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

What's new in ras genes? Physiological role of ras genes in signal transduction and significance of ras gene activation in tumorigenesis

Ras gene mutations have been found with variable prevalence in different tumor types. While during the past decade a lot of information has been accumulated on the frequency of ras oncogene activation in tumors, the last two years brought considerable progress in elucidating molecular mechanisms of signal transduction for which cellular ras proteins are key elements. They transmit signals from upstream tyrosine kinases to downstream serine/threonine kinases ultimately leading to changes of gene expression cytoskeletal architecture, cell-to-cell interactions and metabolism. These signalling pathways are of interest for the physiological regulation of proliferation and differentiation in normal, as well as in cancer tissue. Mutational activation of cellular ras genes to transforming oncogenes is thought to promote cell growth even in the absence of extracellular stimuli, and may thereby contribute to the initiation and/or progression of tumors.

Ki-ras point mutations and proliferation activity in biliary tract carcinomas

The association between Ki-ras mutations and proliferation activity was investigated in a comprehensive series of biliary tract carcinomas (BTCs). We precisely microdissected samples of tissue from paraffin-embedded sections of 77 BTCs including 22 intrahepatic cholangiocarcinomas (ICCs), 36 extrahepatic cholangiocarcinomas (ECCs), and 19 gall bladder carcinomas (GBCs). Ki-ras mutations at exons 1 and 2 were determined by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method and confirmed by direct sequencing. Proliferation activity was immunohistochemically assessed to generate proliferating cell nuclear antigen labelling indices (PCNA LIs). Ki-ras mutations were detected in 10 of 22 ICCs (45%), 24 of 36 ECCs (67%), and in 16 of 19 GBCs (84%). The frequency of Ki-ras mutations in peripheral type ICCs was 33% (4 of 12) and that in the hilar type ICCs was 60% (6 of 10). In ECCs the highest value of 82% (9 of 11) was found for carcinomas located in the lower part of the biliary tree. Mean PCNA LI in mutation-positive BTCs was significantly elevated compared with the mutation-negative value. These results indicate frequent involvement of Ki-ras mutations in BTCs, especially in GBCs and in distal ECCs, and that carcinomas harbouring a mutation feature high cell proliferation activity.

Laboratory probing of oncogenes from human liquid and solid specimens as markers of exposure to toxicants

Recent discoveries regarding the mechanistic role of oncogenes and tumor suppressor genes in cancer development have opened a new era of molecular diagnosis. It has been observed repeatedly that genetic lesions serve as tumor markers in a broad variety of human cancers. The ras gene family, consisting of three related genes, H-ras, K-ras, and N-ras, acquires transforming activity through amplification or mutation in many tissues. If not all, then most types of human malignancies have been found to contain an altered ras gene. Because the ras oncogenes actively participate in both early and intermediate stages of cancer, several highly specific and sensitive approaches have been introduced to detect these genetic alterations as biomarkers of exposure to carcinogens. There is also mounting evidence that implicate chemical-specific alterations of the p53 tumor suppressor gene detected in most human tumors. Therefore, it seems a reliable laboratory approach to identify both altered p53 and ras genes as biomarkers of human chronic or intermittent exposure to toxicants in a variety of occupational settings.

Detection of rare circulating human colon tumor cells in a nude mouse xenograft model

A highly sensitive allele specific polymerase chain reaction was developed and applied to the detection of K-ras mutation in human colon tumor cells both in the blood and in tissues. An experimental model of human colon carcinoma cells, carrying a GAT mutation in the 12th codon of the K-ras gene, and grafted into nude mice has been selected for evaluating the occurrence of cells in the course of disseminating into the host. We have found tumor cells circulating in the blood starting 37 days following subcutaneous primary implantation. Occasional micrometastatic deposits could be detected in lymph node draining the xenograft, but no tumor cells were found in lungs and mediastinum. In this experimental model, our results indicate that the mere presence of tumor cells in the blood does not imply the full accomplishment of the multi-step metastatic process.

Maintenance of growth factor signaling through Ras in human colon carcinoma cells containing K-ras mutations

Fifty percent of human colon carcinomas contain activating mutations in the K-ras gene. However, whether these alterations in K-ras affect the function of Ras proteins in growth factor (GF) signal transduction is now known. Here we have characterized a previously defined human colon carcinoma cell model system for K-ras gene mutations and for altered levels of Ras protein expression and have examined whether these alterations affect Ras function in GF signal transduction. Sequence analysis of PCR-amplified K-ras gene fragments indicated that among the more aggressive cell lines, four had a normal K-ras sequence, whereas 3 others (isolated from the same human tumor) contained a mutation at codon 13. In contrast, all 7 of the less aggressive cell lines contained a mutation at either codon 12 or 13. In addition to the presence of a K-ras mutation, one cell line expressed higher levels of the K-Ras protein and displayed elevated Ras-GTP loading (in the absence of GF addition) compared with the other cell lines examined. Despite these alterations, the mitogenic GF combination epidermal growth factor + insulin + transferrin resulted in an activation of Ras and extracellular signal-regulated kinase 2. Collectively, our results indicate that the malignant phenotype of the cell lines was not correlated with the presence of K-ras mutations or with higher levels of Ras protein expression. Furthermore, K-ras mutations, high levels of K-Ras protein expression, and elevated Ras-GTP loading, as they occur naturally in human colon carcinomas, do not abolish the function of Ras in GF signaling.

K-ras mutations and HLA-DR expression in large bowel adenomas

A total of 72 sporadic colorectal adenomas in 56 patients were studied for the presence of point mutations in codons 12 and 13 of the K-ras gene and for HLA-DR antigen expression related to clinicopathological variables. Forty K-ras mutations in 39 adenomas were found (54%): 31 (77%) in codon 12 and nine (23%) in codon 13. There was a strong relationship between the incidence of K-ras mutations and adenoma type, degree of dysplasia and sex. The highest frequency of K-ras mutations was seen in large adenomas of the villous type with high-grade dysplasia. Fourteen out of 15 adenomas obtained from 14 women above 65 years of age carried mutations. HLA-DR positivity was found in 38% of the adenomas, large tumours and those with high-grade dysplasia having the strongest staining. Coexpression of K-ras mutations and HLA-DR was found significantly more frequently in large and highly dysplastic adenomas, although two-way analysis of variance showing size and grade of dysplasia to be the most important variable. None of the adenomas with low-grade dysplasia showed both K-ras mutation and HLA-DR positivity (P = 0.004). K-ras mutation is recognised as an early event in colorectal carcinogenesis. The mutation might give rise to peptides that may be presented on the tumour cell surface by class II molecules, and thereby induce immune responses against neoplastic cells.

