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

Autonomous proliferation of colon cancer cells that coexpress transforming growth factor alpha and its receptor. Variable effects of receptor-blocking antibody

Four human colon adenocarcinoma cell lines, SNU-C1, SNU-C4, SNU-C5, and NCI-H716, that are capable of proliferating autonomously in serum-free medium containing no added peptide growth factors were identified. All four cell lines show epidermal growth factor (EGF) receptors (EGFRs), express transforming growth factor alpha (TGF-alpha) messenger RNA, and release anti-TGF-alpha-immunoreactive molecules. The blocking anti-EGFR monoclonal antibody (mAb) 225 blocks autonomous proliferation of SNU-C1 and SNU-C4 cells. In both of these cell lines, the inhibitory effect of mAb 225 is reversible by the addition of EGF, TGF-alpha, or conditioned medium from any of the four cell lines. In contrast, autonomous proliferation of SNU-C5 and NCI-H716 cells is not inhibited by mAb 225 and is not affected by exogenous EGF, TGF-alpha, or conditioned medium. Together, these data confirm the previous finding that anti-EGFR antibodies can inhibit the proliferation of some carcinoma cell lines that coexpress TGF-alpha and EGFR. However, here it is shown that the mechanisms of autonomous proliferation of colon carcinoma cell lines are heterogeneous and not always sensitive to antibody disruption of TGF-alpha/EGFR autocrine interactions.

Protein kinase C activity in human colonic adenoma and colorectal carcinoma

To additionally understand the molecular mechanisms and biologic indicators of colonic tumorigenesis through the adenoma-carcinoma sequence, protein kinase C (PKC) activity was examined in the cytosol and particulate fraction of specimen homogenates from 18 human colonic carcinomas and seven coexisting colonic adenomas and was compared with the adjacent normal mucosal tissues. This study showed that PKC activity could be detected precisely using mini DEAE-Sephacel column purification and histone III-S as a substrate. The PKC activity in both colonic adenoma and carcinoma progressively was reduced in the particulate fraction compared with that of the adjacent normal mucosa from each patient (74.9 +/- 11.3 and 42.4 +/- 9.37 versus 112 +/- 16.8 pmol/min/mg, P less than 0.001), although PKC activity in the cytosolic fraction was not significantly different (62.6 +/- 17.7 and 63.1 +/- 8.08 versus 56.4 +/- 7.32 pmol/min/mg) with respect to protein concentration. Both colonic adenomas and carcinomas showed a significant progressive decrease in total particulate PKC activity compared with the adjacent normal mucosa of each patient (13.5 +/- 2.18 and 7.64 +/- 1.35 versus 19.8 +/- 2.74 pmol/min/g tissue, P less than 0.001) and no difference in total cytosolic PKC activity (15.2 +/- 3.80 and 16.5 +/- 2.02 versus 14.6 +/- 1.81 pmol/min/g tissue). Among PKC activities in carcinomas, there was no difference related to histologic type, Dukes' staging, or carcinoembryonic antigen values. Among PKC activities in colonic adenomas, a significant decrease in particulate PKC correlated with size. The specific PKC activity in the particulate fraction decreased with advancing adenoma size (P less than 0.05). This study showed that colonic carcinogenesis might be associated with alterations in cellular levels of PKC activity and that the decrease in particulate PKC activity in the adenoma had a possible correlation with adenoma size.

Multistage carcinogenesis in paediatric and adult cancers

Retinoblastoma (RB) and the familial adenomatous polyposis/colorectal cancer (FAP/CRC) complex provide well-characterised examples of multistage carcinogenesis and inheritance of a predisposition to cancer. Retinoblastoma appears to conform to the simple two-step model first proposed by Knudson. The gene responsible for RB, now called Rb1, has been located in chromosome region 13q14. The Rb1 gene has been cloned and subjected to extensive analysis. It is probable that the Rb1 gene product has a role in the regulation of transcription. The familial form of RB occurs as the result of a germline mutation of one of the copies of the Rb1 gene. Colorectal cancer, in contrast, appears to be the result of four or five steps involving both activation of oncogenes and inactivation of antioncogenes. The FAP gene has been located in chromosome region 5q21 by genetic linkage, and a candidate gene, MCC (mutated in colon cancer), has been cloned. Other mutations in previously-identified genes that have been identified as important in the genesis of CRC include the activation of p53 and of Ki-ras. A gene lying in chromosome region 18q which is deleted in colorectal cancer, and hence named DCC has been cloned. Its protein product has sequence homology to neural cell adhesion molecules and other related cell-surface glycoproteins. Delineation of the genes involved in the development of tumours such as RB and CRC provides insight into the mechanisms by which sequential mutations result in carcinogenesis.

Ki-ras oncogene activation in preinvasive pancreatic cancer

Activation of the Ki-ras oncogene by specific point mutations at codon 12 occurs at a remarkably high frequency in pancreatic ductal adenocarcinoma and is likely to be an important event in the pathogenesis of this cancer. To determine whether ras activation also occurs in noninvasive proliferative lesions of the pancreas, a series of cases of ductal papillary hyperplasia, intraductal papillary neoplasia, and intraduct extensions of ductal adenocarcinoma were examined for activating mutations of Ki-ras at codons 12, 13, and 61 using polymerase chain reaction amplification. Specific mutations at Ki-ras codon 12 were found in 5 of 6 cases (83%) of intraduct extensions of carcinomas and in 12 of 16 (75%) invasive carcinomas. In cases with both intraductal and invasive components, the same mutation was identified in each. No mutations were found in 5 intraductal papillary neoplasms and 9 cases of ductal papillary hyperplasia. The authors conclude that Ki-ras activation at codon 12 is important in the tumorigenesis of ductal adenocarcinoma of the pancreas but is not required in the pathogenesis of ductal papillary hyperplasia or intraductal papillary neoplasm.

Molecular biology in the diagnosis and prognosis of solid and lymphoid tumors

The application of molecular biology to the study of human malignancies has led to tremendous gains in our understanding of their pathogenesis. Although their practical applications are still somewhat limited at this point, the use of molecular diagnostic tools is likely to grow at a very rapid rate as newer and more accurate prognostic markers are identified. The availability of reliable prognostic markers should allow earlier intervention in patients with aggressive disease but exhibiting only limited extent of disease at the time of initial diagnosis. Early intervention in such cases could realistically increase the probability of cure, since highly aggressive tumor cells are more likely to be eliminated by early institution of cytotoxic chemotherapy (4). The p53 tumor suppressor gene clearly represents the most promising potential prognostic marker at present, because of both the multiple phenotypic alterations caused by different p53 mutations and the high frequency of p53 mutations which have been observed in a variety of human cancers. Other prognostic markers related to oncogenes and tumor suppressor genes are almost certain to follow. Validation of new prognostic markers requires a knowledge of both histopathologic diagnostic criteria as well as the consequences for the patient of each diagnosis. There is bound to be some "shake-out" in the field of molecular diagnostics just as there was with other recently introduced techniques such as immunohistochemistry and flow cytometry which were found to provide additional useful information for some tumors and not for others. Since the clinical-pathologic studies needed for verification of putative prognostic markers require relatively long periods of follow up, progress in this area will almost certainly lag behind the ability of molecular biologists to identify new and potentially useful prognostic markers. Our collective ability to reap tangible gains in the clinical arena from our heavy investments in molecular biology and biotechnology depends to a large extent on open channels of communication between clinical and basic scientists. As our ever-increasing insights into oncogenic processes spawn new diagnostic and prognostic markers, our priorities should remain focused on those areas which are inadequately addressed by current methods, and we should avoid the technological trap of devising redundant solutions which increase the expense, but not the efficiency of patient care.

