Detection of high incidence of K-ras oncogenes during human colon tumorigenesis

Specific Ki-ras codon 61 mutations may determine the development of urethan-induced mouse lung adenomas or adenocarcinomas

In A/J strain mice, the carcinogen urethan induces lung adenomas and adenocarcinomas that contain Ki-ras-activating mutations primarily in codon 61. These mutations affect the middle adenine in codon 61 resulting in the substitution of either arginine (AT----GC transition) or leucine (AT----TA transversion) for the wild-type glutamine. To analyze the expression of the wild-type and mutant Ki-ras mRNAs in primary mouse lung tumors and transformed mouse lung cell lines, we utilized reverse transcription of total mRNA and DNA amplification by the polymerase chain reaction. The wild-type allele of codon 61 was expressed in all normal lung and primary tumor samples and in all transformed cell lines, except one. Significantly, the leucine-substituted allele was expressed primarily in very small lung adenomas, whereas the arginine-substituted allele was expressed in large lung adenocarcinomas and transformed lung cell lines. The relative amounts of expression of the mutant versus wild-type Ki-ras alleles and the total Ki-ras mRNA expression was similar in both lung adenomas and adenocarcinomas. Further, the arginine mutant allele was present in adenocarcinomas having either alveolar or papillary tumor morphologies. These results suggest that the specific activating Ki-ras mutation is more critical to either lung adenoma or adenocarcinoma development than is the tumor's cell of origin or the extent to which the mutant alleles are expressed. A distinct role of the specific activating Ki-ras mutations in affecting lung tumor growth or malignant potential is indicated.

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

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

Expression of the ras-related rap genes in human tumors

The expression of the recently described rap genes, closely related in the effector region to the ras proto-oncogenes, was examined by Northern blot analysis in 41 primary human tumors. The structural and in vitro biological properties of the rap gene products suggest their possible antagonistic action in the same effector pathway as the ras proteins. In order to determine whether a deregulation in the rap transcription levels could be involved per se in the multistep carcinogenic process, we chose to analyze tumors for which the ras mutation rate was previously reported to be extremely rare or unknown, i.e., non-Hodgkin's lymphomas, certain types of carcinoma, sarcomas, germinal neoplasms of the testes and various tumors of the nervous system. A severe decrease in the expression of the rap1A gene was shown in the fibrosarcomas and the adenocarcinoma of the salivary gland studied, as compared to their normal counterparts, whereas no rap2 expression was found in the polyadenylated RNA of sarcoma samples.

DNA content of rectal scrapings from individuals at low and high risk for the development of colorectal cancer. A feasibility study

Scrapings of superficial rectal mucosa were collected from 31 patients with colorectal carcinoma, 66 patients with sporadic adenoma, and 53 control subjects with no personal or family history of colorectal cancer. The DNA ploidy level and proliferative patterns of each specimen were analyzed by flow cytometry (FCM). A GMS index, calculated as the ratio of G2 + M:S, was found to be significantly lower in control subjects than in any of the high-risk groups studied. Aneuploidy was more prevalent in rectal scrapings from cancer patients and adenoma patients than in those from control subjects. Aneuploid cell populations were detected in apparently normal rectal scrapings from two control subjects. Some high-risk individuals (i.e., cancer patients and patients with adenomas and a family history of cancer) exhibited higher proportions of tetraploid (designated G2/M) cells and a higher G2/M:S phase ratio than control subjects. The results accumulated thus far show that the rectal scraping procedure is safe and easy to perform. Our limited findings give hope that the DNA content analysis of cells obtained by rectal scraping may eventually prove useful in mass screening for colorectal cancer risk. However, definitive evaluation will require further refinement and elaboration of analytic technique and testing on more patients at various levels of predetermined risk.

Tissue-specific expression of c-Ha-ras in premalignant gastrointestinal mucosae

The molecular mechanisms underlying premalignant gastrointestinal diseases, such as ulcerative colitis and Barrett's esophagus, remain unknown. For this reason, the expression of the protooncogene c-Ha-ras was studied in ulcerative colitis and Barrett's esophagus. Total cellular RNA was extracted from different regions of the gastrointestinal tract in these two diseases. Expression of c-Ha-ras was greater in proximal than in distal colon and undetectable in Barrett's esophagus. These regional differences in expression were not seen with the control gene beta-actin or with the protooncogenes c-myc and p53. In order to evaluate structural factors contributing to expression, amplification and methylation of c-Ha-ras DNA were studied in these tissues by Southern and slot blotting. No amplification of c-Ha-ras or six other protooncogenes was detected. These data suggest tissue-specific regulation of c-Ha-ras expression in the gastrointestinal tract in certain premalignant disease states.

