Gestational mutations and carcinogenesis

We present a mathematical formulation to evaluate the effects of gestational mutations on cancer risk. The hazard or incidence function of cancer is expressed in terms of the Probability Generating Function (PGF) of the number of normal and mutated cells at birth. Using Filtered Poisson Process Theory, we obtain the PGF for several models for the accumulation of gestational mutations. In particular, we develop expressions for the hazard function when one or two successive mutations could occur during gestation. We also calculate the hazard when the background gestational mutation rates are increased due to exposure to mutagens, such as prenatal radiation. To illustrate the use of our models, we apply them to colorectal cancer in the SEER database. We find that the proportion of cancer risk attributable to developmental mutations depends on age and that it could be quite significant when gestational mutation rates are high. The analysis of the SEER data also shows that gestational mutations could contribute to inter-individual variations in colorectal cancer risk.     

Identification of biomarkers for colorectal cancer through proteomics-based approaches

The early detection of colorectal cancer is one of the great challenges in the battle against this disease. However, owing to its heterogeneous character, single markers are not likely to provide sufficient diagnostic power to be used in colorectal cancer population screens. This review provides an overview of recent studies aimed at the discovery of new diagnostic protein markers through proteomics-based approaches. It indicates that studies that start with the proteomic analysis of tumor tissue or tumor cell lines (near the source) have a high potential to yield novel and colorectal cancer-specific biomarkers. In the next step, the diagnostic accuracy of these candidate markers can be assessed by a targeted ELISA assay using serum from colorectal cancer patients and healthy controls. Instead, direct proteomic analysis of serum yields predominantly secondary markers composed of fragments of abundant serum proteins that may be associated with tumor-associated protease activity, and alternatively, immunoproteomic analysis of the serum antibody repertoire provides a valuable tool to identify the molecular imprint of colorectal cancer-associated antigens directly from patient serum samples. The latter approach also allows a relatively easy translation into targeted assays. Eventually, multimarker assays should be developed to reach a diagnostic accuracy that meets the stringent criteria for colorectal cancer screening at the population level.     

Transposon-mediated mutagenesis of somatic cells in the mouse for cancer gene identification

To successfully treat cancer we will likely need a much more detailed understanding of the genes and pathways meaningfully altered in individual cancer cases. One method for achieving this goal is to derive cancers in model organisms using unbiased forward genetic screens that allow cancer gene candidate discovery. We have developed a method using a “cut-and-paste” DNA transposon system called Sleeping Beauty (SB) to perform forward genetic screens for cancer genes in mice. Although the approach is conceptually similar to the use of replication competent retroviruses for cancer gene identification, the SB system promises to allow such screens in tissues previously not amenable to forward genetic screens such as the gastrointestinal tract, brain, and liver. This article describes the strains useful for SB-based screens for cancer genes in mice and how they are deployed in an experiment.     

Expression of p27Kip1 and bcl-2, cigarette smoking, and colorectal cancer risk

Although a positive association between cigarette smoking and colorectal adenoma development is consistently found, the association with colorectal cancer remains controversial. We evaluated the potential roles of p27^Kip1 and bcl-2 protein expressions in conjunction with cigarette smoking exposure and colorectal cancer risk in a hospital-based case-control study. A total of 163 colorectal cancer patients from Roswell Park Cancer Institute and Buffalo General Hospital and 326 healthy controls responded to a standardized questionnaire on colorectal cancer risk factors including detailed information on their history of cigarette smoking; 110 of the patientsfitumours were available for immunohistochemical analysis of p27^Kip1 and bcl-2 protein overexpression. An avidin?biotin immunoperoxidase procedure was used to determine expression after incubation with mouse monoclonal p27^Kip1 and mouse monoclonal bcl-2 antibodies, respectively. A statistically significant trend for total pack-years of smoking was found when p27^Kip1 positive cases were compared with p27^Kip1 negative cases (trend test, p = 0.007). Although a weak inverse association was observed with smoking exposure among p27^Kip1 negative tumour cases in comparison to controls, a significant dose?response association was seen with p27^Kip1 positive tumours. The relative risk of developing a p27^Kip1 positive tumour was estimated to be 1.17 (95% CI 0.54?2.54) for those with less than 20 pack-years, 1.95 (95 % CI 0.95?3.97) for those with 20?39 pack-years, and 2.25 (95% CI 1.14?4.45) for those with greater than 39 pack-years of smoking exposure (trend test, p = 0.009) when compared with controls. When cases with bcl-2 expression were compared with cases without bcl-2 expression, suggestion of a trend was also observed with pack-years smoked (trend test, p = 0.09). In our study of 110 patients with sporadic colorectal cancer and 326 controls, we observed differences in associations between cigarette smoking and expressions in p27^Kip1 and bcl-2. Our data suggest that bcl-2 overexpression (or a bcl-2 dependent pathway) is associated with cigarette smoking in the development of colorectal cancer, whereas a loss of p27^Kip1 expression is not. These associations indicate that there is aetiological heterogeneity in colorectal cancer development, and that they can indirectly allude to where these changes in protein expression occur in the adenoma?carcinoma sequence (i.e. early versus late events).     

