Genomic Aberrations in an African American Colorectal Cancer Cohort Reveals a MSI-Specific Profile and Chromosome X Amplification in Male Patients

Objective

DNA aberrations that cause colorectal cancer (CRC) occur in multiple steps that involve microsatellite instability (MSI) and chromosomal instability (CIN). Herein, we studied CRCs from AA patients for their CIN and MSI status.

Experimental Design

Array CGH was performed on 30 AA colon tumors. The MSI status was established. The CGH data from AA were compared to published lists of 41 TSG and oncogenes in Caucasians and 68 cancer genes, proposed via systematic sequencing for somatic mutations in colon and breast tumors. The patient-by-patient CGH profiles were organized into a maximum parsimony cladogram to give insights into the tumors'' aberrations lineage.

Results

The CGH analysis revealed that CIN was independent of age, gender, stage or location. However, both the number and nature of aberrations seem to depend on the MSI status. MSI-H tumors clustered together in the cladogram. The chromosomes with the highest rates of CGH aberrations were 3, 5, 7, 8, 20 and X. Chromosome X was primarily amplified in male patients. A comparison with Caucasians revealed an overall similar aberration profile with few exceptions for the following genes; THRB, RAF1, LPL, DCC, XIST, PCNT, STS and genes on the 20q12-q13 cytoband. Among the 68 CAN genes, all showed some level of alteration in our cohort.

Conclusion

Chromosome X amplification in male patients with CRC merits follow-up. The observed CIN may play a distinctive role in CRC in AAs. The clustering of MSI-H tumors in global CGH data analysis suggests that chromosomal aberrations are not random.     

Microsatellite instability typing in serum and tissue of patients with colorectal cancer: comparing real time PCR with hybridization probe and high-performance liquid chromatography

Allelic variation of BAT-25 (a 25-repeat quasimonomorphic poly T) and BAT-26 (a 26-repeat quasimonomorphic polyA) loci as two mononucleotide microsatellite markers, were analyzed with high-performance liquid chromatography (HPLC) compared with Real-Time PCR using hybridization probes. BAT-26 and BAT-25 markers were used to determine an appropriate screening technique with high sensitivity and specificity to diagnose microsatellite instability (MSI) status in patients with colorectal cancer (CRC). One of the pathways in colorectal tumor genesis is microsatellite instability (MSI⁺). MSI is detected in about 15 % of all CRCs; 3 % are of these are associated with Lynch syndrome and the other 12 % are caused by sporadic. Colorectal tumors with MSI have distinctive features compared with microsatellite stable tumors. Due to the high percentage of MSI⁺ CRC in Iran, screening of this type of CRC is imperative. Two markers were analyzed in tissues and sera of 44 normal volunteers and tumor and matched normal mucosal tissues as well as sera of 44 patients with sporadic CRC. The sensitivity and specificity of BAT-26 with real time PCR method (Hybridization probe) were 100 % in comparison with sequencing method as the gold standard, while HPLC had a lower sensitivity and specificity. According to HPLC data, BAT-26 was more sensitive than BAT-25 in identifying MSI tumors. Therefore, MSI typing using the BAT-26 hybridization probe method compared to HPLC could be considered as an accurate method for diagnosing MSI in CRC tumors but not in serum circulating DNAs.     

Mismatch repair (MMR) efficiency and MSH2 gene mutation in human colorectal carcinoma cell line COLO320HSR

