beta-Catenin and ras oncogenes detect most human colorectal cancer.

PURPOSE AND STUDY DESIGN: Recent studies have shown that beta-catenin translocated into the cell nucleus functions like an oncogene. Accumulating evidence suggests that activation of the beta-catenin oncogenic signaling cascade along with its twin, the K-ras cascade, may exert syngeneic or synergistic effects on tumor development and progression. In the study reported here, we analyzed oncogenic beta-catenin activation on the basis of its nuclear accumulation (NA) and compared the results with those of mutational activation of K-ras in 74 patients with colorectal cancer to determine whether the two oncogene-mediated signaling cascades interact. RESULTS: We found two distinct patterns of beta-catenin activation, i.e., diffuse NA in 20 cases (27%) and selective NA at the tumor invasion front (NAinv) in 19 cases (26%). The presence of the NAinv pattern was significantly correlated with advanced Dukes' stage tumor (P = 0.0005) and the presence of distant metastases (P = 0.0064). K-ras proto-oncogene was mutated in the tumors of 31 cases (42%). Activated beta-catenin or K-ras was detected in most (78%) colorectal cancers analyzed, although a weak inverse correlation was found between the activities of the two oncogenes in the tumors. Importantly, most (7 of 8) patients with tumor showing both K-ras activation and the NAinv pattern of beta-catenin activation were in Dukes' stage C at surgery, and half of them developed distant metastases to the liver and lungs. CONCLUSION: The results suggest that although oncogenic activation of beta-catenin and K-ras is independent in the process of clinical cancer development, combined analysis of the two major oncogenes can detect most colorectal cancers and identify a subset of patients with poorer outcomes. Consequently, activation of either or both of these oncogenes may serve as a genetic marker for molecular diagnosis.     

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.     

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.     

An experimental analysis of cancer: role of ras oncogenes in multistep carcinogenesis

Carcinogen-induced animal tumor models are invaluable resources for studies aimed at understanding the participation of ras oncogenes in multistep carcinogenesis. Mutationally activated ras oncogenes are frequently detected in chemically induced animal tumors. The nature of the mutations in ras oncogenes reflects the chemical specificity of the carcinogen, implying that the carcinogen interacts with ras sequences. In chemically induced rat mammary tumor models, ras activation is the earliest detectable change in the mammary gland cells following administration of the chemical. Further, expression of the tumorigenic phenotype of cells containing activated ras requires the cooperation of normal physiological factors that are active during puberty.     

Rapid detection of ras oncogenes in human tumors: applications to colon, esophageal, and gastric cancer

We have developed a rapid, nonradioactive large scale method for the detection of ras oncogenes in human tumors. DNA is amplified by the polymerase chain reaction (PCR), and then digested with specific restriction enzymes to detect either endogenous or primer-mediated Restriction Fragment Length Polymorphisms (RFLPs). We report here that three of 15 colon tumors tested contain K-ras codon 12 aspartic acid mutations and one, along with the HCT 116 colon carcinoma cell line, contains a K-ras codon 13 aspartic acid mutation. On the other hand, we did not detect H- or K-ras codon 12 mutations or the K-ras codon 13 aspartic acid mutation in 25 esophageal and 27 gastric cardia tumors isolated from patients in Lin-xing County, China. By incorporating nucleotide substitutions in PCR primers, this method can be applied towards the rapid, non-radioactive screening of virtually any genetic disease caused by known point mutations.     

Frequency of active ras oncogenes in human bladder cancers associated with schistosomiasis

The frequency of active ras oncogenes in human bladder cancers associated with schistosomiasis, the cause of which is suspected to be a chemical carcinogen(s) in urine, was examined. Of 9 squamous cell carcinomas of the bladder surgically obtained in Egypt, none scored as positive in the regular DNA transfection assay using NIH/3T3 cells as recipients. The restriction fragment length polymorphism assay at codon 12 of the H-ras gene confirmed the absence of an activating mutation at this site in all of them. Western blotting analysis of electrophoretic mobilities of the ras p21 proteins, a method which can detect at least some of the point mutations within codons 12 and 61 of ras genes, suggested a point mutation within codon 61 in one out of the 7 tumors analyzed. In contrast to the low frequency of detection of mutationally activated ras oncogenes, enhanced expression of the ras p21 proteins was demonstrated in 4 of them by this analysis. The carcinogenic process involved in the endemic bilharzial bladder cancers is thus not associated with detectable point mutations within ras genes at a higher frequency than those in non-bilharzial bladder cancers in Japan or the USA.     