Low penetrance genetic polymorphisms as potential biomarkers for colorectal cancer predisposition

Colorectal cancer is a leading form of cancer in both males and females. Early detection of individuals at risk of colorectal cancer allows proper treatment and management of the disease to be implemented, which can potentially reduce the burden of colorectal cancer incidence, morbidity and mortality. In recent years, the role of genetic susceptibility factors in mediating predisposition to colorectal cancer has become more and more apparent. Identification of high‐frequency, low‐penetrance genetic polymorphisms associated with the cancer has therefore emerged as an important approach which can potentially aid prediction of colorectal cancer risk. However, the overwhelming amount of genetic epidemiology data generated over the past decades has made it difficult for one to assimilate the information and determine the exact genetic polymorphisms that can potentially be used as biomarkers for colorectal cancer. This review comprehensively consolidates, based primarily on results from meta‐analyses, the recent progresses in the search of colorectal cancer‐associated genetic polymorphisms, and discusses the possible mechanisms involved.     

Use of Genome-Wide Association Studies for Cancer Research and Drug Repositioning

Although genome-wide association studies have identified many risk loci associated with colorectal cancer, the molecular basis of these associations are still unclear. We aimed to infer biological insights and highlight candidate genes of interest within GWAS risk loci. We used an in silico pipeline based on functional annotation, quantitative trait loci mapping of cis-acting gene, PubMed text-mining, protein-protein interaction studies, genetic overlaps with cancer somatic mutations and knockout mouse phenotypes, and functional enrichment analysis to prioritize the candidate genes at the colorectal cancer risk loci. Based on these analyses, we observed that these genes were the targets of approved therapies for colorectal cancer, and suggested that drugs approved for other indications may be repurposed for the treatment of colorectal cancer. This study highlights the use of publicly available data as a cost effective solution to derive biological insights, and provides an empirical evidence that the molecular basis of colorectal cancer can provide important leads for the discovery of new drugs.     

The interactive effect of methyl-group diet and polymorphism of methylenetetrahydrofolate reductase on the risk of colorectal cancer

Higher intakes of vegetables have been reported to be associated with a reduced risk of colorectal cancer. Folate, a water-soluble B vitamin, and one of the major micronutrients in vegetables, may be partly responsible for this beneficial effect. Conversely, a high alcohol intake has been related to an increased risk of colorectal cancer. The combination of high folate and low alcohol intake, "methyl group diets", was reported to have a strong protective effect. These findings support a role of methyl group availability as an underlying mechanism for an effect of folate on colorectal carcinogenesis. The protective effect of the homozygous variant TT form of the MTHFR genotype (C677T) on the risk of colorectal cancer seems to be modified by the level of methyl diets, that is, by folate, which has a protective effect, or conversely by alcohol. Recommendation of higher intake of folate and lower intake of alcohol to the target population, especially those with TT genotype of MTHFR, may be an effective preventive approach against colorectal cancer.     

