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Query: UMLS:C0699790 (colon cancer)
 28,837 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although epidemiological and experimental studies have indicated a strong relationship between types and amount of dietary fat and colon tumorigenesis, the modulating effects of these nutritional factors at the molecular level have not been fully elucidated. Transforming proteins encoded by activated ras genes have been implicated in the etiology of many human malignancies, including colon cancer. It is now well established that the transforming ability of ras-p21 critically depends on its correct localization in plasma membrane. The posttranslational processing of the cytosolic precursor (pro-ras), as it is synthesized in the cytoplasm, and its proper anchorage to the cytoplasmic face of plasma membrane are determined by an important intermediate metabolite of dietary fat and an enzyme system that includes farnesyl protein transferase. To provide an understanding of the molecular basis of the relationship between the types and amount of dietary fat and the transforming function of ras, especially during the stages of promotion and progression of colon tumor development, we investigated the effect of various types and amount of dietary fat on the expression of ras-p21 during azoxymethane (AOM)-induced colon carcinogenesis. Male F344 rats were fed the semipurified American Institute of Nutrition-76A diet containing low-fat corn oil and were given s.c. injections of AOM dissolved in normal saline at a dose rate of 15 mg/kg body weight, once weekly, for 2 weeks. Control animals received s.c. injections of equal volumes of normal saline. Beginning 1 day after the second AOM or saline injection, groups of animals intended for the treatment with different types of high-fat dietary regimens were fed the semipurified American Institute of Nutrition-76A diets containing high levels of high-fat corn oil (HFCO) rich in omega-6 fatty acids or high levels of high-fat fish oil (HFFO) rich in omega-3 fatty acids; the remaining animals in experimental and control groups were continued on the low-fat corn oil diet until termination of the experiment. Groups of animals were sacrificed 1, 12, or 36 weeks after the last AOM or saline injection, and their colonic mucosa and grossly visible colon tumors from rats sacrificed 36 weeks after the last AOM injection were analyzed for the levels of expression of ras-p21. We found that AOM induced increasingly higher levels of ras-p21 expression with advancing stages of colon tumor development. The HFCO diet resulted in enhanced expression of AOM-induced ras-p21 as observed 36 weeks after the last AOM injection. In contrast, feeding the HFFO diet inhibited AOM-induced ras-p21 expression. These results correlate with increased incidence and multiplicity of grossly visible colon tumors in AOM-treated animals fed a HFCO diet versus decreased incidence and lower multiplicity of colon tumors in their counterparts on the HFFO diet. Further analysis of ras-p21 levels in cytosol and plasma membrane revealed that feeding a HFFO diet resulted in increasing accumulation of ras-p21 in cytoplasm with a concomitant decrease in membrane-bound ras-p21 levels as observed in animals sacrificed 12 and 36 weeks after the last AOM injection. Thus, the dietary HFCO may promote colon tumorigenesis by increasing ras-p21 expression, whereas HFFO appears to exert its antitumor activity by interfering with posttranslational modification and membrane localization of ras-p21.
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PMID:Dietary fat and colon cancer: modulating effect of types and amount of dietary fat on ras-p21 function during promotion and progression stages of colon cancer. 900 May 64

Significant alarm has existed among the general public in the past few years that eating red meat may cause human colon cancer. Iron in beef has been hypothesized as one of the factors in the etiology of this cancer. The present study was designed to test the hypothesis that dietary iron solely from beef would enhance colon tumorigenesis induced in rats. Tumors were induced in Sprague-Dawley rats with 1,2-dimethylhydrazine (20 mg/kg body weight for 10 weeks). Seventy male weanling rats were randomized to two dietary treatment groups with two iron sources (very lean beef vs. iron citrate) as the factor. The rats were allowed free access to the respective diet and deionized water for 27 weeks. At termination of the study, the rats were examined for location, size and type of colon or extracolonic lesions. No significant differences were found in total incidence and number of colon tumors between the beef (51.7%, 0.8 tumors/rat) and casein (62.1%, 0.9 tumors/rat) diets, although the serum iron levels of rats fed the beef diet were higher than for those fed the casein diet. The results demonstrate that, when lean beef is used as an iron source, the risk for colon carcinogenesis is not increased.
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PMID:Non-promoting effects of iron from beef in the rat colon carcinogenesis model. 902 73

