L-myc, a new myc-related gene amplified and expressed in human small cell lung cancer

A DNA microarray screen for genes involved in c-MYC and N-MYC oncogenesis in human tumors

MYC proto-oncogenes play a major role in various types of human tumors. The products of these genes are transcription factors that bind to specific sequences and activate the expression of target genes. Identifying these target genes and their downstream effectors is a crucial step in understanding and preventing MYC induced oncogenesis. Until now, most of the efforts to identify such genes were performed by analysing in vitro systems whose relevance to the malignant process in vivo remains unclear. We aimed at identifying genes that play a major role in the malignant process of MYC induced carcinogenesis. Thus, we analysed the expression profiles of human MYC induced tumors and compared them to similar, non-MYC tumors. Moreover, we looked for the common characteristics of different types of MYC induced tumors. We identified several genes, most of them involved in cell cycle regulation, that are over expressed in MYC induced lymphomas as well as MYC induced neuronal-like tumors. In order to determine whether MYC induced oncogenesis is similar in human and in the mouse model system, we analysed the expression of the identified genes in cells derived from transgenic mice tumors. We also present the distribution of MYC putative binding sites in the regulatory sequences of the genes identified in our analysis. This analysis pointed to two genes (E2F1 and TSC2) as candidates to be targets of Myc activity. We thus further analysed the expression of these genes in the tumor cell lines, and examined the plausibility that elements in their promoter bind the Myc protein. Our data points to several genes that may be involved in c-MYC and N-MYC induced tumors and to two genes that may be targets for MYC activity.

Different susceptibility of each L-myc genotype to esophageal cancer risk factors

To understand the relationship between the L-myc genotypes and esophageal cancer risk, a polymerase chain reaction-based restriction fragment length polymorphism analysis was performed on 91 Japanese patients with esophageal cancer and 241 non-cancer outpatients. No significant difference in the distribution of genotypes was observed between patients and controls; 18.7% LL genotype, 56.0% LS and 25.3% SS among patients, and 24.5%, 55.6% and 19.9%, respectively, among controls. Frequency of the s-allele in patients (0.533) was slightly higher than in controls (0.477), but the difference was not statistically significant. However, the odds ratios (ORs) for smoking or heavy drinking were markedly higher in SS and LS genotypes than in LL genotype; age-sex-adjusted ORs for smoking was 7.57 in the SS genotype, 6.40 in the LS genotype and 1.77 in the LL genotype. Age-sex-adjusted ORs for heavy drinking were 19.78, 18.20 and 7.40, respectively. The age-sex-adjusted ORs for both factors combined were 12.77, 18.45 and 1.44, respectively. These results suggested that the L-myc polymorphism might modify the effects of lifestyle factors on esophageal cancer risk.

Biological considerations in lung cancer

Our understanding of lung cancer biology has rapidly expanded in recent years. Lung cancer, unlike most human cancers, can be traced to an environmental risk factor in the majority of cases, and this fact is reflected in the vast number of genetic alterations discovered in lung tumors whose pathogenesis is believed to be mediated by carcinogen exposure. The discovery of these alterations has led to a greater understanding of tumor development. The dramatic progress in the understanding of the genetic and molecular basis of oncogenesis and the induction of immunity has led to a rejuvenation of efforts to apply this new knowledge to this common and refractory disease. Further, the resurgent interest in cancer immunology and tumor-host interactions holds promise for the development of new approaches to treatment based on harvesting the immune systems ability to recognize these alterations. Hopefully, this understanding will lead to novel approaches with real and convincing clinical efficacy once some of these strategies are tested in carefully performed randomized clinical trials with appropriate power to detect meaningful differences.

Two consistently deleted regions within chromosome 1p32-pter in human non-small cell lung cancer

Allelic losses at 1p32-pter have been reported as frequent events in human non-small cell lung cancer (NSCLC). To further characterize the region of deletions, we studied loss of heterozygosity on a panel of 102 microdissected NSCLC samples with 20 polymorphic markers spanning 1p32-pter. Two shortest regions of the overlap of the deletions (SROs) were found: SRO 2a (D1S417--D1S57) and SRO 2b (D1S450--D1S243). Allelic losses at either region correlated independently with advanced stage of disease and with postoperative metastasis and relapse (P < 0.05), suggesting that crucial genes in these regions are involved in NSCLC progression. Mol. Carcinog. 30:151--158, 2001.

Genetic instability and aberrant DNA methylation in chronic hepatitis and cirrhosis--A comprehensive study of loss of heterozygosity and microsatellite instability at 39 loci and DNA hypermethylation on 8 CpG islands in microdissected specimens from patients with hepatocellular carcinoma

A study was conducted to examine the significance of genetic instability and aberrant DNA methylation during hepatocarcinogenesis. Genomic DNA was extracted from 196 microdissected specimens of noncancerous liver tissue that showed no marked histologic findings or findings compatible with chronic hepatitis or cirrhosis, and 80 corresponding microdissected specimens of hepatocellular carcinoma (HCC) from 40 patients. Loss of heterozygosity (LOH) and microsatellite instability (MSI) were examined by polymerase chain reaction (PCR) using 39 microsatellite markers, and DNA methylation status on 8 CpG islands was examined by bisulfite-PCR. In noncancerous liver tissues, LOH, MSI, and DNA hypermethylation were found in 15 (38%), 6 (15%), and 33 (83%) of 40 cases, respectively. The incidence of DNA hypermethylation in histologically normal liver was similar to that in chronic hepatitis and cirrhosis, although neither LOH nor MSI was found in histologically normal liver. In cancerous tissues, LOH, MSI, and DNA hypermethylation were found in 39 (98%), 8 (20%), and 40 (100%) of 40 cases, respectively. CpG islands of the p16 gene and methylated in tumor 1, 2, 12, and 31 clones were frequently methylated in cancerous tissues, although neither the thrombospondin-1 nor the human Mut L homologue (hMLH1) gene was methylated. Absence of silencing of the hMLH1 gene by DNA hypermethylation is consistent with the low incidence of MSI in HCCs. The results of this study indicate that LOH and aberrant DNA methylation contribute to hepatocarcinogenesis; DNA hypermethylation in particular, which precedes or may even cause LOH, is as an early event during hepatocarcinogenesis.

Promotion of growth and apoptosis in c-myc nullizygous fibroblasts by other members of the myc oncoprotein family

c-myc nullizygous fibroblasts (KO cells) were used to compare the abilities of c-myc, N-myc and L-myc oncoproteins to accelerate growth, promote apoptosis, revert morphology, and regulate the expression of previously described c-myc target genes. All three myc oncoproteins were expressed following retroviral transduction of KO cells. The proteins all enhanced the growth rate of KO cells and significantly shortened the cell cycle transition time. They also accelerated apoptosis following serum deprivation, reverted the abnormal KO cell morphology, and modulated the expression of previously described c-myc target genes. In most cases, L-myc was equivalent to c-myc and N-myc in restoring all of the c-myc-dependent activities. These findings contrast with the previously reported weak transforming and transactivating properties of L-myc. Myc oncoproteins may thus impart both highly similar as well as dissimilar signals to the cells in which they are expressed.