Discrepancies between estimated and perceived risk of cancer among individuals with hereditary nonpolyposis colorectal cancer

Communicating cancer risk and recommending adequate control programs is central for genetic counseling. Individuals affected by hereditary nonpolyposis colorectal cancer (HNPCC) are at about 80% life-time risk of colorectal cancer and for female carriers 40-60% risk of endometrial cancer and 10-15% risk of ovarian cancer. The perceived risk among mutation carriers may, however, deviate from the risk communicated and has been demonstrated to influence adherence to control programs. We investigated the perceived cancer risk among HNPCC mutation carriers (n = 47) and correlated the findings to individual characteristics. A perceived risk of colorectal cancer above 60% was reported by 22/45 individuals, and only one out of five mutation carriers reported a perceived risk > 80%. Female mutation carriers, individuals below age 50, and individuals who received their oncogenetic counseling within 1 year prior to the study reported higher, albeit not significantly, perceived risks of colorectal cancer. Higher perceived risks were also reported by individuals who had lost a parent to HNPCC-related cancer at early age, whereas individuals with a personal history of cancer did not report a higher perceived risk. Regarding gynecological cancer, 6/18 females reported a perceived risk of 40-60% for endometrial cancer, whereas the remaining women both underestimated and overestimated their risk, and none of the women referred to the risk of ovarian cancer. We conclude that despite educational efforts and an increasing amount of data on the cancer risk in HNPCC, a minority of the mutation carriers report a perceived risk at the same level as that communicated during oncogenetic counseling.     

Semiparametric estimation for joint modeling of colorectal cancer risk and functional biomarkers measured with errors

This research is motivated by a pilot colorectal adenoma study, where the outcome of interest is the presence of colorectal adenoma representing risk for colorectal cancer, and the predictors of interest are protein biomarkers that are repeatedly measured with errors along the length of a microscopic structure in the human colon, the colon crypt. Biomarkers of this type are referred to as functional biomarkers. The investigators are interested in identifying features of functional biomarkers that are associated with risk for colorectal cancer. In this paper, we investigate a joint modeling approach, where the binary clinical outcome is modeled using a logistic regression model with the unobserved true functional biomarkers as the predictors. Most existing methods are developed either for linear models or for functional biomarkers measured without errors and cannot be directly applied to our data. The applicable methods include a two-step method and a maximum likelihood method, which have some limitations. We propose a robust semiparametric method to overcome the limitations of the existing methods. We study the properties of the proposed method, and show in simulations that it compares favorably with other methods and also offers significant savings in CPU time. We analyze the pilot colorectal adenoma data and show that expression levels of AFC, a tumor suppressor gene, in the transitional area from the proliferation zone to the differentiation zone of colon crypts are likely to be associated with risk for colorectal cancer. Given the relatively small sample size in the pilot study, our results need to be validated in the future full-scale studies.     

Expression of p27Kip1 and bcl-2, cigarette smoking,and colorectal cancer risk

Although a positive association between cigarette smoking and colorectal adenoma development is consistently found, the association with colorectal cancer remains controversial. We evaluated the potential roles of p27^Kip1 and bcl-2 protein expressions in conjunction with cigarette smoking exposure and colorectal cancer risk in a hospital-based case-control study. A total of 163 colorectal cancer patients from Roswell Park Cancer Institute and Buffalo General Hospital and 326 healthy controls responded to a standardized questionnaire on colorectal cancer risk factors including detailed information on their history of cigarette smoking; 110 of the patients' tumours were available for immunohistochemical analysis of p27^Kip1 and bcl-2 protein overexpression. An avidin-biotin immunoperoxidase procedure was used to determine expression after incubation with mouse monoclonal p27^Kip1 and mouse monoclonal bcl-2 antibodies, respectively. A statistically significant trend for total pack-years of smoking was found when p27^Kip1 positive cases were compared with p27^Kip1 negative cases (trend test, p = 0.007). Although a weak inverse association was observed with smoking exposure among p27^Kip1 negative tumour cases in comparison to controls, a significant dose-response association was seen with p27^Kip1 positive tumours. The relative risk of developing a p27^Kip1 positive tumour was estimated to be 1.17 (95% CI 0.54-2.54) for those with less than 20 pack-years, 1.95 (95 % CI 0.95-3.97) for those with 20-39 pack-years, and 2.25 (95% CI 1.14-4.45) for those with greater than 39 pack-years of smoking exposure (trend test, p = 0.009) when compared with controls. When cases with bcl-2 expression were compared with cases without bcl-2 expression, suggestion of a trend was also observed with pack-years smoked (trend test, p = 0.09). In our study of 110 patients with sporadic colorectal cancer and 326 controls, we observed differences in associations between cigarette smoking and expressions in p27^Kip1 and bcl-2. Our data suggest that bcl-2 overexpression (or a bcl-2 dependent pathway) is associated with cigarette smoking in the development of colorectal cancer, whereas a loss of p27^Kip1 expression is not. These associations indicate that there is aetiological heterogeneity in colorectal cancer development, and that they can indirectly allude to where these changes in protein expression occur in the adenoma-carcinoma sequence (i.e. early versus late events).     