A detailed analysis of K-ras point mutations in relation to tumor progression and survival in colorectal cancer patients

Point mutations in codon 12, 13, and 61 of the K-ras gene are an early event in tumorigenesis of colorectal cancer, but the impact of number, type, and position of such mutations on the progression of adenomas as well as the clinical behaviour of colorectal carcinomas is not clearly established. A series of 35 adenomas and 117 carcinomas at various stages was subjected to single-strand conformation polymorphism (SSCP) to analyse type, position and number of exon-I K-ras point mutations and to relate the results with patients survival. From our data we conclude that the number of K-ras point mutated tumors shows a trend to increase with tumor progression. The number of multiple K-ras point mutations, however, significantly increases with stage. Most mutations occur in the 1st or 2nd base of codon 12, whereas point mutations in the 3rd base are rare. In adenomas mutations, particularly G-T transversions, in the K-ras gene could indicate a propensity to malignant transformation. G-A transitions and G-C transversions of the second base are associated with metastasized tumors. Regarding survival, patients with K-ras point mutated tumors did worse than their non-mutated counterparts. G-A transitions in the 1st and 2nd base and G-C transversions in the 2nd base were associated with a poor prognosis as compared with G-T transversions in both the 1st and 2nd base. Patient survival therefore is related to the occurrence and type, but not the location, of K-ras point mutations.

Detection of ras oncogene point mutations and simultaneous proliferative fraction estimation in gallbladder cancer

Gallbladder cancer is notorious for its poor clinical evolution; so, a study of parameters with any prognostic potential is of particular interest. In this study, we investigated 23 adenocarcinomas regarding both the presence of point mutations in the ras gene family and the quantitative expression of Proliferating Cell Nuclear Antigen (PCNA). We respectively used molecular biology techniques and immunohistochemistry. Our results were related to several clinicopathologic determinators as well as to patients' survival. Mutations in codon 12 of the K-ras gene were detected in four gallbladder neoplasms (17%). This specific type of mutation is likely to be partially involved in this organ's tumourigenesis, particularly since no H-ras codon 12 or K-ras codon 13 (aspartic acid) mutations were detected in any of our specimens. PCNA immunoreactivity was generally limited in all tumours studied except for those morphologically characterized as being particularly aggressive. Notably, the four tumours in which K-ras mutation was detected, demonstrated relatively high PCNA positive immunoexpression in their malignant cells. This finding reinforces a possible correlation between the presence of ras mutations and increased cell growth. Staging was the only factor which was statistically associated with survival (p < 0.01). Therefore, the poor evolution of this cancer is probably due to late diagnosis and not related to a model of increased biologic aggressiveness.

APC, K-ras codon 12 mutations and p53 gene expression in carcinoma and adenoma of the gall-bladder suggest two genetic pathways in gall-bladder carcinogenesis

Current histopathological evidence suggests that gall-bladder cancer has two main morphological pathways for its development: de novo (ab initio) origin and adenoma-carcinoma sequence. In order to investigate the genetic difference between them, APC mutations were examined by RNase protection analysis, K-ras mutations by nested polymerase chain reaction-restriction fragment length polymorphism analysis, and p53 gene overexpression by immunohisto-chemical analysis in both tumors and benign lesions of the gall-bladder. Overexpression of the p53 gene was detected in 105 of 164 (64%) de novo carcinomas regardless of size and depth of invasion, but not in 16 tumors of carcinoma-in-pyloric-gland-type adenoma, or in 51 adenomas (47 pyloric gland-type and 4 intestinal-type). K-ras codon 12 mutation was detected in 4 of 40 (10%) de novo carcinomas, all four being associated with p53 gene overexpression, but not in 12 tumors of carcinoma in adenoma or 16 adenomas (14 pyloric gland-type and 2 intestinal-type). APC mutation was not found in 16 de novo carcinomas or the one pyloric gland-type adenoma examined. These results suggest that there are two distinct genetic pathways in gall-bladder carcinogenesis; that is, de novo carcinoma develops from a predominant p53 alteration with low K-ras mutation, and carcinoma-in-pyloric-gland-type adenoma develops from p53-, K-ras-, and APC-gene-unrelated, as yet unknown, alteration.

K-ras point mutations in cancerous and noncancerous biliary epithelium in patients with pancreaticobiliary maljunction

BACKGROUND

Pancreaticobiliary maljunction (PBM), an anomalous union of the pancreatic duct with the common bile duct, has frequently been shown to be associated with biliary carcinoma. However, the mechanism of carcinogenesis is unknown.

METHODS

Mutations of the K-ras oncogene were examined in cancerous and noncancerous biliary tract epithelium of 20 patients with PBM by an extraction of DNA from surgically resected histologic specimens. DNA was analyzed by a polymerase chain reaction single strand conformation polymorphism (PCR-SSCP) method and direct sequencing.

RESULTS

An abnormally mobilized DNA band was detected not only in cancerous epithelium but also in hyperplastic, metaplastic, and inflammatory epithelium of the gallbladder and/or common bile duct in patients with PBM. Among the biliary epithelium of patients with PBM, point mutation of K-ras oncogenes were detected in 4 of 5 (80%) cancerous epithelium, 7 of 12 (58%) hyperplastic and metaplastic epithelium, and 8 of 18 (44%) inflammatory epithelium, whereas no point mutation of the K-ras oncogene was detected in the gallbladder epithelium in 3 control patients without PBM. Direct sequence analysis of the K-ras oncogene revealed the mutation at codon 12 substituting the wild-type glycine (GGT) for aspartic acid (GAT) in all cancerous lesions of patients with PBM. Simultaneous two-point mutations from the wild-type glycine (GGC) to arginine (CGC) at codon 13 associated with the mutation at codon 12 were also found in one case of gallbladder carcinoma and one case of bile duct carcinoma.

CONCLUSIONS

K-ras gene mutation is involved in the carcinogenesis of biliary tract epithelium in patients with PBM, and appears to be a high risk factor for carcinogenesis of the biliary tract.

Detection of DCC and Ki-ras gene alterations in colorectal carcinoma tissue as prognostic markers for liver metastatic recurrence

BACKGROUND

The mortality of patients with colorectal carcinoma depends mainly upon subsequent liver metastasis even after curative operation. However, it is very difficult to predict the incidence of liver metastasis by analyzing conventional tumor markers or pathologic findings. In the current study, the authors examined the genetic alterations of p53/DCC loci and Ki-ras in colorectal carcinoma in relation to liver metastasis, and investigated whether these gene alterations could be prognostic markers for liver metastasis.