Frequent chromosome 8q gains in human small cell lung carcinoma detected by arbitrarily primed-PCR genomic fingerprinting

The arbitrarily primed-polymerase chain reaction (AP-PCR) genomic fingerprinting method was applied to detect chromosomal numerical imbalances in 13 small cell lung carcinomas (SCLC). Increases and decreases in the intensity of the AP-PCR bands from several chromosomes, representing gains of chromosomes 1, 7, 16, and X, and losses of chromosomes 2, 10, and 22, were recurrent events in independent tumors. In addition, the most common alterations detected were increases in signal intensity of three AP-PCR bands derived from genomic sequences on chromosome 8q (eight of 13 tumors: 62%). To define whether the 8q gains observed in the AP-PCR analysis include the C-MYC gene at chromosome 8q24 or not, we performed targeted AP-PCR analysis of the C-MYC gene. The C-MYC gene was amplified in five of the eight tumors with gains of 8q, but in none of the remaining five tumors in which 8q gains were not detected. These results indicate that chromosome 8q gain occurs frequently in SCLC and gained regions often, but do not always, include the C-MYC gene. Moderate increases in copy number of the C-MYC gene and additional gene(s) in the 8q region appear to be under positive selection during SCLC progression.

Protooncogenes as mediators of apoptosis

Apoptosis has been well established as a vital biological phenomenon that is important in the maintenance of cellular homeostasis. Three major protooncogene families and their encoded proteins function as mediators of apoptosis in various cell types and are the subject of this chapter. Protooncogenic proteins such as c-Myc/Max, c-Fos/c-Jun, and Bcl-2/Bax utilize a synergetic effect to enhance their roles in the pro- or antiapoptotic action. These family members activate and repress the expression of their target genes, control cell cycle progression, and execute programmed cell death. Repression or overproduction of these protooncogenic proteins induces apoptosis, which may vary as a result of either cell type specificity or the nature of the apoptotic stimuli. The proapoptotic and antiapoptotic proteins exert their effects in the membrane of cellular organelles. Here they generate cell-type-specific signals that activate the caspase family of proteases and their regulators for the execution of apoptosis.

Allelotype and loss of heterozygosity around the L-myc gene locus in primary lung cancers

L-myc S-allele was reported to be associated with metastasis of lung cancer, indicating the existence of a putative tumor suppressor gene around the L-myc locus, in linkage disequilibrium. The relationship between the S-allele and inactivation of some tumor suppressor gene should be indicated by allelic loss. Therefore, we examined the association between the L-myc S-allele and loss of heterozygosity at 11 loci around the L-myc locus (1p34.3) in primary lesions or other biological characteristics in lung cancer. No associations between the S-allele and allelic loss around the L-myc locus or other characteristics were found. According to the deletion map, three shortest regions of overlap between D1S230 and D1S76 were identified. While loss of heterozygosity at SRO1, between D1S2797 and MYCL1, showed no relationship with the pathological stage, it was more frequently observed in squamous cell carcinoma than adenocarcinoma (P=0.019), and associated with high telomerase activity (P=0.046), an indicator of cellular immortality. In conclusion, we found three shortest regions of overlap (SROs) from D1S2797 to pter, and a tumor suppressor gene, which might be associated with suppression of lung cancer development but not with L-myc S-allele, may exist in SRO1.

Differentiation and proliferation of pulmonary neuroendocrine cells

In this review article the morphological profiles of pulmonary neuroendocrine cells (PNEC) in experimental animals and humans are described. Although the mechanisms of differentiation and proliferation of neuroendocrine cells in the airway epithelium remain to be solved, several experimental studies using explant culture and cell culture systems of fetal animal lungs have been performed to clarify fundamental phenomena associated with neuroendocrine differentiation and proliferation. Experimental animal studies using chronic hypoxia, toxic substances and carcinogens have succeeded in inducing alterations in PNEC systems, and these studies have elucidated the reactions of PNEC in cell injury and inflammation, and functional aspects of PNEC in disease conditions. Human pulmonary neuroendocrine tumors include various histological subtypes, and show divergent morphological and biological varieties. Molecular abnormalities of small cell carcinoma, the most aggressive subtype of pulmonary neuroendocrine tumors, have been extensively studied, but the mechanism of neuroendocrine differentiation of this tumor is still largely unknown. PNEC share common phenotypes with neuronal cells, and developmental studies have begun contributed evidence that similar transcriptional networks, including active and repressive basic helix-loop-helix (bHLH) factors, function in the differentiation of both PNEC and neuronal cells. Such a bHLH network may also play a central role in determining cell differentiation in lung carcinomas. Further studies of the neuronal bHLH network, its regulatory system and related signal transduction pathways, will be required for understanding the mechanisms of neuroendocrine differentiation and proliferation in normal and pathological lung conditions.

L-myc restriction fragment length polymorphism in Japanese patients with esophageal cancer

L-myc polymorphism is a representative genetic trait related to an individual's susceptibility to several cancers. However, there have been no reports concerning the association between esophageal cancer and L-myc polymorphism. To analyze the distribution of polymorphism in Japanese patients with esophageal cancer, a molecular genotyping method using a polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) was used. Based on an analysis of 65 Japanese patients with esophageal cancer and 107 healthy control subjects, a significant difference was observed in either the distribution of genotypes (P=0.012) or of allele frequencies between the two groups (P=0.004). The relative risk of esophageal cancer for genotypes including the shorter allele was 2.9 compared to the longer allele homozygote. Furthermore, the patients with S-allele had a tendency for poor prognosis among those with three genotypes. A significant difference between the distribution of genotypes and the incidence of lymph node metastasis was found based on the clinicopathological features of the cancers. These results suggest that L-myc polymorphism may be implicated as a genetic trait affecting an individual's susceptibility to esophageal cancer, at least among Japanese patients.

Molecular pathogenesis of lung cancer

Lung cancer is the largest cancer killer of men and women in the united states. In addition to the progress made from antismoking primary prevention measures, new tools to help treat patients with lung cancer are emerging from the rapid advances in knowledge of the molecular pathogenesis of lung cancer. These tools include molecular and cellular biology and are starting to provide an insight into how the tumor cell, by altering oncogenes and tumor suppressor genes, achieves growth advantage, uncontrolled proliferation and metastatic behavior via disruption of key cell-cycle regulators and signal transduction cascades. Moreover, new knowledge is being developed in terms of the molecular definition of individual susceptibility to tobacco smoke carcinogens. These tools are being translated into clinical strategies to complement surgery, radiotherapy, and chemotherapy and also to assist in primary and secondary prevention efforts. This review summarizes current knowledge of the molecular pathogenesis of lung cancer. From this we know that respiratory epithelial cells require many genetic alterations to become invasive and metastatic cancer. We can detect cells with a few such changes in current and former smokers, offering the opportunity to intercede with a biomarker-monitored prevention and early detection effort. This will be coupled with new advances in computed tomography-based screening. Finally, because the molecular alterations are known, new mechanism-based therapies are being developed and brought to the clinic, including new drugs, vaccines, and gene therapy, which also must be integrated with standard therapies.