Colorectal cancer (CC) is one of two diseases, in which the link between cancer proneness and DNA repair deficiency appears to be proved. A strict relationship between mismatch repair (MMR) gene mutations, microsatellite instability (MSI) has been found in familiar colorectal cancer (Lynch syndrome). Tumorigenesis at familiar cancer is initiated by biallelic mutations in the major MMR genes, namely MSH2 or MLH1. One of these mutations is an inherited germline alteration and the other is a somatic one. The initiating mutation in sporadic colorectal tumors was not still identified although biochemical and genetic signs of MMR deficiency are observed in tumor cells. Two currently used colorectal tumor cell lines HCT116 and COLO320HSR were derived from hereditary and sporadic tumors accordingly. HCT116 cell line exhibits MMR-deficiency due to biallelic deletion in MLHL. As a consequence this shows MSI phenotype and a near-diploid karyotype. COLO320HSR cell line is characterized by MSS phenotype with mostly imbalanced aberrations. This indicates MMR proficiency in these cells. However, both MMR-deficient HCT116 and COLO320HSR cells reveal near-diploid karyotype. Earlier we have shown that the number of secondary DNA double strand breaks, induced by methylnitrosourea (MNU), represent functional activity of cellular MMR. In the present study, using this approach we evaluated sensitivity to MNU and MMR activity in two colorectal tumor cell lines (HCT 116, COLO320HSR) and compared them to that in the HeLa cell line, which have MMR-proficient phenotype. We showed that cell line COLO320HSR exhibits low MMR activity, close to the level of MMR-activity in HCT116 cell line. We found a mutation in MSH2-G520A gene in COLO320HSR. This neutral mutation apparently is not related to polymorphism as we failed to identify the same mutation in any of MSH2 gene sequences of lymphocytes from 30 patients with sporadic colorectal cancer.     

Reduced ATR or Chk1 Expression Leads to Chromosome Instability and Chemosensitization of Mismatch Repair–deficient Colorectal Cancer Cells

Genomic instability in colorectal cancer is categorized into two distinct classes: chromosome instability (CIN) and microsatellite instability (MSI). MSI is the result of mutations in the mismatch repair (MMR) machinery, whereas CIN is often thought to be associated with a disruption in the APC gene. Clinical data has recently shown the presence of heterozygous mutations in ATR and Chk1 in human cancers that exhibit MSI, suggesting that those mutations may contribute to tumorigenesis. To determine whether reduced activity in the DNA damage checkpoint pathway would cooperate with MMR deficiency to induce CIN, we used siRNA strategies to partially decrease the expression of ATR or Chk1 in MMR-deficient colorectal cancer cells. The resultant cancer cells display a typical CIN phenotype, as characterized by an increase in the number of chromosomal abnormalities. Importantly, restoration of MMR proficiency completely inhibited induction of the CIN phenotype, indicating that the combination of partial checkpoint blockage and MMR deficiency is necessary to trigger CIN. Moreover, disruption of ATR and Chk1 in MMR-deficient cells enhanced the sensitivity to treatment with the commonly used colorectal chemotherapeutic compound, 5-fluorouracil. These results provide a basis for the development of a combination therapy for those cancer patients.     

Mismatch repair (MMR) efficiency and <Emphasis Type="Italic">MSH2</Emphasis> gene mutation in human colorectal carcinoma cell line COLO320HSR

Colorectal cancer (CC) is one of two diseases, in which the link between cancer proneness and DNA repair deficiency appears to be proved. A strict relationship between mismatch repair (MMR) gene mutations, microsatellite instability (MSI) has been found in familiar colorectal cancer (Lynch syndrome). Tumorigenesis at familiar cancer is initiated by biallelic mutations in the major MMR genes, namely MSH2 or MLH1. One of these mutations is an inherited germline alteration and the other is a somatic one. The initiating mutation in sporadic colorectal tumors was not still identified although biochemical and genetic signs of MMR deficiency are observed in tumor cells. Two currently used colorectal tumor cell lines HCT116 and COLO320HSR were derived from hereditary and sporadic tumors accordingly. HCT116 cell line exhibits MMR-deficiency due to biallelic deletion in MLH1. As a consequence this shows MSI phenotype and a near-diploid karyotype. COLO320HSR cell line is characterized by MSS phenotype with mostly imbalanced aberrations. This indicates MMR proficiency in these cells. However, both MMR-deficient HCT116 and COLO320HSR cells reveal near-diploid karyotype. Earlier we have shown that the number of secondary DNA double strand breaks, induced by methylnitrosourea (MNU), represent functional activity of cellular MMR. In the present study, using this approach we evaluated sensitivity to MNU and MMR activity in two colorectal tumor cell lines (HCT116, COLO320HSR) and compared them to that in the HeLa cell line, which have MMR-proficient phenotype. We showed that cell line COLO320HSR exhibits low MMR activity, close to the level of MMR-activity in HCT116 cell line. We found a mutation in MSH2-G520A gene in COLO320HSR. This neutral mutation apparently is not related to polymorphism as we failed to identify the same mutation in any of MSH2 gene sequences of lymphocytes from 30 patients with sporadic colorectal cancer.     

