Activated oncogenes in human tumors

The search for the genetic targets responsible for tumorigenesis has led to the identification of a number of cancer genes or cellular oncogenes (c-oncogenes). The oncogenes are activated forms of the proto-oncogenes, which are normal cellular genes and are scattered throughout the cellular genome. The number of known cellular proto-oncogenes and associated oncogenes now exceeds 30. There are different proto-oncogene families and their products have different functions and cellular localisation. They may function in normal cells in the process of proliferation, regulation of cellular metabolism through signal transfer, or cell differentiation. Activation of proto-oncogenes in man is now assumed to be due to: 1) point mutation; 2) overexpression or 3) gene rearrangement. The observation that in some tumors multiple oncogenes are altered could be interpreted in terms of a multigene hypothesis. However, in some cases, a single properly-activated oncogene may be able to trigger the whole process of malignant conversion. It is difficult to correlate, without ambiguity, tumor induction to specific types of DNA lesions in human tumors. Xeroderma pigmentosum (XP), a rare recessive autosomal skin disorder characterized biochemically as a DNA repair-deficient disease, is the first example in which unrepaired UV-induced DNA lesions are directly responsible for tumorigenesis. In two independent XP skin tumors, isolated from the same patient, we have detected several (N-ras, c-myc, Ha-ras) altered oncogenes in the same tumor. We postulate that the modifications we have found in these tumors are primarily due to the presence of unrepaired UV-adducts. Long term treatment of human tumoral cell lines bearing an activated ras oncogene, with Interferon-alpha (IFN), showed that IFN can affect the phenotype of the tumor cells without altering the expression of the activated ras gene. IFN may have the capacity to affect diverse cellular pathways. Consequently, the nature of the biological response of a given type of tumor cell to IFN may depend on its inherent properties.     

Activated oncogenes in human tumors

ras oncogenes are cellular genes altered by point mutation in 10 to 30% of human tumors. Under this mutated form they play a role in the malignant process, probably in association with other oncogenes. The different ras genes identified in human cancers, the point mutations that activate the ras genes and the properties of the ras proteins are described.     

Activated N-ras oncogenes in human neuroblastoma

Fifteen primary neuroblastomas and four bone marrow samples from neuroblastoma patients, representing clinical Stages I to IV, have been screened for mutations in codons 12, 13, and 61 of N-ras. Neuroblastoma DNAs were subjected to the polymerase chain reaction to amplify the relevant sequences and were then hybridized with specific oligonucleotides to locate and identify point mutations. The results show that one Stage I tumor contained an N-ras gene that was activated by a GC-CG transversion of the first base of codon 61, while in one Stage II tumor, activation of N-ras involved a GC-CG transversion of the first position of codon 13. N-ras activations were not detected in the six Stage III tumors and eight Stage IV tumors that were examined.     

Activated ras oncogenes in human thyroid cancers

Human thyroid epithelial (follicular) cells give rise to two malignant tumors--"follicular" carcinomas, which metastasize almost exclusively via the bloodstream, and "papillary" carcinomas, which metastasize predominantly via lymphatics (Williams, E. D. In: W. Duncan (ed.), Recent Results in Cancer Research: Thyroid Cancer, pp. 47-55. Berlin: Springer-Verlag, 1980). We have investigated whether this contrast in biological behavior might be associated with different patterns of oncogene activation. DNA transfection analysis of five follicular and ten papillary cancers indeed showed a statistically significant difference in the pattern of genes responsible, activated ras oncogenes being found in 80% of follicular tumors but only 20% of papillary tumors. In addition, in follicular cancers we have found activation of all three ras oncogenes (H-ras, K-ras, and N-ras), the first time that this has been demonstrated in a primary human tumor type (as opposed to cell lines). We suggest therefore that ras activation may be an important determinant of metastatic capability in these epithelial cancers.     

Expression of oncogenes in human breast cancer specimens

More than 60 breast cancer specimens were screened for their expression status of 25 different proto-oncogenes. The screening method is based on in vitro synthesis of a radioactive cDNA copied from the total cellular RNA of tumor tissue. This cDNA is hybridized to cloned oncogene probes which are immobilized to a GeneScreen membrane. Frequently multiple oncogenes were found expressed although expression levels were rather moderate. 25-30% of the analyzed tumors showed significant expression of either erbB, src, raf1, lck or H-ras. Although neu expression--an oncogene believed to be particular relevant as prognostic parameter for mamma carcinoma--was screened for most of the tumors with a heterologous gene probe, expression signals could be detected in about 20% cases. The only notable correlation with classical clinical parameters such as tumor size and proliferation stage, hormone receptor status and different DNA indices was the observation that tumors lacking the progesterone receptor frequently express multiple oncogenes. Advantages and limitations of the cDNA/dot-blot screening for oncogene expression are discussed.     