Affinity and selectivity of matrix metalloproteinase inhibitors: a chemometrical study from the perspective of ligands and proteins

A novel strategy to understand affinity and selectivity for enzyme inhibitors using information from ligands and target protein 3D structures is described. It was applied to 2-arylsulfonyl-1,2,3, 4-tetrahydro-isoquinoline-3-carboxylates and -hydroxamates as inhibitors of the matrix metalloproteinases MMP-3 (stromelysin-1) and MMP-8 (human neutrophil collagenase). As the first step, consistent and predictive 3D-QSAR models were derived using CoMFA, CoMSIA, and GRID/Golpe approaches, leading to the identification of binding regions where steric, electronic, or hydrophobic effects are important for affinity. These models were validated using multiple analyses using two or five randomly chosen cross-validation groups and randomizations of biological activities. Second, 3D-QSAR models were derived based on the affinity ratio IC(50)(MMP-8)/IC(50)(MMP-3), allowing the identification of key ligand determinants for selectivity toward one of both enzymes. In addition to this ligands' view, the third step encompasses a chemometrical approach based on principal component analysis (PCA) of multivariate GRID descriptors to uncover the major differences between both protein binding sites with respect to their GRID probe interaction pattern. The resulting information, based on the accurate knowledge of the target protein 3D structures, led to a consistent picture in good agreement with experimentally observed differences in selectivity toward MMP-8 or MMP-3. The interpretation of all three classes of statistical models leads to detailed SAR information for MMP inhibitors, which is in agreement with available data for binding site topologies, ligand affinities, and selectivities. Thus the combined chemical analyses provide guidelines and accurate activity predictions for designing novel, selective MMP inhibitors.

PGP9.5 as a candidate tumor marker for non-small-cell lung cancer

PGP9.5 is a neurospecific peptide that functions to remove ubiquitin from ubiquitinated proteins and prevents them from targeted degradation by proteasomes. Using the serial analysis of gene expression method (SAGE), we observed that the PGP9.5 transcript was highly expressed in primary lung cancers and lung cancer cell lines but was not detectable in the normal lung. Here we examined the expression of PGP9.5 protein in normal lung epithelium, lung tumor cell lines, and 98 resected primary non-small-cell lung carcinomas (NSCLCs). We found PGP9.5 reactivity in normal lung in a pattern compatible with K-cells of the diffuse neuroendocrine system. However, the PGP9.5 was present in both small-cell lung cancer (SCLC) and NSCLC cell lines (22/24) independent of neuronal differentiation. In primary NSCLCs, 54% (53/98) of the cases had positive PGP9.5 staining, and the expression of protein was strongly associated with pathological stage of the cancer. It was present in 44% (29/66) of stage I NSCLCs and in 75% (24/32) of stage II and IIIA NSCLCs (p = 0.0032). These results suggest that the increased expression of PGP9.5 is specifically associated with lung cancer development and may serve as a potential marker for the detection of lung cancer.

MYC oncogenes and human neoplastic disease

c-myc, N-myc and L-myc are the three members of the myc oncoprotein family whose role in the pathogenesis of many human neoplastic diseases has received wide empirical support. In this review, we first summarize data, derived mainly from non-clinical studies, indicating that these oncoproteins actually serve quite different roles in vivo. This concept necessarily lies at the heart of the basis for the observation that the deregulated expression of each MYC gene is reproducibly associated with only certain naturally occurring malignancies in humans and that these genes are not interchangeable with respect to their aberrant functional consequences. We also review evidence implicating each of the above MYC genes in specific neoplastic diseases and have attempted to identify unresolved questions which deserve further basic or clinical investigation. We have made every attempt to review those diseases for which significant and confirmatory evidence, based on studies with primary tumor material, exists to implicate MYC members in their causation and/or progression.

Restriction fragment length polymorphism of the L-myc gene is not a prognostic factor in bladder cancer patients

The L-myc restriction fragment length polymorphism has been suggested to be of prognostic significance in some types of primary tumours. We examined the prognostic and susceptibility significance of the L-myc genotype in a group of 98 bladder cancer patients. The L-myc genotype did not correlate with any pathologic parameter and does not offer any clinical utility in patients with bladder cancer.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

Constitutive and Interleukin-7/Interleukin-15 Stimulated DNA Binding of Myc, Jun, and Novel Myc-Like Proteins in Cutaneous T-Cell Lymphoma Cells

Members of the Myc and Jun/Fos gene families have been found to be expressed in late stages of cutaneous T-cell lymphoma (CTCL) and may be responsible for the transition from low-grade to high-grade tumors. The composition of these complexes is an important parameter, as the different homo- and heterodimeric jun and myc complexes can have gene transcription activating or suppressing activities. We determined the composition of the jun and myc DNA-binding complexes in three CTCL cell lines and malignant cells of seven Sézary patients by electrophoretic mobility shift assays (EMSAs) and “supershift” assays in which specific antibodies against the different members of the tested gene families were included in the binding reactions. Complexes containing JunD were found in three cell lines and two patients. The three cell lines and one patient contained also c-Myc/Max heterodimers. Because c-Myc/Max heterodimers are strong gene transcription activators and are necessary for cell-cycle progression, they may play a role in the progression of CTCL. JunD may also promote cell-cycle progression and influence the expression of cell death survival genes. Interleukin-7 (IL-7) and IL-15, which have been identified as growth factors for CTCL cells, stimulated the DNA binding of JunD and two novel c-Myc recognition site (E-box) binding proteins, but not the DNA binding of c-Myc/Max heterodimers.

Genetics and pulmonary medicine. 7. Somatic mutations in the development of lung cancer

Lung cancers exhibit complex heterogeneous karyotypes and to date sequencing the serial somatic mutations which give rise to malignant change has proved difficult. Cigarette smoke causes a field change in the respiratory mucosa with mutations demonstrable even in histologically normal areas. After smoking cessation many of these mutations seem to persist indefinitely so that the risk of an ex-smoker developing lung cancer never reverts to that of a life-long non-smoker. Demonstration of specific somatic mutations in biopsy or sputum samples may eventually provide a useful method of screening for lung cancer. Somatic mutations give useful information about prognosis in non-small cell lung cancer and they are the key to exciting future retroviral and monoclonal antibody mediated therapies.