Induction of a mitogen-responsive gene after expression of the Ha-ras oncogene in NIH 3T3 fibroblasts

A cDNA clone, T1, has been isolated whose corresponding mRNA was transiently expressed at highly elevated levels after conditional expression of the Ha-ras(EJ) gene and after mitogenic activation of quiescent NIH 3T3 cells. Glucocorticoid hormone stimulated substantial T1 expression as well but only in proliferating cells. At least two different signaling pathways participate in the regulation of the T1 gene: a protein kinase C-dependent signal is involved in the response of proliferating NIH 3T3 cells to glucocorticoid in the absence but not the presence of p21ras, whereas a protein kinase C-independent mechanism mediates the response to serum factors. Treatment of cells with the protein kinase inhibitor 2-aminopurine blocked induction of expression of the T1 gene. T1 mRNA accumulation is regulated at the transcriptional level.

Ras gene activation and epidermal growth factor receptor expression in human colon cancer

The expression of various epitopes of epidermal growth factor receptor (EGFr) and mutational activations of ras gene product p21 in colorectal primary cancers from 16 patients have been analyzed in this study. Eight noncancerous colons were used as controls. Indirect immunoperoxidase staining was performed using Avidin-Biotin Complex assay. Monoclonal antibodies against carbohydrate and polypeptide epitopes of EGFr and monoclonal antibodies against "wild-type" and "mutant" ras p21 were used as specific probes. There was no specific expression of the polypeptide epitope of EGFr observed in any of the colon cancers or normal colon tissues. Four of the sixteen tumors (25%) expressed the carbohydrate epitope of EGFr. Glycine----arginine mutation and glycine----valine mutation of codon 12 in ras p21 was observed in 40 and 31% of colon cancers, respectively. Although normal colon showed expression of wild-type ras in about half the cases studied, there was no mutational activation of the ras genes. The morphologically adjacent normal colon mucosa in cancer patients expressed varying levels of mutational activation involving the codon 12. The presence of unusual carbohydrates relating to the EGFr and the products of ras gene activation by point mutations in colon cancers may imply a functional role in transformation.

Chromosome localization and cDNA sequence of murine and human genes for ras p21 GTPase activating protein (GAP)

The cDNA coding for mouse and human ras p21 GTPase-activating protein (GAP) was isolated; the deduced amino acid sequences share over 96% homology with that previously determined for bovine brain GAP. Both the mouse and human GAP cDNAs were used as probes for the chromosomal localization of this gene. The locus designations for the gene encoding GAP in human and mouse are RASA and Rasa (for ras-activating protein), respectively. By somatic cell hybrid analysis and in situ chromosomal hybridization, we have assigned the RASA gene to human chromosome band 5q13.3. In addition, with somatic cell genetics and linkage analysis in recombinant inbred mouse strains, the murine Rasa gene was localized to the distal end of mouse chromosome 13. These assignments place the gene encoding GAP in a known conserved syntenic region.

ras p21 oncoprotein is autoregulated and acts as a potential mediator of insulin action or the H-ras1 promoter

Rat fibroblast cells carrying an exogenous normal or mutant T24 human H-ras1 gene were transfected with plasmids carrying the normal or mutant T24 H-ras1 gene promoter linked to the reporter chloramphenicol acetyl transferase (CAT) gene and the cells were treated with insulin. We found that the H-ras1 gene was positively autoregulated and that insulin potentiated the response of the T24 ras p21 to the H-ras1 gene promoter. We have also examined the effect of insulin directly on the H-ras1 promoter by treating stable transfectants obtained after transfection of rat fibroblasts with plasmids carrying the normal or mutant T24 H-ras1 gene promoter linked to the reporter CAT gene and the selectable marker aminoglycoside phosphotransferase (aph) gene. We found that insulin appeared to have no direct effect on the H-ras1 promoter in this case, suggesting that the effect is mediated through the ras p21 oncogene product. We suggest that the mutant T24 H-ras p21 protein mediates the action of insulin.

Detection of minority point mutations by modified PCR technique: a new approach for a sensitive diagnosis of tumor-progression markers

The detection of point mutations correlated with diseases, in enzymatically amplified DNA sequences (Polymerase Chain Reaction), is currently performed by digestion of PCR products when an existing restriction site disappears at least in one allele of the amplified mutated sequence or by allele specific radiolabeled probes in all other cases. These methods are the most sensitive but they cannot detect a mutation if it is present in less than 5% of the studied cells. We describe here a method based on the introduction of an artificial restriction site, using a modified primer during the PCR, which creates a RFLP indicative of the studied mutation. This RFLP is detected by a radiolabeled oligonucleotide probe which is not related to the mutation. Our approach multiplies the sensitivity by a factor of 1000 and it is practical for use in screening purposes and the detection, after treatment, of the residual disease in human malignancies. Using this method we detected 20% more mutations at codon 12 in the Ki ras oncogene in DNA from colorectal cancers that were undetectable with all the previous methods.