Array CGH analysis reveals chromosomal aberrations in mouse lung adenocarcinomas induced by the human lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Exposure to genotoxic carcinogens in tobacco smoke is a major cause of lung cancer. However, the effect this has on DNA copy number and genomic stability during lung carcinogenesis is unclear. Here we used bacterial artificial chromosome array-based comparative genomic hybridization to examine the effect of NNK, a potent human lung carcinogen present in tobacco smoke, on the major genomic changes occurring during mouse lung adenocarcinogenesis. Observed were significantly more gross chromosomal changes in NNK-induced tumors compared with the spontaneous tumors. An average of 5.6 chromosomes were affected by large-scale changes in DNA copy number per NNK-induced tumor compared with only 2.0 in spontaneous lung tumors (p = 0.017). Further analysis showed that gains on chromosomes 6 and 8, and losses on chromosomes 11 and 14 were more common in NNK-induced tumors (p 相似文献   

High frequency of microsatellite instability in sporadic colorectal cancer patients in Iran

Microsatellite instability in sporadic colorectal cancer patients was assessed, and the clinicopathological associations were evaluated in northeastern Iran, which is a high-risk region for gastrointestinal malignancies. Microsatellite instability (MSI) status of tumoral tissue, compared to normal tissue, was assessed with a standard panel of MSI markers on paraffin-embedded surgically resected tissues from 67 consecutive sporadic colorectal cancer patients. Eleven of the patients were under 40 years old. Female patients were significantly younger than male patients (mean age 54.2 vs 62.1 years, P = 0.020). MSI analysis revealed 18 cases of MSI-H (26.9%), 11 MSI-L (16.4%) and 38 MSS (microsatellite stable tumors; 56.7%). While a greater proportion of patients consisted of males, 56.7 vs 43.3% females, MSI-H was more frequent in females (34.5 vs 21.5%). MSI was associated with proximal location of tumor (P = 0.003) and lower stages of tumor (P = 0.002), while MSS tumors were associated with node metastasis. MSI has a higher frequency in sporadic colorectal cancer patients, suggesting that molecular epidemiology of the genetic alterations involved in colorectal cancer carcinogenesis has a different pattern in the Iranian population, which deserves further epidemiological attention. The high frequency of MSI-H in this population suggests that we should look at microsatellite instability prior to chemotherapy to determine the most appropriate chemotherapeutic strategy in our population.     

Expression of a mutant HSP110 sensitizes colorectal cancer cells to chemotherapy and improves disease prognosis

Heat shock proteins (HSPs) are necessary for cancer cell survival. We identified a mutant of HSP110 (HSP110ΔE9) in colorectal cancer showing microsatellite instability (MSI CRC), generated from an aberrantly spliced mRNA and lacking the HSP110 substrate-binding domain. This mutant was expressed at variable levels in almost all MSI CRC cell lines and primary tumors tested. HSP110ΔE9 impaired both the normal cellular localization of HSP110 and its interaction with other HSPs, thus abrogating the chaperone activity and antiapoptotic function of HSP110 in a dominant-negative manner. HSP110ΔE9 overexpression caused the sensitization of cells to anticancer agents such as oxaliplatin and 5-fluorouracil, which are routinely prescribed in the adjuvant treatment of people with CRC. The survival and response to chemotherapy of subjects with MSI CRCs was associated with the tumor expression level of HSP110ΔE9. HSP110 may thus constitute a major determinant for both prognosis and treatment response in CRC.     

