Low frequency of ras gene mutations in neuroblastomas, pheochromocytomas, and medullary thyroid cancers

Little is known about the prevalence and significance of ras gene activation in neural crest tumors such as neuroblastomas, pheochromocytomas, and medullary thyroid cancers (MTCs). Therefore, we analyzed DNA from 10 human neuroblastoma cell lines and 10 primary human pheochromocytomas for activating mutations in N-ras, H-ras, and K-ras. We also studied DNA from 24 primary neuroblastomas and 10 MTCs for N-ras mutations. ras genes were analyzed by direct sequencing of specific DNA fragments amplified by the polymerase chain reaction. With the exception of the SK-N-SH cell line, the examined ras gene sequences were normal in all the neuroblastomas, pheochromocytomas, and MTCs tested. A single point mutation was identified at codon 59 (GCT(ala)----ACT(thr)) in one N-ras allele in an SK-N-SH subline. Interestingly, this mutation is different from the activating codon 61 mutation which resulted in the initial identification of N-ras from SK-N-SH DNA. Therefore, we analyzed the sequences of earlier passages and sublines of the SK-N-SH cell line, but mutations at codon 59 or 61 were not detected, suggesting that neither mutation was present in the primary tumor. Our results indicate that N-ras mutations may occur spontaneously during in vitro passage of cell lines but rarely, if ever, occur in primary neuroblastomas, pheochromocytomas, and MTCs. In addition, we have not found H-ras or K-ras mutations in any neuroblastoma cell line or primary pheochromocytoma.     

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.     

Infrequent mutation of the ras genes in skin tumors of xeroderma pigmentosum patients in Japan.

By using PCR amplification and oligonucleotide mismatch hybridization, base-substitution mutations of the ras genes in 26 skin tumors of Japanese xeroderma pigmentosum (XP) patients were studied. Thin sections of tumor tissues which were fixed and embedded in paraffin blocks were used in this study. After analyzing codons 12, 13 and 61 of the H-, K- and N-ras genes by using 66 oligomer probes, we detected only one mutation of the K-ras gene at codon 61 in one tumor sample. All the other tumors were therefore considered not to have a mutation in the ras genes. These results suggest that mutations of the ras genes are not particularly associated with skin tumors of Japanese XP patients.     

Detection of activating mutations in the ras family genes in cytological specimens from lung-tumors

Mutations in the ras family genes (K-ras mainly) represent a common event in lung tumorigenesis which is frequently associated with poor clinical outcome. In order to investigate whether K-ras mutations are detectable in cytological material obtained from patients with lung cancer, 37 cytological specimens (16 fine needle aspiration and 21 bronchoscopy) were assessed for codon 12 point mutations in the H-, K- and N-ras genes by combined polymerase chain reaction-restriction fragment length polymorphism. K-ras codon 12 point mutations were found in 8 out of 37 (22%) specimens while no mutations were found in the H-ras and N-ras genes. Mutations were found in 27% (3 out of 11) of adenocarcinomas while in squamous cell carcinomas the incidence of mutations was 18% (3 out of 17). In addition, a K-ras codon 12 point mutation was found in one (12%) among 8 small cell carcinomas and in the only Hodgkin's lymphoma with metastasis in the lung. Our results are in agreement with previous results that recognise high incidence of K-ras activation in lung carcinomas, and indicate that detection of mutant ras alleles is possible in cytological material.     

Analysis of the c-myc, K-ras and p53 genes in methylcholanthrene-induced mouse sarcomas.