Activating point mutation in Ki-ras codon 63 in a chemically induced rat renal tumor

Renal mesenchymal tumors induced in F344 rats with methyl(methoxymethyl)nitrosamine (DMN-OMe) have previously been shown by our laboratory to contain transforming Ki-ras sequences, activated most commonly by a variety of codon 12 mutations. Further sequence analysis of the one DMN-OMe-induced tumor with transforming Ki-ras sequences detected by NIH 3T3 transfection assay but with no mutation in codon 12 detected by selective oligonucleotide hybridization has now revealed an activating point mutation in codon 63. The observed GAG----AAG transition in codon 63, which replaces glutamic acid with lysine, was the only detectable mutation in exon 1 and 2 hotspot regions of Ki-ras in this tumor. The same mutation was also detected in Ki-ras sequences derived from first- and second-cycle transformants in NIH 3T3 transfection assays. Although random mutagenesis studies of cloned Ha-ras sequences by Fasano et al. (Proc Natl Acad Sci USA 81:4008-4012, 1984) had already indicated that GAG----AAG mutations in codon 63 of ras are transforming, this is the first demonstration of the natural occurrence of this particular activating mutation in a tumor.

Oncogene alterations in rat colon tumors induced by N-methyl-N-nitrosourea

The authors assayed oncogene alterations in rat colon tumors induced by the direct-acting chemical carcinogen, N-methyl-N-nitrosourea (MNU). DNA isolated from 34 adenomas and eight carcinomas, as well as adjacent normal colon, of 11 rats was assayed by Southern blotting for restriction fragment length polymorphisms and gene amplifications and deletions in 13 oncogenes known to be involved in human or other animal tumors. In addition to finding apparent point mutations or other small alterations in the fos and abl genes in individual rat colon tumors, the authors observed what appear to be larger alterations (ie, rearrangements, or intragenic insertions or deletions) in the H-ras and myb loci in several tumors. In contrast, no changes in the K-ras, N-ras, myc, N-myc, neu, raf, fms, met, and hst genes were seen in any of these tumors. The frequency of myb gene alterations was higher in carcinomas than in adenomas, suggesting that these changes occurred relatively late during tumorigenesis and were not direct effects of the carcinogen. In addition, the finding of alterations in two or three oncogenes in several MNU-induced rat colon tumors suggests the possibility of more widespread genomic lesions in this model.

Prognostic significance of the expression of ras oncogene product in non-small cell lung cancer

The clinical significance of ras oncogene expression in non-small cell lung cancer was evaluated in 116 surgically treated patients. Archival paraffin sections of the tumors were analyzed immunohistochemically using anti-ras p21 monoclonal antibody (MoAb) rp-35, and p21 staining was correlated with clinicopathologic parameters and survival. Positive reactions (+ and ++) were observed in 72.5% of the adenocarcinomas and 55.6% of the squamous cell carcinomas studied. The T1 tumors showed a ++ reaction less frequently than T2 and T3 tumors (P less than 0.05). Stage I tumors also were less reactive with MoAb rp-35 than tumors in more advanced stages (P less than 0.05). Survival analysis showed that patients with p21-negative tumors had significantly longer survival times (a 5-year survival rate of 64.1%) than those with p21 + tumors (38.0%, P less than 0.05) or those with p21 ++ tumors (11.5%, P less than 0.005). The significant correlation between p21 staining and patient survival was independent of histologic type, stage of disease, tumor or node status, and the resectability of tumors. On Cox's multivariate analysis, p21 staining was a major and independent prognostic determinant of survival. These results suggest that enhanced ras p21 expression may be one of the important biologic and clinical markers indicating the malignant potential of non-small cell lung cancer.

Multistage carcinogenesis in mouse skin

The mouse skin model of multistage carcinogenesis has for many years provided a conceptual framework for studying carcinogenesis mechanisms and potential means for inhibiting specific stages of carcinogenesis. The process of skin carcinogenesis involves the stepwise accumulation of genetic change ultimately leading to malignancy. Initiation, the first step in multistage skin carcinogenesis involves carcinogen-induced genetic changes. A target gene identified for some skin tumor initiators is c-Ha-ras. The second step, the promotion stage, involves processes whereby initiated cells undergo selective clonal expansion to form visible premalignant lesions termed papillomas. The process of tumor promotion involves the production and maintenance of a specific and chronic hyperplasia characterized by a sustained cellular proliferation of epidermal cells. These changes are believed to result from epigenetic mechanisms such as activation of the cellular receptor, protein kinase C, by some classes of tumor promoters. The progression stage involves the conversion of papillomas to malignant tumors, squamous cell carcinomas. The accumulation of additional genetic changes in cells comprising papillomas has been correlated with tumor progression, including trisomies of chromosomes 6 and 7 and loss of heterozygosity. The current review focuses on the mechanisms involved in multistage skin carcinogenesis, a summary of known inhibitors of specific stages and their proposed mechanisms of action, and the relevance of this model system to human cancer.

Cholangiocarcinomas in Japanese and Thai patients: difference in etiology and incidence of point mutation of the c-Ki-ras proto-oncogene

Point-mutational activation of the c-Ki-ras proto-oncogene has been shown to be rare in human hepatocellular carcinoma, the most common primary liver cancer and one usually associated with chronic viral infection. To reveal the association of c-Ki-ras activation with cholangiocarcinogenesis under different etiological backgrounds, the incidence of point mutation at codons 12 and 13 of the c-Ki-ras proto-oncogene was examined in three groups of human liver cancers with differentiation to biliary epithelial cells: Group 1, cholangiocellular carcinoma in Japanese with normal livers; Group 2, cholangiocellular carcinoma in Thais who had lived in an area where the liver fluke Opisthorchis viverrini is endemic; and Group 3, combined hepatocellular-cholangiocellular carcinoma, a rare type showing features of both hepatocellular and biliary epithelial differentiation, in Japanese with chronic viral hepatitis with or without cirrhosis. The polymerase chain reaction and direct sequencing of its product were used to detect the mutation. Point mutation at codon 12 of the c-Ki-ras gene was detected in five (56%) of nine cases in Group 1. In contrast, the mutation was not detected in any of the cases in Groups 2 and 3. Therefore, point-mutational activation of c-Ki-ras did not seem to be involved in the development of primary liver cancers associated with apparent chronic irritation of liver cells or biliary epithelial cells caused by exogenous liver-fluke or viral infection. On the other hand, point-mutational activation of the c-Ki-ras proto-oncogene may be involved in cholangiocarcinogenesis in liver without preexisting liver-fluke or viral infection.