2n or not 2n: Aneuploidy,polyploidy and chromosomal instability in primary and tumor cells

Mitotic defects leading to aneuploidy have been recognized as a hallmark of tumor cells for over 100 years. Current data indicate that ∼85% of human cancers have missegregated chromosomes to become aneuploid. Some maintain a stable aneuploid karyotype, while others consistently missegregate chromosomes over multiple divisions due to chromosomal instability (CIN). Both aneuploidy and CIN serve as markers of poor prognosis in diverse human cancers. Despite this, aneuploidy is generally incompatible with viability during development, and some aneuploid karyotypes cause a proliferative disadvantage in somatic cells. In vivo, the intentional introduction of aneuploidy can promote tumors, suppress them, or do neither. Here, we summarize current knowledge of the effects of aneuploidy and CIN on proliferation and cell death in nontransformed cells, as well as on tumor promotion, suppression, and prognosis.     

Defining 'chromosomal instability'

Most scientists agree that the majority of human solid malignant tumors are characterized by chromosomal instability (CIN) involving gain or loss of whole chromosomes or fractions of chromosomes. CIN is thought to be an early event during tumorigenesis and might therefore be involved in tumor initiation. Despite its frequent occurrence in tumors and its potential importance in tumor evolution, CIN is poorly defined and is used inconsistently and imprecisely. Here, we provide criteria to define CIN and argue that few experimental approaches are capable of assessing the presence of CIN. Accurate assessment of CIN is crucial to elucidate whether CIN is a driving force for tumorigenesis and whether a chromosomally unstable genome is necessary for tumor progression.     

Chromosomal Instability in BRAF Mutant,Microsatellite Stable Colorectal Cancers

The BRAF oncogene is mutated in 15% of sporadic colorectal cancers. Approximately half of these BRAF mutant cancers demonstrate frequent frameshift mutations termed microsatellite instability (MSI), but are diploid and chromosomally stable. BRAF wild type cancers are typically microsatellite stable (MSS) and instead acquire chromosomal instability (CIN). In these cancers, CIN is associated with a poor outcome. BRAF mutant cancers that are MSS, typically present at an advanced stage and have a particularly poor prognosis. We have previously demonstrated clinical and molecular similarities between MSS cancers with or without a BRAF mutation, and therefore hypothesised that CIN may also be frequent in BRAF mutant/MSS cancers. BRAF mutant/MSS (n = 60), and BRAF wild type/MSS CRCs (n = 90) were investigated for CIN using loss of heterozygosity analysis over twelve loci encompassing chromosomal regions 5q, 8p, 17p and 18q. CIN was frequent in BRAF mutant/MSS cancers (41/57, 72%), which was comparable to the rate found in BRAF wild type/MSS cancers (74/90, 82%). The greatest loss in BRAF mutant/MSS cancers occurred at 8p (26/44, 59%), and the least at 5q (19/49, 39%). CIN in BRAF mutant/MSS cancers correlated with advanced stage (AJCC III/IV: 15/17, 88%; p = 0.02); showed high rates of co-occurrence with the CpG Island Methylator Phenotype (17/23, 74%); and CIN at 18q and 8p associated with worse survival (p = 0.02, p<0.05). This study demonstrates that CIN commonly occurs in advanced BRAF mutant/MSS colorectal cancers where it may contribute to poorer survival, and further highlights molecular similarities occurring between these and BRAF wild type cancers.     

结直肠腺瘤中的微卫星不稳定性类型

应用微切割 聚合酶链反应 单链长度多态性 (PCR SSLP)的方法 ,检测 1 6个微卫星位点在 5 9例 6 2个结直肠腺瘤标本的微卫星不稳定性状态 .结果表明 :腺瘤 1 6个位点的总微卫星不稳定性(microsatelliteinstability ,MSI)发生率为 1 4 4 % ,MSI H所占的比率为 9 7% ;在 1 0例可以同时微切割得到腺瘤和癌变成分的病例中 ,腺瘤和癌变成分在每个微卫星位点的改变情况不完全相同 ,并且当在某一位点同时表现为阳性时 ,部分凝胶电泳的图像相同 ,而部分不同 ;在某些位点表现为癌变成分的异常条带泳动速度更快 ,说明序列比腺瘤中更短 ;MSI H与病人的年龄、性别、腺瘤发生部位和病理学亚型之间未见统计学差异 ,但MSI H组的平均年龄 (5 6 5 0± 1 1 38)低于MSI L组 (6 0 36±1 1 34) ,女性所占比率 (5 6 )明显高于男性 ,6例MSI H中无 1例组织学类型为管状腺瘤 ;各位点在MSI H组的MSI改变率明显高于MSI L组 ,在TGFβRⅡ (A) 1 0 、hMSH6、TCF4、BAT2 6等位点有明显差异 (P <0 0 5 ,其中BAT2 6的P <0 0 1 ) .可以推断 :在结直肠癌发生发展的早期即腺瘤阶段即可表现微卫星不稳定性 ;微卫星不稳定性可以随结直肠肿瘤的发展过程而发展 ,并且特定的微卫星位点的改变可能仅发生于肿瘤进程的特定阶段 ;在结直肠癌     