Toward an integrated map of genetic interactions in cancer cells

Cancer genomes often harbor hundreds of molecular aberrations. Such genetic variants can be drivers or passengers of tumorigenesis and create vulnerabilities for potential therapeutic exploitation. To identify genotype‐dependent vulnerabilities, forward genetic screens in different genetic backgrounds have been conducted. We devised MINGLE, a computational framework to integrate CRISPR/Cas9 screens originating from different libraries building on approaches pioneered for genetic network discovery in model organisms. We applied this method to integrate and analyze data from 85 CRISPR/Cas9 screens in human cancer cells combining functional data with information on genetic variants to explore more than 2.1 million gene‐background relationships. In addition to known dependencies, we identified new genotype‐specific vulnerabilities of cancer cells. Experimental validation of predicted vulnerabilities identified GANAB and PRKCSH as new positive regulators of Wnt/β‐catenin signaling. By clustering genes with similar genetic interaction profiles, we drew the largest genetic network in cancer cells to date. Our scalable approach highlights how diverse genetic screens can be integrated to systematically build informative maps of genetic interactions in cancer, which can grow dynamically as more data are included.     

Pre-Diagnostic Leukocyte Genomic DNA Methylation and the Risk of Colorectal Cancer in Women

Background

Abnormal one-carbon metabolism may lead to general genomic (global) hypomethylation, which may predispose an individual to the development of colorectal neoplasia.

Methods

We evaluated the association between pre-diagnostic leukocyte genomic DNA methylation level and the risk of colorectal cancer in a nested case-control study of 358 colorectal cancer cases and 661 matched controls within the all-female cohort of the Nurses’ Health Study (NHS). Among control subjects, we further examined major plasma components in the one-carbon metabolism pathway in relation to genomic DNA methylation level. Liquid chromatography/tandem mass spectrometry was used to examine leukocyte genomic DNA methylation level. We calculated odds ratios (ORs) and 95% confidence intervals (95% CIs) using logistic regression.

Results

Overall genomic DNA methylation level was not associated with the risk of colorectal cancer (p for trend, 0.45). Compared with women in the lowest quintile of methylation, the multivariate OR of colorectal cancer risk was 1.32 (95% CI, 0.82–2.13) for those in the highest quintile. We did not find significant associations between major plasma components of one-carbon metabolism or risk factors for colorectal cancer and genomic DNA methylation level (all p for trend >0.05). Also, neither one-carbon metabolism-related plasma components nor well-known risk factors for colorectal cancer modified the association between genomic DNA methylation level and the risk of colorectal cancer (all p for interaction >0.05).

Conclusions

We found no evidence that hypomethylation of leukocyte genomic DNA increases risk of colorectal cancer among women. Additional studies are needed to investigate the association between pre-diagnostic genomic DNA methylation level and colorectal cancer risk among diverse populations.     

Interaction between smoking, GSTM1 deletion and colorectal cancer: results from the GSEC study.