We have examined 63 methylcholanthrene (MCA)-induced mouse sarcomas for possible correlations of mutations involving the c-myc, ras and p53 genes. The c-myc gene was found to be amplified in 18 of these sarcomas (29%). Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and subsequent direct sequencing identified 18 cases carrying K-ras mutation at codons 12, 13 and 61 (29%). No mutation was detected in the H-ras and N-ras genes. Mutations of the p53 gene in exons 5 to 8 were found in 45 cases (71%). Comparison of these mutations revealed that out of 18 cases with c-myc gene amplifications, 10 carried K-ras mutations (56%) and 14 carried p53 mutations (78%). In contrast, among 45 cases of sarcomas without c-myc gene amplification, 8 were found to have K-ras mutations (18%). The same 45 cases were found to have 31 p53 mutations (69%). The present study suggests a strong correlation between c-myc gene amplification and K-ras gene mutation (P < 0.01). p53 gene mutation was frequently found among MCA-induced mouse sarcomas, indicating the importance of this mutation in the etiology of these tumors. However, p53 mutations were present in sarcomas regardless of the state of c-myc amplification and K-ras mutation. Therefore, a defect in the p53 gene is independent of amplification of the c-myc gene or point mutation of the K-ras gene.     

Analysis of the c-myc, K-ras and p53 Genes in Methylcholanthrene induced Mouse Sarcomas

We have examined 63 methylcholanthrene (MCA)-induced mouse sarcomas for possible correlations of mutations involving the c-myc, ras and p53 genes. The c-myc gene was found to be amplified in 18 of these sarcomas (29%). Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and subsequent direct sequencing identified 18 cases carrying K-ras mutation at codons 12, 13 and 61 (29%). No mutation was detected in the H-ras and N-ras genes. Mutations of the p53 gene in exons 5 to 8 were found in 45 cases (71%). Comparison of these mutations revealed that out of 18 cases with c-myc gene amplifications, 10 carried K- ras mutations (56%) and 14 carried p53 mutations (78%). In contrast, among 45 cases of sarcomas without c-myc gene amplification, 8 were found to have K- ras mutations (18%). The same 45 cases were found to have 31 p53 mutations (69%). The present study suggests a strong correlation between c-myc gene amplification and K- ras gene mutation ( P < 0.01). p53 gene mutation was frequently found among MCA-induced mouse sarcomas, indicating the importance of this mutation in the etiology of these tumors. However, p53 mutations were present in sarcomas regardless of the state of c-myc amplification and K- ras mutation. Therefore, a defect in the p53 gene is independent of amplification of the c-myc gene or point mutation of the K- ras gene.     

Incidence and possible clinical significance of K-ras oncogene activation in adenocarcinoma of the human lung

47 tumor samples, 45 of which were obtained at thoracotomy for non-small cell lung cancer were examined for mutational activation of the oncogenes H-ras, K-ras, and N-ras. A novel, highly sensitive assay based on oligonucleotide hybridization following an in vitro amplification step was employed. ras gene mutations were present in nine of 35 adenocarcinomas of the lung (all K-ras), in two of two lung metastases of colorectal adenocarcinomas (1 x K-ras, 1 x N-ras) and in one adenocarcinoma sample obtained at autopsy (H-ras). All K-ras and H-ras mutations were in either position 1 or 2 of codon 12, while the N-ras mutation was in position 2 of codon 61. The potential clinical significance of K-ras activation was analyzed using the combined results of this and of our earlier study (S. Rodenhuis et al., New Engl. J. Med., 317: 929-935, 1987). Lung adenocarcinomas with K-ras mutations tended to be smaller and were less likely to have spread to regional lymph nodes at presentation. With a median follow up of 10 months, survival data are still immature. None of six adenocarcinomas of nonsmokers had a K-ras mutation and only one of four who had stopped smoking more than 5 years before. We conclude that mutational K-ras activation is present in about a third of adenocarcinomas of the lung and that the mutational event may be a direct result of one or more carcinogenic ingredients of tobacco smoke. Studies involving larger numbers of patients are required to confirm the association of K-ras activation with smoking and the inverse relation with tumor progression.     