Genetic Characteristics of Mitochondrial DNA Was Associated with Colorectal Carcinogenesis and Its Prognosis

Clinical value of mitochondrial DNA has been described in colorectal cancer (CRC). To clarify its role in colorectal carcinogenesis, mitochondrial microsatellite instability (mtMSI) and other markers were investigated in CRCs and their precancerous lesions, as a multitier genetic study. DNA was isolated from paired normal and tumoral tissues in 78 tubular adenomas (TAs), 34 serrated polyps (SPs), and 100 CRCs. mtMSI, nucleus microsatellite instability (nMSI), KRAS mutation, and BRAF mutation were investigated in these tumors and their statistical analysis was performed. mtMSI was found in 30% of CRCs and 21.4% of precancerous lesions. Mitochondrial copy number was higher in SPs than TAs and it was associated with mtMSI in low grade TAs. KRAS and BRAF mutations were mutually exclusive in TAs and SPs. CRCs with mtMSI showed shorter overall survival times than the patients without mtMSI. In CRCs without nMSI or BRAF mutation, mtMSI was a more accurate marker for predicting prognosis. The genetic change of mitochondrial DNA is an early and independent event in colorectal precancerous lesions and mtMSI and mitochondrial contents are associated with the tubular adenoma-carcinoma sequence, resulting in poor prognosis. This result suggested that the genetic change in mitochondrial DNA appears to be a possible prognosis marker in CRC.     

Missense mutations in hMLH1 associated with colorectal cancer

One of the most prevalent hereditary syndromes associated with colorectal cancer is hereditary nonpolyposis colorectal cancer (HNPCC). The inherited gene defects in HNPCC have been shown to reside in DNA mismatch repair genes, mostly hMSH2 or hMLH1. Most HNPCC patients are heterozygous with regard to the relevant mismatch repair gene; they have one normal and one mutated allele, and mismatch repair in normal somatic cells is functional. Cancer predisposition in HNPCC is believed to be associated with the loss of the wild-type allele in somatic cells, resulting in defective DNA mismatch repair. This gives rise to DNA microsatellite instability (MSI), an increased somatic mutation rate, and eventually, to the accumulation of mutations in genes involved in colorectal carcinogenesis. In support of this theory, colorectal tumors in HNPCC patients and in mice deficient for hMSH2 or hMLH1 show MSI. Here, we describe two missense mutations in hMLH1 exon 16 associated with colorectal cancer. Interestingly, the tumors do not show MSI. This raises some potentially important issues. First, even microsatellite-negative colorectal tumors can be associated with germline mutations and these will be missed if an MSI test is used to select patients for mutation screening. Second, the lack of MSI in these cases suggests that the mechanism involved in carcinogenesis could be different from that generally hypothesized.     