Preclinical diagnosis of familial hypertrophic cardiomyopathy by genetic analysis of blood lymphocytes

BACKGROUND

The clinical diagnosis of familial hypertrophic cardiomyopathy is usually made on the basis of the physical examination, electrocardiogram, and echocardiogram. Making an accurate diagnosis can be particularly difficult in children, who may not have cardiac hypertrophy until adulthood. Recently, we demonstrated that mutations in the cardiac myosin heavy-chain genes cause familial hypertrophic cardiomyopathy in some families. We report a diagnostic test for familial hypertrophic cardiomyopathy that relies on the detection of mutations in the beta myosin heavy-chain gene in circulating lymphocytes that we used to evaluate three generations of a family, including the children.

METHODS AND RESULTS

Using the polymerase chain reaction, we found that normal and mutant beta cardiac myosin heavy-chain genes are transcribed in circulating lymphocytes. This allowed us to examine beta cardiac myosin heavy-chain messenger RNA from blood lymphocytes, even though ordinary expression of the gene is virtually restricted to the heart. Base sequences amplified from this messenger RNA were analyzed with a ribonuclease protection assay to identify small deletions, abnormal splicing, or missense mutations. Using this technique we identified a novel missense mutation in a patient with familial hypertrophic cardiomyopathy. We evaluated 15 of the patient's adult relatives and found perfect agreement with the clinical diagnosis (8 affected and 7 not affected). Clinical analysis of 14 of the children (age, 1 to 20 years) of these affected family members revealed 1 child with echocardiographic findings diagnostic of familial hypertrophic cardiomyopathy. However, genetic analyses showed that six other children had also inherited the missense mutation and might later manifest the disease.

CONCLUSIONS

Transcripts of beta cardiac myosin heavy-chain gene can be detected in blood lymphocytes and used to screen for mutations that cause familial hypertrophic cardiomyopathy. This approach makes practical the identification of mutations responsible for this disorder and may be applicable to other diseases in which direct analysis is difficult because the mutated gene is expressed only in certain tissues. Preclinical or prenatal screening in an affected family will make it possible to study the disease longitudinally and to develop preventive interventions.

Diagnostic utility of oncogenes and their products in human cancer

The first clear cut association of an oncogene with a specific cancer is the c-abl translocation in chronic myelogenous leukemia and acute lymphocytic leukemia; it has been observed in 90% of CML cases examined. This is the major contributing factor to its being the target of the first oncogene-based FDA-approved diagnostic test. Although the role of the abl translocation in the tumorigenic process is not yet understood, it is clear that somehow it must be causally related to the disease, and thus is an ideal target for a diagnostic test. The association of this oncogene with a specific cancer is the model on which all others may be based in the future. Second generation tests could easily include PCR on mRNA, and/or in situ hybridization, both of which could be performed using blood samples. Both methods would provide a faster means of testing a large number of cells, however, the methodologies must be improved through automation and computer-aided image analysis, respectively, in order to become useful routine tests. Both neu and epidermal growth factor receptor (EGFR) appear to have a close correlation between overexpression of the gene product and outcome of disease in breast cancer; valuable information for prognosis of the disease. And again, although the actual mechanism of action of these molecules and how this relates to the tumorigenic process is not yet known, it is believed from the very nature of the molecules that they must in some way contribute to the progression of the disease. In both cases, the protein products are overexpressed in tissue, and in the case of Neu, it appears as through at least some of the patients have a Neu-related protein in their serum. These molecules present relatively easy targets for the development of diagnostic/prognostic assays, as antibodies are easily made and can be incorporated into a variety of assay formats. Current assays available, an ELISA for Neu and a radio-ligand binding assay for EGFR, are highly sensitive, reproducible and relatively easy to perform. Only the ELISA is commercially available, however, and hence allows for easy comparison between laboratories. An abvious step towards the routine measurement of EGFR then is the development of a comparable commercially available test. An improvement for both types of assay would be the incorporation of an internal control to gauge the cellular component of the tissue samples that are tested. The outcome of the applications of myc and ras to cancer diagnostics is not so easily predictable, with a couple of exceptions.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential activation of ras genes by point mutation in human colon cancer with metastases to either lung or liver

To study the possible role of ras oncogene activation in the dissemination of colon cancer, we determined point mutations in codons 12, 13 and 61 in K- and N-ras in 3 groups of tumors: (A) primary tumors of patients who had undergone surgery for Dukes' B (early-stage) colon cancer, (B) primary tumors and metastases from patients undergoing resection of isolated lung metastases and (C) primary tumors and metastases from patients undergoing resection of isolated liver metastases. In 129 samples from 93 patients, 54 (42%) were positive for point mutations in either K- or N-ras. Most mutations (89%) were found in the K-ras gene. In group A (n = 50) ras point mutations were detected in 16 cases (32%) (15 in K-ras and 1 in N-ras). Thirteen out of 23 cases in group B (57%) were positive for a ras point mutation: 10 in K-ras and 3 in N-ras. In group C (n = 20), point mutations in codon 12 of K-ras, but none in H- or N-ras, were found in 10 cases (50%). In 31 cases the primary tumors from the metastases in groups B and C were available for analysis and 15 contained a ras point mutation (48%). Not all mutations were present in both the primary tumor and the metastasis. In 3 instances, a mutation was detected in the metastasis but not in the primary tumor, whereas in 1 case a mutation was found in the primary tumor.

Tumor suppressor genes

For the past decade, cellular oncogenes have attracted the attention of biologists intent on understanding the molecular origins of cancer. As the present decade unfolds, oncogenes are yielding their place at center stage to a second group of actors, the tumor suppressor genes, which promise to teach us equally important lessons about the molecular mechanisms of cancer pathogenesis.

Quantitation of DNA hybridization in a silicon sensor-based system: application to PCR

Rapid, quantitative hybridization assays with good sensitivity are needed in many applications, for example, determining the amount of specific product from PCR. We have developed an assay which relies on the hybridization of a biotinylated oligomer and a fluoresceinated oligomer to a single-stranded target in solution. The hybridized complex is captured by streptavidin to a biotinylated membrane. After capture, the hybridization complex is detected by an antifluorescein-urease conjugate which binds to the fluoresceinated probe. The membrane-bound urease conjugate is exposed to urea and assayed with a pH-sensitive silicon sensor. The total assay time is less than 2 h and the sensitivity limit is 20 x 10(6) molecules with a coefficient of variation, CV, of less than 10%. The assay was applied to the analysis of a model target using PCR. We were able to measure the amount of specific product and the amplification factor during the exponential phase of PCR. Using extrapolation from the measured amounts of amplified product, the initial amounts of target molecules were calculated to be 1.2 x 10(6) and 4.0 x 10(2) when the added quantities were 3 x 10(6) and 3 x 10(3), as determined by serial dilution.