METHODS

Primary tumor tissue samples were collected at surgery from 30 patients with no liver metastasis and 24 patients with liver metastasis. Among the 30 patients with no liver metastasis at surgery, 9 developed liver metastasis after surgery. After the extraction of DNA, we investigated the loss of heterozygosity at p53/DCC loci and mutations of Ki-ras codon 12 in the colorectal carcinoma tissue from these patients.

RESULTS

The incidence of allelic loss of the DCC locus was significantly greater for patients with liver metastasis that for patients who had no liver metastasis for more than 2 years (19/20:95% vs 2/5:40%, P < 0.05). However, mutations of Ki-ras codon 12 were significantly less in patients with liver metastasis than in patients with no liver metastasis for more than 2 years (6/33:18% vs 6/11:55%, P < 0.05).

CONCLUSION

The current study indicated that detection of allelic loss of DCC and absence of Ki-ras codon 12 mutations are associated with the metastatic potential of colorectal carcinoma in the liver. These results suggested that these gene alterations might be reliable biologic markers for assessing the potential of liver metastasis after colorectal resection.

C-KI-RAS activation and the biological behaviour of proximal and distal colonic adenocarcinomas

One hundred and forty colonic adenocarcinomas originating on the left side of the colorectum and 70 colorectal carcinomas originating on right side of the colorectum were examined for activating mutations of codons 12 and 13 of the C-KI-RAS proto-oncogene. Rates of mutation were significantly different (right colon 43%, 30/70 versus left colon 23%, 32/140; P = 0.0025). Adenocarcinomas from the left side of the colorectum showed a significant association between C-KI-RAS activation and tumour progression, including the presence of distant organ metastasis at the time of surgery (P = 0.0039), and during patient follow-up (P = 0.00027), whereas those from the right of the colorectum did not (P = 0.4 and P = 0.5, respectively). Mutation of the C-KI-RAS proto-oncogene was found to be associated with a significantly poorer patient prognosis on the left of the colorectum (P = 0.0001 by log rank analysis of Kaplan-Meier plots) but not on the right (P = 0.7). These results demonstrate that, not only is the timing and frequency of C-KI-RAS activation different between carcinomas originating on the left or right of the colorectum, but also that the biological consequences of such mutations may differ.

Ras oncogene mutations in thyroid tumors: polymerase chain reaction-restriction-fragment-length polymorphism analysis from paraffin-embedded tissues

Ras mutations have been found in thyroid lesions. Different studies have shown different frequencies of mutations among benign and malignant lesions. The presence of point mutations in codons 12 and 13 of the c-K-ras, c-H-ras, and N-ras genes was studied in 58 thyroid lesions (10 nodular goiters, 10 follicular adenomas, and 15 papillary, 10 follicular, and 13 anaplastic carcinomas). DNA was extracted from formalin-fixed paraffin-embedded tissue, and target sequences were amplified in vitro by the polymerase chain reaction. Mutations were detected by the presence of restriction-fragment-length polymorphisms either occurring naturally or introduced artificially by the use of mutant primers. No characterization of the mutations was performed. Results were correlated with clinicopathologic features and patient follow-up. One goiter showed a mutation at codon 13, c-K-ras. All follicular adenomas, including three hyalinizing trabecular adenomas, were negative. Four papillary carcinomas presented mutations (one at codon 13, c-K-ras; three at codon 12, N-ras). Two follicular carcinomas showed mutations at codon 12, N-ras. Five anaplastic carcinomas showed mutations (two at codon 12 and two at codon 13, c-K-ras; one at codon 12, N-ras). In summary, the results confirm that ras oncogenes play a role in thyroid tumorigenesis, probably at an early step. Ras mutations appear not to be related to prognosis.

Synergy between Apc min and an activated ras mutation is sufficient to induce colon carcinomas

Colon carcinomas appear to arise from the cumulative effect of mutations to several genes (APC, DCC, p53, ras, hMLH1, and hMSH2). By using novel colonic epithelial cell lines derived from the Immorto mouse, named the YAMC (young adult mouse colon) cell line, and an Immorto-Min mouse hybrid, named the IMCE (Immorto-Min colonic epithelial) cell line, carrying the Apc min mutation, we investigated the effect of an activated v-Ha-ras gene on tumor progression. The YAMC and IMCE cell lines are normal colonic epithelial cell lines which are conditionally immortalized by virtue of expression of a temperature-sensitive simian virus 40 (SV40) large T antigen. Under conditions which permit expression of a functional SV40 large T antigen (33 degrees C plus gamma interferon), neither the YAMC nor the IMCE cell line grows in soft agar or is tumorigenic in nude mice. In vitro, when the SV40 large T antigen is inactivated (39 degrees C without gamma interferon), the cells stop proliferating and die. By infecting the YAMC and IMCE cell lines with a replication-defective psi2-v-Ha-ras virus, we derived cell lines which overexpress the v-Ha-ras gene (YAMC-Ras and IMCE-Ras). In contrast to the parental cell lines, under conditions in which the SV40 large T antigen is inactive, both the YAMC-Ras and IMCE-Ras cell lines continue to proliferate. Initally YAMC-Ras cells do not form tumors; however, tumors are visible after 90 days of incubation. IMCE-Ras cells form colonies in soft agar under both permissive and nonpermissive culture conditions. Furthermore, IMCE-Ras cells form tumors in nude mice within 3 weeks. The phenotype of the IMCE-Ras cell line thus clearly demonstrates that a defective Apc allele and an activated ras gene are sufficient to transform normal colonic epithelial cells and render them tumorigenic.

G --> A mutation of ras genes and infrequent p53 gene mutation in rat transplantable thyroid carcinoma lines from tumors induced in vivo by N-bis(2-hydroxypropyl)nitrosamine

In a comparative study, we have investigated mutational activation of three kinds of ras genes and the p53 gene (exons 5-8) in 19 rat transplantable thyroid carcinoma lines derived from in vivo tumors induced by DHPN. Mutations were identified using single-strand conformation polymorphism and DNA sequencing analysis, and activated ras oncogenes were detected in 6 lines (31%). These all had mutations in Ki-ras codons at 12 or 63, and one of them also possessed a Ha-ras mutation at codon 12 as a double mutation. Three mutations of Ki-ras at codon 12 involved the second nucleotide and two the first position, the other being found at the first nucleotide in codon 63. Base alterations of p53 gene were found in two lines. One had an insertion of 1 base (thymine) between codon 206 and codon 207. Historically, it was diagnosed as a poorly differentiated papillary carcinoma (scirrhous pattern). In the another case, there was no amino acid change although one base substitution occurred at codon 283 (GAG --> GAA) of exon 8. These results indicate that, in the ras family, DHPN induces Ki-ras gene activation preferentially and that p53 mutation may be infrequent in thyroid carcinogenesis in rats, our data thus corresponding well with the previous reports that an inactivated p53 gene only plays a major role in human undifferentiated thyroid carcinomas.