H-ras activation and ras p21 expression in bladder tumors induced in F344/NCr rats by N-butyl-N-(4-hydroxybutyl)nitrosamine

Bladder tumors were induced in male F344/NCr rats by administration of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) at 500 p.p.m. in their drinking water for 12 weeks. Twenty-one bladder tumors that developed between 25 and 50 weeks after BBN administration was begun were evaluated for immunoreactivity with polyclonal or monoclonal antibodies raised against ras p21, for amplification of ras genes by Southern blotting, and for activating point mutations in ras genes by selective oligonucleotide hybridization of products from polymerase chain reaction (PCR). Increased expression of ras p21 was detected by avidin-biotin immunohistochemistry in 18/21 (85%) of the neoplastic bladder lesions. By Southern analysis, there was no significant amplification of H-ras, K-ras or N-ras in any of the tumors except one that showed a 5-fold amplification of K-ras. Point mutations in ras genes were detected by selective oligonucleotide hybridization of the products of PCR. Of the 21 bladder tumors, three tumors were shown to have mutations in codon 12 (GGA----GAA), six tumors in codon 61 (two CAA----CTA, four CAA----CGA), and one in both codon 12 (GGA----GAA) and codon 61 (CAA----CGA), all in H-ras. Thus 10 of 21 tumors has ras gene mutations in a portion of the tumor cells. The variable pattern of point mutation in H-ras suggests that these mutations may not all be a direct consequence of interaction of BBN metabolites with H-ras. Enhanced expression of ras p21 was always focal and was not necessarily associated with transforming ras mutations. It is therefore suggested that tumorigenesis in BBN-initiated bladder cells might involve H-ras activation as part of a multistep pathway; however, H-ras involvement is not obligatory for tumor development.     

High rates of ras codon 61 mutation in thyroid tumors in an iodide-deficient area

Using polymerase chain reaction and sequence-specific oligonucleotide hybridization, the frequency of three ras oncogene mutations (N-ras, Ha-ras, and K-ras) in thyroid tumors (25 adenomas, 16 follicular carcinomas, and 22 papillary carcinomas) was investigated in both iodide-deficient and iodide-sufficient areas. The ras oncogene mutation rate was significantly higher in the iodide-deficient area, being 85 versus 17% in the adenomas, and 50 versus 10% in the follicular carcinomas. No mutations were found in papillary carcinomas. The most common mutation site was Ha-ras codon 61 with Gln----Arg substitution. Two ras mutations at codon 61 (Gln----Lys in N-ras and Gln----Arg in Ha-ras) were found in a microfollicular adenoma specimen from Eastern Hungary. We conclude that dietary iodine may modulate ras oncogene mutations, and that in the iodide-deficient area, ras oncogene activation may play a more important role in the initiation and/or maintenance of follicular tumors. Additional factors are, however, necessary to initiate carcinogenesis.     

Multiple point mutation of N-ras and K-ras oncogenes in myelodysplastic syndrome and acute myelogenous leukemia.

We analyzed activating mutations of N-ras and K-ras by the polymerase chain reaction and oligonucleotide hybridization in hematological disorders. Activating mutations of these codons were detected in 4 of 20 cases of myelodysplastic syndrome (MDS) and 15 of 77 cases of acute myelogenous leukemia (AML). Our of 19 cases of MDS and AML who carried active mutations, 7 cases were found to have two or more distinct mutations in activating codons of N-ras and K-ras. Ras mutation was found preferentially in progressive disease such as refractory anemia with excess of blasts (RAEB) of RAEB in transformation (RAEB-t). A relatively high incidence of ras mutation was found in M5 AML (40%). No ras mutations were found in other hematological disorders, such as acute lymphoblastic leukemia and chronic myelogenous-leukemia. The most frequent amino acid substitution was that of an aspartate for glycine at codon 12 of N-ras resulting from G to A mutation (11/35). The survival of AML patients who carried ras mutations showed no significant differences from those without ras mutations calculated by Kaplan-Meier. Seven cases of MDS and 7 cases of AML patients could be investigated at various points during their clinical course. Among these 14 cases, we found 2 interesting cases of MDS. The first case lost multiple clones carrying ras mutations during disease progression, the second case acquired mutation of the ras gene during disease progression. These results suggested that multiple point mutations of ras genes may not be initiating events but may contribute to a clonal evolution of MDS and AML.     