Molecular and biological features of two new human squamous and adenocarcinoma of the lung cell lines

Two human cancer cell lines were established from metastatic lesions of an adenocarcinoma (RAL) and a squamous cell (CAEP) carcinoma of the lung. The clinical histories of the patients from whom the cell lines were derived are reported. The lines were maintained in continuous culture with doubling times of 65 (RAL) and 50 (CAEP) hours. The RAL and CAEP cell lines, whose morphology and ultrastructural features are presented, showed extensively rearranged karyotypes with modal number of 85 (RAL) and 98 (CAEP). In particular, chromosome 2 pentasomy and several clonal markers were evident in the RAL cells, whereas a telomeric deletion of chromosome 1, del (1)(q32), was observed in the CAEP cells. The morphologic data were confirmed by high expression of specific antigens for each histotype. A marked positivity of the neuron-specific enolase (NSE) levels was evident by immunoenzymatic assays in the cell lines cytosol with respect to those present in the respective patient's sera. No amplification or rearrangements were evident in the CMYC, LMYC, NMYC, INT-2, ERBB2, HRAS, KRAS, MOS, HST-1 genes by Southern blotting analysis in each cell line. Point mutations in exon 1 of KRAS and in exon 7 of TP53 were evident by polymerase chain reaction (PCR)-DNA sequencing in the RAL cell line, whereas no alterations were present in the HRAS and RB genes. The four genes studied did not show point mutations in the CAEP cell line. The RAL cell line was resistant to all the drugs tested, whereas the CAEP cells were sensitive to vinblastine. These cell lines may represent useful experimental models to investigate lung cancer biology and anticancer drug response.

Delivery to cancer cells of antisense L-myc oligonucleotides incorporated in fusogenic, cationic-lipid-reconstituted influenza-virus envelopes (cationic virosomes)

Antisense oligodeoxy-nucleoside phosphorothioates (OPTs) of L-myc were encapsulated into reconstituted influenza-virus-A envelopes (virosomes). The envelopes of the virosomes consisted of a single positively charged (cationic) lipid bilayer. Binding of cationic virosomes to cellular receptors that are membrane glycoproteins or glycolipids containing terminal sialic acid is mediated by the hemagglutinin glycoprotein (HA) of the influenza virus. After internalization through receptor-mediated endocytosis, cationic virosomes fuse efficiently with the membranes of the endosomal-cell compartment, and as a consequence the encapsulated OPT are delivered to the cell cytoplasma. Examination by fluorescence microscopy of the cellular uptake of cationic virosomes containing fluorescein-labeled OPT showed rapid and efficient incorporation of virosomes. Addition of cationic virosomes (75-150 microl) containing antisense L-myc OPT in the picomolar range to small-cell-lung-cancer (SCLC) cell cultures that expressed highly the L-myc oncogene led to strong inhibition of thymidine incorporation in a concentration-dependent manner. Virosome-entrapped sense L-myc OPT and random-order OPT had only minimal effects on the thymidine uptake. Cells of SCLC cell line NCI-H82 expressing a very low level of L-myc were not affected by antisense-L-myc virosomes. In Western-blot analysis, expression of L-myc protein was suppressed in the antisense-virosome-treated NCI-H209 cells but not in untreated control NCI-H209 cells. These results suggest that cationic virosomes may have great potential as an efficient delivery system for antisense oligonucleotides in cancer therapy.

Molecular characterization of a novel amplicon at 1q21-q22 frequently observed in human sarcomas

In a recent comparative genomic hybridization (CGH) study of a panel of sarcomas, we detected recurrent amplification of 1q21-q22 in soft tissue and bone tumours. Amplification of this region had not previously been associated with sarcoma development, but occasional amplification of CACY/S100A6 and MUC1 in 1q21 had been reported for melanoma and breast carcinoma respectively. Initial screening by Southern blot analysis showed amplification of S100A6, FLG and SPRR3 in several sarcomas and, in a first attempt to characterize the 1q21-q22 amplicon in more detail, we have now investigated the amplification status of these and 11 other markers in the region in 35 sarcoma samples. FLG was the most frequently amplified gene, and the markers located in the same 4.5-Mb region as FLG showed a higher incidence of amplification than the more distal ones. However, for most of the 14 markers, amplification levels were low, and only APOA2 and the anonymous marker D1S3620 showed high-level amplifications (> tenfold increases) in one sample each. We used fluorescence in situ hybridization (FISH) to determine the amplification patterns of two overlapping yeast artificial chromosomes (YACs) covering the region between D1S3620 and FLG (789f2 and 764a1), as well as two more distally located YACs in nine selected samples. Six samples had amplification of the YAC containing D1S3620 and, in three, 764a1 was also included. Five of these tumours showed normal copies of the more distal YACs; thus, it seems likely that an important gene may be located within 789f2, or very close. Two samples had high copy numbers of the most distal YACs. Taken together, FISH and molecular analyses indicate complex amplification patterns in 1q21-q22 with at least two amplicons: one located near D1S3620/789f2 and one more distal.

Kinetic analysis of the mechanism of interaction of full-length TIMP-2 and gelatinase A: evidence for the existence of a low-affinity intermediate

We have undertaken a detailed analysis of the mechanism of inhibition of matrix metalloproteinase-2 (gelatinase A) by tissue inhibitor of metalloproteinase-2 (TIMP-2). Quenched fluorescent substrates have been used to analyze the rate of inhibition of gelatinase A by TIMP-2 over a wide range of TIMP-2 concentrations. When the values of the observed rate constant for the inhibition are plotted against TIMP-2 concentration, saturation is observed at high concentrations, providing evidence for formation of an intermediate in the pathway. Rate constants for the formation and dissociation of the intermediate are 5.9 x 10(6) M-1 s-1 and 6.3 s-1 respectively, giving a Ki for the initial step of approximately 1 microM. The rate constant for the association of the final complex is 33 s-1. By studying the dissociation of 125I-labeled TIMP-2 from a gelatinase A-TIMP-2 complex using ligand exchange experiments, we obtained a rate constant for the dissociation of the final stable complex of 2 x 10(-)8 s-1. This gives a value for the overall dissociation constant of approximately 0.6 fM.

Association between restriction fragment length polymorphism of the L-myc gene and susceptibility to gastric cancer

BACKGROUND

L-myc polymorphism has been documented to be a representative genetic trait which is related an individual's susceptibility to several cancers. However, there have been no reports concerning any significant association between susceptibility to gastric cancer and L-myc polymorphism.

METHODS

The distribution of L-myc polymorphism in 61 patients with gastric cancer was determined by polymerase chain reaction-based restriction fragment length polymorphism and compared with that of 107 healthy control subjects.

RESULTS

There was a significant difference in the distribution of both genotypes (P = 0.024) and allele frequencies (P = 0.026) between the two groups. The relative risk of gastric cancer for genotypes with the shorter (S) allele was 3.09 compared with the longer (L) allele homozygote. No significant correlation with clinicopathological features of the cancers except for prognosis was found. The patients with SS genotypes had a worse prognosis than those with LL or LS genotypes (P = 0.029).

CONCLUSION

L-myc polymorphism may be significant in an individual's susceptibility to gastric cancer in Japan, and may be a useful marker for identifying patients at high risk of developing gastric cancer.