Co-incident N and K ras gene mutations in a case of AML, restricted to differing cell lineages

Peripheral blood from a patient with acute myeloid leukaemia (AML) of M5 FAB classification, was shown to have mutations to both the N and K ras genes. Leucophoresed blood was separated on a discontinuous Percoll density gradient to provide fractions enriched for different cell lineages. DNA extracted from these fractions was amplified using the polymerase chain reaction (PCR) technique, and hybridized with oligonucleotide probes specific for the single base mutations previously demonstrated. The N-ras mutation was shown to be restricted to the blast and monocytic cell fractions, concordant with the FAB subtype of M5. The K-ras mutation, however, was present in all fractions, suggesting it had occurred in a multi-potential stem cell representing an earlier stage in the generation of the leukaemia, or possibly an incidental background phenomenon.

Tissue-specific hypomethylation of the human c-K-ras gene

Methylation of the c-K-ras gene was examined in a wide variety of human tissues using the methylation sensitive restriction endonuclease HpaII. All tissues showed hypomethylation in the region of exon zero. Specific hypomethylation of a particular HpaII site in the second intron was observed in gastrointestinal and tracheobronchial epithelial cell DNAs. Specific hypomethylation was also observed in a cluster of HpaII sites within the first intron in sperm, endometrium and placenta DNAs. These regions were predominantly methylated in a wide variety of other tissues, including fetal gut. The possible implications are discussed.

New cancer markers

In recent years many new and improved cancer markers have become available. From a clinical point of view, the most useful of the new markers include CA 19-9 for pancreatic adenocarcinoma, CA 125 for epithelial ovarian cancer, CA 15-3 for breast cancer, prostate specific antigen for prostatic adenocarcinoma, placental alkaline phosphatase for testicular seminomas and neuron-specific enolase for small cell carcinoma of lung. None of these new markers are specific for cancer. Furthermore, none are organ specific, except prostate specific antigen for prostatic tissue. The main application of these markers is in monitoring patients with the specific malignancies indicated. Whether routine use of any of these new markers leads to higher quality of life or enhanced survival remains to be determined.

Resistance to oncogenic transformation in revertant R1 of human ras-transformed NIH 3T3 cells

A flat revertant, R1, was isolated from human activated c-Ha-ras-1 (hu-ac-Ha-ras) gene-transformed NIH 3T3 cells (EJ-NIH 3T3) treated with mutagens. R1 contained unchanged transfected hu-ac-Ha-ras DNA and expressed high levels of hu-ac-Ha-ras-specific mRNA and p21 protein. Transfection experiments revealed that NIH 3T3 cells could be transformed by DNA from R1 cells but R1 cells could not be retransformed by Kirsten sarcoma virus, DNA from EJ-NIH 3T3 cells, hu-ac-Ha-ras, v-src, v-mos, simian virus 40 large T antigen, or polyomavirus middle T antigen. Somatic cell hybridization studies showed that R1 was not retransformed by fusion with NIH 3T3 cells and suppressed anchorage independence of EJ-NIH 3T3 and hu-ac-Ha-ras gene-transformed rat W31 cells in soft agar. These results suggest that the reversion and resistance to several oncogenes in R1 is due not to cellular defects in the production of the transformed phenotype but rather to enhancement of cellular mechanisms that suppress oncogenic transformation.

Multiple genetic alterations in distal and proximal colorectal cancer

Multiple genetic alterations were investigated in colorectal cancer, including changes in DNA content, mutations in ras oncogenes, and deletions involving chromosomes 5, 17, and 18. A non-random association of deletions and mitotic abnormalities by site was seen, with both types of alterations occurring significantly more frequently in distal tumours. In contrast, the frequency of c-Ki-ras mutations did not differ between proximal and distal cancers. In addition, deletions were significantly associated with each other and with change in DNA content. The data provide strong support for the hypothesis that proximal and distal colon carcinoma might differ in the genetic mechanisms in their initiation and/or progression.

Increased expression of ras genes in non-Hodgkin's lymphomas is not associated with oncogenic activation of those genes by point mutation

Twenty-three cases of non-Hodgkin's lymphoma (NHL) were analyzed for expression of ras genes by in situ hybridization utilizing biotinylated DNA probes. Increased expression of Ki-ras, Ha-ras and N-ras genes was observed in 12 cases, 6 cases and 1 case of NHL, respectively. Genomic DNA extracted from these 23 cases of NHL was region-specifically amplified by means of polymerase chain reaction to examine the presence of point mutations at the 12th, 13th and 61st codons of Ki-, Ha- and N-ras genes. Dot hybridization assays with appropriate oligonucleotide probes showed no evidence of point mutation in any case of NHL examined. These results indicate that increased expression of ras genes in NHL is not associated with ras gene activation by point mutation.

Oncogene activation in human benign tumors of the skin (keratoacanthomas): is HRAS involved in differentiation as well as proliferation?