Dietary fiber and the chemopreventive modelation of colon carcinogenesis

Comparative international epidemiological data indicate that the difference between the highest and lowest colon cancer incidence is approximately 10-fold. This suggests that the dominant causes of colon cancer are environmental rather than genetic in origin, with the dominant environmental cause being the typical diet of Western industrialized countries. Many epidemiological and experimental studies have suggested an important role for dietary fiber in the prevention of colon cancer. Using the Fischer-344 rat as the experimental model, data clearly demonstrate a strong protective effect of a diet that is low in fat, high in fiber and high in calcium (low-risk diet). Such a diet prevents the development of both preneoplastic aberrant crypt foci (ACF) and colon tumors. Recent experiments have also demonstrated a direct relationship between a ras point mutation in ACF at different stages of rat colon carcinogenesis, and a ras point mutation that is subsequently present in colon tumors. Using wheat bran as the model dietary fiber source, its effects were compared to the effects of psyllium, phytic acid, vitamin E, beta-carotene, folic acid, alone or in combination, for their ability to prevent colon cancer in rats on high-risk Western-style diets. Our studies clearly demonstrated the ability of wheat bran to reduce ACF and colon tumors in rats that consumed high-fat, Western-style diets. Although phytic acid, which is a constituent of wheat bran, alone demonstrated strong cancer-preventive potential, our experiments provided evidence for the cancer-preventive effect of the crude fiber fraction that is independent of the effect of phytic acid. The synergistic combination of wheat bran with the soluble fiber psyllium led to enhanced protection; while the combination of wheat bran with beta-carotene showed only an additive effect. Beta-carotene appeared to show higher protection than wheat bran at an intake level that is nutritionally relevant to humans, suggesting the possibility of using beta-carotene to enhance the effects of dietary fiber in high-risk Western populations. Using ACF as an intermediate endpoint, it was also shown that vitamin E and beta-carotene appear to inhibit progression of ACF to colon cancer, while wheat bran and folic acid appeared to have weak cancer-preventive potential at this late stage of carcinogenesis. In conclusion, wheat bran alone, or in combination with psyllium, appears to have greater potential to inhibit earlier phases of carcinogenesis, while beta-carotene and vitamin E may also inhibit later stages of carcinogenesis. Despite considerable epidemiological and experimental evidence that increasing the fiber and lowering the fat content of the Western diet could substantially reduce the risk of cancer and heart disease, the real challenge is to find effective ways to educate and motivate people to overcome their intrinsic cultural resistance to such changes in their eating habits.

Regional distribution of carcinogen-induced colonic neoplasia in the rat

Carcinogen induction of neoplasms in rodent colon has been used as a model for human colon cancer development and for evaluating chemopreventive regimens. We studied the regional distribution of small and large intestinal tumors in 229 rats given azoxymethane (AOM) once weekly for two weeks (15 mg/kg sc). The AOM regimen induced 63% more tumors in distal (DC) than in proximal colon (PC), although tumor volume was greater in PC. A high-fat (23% corn oil) diet increased tumors in PC and DC (p < 0.01). Caloric restriction of 10-30% of the ad libitum diet progressively reduced DC tumor formation but did not alter PC tumors. Tumor volume was unaffected by either regimen. Small intestinal tumors were concentrated in the proximal 15 cm of the intestine and were unaffected by dietary manipulation. This AOM model of colon tumor formation approximates human colon cancer distribution and is an appropriate model for rodent chemopreventive studies.

Is mucinous carcinoma of the colorectum a distinct genetic entity?

Mucinous carcinomas are defined on the basis of the amount of the mucus component in the tumour mass. Apart from this quantitative criterion, a number of clinicopathological parameters (such as localisation, prevalence in different countries and age groups, association with HNPCC and inflammatory processes) and genetic alterations (e.g. frequency of mutation in Ki-ras and p53 genes, level of MUC2 expression) differentiate these tumours from the non-mucinous ones. Since a different set of genetic lesions implies different inducing agents, these observations suggest that there may be a 'mucinous pathway of carcinogenesis'. Further identification of genetic changes characteristic of the mucinous phenotype will help to understand the aetiology of these tumours and possibly establish markers for detection of the high-risk group.

Ki-ras mutations and p53 protein expressions in intrahepatic cholangiocarcinomas: relation to gross tumor morphology

BACKGROUND & AIMS

We previously reported that intrahepatic cholangiocarcinomas (ICCs) can be divided into three categories according to their gross appearance with possible links to biological behavior. Ki-ras and p53 gene alterations are thought to be involved in early and late phases of carcinogenesis, respectively. This study was performed to investigate the relationship between the gross appearance and genetic alterations of ICC.

METHODS

We examined 21 patients with ICC. Ki-ras point mutations were assessed by polymerase chain reaction/single-strand conformation polymorphism methods followed by direct DNA sequencing. Expressions of p53 protein were immunohistochemically assessed.

RESULTS

Ki-ras point mutations were found in 10 patients (48%), and expressions of p53 protein were detected in 4 (19%). Applying the gross classification that we previously proposed, Ki-ras mutations were prominent in the periductal extension type (4 of 6; 67%) and the spicula-forming type (6 of 10; 60%). On the other hand, none of the five mass-forming-type tumors harbored Ki-ras mutations. Expressions of p53 protein did not show any clear association with gross appearance.

CONCLUSIONS

Ki-ras gene alterations may be involved in the cholangiocarcinogenesis of periductal extension and spicula-forming but not mass-forming types, suggesting that the underlying processes of development are different.

Both v-Ha-Ras and v-Raf stimulate expression of the vascular endothelial growth factor in NIH 3T3 cells

Stimulation of NIH 3T3 cells with platelet-derived growth factor (PDGF)-BB and 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances vascular endothelial growth factor (VEGF) gene expression. To address the question of whether Ras and Raf are involved in the induction of VEGF gene expression by PDGF and TPA, we examined the effects of both factors on NIH 3T3 cells stably transfected with v-Ha-ras or v-raf. In serum-starved NIH 3T3 cells, only low levels of mRNA expression can be detected, whereas both ras and raf transformed cell lines express enhanced levels of a 4.3-kilobase VEGF transcript. Stimulation with PDGF or TPA resulted in increased VEGF mRNA in all cell lines, with highest levels found in the transformed cells. Immunofluorescence studies confirmed that the elevated VEGF mRNA expression correlated with enhanced protein levels. Positive immunofluorescence signals could be detected in v-Ha-ras or v-raf transformed cell lines but not in unstimulated NIH 3T3 cells. VEGF from conditioned medium of v-raf transformed NIH 3T3 cells was partially purified by chromatography on heparin-Sepharose. Biological activity of this VEGF protein was demonstrated by competition with binding of recombinant 125I-VEGF165 to human umbilical vein endothelial cells and by its ability to stimulate proliferation of these cells.