Association of Ki-ras mutation with differentiation and tumor-formation pathways in colorectal carcinoma

The occurrence of a point mutation on the 12th and 13th codons of the Ki-ras oncogene has been investigated in 99 colorectal carcinomas in relation to 3 histological parameters: extent of differentiation, occurrence of a mucinous component within the tumor, and presence of peripheral adenomatous polyp remnants. The mutation frequency increased with each parameter: from 13% (2/15) to 44% (37/84) with differentiation, from 33% (26/79) to 65% (13/20) with mucinous character, and from 27% (15/56) to 56% (24/43) with the presence of polyp remnants. The frequency was highest in well-differentiated mucinous tumors with adenomatous remnants 83% (5/6). We suggest that Ki-ras mutation is preferentially involved in carcinomas that have developed from adenoma and that the mutation preserves differentiation and mucin secretion in these cancer cells.

Oncogenes: a review of their clinical application

One objective of this review is to sort through and collate the recent data that suggest that human cellular oncogenes, which have been implicated as the etiologic agents in both animal and human malignancies, have also the potential to be employed as clinical tools in the struggle against cancer. For nearly 10 years, reports have been suggesting that advantage can be taken of cellular oncogenes as to their use as diagnostic and prognostic indicators of cancer and eventually as therapeutic cancer agents. It is also the purpose of this review to give an objective evaluation of these predictions. Moreover, this review will try to highlight some of the significant advances in this most rapidly evolving field of biology. Although the enormity of what has been learned about cellular oncogenes is nothing less than impressive, it is the view here that the routine implementation of oncogenes into the clinical setting will not become evident as early as the many predictions had purported.

Ribosomal protein genes are overexpressed in colorectal cancer: isolation of a cDNA clone encoding the human S3 ribosomal protein

We have isolated a cDNA clone encoding the human S3 ribosomal protein from a normal human colon cDNA library. The clone was identified as one of many that detected genes whose level of expression was increased in adenocarcinoma of the colon relative to normal colonic mucosa. Increased levels of the S3 transcript were present in the tumors of all eight patients examined. Moreover, the S3 mRNA was also more abundant in 7 of 10 adenomatous polyps, the presumed precursor of carcinoma. Additional studies demonstrated that increased levels of mRNAs encoding several other ribosomal proteins, including S6, S8, S12, L5, and P0, were present in colorectal tumors and polyps. These results suggest that there is increased synthesis of ribosomes in colorectal tumors and that this increase is an early event in colon neoplasia.

Ribosomal protein genes are overexpressed in colorectal cancer: isolation of a cDNA clone encoding the human S3 ribosomal protein

We have isolated a cDNA clone encoding the human S3 ribosomal protein from a normal human colon cDNA library. The clone was identified as one of many that detected genes whose level of expression was increased in adenocarcinoma of the colon relative to normal colonic mucosa. Increased levels of the S3 transcript were present in the tumors of all eight patients examined. Moreover, the S3 mRNA was also more abundant in 7 of 10 adenomatous polyps, the presumed precursor of carcinoma. Additional studies demonstrated that increased levels of mRNAs encoding several other ribosomal proteins, including S6, S8, S12, L5, and P0, were present in colorectal tumors and polyps. These results suggest that there is increased synthesis of ribosomes in colorectal tumors and that this increase is an early event in colon neoplasia.

Low incidence of point mutation at codon 12 of K-ras proto-oncogene in squamous cell carcinoma of the upper aerodigestive tract

Forty-two cases of squamous cell carcinoma arising in the upper aerodigestive tract were examined to determine the incidence and type of point mutation in codon 12 of the c-K-ras gene by using the polymerase chain reaction and oligonucleotide hybridization techniques on DNA extracted from paraffin blocks. DNA sequencing, in addition, was performed in 4 cases. No point mutation was detected in codon 12 of c-K-ras in the 42 squamous cell carcinomas we examined. According to the results of DNA sequencing of 4 cases, codon 13 also revealed no point mutation. Thus, point mutational activation of codon 12 of c-K-ras oncogene is an uncommon event in human upper aerodigestive tract squamous cell carcinoma.

K-ras activation in gastric epithelial tumors in Japanese

Point mutation in codons 12, 13 and 61 of the K-ras oncogene in gastric epithelial tumors were investigated by polymerase chain reaction from sections of formalin-fixed, paraffin-embedded tissue followed by dot-blot hybridization with mutation-specific oligonucleotide probes. Point mutations were found specifically in four of 20 tumors of intestinal histological subtype; GGT to GAT in three cases and to GTT in one case, all in codon 12 of K-ras. These mutations were also confirmed by direct sequencing. In contrast, none of 11 diffuse-type tumors showed K-ras point mutations. While K-ras point mutations may not be frequent events in gastric tumorigenesis, the similarity of the intestinal-type gastric tumors and colorectal tumors for K-ras point mutations as well as the association of mutations in K-ras with a particular gastric tumor histology implicates K-ras activation in the development of these tumors.

Identification of patients at high risk for colorectal carcinoma from biopsy studies of the apparently normal colorectal mucosa. A multivariate analysis

A number of phenotypic abnormalities of the colorectal mucosa which appears normal have been described to be biomarkers of cancer development. To improve their sensitivity and specificity, we simultaneously determined 10 morphological and histochemical parameters in biopsies from the colonoscopically normal mucosa of the descending colon, sigmoid, and rectum. The results were analysed by multivariate statistical methods. We tested the discriminating power of proliferative, morphometric, enzyme and mucin histochemical parameters from 80 patients either at average risk (controls), with an increased risk for colorectal carcinoma (high-risk), or with a manifest carcinoma. The following parameters were investigated: number of mitotic figures per crypt, crypt length, apical, medial and basal crypt diameter, crypt surface, activity of succinate dehydrogenase (EC 1.3.99.1), activity of acid beta-galactosidase (EC 3.2.1.23), sulpho- and sialomucin contents. Univariate statistical analyses revealed that crypt length, crypt diameter and crypt surface were significantly increased in the high-risk group, the carcinoma carriers having intermediate values between average-risk and high-risk patients. In a two-group discriminant analysis, high-risk or carcinoma patients could be separated from average-risk patients with a sensitivity of 92.9% and a specificity of 100%. When the analysis was repeated for three groups (carcinoma carriers separated from high-risk patients), sensitivity and specificity were 100% for each group. We conclude that identification of patients at risk for colorectal carcinoma is possible from the normal-appearing left colonic and rectal mucosa by morphometric and cytochemical analysis of biopsies.

