APC mutations and other genetic and epigenetic changes in colon cancer

Relationships between adenomatous polyposis coli (APC) mutations, BRAF V600E mutations, and the CpG island methylator phenotype (CIMP) in colon cancer have not been explored. In addition, controversies exist about the proportion of tumors with APC mutations in the mutation cluster region (MCR); how commonly APC, Ki-ras, and p53 mutations occur in the same tumor; and whether APC mutations occur in sporadic microsatellite-unstable tumors. The APC gene was therefore sequenced in 90 colonic adenocarcinomas previously evaluated for CIMP, microsatellite instability, BRAF, Ki-ras, and p53. APC mutations were inversely related to BRAF mutations (P = 0.0003) and CIMP (P = 0.02) and directly related to p53 and Ki-ras mutations (P = 0.04). Slightly more than half of APC mutations occurred outside of the MCR, and frameshift mutations were more likely than nonsense mutations to occur in the MCR (21 of 28 versus 12 of 40, P = 0.0003). APC mutations were found in sporadic microsatellite-unstable tumors and were more likely to be frameshifts in short nucleotide repeats (P = 0.007). The occurrence of APC, Ki-ras, and p53 mutations together in the same tumor was uncommon (11.1%). In conclusion, an analysis restricted to the MCR will miss more than half of APC mutations as well as mischaracterize their mutational spectrum. The conventional wisdom that most colon cancers contain APC, Ki-ras, and p53 mutations is incorrect. Microsatellite instability may precede acquisition of APC mutations in sporadic microsatellite-unstable tumors. The relationships of APC mutations to other genetic and epigenetic alterations add to the already impressive genetic heterogeneity of colon cancer.     

Chromosome missegregation causes colon cancer by APC loss of heterozygosity

A longstanding hypothesis in the field of cancer biology is that aneuploidy causes cancer by promoting loss of chromosomes that contain tumor suppressor genes. By crossing aneuploidy-prone Bub1 hypomorphic mice onto a heterozygous null background for p53, we provided conclusive evidence for this idea.1 Surprisingly, the tumors that developed in this model had not just lost the chromosome 11 copy harboring wildtype p53, but had also gained an extra copy of chromosome 11 bearing the p53 null allele. Here we report that a similar chromosome-reshuffling blueprint drives colonic tumorigenesis in Bub1 hypomorphic mice that are heterozygous for ApcMin, but now involving chromosome 18. These extended studies highlight that in order for whole chromosome instability to drive tumorigenesis, it needs to establish tumor suppressor gene loss of heterozygosity while retaining two copies of the other genes on the chromosome. Additional restrictions seem to apply to whole chromosome instability as a cancer causing mechanism, which will be discussed in this paper.     

Adenomatous polyposis coli (APC) differentially regulates beta-catenin phosphorylation and ubiquitination in colon cancer cells

Most colorectal cancers have mutations of the adenomatous polyposis coli (APC) gene or the beta-catenin gene that stabilize beta-catenin and activate beta-catenin target genes, leading ultimately to cancer. The molecular mechanisms of APC function in beta-catenin degradation are not completely known. APC binds beta-catenin and is involved in the Axin complex, suggesting that APC regulates beta-catenin phosphorylation. Some evidence also suggests that APC regulates beta-catenin nuclear export. Here, we examine the effects of APC mutations on beta-catenin phosphorylation, ubiquitination, and degradation in the colon cancer cell lines SW480, DLD-1, and HT29, each of which contains a different APC truncation. Although the current models suggest that beta-catenin phosphorylation should be inhibited by APC mutations, we detected significant beta-catenin phosphorylation in these cells. However, beta-catenin ubiquitination and degradation were inhibited in SW480 but not in DLD-1 and HT29 cells. The ubiquitination ofbeta-catenin in SW480 cells can be rescued by exogenous expression of APC. The APC domains required for beta-catenin ubiquitination were analyzed. Our results suggest that APC regulates beta-catenin phosphorylation and ubiquitination by distinct domains and by separate molecular mechanisms.     