High-frequency microsatellite instability and BRAF mutation (V600E) in unselected Serbian patients with colorectal cancer

Microsatellite instability (MSI) is a genetic consequence of a MisMatch Repair defect in colorectal cancer (CRC). We compared clinicopathohistological features with MSI status of CRC and evaluated prognostic significance of MSI status and BRAF mutation in the group of MSI-H tumors. 155 primary CRCs were excised surgically, 2006–2008. MSI analysis was carried out using a fluorescence-based pentaplex polymerase chain reaction technique. BRAF mutation (V600E) was analyzed by direct sequencing in MSI-H tumors. For all patients were evaluated: age, gender, localization, tumor cell type, tumor differentiation, mucin production, lymphocytic infiltration (TILs) and TNM stage. Patients’ disease-free survival (DFS) was compared according to MSI and BRAF status using Kaplan–Meier test. Of the 155 CRCs, 19 (12.3%) were MSI-H, and 136 (87.7%) were MSS/L. BRAF mutations were found in 4 of the MSI-H tumors. Patients with MSI-H CRC had lower recurrence rate (log rank test; P = 0.04) than MSS/L group. Patients with MSI-H tumor and BRAF mutation had worse DFS than MSI-H tumors without this mutation (log rank test; P = 0.01). Most of the clinicopathologic characteristics of MSI-H CRC in Serbian patients are similar to those reported in previous studies. Patients with MSI tumor phenotype had favourable prognosis, but in those with BRAF mutation higher recurrence rate was observed.     

Genomic heterogeneity and instability in colorectal cancer: spectral karyotyping, glutathione transferase-Ml and ras

Genomic instability in cancer is frequently described as being either chromosomal instability or microsatellite instability, although when events within chromosomes are monitored, extensive intrachromosomal instability is also found. Spectral karyotyping was used to visualize how extensively genomic instability gives rise to intratumor genomic heterogeneity in sporadic colorectal carcinomas. Two factors were then examined which might relate to intrachromosomal instability in colorectal cancers: the presence of the glutathione transferase-Ml gene to detoxify potential carcinogens, and the presence of activated ras which has been associated with chromosomal instability when first expressed. Intrachromosomal genomic instability was previously determined by inter-(simple sequence repeat) PCR (inter-SSR PCR) and by fractional allelic loss rate for 348 markers. GSTM1 status was determined for each of 49 tumors through use of specific PCR, and 28 of the tumors showed the GSTM1 null genotype. A significant association was found between GSTMl-null status and elevated inter-(simple sequence repeat) PCR instability. In contrast, no association was found with fractional allelic loss rate. The first exons of the K-ras and H-ras oncogenes were sequenced in 72 colorectal cancers; 19 of the tumors had a mutation in codon 12 of the K-ras gene (24.5%), but no H-ras mutations were found. A weak correlation (p=0.10) was observed between mutant K-ras and inter-(simple sequence repeat) PCR genomic instability, and no association existed with fractional allelic loss rate.     

MSI-H colorectal cancers preferentially retain and expand intraepithelial lymphocytes rather than peripherally derived CD8<Superscript>+</Superscript> T cells

The healthy colorectal mucosa contains many resident intraepithelial lymphocytes (IELs) consisting of partially activated yet hyporesponsive CD8⁺ T cells. A predominant feature of colorectal cancers (CRCs) characterized by high levels of microsatellite instability (MSI-H) is heavy infiltration by an intraepithelial population of tumor infiltrating lymphocytes (iTILs). While it has been assumed that these iTILs originate from tumor infiltration by peripheral CD8⁺ effector T cells, their origin remains unknown. In light of the phenotypic and functional differences exhibited by IELs and peripheral T cells, elucidation of the precursor population of iTILs in MSI-H CRCs could clarify the role played by these lymphocytes in tumor progression. The aim of the present study was to investigate whether MSI-H CRCs interact differently with IEL- versus peripherally-derived CD8⁺ T cells. Using a Transwell assay system to mimic basolateral infiltration of tumor cells by lymphocytes, T cell migration, retention, proliferation and phenotypic alterations were investigated. Results indicate that MSI-H CRCs preferentially retain and expand IEL-derived cells to a greater degree than their microsatellite stable (MSS) counterparts. While MSI-H CRCs also retained more peripherally derived T cells, this number was considerably less than that from the IEL population. While interaction of IELs with either CRC type led to baseline lymphocyte activation, MSS CRCs induced upregulation of additional activation markers on retained IELs compared to MSI-H CRCs. These results suggest that the abundant iTILs present in MSI-H CRCs result from expansion of the preexisting mucosal IEL population and imply a limited prognostic role for iTILs in MSI-H CRC.     