Ultraviolet-B-light-induced mutagenesis of C-H-ras codons 11 and 12 in human skin fibroblasts

Mutations in the ras oncogene are detected with a high frequency in non-melanoma skin cancer. Approximately half of the squamous-cell carcinomas (SCC) and one third of the basal-cell carcinomas (BCC) carry mutations at the second position of Ha-ras codon 12 (GGC to GTC), whereas mutations in Ki-ras codon 12 occur less frequently. Since the mutations in the Ha-ras and Ki-ras oncogenes are located opposite potential pyrimidine dimer sites (C-C), it is likely that the mutations are induced by ultraviolet radiation present in sunlight. We studied the capacity of ultraviolet B (UVB) light to induce base-pair changes in Ha-ras codons 11 and 12 in human skin fibroblasts. UVB induced mostly C to T and G to A transitions and C to A and G to T transversions. The base-pair change with the highest relative abundance was C to T in the middle position of codon 11 followed by (in diminishing relative abundance) C to A in the middle position of codon 11, G to A and G to T in the middle position of codon 12. The C to T and G to A transitions are compatible with pyrimidine photodimers as pre-mutagenic lesions, whereas the C to A and G to T transversions could be generated due to the formation of 8-hydroxyguanine, which is the major oxidation product of guanine. The relative abundance of mutations induced by UVB in Ha-ras codons 11 and 12 does not correlate with mutations observed in the DNA from non-melanoma skin cancer, where the G to T transversion in the middle position of codon 12 is selected.

Absence of p53 gene mutations in rat colon carcinomas induced by azoxymethane

The K-ras and p53 genes are two of the most frequently mutated genes found in the human colonic tumors. Since azoxymethane (AOM) induced rat colonic neoplasms are similar to human colonic tumors in their histological features and proliferation characteristics, the rat has been used as an experimental model to study the pathogenesis of colon cancer in humans. Although the presence of K-ras point mutations has been reported in AOM induced rat colonic tumors, there are no reports describing the frequency for mutation of the p53 gene in these tumors. In this study, colon adenocarcinomas induced in rats by AOM were examined for the presence of point mutations in exons 5-8 of the p53 gene, using a combination of single strand conformation (SSCP) analysis, immunohistochemistry and direct DNA sequencing. SSCP analysis showed no differences in banding patterns between the normal mucosa and any of the 20 adenocarcinomas analyzed. Nuclear p53 immunoreactivity was absent in all tumors examined. Since p53 point mutations predominate in malignant colonic tumors, five adenocarcinomas with the greatest local invasiveness were analyzed by direct DNA sequencing of exons 5-8 of the p53 gene. Direct DNA sequencing did not reveal mutations in any of the adenocarcinomas analyzed, within the coding region of p53 gene that were sequenced. The results from the present study indicate that point mutations in the p53 gene, at least in the coding region (exons 5-8) are not involved in the development of colon cancer induced by AOM in the rat.

Microallelotyping defines the sequence and tempo of allelic losses at tumour suppressor gene loci during colorectal cancer progression

Microallelotyping of many regions from individual colorectal tumours was used to determine the sequence and tempo of allelic loss on 5q, 17p and 18q during neoplastic progression. No allelic losses were found in normal tissues surrounding colorectal neoplasms, but losses occurred abruptly on 5q at the transition from normal colonic epithelium to the benign adenoma, and on 17p at the transition from adenoma to carcinoma, indicating an essential role for these losses in tumour progression. Allelic losses were uniform throughout extensively microdissected benign adenomas and carcinomas. However, substantial allelic heterogeneity was found in high-grade dysplasia, the transition lesion between adenoma and carcinoma. Thus, allelic losses on 5q and 17p are associated with abrupt waves of clonal neoplastic expansion, and high-grade dysplasia is characterized by a high degree of allelic heterogeneity.

Review article: The role of oncogenes, tumour suppressor genes and growth factors in oral squamous cell carcinoma: a case of apoptosis versus proliferation

Mutation, deactivation and disregulated expression of oncogenes and tumour-suppressor genes may be involved in the pathogenesis of oral squamous cell carcinoma (SCC). Deactivation of the p53 tumour-suppressor gene allows cell proliferation and blocks apoptosis of malignant oral keratinocytes. Mutation in the ras oncogene results in persistent mitogenic signalling. Upregulatioed c-Myc expression, in the presence of growth factors, provides an additional proliferative signal. Loss of retinoblastoma tumour-suppressor gene (Rb) function may contribute to oral keratinocyte hyperproliferation and recent evidence suggests that simultaneous deactivation of both p53 and Rb is required for tumourigenesis. Enhanced Bcl-2 and reduced Fas expression inhibit tumour cell apoptosis and may convey resistance to cytotoxic drugs and T cell-mediated cytotoxicity, respectively. Exogenous mutagens such as tobacco, alcohol and viral oncogenes may cause altered expression of oncogenes and tumour-suppressor genes in some cases of oral SCC. The impact of these mechanisms on future therapies for oral SCC is highlighted.

Detection of p21ras mutations in colorectal adenomas and carcinomas by enzyme-linked immunosorbent assay

BACKGROUND

Point mutations of the ras protooncogene, primarily within codons 12 and 13, are commonly identified in colorectal carcinomas and large adenomas. Despite data suggesting that ras genotyping may have clinical significance with respect to colorectal cancer screening and prognosis, more widespread use has been limited because of the lack of a suitable assay system. The principal objective of this study was to assess the feasibility and validity of a qualitative enzyme-linked immunosorbent assay (ELISA) for detecting the four most common ras mutations in human colorectal tumors at the protein (p21ras) level.

METHODS

Tissue homogenates (11-121 micrograms) from endoscopically or surgically resected colorectal adenomas, carcinomas, and normal mucosae were evaluated by a commercially available ELISA (Oncogene Science, Inc. Cambridge, MA) for mutant p21ras containing arginine position 12 (arg12), valine position 12 (val12), aspartate position 12 (asp12), and aspartate position 13 (asp13) amino acid substitutions. Portions of the same tissue from an initial series of 27 specimens also were subjected to mutant-enriched polymerase chain reaction (PCR) and/or PCR amplification with subsequent DNA sequence analysis to validate the ELISA data.