Ras mutations in United Kingdom examples of oral malignancies are infrequent

Point mutations in codons 12, 13 or 61 of the oncogenes Ha-ras, Ki-ras or N-ras have been identified in human malignancies of many types. Using the PCR (polymerase chain reaction) technique for DNA amplification in vitro and stringent probing of the amplified DNA on dot blots with a library of specific oligonucleotides, we have screened for the presence of ras mutations in oral and para-oral malignancies and some associated lesions. The material, from UK patients, consisted of 22 oral squamous-cell carcinomas including 5 neck metastases, 1 oral mucosal dysplasia, 1 proliferative verrucous leukoplakia, 1 antral and 1 tonsillar carcinoma, 1 basal-cell carcinoma, 1 salivary adenocarcinoma, 1 salivary adenoid cystic carcinoma and 1 lung adenocarcinoma metastatic to the gingiva. Genomic DNA was extracted from tissues which were fresh or preserved in liquid nitrogen. Two DNA samples contained point mutations in codon 61 of Ki-ras. One of these mutations was in the lymphocytes infiltrating a retromolar SCC. The other mutation (CAA to CAU; substitution of glutamine by histidine) was in the lung adenocarcinoma metastasis. The absence of ras mutations in the epithelium of primary oral squamous-cell carcinomas is of considerable interest as other work in our Department on Indian cases of oral carcinomas associated with chewing tobacco (quid) revealed that 35% of these had a codon 12, 13 or 61 mutation in Ha-ras. While ras activations arising from point mutations may occur in a high proportion of oral malignancies associated with chewing tobacco (quid), this was not the case in UK oral malignancies, even where tobacco was smoked.

A method to detect ras point mutations in small subpopulations of cells

Biochemical assays for ras mutations are capable of detecting a mutant allele only if it is present in at least 5% of cells tested. Further, ras mutation assays which utilize the polymerase chain reaction (PCR) are unable to distinguish a ras mutation in a small population of cells from mutations resulting from Taq DNA polymerase base misincorporation. We used a standard restriction fragment length polymorphism assay of PCR-amplified c-Ki-ras to detect codon 12 mutations in tumor cells and found a cumulative error frequency for Taq DNA polymerase of one codon 12 mutation per 2 X 10(4) molecules of total amplification product. The Taq polymerase-induced mutations were found to be multiple base transitions and represented a constant proportion of the amplification product at each step of the PCR. The ability to detect the in vitro generated mutation was dependent on the number of thermal cycles and the sensitivity of the detection assay. With these considerations in mind, we developed a two-step RFLP assay in which the thermal cycle number was kept low and molecules containing mutations at codon 12 were selectively amplified in the second step. We were able to detect a ras mutation occurring in 1 per 1000 cells (a two log improvement over standard RFLP methods) without detecting mutations resulting from Taq DNA polymerase infidelity.

Molecular and cellular lesions associated with breast cancer progression

Breast cancer may be more than one disease with differing etiologies. At the molecular level, breast cancer may be the result of a complex, dynamic, and stochastic process where there is more than one way to accomplish each of the steps necessary for malignant growth. The well documented biologic heterogeneity of breast cancers may arise from the many possible molecular changes that can accomplish a given step with variable efficiency. Alternatively, this heterogeneity may also reflect various possible orders of acquiring the sum of steps necessary for malignant growth. We have attempted to describe some of the molecular changes associated with breast cancer in the context of this broad conceptual framework. We have found that the capacity for infinite growth in culture usually occurs at a late stage of malignant progression and is frequently associated with activating ras mutations. Loss of heterozygosity at chromosome 11p can occur either early or late in progression, while losses at chromosome loci 1q and 17p, although independent of each other, are found in primary breast cancers. Whether the same molecular and cellular changes are to be found in Japanese patients remains to be determined.

Loss of heterozygosity on the short arm of chromosome 17 is associated with high proliferative capacity and DNA aneuploidy in primary human breast cancer

Loss of heterozygosity (LOH) on the short arm of chromosome 17 (17p) was found in 27 of 52 (52%) previously untreated primary breast cancers. There was a significant correlation between this 17p allelic loss and two parameters associated with aggressive tumor behavior: high cellular proliferative fraction and DNA aneuploidy. These correlations with high cellular proliferative fraction and DNA aneuploidy were not found in tumors with LOH at nine other chromosome locations. The p53 gene, a putative tumor suppressor gene located at 17p13, was examined for aberrations to determine whether it is the target for the 17p LOH in breast cancer. Unlike other types of human cancer, there were no homozygous deletions or rearrangements of the p53 gene, and only 2 of 13 (15%) were mutated in the conserved region where mutational "hot spots" have been previously located. Therefore, we hypothesize that, in breast cancer, either loss or inactivation of gene(s) on chromosome 17p other than the p53 gene or a different mechanism of p53 gene inactivation may be responsible for the observed high labeling index and DNA aneuploidy associated with LOH at 17p.

Allele-specific detection of K-ras oncogene expression in human non-small-cell lung carcinomas

Point mutations in codon 12 of the K-ras oncogene are frequent in human lung adenocarcinomas. To study the expression of the K-ras gene in these tumors we have developed a mRNA detection technique based on the polymerase chain reaction (PCR). By this technique, K-ras expression can be detected semi-quantitatively in samples of less than 100 ng total RNA. Hybridization of the amplified cDNA sequences with mutation-specific oligonucleotides allows separate quantification of the expression of normal and point-mutated alleles in a single sample. RNA samples from 24 human non-small-cell lung carcinomas (NSCLC), from 2 lung metastases of colonic adenocarcinomas, from 3 human lung adenocarcinoma cell lines, and from normal lung tissue were analyzed. In most tumors, expression of K-ras was detected at levels equal to or several times higher than those found in normal lung tissue. A lung metastasis from a colon adenocarcinoma, known to contain an amplified K-ras gene, highly over-expressed the K-ras gene. In those tumors in which the K-ras oncogene was activated by a point mutation, both alleles of the gene were expressed. Our results show that a high over-expression of K-ras is a rare event in human lung carcinomas, but that a certain degree of over-expression of the mutated allele can be demonstrated in tumors with an activated K-ras gene. With the technique we describe here, adequate estimation of the expression of specific genes in minimal amounts of tumor cells becomes possible.

Patterns of gene expression that characterize the colonic mucosa in patients at genetic risk for colonic cancer

We have used a computer-driven scanning and image-processing system to identify a panel of 30 cDNA clones whose pattern of expression in individual biopsy specimens distinguishes the flat, normal-appearing colonic mucosa of patients in two genetic groups at high risk for development of colorectal cancer from that of normal colonic mucosa in low-risk individuals. The two high-risk groups, familial adenomatous polyposis and hereditary nonpolyposis colon cancer, are indistinguishable based on the pattern of expression of the 30 selected clones. This suggests that the extensive pleiotropic effects of the inherited loci, which may play an important role in the mechanism of increased risk and early onset of the disease, are similar in these populations.

Enhanced expression of oncogene-encoded mRNA in a rat model of colon cancer

We have studied the expression of oncogene-encoded mRNAs in a rat model of colon cancer. In this model, rats are intrarectally administered several low doses of the direct-acting carcinogen, N-methyl-N-nitrosourea (MNU). Tumors, predominantly adenomas, develop 5-7 months following administration of the carcinogen, and many of these progress to carcinomas. Upon assaying the steady-state levels of oncogene-encoded transcripts in normal rat colon, we found that fos and N-myc are highly expressed; H-ras, K-ras, myc, myb, and neu messages are present at lower levels; and N-ras, abl, and raf mRNAs are absent. When we compared transcript levels in rat tumors to those in normal colons from the same animal, we observed a 2-4 fold increase in both myc- and H-ras-encoded mRNAs and a 2-7 fold increase in myb message, but no change in expression of any of the 7 other genes. To test whether this increased expression is related to tumor production or is simply a result of the more rapid cellular turnover observed in tumor tissue, the level of oncogene-encoded transcripts was assayed in colonic mucosae of rats given two treatments known to enhance cell turnover and DNA synthesis in the colon. Neither acute application of MNU nor a diet containing 1% cholic acid caused any change in the level of oncogene-encoded mRNAs in rat colons, thus suggesting that the increased abundance of myc, myb, and H-ras messages in tumors is associated with tumor formation. The enhancement of expression of these genes in adenomas, as well as in carcinomas, further suggests that these alterations occur relatively early during the tumorigenic process.