Expression of ras and myc oncogenes in human hepatocellular carcinoma and non-neoplastic liver tissues

An immunohistochemical assay was used to assess expression of ras p21 and myc p62 oncogene products in human hepatocellular carcinoma (HCC) and non-neoplastic liver tissues. The monoclonal antibodies Y13 259 and Myc1-9E10, specific for ras p21 and myc p62 oncoproteins, were employed on paraffin-embedded sections. Most HCCs showed enhanced ras p21 and myc p62 expression, as indicated by staining intensity. Cirrhotic livers revealed increased myc p62 and occasionally increased ras p21 expression. HBsAg+ hepatocytes showed intense immunostaining for ras p21. Fibrotic, cholestatic, fetal and normal adult liver did not present enhancement of oncoprotein production. We suggest that combined over-expression of ras and myc oncoproteins may be important for the malignant phenotypic alteration in human HCC.     

The role of ras and myc oncogenes in human solid tumours and their relevance in diagnosis and prognosis (review)

Advances in the field of oncogenes have produced a tool to investigate the different stages in multistep carcinogenesis. The role of the ras and myc gene families have been extensively investigated in the progression of carcinogenesis in a range of human solid tumours. This review critically analyses the data available on the role of these oncogenes in the six most common cancers worldwide, (i.e. cancer of the stomach, lung, breast, colon, cervix, and mouth and pharynx). In certain cases the incidence of aberrant gene expression and genetic alterations of the ras and myc gene families have been shown to be important in the progression of these cancers and may be of use as prognostic indicators.     

ras gene mutations in human prostate cancer

Point mutations at codons 12, 13, or 61 of the Ha-, Ki-, and N-ras genes are able to convert these normal cellular genes into activated oncogenes. Previous studies have shown that ras gene mutations occur in a variety of human solid tumors and may be important in the pathogenesis of some of these tumors. In order to test the hypothesis that ras gene mutations may be associated with prostate cancer, we have used an oligodeoxynucleotide hybridization assay to detect wild-type and mutant alleles in genomic DNA from prostate tumors and prostate tumor cell lines amplified using the polymerase chain reaction. Twenty-four primary prostate tumors (23 acinar tumors and one ductal tumor) and five prostate tumor cell lines were examined for mutations at codons 12, 13, and 61 of the Ki-ras, Ha-ras, and N-ras genes. Two mutations were detected: an A----G transition causing a glutamine to arginine amino acid substitution at codon 61 of the Ha-ras gene in a primary prostatic duct adenocarcinoma and a G----T transversion causing a glycine to valine amino acid substitution at codon 12 of the Ha-ras gene in a prostate tumor cell line (TSU-PR1) derived from a lymph node metastasis. While the overall frequency of ras gene mutations in prostate tumors is low, when these mutations do occur they may have a role in the progression of disease or the development of the unusual ductal variant of prostatic adenocarcinoma.     

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.     

Suppression of tumorigenicity in human cell hybrids derived from cell lines expressing different activated ras oncogenes

Four different human tissue-derived cell lines, each previously shown to express either a Ha-, Ki-, or N-ras-activated oncogene, were fused in four different paired combinations. The three combinations that involved the tumor line HT1080 (activated N-ras oncogene) were found to be tumorigenic in nude mice, but to different degrees. However, the fusion of the tumor lines EJ and SW480 (activated Ha-ras and Ki-ras, respectively) resulted in hybrid cells suppressed for tumorigenicity. The EJ x SW480 hybrids were found to harbor and express both of the activated ras oncogenes. The results suggest that tumorigenic suppression can occur in the presence of two transforming oncogenes of the ras family and that tumorigenicity associated with ras oncogene activation involves additional mechanisms that may differ among tumor cells.     