In vitro DNA amplification followed by oligonucleotide mismatch hybridization was used to study the frequency of HRAS mutations in the benign self-regressing skin tumors keratoacanthomas and in squamous cell carcinomas. We used freshly obtained keratoacanthomas as well as Formalin-fixed paraffin-embedded tissues from both types of tumors. DNA from 50 samples of each tumor type was analyzed for activating mutations involving codons 12 and 61. A relatively high percentage (30%) of HRAS mutations was found in the keratoacanthomas compared with 13% in the squamous cell carcinomas. The most frequent mutation identified is the A-T-to-T.A transversion in the second position of codon 61. The present findings demonstrate the involvement of the HRAS oncogene in human benign tumors. Moreover, they indicate that an activated HRAS oncogene is not sufficient to maintain a neoplastic phenotype and argue against a role of HRAS in the progression of skin tumorigenesis.

Detection of ras gene alterations and ras proteins in colorectal cancer

DNA extracted from 31 primary colorectal carcinomas was analyzed for the presence of ras gene amplification and mutations. Nine carcinomas had Ha-ras amplification and seven Ki-ras amplification. Nine carcinomas had codon 12 Ki-ras mutations. Immunohistochemical staining for ras proteins revealed a normal membrane association in normal mucosa and benign polyps but an abnormal cytoplasmic distribution in carcinomas. Amplification, mutations, and immunohistochemical staining were independent of histologic differentiation, Dukes' stage, or DNA ploidy status. This study demonstrates that abnormalities of ras genes are a common finding in colorectal carcinomas. They are potentially important biologic changes associated with malignancy, although they do not appear to be related to clinical behavior.

Serum- and oncoprotein-mediated induction of a gene with sequence similarity to the gene encoding carcinoembryonic antigen

We describe the molecular identification of a gene, designated T1, whose expression in mouse NIH 3T3 cells is strongly induced by the Ha-ras(EJ) and v-mos oncogenes and by serum. The T1 gene encodes a 38.5-kDa protein, as predicted from its primary sequence and shown by in vitro translation. The protein was processed at its amino terminus and extensively modified by N-linked glycosylation in vitro in the presence of microsomal vesicles. Sequence comparison of T1 with the MIPSX data base (Max-Planck-Institut für Biochemie, Martinsried/Munich) revealed similarity to the human carcinoembryonic antigen, a tumor marker which is overexpressed in colon adenocarcinomas and in fetal tissues. Considerable sequence similarity has also been observed to the short conserved region of other proteins which, like carcinoembryonic antigen, are encoded by members of the immunoglobulin gene superfamily.

Expression of c-myc oncogene in colorectal polyps as a biological marker for monitoring malignant potential

The expression of oncogenes (c-myc, c-fos, c-Ki-ras, c-Ha-ras, and p53) was examined by Northern blot analysis using freshly isolated human colorectal and gastric cancers and noncancerous portions as the controls. Remarkably high levels of c-myc expression were found in colorectal cancers (eight of 11), but not in gastric cancers. High levels of c-myc expression were also detected in colorectal polyps and in metastatic liver tumors. In colorectal polyps, the transcript levels significantly correlated with the histologic malignancy and the size. In contrast, neither c-fos nor c-Ki-ras was overexpressed in colorectal and gastric cancers, and transcripts of c-Ha-ras and p53 were not evident in any tissue examined. In light of these observations the c-myc expression may be specifically associated with the evolution of colorectal cancer as well as progression and maintenance stages, hence may prove to be a useful marker to evaluate the malignant potential of colorectal polyps.

Frequency and types of point mutation at the 12th codon of the c-Ki-ras gene found in pancreatic cancers from Japanese patients

Point mutations at the 12th codon of c-Ki-ras in pancreatic cancer from Japanese patients were examined using the polymerase chain reaction, followed by cloning of the amplified gene fragments in pTZ phagemid and nucleotide sequence determination. The frequency of the point mutations found in the tumors was quite high (75%). The mutation most frequently detected was a G---A transition at the second position of codon 12 (GGT---GAT), but other types of mutations such as GGT----GTT and GGT----CGT were also found. In one case, silent mutation of GGT to GGC was detected in addition to the frequent mutation of GGT to GAT. These observations suggest that the 12th codon of pancreatic c-Ki-ras is highly mutatable.

Human bladder and colon carcinomas contain activated ras p21. Specific detection of twelfth codon mutants

Members of the ras family of proto-oncogenes code for 21,000-dalton molecular weight protein products (p21s). Transformation of cells from the normal to the malignant phenotype in experimental studies has been associated with point mutations within the coding region for these ras proteins. Recent reports demonstrate that 40% of human colon cancers and 20% of acute leukemias contain ras mutations in the twelfth or thirteenth codon that can result in amino acid substitutions at these positions in the p21 products. Similarly, studies of ras mRNA detected 40% of human colon tumors with twelfth codon c-Ki-ras mutant mRNA. The authors previously developed a nonradioactive double-antibody enzyme-linked immunoblot assay (ELIBA) for detection of normal and mutant ras p21. They have adapted that technology to specifically detect twelfth codon activated ras p21 utilizing mutation-specific antisera. In this report the authors show that one of seven de novo human bladder cancers and four of seven colon cancers express a twelfth codon activated ras p21. These results document that mutations at both the DNA and mRNA levels are ultimately translated into an abnormal protein product present in human tumors.