Alteration in copy numbers of genes as a mechanism for acquired drug resistance

Chemoresistance is a major obstacle for successful treatment of cancer. To identify regions of the genome associated with acquired resistance to therapeutic drugs, we conducted molecular cytogenetic analyses of 23 cancer-cell lines, each resistant to either camptothecin, cisplatin, etoposide (VP-16), Adriamycin, or 1-beta-D-arabinofuranosylcytosine, although the parental tumor lines were not. Subtractive comparative genomic hybridization studies revealed regions of gain or loss in DNA-copy numbers that were characteristic of drug-resistant cell lines; i.e., differences from their drug-sensitive parental cell lines. Thirteen ATP-binding cassette (ABC) transporter genes [ABCA3, ABCB1 (MDR1), ABCB6, ABCB8, ABCB10, ABCB11, ABCC1 (MRP1), ABCC4, ABCC9, ABCD3, ABCD4, ABCE1, and ABCF2] were amplified among 19 of the resistant cell lines examined. Three genes encoding antiapoptotic BCL-2 proteins (BCL2L2, MCL1, and BCL2L10) were also amplified and consequently overexpressed in three of the derivative lines. Down-regulation of BCL2L2 with an antisense oligonucleotide sensitized a VP-16 resistant ovarian-cancer cell line (SKOV3/VP) to VP-16. A decrease in copy numbers of genes encoding deoxycytidine kinase, DNA topoisomerase I, and DNA topoisomerase II alpha reduced their expression levels in one cytosine arabinoside-resistant line, two of three camptothecin-resistant lines, and two of five VP-16-resistant cell lines, respectively. Our results indicated that changes in DNA-copy numbers of the genes mentioned can activate or down-regulate them in drug-resistant cell lines, and that such genomic alterations might be implicated in acquired chemoresistance.     

ras oncogenes in human cancer: a review

Mutations in codon 12, 13, or 61 of one of the three ras genes, H-ras, K-ras, and N-ras, convert these genes into active oncogenes. Rapid assays for the detection of these point mutations have been developed recently and used to investigate the role mutated ras genes play in the pathogenesis of human tumors. It appeared that ras gene mutations can be found in a variety of tumor types, although the incidence varies greatly. The highest incidences are found in adenocarcinomas of the pancreas (90%), the colon (50%), and the lung (30%); in thyroid tumors (50%); and in myeloid leukemia (30%). For some tumor types a relationship may exist between the presence of a ras mutation and clinical or histopathological features of the tumor. There is some evidence that environmental agents may be involved in the induction of the mutations.     

EXPRESSION OF CELLULAR ONCOGENES IN HUMAN PRIMARY HEPATOCELLULAR CARCINOMA

With DNA-mRNA hybridization in situ technique, the expression of five oncogenes, c-N-ras, c-Ki-ras. c-Ha-ras, c-myc and c-fos, was observed in two cases of human hepatocellular carcinoma. The expression of c-N-ras &; c-fos was greatly enhanced in tumor tissues of the two cases, and about 25%–50% of the tumor cells showed positive expression. The other three oncogenes namely c-Ki-ras, c-Ha-ras &; c-myc, were not detected in these two carcinomas or in the non-cancerous liver tissues adjacent to the carcinomas. It is surmised that c-N-ras and c-fos may play coordinative role in maintaining the malignant phenotype of human primary hepatocellular carcinoma.     

Detection of activated ras oncogenes in human thyroid carcinomas

Focus formation following DNA transfection of mouse 3T3-Vill cells was used to search for the presence of activated oncogenes in human thyroid tumors. Oncogenes belonging to the ras family were detected in four out of six thyroid carcinomas (Ki-ras in one anaplastic tumor and one follicular moderately differentiated tumor and Ha-ras and N-ras in two papillary tumors). Normal thyroid tissue samples obtained from two patients, one with an anaplastic tumor and one with a benign adenoma, and samples from 4 benign adenomas and from one toxic goiter of a patient with Graves' disease gave negative results. In one case, restriction enzyme analysis demonstrated the presence of a mutation in codon 12 of the activated Ha-ras oncogene. Our data show that all three ras proto-oncogenes can become activated in malignant thyroid tumors.     

GSTM1 and GSTT1 copy numbers and mRNA expression in lung cancer

Large fractions of the human population do not express GSTM1 and GSTT1 (GSTM1/T1) enzymes because of deletions in these genes. These variations affect xenobiotic metabolism and have been evaluated in relation to lung cancer risk, mostly based on null/present gene models. We measured GSTM1/T1 heterozygous deletions, not tested in genome-wide association studies, in 2,120 controls and 2,100 cases from the Environment And Genetics in Lung cancer Etiology (EAGLE) study. We evaluated their effect on mRNA expression on lung tissue and peripheral blood samples and their association with lung cancer risk overall and by histology types. We tested the null/present, dominant, and additive models using logistic regression. Cigarette smoking and gender were studied as possible modifiers. Gene expression from blood and lung tissue cells was strongly down regulated in subjects carrying GSTM1/T1 deletions by both trend and dominant models (P?相似文献   

An integrated analysis of miRNA and gene copy numbers in xenografts of Ewing's sarcoma

Background

Xenografts have been shown to provide a suitable source of tumor tissue for molecular analysis in the absence of primary tumor material. We utilized ES xenograft series for integrated microarray analyses to identify novel biomarkers.