RESULTS

Forty-seven adenomas, 9 carcinomas, and 14 normal mucosae were assayed. Mutations were identified in 16 (34%) of the adenomas (7-asp12, 7-val12, 2-asp13), 3 (33%) of the carcinomas (1-asp12, 1-arg12, 1-asp13), and none of the normal mucosae by ELISA: Polymerase Chain Reaction and DNA sequencing analyses demonstrated identical results for 21 of the 23 (91%) and 14 of 16 (88%) homogenates tested, respectively. The ELISA demonstrated an overall sensitivity of 80-86%, specificity of 90-92%, positive predictive value of 86-100%, and negative predictive value of 86-91%.

CONCLUSIONS

The ELISA is a feasible and valid approach for identifying p21ras mutations in human colorectal adenomas and carcinomas.

Increased mRNA expression of the receptor-like protein tyrosine phosphatase alpha in late stage colon carcinomas

The protein tyrosine phosphatase alpha (PTP alpha) mRNA level in paired samples of late stage (Dukes' D) colorectal tumors and adjacent normal colon mucosa was quantified by RNase protection assays. After normalization against 18S RNA or beta-actin mRNA level, a 2-10-fold increase in PTP alpha mRNA was detected in 10 of 14 tumors (approximately 70%) compared to mucosa. In situ hybridization of digoxigenin-labelled antisense PTP alpha RNA to tumor and mucosa sections produced a signal only in neoplastic cells of the tumor sample, consistent with the high increase in PTP alpha mRNA detected by RNase protection assays of some of the tumors. This is the first report suggesting an association of a protein tyrosine phosphatase with colorectal carcinoma. PTP alpha is a receptor-like PTP thought to be involved in regulating cell proliferation. Its oncogenic properties when overexpressed in cultured fibroblasts suggest that PTP alpha overexpression could contribute to the tumorigenic process in colon carcinoma.

N-ras mutation in 7,12-dimethylbenz[a]anthracene (DMBA)-induced erythroleukemia in Long-Evans rats

Intravenous injections of 7,12-dimethylbenz[a]anthracene (DMBA) induce erythroblastic leukemia (erythroleukemia) with No.2 trisomy in Long-Evans rats. Activation of some oncogenes such as abl and Ha-ras has been reported to occur in relation to the secondary chromosomal translocations. In the present studies, a consistent type of mutation, A to T transversion in codon 61 of N-ras gene, was found in all of 6 cultured leukemia cell lines and 5 primary leukemias induced by DMBA. The N-ras mutation was also found in bone marrow cells of 2 out of 8 preleukemias. On the contrary, no mutation was observed in Ha- and Ki-ras genes in all leukemias and preleukemias. The consistent occurrence of above N-ras mutation in leukemias indicates that it plays an important role in DMBA-leukemogenesis.

Ras farnesyltransferase inhibitors suppress the phenotype resulting from an activated ras mutation in Caenorhabditis elegans

Attachment of Ras protein to the membrane, which requires farnesylation at its C terminus, is essential for its biological activity. A promising pharmacological approach of antagonizing oncogenic Ras activity is to develop inhibitors of farnesyltransferase. We use Caenorhabditis elegans vulval differentiation, which is controlled by a Ras-mediated signal transduction pathway, as a model system to test previously identified farnesyltransferase inhibitors. We show here that two farnesyltransferase inhibitors, manumycin and gliotoxin, suppress the Multivulva phenotype resulting from an activated let-60 ras mutation, but not the Multivulva phenotype resulting from mutations in the lin-1 gene or the lin-15 gene, which act downstream and upstream of let-60 ras, respectively, in the signaling pathway. These results are consistent with the idea that the suppression of the Multivulva phenotype of let-60 ras by the two inhibitors is specific for Ras protein and that the mutant Ras protein might be more sensitive than wild-type Ras to the farnesyltransferase inhibitors. This work suggests that C. elegans vulval development could be a simple and effective in vivo system for evaluation of farnesyltransferase inhibitors against Ras-activated tumors.

Evidence for ras gene mutation in 2-amino-3-methylimidazo[4,5-f]quinoline-induced colonic aberrant crypts in the rat

Aberrant crypt foci (ACF) are putative preneoplastic lesions that develop after treatment of animals with colon carcinogens, including cooked-meat heterocyclic amines such as 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Male F344 rats given IQ by gavage on alternating days for 2 wk (130 mg/kg body weight) and killed 12 wk after the final carcinogen dose had an average of 4.4 ACF/colon and an average of 3.2 crypts/focus. The DNA from these ACF was amplified by the polymerase chain reaction and analyzed by 3'-primer mismatch and direct sequencing methods for mutations in the Ki-ras proto-oncogene. Of the 37 IQ-induced ACF screened, three contained a GGT-->GAT mutation in codon 12 and one contained a GGC-->GCC mutation in codon 13. The approximately 11% frequency of mutation in IQ-induced ACF is within the range of previous ACF studies of azoxymethane, which reported a 7-37% incidence of Ki-ras mutation. These findings suggest that for both compounds, ras mutations occur during early stages of colorectal tumorigenesis. However, while ras mutations can be detected with increasing frequency in azoxymethane-induced adenomas and carcinomas, they are reportedly absent in IQ-induced colon tumors. Thus, for IQ and related compounds additional factors (possibly increased cell proliferation) may be important in the later stages of colorectal tumorigenesis.

Screening for colorectal cancer

In the past few years, knowledge of the clinical, biologic, and molecular genetic characteristics of colorectal cancer has greatly increased. Although the most cost-effective approach remains to be identified, screening for colorectal cancer can decrease mortality due to this disease by detecting cancers at earlier stages and allowing the removal of adenomas, thus preventing the subsequent development of cancer. Molecular studies that have helped define the genetic basis for this disease hold great promise for the development of better and more powerful methods to identify populations at risk. Individually, these technological, clinical, and basic-science advances are exciting; together, they promise to move us closer to the goal of substantially reducing mortality due to colorectal cancer.

The clinical and genetic manifestations of hereditary nonpolyposis colorectal carcinoma

BACKGROUND

Hereditary nonpolyposis colorectal cancer (HNPCC) is a syndrome that affects a significant percentage of the total cancer population but is not easily recognized because of a lack of a distinctive clinical marker such as multiple polyps.