Nonsense-mediated mRNA decay impacts MSI-driven carcinogenesis and anti-tumor immunity in colorectal cancers

Nonsense-mediated mRNA Decay (NMD) degrades mutant mRNAs containing premature termination codon (PTC-mRNAs). Here we evaluate the consequence of NMD activity in colorectal cancers (CRCs) showing microsatellite instability (MSI) whose progression is associated with the accumulation of PTC-mRNAs encoding immunogenic proteins due to frameshift mutations in coding repeat sequences. Inhibition of UPF1, one of the major NMD factors, was achieved by siRNA in the HCT116 MSI CRC cell line and the resulting changes in gene expression were studied using expression microarrays. The impact of NMD activity was also investigated in primary MSI CRCs by quantifying the expression of several mRNAs relative to their mutational status and to endogenous UPF1 and UPF2 expression. Host immunity developed against MSI cancer cells was appreciated by quantifying the number of CD3epsilon-positive tumor-infiltrating lymphocytes (TILs). UPF1 silencing led to the up-regulation of 1251 genes in HCT116, among which a proportion of them (i.e. 38%) significantly higher than expected by chance contained a coding microsatellite (P<2x10(-16)). In MSI primary CRCs, UPF1 was significantly over-expressed compared to normal adjacent mucosa (P<0.002). Our data provided evidence for differential decay of PTC-mRNAs compared to wild-type that was positively correlated to UPF1 endogenous expression level (P = 0.02). A negative effect of UPF1 and UPF2 expression on the host's anti-tumor response was observed (P<0.01). Overall, our results show that NMD deeply influences MSI-driven tumorigenesis at the molecular level and indicate a functional negative impact of this system on anti-tumor immunity whose intensity has been recurrently shown to be an independent factor of favorable outcome in CRCs.     

直结肠癌BUBR1的过度表达与TP53突变及微卫星状态关系提示其过度表达与染色体不稳定表型有关

在有丝分裂过程中BUBR1监视微管与着丝点的结合,是保证染色体均等分离的重要分子机制之一.BUBIB变异家谱研究及其敲除模型的研究表明,BUBR1缺陷与染色体不稳定性及肿瘤的发生直接相关.近来在数种人类肿瘤,对BUBR1蛋白过度表达有所报道.但在直结肠癌,BUBR1的过度表达是否与染色体不稳定性的发生有关目前仍无定论.在人类结直肠癌的遗传不稳定性主要表现为两种类型,染色体不稳定性及微卫星不稳定性,它们提示了两条独立的肿瘤发生路径.一般认为不存在高频度微卫星不稳定性表型的肿瘤通过染色体不稳定途径癌变.P53蛋白通过多种机制对维护遗传稳定性起到重要的作用,TP53基因突变经常与染色体不稳定现象并存.DNA倍体情况也是染色体不稳定研究不可缺少的指标.本研究采用免疫组织化学法检测了一组93例进展期散发结直肠癌BUBR1蛋白的表达情况,直接测序法检测TP53变异.高分辨率荧光标记微卫星不稳定检测技术检测微卫星状态,固相激光扫描细胞仪技术检测DNA倍体情况.我们分析了BUBR1表达与三种反映遗传背景的因子的关系.BUBR1蛋白过度表达在人结直肠癌较为常见.在非高频度微卫星不稳定的结直肠癌,BUBR1蛋白过度表达率明显为高(P＜0.01),在TP53基因突变的病例其过度表达率亦较高(P＜0.05).BUBR1蛋白的过度表达与DNA异倍体无统计学相关,但DNA异倍体病例的BuBRl过度表达有偏高倾向.BuBRl表达情况与常用的临床病理学指标无统计学相关.BuBRl过度表达同微卫星状态及TP53突变的关系明确的提示,在人类散发结直肠癌,BUBR1蛋白过度表达与染色体不稳定状态有关.BUBR1过度表达作为一种常见的分子异常,对于肿瘤的早诊预防提供新的标志物.并可能成为治疗的新靶点.