27 involve posttranscriptional processing of target gene transcripts (R. M. Sandri-Golding and G. E. Mendoza, Genes Dev. 6:848-863, 1992). The ICP27 homolog in varicella-zoster virus is a 452-amino-acid polypeptide encoded by the open reading frame 4 (ORF4) gene. Contrary to what is found with ICP27, we show that the ORF4 polypeptide is a transcriptional activator of diverse target promoters and has a critical requirement for the presence of upstream elements within these promoters to mediate its transcriptional effects. Evidence is also presented to implicate a critical role for the cysteine-rich, C-terminal region of the ORF4 polypeptide in its trans-regulatory functions. Specifically, by oligonucleotide-directed site-specific mutagenesis, we demonstrate that of 10 cysteine residues in the ORF4 polypeptide, only C-421 and C-426 are essential for transactivator function and suggest that these cysteine residues may participate in critical protein-protein interactions rather than protein-nucleic acid interactions to mediate ORF4 inducibility.

Alignment of physical and genetic maps of human 8q23-qter using somatic cell hybrid mapping panel

We describe a mapping panel for the 8q23-qter region composed of human-hamster hybrid cell lines carrying deletion and translocation derivatives of human chromosome 8. The panel divides this region of the chromosome into nine intervals and has been used to map 40 loci by Southern blot hybridization and PCR. Use of this mapping panel has allowed us to align the terminal portions of two different genetic maps of chromosome 8 with each other and with the physical map of the chromosome.

Two novel human B-cell lymphoma lines of lymphatic follicle origin: cytogenetic, molecular genetic and histopathological characterisation

Two B-cell lines, designated as HF-1 and HF-4, were characterised. The cell lines have complicated karyotype abnormalities including a 14;18 translocation and an 8q24 breakpoint originating from t(2;8)(p11;q24) (HF-1) or t(1;8)(p21;q24) (HF-4). The lines have BCL2 rearrangement and they are positive for CD19, CD20, CD22, CD39. HF-1 is also positive for IgG, and HF-4 is positive for IgM and IgD. On Northern blot analyses, the 2.6-kb and 4.2-kb transcripts corresponding to the major transcripts of CMYC and BCL2, respectively, were seen. In Western blot as well as in FACS (fluorescence-activated cell sorting) analysis the presence of BCL2 protein in the both HF-1 and HF-4 cells was demonstrated. The cell lines are expected to serve as an important tool in the study of the chromosomal mechanism activating cellular oncogenes, the somatic hypermutation mechanism of antigen-activated B cells and the apoptosis of B cells.

Effects of granulocyte-macrophage colony-stimulating factor and interleukin-3 on small cell lung cancer cells

Nonhematopoietic malignant cells may express receptors for hematopoietic growth factors and respond to these peptides. The aim of the present study was to investigate whether small cell lung cancer (SCLC) cells may be stimulated to proliferate by hematopoietic growth factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3), which are currently used in clinical trials in combination with cytotoxic chemotherapy. We studied two SCLC cell lines, H69 and N417. The effects of GM-CSF and IL-3 were evaluated by studying clonal growth, 3H-thymidine incorporation, BUDR/DNA bivariate flow cytometry, c-myc and N-myc oncogene expression, and myeloid surface markers. Our experiments show that both GM-CSF and IL-3 can increase 3H-thymidine incorporation and cloning efficiency and reduce DNA synthesis time of H69 and, to a lesser extent, N417 cells, supporting the hypothesis that hematopoietic growth factors can stimulate the growth of some malignant nonhematopoietic cells in vitro. Further in vitro and in vivo studies are needed to determine whether clinical trials applying these factors for bone marrow recovery after chemotherapy of solid tumors may be hazardous by potentially stimulating growth of remaining tumor tissue.

Expression and chromosomal assignment of PTPH1 gene encoding a cytosolic protein tyrosine phosphatase homologous to cytoskeletal-associated proteins

We have investigated the mRNA expression of 2 human protein tyrosine phosphatases with sequence homology to cytoskeletal proteins, PTPH1 and PTPMEG. Northern-blot analysis of PTPH1 using poly (A)+ RNA from normal human colon tissue showed a low-abundance message of 4.3 kb. Reverse-transcriptase/polymerase-chain reaction (RT-PCR) was therefore used to detect it in a wide variety of cell lines including 9 colorectal, 5 gastric, 5 hepatic and 6 hematopoietic tumor cells. PTPH1 mRNA was not detected only in Colo 320 cells over-expressing c-myc mRNA, among the colorectal cancer cell lines examined. When Colo 320 cells were incubated with 5 mM sodium butyrate for 5 days, PTPH1 mRNA became detectable, concomitant with the marked decrease in the expression level of c-myc mRNA. Moreover, the chromosomal localization of PTPH1 gene was investigated by fluorescence in situ hybridization. Interestingly, PTPH1 gene was mapped to 9q31 where the gene for Gorlin syndrome, a putative tumor suppressor gene, exists.