Mutations in ras oncogenes: Rare events in ultraviolet B radiation-induced mouse skin tumorigenesis

The activation of ras proto-oncogenes by point mutation in a broad spectrum of clinical malignancies and experimentally induced tumors suggests their critical role in cancer induction. To determine whether the activation of ras proto-oncogenes by point mutation also contributes to ultraviolet B radiation (UVB)-induced skin tumorigenesis and whether this event is responsible for the different tumorigenic potentials of UVB radiation in different mouse strains, we analyzed the skin tumors induced by UVB in SKH-1 hairless and C3H mice for specific mutations in the Ha-, Ki-, and N-ras oncogenes. With the same UVB irradiation protocol, the latency period for tumor appearance was longer in C3H mice than in SKH-1 hairless mice. In addition, tumor incidence and multiplicity were also significantly higher (P < 0.001, χ² and Wilcoxon rank sum tests) in SKH-1 hairless mice compared with C3H mice. None of the 30 skin tumor specimens (15 from each mouse strain) analyzed by polymerase chain reaction (PCR) amplification of specific codons followed by dot-blot hybridization with specific probes contained mutation in codons 13 of Ha-ras; 12, 13, and 61 of Ki-ras; or 12 and 13 of N-ras. However, three of the 15 tumors in SKH-1 hairless mice showed either a G³⁵ → A or G³⁵ → T transition at second position of Ha-ras codon 12. Interestingly, one of these tumors (with a G³⁵ → A transition) also harbored an A¹⁸² → G mutation at second position of Ha-ras codon 61. None of the tumors from C3H mice showed mutations in codons 12 or 61 of the Ha-ras oncogene. With regard to codon 61 of the N-ras oncogene, six tumors from SKH-1 hairless mice and 10 tumors from C3H mice showed an A¹⁸³ → T transversion. While G³⁵ → A or G³⁵ → T transition detected by PCR and dot-blot hybridization was confirmed by sequencing, the mutations identified similarly at codon 61 in either the Ha- or N-ras oncogenes could not be verified by sequencing of PCR-amplified products subcloned into plasmid vectors. With the exception of the low incidence of Ha-ras oncogene mutations at codon 12 in SKH-1 hairless mouse skin tumors induced by UVB, the striking absence of mutations in the Ha-, Ki-, and N-ras oncogenes in UVB-induced mouse skin tumors suggests that ras oncogene mutations are rare and thus are not an initiating event in photocarcinogenesis. © 1996 Wiley-Liss, Inc.     

Rare activation of ras oncogenes in radiation induced rat skin tumors

We examined a large panel of radiation induced rat skin tumors for activation of the H- or K-ras oncogenes. Using oligonucleotide hybridization analysis of tumor DNA we found that only 1 out of 96 tumors tested had an activated K-ras gene, and none of the 78 tumors examined for H-ras mutations were positive. Tumors were induced by high and low LET, and included lesions of various sizes and histologic type. DNA sequencing of tumors and NIH3T3 transfectants from a previous study gave results consistent with a rare occurence of ras activation in this system.     

Mutations of ras genes in human tumors (review)

Ras family genes (H-, K- and N-ras) are implicated in a wide range of human rumours. Mutations are a major activating mechanism for the ras family genes, mainly in codons 12, 13 and 61, resulting in their conversion from proto-oncogenes to activated oncogenes. The detection of mutant ras alleles in human tumours has been performed by several investigators in a wide range of tissues. The aim of our review was to summarize the data obtained from these studies and to investigate whether the presence of mutant ras alleles was associated with particular clinical parameters.     

Genomic alterations in human breast cancer: a review

We review and discuss data on the genetic alterations documented in human breast carcinomas at the molecular level. These alterations may result in: 1) deletion of genetic material (chromosome 11p, 13q, 3p, 1q, 17p); 2) amplification of genes or entire chromosomal segments (c-myc, c-erb-B2, locus DF3/PUM, loci on 11q13); 3) rearrangements (c-myc); 4) point mutations (c-ras). Presently available informations do not allow the development of cohesive pathogenetic models but indicate that the molecular basis of human breast cancer is heterogeneous.