DATA SOURCES

The present review discusses the clinical characteristics, pathology, genetics, management, and surveillance of HNPCC. The diagnosis of HNPCC is dependent upon family history. It is defined by the Amsterdam criteria consisting of: (1) 3 or more relatives with histologically verified colorectal carcinoma, 1 of whom is a first-degree relative of the other 2; (2) colorectal carcinoma involving at least two generations; and (3) one or more colorectal carcinoma cases diagnosed at less than 50 years of age.

CONCLUSIONS

The diagnosis of HNPCC requires the demonstration of vertical transmission of the syndrome in the family pedigree. Attention should be focused on reports of cancer of all anatomic sites and the determination of site, histology, and age at diagnosis.

Expression of growth factor receptor-encoded mRNA by colonic epithelial cells is altered in inflammatory bowel disease

A link between inflammation of the colon in inflammatory bowel disease (IBD) and the increased risk of colon cancer in ulcerative colitis (UC) may be provided by growth factor receptor genes. Their expression may be altered in response to growth factors present in the mucosa, and this, in turn, may induce further genetic changes, linked to carcinogenesis, in the cells of the colonic epithelium. To test this hypothesis, we assayed steady-state levels of eight growth factor receptor mRNAs in colonic epithelial cells of IBD patients and controls. Four of these genes (EGF-R, IGFI-R, CSF1-R, and PDGF-R-beta) were expressed in epithelial cells, whereas four (erbB-2, erbB-3, NGF-R, and met) were not. The level of the former in involved or uninvolved IBD was considerably lower than in normal epithelial cells from either sporadic colon cancer or diverticulitis patients. In contrast, expression was much higher in IBD patients with colon tumors than in active chronic IBD. The level of PDGF-R-beta mRNA was two- to fourfold higher in involved than in uninvolved areas of the colons of two UC patients, but not in one Crohn's disease patient. Message abundance of its ligand, PDGF-beta, however, was the same in paired UC samples. The pattern of expression of PDGF-beta and cripto was identical to that of EGF-R, whereas the level of mRNA of amphiregulin was the same in active chronic IBD and IBD patients with tumors. A fourth growth factor, Kfgf, was not expressed. Increased levels of PDGF-R-beta mRNA in involved UC relative to uninvolved UC may be related to the disease process in UC. Decreased expression of growth factor- and growth factor receptor-encoded mRNA in active chronic IBD may be related to the disease process, or it may be an effect of steroid therapy undergone by these patients. Enhanced expression of these genes in IBD patients with tumors compared to those without tumors suggests that this may be a marker for development of colon cancer in IBD.

K-ras gene mutation related to histological atypias in human colorectal adenomas

To investigate the relationship of oncogene analysis to morphology, we analyzed K-ras gene mutations by dot-blot hybridization with and without consideration of histological atypias in individual colorectal adenomas. Each of 54 colon polyps were divided into two parts after fixation. One part was used as a mass to assess point mutations; the remaining portion of each polyp was paraffin-embedded, stained with hematoxylin and eosin, and examined for point mutations related to histological atypias. In the first part of our study, K-ras gene mutations at codon 12 were detected in 13 cases (24%). In the second part of our study, 12 cases had distinctly different histological atypias. From each of these 12 cases, two areas, one with higher or one with lower grade atypia in the same polyp were excised to analyze for K-ras gene mutation. Two of these 12 cases (17%) had the mutation in different areas of the same tumor. These two cases contained the mutation only in the areas with higher grade atypia, and only one case added information regarding ras mutation upon microdissection when compared to the entire biopsy. These results suggest that oligonucleotide hybridization can identify the majority of cases containing ras mutations despite regional morphologic variation. Individual cases, however, may contain clonal subpopulations within adenomas with different ras sequences from other regions within the same adenoma.

Ras oncogene and p53 gene hotspot mutations in colorectal cancers

Ras oncogene and p53 gene mutations are frequently observed in colorectal cancers. The role of co-operation between these two genes in the tumorigenesis of colorectal cancer was evaluated. Point mutations in K-ras oncogene and hotspot codons of p53 gene of colorectal cancers were evaluated by naturally created or amplified created restriction site method. Nine of 42 cases (21.4%) of colorectal cancer showed K-ras oncogene mutations. Six of 42 cases (14.3%) of colorectal cancer showed p53 gene hotspot point mutations. The low frequency of p53 gene mutation in this series may be due to racial difference or different hotspot codons. When six cases with mutated p53 gene were examined, only one (16.7%) showed concurrent K-ras oncogene codon 12 and p53 gene codon 248 mutations. We concluded that the co-operation between ras oncogene and p53 gene hotspot point mutations in the tumorigenesis of colorectal cancer in Chinese was not common. Other factors such as adenomatous polyposis coli gene mutations, oncogene activation or tumour suppression gene inactivation may be involved.

Common occurrence of APC and K-ras gene mutations in the spectrum of colitis-associated neoplasias

BACKGROUND/AIMS

Chronic colitis is associated with an increased risk of colorectal neoplasia, creating a need for early diagnosis in this population. Little is yet known of the genetic changes of early lesions. Cases of colitis-associated neoplasia were analyzed for APC and K-ras mutations with special emphasis given to the spectrum of noninvasive lesions.

METHODS

Ten patients were studied. APC mutations were screened by an in vitro synthesized protein assay, and K-ras mutations were screened by a ligation assay.

RESULTS

APC mutations were found in 5 patients, including dysplasias. K-ras mutations were present in 5 patients and in all classes of lesions, including 5 of 14 lesions indefinite for dysplasia. In only 2 patients were no mutations found.

CONCLUSIONS

Mutations of APC and K-ras are common in colitis-associated neoplasia and can occur early in neoplastic progression. Serrated lesions and lesions indefinite for dysplasia may harbor genetic changes and thus are clonal, highlighting the importance of distinguishing them histologically. Assays for APC and K-ras mutations are promising as adjuncts to surveillance programs. Care will be needed in their application because the confident diagnosis of early lesions presumed to be of lesser clinical importance will raise new issues concerning prudent patient management.

The usefulness of severe combined immunodeficiency (SCID) mice to study human carcinogenesis

In the present study, we engrafted normal colonic epithelial and histologically diagnosed colonic adenomas from a familial adenomatous polyposis (FAP) patient into severe combined immunodeficient (SCID) mice and subsequently examined them histologically and molecular biologically. Successful engraftment and metastasis was observed. The facts that human normal colonic epithelium and adenomatous polyps can take in SCID mice indicates the possibility that this human SCID mouse system will be useful for investigating the dynamics of human carcinogenesis in various tissues.