Occurrence and relevance of chemically induced benign neoplasms in long-term carcinogenicity studies

Recent carcinogenicity studies conducted and evaluated by the National Toxicology Program/National Institute of Environmental Health Sciences were examined to determine the frequency of chemically increased incidences of neoplasia. Many of the chemicals originally selected for study were chosen because of an a priori suggestion that they might be carcinogens. Of the 143 chemical studies evaluated, usually involving male and female rats and mice, 42 (29%) did not induce any neoplasms, 20 (14%) gave marginal or equivocal neoplastic responses, and 81 (57%) showed positive neoplastic responses in one or more of the 524 species-gender experiments. Of these 81 positive studies, 60 (74%) were considered positive based on malignant neoplasia, 16 (20%) were positive due primarily to benign neoplasia, but had supporting evidence of malignant neoplasia in the same organ/tissue, and 5 (6%) were positive based only on benign neoplasia. These five chemicals are a) allyl isothiocyanate (transitional cell papillomas of the urinary bladder in male rats), b) 2-amino-4-nitrophenol (tubular cell adenomas of the kidney in male rats), c) asbestos intermediate range chrysotile (adenomatous polyps of the large intestine in male rats), d) decabromodiphenyl oxide (neoplastic nodules of the liver in male and female rats), and e) nitrofurazone (fibroadenomas of the mammary gland in female rats and benign mixed tumors and granulosa cell tumors of the ovary in female mice). For all but one of these lesions (mammary gland), the occurrence in historic controls is low. Thus, only 5 of the 143 chemicals studied (3.5%) induced benign neoplasia alone, and those observed benign neoplasms are known to progress to malignancy. Accordingly, we consider chemically induced benign neoplasia to be an important indicator of a chemical's carcinogenic potential in rodents, and believe it should continue to be made an integral part of the overall weight-of-the-evidence evaluation process for identifying potential human health hazards.

pp60c-src activation in human colon carcinoma

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

RNA fingerprinting of respiratory syncytial virus using ribonuclease protection. Application to molecular epidemiology

We have used the technique of ribonuclease protection to define genomic variation among circulating isolates of subgroup A respiratory syncytial (RS) virus. RNAs extracted from HEp-2 cells infected with strains to be analyzed were hybridized with a 32P-labeled RNA probe corresponding to the RS virus G glycoprotein (A2 strain). Areas of nonhomology were detected by cleavage with ribonuclease A. Using this technique, multiple distinct RNA cleavage patterns could be distinguished among viral isolates recovered from infants residing in the same metropolitan area and infected during the same epidemic season. Epidemiologically related isolates (from coinfected twins, from infants infected during a nosocomial outbreak at an extended care facility, and from institutionalized adults infected during an outbreak) yielded identical patterns. In two separate outbreaks, differences in cleavage patterns among certain isolates corresponded to epidemiologically significant differences among the individuals from whom the isolates were recovered. We conclude that substantial genomic heterogeneity exists among circulating isolates of subgroup A RS virus. Ribonuclease protection can be used as a molecular fingerprinting tool for expanded studies of the molecular epidemiology of this virus.

Can mortality from rectal and rectosigmoid carcinoma be predicted from histopathological variables in the diagnostic biopsy?

The prognostic information provided by histopathological variables in the diagnostic biopsy was evaluated retrospectively in 276 consecutive patients "potentially curable" by surgery using criteria recently proposed by Jass et al. concerning the main specimen. In 252 (91%) cases, the biopsy material was appropriate for the intended assessment. The majority of tumours were tubular (67%), tubular configuration mostly irregular (76%) and the tumour cells usually had small nuclei (81%). Remnants of adenomatous structures were identified in 21%. Most tumours were moderately differentiated (57%), and poorly differentiated tumours were somewhat more common (27%) than highly differentiated ones (16%). There was no real correlation between these histopathological variables, as expressed in biopsy, and Dukes' stage. Patients with a well-differentiated tumour had somewhat better survival than those with a moderately or poorly differentiated one (p = 0.04). Tumour type tended to influence cancer-specific mortality in that patients with papillary tumour had a slightly better prognosis than those with a different type. An attempt was also made to classify the patients into two groups on the basis of the observers' subjective impression of the tumour pattern and the expected outcome. Among the 143 patients in whom the over-all subjective impression was an "aggressive tumour pattern", 43% died (median follow-up 47 months). The cancer-specific death rate in patients in whom the tumour pattern was "non-aggressive" was 27% (p = 0.04). In summary, the extent to which these variables predicted mortality was far from clinically useful.