IGF-I is a mitogen involved in differentiation-related gene expression in fetal rat brown adipocytes

Fetal rat brown adipocytes at time zero of culture constitute a population of cells of broad spectrum, as estimated by cell size, endogenous fluorescence and lipid content, and show an intrinsic mitogenic competence. They express constitutively early growth-related genes such as c-myc, c-fos, and beta-actin, tissue specific-genes such as the uncoupling protein (UCP) and the lipogenic marker malic enzyme (ME). Fetal brown adipocytes bear a high expression of insulin-like growth factor receptor (IGF-IR), and show a high affinity IGF-I specific-binding to its receptor, and a high number of binding sites per cell. After cell quiescence, insulin-like growth factor I (IGF-I) was as potent as 10% FCS in inducing DNA synthesis, cell number increase, and the entry of cells into the cell-cycle. In addition, IGF-I or 10% FCS for 48 h increased the percentage of [3H]thymidine-labeled nuclei as compared to quiescent cells. Single cell autoradiographic microphotographs show typical multilocular fat droplets brown adipocytes, resulting positive to [3H]thymidine-labeled nuclei in response to IGF-I. IGF-I increased mRNA expression of the early-response genes c-fos (30 min), c-myc (2 and 24 h), and H-ras (4 and 24 h). 10% FCS also increased c-fos and c-myc, but failed to increase H-ras as an early event. IGF-I or 10% FCS, however, similarly increased the mRNA late expression of c-myc, H-ras, c-raf, beta-actin, and glucose 6-phosphate dehydrogenase (G6PD) at 72 h, as compared to quiescent cells. IGF-I or FCS maintained at 24 h or increased at 48 and 72 h UCP mRNA expression. The results demonstrate that IGF-I is a mitogen for fetal rat brown adipocytes, capable of inducing the expression of early and late growth-regulated genes, and of increasing the lipogenic marker ME and the tissue-specific gene UCP, suggesting the involvement of IGF-I in the differentiation as well as in the proliferation processes.

Calcium ionophore-induced apoptosis of human B cells is preceded by the induced expression of early response genes

We have investigated the effects of calcium ionophore on apoptosis of Ramos human B cells. Our results show that the calcium ionophore A23187 at defined concentrations leads to apoptosis of Ramos cells. The majority of cells (> 90%) undergo apoptosis in response to ionophore. The response is rapid and nuclear condensation and DNA degradation can be detected within 2 h after addition of ionophore. In attempts to define the changes in gene expression preceding apoptosis, we investigated the expression of a panel of early response genes in these cells after ionophore addition. We show that calcium ionophore-induced apoptosis of Ramos cells is preceded by the induced expression of a number of early response genes. These results are consistent with calcium ionophore initiating changes in gene expression which may be important in signaling these cells to undergo apoptosis.

Stabilization of c-myc protein in human glioma cells

The regulation of c-myc protein, product of c-myc/genes, was studied in four glioma cell lines by Northern blot, pulse-chase dot blot, immunoblot and immunoprecipitation analyses. Northern blot analysis revealed no overexpression of c-myc transcript, and pulse-chase dot blot analysis showed normal turnover rate of c-myc transcript, suggestive of no evidence of aberrant regulation of c-myc at post-transcriptional level. The synthesis levels of c-myc protein were shown by immunoprecipitation and closely associated with the c-myc transcript levels demonstrated by Northern blot, suggestive of no evidence of aberrant translational control of c-myc, whereas they were dissociated from the accumulation levels of c-myc protein shown by immunoblot, suggestive of an evidence of aberrant regulation of c-myc at post-translational level. The mean (+/- standard deviation) half-lives of c-myc protein in four glioma cell lines were calculated from the pulse-chase immunoprecipitation analysis, and being 98 +/- 8 to 143 +/- 11 min, were about four- to sixfold longer than normal. In surgical specimens, the immunostain of c-myc protein was not found in normal astrocytes but localized heterogenously in nuclei of reactive astrocytes and glioma cells, and increased in stained cell number in proportion to malignancy. Although this study was limited to four glioma cell lines, it suggests that the c-myc protein in glioma cells may be accumulated due to its prolonged half-life contributing to an uncontrolled proliferation.