E-cadherin-mediated cell-cell adhesion prevents invasiveness of human carcinoma cells

The ability of carcinomas to invade and to metastasize largely depends on the degree of epithelial differentiation within the tumors, i.e., poorly differentiated being more invasive than well-differentiated carcinomas. Here we confirmed this correlation by examining various human cell lines derived from bladder, breast, lung, and pancreas carcinomas. We found that carcinoma cell lines with an epithelioid phenotype were noninvasive and expressed the epithelium-specific cell-cell adhesion molecule E-cadherin (also known as Arc-1, uvomorulin, and cell-CAM 120/80), as visualized by immunofluorescence microscopy and by Western and Northern blotting, whereas carcinoma cell lines with a fibroblastoid phenotype were invasive and had lost E-cadherin expression. Invasiveness of these latter cells could be prevented by transfection with E-cadherin cDNA and was again induced by treatment of the transfected cells with anti-E-cadherin mAbs. These findings indicate that the selective loss of E-cadherin expression can generate dedifferentiation and invasiveness of human carcinoma cells, and they suggest further that E-cadherin acts as an invasion suppressor.

Quantitative protein changes in metastatic versus primary epithelial ovarian carcinoma

Primary and metastatic ovarian carcinomas from six patients were obtained during primary exploratory laparotomy. Tumor cells were synthetically radiolabeled with [35S]methionine. Radiolabeled cellular proteins of the primary and metastatic cells were examined by two-dimensional polyacrylamide gel electrophoresis followed by autoradiography. Computer assisted analysis of the resultant autoradiograms revealed that the amounts of only two proteins, p35 and p36, were consistently and significantly decreased in the metastatic tumor cells. No other consistent differences in protein synthesis between primary and metastatic tumors were detected.

High frequency mutation in codons 12 and 61 of H-ras oncogene in chewing tobacco-related human oral carcinoma in India

57 primary tumour samples from Indian oral cancer patients with a 5-15 year tobacco chewing habit, were examined for mutational activation in codons 12, 13 and 61 of the H-ras, K-ras and N-ras oncogenes. The highly sensitive assay based on specific oligonucleotide hybridisation following in vitro amplification of unique sequences by polymerase chain reaction was employed. Mutations were detected in twenty (35%) of the samples and were restricted to H-ras, codons 12, 13 and 61. Two cases had concurrent mutations in codons 12 and 61. The majority of the mutations were at H-ras 61.2 (Glutamine to Arginine) and H-ras 12.2 (Glycine to Valine). Three of the less frequent mutations are apparently novel. Interestingly, eight of the samples with H-ras mutations also showed loss of wild-type H-ras, as judged by absence of signals for wild-type codons 12 or 61 on dot blots. The specific H-ras mutations in these oral malignancies associated with tobacco chewing, may represent an important example of an environmental carcinogen-induced step, in a pathway leading to malignant transformation.

Transforming function of proto-ras genes depends on heterologous promoters and is enhanced by specific point mutations

Based on transfection into cells in culture or natural transduction into retroviruses, proto-ras genes seem to derive transforming function either from heterologous promoters or from point mutations. Here we ask how such different events could achieve the same results. To identify homologous regulatory elements, about 3 kilobases of rat DNA upstream of the first untranslated proto-Ha-ras exon was sequenced. Surprisingly, the sequence shares at -1858 a homology of 148 nucleotides with Harvey (Ha) sarcoma virus, 5' of viral ras, signaling possibly a second untranslated proto-Ha-ras exon. In addition the sequence contains a perfect repeat of 25 CA dinucleotides at -2655. A retroviral promoter, even from upstream of the poly(CA), conferred transforming function on proto-Ha-ras and increased transcription greater than 100-fold compared with that of unrearranged proto-ras. Point mutations were not necessary for transforming function of rat and human proto-Ha-ras genes with retroviral promoters but did enhance it greater than 10-fold. A unifying hypothesis proposes that proto-ras genes depend on high expression from heterologous promoters or enhancers for transforming function, which is modulated by ras point mutations. The hypothesis makes two testable predictions. (i) Unrearranged proto-ras genes with point mutations, which occur in some cancers, have no transforming function. Indeed, tumors with mutated proto-ras genes, even those that also lack hypothetical tumor-suppressor genes, are indistinguishable from counterparts with normal proto-ras genes. (ii) Proto-ras genes in transfected cells derive transforming function from heterologous promoters or enhancers acquired via illegitimate recombination from vector DNAs and particularly from viral helper genes that must be cotransfected for transformation of primary cells. Indeed, expression of exogenous proto-ras genes in cells transformed by transfection is as high as for viral ras genes and is much higher than in the cells of origin.

Identification of a gene located at chromosome 5q21 that is mutated in colorectal cancers

Recent studies have suggested the existence of a tumor suppressor gene located at chromosome region 5q21. DNA probes from this region were used to study a panel of sporadic colorectal carcinomas. One of these probes, cosmid 5.71, detected a somatically rearranged restriction fragment in the DNA from a single tumor. Further analysis of the 5.71 cosmid revealed two regions that were highly conserved in rodent DNA. These sequences were used to identify a gene, MCC (mutated in colorectal cancer), which encodes an 829-amino acid protein with a short region of similarity to the G protein-coupled m3 muscarinic acetylcholine receptor. The rearrangement in the tumor disrupted the coding region of the MCC gene. Moreover, two colorectal tumors were found with somatically acquired point mutations in MCC that resulted in amino acid substitutions. MCC is thus a candidate for the putative colorectal tumor suppressor gene located at 5q21. Further studies will be required to determine whether the gene is mutated in other sporadic tumors or in the germ line of patients with an inherited predisposition to colonic tumorigenesis.

Point mutation of c-Ki-ras oncogene in gastric adenoma and adenocarcinoma with tubular differentiation

The presence of point mutation at codons 12, 13 and 61 of the c-Ki-ras oncogene was investigated in 7 cases of gastric adenoma and 35 cases of gastric adenocarcinoma using DNA samples from formalin-fixed and paraffin-embedded tissues. Oligonucleotides encompassing the three codons were amplified by using the polymerase chain reaction (PCR), and then examined for point mutation by the selective oligonucleotide hybridization technique. Point mutation was detected in three of the 7 adenomas (43%) and three of the 35 carcinomas (9%). All the gastric adenomas showed the histology of tubular adenoma, being very similar to that of colonic adenoma. The 35 cases of gastric adenocarcinoma were classified into 17 cases of differentiated type and 18 cases of undifferentiated type including signet-ring cell carcinoma. The point mutation of c-Ki-ras oncogene was detected only in the differentiated type (3/17, 18%), and there was no case with point mutation in the undifferentiated type. These results suggest that the genetic mechanism of carcinogenesis differs between the differentiated type and the undifferentiated type of gastric adenocarcinoma, and also that c-Ki-ras activation is possibly involved in a relatively early step of the "adenoma-carcinoma sequence," which leads to the development of a portion of differentiated adenocarcinomas in the stomach.