Resistance to oncogenic transformation in revertant R1 of human ras-transformed NIH 3T3 cells

A flat revertant, R1, was isolated from human activated c-Ha-ras-1 (hu-ac-Ha-ras) gene-transformed NIH 3T3 cells (EJ-NIH 3T3) treated with mutagens. R1 contained unchanged transfected hu-ac-Ha-ras DNA and expressed high levels of hu-ac-Ha-ras-specific mRNA and p21 protein. Transfection experiments revealed that NIH 3T3 cells could be transformed by DNA from R1 cells but R1 cells could not be retransformed by Kirsten sarcoma virus, DNA from EJ-NIH 3T3 cells, hu-ac-Ha-ras, v-src, v-mos, simian virus 40 large T antigen, or polyomavirus middle T antigen. Somatic cell hybridization studies showed that R1 was not retransformed by fusion with NIH 3T3 cells and suppressed anchorage independence of EJ-NIH 3T3 and hu-ac-Ha-ras gene-transformed rat W31 cells in soft agar. These results suggest that the reversion and resistance to several oncogenes in R1 is due not to cellular defects in the production of the transformed phenotype but rather to enhancement of cellular mechanisms that suppress oncogenic transformation.

Applications of molecular genetics to gastrointestinal and liver diseases. II. Clinical relevance

The use of DNA probes within or near disease genes is becoming increasingly important in clinical medicine. Probes are available for prenatal and carrier diagnosis for several of the more than 100 genetic diseases of the gastrointestinal tract and liver. These include familial adenomatous polyposis, haemochromatosis, cystic fibrosis, alpha 1-antitrypsin deficiency and the hereditary porphyrias. This review uses examples drawn from such diseases to show the relevance of these approaches to the clinician.

N-RAS mutations in T-cell acute lymphocytic leukaemia: analysis by direct sequencing detects a novel mutation

A novel mutation of the N-RAS gene of T-ALL blast cells was detected by a direct sequencing of in vitro amplified exon-1 of the N-RAS gene. Threonine (ACA) was substituted for alanine (GCA) at codon 11. This mutation would have been overlooked by conventional probe hybridization techniques. A search for other mutations in N-RAS exon-1 in T-ALL revealed a codon 13 mutation substituting aspartic acid (GAT) for glycine (GGT) in one of 18 patients. No mutations at codon 12 were detected.

Transfection of insulin-producing cells with a transforming c-Ha-ras oncogene stimulates phospholipase C activity

Pancreatic islet beta-cells and insulin-producing RINm5F cells were electroporated in the presence of the c-Ha-ras oncogene, to assess the possible involvement of the encoded product in coupling extracellular receptors to phospholipase C. After two days the c-Ha-ras-transfected cells increased their expression of c-Ha-ras mRNA. These cells were also found to contain more [3H]InsP3, suggesting an increased basal (non-ligand-activated) phospholipase C activity. In addition, the transfected cells were unable to respond to ligand (bombesin) activation of phospholipase C. The ras-transfected insulin-producing cells showed enhanced phosphorylation of a 200 kDa substrate crossreacting with an antibody to an 80 kDa protein kinase C substrate. The phorbol ester 12-O-tetradecanoyl 13-acetate and bombesin also induced phosphorylation of the 200 kDa substrate. All of these changes occurred without changes in the rates of [3H]thymidine incorporation. The results suggest that the mutated c-Ha-ras oncogene directly or indirectly stimulates the basal phospholipase C activity of these cells.

Cytogenetic analysis of in vitro karyotype evolution in a cell line established from nonmalignant human mammary epithelium

Cytogenetic analysis was carried out on six passages (pass. 16, 19, 21, 25, 34, and 47) of the nontumorigenic epithelial cell line, HMT-3522, established from a fibrocystic lesion of the human breast. Minor chromosome abnormalities were present in the first passage (pass. 16) available for study, and limited cytogenetic progression was observed during the in vitro growth. A modal chromosome number of 45 chromosomes was found in all passages. Each passage contained 4-5 marker chromosomes. Three markers were consistently present in all passages studied. During in vitro growth two markers were gained and two markers were lost from the stemline karyotype. The two latest passages studied had identical karyotypes: 45,XX, del(1)(q44----p32:),t(5;14)(14p13----14q32::5q22----++ +5q35),t(6;8;12;17)(8p23---- 8q24::6p21.1----6p23;12q24----12p13::6p23- --- 6p25;17p13----17q25::6q11----6q27). The present study demonstrates chromosome abnormalities and karyotypic evolution in a nontumorigenic (in nude mice) and noninvasive (in vitro tested) cell line established from nonmalignant epithelial breast tissue. The results are discussed in relation to gene amplification, double minutes and oncogene localization.