Chromosomal alterations, biological features and in vitro chemosensitivity of SCLC-R1, a new cell line from human metastatic small cell lung carcinoma

A new human cancer cell line was established from a metastatic lesion of a small cell lung carcinoma (SCLC-R1) and maintained in continuous culture with a doubling time of 62 h. The SCLC-R1 line, whose ultrastructural features are presented, showed a diploid DNA content, a translocation involving chromosome 16 [t(16;?)(q24;?)] and noticeable deletions in the FHIT (fragile histidine triad) region in the short arm of chromosome 3 [del(3)(p14)] and in the telomeric region of the short arm of chromosome 12 [del(12)(p13)]. The involvement of 12p in metastatic small cell lung cancer is reported here for the first time. No amplification or rearrangements were evident in the c-myc, L-myc, N-myc, int-2, c-erbB-2, H-ras, K-ras, c-mos, and hst-1 genes by Southern blot analysis. Wild-type p53, RB, K-ras and H-ras genes were evident by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) analysis. The neuron specific enolase (NSE) level was much higher in the cell line's cytosol than in the patient's serum and the cell line also had high expression of chromogranin A and cytokeratin 19. SCLC-R1 cells were sensitive to cisplatin, carboplatin and doxorubicin. The clinical history of the patient from whom the cell line was derived is reported. The characteristics of this new cell line indicate it to be a useful experimental model to investigate lung cancer biology and anticancer drug response.

Restriction fragment length polymorphism of the L-myc oncogene in non-Hodgkin's lymphoma patients from India

We examined 89 non-Hodgkin's lymphoma (NHL) patients of Indian origin for EcoRI restriction fragment length polymorphism (RFLP) of the L-myc gene with a view to testing the hypothesis that the presence of the L-myc S-allele predisposes towards NHL. We found no significant difference either in the distribution of the LL, LS and SS genotypes or in the allelic frequencies between the patient group and the control group with the frequencies of L-myc alleles, L (10.0 kb) and S (6.6 kb), being 0.56 and 0.44, respectively, in the patient group and 0.54 and 0.46, respectively, in the control group. However, a higher proportion (70%) of the S-allele was observed in our control group of normal healthy volunteers. Thus, the presence of L-myc S-allele did not indicate increased susceptibility or predisposition to the malignancy.

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.

High Prevalence of p53 Gene Mutation in Esophageal Cancer

Tissue samples from 24 patients with esophageal cancer were studied to determine the incidence and clinical implications of alterations of the p53 gene. Allelic deletion of chromosome 17p and mutation of the p53 gene were determined by Southern blot analysis and polymerase chain reaction single-stranded conformation polymorphism. Nucleotide sequence analysis was performed using the direct sequencing method when abnormalities were detected. Eighteen of the 24 cases of esophageal cancer showed either gene deletions or mutations of the p53 gene. Among 15 tumors with p53 gene deletion or mutation, 13 point mutations and 2 frame shifts were identified. The clinical data were also analyzed in relation to genetic alteration of the p53 gene. These results indicate that allelic deletion of 17p 13 and mutation of the p53 gene are frequent and may occur simultaneously in esophageal cancer cells. Such changes might be an important step in the development of esophageal cancer. However, the presence of a p53 gene mutation was not significantly associated with tumor stage, nodal stage, age, or smoking. There was no evidence to suggest that p53 gene mutation could be a prognostic factor in esophageal cancer patients.

Expression and regulation of the myc proto-oncogene in the pituitary gland of rainbow trout

We have isolated two c-myc cDNA clones from a trout pituitary gland (PG). One of these clones (tmyc2) is expressed as a 1.9-2.0 kb transcript in the PG, brain and heart, but not in the liver and codes for a protein of 398 amino acids. The second clone (tmyc3) is expressed in the PG (1.6 kb), but not in brain, liver or heart and codes for a protein of 401 amino acids. The expression level of tmyc3 in the PG is 10-fold greater than that of tmyc2. This profile is markedly different from a previously isolated genomic c-myc clone (tmyc1) that is expressed primarily in the liver (2.4 kb) and codes for a larger protein consisting of 417 amino acids. In situ hybridization and Northern blot analysis showed that tmyc3 is expressed primarily in somatolactotrophs of the intermediate lobe (IL) of the PG. Tmyc2 is expressed at similar levels in both the IL and the pars distalis (PD). In vitro stimulation experiments show that releasing factors, known to control cells in the PD, failed to stimulate tmyc2 or tmyc3. However, dopamine and norepinephrine (two neurotransmitters known to control hormone release from the IL) increased tmyc3 expression two to five times. Two other neurotransmitters (GABA and serotonin) failed to stimulate tmyc3 expression. None of the neurotransmitters tested affected tmyc2 expression. These results suggest that tmyc3 is involved in regulating hypertrophy of somatolactotrophs and may have a role in stimulating production of somatolactin, the only hormone known to be synthesised by these cells.

Mapping the binding site for matrix metalloproteinase on the N-terminal domain of the tissue inhibitor of metalloproteinases-2 by NMR chemical shift perturbation

Changes in the NMR chemical shift of backbone amide nuclei (1H and 15N) have been used to map the matrix metalloproteinase (MMP) binding site on the N-terminal domain of the tissue inhibitor of metalloproteinase-2 (N-TIMP-2). Amide chemical shift changes were measured on formation of a stable complex with the catalytic domain of stromelysin-1 (N-MMP-3). Residues with significantly shifted amide signals mapped specifically to a broad site covering one face of the molecule. This site (the MMP binding site) consists primarily of residues 1-11, 27-41, 68-73, 87-90, and 97-104. The site overlaps with the OB-fold binding site seen in other proteins that share the same five-stranded beta-barrel topology. Sequence conservation data and recent site-directed mutagenesis studies are discussed in relation to the MMP binding site identified in this work.

Carcinoma of the lung in Okinawa, Japan: with special reference to squamous cell carcinoma and squamous metaplasia

In Okinawa, a subtropical island in southern Japan, squamous cell carcinoma (SCC), especially the well-differentiated form, is prevalent, while this form is relatively rare in both the mainland and other countries (e.g. United States of America). More patients with SCC from Okinawa, moreover, were positive for human papillomavirus (HPV) DNA by polymerase chain reaction (PCR) (79%), and harbored HPV types 6, 16 and 18, in combination. On the other hand, less than 30% of the mainland patients were positive for HPV DNA by PCR. Those patients who were positive all harbored only one HPV type. Furthermore, in Okinawa, there were a significant number of cases with adenosquamous carcinoma, and they too were positive for HPV DNA. The SCC and the adenocarcinoma cells adjacent to the SCC component in these cases were also positive for HPV DNA, and such adenocarcinoma cells were enlarged in size with relatively wide cytoplasm. The authors postulate that HPV infects adenocarcinoma cells and changes them to enlarged cells, followed by squamous metaplasia. In this report, HPV DNA was transfected to adenocarcinoma cells (cultured cell lines) and this showed that HPV causes squamous metaplasia. In addition, aberrant expression of p53 was demonstrated in a large number of the SCC cases in Okinawa. The enlarged adenocarcinoma cells adjacent to the SCC components in adenosquamous carcinomas also showed aberrant expression of p53. The recent advances in the studies of anti-oncogenes, p53, etc. and oncogenes are outlined. It is to be noted that the molecular mechanisms of carcinogenesis in the lung have been studied in general, classifying lung tumors into two groups, namely, small cell carcinoma (SCLC) and non-small cell carcinoma (NSCLC). However, because human lung cancer is represented by a wide variety of histologic types, molecular genetic studies according to a more detailed histological subclassification is needed.