Point mutations in the c-K-ras 2 gene in multiple colorectal carcinomas

The c-K-ras 2 gene mutations were examined in colorectal tumours from patients with synchronous or metachronous tumours in order to investigate tumorigenesis. Sixty-seven colorectal carcinomas from patients with a single lesion, 50 from patients with synchronous lesions, and 12 from patients with metachronous lesions were analysed for the presence of point mutations in codons 12 and 13 of c-K-ras proto-oncogene. In the patients with metachronous or synchronous lesions, the finding of the mutation in one tumour was not associated with a greater frequency of the mutation in other carcinomas from the same patient. In the patients with tumours that each contained the mutation, the mutations were not always the same. In tumours from the patients with original and synchronous lesions, the mutation frequency was significantly lower in advanced carcinomas invading through the entire muscularis propria (10.5%) than in early carcinomas confined to the mucosa (47.8%), and the mutation frequency in carcinomas invading through the entire muscularis propria was significantly lower in patients with synchronous lesions (10.5%) than in patients with a single lesion (37.7%). These results suggest that the tumorigenesis of colorectal carcinomas from patients with synchronous lesions is different from that in patients with a single lesion.

Tumour diagnosis by PCR-based detection of tumour cells

Tumour cells shed from solid primary tumours can be detected by the polymerase chain reaction (PCR) based on the selective amplification of mutated tumour genes or of genes expressed in a tissue specific manner. When tumour specific alterations are amplified, few tumour cells can be detected in excess of normal cells derived from the same tissue. Thus, malignant cells can be detected specifically in pancreatic juice, stool, urine, and sputum. Here we describe the adaptation of the mutant enriched PCR in conjunction with the introduction of artificial primer mediated restriction sites to the selective amplification of mutant K-ras genes in stool samples from patients with colorectal carcinomas. In reconstitution experiments, down to 10 colorectal carcinoma cells could be detected in 100 mg of stool. For the diagnosis of micrometastatic disease, a sensitive and specific technique was established based on the reverse transcription of mRNA specific for the carcinoembryonic antigen followed by the amplification of the cDNA (RT-PCR). Attempts to establish a specific RT-PCR for cytokeratin-18 failed because of the existence of at least one processed pseudogene.

Expression of matrix metalloproteinase matrilysin (MMP-7) was induced by activated Ki-ras via AP-1 activation in SW1417 colon cancer cells

The matrix metalloproteinase matrilysin (MMP-7) is a member of the matrix metalloproteinase gene family, which is believed to play an important role in tumor invasion and metastasis. We have previously found that matrilysin mRNA is specifically expressed in colorectal cancers and adenomas and that its message is localized in the tumor cells themselves. We examined the effects of activated Ki-ras oncogene on the expression of matrilysin in colon cancer cells. We showed that both mRNA and the enzymatic activity of matrilysin were induced by the introduction of activated Ki-ras into SW1417 colon cancer cells. To understand the mechanisms regulating this induction, we analyzed alterations of AP-1 activity induced by activated Ki-ras, using the chloramphenicol acetyltransferase assay. AP-1 activity in SW1417 cells expressing activated Ki-ras was higher than that in control cells. The gel-shift assay also showed higher levels of AP-1 binding protein in SW1417 cells expressing activated Ki-ras than those in control cells. Our results suggest that activated Ki-ras may play a role in inducing expression of matrilysin through an AP-1-dependent pathway in colon cancer cells.

Analysis of N-ras mutations in human cutaneous melanoma: tumor heterogeneity detected by polymerase chain reaction/single-stranded conformation polymorphism analysis

Determination of the activation state of oncogenes as well as tumor suppressor genes is a main subject of interest in the analysis of the mechanism of tumor initiation. In human melanoma, the c-myc and N-ras oncogenes have been found to be activated in approximately 50% and 15% of the analyzed material, respectively. These studies have mostly been done on fresh tumor material or cell lines. Only in a few cases has an attempt been made to look at tumor heterogeneity or clonality with respect to the activation of oncogenes. We have adjusted the polymerase chain reaction (PCR)/single-stranded conformation polymorphism analysis (SSCP) technique to screen paraffin-embedded melanoma material for the presence of N-ras mutations and found genetic defects at particular progression stages. In one melanoma of the skin, we were able to sublocalize an N-ras mutation in the intraepidermal tumor part, that was absent in the part deeply invading the dermal layer. We conclude that a thorough investigation of N-ras activation in human melanoma should include analysis of histologically different parts of the tumor.

Factors controlling growth, motility, and morphogenesis of normal and malignant epithelial cells

Factors that control epithelial growth, motility, and morphogenesis play important roles in malignancy and in normal development. Here we discuss the molecular nature and the function of two types of molecules that control the development and maintenance of epithelia: Components that regulate epithelial cell adhesion; and soluble factors and their receptors that regulate growth, motility, differentiation, and morphogenesis. In development, the establishment of epithelial cell characteristics and organization is crucially dependent on cell adhesion and the formation of functional adherens junctions. The integrity of adherens junctions is frequently disturbed late in tumor progression, and the resulting loss of epithelial characteristics correlates with the metastatic potential of carcinoma cells. Various soluble factors that induce epithelial growth, motility, or differentiation in cell culture, function via tyrosine kinase receptors. We concentrate here on receptors that are expressed exclusively or predominantly on epithelia, and on ligands that are derived from the mesenchyme. In development, these receptors and their ligands function in mesenchymal-epithelial interactions, which are known to govern growth, morphogenesis, and differentiation of epithelia. During tumor development, mutations or overexpression of the receptors are frequently observed; these alterations contribute to the development and progression of carcinomas.

Mutations of Ki-ras and p53 genes in colorectal cancer and their prognostic significance

The series of genetic changes leading to malignancy in colorectal cancer is well reported. This includes mutational activation of the proto-oncogene Ki-ras and mutation/deletion of the p53 tumour suppressor gene. The frequency of these mutations was investigated in a panel of 52 colorectal cancer patients using a combination of immunocytochemistry and non-radioactive, digoxigenin-labelled in situ hybridisation. Sixty two per cent (32 of 52) of the study population were positive for p53 overexpression and 36% (19 of 52) positive for Ki-ras mutation. Twenty seven per cent (14 of 52) of the patients expressed both mutations. Mutation of either the p53 or the Ki-ras gene did not correlate with Dukes's stage, tumour differentiation or 5 year survival rate of the patients. Most of the rectal carcinoma specimens (11 of 15) showed p53 over-expression but the significance of this was not supported statistically. Thus detection of molecular changes is becoming more amenable to incorporation into routine histological carcinoma assessment because of the advent of non-radioactive labelling in in situ hybridisation and antibodies suitable for paraffin wax embedded specimens. The significance of these mutations in disease prognosis, however, remains questionable.