N-myc oncogene RNA expression in neuroblastoma

Tumor specimens from 33 patients with neuroblastoma were assayed for amplification of the N-myc oncogene and RNA expression to determine whether N-myc RNA expression levels correlated with N-myc gene amplification and clinical outcome. N-myc gene amplification was detected in one stage II tumor, one stage IV-S tumor, and seven stage III or IV tumors. In each case, N-myc RNA expression roughly paralleled N-myc gene amplification. However, enhanced N-myc RNA expression was not confined to tumors with N-myc gene amplification: all of the early (stage I and II) tumors, five stage IV-S tumors, and 12 advanced (stage III and IV) tumors had levels of N-myc RNA that were elevated up to 50-fold. While N-myc gene amplification correlated with prognosis, there was no such correlation with levels of N-myc RNA expression. The precise role of the N-myc gene in the pathogenesis of neuroblastoma remains unclear.     

Detection of point mutations in N-ras and K-ras genes of human embryonal rhabdomyosarcomas using oligonucleotide probes and the polymerase chain reaction

Previous studies have demonstrated that genes of the ras family (H, K, and N) can be activated by point mutations at codons 12, 13, and 61. In the present study we have used oligonucleotide probes corresponding to these regions to assess the role of ras gene mutations in the genesis of human rhabdomyosarcoma. To increase the sensitivity of this method the appropriate regions of the three ras genes were first amplified using the polymerase chain reaction. The results show that 35% (5/14) embryonal rhabdomyosarcomas investigated contain mutations in the N-ras or K-ras genes. Thus ras gene mutation is implicated in the development of mesenchymal and embryonal tumors in addition to its previously documented role in epithelial and hematological neoplasia.     

ras and human tumors.

Mutational activation of ras oncogenes is frequently encountered in human tumors. For unexplained reasons, K-ras mutations are predominantly found in pancreatic cancer, colorectal cancer and adeno-carcinoma of the lung, N-ras is predominantly found in a subset of acute leukemias and in myelodysplastic syndromes, while H-ras mutations are rare. In most tumors, ras mutations are not clearly associated with specific clinical or biological features, but in lung cancer, childhood lymphoblastic leukemia and possibly in myelodysplastic syndromes ras mutations may predict a poor prognosis. Accumulating evidence suggests that exposure to chemical carcinogens is responsible for many ras mutations in humans.     

Distinct spectrum of N-ras mutations in aml and mds patients in yugoslavia

Mutations that activate ras genes were demonstrated to be associated with certain types of malignancies. Multiple point mutations were predominantly found in the N-ras and occasionally in the K-ras genes. The analysis of 4 MDS, 23 AML and 11 CML patients from Yugoslavia revealed the prevalence of the N-ras mutation (83%) over K-ras mutations (17%). Although the frequencies of the N- and K-ras mutations in these patients were similar to the ones reported for patients from USA and Japan, the N-ras mutational spectra considerably differed. The prevailing type of mutation in patients from Yugoslavia was G-to-T transversion at the first position in the codon 12 of the N-ras gene. This study supports a hypothesis that different geographical and environmental factors may cause the accumulation of different type of point mutations in the same target gene.     

Activation of ras oncogenes and expression of tumor-specific transplantation antigens in methylcholanthrene-induced murine fibrosarcomas