Regulation of gene expression by natural antisense RNA transcripts

The use of synthetic antisense oligonucleotides as specific inhibitors of gene expression exploits the susceptibility of mRNA to functional blockade at several levels, including mRNA processing, transport, translation and degradation. It is becoming increasingly apparent that the actions of these synthetic oligomers are analogous to those of endogenous RNA molecules involved in the regulation of gene expression in both prokaryotes and eukaryotes. A growing number of eukaryotic genes are now thought to be regulated at least in part by natural antisense RNA transcribed from the presumptive non-coding DNA strand. This possibility is supported by the presence of a complex system of double-stranded (ds) RNA-specific proteins and dsRNA-induced signal transduction pathways in eukaryotic cells. The presence of functional open reading frames in a number of recognized natural antisense RNA transcripts indicates that, in addition to regulating gene function at the RNA level, the antisense strand of many genes may code for as yet unidentified proteins. In the present study we review the current literature on the role(s) played by natural antisense RNA in eukaryotic cells, with an emphasis on genes for which clear evidence of regulation, or potential regulation by natural antisense RNA is available.

Genetic factors in lung disease. Part II: Lung cancer and angiotensin converting enzyme gene

The recent progress in molecular biology has led to the elucidation of pathogenesis of lung cancer. The development of a lung cancer requires multiple genetic changes, consisting of the activation of oncogenes, including the K-ras and myc genes, and of inactivation of tumour suppressor genes, including the Rb, p53 and CDKN2 genes. Knowing the specific genes undergoing such changes should be useful as biomarkers for the early detection of cells destined to become malignant. Moreover, such genetic changes could be targets of newly designed drugs and gene-based therapy. Although the angiotensin I-converting enzyme was originally discovered in equine plasma, it has been recognized in various organs and cells other than vascular endothelial cells. This enzyme is also known to have wide substrate specificity to many peptides. The definite roles of angiotensin converting enzyme (ACE) in the respiratory system are largely unknown. Recent progress in molecular biology of the ACE, however, gives us a good chance to look over the significance of ACE in respiratory diseases as well as cardiovascular disorders. In this review, we show the recent advances in the basic studies of the ACE and refer to its clinical application.

Rox, a novel bHLHZip protein expressed in quiescent cells that heterodimerizes with Max, binds a non-canonical E box and acts as a transcriptional repressor

Proteins of the Myc and Mad family are involved in transcriptional regulation and mediate cell differentiation and proliferation. These molecules share a basic-helix-loop-helix leucine zipper domain (bHLHZip) and bind DNA at the E box (CANNTG) consensus by forming heterodimers with Max. We report the isolation, characterization and mapping of a human gene and its mouse homolog encoding a new member of this family of proteins, named Rox. Through interaction mating and immunoprecipitation techniques, we demonstrate that Rox heterodimerizes with Max and weakly homodimerizes. Interestingly, bandshift assays demonstrate that the Rox-Max heterodimer shows a novel DNA binding specificity, having a higher affinity for the CACGCG site compared with the canonical E box CACGTG site. Transcriptional studies indicate that Rox represses transcription in both human HEK293 cells and yeast. We demonstrate that repression in yeast is through interaction between the N-terminus of the protein and the Sin3 co-repressor, as previously shown for the other Mad family members. ROX is highly expressed in quiescent fibroblasts and expression markedly decreases when cells enter the cell cycle. Moreover, ROX expression appears to be induced in U937 myeloid leukemia cells stimulated to differentiate with 12-O-tetradecanoylphorbol-13-acetate. The identification of a novel Max-interacting protein adds an important piece to the puzzle of Myc/Max/Mad coordinated action and function in normal and pathological situations. Furthermore, mapping of the human gene to chromosome 17p13.3 in a region that frequently undergoes loss of heterozygosity in a number of malignancies, together with the biochemical and expression features, suggest involvement of ROX in human neoplasia.

Advances in the analysis of chromosome alterations in human lung carcinomas

A review of chromosomal analyses of human lung carcinomas is presented. Karyotypic studies have revealed multiple cytogenetic changes in most small cell lung carcinomas (SCLCs) and non-small cell lung carcinomas (NSCLCs). In SCLCs, losses from 3p, 5q, 13q, and 17p predominate; double minutes associated with amplification of members of the MYC oncogene family may be common late in disease. In NSCLCs, deletions of 3p, 9p, and 17p, +7, i(5)(p10), and i(8)(q10) often are reported. The recurrent deletions encompass sites of tumor suppressor genes commonly inactivated in lung carcinomas, such as CDKN2 (9p21), RB1 (13q14), and TP53 (17p13). Despite technical advances in cell culture, the rate of successful karyotypic analysis of lung carcinomas has remained low. Alternative molecular cytogenetic methods to assess chromosome changes in lung cancer, particularly comparative genomic hybridization (CGH) analysis, are discussed. Initial CGH studies confirm the existence of many of the karyotypic imbalances identified earlier in lung cancer and have revealed several recurrent abnormalities, such as 10q- in SCLC, that had not been recognized previously. The further application of such molecular cytogenetic approaches should enable investigators to define more precisely the spectrum and clinical implications of chromosome alterations in lung cancer.

Expression of myc-family, myc-interacting, and myc-target genes during preimplantation mouse development

Previous studies indicated that members of the myc gene family may be essential for preimplantation development. Other studies revealed that preimplantation embryos lacking c-myc, N-myc, or L-myc are viable, indicating that these genes are either not essential for preimplantation development or can be substituted for functionally by other myc gene family members. To investigate the possible role of these genes during preimplantation development, we determined the temporal patterns of expression of four members of the myc gene family, genes encoding myc-associated proteins, and four putative MYC target genes. We observed a sequential pattern of myc gene expression, with the L-myc mRNA expressed as a maternal transcript, the c-myc mRNA expressed during the 4-cell through morula stages, and the B-myc mRNA expressed highly at the morula and blastocysts stages. B-myc was the predominant family member expressed during preimplantation development. The mxi mRNA was not detectable and the mad mRNA was detectable only as a maternal transcript. The max mRNA, however, was expressed both as a maternal mRNA and as an embryonic message throughout most of preimplantation development. Three putative MYC target genes (Odc, cyclin E, and prothymosin-alpha) were transcriptionally induced during the 2-cell stage, and their mRNAs increased sharply in abundance during development to the morula and blastocyst stages. Another putative MYC target gene, cyclin A, was expressed both as a maternal mRNA and as an embryonic transcript. These data support the view that the expression of myc target genes may be supported initially through the expression of maternally inherited MYC proteins and corresponding mRNAs and that subsequent stage-specific changes in expression of myc genes, myc-associated genes, and myc target genes may control early differentiative events around the time of implantation.