Matrix metalloproteinases (MMPs) classically have been implicated in basement membrane destruction associated with late-stage tumor cell invasion and metastasis. However, recent studies have demonstrated that one MMP family member, matrilysin, is expressed in a high percentage of early-stage human colorectal tumors. We analyzed matrilysin expression in benign intestinal tumors from mice heterozygous for the ApcMin allele (Min/+) and found that the mRNA was induced in the majority (88%) of these adenomas. Protein was detected in the tumor cells, where, surprisingly, it was predominantly immunolocalized to the lumenal surface of dysplastic glands rather than the basement membrane or extracellular matrix. To address the role of matrilysin in Min intestinal tumorigenesis, we generated Min/+ mice deficient in this MMP by gene targeting and homologous recombination. The absence of matrilysin resulted in a reduction in mean tumor multiplicity in Min/+ animals of approximately 60% and a significant decrease in the average tumor diameter. Based on these findings, we conclude that matrilysin is a suppressor of the Min phenotype, possibly by functioning in a capacity independent of matrix degradation. These results argue for the use of MMP inhibitors in the treatment and prevention of early-stage colon cancer.
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PMID:Intestinal tumorigenesis is suppressed in mice lacking the metalloproteinase matrilysin. 903 65

Genetic alterations, such as mutation, methylation and aneuploidy, are thought to underlie the multistep genesis and progression of many human cancers. However, the genetic events occurring in prostatic oncogenesis are still relatively poorly understood. This is especially so in early-stage tumours, in which mutations of known oncogenes or tumour-suppressor genes appear to be quite infrequent. Allelic losses of chromosome arms 7q, 8p, 10, 16q and 18q suggest the involvement of novel suppressor loci on these chromosomes; allelic losses of chromosome arm 8p are especially frequent and may be detected even in early-stage tumours. We have used a positional approach to seek novel genetic targets in prostate cancer, including allelic-loss mapping of chromosome 8p and physical mapping of chromosome band 8p22 around the MSR gene. A homozygous somatic deletion in one prostatic nodal metastasis was mapped in this region and spanned 730-970 kb. This region was then examined in detail for expressed sequences. One novel gene, called N33, was found to be silenced by a methylation mechanism in most colon cancer cell lines and some primary colorectal tumours. Characterization of additional chromosome 8p22 candidates is in progress.
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PMID:Tumour-suppressor genes in prostatic oncogenesis: a positional approach. 908 70

Aberrant crypt foci (ACF) are microscopic lesions which can be detected, after methylene blue staining, in the overtly normal looking colonic mucosa of cancer patients. ACF have been postulated to be precursor lesions which develop into colorectal cancer. Mutations of K-ras and p53 are two important genetic events implicated in colon carcinogenesis. Mutations in K-ras are detectable at earlier stages, while mutations in p53 are detectable at later stages of colon carcinogenesis. Our objective was to compare the nature of genetic alterations in K-ras (codon 12 and 13) and in p53 (exon 4-9) between ACF and corresponding colonic tumors from cancer patients. ACF with > or =20 crypts/focus were harvested from overtly normal looking colonic mucosa of cancer patients at a distance of (approx.) 5 cm from the site of colonic tumors. The colonic tumors and ACF samples were compared for K-ras codon 12 and 13 base pair sequence, using DNA sequencing and for p53 (exon 5-9) allelic types, using PCR-SSCP and DNA sequencing. The results demonstrated a perfect correlation in terms of the type of K-ras allele (wild or mutated) between the ACF (> or =20 crypts/focus) and corresponding colonic tumors in 11/13 cancer patients. Analyses of p53 mutations demonstrated the presence of p53 mutations in colonic carcinomas from 10/13 patients. However, p53 mutations could be detected in an ACF from only 1/13 patient. The results provides further evidence to the role of ACF as precursor to colon cancer. The presence of an identical K-ras as well as p53 mutation in an ACF and the corresponding colonic carcinoma in a patient suggests the possibility of existence of ACF that may be at a more advanced stage in the sequence of colonic tumorigenesis than others. In conclusion, the results suggest that a subset of ACF with higher multiplicity might be considered more likely to progress to more advanced lesions and should be explored as markers of colon cancer risk.
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PMID:K-ras and p53 mutations in aberrant crypt foci and colonic tumors from colon cancer patients. 909 77

Cyclin D1 plays an important role in regulating the progression of cells through the G1 phase of the cell cycle. This gene is frequently overexpressed in human colon cancer. To address the role of cyclin D1 in growth control and tumorigenesis in this disease, we have overexpressed an antisense cyclin D1 cDNA construct in the human colon cancer cell line SW480E8, which expresses high levels of cyclin D1. The integration and expression of the antisense construct was verified by Southern and Northern blot analyses, respectively, and resulted in decreased expression of the cyclin D1 protein. This was associated with decreased levels of the Rb and p27Kip1 proteins. In addition, the hypophosphorylated form of Rb was increased in these cells. The SW480E8 antisense cyclin D1 cells displayed an increased doubling time, a decrease in saturation density, decreased plating efficiency and anchorage-independent growth, and a loss of tumorigenicity in nude mice. These findings provide direct evidence that increased expression of cyclin D1 in colon tumor cells contributes to their abnormal growth and tumorigenicity. The ability to revert the transformed phenotype of these cells with antisense cyclin D1 suggests that cyclin D1 or its associated cyclin-dependent kinase 4 may be useful targets in the therapy of colon cancer.
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PMID:Antisense to cyclin D1 inhibits the growth and tumorigenicity of human colon cancer cells. 910 61