The DNA of 22 fibrosarcomas, newly induced in BALB/c mice by subcutaneous doses of 3-methylcholanthrene (3-MCA), was tested in NIH 3T3 transformation assay. Activation of K-ras and N-ras was found in 7 and 3 cases respectively. No H-ras activation was detected. Polymerase chain reaction and oligonucleotide hybridization performed on the DNA of the 22 sarcomas revealed 5 cases of K-ras mutation at codon 12, 3 at codon 13 and 1 at both codons. One case of K13 mutation was not detectable by transfection. Three cases of mutation at codon 61 of N-ras were also found, one of which was simultaneous with a K12 mutation. Tumor-specific transplantation antigens (TSTA) were assessed in the 22 original tumors. Altogether 16 sarcomas were immunogenic, with the highest frequency of TSTA+ tumors (10/11 and 5/6) in the groups given 1.0 and 0.1 mg of 3-MCA respectively, the lowest (1/5) in that with 0.01 mg of carcinogen; ras mutations occurred in the DNAs of 11 out of the 16 TSTA+ sarcomas, but none of the DNAs of the 6 TSTA- tumors showed ras mutation. The results suggest that 3-MCA-induced transformation of subcutaneous fibroblasts can involve mutations in codons 12, 13 or 61 of K- and N- but not H-ras gene and that such mutation is accompanied by the expression of TSTA.     

Prevalence of N-ras mutations in children with myelodysplastic syndromes and acute myeloid leukemia.

The ras proto-oncogene family encodes a group of 21 kDa nucleotide-binding proteins. Activating mutations of ras genes are associated with certain types of malignancies, indicating that they are related in some way to the malignant process. We have examined bone marrow cells from nine children with myelodysplastic syndromes (MDS) and 35 with acute myeloid leukemia (AML) for activating point mutations of ras genes by in vitro amplification using polymerase chain reaction (PCR), oligonucleotide hybridization and sequencing of PCR products. We found N-ras mutations in cells from 3 of 9 children (33%) with MDS and only 2 of 35 children with AML (6%; 95% confidence interval is 0.7-19%). All mutations the second nucleotide of codon 12 or the first nucleotide of codon 61 of N-ras. There was no apparent correlation with clinical or laboratory characteristics, including karyotype; however, an association of N-ras activation with the most aggressive type of MDS was noted. Among the patients with MDS, 2 of 6 with monosomy 7 had N-ras mutations; however, three children with monosomy 7 which presented with AML lacked ras mutations. One patient was studied at time of diagnosis of MDS and again after progression to AML. At the preleukemic stage of disease, an N-ras mutation was identified; however, after development of AML this mutation was not present in the leukemic clone. In conclusion, these data show that ras mutations, while not necessary for leukemic transformation, may be important for the initiation of preleukemias evolving into overt AML.     

Increased N-myc expression following progressive growth of human neuroblastoma

Many human neuroblastoma tumors and cells in culture contain amplified N-myc DNA and this is associated with tumor stage. We have analyzed pairs of neuroblastoma cell cultures derived from two patients at the time of diagnosis and after tumor progression following the initiation of therapy. Cell cultures derived after progression have increased expression of N-myc RNA. In one pair this increase is associated with increased N-myc DNA amplification; in the other, amplification decreases and activation of N-myc is most likely the result of a regulatory change. Analysis of the pattern of DNA amplification in these cell cultures demonstrates additional changes that might be associated with tumor progression.     

ras gene mutations as a prognostic marker in adenocarcinoma of the human lung without lymph node metastasis.

Adenocarcinoma of the lung obtained at surgical resection was examined for mutation at codons 12, 13, and 61 of the oncogenes K-ras, H-ras, and N-ras, using polymerase chain reaction and oligonucleotide hybridization techniques. The mutation was detected in 18 of the 115 cases (15.7%), and 15 of 18 were at codon 12, 2 were at codon 13 of K-ras, and 1 was at codon 61 of N-ras. G to T transversions were most common. The ras gene mutations were more frequent in the male patients (P = 0.0048). No significant differences were found to be related to stage of the disease or tumor-nodes-metastases classification between positive and negative groups of the ras gene mutations. A history of tobacco use was not always a factor contributing to mutation. Of the completely resected group without lymph node metastasis, the 5-year survival rate in the ras-positive group was 53.3%, which was significantly poorer than the 83.6% survival rate in the ras-negative group (P less than 0.05). Our findings suggest that ras gene mutations may be prognostic, especially in the early stage adenocarcinoma of the lung.