Cigarette smoking has inconsistently been associated with an increased risk of colorectal cancer. One of the enzymes responsible for the detoxification of the carcinogenic compounds present in tobacco smoke is glutathione S-transferase-mu (GST-mu). The gene that codes for this enzyme is GSTM1. In this study, we evaluated the associations and interaction between GSTM1 deletion, smoking behaviour and the development of colorectal cancer. We performed a pooled analysis within the International Collaborative Study on Genetic Susceptibility to Environmental Carcinogens (GSEC). We selected six studies on colorectal cancer, including 1130 cases and 2519 controls, and restricted our analyses to Caucasians because the number of patients from other races was too limited. In addition we performed a meta-analysis including the studies from the GSEC database and other studies identified on MEDLINE on the same subject. The prevalence of the GSTM1 null genotype was within the range reported in other studies: 51.8% of the cases had the GSTM1 null genotype versus 56.6% of the controls. No significant association between the GSTM1 null genotype and colorectal cancer was found (odds ratio 0.92, 95% confidence interval 0.73-1.14). Our results suggest a possible positive association between lack of the GST-mu enzyme and colorectal cancer for non-smoking women (odds ratio 1.47, 95% confidence interval 0.80-2.70). There was no interaction between the effects of smoking and GSTM1 genotype on colorectal cancer risk in men and women (chi2=0.007, p=0.97). Our findings do not support an association between the GSTM1 null genotype and colorectal cancer. In addition, we did not find any modification of the smoking-induced colorectal cancer risk by GSTM1 genotype     

Disentangling the Association between Statins,Cholesterol, and Colorectal Cancer: A Nested Case-Control Study

BackgroundSeveral prior studies have found an association between statin use and reduced risk of colorectal cancer. We hypothesized that these findings may be due to systematic bias and examined the independent association of colorectal cancer risk with statin use, serum cholesterol, and change in cholesterol concentration.ConclusionsAlthough the risk of colorectal cancer was lower in statin users versus nonusers, no difference was observed among those who continued versus discontinued statin therapy, suggesting the potential for indication bias. The association between decreased serum cholesterol and colorectal cancer risk suggests a cholesterol-lowering effect of undiagnosed malignancy. Clinical judgment should be used when considering causes of cholesterol reduction in patients, including those on statin therapy.     

MAT2A与NDRG2基因在结直肠癌中表达情况及临床意义的研究

目的研究MAT2A(甲硫氨酸腺苷转移酶2A)和NDRG2(N-Myc下游调节基因-2)基因在结直肠癌组织中的表达及两者的相关性,为结直肠癌的研究及治疗提供重要参考。方法选取68例术中切除结直肠癌组织及相应的癌旁组织标本,应用RT-PCR(逆转录-聚合酶链式反应)和Western blotting(蛋白质印迹法)检测结直肠癌中MAT2A和NDRG2表达水平。结果结直肠癌中MAT2A和NDRG2mRNA表达情况:MAT2A阳性表达率(66.2%,45/68)高于癌旁组织(7.4%,5/68);NDRG2阳性表达率(36.8%,25/68)低于癌旁组织(91.2%,62/68);两者的表达与患者年龄、性别、肿瘤生长位置等因素均无关,与癌肿临床分期、分化水平及淋巴结转移密切相关。癌肿组织中MAT2A蛋白表达量相较于癌旁组织明显增多(t=39.1152,P=0.0000),而癌肿组织中NDRG2蛋白表达量较癌旁组织明显降低(t=46.5103,P=0.0000);且在结直肠癌组织中两基因的表达可能有相关性(χ~2=7.41,P=0.009)。结论在结直肠癌组织中MAT2A表达增高,NDRG2表达下降,两者与肿瘤的发生发展具有一定相关性,推测可能与DNA甲基化异常有关,但具体机制仍待进一步研究。     

Genetic Variants Associated with Colorectal Adenoma Susceptibility

BackgroundCommon low-penetrance genetic variants have been consistently associated with colorectal cancer risk.AimTo determine if these genetic variants are associated also with adenoma susceptibility and may improve selection of patients with increased risk for advanced adenomas and/or multiplicity (≥ 3 adenomas).MethodsWe selected 1,326 patients with increased risk for advanced adenomas and/or multiplicity and 1,252 controls with normal colonoscopy from population-based colorectal cancer screening programs. We conducted a case-control association study analyzing 30 colorectal cancer susceptibility variants in order to investigate the contribution of these variants to the development of subsequent advanced neoplasia and/or multiplicity.ResultsWe found that 14 of the analyzed genetic variants showed a statistically significant association with advanced adenomas and/or multiplicity: the probability of developing these lesions increased with the number of risk alleles reaching a 2.3-fold risk increment in individuals with ≥ 17 risk alleles.ConclusionsNearly half of the genetic variants associated with colorectal cancer risk are also related to advanced adenoma and/or multiplicity predisposition. Assessing the number of risk alleles in individuals within colorectal cancer screening programs may help to identify better a subgroup with increased risk for advanced neoplasia and/or multiplicity in the general population.     