MYCL genotypes and loss of heterozygosity in non-small-cell lung cancer

Some studies have suggested that the S allele of the MYCL oncogene, which results from an intragenic EcoRI restriction fragment length polymorphism (RFLP), may be associated with cancer susceptibility. In addition, this allele has also been linked to metastases and adverse survival in certain cancers, although studies of lung cancer patients from different populations have yielded controversial results. We studied 108 cases of surgical resected non-small-cell lung cancer (NSCLC) and found no evidence that MYCL genotypes were associated with tumour progression or a worse prognosis. However, the presence of loss of heterozygosity (LOH) at this chromosome 1p32 locus correlated significantly with regional lymph node involvement, as well as advanced TNM stage. These data indicate the existence of a chromosome 1p candidate tumour-suppressor gene(s), possibly in linkage disequilibrium with the EcoRI RFLP in specific populations, which appears to play a role in determining tumour progression in NSCLC. Refined mapping of the critical region of loss should help attempts to identify and clone the candidate gene.

Simultaneous detection of genetic and immunological markers in non-small cell lung cancer: prediction of metastatic potential of tumor

The restriction fragment length polymorphism of c-Ha-ras-1 and L-myc genes and expression of cell surface effector molecules were studied to determine their potential utility as markers for assessing risk of metastasis in 84 lung cancer patients. We performed a comparative study of primary lung carcinomas, metastases, adjacent tissues and blood samples in a group of patients with lung cancer of different histological types, grade of differentiation and presence of regional and distant metastasis. No differences in the frequency of c-Ha-ras-1 rare alleles were found between lung cancer patients and unaffected controls. The detection of common a4-allele seems to be associated with metastasis and low differentiation of lung carcinomas. S-allele of L-myc was observed in 82.6% of patients with metastatic lesions. Homozygosity of L-allele patients was not evidence for distant metastasis and only 17.4% of these patients have metastatic lesions of the lymph nodes. The expression of HLA class I and receptor of transferrin (TrRec) were tested immunohistochemically in the same patients. In the group of squamous cell carcinomas with regional metastases the expression of HLA class I antigens was decreased [7/21 (33.3%) positive staining tumors versus 13/20 (65.0%) in the group without metastases]. The opposite situation was observed for TrRec. The data of restriction fragment length polymorphism of oncogenes and expression of two cell surface effector molecules, identified in the same patients, were combined. The registration of more than one poor marker, tested in individuals with squamous cell carcinoma, closely correlated with dissemination and advanced stage of the disease. Nearly 90% (20/22) of patients with well and moderately differentiated tumor revealed metastatic lesions versus 6.6% (1/15) of patients with manifestation of a single poor marker. Finally, proposals could be made for the development of a risk group that incorporates both clinical and molecular biology features in the prediction of metastasis.

Analysis of L-myc and GSTM1 genotypes in Chinese non-small cell lung carcinoma patients

The genotypes of L-myc and GSTM1 genes were studied in normal lung tissues of 98 non-small cell lung carcinoma (NSCLC) patients from Hong Kong using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) techniques. Results showed a statistical difference in L-myc genotypes between Chinese and African Americans (P = 0.02). A significant deficit in heterozygotes resulting in the departure from Hardy-Weinberg equilibrium in lung cancer female patients was detected (0.01 < P < 0.02). There were significant differences in survival times in patients having L-L and S-S genotypes, with shorter survival times in the patients with L-L genotypes (0.01 < P < 0.05). Data on age, size of tumor, histological types, and lymph node metastasis showed no significant association with L-myc genotype. The survival time in the GSTM1-negative (null gene) group was significantly different from the GSTM1 positive group between 16 and 24 months after operation (0.01 < P < 0.05). There was no significant difference in the distribution of GSTM1 genotypes between Chinese and Caucasian Americans.

SAS is amplified predominantly in surface osteosarcoma

The development of several types of human tumors is related to amplification of genes that are involved in cell growth. The protein products of these genes give the cells a selective growth advantage. The q13-15 region of chromosome 12 is frequently altered in human sarcomas, and the SAS gene has been identified in an amplification unit mapping to this region. Gene amplification of SAS was analyzed to determine the frequency of genetic alteration of this gene in osteosarcoma. Using Southern blot analysis as well as quantitative polymerase chain reaction, SAS was found to be amplified in 10 (36%) of 28 osteosarcomas. Gene amplification was evaluated in subtypes of osteosarcoma. All seven surface osteosarcomas displayed amplified SAS. In contrast, SAS was amplified in only two (13%) of 15 intramedullary osteosarcomas. The finding that all surface osteosarcomas demonstrated SAS gene amplification suggests that this gene may play a role in the pathogenesis of osteosarcoma subtypes and that surface osteosarcoma may be genetically different from high-grade intramedullary osteosarcoma.

The genotype of the human cancer cell: implications for risk analysis

An extremely large database describes genotypes associated with the human cancer phenotype and genotypes of human populations with genetic predisposition to cancer. Aspects of this database are examined from the perspective of risk analysis, and the following conclusions and hypotheses are proposed: (1) The genotypes of human cancer cells are characterized by multiple mutated genes. Each type of cancer is characterized by a set of mutated genes, a subset from a total of more than 80 genes, that varies between tissue types and between different tumors from the same tissue. No single cancer-associated gene nor carcinogenic pathway appears suitable as an overall indicator whose induction serves as a quantitative marker for risk analysis. (2) Genetic defects that predispose human populations to cancer are numerous and diverse, and provide a model for associating cancer rates with induced genetic changes. As these syndromes contribute significantly to the overall cancer rate, risk analysis should include an estimation of the effect of putative carcinogens on individuals with genetic predisposition. (3) Gene activation and inactivation events are observed in the cancer genotype at different frequencies, and the potency of carcinogens to induce these events varies significantly. There is a paradox between the observed frequency for induction of single mutational events in test systems and the frequency of multiple events in a single cancer cell, suggesting events are not independent. Quantitative prediction of cancer risk will depend on identifying rate-limiting events in carcinogenesis. Hyperproliferation and hypermutation may be such events. (4) Four sets of data suggest that hypermutation may be an important carcinogenic process. Current mechanisms of risk analysis do not properly evaluate the potency of putative carcinogens to induce the hypermutable state or to increase mutation in hypermutable cells. (5) High-dose exposure to carcinogens in model systems changes patterns of gene expression and may induce protective effects through delay in cell progression and other processes that affect mutagenesis and toxicity. Paradigms in risk analysis that require extrapolation over wide ranges of exposure levels may be flawed mechanistically and may underestimate carcinogenic effects of test agents at environmental levels. Characteristics of the human cancer genotype suggest that approaches to risk analysis must be broadened to consider the multiplicity of carcinogenic pathways and the relative roles of hyperproliferation and hypermutation. Further, estimation of risk to general human populations must consider effects on hypersusceptible individuals. The extrapolation of effects over wide exposure levels is an imprecise process.