Over-expression of the c-myc proto-oncogene in colorectal carcinoma

Alterations in the c-myc proto-oncogene in colorectal cancer were studied at the level of RNA expression, gene amplification and rearrangements. One hundred cases of colorectal cancer, stratified by Dukes' stage were examined. The level of messenger RNA expression was measured in tumours and matched normal mucosa from the same patient. Between 5 and 400 fold over-expression was found in 66% of tumours. Neither the presence nor the level of over-expression correlated with tumour staging. A significant correlation (P < 0.01) was found between over-expression of c-myc in tumours and the presence of synchronous adenomas elsewhere in the colon. In contrast to other tumours, no rearrangements of the gene were found on Southern analysis of colorectal cancers. Similarly, amplification of the gene was not found in the cancers examined.

Overexpression of asparagine synthetase in albizziin-resistant murine diploid embryonic stem cells

Gene amplification is commonly observed in primary tumors and established drug-resistant cell lines, both of which are generally aneuploid. However, this process is undetectable (frequency < 10(-9) in normal diploid mammalian cell lines. To investigate whether gene amplification can occur in pluripotent diploid cells, we have selected drug-resistant mutants of mouse embryonic stem (ES) cells. We had previously found that Chinese hamster ovary (CHO) and human cell lines selected in albizziin (Alb), an amino acid analog of L-glutamine, overexpress asparagine synthetase (AS) due to gene amplification. The same drug selection system was applied to ES cells to isolate single-step and multistep drug-resistant mutants. Albizziin-resistant ES cells exhibited elevated levels of AS; however, drug resistance in ES cells was associated with mRNA overexpression without gene amplification. AS gene amplification was observed in only one drug-resistant cell line and was preceded by AS mRNA overexpression. Gene amplification in the latter coincided with the loss of the pluripotent nature of the ES cells.

Lack of prognostic value of immunoreactivity for p62 oncoprotein in colorectal carcinoma

Immunohistochemical staining for c-myc p62 oncoprotein (p62) was performed in 59 colorectal carcinomas using mouse monoclonal antibody against human c-myc protein (MYC1-6E10). The immunoreactivity for p62 was intense in 22 (37.3%), and weak in 37 (62.7%) of the tumors. Advanced disease and nodal metastasis were more frequently seen in tumors showing intense staining but the difference did not reach statistical significance. Sixteen patients have died of the disease but overall survival rates did not differ between patients with tumors showing intense staining and those with tumors showing weakly staining. In 50 patients undergoing grossly curative resection, local or distant metastasis developed in 15 patients. Immunoreactivity for p62 had no effect on the rate of recurrence or disease free survival rates in these 50 patients undergoing grossly curative resection. The present study revealed that the immunoreactivity for p62 had no prognostic value in colorectal carcinoma.

Hel-N1: an autoimmune RNA-binding protein with specificity for 3' uridylate-rich untranslated regions of growth factor mRNAs

We have investigated the RNA binding specificity of Hel-N1, a human neuron-specific RNA-binding protein, which contains three RNA recognition motifs. Hel-N1 is a human homolog of Drosophila melanogaster elav, which plays a vital role in the development of neurons. A random RNA selection procedure revealed that Hel-N1 prefers to bind RNAs containing short stretches of uridylates similar to those found in the 3' untranslated regions (3' UTRs) of oncoprotein and cytokine mRNAs such as c-myc, c-fos, and granulocyte macrophage colony-stimulating factor. Direct binding studies demonstrated that Hel-N1 bound and formed multimers with c-myc 3' UTR mRNA and required, as a minimum, a specific 29-nucleotide stretch containing AUUUG, AUUUA, and GUUUUU. Deletion analysis demonstrated that a fragment of Hel-N1 containing 87 amino acids, encompassing the third RNA recognition motif, forms an RNA binding domain for the c-myc 3' UTR. In addition, Hel-N1 was shown to be reactive with autoantibodies from patients with paraneoplastic encephalomyelitis both before and after binding to c-myc mRNA.