Method

Microarray technology (array comparative genomic hybridization (aCGH) and micro RNA arrays) was used to screen and identify copy number changes and differentially expressed miRNAs of 34 and 14 passages, respectively. Incubated cells used for xenografting (Passage 0) were considered to represent the primary tumor. Four important differentially expressed miRNAs (miR-31, miR-31*, miR-145, miR-106) were selected for further validation by real time polymerase chain reaction (RT-PCR). Integrated analysis of aCGH and miRNA data was performed on 14 xenograft passages by bioinformatic methods.

Results

The most frequent losses and gains of DNA copy number were detected at 9p21.3, 16q and at 8, 15, 17q21.32-qter, 1q21.1-qter, respectively. The presence of these alterations was consistent in all tumor passages. aCGH profiles of xenograft passages of each series resembled their corresponding primary tumors (passage 0). MiR-21, miR-31, miR-31*, miR-106b, miR-145, miR-150*, miR-371-5p, miR-557 and miR-598 showed recurrently altered expression. These miRNAS were predicted to regulate many ES-associated genes, such as genes of the IGF1 pathway, EWSR1, FLI1 and their fusion gene (EWS-FLI1). Twenty differentially expressed miRNAs were pinpointed in regions carrying altered copy numbers.

Conclusion

In the present study, ES xenografts were successfully applied for integrated microarray analyses. Our findings showed expression changes of miRNAs that were predicted to regulate many ES associated genes, such as IGF1 pathway genes, FLI1, EWSR1, and the EWS-FLI1 fusion genes.     

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.     

人类胃粘膜上皮永生细胞株中APC、Rb、c-met基因拷贝数研究

目的 在分子水平研究人正常胃粘膜上皮永生细胞株（ＧＥＳ－１）多种已知癌基因,抑癌基因的细胞内拷贝数,并对这一细胞的特性进行鉴定。方法 用载有ＡＰＣ,Ｒｂ,ｃ－ｍｅｔ基因的质粒经切口平移直接标记生物素制作 探针,与ＧＥＳ－１间期细胞的位杂志。结果 ＡＰＣ基因双拷贝的核为４８％,三拷贝的核占２２％;Ｒｂ基因双拷贝核占７１％;ｃ－ｍｅｔ基因双拷贝的核占８０％。     

Alterations of oncogenes in metastatic tumours of human gastric carcinomas

To determine whether alterations in oncogenes are associated with tumour progression and metastasis, DNAs from 32 metastatic tumour samples of different sites in 12 autopsy cases of gastric carcinomas were analysed for alterations of ERBB, ERBB2, HST1, INT2 and LMYC genes by Southern blot hybridisation. DNAs from 89 primary gastric carcinomas including 69 advanced carcinomas and 20 early carcinomas were also examined. In primary tumours, no amplification was detected in early carcinomas, while amplification of ERBB and ERBB2 genes was detected in one (1.4%) and four (5.8%) out of 69 advanced carcinomas, respectively. In metastatic tumours, amplification of ERBB gene was detected in three metastatic tumours (9.4%), and all of them had allelic deletion of the LMYC gene. Regardless of histological type, amplification of ERBB2 gene was detected in 8 metastatic tumours (25.0%), out of which three tumours had coamplification of HST1 and INT2 genes. The incidence of ERBB2 amplification in metastatic tumours was significantly higher than that in primary tumours. These results indicate that multi-alterations in oncogenes might occur during tumour progression and metastasis of human gastric carcinomas.     

Clinical implication of recurrent copy number alterations in hepatocellular carcinoma and putative oncogenes in recurrent gains on 1q

To elucidate the pathogenesis of hepatocellular carcinoma (HCC) and develop useful prognosis predictors, it is necessary to identify biologically relevant genomic alterations in HCC. In our study, we defined recurrently altered regions (RARs) common to many cases of HCCs, which may contain tumor-related genes, using whole-genome array-CGH and explored their associations with the clinicopathologic features. Gene set enrichment analysis was performed to investigate functional implication of RARs. On an average, 23.1% of the total probes were altered per case. Mean numbers of altered probes are significantly higher in high-grade, bigger and microvascular invasion (MVI) positive tumors. In total, 32 RARs (14 gains and 18 losses) were defined and 4 most frequent RARs are gains in 1q21.1-q32.1 (64.5%), 1q32.1-q44 (59.2%), 8q11.21-q24.3 (48.7%) and a loss in 17p13.3-p12 (51.3%). Through focusing on RARs, we identified genes and functional pathways likely to be involved in hepatocarcinogenesis. Among genes in the recurrently gained regions on 1q, expression of KIF14 and TPM3 was significantly increased, suggesting their oncogenic potential in HCC. Some RARs showed the significant associations with the clinical features. Especially, the recurrent loss in 9p24.2-p21.1 and gain in 8q11.21-q24.3 are associated with the high tumor grade and MVI, respectively. Functional analysis showed that cytokine receptor binding and defense response to virus pathways are significantly enriched in high grade-related RARs. Taken together, our results and the strategy of analysis will help to elucidate pathogenesis of HCC and to develop biomarkers for predicting behaviors of HCC.