Biochemical and genetic approaches have been used to demonstrate that basic elements of a DNA mismatch repair (MMR) pathway are conserved between bacteria, yeast and mammals. Recently, mutations in the human MMR genes MSH2, MLH1, PMS1 and PMS2 have been implicated in a common form of hereditary colon cancer and in sporadic tumors of various tissues. In order to better understand the consequences of MMR deficiency in mammalian organisms, mice deficient for the Pms2, Mlh1 and Msh2 MMR gene homologues have been generated. MMR deficient mice display a general increase in spontaneous mutation rate and develop tumors during the first year of life. Additionally, loss of MMR appears to accelerate tumorigenesis in an Apc deficient background.
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PMID:DNA mismatch repair deficient mice in cancer research. 911 Apr 1

Butyrate, a short-chain fatty acid produced during microbial fermentation of fiber, induces growth arrest, differentiation, and apoptosis of colonic epithelial cells in vitro, and our prior work has shown that this induction is tightly linked to mitochondrial activity. Here we demonstrate that 12 h following induction, SW620 human colonic carcinoma cells accumulate simultaneously in G0-G1 and G2-M of the cell cycle. Four h later, during this G0-G1 to G2-M arrest, cells begin to undergo apoptosis. Using a series of unrelated agents that modulate mitochondrial functions, we demonstrate that mitochondrial electron transport and membrane potential are critical in initiation of this butyrate-mediated growth arrest and apoptosis. Colonic tumorigenesis is characterized by abnormalities in proliferation, apoptosis, and mitochondrial activities. Thus, butyrate may reduce risk for colon cancer by inducing a pathway that enhances mitochondrial function, ultimately resulting in initiation of growth arrest and apoptosis of colonic epithelial cells.
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PMID:Short-chain fatty acid-initiated cell cycle arrest and apoptosis of colonic epithelial cells is linked to mitochondrial function. 914 3

A considerable amount of evidence collected from several different experimental systems indicates that cyclooxygenase-2 (COX-2) may play a role in colorectal tumorigenesis. Large epidemiologic studies have shown a 40-50% reduction in mortality from colorectal cancer in persons taking aspirin or other nonsteroidal antiinflammatory drugs on a regular basis. One property shared by all of these drugs is their ability to inhibit COX, a key enzyme in the conversion of arachidonic acid to prostaglandins. Two isoforms of COX have been characterized, COX-1 and COX-2. COX-2 is expressed at high levels in intestinal tumors in humans and rodents. In this study, we selected two transformed human colon cancer cell lines for studies on the role of COX-2 in intestinal tumorigenesis. We evaluated HCA-7 cells which express high levels of COX-2 protein constitutively and HCT-116 cells which lack COX-2 protein. Treatment of nude mice implanted with HCA-7 cells with a selective COX-2 inhibitor (SC-58125), reduced tumor formation by 85-90%. SC-58125 also inhibited colony formation of cultured HCA-7 cells. Conversely, SC-58125 had no effect on HCT-116 implants in nude mice or colony formation in culture. Here we provide evidence that there may be a direct link between inhibition of intestinal cancer growth and selective inhibition of the COX-2 pathway.
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PMID:Inhibition of human colon cancer cell growth by selective inhibition of cyclooxygenase-2. 915 99

Colorectal cancer remains a major health problem. Few therapies are effective apart from surgery, and survival has increased little in recent years. This is despite the fact that screening by colonoscopy can potentially remove nearly all colorectal tumours before they become malignant. Molecular genetics has identified some inherited mutations (such as at APC and the mismatch repair loci) that predispose to colon cancer and some somatic mutations (such as at APC and p53) that cause sporadic colon tumours. We review the likely role of these and other genes in colorectal tumorigenesis. We also highlight areas of relative ignorance in colon cancer and emphasise that many important genes, especially those that cause invasion and metastasis, remain to be identified. Colorectal cancer is, however, a well characterised tumour, as regards both its natural history and its histopathology; there are consequently good prospects for advances in colon cancer genetics, with probable benefits for its treatment. We anticipate: (a) that new genes predisposing to colon tumours, including those conferring relatively minor risks, will be characterised; (b) genes and proteins important in invasion and metastasis will be identified; (c) the network of protein interactions in which molecules such as APC are involved will be elucidated; (d) large-scale studies of somatic mutations in tumours will provide accurate predictions of prognosis and suggest optimal therapeutic regimens; and (e) new potential targets for therapy will be identified. Whilst molecular genetics is by no means sufficient for progress in preventing and treating colon cancer, it is a necessary and central part of such advances.
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PMID:Molecular genetics of colon cancer. 915 80


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