Hel-N1: an autoimmune RNA-binding protein with specificity for 3' uridylate-rich untranslated regions of growth factor mRNAs

We have investigated the RNA binding specificity of Hel-N1, a human neuron-specific RNA-binding protein, which contains three RNA recognition motifs. Hel-N1 is a human homolog of Drosophila melanogaster elav, which plays a vital role in the development of neurons. A random RNA selection procedure revealed that Hel-N1 prefers to bind RNAs containing short stretches of uridylates similar to those found in the 3' untranslated regions (3' UTRs) of oncoprotein and cytokine mRNAs such as c-myc, c-fos, and granulocyte macrophage colony-stimulating factor. Direct binding studies demonstrated that Hel-N1 bound and formed multimers with c-myc 3' UTR mRNA and required, as a minimum, a specific 29-nucleotide stretch containing AUUUG, AUUUA, and GUUUUU. Deletion analysis demonstrated that a fragment of Hel-N1 containing 87 amino acids, encompassing the third RNA recognition motif, forms an RNA binding domain for the c-myc 3' UTR. In addition, Hel-N1 was shown to be reactive with autoantibodies from patients with paraneoplastic encephalomyelitis both before and after binding to c-myc mRNA.

Amplification of the 11q13 region in human carcinoma cell lines: a mechanistic view

We previously proposed that a local duplication, not the loss of the subsequently amplified marker from its original site, might be the first step in gene amplification in human cells. It is important to investigate this issue in naturally occurring amplification and when copy numbers are relatively low. We have examined the location of single-copy and amplified 11q13 sequences in cell lines from human breast cancers and squamous cell carcinomas using fluorescence in situ hybridization both with a probe specific for the 11q13 amplifying region and with a chromosome 11-specific library. We show that in most cell lines the 11q13 amplicons are physically linked to chromosome 11 or to a chromosome derived from chromosome 11 by various rearrangements near the 11q13 region. In none of the cell lines were interstitial deletions of 11q13 detected. These results indicate that 11q13 amplification in human tumor cells generally does not involve deletion as the initial step. One cell line with chromosomally located amplified 11q13 sequences contained double minutes that harbored the MYC gene but no 11q13 sequences. This suggests that the genetic outcome and the mechanism of gene amplification are probably dependent on specific DNA sequences rather than on the origin of the cells.

Changes of proliferative activity and phenotypes in spontaneous differentiation of a colon cancer cell line

We examined the alterations of proliferative activity and c-myc expression of a colon cancer cell line (Caco-2) during its spontaneous differentiation. Caco-2 cells were cultured in various types of media and the degree of differentiation was monitored in terms of dome formation in cell monolayers and expression of alkaline phosphatase (ALP) activity. In Caco-2 cells cultured with Eagle's minimum essential medium (EMEM) containing 10% fetal calf serum (FCS), dome formation was demonstrated and ALP activity was markedly increased after the cells reached confluence. Five-fold reduction of c-myc mRNA and a marked decrease in S-phase cells were observed in the differentiated cells. These changes were not induced in FCS-free EMEM. The addition of insulin and transferrin to FCS-free EMEM did not induce cell differentiation or reduction of c-myc mRNA expression. When Caco-2 cells were cultured with three different serum-free media, the induction of dome formation and the increase of ALP activity were observed to varying degrees. Expression of c-myc mRNA in the cells cultured with one serum-free medium decreased to a level similar to that in fully differentiated cells cultured with EMEM containing 10% FCS. These results suggest that a spontaneous switch from a proliferative state with high c-myc expression to differentiated phenotype occurs after cells reach confluence and depends on the culture conditions.

Expression of myc family oncoproteins in small-cell lung-cancer cell lines and xenografts

A number of genes have altered activity in small-cell lung cancer (SCLC), but especially genes of the myc family (c-myc, L-myc and N-myc) are expressed at high levels in SCLC. Most studies have explored expression at the mRNA level, whereas studies of myc family oncoprotein expression are sparse. WE examined the expression of myc proto-oncogenes at the mRNA and protein level in 23 cell lines or xenografts. In the cell lines, the doubling time and the cell-cycle distribution, as determined by flow-cytometric DNA analysis, were examined to establish whether the level of myc-gene-family expression correlated with proliferative parameters. All tumours expressed at least one myc family member at the mRNA level. Exclusive c-myc mRNA expression was demonstrated in 8 tumours, L-myc in 7 and N-myc in I. Five tumours expressed both c-myc and L-myc, and 2 tumours expressed both c-myc and N-myc. In general, the level of expression of c-myc and N-myc was similar at the mRNA and the protein level. Expression of c-myc was positively correlated with the proliferative index (sum of S and G2+M phases) of cell lines, but not with the population doubling time. In general, L-myc-expressing cell lines had a low proliferative index. There was no systematic difference in myc expression between cell lines and xenografts of individual tumours.