Clonal allele loss in gastrointestinal cancers

Using a panel of DNA probes for hypervariable DNA regions we screened 52 gastrointestinal carcinomas for clonal allele losses on chromosomes 1, 5, 7, 12, 16 and 17. A total of 24/35 informative cases of colorectal cancers showed loss of constitutional heterozygosity at a locus on chromosome 17p, while 9/31 cases informative for a locus on 5q showed allele loss. Loss of sequences at 5q was linked to allele loss at 17p with a single exception. In gastric cancers loss of heterozygosity most frequently occurred at 1q (5/10 tumours) and at 12q (6/11 tumours). Gastrointestinal tumours show consistent chromosomal losses and the loci involved are different in gastric and colorectal cancers.

Retroviral transduction of the human c-Ha-ras-1 oncogene into midgestation mouse embryos promotes rapid epithelial hyperplasia

Infection of mouse embryos at 8 days of gestation with a replication-defective retrovirus carrying the human c-Ha-ras-1 oncogene led to efficient and rapid induction of hyperplastic lesions. Twenty-four percent of viable off-spring developed abnormal growths after infection with purified virus. The lesions contained a single integrated provirus and produced viral RNA and the Ha-ras oncogene product (p21). The latency period between the time of infection and appearance of the lesions suggested that secondary alterations in addition to activated ras were necessary for neoplasms to develop. The earliest and most abundant growths were cutaneous and appeared from 4 to 36 weeks of age, with a median of 4 weeks of age. A number of subcutaneous lesions also developed over the same time span but at a median of 18 weeks of age. The rapid development of cutaneous lesions in response to transduction of the ras oncogene contrasts with other studies in which adult skin required secondary treatment with promoters prior to ras induction of epithelial hyperplasia. These results demonstrate that infection of midgestation mouse embryos allows rapid analysis of oncogene potency in skin.

Allelotype of colorectal carcinomas

To examine the extent and variation of allelic loss in a common adult tumor, polymorphic DNA markers were studied from every nonacrocentric autosomal arm in 56 paired colorectal carcinoma and adjacent normal colonic mucosa specimens. This analysis was termed an allelotype, in analogy with a karyotype. Three major conclusions were drawn from this analysis: (i) Allelic deletions were remarkably common; one of the alleles of each polymorphic marker tested was lost in at least some tumors, and some tumors lost more than half of their parental alleles. (ii) In addition to allelic deletions, new DNA fragments not present in normal tissue were identified in five carcinomas; these new fragments contained repeated sequences of the variable number of tandem repeat type. (iii) Patients with more than the median percentage of allelic deletions had a considerably worse prognosis than did the other patients, although the size and stage of the primary tumors were very similar in the two groups. In addition to its implications concerning the genetic events underlying tumorigenesis, tumor allelotype may provide a molecular tool for improved estimation of prognosis in patients with colorectal cancer.

Chromosome 17 deletions and p53 gene mutations in colorectal carcinomas

Previous studies have demonstrated that allelic deletions of the short arm of chromosome 17 occur in over 75% of colorectal carcinomas. Twenty chromosome 17p markers were used to localize the common region of deletion in these tumors to a region contained within bands 17p12 to 17p13.3. This region contains the gene for the transformation-associated protein p53. Southern and Northern blot hybridization experiments provided no evidence for gross alterations of the p53 gene or surrounding sequences. As a more rigorous test of the possibility that p53 was a target of the deletions, the p53 coding regions from two tumors were analyzed; these two tumors, like most colorectal carcinomas, had allelic deletions of chromosome 17p and expressed considerable amounts of p53 messenger RNA from the remaining allele. The remaining p53 allele was mutated in both tumors, with an alanine substituted for valine at codon 143 of one tumor and a histidine substituted for arginine at codon 175 of the second tumor. Both mutations occurred in a highly conserved region of the p53 gene that was previously found to be mutated in murine p53 oncogenes. The data suggest that p53 gene mutations may be involved in colorectal neoplasia, perhaps through inactivation of a tumor suppressor function of the wild-type p53 gene.

Mutations in the KRAS2 oncogene during progressive stages of human colon carcinoma

A series of colon carcinomas, adenomas, and adjacent tissues were analyzed for ploidy alterations and mutations in KRAS2. To increase the sensitivity for identifying mutations, we used histological enrichment, cell sorting, and DNA amplification by the polymerase-catalyzed chain reaction followed by direct DNA sequence analysis. Of the 40 carcinomas analyzed, 27 contained aneuploid cells and 26 contained mutations at the first position of codon 12 of KRAS2. Of the 12 adenomas studied, 4 contained aneuploid cells and 9 contained the same mutation at codon 12. In both adenomas and carcinomas, mutations were identified in both diploid and aneuploid cells. In some cases, regions of histologically benign mucosa adjacent to the carcinoma contained mutations. These combined results suggest that mutations in KRAS2 occur early in the development of human colon carcinoma, before change in ploidy, and that these mutations exist in diploid cells from which an aneuploid subpopulation arises. Furthermore, mutations may exist in histologically normal mucosa in regions adjacent to carcinoma, suggesting that a field of genetically abnormal mucosa may surround these tumors.