Higher frequency of point mutations in the c-K-ras 2 gene in human colorectal adenomas with severe atypia than in carcinomas

Human colorectal carcinomas may be induced from adenomas or they may occur de novo. To examine which is the main pathway, we analyzed point mutations at codon 12 in the c-K-ras 2 gene in 73 colorectal carcinomas, 13 metastatic tumors, 72 adenomas and 30 normal tissues. The c-K-ras 2 codon 12 mutation frequency was 0/30 in normal tissues, 0/17 in adenomas with mild atypia, 3/37 (8.1%) in adenomas with moderate atypia, 15/18 (83.3%) in adenomas with severe atypia, 19/73 (26.0%) in primary carcinomas and 3/13 (23.1%) in metastatic tumors. The mutation frequency in adenomas with severe atypia was much higher than that in carcinomas. These results indicate that many colorectal carcinomas may not be induced through adenomas with severe atypia.

Mutations in the K-ras oncogene induced by 1,2-dimethylhydrazine in preneoplastic and neoplastic rat colonic mucosa

These experiments were conducted to determine whether point mutations activating K-ras or H-ras oncogenes, induced by the procarcinogen 1,2-dimethylhydrazine (DMH), were detectable in preneoplastic or neoplastic rat colonic mucosa. Rats were injected weekly with diluent or DMH at 20 mg/kg body wt for 5, 10, 15, or 25 wk, killed, and their colons dissected. DNA was extracted from diluent-injected control animals, histologically normal colonic mucosa from carcinogen-treated animals, and from carcinomas. Ras mutations were characterized by differential hybridization using allele-specific oligonucleotide probes to polymerase chain reaction--amplified DNA, and confirmed by DNA sequencing. While no H-ras mutations were detectable in any group, K-ras (G to A) mutations were found in 66% of DMH-induced colon carcinomas. These mutations were at the second nucleotide of codons 12 or 13 or the first nucleotide of codon 59 of the K-ras gene. The same type of K-ras mutations were observed in premalignant colonic mucosa from 2 out of 11 rats as early as 15 wk after beginning carcinogen injections when no dysplasia, adenomas, or carcinomas were histologically evident, suggesting that ras mutation may be an early event in colon carcinogenesis.

Generation of monoclonal antibodies specific for ras p21 Glu-12 oncoproteins: detection in carcinogen-induced mammary carcinomas

ras genes have been shown to become oncogenes by single point mutations which result in amino acid substitutions that affect either their GTPase activity (positions 12, 13, 59, 61) or their affinity for GTP and GDP. Ras oncogenes and their corresponding proteins have been described in a variety of human cancers as well as in animal tumors induced by physical and chemical carcinogens. One of these animal tumor systems involves the induction of mammary carcinomas in rats by a single dose of N-nitroso-N-methylurea (NMU), a methylating carcinogen. These NMU-induced mammary carcinomas contain transforming H-ras genes activated by G----A transitions in the second nucleotide of their 12th codon, presumably a consequence of the pre-mutagenic lesions induced by NMU. These G----A mutations result in the replacement of the normal glycine in the 12th position of the ras p21 protein by a glutamic acid residue. In this study, we report the generation of monoclonal antibodies (Mab) reactive with oncogenic ras p21 proteins containing glutamic acid at position 12 (p21 Glu-12). Mab designated E184 specifically recognized activated ras p21 Glu-12 proteins but not normal p21 (Gly-12) or p21 proteins activated by other position 12 substitutions including arginine, aspartic acid, cysteine, valine or serine residues. Western blot analysis of NMU-induced mammary carcinomas demonstrated that Mab E184 recognized p21 proteins expressed in these rat tumors but not p21 present in normal tissues nor in other carcinogen-induced tumors known to carry H-ras oncogenes activated by mutations at position 61.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered protein tyrosine kinase levels in human colon carcinoma

To further understand the molecular mechanisms and the biological indicators of colonic tumorigenesis, the authors examined tyrosine kinase activity in the cytosol and in the particulate fraction of the homogenates of specimens from 20 human colonic carcinomas and compared them with the adjacent normal mucosal tissues. Total protein tyrosine kinase activity could be precisely detected using miniphosphocellulose column purification and a synthetic peptide, Glu-asparagine (Asp)-alanine (Ala)-Glu-tyrosine (Tyr)-Ala-Ala-arginine (Arg)-Arg-Arg-glycine (Gly) (E11-G1), as an artificial substrate. Tyrosine kinase activity of colonic carcinoma and normal mucosa was reduced in the cytosol fraction whereas activity in the particulate fraction was elevated with respect to protein concentration. The average specific activity ratios were 1.95 +/- 0.27 (normal cytosolic/carcinoma cytosolic) and 0.57 +/- 0.01 (normal particulate/carcinoma particulate) for tyrosine kinase activity. Cellular distribution (% cytosol) of tyrosine kinase activity in normal mucosa and in carcinoma varied from 21.0% to 91.2% and from 7.0% to 61.4%, respectively. In nearly all cases the percentage of cytosolic tyrosine kinase activity in carcinoma tissues was lower than in normal tissues. There was no difference due to histologic type or the presence of adenomatous components. A significant decrease of cytosolic tyrosine kinases was correlated with Dukes' Stage A. With advancing Dukes' stage, the average specific activity ratios (normal cytosol/carcinoma cytosol) were decreased. This study indicates that colonic carcinogenesis might be associated with alterations in cellular levels of tyrosine kinase activity and that the average specific activity ratio (normal cytosol/carcinoma cytosol) had a possible correlation with colonic tumor growth.

Establishment and characterization of an epithelial cell line with quasi-normal chromosomes from a tubular adenoma of a familial polyposis coli patient

An epithelial cell line designated FPCK-1 has been established from a tubular adenoma developing in a male familial polyposis coli (FPC) patient. The FPCK-1 cells grow very slowly with abundant mucus production and have been maintained stably for 3 years in culture. No growth was evident either in soft agar or nude mice. FPCK-1 cells present a normal male karyotype and do not show loss of specific loci on chromosomes 5, 17, 18, and 22 which have been reported to be lost frequently in human colon carcinomas. The cells have neither a point mutation on codon 12 of K-ras gene nor gene amplification of myc, c-H-ras, and/or c-K-ras genes. These results thus suggest the existence of hitherto unknown causative event(s) underlying adenoma development in FPC patients. The FPCK-1 cell line should prove useful for further analytical investigation of the multiple steps involved in human colon carcinogenesis.