Uncoupling of growth inhibition and differentiation in dexamethasone-treated human rhabdomyosarcoma cells

The effects of dexamethasone, a synthetic glucocorticoid, and of N,N-dimethylformamide on in vitro growth and differentiation and on proto-oncogene expression of human rhabdomyosarcoma cells were studied. RD/18 clone cells (derived from the embryonal rhabdomyosarcoma cell line RD) treated with 100 nM dexamethasone showed an almost complete block of differentiation: about 5% myosin-positive cells were observed after 2 weeks of culture in dexamethasone-supplemented differentiation medium, compared to 20% of untreated cultures. Dexamethasone also induced a 20-30% growth inhibition and a more flattened morphology. The treatment with N,N-dimethylformamide induced a significantly increased proportion of myosin-positive cells (reaching about 30%) and a 40% growth inhibition. Induction of differentiation inversely correlated with the levels of c-myc proto-oncogene expression: after a 2 week culture dexamethasone-treated cells showed the highest c-myc expression and N,N-dimethylformamide-treated cells the lowest. Culture conditions per se down-modulated c-erbB1 and up-regulated c-jun expression, with no relationship to the differentiation pattern. Other proto-oncogenes were not expressed (c-sis, N-myc, c-mos, c-myb) or were not modulated (c-fos, c-raf). Therefore dexamethasone and N,N-dimethylformamide, both causing a decreased growth rate, showed opposing actions on myogenic differentiation and on c-myc proto-oncogene expression of human rhabdomyosarcoma cells.

Recombination between separate MYC amplification structures in COLO320 cells

Cytogenetically visible gene amplification structures can consist of arrays of amplicons presumably formed by secondary "rearrangements" following amplicon formation. The structural evolution of gene amplification sites in tumor cells suggests that complex secondary structures may have some selective advantage in the tumor cell environment. Although secondary amplicon rearrangements are a hallmark of the gene amplification process, little is known about the mechanics of this process. COLO320 neuroendocrine tumor cells carry two different types of amplified MYC oncogene sequences, one type with an intact MYC gene and the other with a rearranged "chimeric" MYC gene. We have studied various clonal subpopulations of COLO320 cells and identified regions within and downstream of the MYC locus that are unique to each amplicon type. Using double-label fluorescence in situ hybridization with DNA probes unique to each amplicon type, we have observed that both chromosomal and extrachromosomal MYC amplicon arrays in COLO320 cells frequently consist of heterogeneous mixtures of each MYC amplicon type. Our results suggest that the two MYC amplicon types of COLO320 cells were formed simultaneously but independently, and that double minute chromosomes observed in COLO320 cells were formed by intermolecular homologous recombination secondary to amplicon formation.

Tumour necrosis factor-induced cytotoxicity is accompanied by intracellular mitogenic signals in ME-180 human cervical carcinoma cells

Tumour necrosis factor-alpha (TNF) induced a cytotoxic response in ME-180 human cervical carcinoma cells in vitro. This cytotoxic response was accompanied by a temporal series of intracellular signals that are commonly triggered by a mitogenic stimulus: increased c-fos (20-30 min) and c-myc (40-60 min) expression, increased activity of ornithine decarboxylase (3 h), increased intracellular polyamine content (7 h) and increased thymidine incorporation into DNA (14 h). A cytotoxic response independent of these mitogenic signals could not be explained by an induction of interleukin-6, which is an autocrine cytotoxic agent in some cell types; nor by a biphasic, dose-dependent response in which low concentrations of TNF are mitogenic and higher concentrations are cytotoxic. Conversely, a dependent role of these mitogenic signals was suggested by the absence of a TNF-promoted increase in thymidine incorporation into DNA in an ME-180 clone that is resistant to TNF-induced cytotoxicity. A decrease in the proliferation rate of TNF-sensitive cells induced by either alpha-difluoromethylornithine treatment (resulting in polyamine depletion) or serum starvation rendered the cells insensitive to TNF-induced cytotoxicity, further suggesting a role for mitogenic signals and cell division in TNF-mediated cytotoxicity. However, inhibiting proliferation with cycloheximide resulted in increased sensitivity to TNF, implying that mitogenesis itself was not essential for a cytotoxic response. TNF induced DNA fragmentation in sensitive cells, suggesting that cytotoxicity occurred via apoptosis.

Biochemical markers for colorectal cancer. Diagnostic and therapeutic implications

The development of the understanding of oncogenes, tumor suppressor genes, and signal transduction has provided a significant advance in the concepts of the mechanisms of carcinogenesis in the colon and rectum. The tools provided by the molecular geneticist and the immunobiologist may yield powerful new techniques for screening individuals at risk, for identifying those patients with biologically more aggressive tumors, for developing novel therapies targeted directly at tumor cells, and for providing the means for more sensitive and specific detection of recurrence of disease.