Zinc stabilizes adenomatous polyposis coli (APC) protein levels and induces cell cycle arrest in colon cancer cells

In the present study, we investigated the mechanisms by which zinc causes growth arrest in colon cancer cells. The results suggest that zinc treatment stabilizes the levels of the wild-type adenomatous polyposis coli (APC) protein at the post-translational level since the APC mRNA levels and the promoter activity of the APC gene were decreased in HCT-116 cells (which express the wild-type APC gene) after treatment with ZnCl2. Increased levels of wild-type but not truncated APC proteins were required for the ZnCl2-mediated G2/M phase arrest in different colon cancer cell lines. We further tested whether serum-stimulation, which induces cell cycle arrest in the S phase, can relieve ZnCl2-induced G2/M phase arrest of HCT-116 cells. Results showed that in the HCT-116 cells pretreated with ZnCl2, the serum-stimulation neither changed the distribution of G2/M phase arrested cells nor the increased levels of APC protein. The G2/M phase arrest correlated with retarded growth of HCT-116 cells. To further establish that wild-type APC protein plays a role in ZnCl2-induced G2/M arrest, we treated SW480 colon cancer cells that express truncated APC protein. We found that ZnCl2 treatment did not induce G2/M phase arrest in SW480 cells; however, the cell growth was retarded due to the loss of E-cadherin and alpha-tubulin levels. These results suggest that ZnCl2 inhibits the proliferation of colon cancer cells (which carry the wild-type APC gene) through stabilization of the APC protein and cell cycle arrest in the G2/M phase. On the other hand, ZnCl2 inhibits the proliferation of colon cancer cells (which carry the mutant APC gene) by disrupting cellular attachment and microtubule stability.     

Energy biogenesis: one key for coordinating two genomes

In metazoan organisms, energy production is the only example of a process that is under dual genetic control: nuclear and mitochondrial. We used a genomic approach to examine how energy genes of both the nuclear and mitochondrial genomes are coordinated, and discovered a novel genetic regulatory circuit in Drosophila melanogaster that is surprisingly simple and parsimonious. This circuit is based on a single DNA regulatory element and can explain both intra- and inter-genomic coordinated expression of genes involved in energy production, including the full complement of mitochondrial and nuclear oxidative phosphorylation genes, and the genes involved in the Krebs cycle.     

口腔健康相关生活质量的研究应用与进展

近20年来,口腔健康相关生活质量的测评越来越受到学者们的关注,它是反映口腔疾病及其防治对患者的身体机能、心理功能、社会功能等影响的多维综合评估体系.有关这方面的研究,国外在临床和基础科研领域都取得了一定的成果,而国内的报导却凤毛麟角,乏善可陈.本文旨在通过对口腔健康相关生活质量的测评体系的综述,以探讨我国口腔健康相关生活质量的未来发展方向.     

Nucleocytoplasmic shuttling signals: two for the price of one

It has been appreciated for some time that basic-amino-acid-type nuclear localization signals control nuclear uptake of proteins and that leucine-rich nuclear export signals mediate export back into the cytoplasm. The machinery that recognizes and escorts these well-defined protein transport signals through the nuclear pore complex has been identified and characterized. Does this mean that the nuclear transport field knows all it needs to about transport signals? Not quite, as several recent publications have expanded the membership of a growing family of transport signals, known as nucleocytoplasmic shuttling (NS) signals. All proteins currently known to contain this type of signal also associate with mRNA. This article reviews what is currently known about mediators of NS signal transport and discusses the link between NS signal-containing proteins and RNA export.     

Bilateral olfaction: two is better than one for navigation

Do animals require bilateral input to track odors? A recent study reveals that fruit fly larvae can localize odor sources using unilateral inputs from a single functional sensory neuron, but that an enhanced signal-to-noise ratio provided by dual inputs is helpful in more challenging environments.     