The ras and myc oncogenes cooperate in tumor induction in many tissues when introduced into midgestation mouse embryos by retroviral vectors

Midgestation embryos were infected with replication-defective retroviral vectors that either transduced the myc oncogene, the ras oncogene, or both oncogenes simultaneously. The myc virus induced tumors in diverse organs at a very low frequency and with a long latency period, while approximately 20% of the mice derived from embryos infected with the ras virus developed tumors in the skin with a latency of 4-8 weeks. In contrast, infection of embryos with the ras/myc double oncogene virus resulted in 27% of the animals developing rapidly growing and malignant tumors in a great variety of tissues after a median latency period of 2-3 weeks. All tumors were of monoclonal origin, as shown by Southern analysis using the provirus as a molecular marker. Our results are consistent with the hypothesis that the ras and myc oncogenes cooperate in transforming cells, but that additional alterations are necessary for realization of the fully malignant phenotype. Our observations also suggest that a much wider range of cell types become targets for malignant transformation when the embryos are exposed to the myc and the ras oncogenes simultaneously than when exposed to the same oncogenes separately. Infection of mouse embryos with vectors carrying different oncogenes or oncogene combinations may be an efficient and rapid method for evaluating the spectrum of cell types at risk for malignant conversion following mutation of a protooncogene to a transforming gene.

Multistage carcinogenesis induced by ras and myc oncogenes in a reconstituted organ

ras and myc oncogenes were able to induce distinct phenotypic alterations, resembling different types of premalignant lesions, when introduced into approximately 0.1% of the cells used to reconstitute the mouse prostate gland. While ras induced dysplasia in combination with angiogenesis, myc induced a hyperplasia of the otherwise normally developed organ. ras and myc together induced primarily carcinomas. However, tumor progression was also associated with additional genetic alterations involving gene amplification. Our data indicate that specific types of benign premalignant lesions may reflect the activation of different single oncogenes, and that the consecutive activation of multiple oncogenes could be a causal event in the step-like progression of tumorigenesis.

Amplification of c-ras-Ki oncogene in human ovarian tumours

Amplification of the c-ras-Ki oncogene has been the most consistent finding reported in studies on oncogene activation in ovarian cancer, but for the most part the studies have been small and the results conflicting. In order to determine whether amplification occurred de novo in primary tumours or was associated with tumour progression and metastasis, 81 tumour samples from different sites in 26 patients with ovarian tumours and 7 xenografted ovarian tumour cell lines were assayed. Amplification of c-ras-Ki occurred infrequently and was apparent in a single metastatic site in a patient with poorly differentiated serous cystadenocarcinoma of the ovary. Ten-fold amplification of the c-ras-Ki oncogene was also evident in a benign ovarian fibroma. Amplification of the c-ras-Ki oncogene is rare in ovarian tumours and does not appear to play a fundamental role in tumor development or progression.

Low incidence of point mutation of c-Ki-ras and N-ras oncogenes in human hepatocellular carcinoma

We examined the incidence of point mutation in codons 12, 13 and 61 of c-Ki-ras and N-ras genes in human hepatocellular carcinoma (HCC) using the polymerase chain reaction and oligonucleotide hybridization techniques. Among 34 tissues specimens surgically resected from 30 patients and 5 cell lines of human HCC, only two had ras point mutations; in one case, codon 12 of c-Ki-ras was altered from GGT, coding glycine, to GTT, coding valine; in the other case, codon 61 of N-ras was altered from CAA, coding glutamine, to AAA, coding lysine. Thus, point-mutational activation of ras oncogenes is an uncommon event in human HCC.

Protooncogene structure in the cancer family syndrome

Protooncogene loci in constitutional DNA from affected members of a kindred with the cancer family syndrome were studied by Southern blot hybridization analysis. No structural rearrangements or amplification of 16 protooncogenes were detected. These studies demonstrated that gross structural alteration of the tested protoocongenes is not responsible for cancer susceptibility in this syndrome.

Molecular cloning of the 25 kbp region upstream of exon 0 of the human Ki-ras oncogene and its conservation in transformed mouse NIH 3T3 cells

Human sequences associated with the Ki-ras oncogene of the mammary tumour cell line, H-466B have been cloned from a tertiary NIH3T3 mouse transfectant. These sequences are located 5' upstream of exon 0 of the Ki-ras oncogene, span over 25 kbp of DNA and are conserved in half of the primary transfectants obtained with the Ki-ras gene of different types of tumours. No gross alterations were observed in the sequences upstream of the Ki-ras gene. The partial or total deletion of these sequences in the other half of primary transformants argues that they are not absolutely required for the transforming activity of the Ki-ras oncogene. The even distribution of the human-mouse junction points in primary transformed mouse cells suggests the absence of a specific region of recombination in the 5' flanking region of Ki-ras.