Atractylenolide II reverses the influence of lncRNA XIST/miR‐30a‐5p/ROR1 axis on chemo‐resistance of colorectal cancer cells

This investigation was conducted to elucidate whether atractylenolide II could reverse the role of lncRNA XIST/miR‐30a‐5p/ROR1 axis in modulating chemosensitivity of colorectal cancer cells. We totally collected 294 pairs of colorectal cancer tissues and adjacent normal tissues and also purchased colorectal cancer cell lines and human embryonic kidney cell line. 5‐fluorouracil, cisplatin, mitomycin and adriamycin were designated as the chemotherapies for colorectal cell lines, and atractylenolides were arranged as the Chinese drug. The expressions of XIST, miR‐30a‐5p and ROR1 were quantified with aid of qRT‐PCR or Western blot, and luciferase reporter gene assay was implemented to determine the relationships among XIST, miR‐30a‐5p and ROR1. Our results demonstrated that XIST and ROR1 expressions were dramatically up‐regulated, yet miR‐30a‐5p expression was down‐regulated within colorectal cancer tissues (P < 0.05). The overexpressed XIST and ROR1, as well as under‐expressed miR‐30a‐5p, were inclined to promote viability and proliferation of colorectal cells under the influence of chemo drugs (P < 0.05). In addition, XIST could directly target miR‐30a‐5p, and ROR1 acted as the targeted molecule of miR‐30a‐5p. Interestingly, atractylenolides not only switched the expressions of XIST, miR‐30a‐5p and ROR1 within colorectal cancer cells but also significantly intensified the chemosensitivity of colorectal cancer cells (P < 0.05). Finally, atractylenolide II was discovered to slow down the viability and proliferation of colorectal cancer cells (P < 0.05). In conclusion, the XIST/miR‐30a‐5p/ROR1 axis could be deemed as pivotal markers underlying colorectal cancer, and administration of atractylenolide II might improve the chemotherapeutic efficacy for colorectal cancer.     

Genetic variants on chromosome 8q24 and colorectal neoplasia risk: a case-control study in China and a meta-analysis of the published literature

Previous studies have found that common genetic variants on chromosome 8q24 are associated with the risk of developing colorectal neoplasia. We conducted a hospital-based case-control study, including 435 cases and 788 unrelated controls to investigate the associations between common variants on 8q24 and the risk of colorectal cancer in a Chinese population. We also evaluated the association of rs6983267 with colorectal neoplasia in the published literature via a meta-analysis study. We found that rs6983267 was significantly associated with the risk of colorectal cancer in the Chinese population, with an adjusted odds-ratio (OR) for the GT heterozygotes and GG homozygotes of 1.30 (95% CI  = 0.98–1.71, P = 0.069) and 1.66 (95% CI  = 1.18–2.34, P = 0.004), respectively, compared to the TT homozygotes, with a P-trend value of 0.003. No association was found for the other three loci (rs16901979, rs1447295 and rs7837688). In the meta-analysis of the published genetic association studies, the rs6983267 variant was found to be associated with an increased risk of colorectal neoplasia. The heterozygous GT carriers showed a 20% increased risk of colorectal neoplasia (OR  = 1.20, 95% CI  = 1.16–1.25; random effects model) with a summary OR for homozygous GG carriers of 1.39 (95% CI  = 1.32–1.48; random effects model) compared to the TT genotype carriers. We found no significant differences between the association of rs6983267 and colorectal cancer and colorectal adenomas. In summary, our study confirms that the variant rs6983267 is a risk factor for colorectal neoplasia in various populations, including the Chinese population.