Ras gene mutation and amplification in human nonmelanoma skin cancers

Our previous studies have shown that human skin cancers occurring on sun-exposed body sites frequently contain activated Ha-ras oncogenes capable of inducing morphologic and tumorigenic transformation of NIH 3T3 cells. In this study, we analyzed human primary squamous cell carcinomas (SCCs) and basal cell carcinomas (BCCs) occurring on sun-exposed body sites for mutations in codons 12, 13, and 61 of Ha-ras, Ki-ras, and N-ras oncogenes by amplification of genomic tumor DNAs by the polymerase chain reaction, followed by dot-blot hybridization to synthetic oligonucleotide probes designed to detect single base-pair mutations. In addition to the primary human skin cancers, we also analyzed Ha-ras-positive NIH 3T3 transformants for mutations in the Ha-ras oncogene. The results indicated that all three NIH 3T3 transformants, 11 of 24 (46%) SCCs, and 5 of 16 (31%) BCCs contained mutations at the second position of Ha-ras codon 12 (GGC----GTC), predicting a glycine-to-valine amino acid substitution, whereas only 1 of 40 skin cancers (an SCC) displayed a mutation in the first position of Ki-ras codon 12 (GGT----AGT), predicting a glycine-to-serine amino acid change. In addition, three of the SCCs contained highly amplified copies of the N-ras oncogene in their genomic DNA. Interestingly, two of the SCCs containing amplified N-ras sequences also had G----T mutations in codon 12 of the Ha-ras oncogene. These studies demonstrate that mutations in codon 12 of the Ha-ras oncogene occurred at a high frequency in human skin cancers originating on sun-exposed body sites, whereas mutation in codon 12 of Ki-ras or amplification of N-ras occurred at a low frequency. Since the mutations in the Ha-ras and Ki-ras oncogenes were located opposite potential pyrimidine dimer sites (C-C), it is likely that these mutations were induced by ultraviolet radiation present in sunlight.

The molecular progression of plutonium-239-induced rat lung carcinogenesis: Ki-ras expression and activation

Specific, transforming point mutations of ras and alterations in ras expression have been associated with many neoplastic processes, and their presence may be pivotal in neoplastic transformation. Our objective were to evaluate the molecular and genetic alterations of Ki-ras in preneoplastic foci and neoplasms in the lungs of rats that inhaled 239PuO2 aerosols. Histologically classified pulmonary lesions were evaluated by in vitro nucleic acid amplification, oligonucleotide hybridization, and direct nucleic acid sequencing for activating Ki-ras point mutations. We evaluated ras expression in similar lesions using immunohistochemistry and in situ hybridization. Specific Ki-ras point mutations were present in 46% of the radiation-induced malignant neoplasms. Spontaneous pulmonary neoplasms, which are rare in rats, had similar activating mutations and frequencies (40%). We found similar mutation frequencies in radiation-induced adenomas and foci of alveolar epithelial hyperplasia. No mutations were identified in normal lung tissue. Ras expression in hyperplastic lesions and neoplasms was similar to that observed in normal pulmonary epithelia. These findings suggest that Ki-ras activation, not alterations in expression, is an early lesion associated with many radiation-induced, proliferative pulmonary lesions and that this molecular alteration may be an important component of both radiation-induced and spontaneous pulmonary carcinogenesis in the rat.

Metabolic phenotypes and colorectal neoplasia

It now appears likely that the development of colonic adenomas and carcinomas involves a series of steps in which environmental or endogenous carcinogens induce or promote neoplasia through the accumulation of multiple, specific genetic mutations. Genetic predisposition to this process may take the form of inherited defects in control of cellular proliferation as in familial polyposis coli, or genetically determined polymorphism which affects enzyme activities relevant to the production or detoxication of carcinogens. Genetic effects may also influence levels of hormones and/or their target cell receptors which regulate the metabolic and proliferative activity of colonocytes. This review highlights data suggesting a role for polymorphism associated with xenobiotic acetylation, hydroxylation, and conjugation with glutathione in the metabolism of potential carcinogens, as well as for dehydroepiandrosterone in the metabolic control of cell proliferation. The study of genetically determined polymorphism in colorectal cancer may provide new insights into the epidemiology of cancer and result in new methods for the detection of higher risk groups.

[Dietary fiber. Effect on colon carcinogenesis]

The etiopathogenesis of colon carcinogenesis is supposed to be a two-step process consisting of initiation and promotion. In human nutrition the range of xenobiotics acting possibly as initiators occurs mostly in very low concentrations. Therefore, performing a one-factorial consideration they are not claimed seriously to account for initiation. On the contrary, it can be taken for granted that bile acids exert promoting effects in connection with colon carcinogenesis. All factors influencing the promoting effect of bile acids are able to do so probably due to a decrease of pH and as a result the shift of the two bile acid fractions in favour of the soluble fraction, and/or due to the intensification of shift of bile acid metabolism (7-alpha-dehydroxylase). These processes are indirectly influenced to a large extent by the lipid content of food as a result of cholegenesis induction. The "protective Effect" of dietary fibre in colon carcinogenesis (reduced number of tumour carriers, and/or number of tumors per animal) cannot been interpreted as such. Only a delayed promotion phase could been proven. It can be reached only by plant products (bran, lupin), but not by dietary fibre in general.

Analysis of oncogene alterations in human endometrial carcinoma: prevalence of ras mutations

The molecular genetics of human endometrial carcinoma have yet to be defined to any significant extent. Cell lines from 11 endometrial carcinomas were examined for alterations in proto-oncogenes that might predictably be present, based on existing data from the better-characterized human carcinomas of the uterine cervix, ovary, and breast. Codons 12, 13, and 61 of the Ha-ras, Ki-ras, and N-ras genes were examined for possible point mutations, and the c-erbB2/neu, c-myc, and epidermal growth factor receptor (EGFR) genes were examined for amplification or overexpression. Ras mutations were found in seven of 11 (64%) tumors, including three in codon 61 of Ha-ras (CAG----CAT) and four in codon 12 of Ki-ras (GGT----GAT in two and GGT----GTT in two). No evidence was found for amplification or overexpression of the c-erbB2 or EGFR genes in any tumor. One tumor contained amplified c-myc sequences and exhibited relative overexpression of c-myc. These data suggest that the amplification or overexpression of several proto-oncogenes frequently observed in other human gynecologic and breast tumors are not prevalent in endometrial carcinoma and that ras gene mutations are relatively common in this tumor type.

A novel point mutation at codon 146 of the K-ras gene in a human colorectal cancer identified by the polymerase chain reaction

In this report, point mutations of the K-ras gene at codon 146 were analyzed in 25 cases of colon cancer, 4 cases of lung cancer, and 41 cases of lymphoid malignancy. A codon 146 mutation substituting threonine (ACA) for alanine (GCA) was detected in the tumor tissue of a patient with colon cancer and was not detected in the normal tissue of the same patient. Any additional mutations of the ras gene family were not detected in this patient. These results suggest that the codon 146 mutation of the K-ras gene could be involved in the development of naturally occurring human malignancies.