Isolation and characterization of two novel colon cancer cell lines from Chinese patients

Incidence of colon cancer has increased rapidly in China. Although many colon cancer cell lines have been established previously, most of them were derived from patients from western countries. Epidemiological, clinical, cytogenetic, and molecular biological studies showed that there are considerable differences between Chinese and western countries colon cancer patients. Therefore, establishment of novel colon cancer cell line from Chinese is useful for studying the racial difference of this disease and can be important for studying the pathogenesis of colon cancer in China. In our laboratory, two novel continuous human colon cancer cell lines, SHT-1 and SHH-1, have been established in vitro from Chinese patients, and both cell lines have been passaged for 4 yr, and they have been continuously subcultured with more than 800 population doubling and without signs of senescence. Both cell lines were obtained from primary tumor tissues during colon cancer surgery. Cells grew rapidly with a doubling time of 36–39 h and a plating efficiency of 26–28%. These cells exhibited an epithelial morphology and expressed cytokeratin. Tumor developed in severe combined immunodeficient (SCID) mice 4–6 wk after inoculated subcutaneously with the cultured cancer cells. Karyotypic analysis and comparative genomic hybridization (CGH) analysis in SHT-1 cells revealed a hypertriploid modal number of 76 with numerous numerical and structural abnormalities previously linked to colon cancer. In another cell line (SHH-1), CGH analysis revealed that −1p13 was the only cytogenetic anomaly.     

Evidence for two mechanisms of thrombin-induced platelet activation: one proteolytic, one receptor mediated

The possibility that thrombin-induced platelet reactivity could occur via both a receptor-related and a proteolytic process was examined. Thrombin elicited the formation of considerably more [32P]phosphatidic acid (an index of phospholipase C catalysed phosphoinositide metabolism) than did platelet activating factor, 5-hydroxytryptamine, ADP, and the thromboxane A2 analogue EP171, when these agents were added either alone or in combination. Co-addition of thrombin and EP171 did not evoke significantly more [32P]phosphatide acid than did thrombin alone. The protease inhibitor leupeptin, decreased but did not abolish [32P]phosphatidic acid formation elicited by either thrombin alone or thrombin in combination with EP171. The serine protease, trypsin, stimulated an increase in [32P]phosphatidic acid and this effect was additive with that of EP171. This augmentation by trypsin of EP171-induced [32P]phosphatidic acid formation was inhibited by leupeptin. These results are consistent with the concept that thrombin-induced activation of phospholipase C occurs by two distinct mechanisms: one via proteolysis, which is sensitive to leupeptin, and the other via receptor activation, a process shared by EP171. The individual components of this dual mechanism can be mimicked by the co-addition of a receptor-directed agonist (EP171) and a proteolytic agent (trypsin).     

Polyamines and colon cancer

In colon cancer, the activities of polyamine-synthesizing enzymes and polyamine content are increased 3-4-fold over that found in the equivalent normal colonic mucosa, and polyamines have even been attributed as markers of neoplastic proliferation in the colon. Furthermore, and in contrast with all other cell systems in the body, normal and neoplastic cells in the colon are exposed to high concentrations of putrescine from the lumen, synthesized by colonic microflora. While such a high polyamine supply may be of benefit in non-neoplastic colonic mucosal growth, the role of luminal polyamines in colon cancer is a clear concern. Luminal polyamines are readily taken up by neoplastic colonocytes, they are utilized in full to support neoplastic growth, and their uptake is strongly up-regulated by the mitogens known to play an important role in colonic carcinogenesis. Inhibition of polyamine synthesis and their uptake, impaired utilization of exogenous polyamines, and enhanced catabolism of polyamines in neoplastic colonocytes are therefore logical approaches in the chemoprevention of colorectal cancer.     

Gene therapy strategies for colon cancer

Colorectal cancer is the second most common cause of cancer mortality in Western countries. Gene therapy represents a novel approach to the treatment of colorectal cancer, and this review addresses the current strategies and ongoing clinical trials, including gene correction, immunomodulatory approaches and virus-directed enzyme-prodrug systems. Although the pre-clinical results for these strategies have been encouraging, clinical trials have not yet reflected these data. However, gene therapy for colorectal cancer is still in the early stages of development, and its potential, particularly in combination with conventional cancer therapies, warrants further investigation.