Detection of auto-antibodies against L-myc oncogene products in sera from lung cancer patients

Auto-antibodies against L-myc oncogene products (L-Myc) in sera from lung cancer patients were examined using bacterially synthesized glutathione S-transferase (GST) L-Myc fusion proteins and Western blot analysis. The detection rate of anti-L-Myc antibodies in sera from lung cancer patients was 10%, while that in sera obtained from normal volunteers was 0%. Five patients with non-small-cell lung cancers (2 adenocarcinomas, 2 squamous-cell carcinomas and I large-cell carcinoma) were included in the group with anti-L-Myc antibodies. These auto-antibodies belonged to the IgG class and recognized the carboxy terminus of L-Myc. Circulating L-Myc was not detected in sera from patients with anti-L-Myc antibodies. Differences in age, sex, performance status, histology, stage, smoking history and prior treatment were not significantly different between anti-L-Myc antibody-positive and antibody-negative patients. Anti-nuclear antibodies were detected in 40% of lung cancer patients and 57% of those with anti-L-Myc antibodies. Our data suggest that detection of anti-L-Myc antibodies may be helpful in the diagnosis and evaluation of the host-immune response to L-Myc in a subset of lung cancer patients.

Genomic instability in 1p and human malignancies

Both cytogenetic and molecular genetic approaches have unveiled non-random genomic alterations in 1p associated with a number of human malignancies. These have been interpreted to suggest the existence of cancer-related genes in 1p. Earlier studies had employed chromosome analysis or used molecular probes mapped by in situ hybridization. Further, studies of the various tumor types often involved different molecular probes that had been mapped by different technical approaches, like linkage analysis, radioactive or fluorescence in situ hybridization, or by employing a panel of mouse x human radiation reduced somatic cell hybrids. The lack of maps fully integrating all loci has complicated the generation of a comparative and coherent picture of 1p damage in human malignancies even among different studies on the same tumor type. Only recently has the availability of genetically mapped, highly polymorphic loci at (CA)n repeats with sufficient linear density made it possible to scan genomic regions in different types of tumors readily by polymerase chain reaction (PCR) with a standard set of molecular probes. This paper aims at presenting an up-to-date picture of the association of 1p alterations with different human cancers and compiles the corresponding literature. From this it will emerge that the pattern of alterations in individual tumor types can be complex and that a stringent molecular and functional definition of the role that Ip alterations might have in tumorigenesis will require a more detailed analysis of the genomic regions involved.

DNA supercoiling changes and nuclear matrix-associated proteins: possible role in oncogene-mediated radioresistance

PURPOSE

Transfection with either H-ras or H-ras and c-myc has been shown to confer radioresistance in rat embryonal cells (REC). REC primary, transfected with either c-myc, H-ras or cotransfected with c-myc and H-ras (in ascending order of radioresistance and tumorigenicity), were used as an in vitro model system to determine if nuclear matrix-mediated higher order DNA organization contributes to oncogene-mediated radioresistance.

METHODS AND MATERIALS

DNA damage induction and repair were measured by the alkaline and neutral filter elution assays. Analysis of the ability of DNA loop domains to undergo supercoiling changes in the presence of radiation-induced damage was determined by the fluorescent halo assay (FHA). Because DNA loops are organized by the nuclear matrix (NM), a study of NM-associated proteins by high resolution two-dimensional gel electrophoresis was performed.

RESULTS

Induction and repair rates of DNA single- and double-strand breaks were similar for the relatively radiosensitive c-myc transfected and the radioresistant c-myc + H-ras transfected cells. However, the degree of inhibition of DNA supercoil rewinding in the presence of radiation-induced damage was less in the radioresistant cells and was inversely correlated with survival. A progressive loss of NM-associated proteins was observed, which correlated with increasing radioresistance and tumorigenicity in these cell lines. In addition, some protein changes were consistent with the possibility that these changes could be involved in DNA anchoring.

CONCLUSIONS

Increased radioresistance associated with increasing tumorigencity in these oncogene-transfected cell lines could be due to changes in NM-mediated DNA organization, possibly via differences in NM protein composition that occur following oncogenic transfection.

The amplification of oligonucleotide themes in the evolution of the myc protooncogene family

The evolutionary past of intragenic repeats in protein-coding exons of c-, N-, L-, and s-myc-protooncogene subfamilies was elucidated. Apparently these genes evolved by succession of distinct unit events rather than by a steady flow of random point mutations. An evolutionary event probably involved a duplication of the whole gene, which was followed by amplification of progressively shorter oligonucleotide themes and motifs. The repeats were either joined in tandem or one of the copies was transposed and integrated elsewhere within the same exon. In some instances multiple fragments of an amplified theme were integrated at several sites. Direct repeats were found to prevail over inverted ones. By reconstructing the fate of repeats in the course of evolution of vertebrates, the origins of some functional domains could be traced to the initial amplification event. For example, an N-myc-specific domain was created by tandem duplication of a single-copy theme of L-myc exon; at the time of divergence of the c-myc and N-myc, the tandem duplex underwent a new round of duplication followed by transposition of the new copy, thus accounting for the formation of a new domain specific for c-myc. The model proposed here may be regarded as a molecular-level equivalent of the theory of punctuated equilibria.

Expression and activity of L-Myc in normal mouse development

To determine the role of L-Myc in normal mammalian development and its functional relationship to other members of the Myc family, we determined the normal patterns of L-myc gene expression in the developing mouse by RNA in situ hybridization and assessed the phenotypic impact of L-Myc deficiency produced through standard gene targeting methodology. L-myc transcripts were detected in the developing kidney and lung as well as in both the proliferative and the differentiative zones of the brain and neural tube. Despite significant expression of L-myc in developing mouse tissue, homozygous null L-myc mice were found to be viable, reproductively competent, and represented in expected frequencies from heterozygous matings. A detailed histological survey of embryonic and adult tissues, characterization of an embryonic neuronal marker, and measurement of cellular proliferation in situ did not reveal any congenital abnormalities. The lack of an apparent phenotype associated with L-Myc deficiency indicates that L-Myc is dispensable for gross morphological development and argues against a unique role for L-Myc in early central nervous system development as had been previously suggested. Although overlapping expression patterns among myc family members raise the possibility of complementation of L-Myc deficiency by other Myc oncoproteins, compensatory changes in the levels of c- and/or N-myc transcripts were not detected in homozygous null L-myc mice.

Myc oncogenes: the enigmatic family

The myc family of proto-oncogenes is believed to be involved in the establishment of many types of human malignancy. The members of this family have been shown to function as transcription factors, and through a designated target sequence bring about continued cell-cycle progression, cellular immortalization and blockages to differentiation in many lineages. However, while much of the recent work focusing on the c-myc oncogene has provided some very important advances, it has also brought to light a large amount of conflicting data as to the mechanism of action of the gene product. In this regard, it has now been shown that c-myc is effective in transcriptional repression as well as transcriptional activation and, perhaps more paradoxically, that it has a role in programmed cell death (apoptosis) as well as in processes of cell-cycle progression. In addition, particular interest has surrounded the distinct roles of the two alternative translation products of the c-myc gene, c-Myc 1 and c-Myc 2. The intriguing observation that the ratio of c-Myc 1 to c-Myc 2 increases markedly upon cellular quiescence led to the discovery that the enforced expression of the two proteins individually showed that c-Myc 2 stimulates cell growth, whereas c-Myc 1 appears to be growth suppressing. Clearly, the disparities in the activities of c-Myc, together with the consistent occurrence of mutations of c-myc in human malignancies, means that, although reaching an understanding of the functions of the myc gene family might not be simple, it remains well worthy of pursuit.