Analysis of Ki-ras gene mutations associated with DNA diploid, aneuploid, and multiploid colorectal carcinomas using a crypt isolation technique.

BACKGROUND AND AIM: Current evidence suggests a possible relationship between DNA ploidy status and Ki-ras gene mutations in human cancers. However, the conventional method does not enable accurate determination of DNA ploidy status of a tumor cell. The present study attempts to clarify whether Ki-ras gene mutations are associated with DNA ploidy status in sporadic colorectal carcinomas using a crypt isolation technique coupled with DNA cytometric sorting. METHODS: Polymerase chain reaction and single-strand conformation polymorphism and direct sequencing were used to analyze Ki-ras gene mutations in 82 sporadic colorectal carcinomas: 21 diploid, 12 aneuploid, and 49 multiploid. In addition, microsatellite instability (MSI) was assessed using seven microsatellite markers to study the relationship to Ki-ras mutations. RESULTS: Ki-ras mutations were found in 12 of 21 diploid carcinomas and in 8 of 12 aneuploid carcinomas. In contrast, Ki-ras gene mutations were detected infrequently in the 34 multiploid carcinomas examined, 8 of which were seen in diploid populations and 10 in aneuploid populations. On the other hand, Ki-ras gene mutations were inversely correlated with MSI, which was found in diploid carcinomas only. CONCLUSIONS: The low frequency of Ki-ras gene mutations that we observed in multiclonal colorectal carcinomas suggests that development of multiclonal colorectal carcinoma may involve a mechanism different from that involved in the development of diploid or aneuploid colorectal carcinomas.     

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.     

New mutations in the human p53 gene — a regulator of the cell cycle and carcinogenesis

Mutations in the tumor suppressor gene p53 often lead to disarrangement of the cell cycle and of genetic integrity control of cells that may contribute to tumor development. We studied p53 gene mutations in 26 primary tumors of colorectal cancer patients. Mutations in p53 were found in 17 tumors (65.4%). All point mutations affected the DNA binding domain of p53 and were localized in exons 4-8 of the gene. Mutant p53 isoforms with altered domain structure and/or with alternative C-terminus arising from frameshift mutations or abnormal splicing were found in six tumors. Mutations Leu111Gln and Ser127Phe were shown in colorectal cancer for the first time. Isoforms p53-305 with C(4) insertion in codons 300/301 and p53i9* including an additional 44 nucleotides of the 3 -end of intron 9 were discovered for the first time. Mutations of p53 were associated with lymph node metastases and III/IV stage of tumors that are signs of unfavorable prognosis in colorectal cancer.     

Prognostic significance of proliferative activity, DNA-ploidy, p53 and Ki-ras point mutations in colorectal liver metastases

Paired colorectal liver metastases (CLM) and normal tissue samples from a consecutive series of 36 patients were studied prospectively. MIB-1 expression was studied by immunohistochemistry on paraffin-embedded sections. DNA ploidy and S-phase fraction (SPF) measurements were performed by flow cytometry on frozen tissues. Mutations within the p53 (exons 5-8) and c- Ki-ras (codons 12 and 13) genes were detected by PCR single-strand conformation polymorphism analysis followed by sequencing. A high correlation was observed between the MIB-1 LI and SPF value (rho=0.81; P <0.01). Moreover, p53 gene mutations were associated with either high MIB-1 LI and high SPF. In univariate analysis, SPF and MIB-1 levels were related to risk of death. The association between overall survival and DNA-ploidy or p53 mutations did not reach statistical significance, but a slightly better survival was observed for patients either with DNA-diploid tumours or without mutations ( P =0.05 and P =0.06, respectively). SPF was shown by multivariate Cox model analysis to be an independent prognostic variable and thus it might be a useful prognostic factor in patients with CLM.     

Characterization of p21Ras-mediated apoptosis induced by protein kinase C inhibition and application to human tumor cell lines

Suppression of PKC activity can selectively induce apoptosis in cells expressing a constitutively activated p21Ras protein. We demonstrate that continued expression of p21Ras activity is required in PKC-mediated apoptosis because farnesyltransferase inhibitors abrogated the loss of viability in p21Ras-transformed cells occurring following PKC inhibition. Studies utilizing gene transfer or viral vectors demonstrate that transient expression of oncogenic p21Ras activity is sufficient for induction of apoptosis by PKC inhibition, whereas physiologic activation of p21Ras by growth factor is not sufficient to induce apoptosis. Mechanistically, the p21Ras-mediated apoptosis induced by PKC inhibition is dependent upon mitochondrial dysregulation, with a concurrent loss of mitochondrial membrane potential (psim). Cyclosporine A, which prevented the loss of psim, also inhibited HMG-induced DNA fragmentation in cells expressing an activated p21Ras. Induction of apoptosis by PKC inhibition in human tumors with oncogenic p21Ras mutations was demonstrated. Inhibition of PKC caused increased apoptosis in MIA-PaCa-2, a human pancreatic tumor line containing a mutated Ki-ras allele, when compared to HS766T, a human pancreatic tumor line with normal Ki-ras alleles. Furthermore, PKC inhibition induced apoptosis in HCT116, a human colorectal tumor line containing an oncogenic Ki-ras allele but not in a subline (Hke3) in which the mutated Ki-ras allele had been disrupted. The PKC inhibitor 1-O-hexadecyl-2-O-methyl-rac-glycerol (HMG), significantly reduced p21Ras-mediated tumor growth in vivo in a nude mouse MIA-PaCa-2 xenograft model. Collectively these studies suggest the therapeutic feasibility of targeting PKC activity in tumors expressing an activated p21Ras oncoprotein.     

p53突变蛋白在胃癌组织中的表达及免疫电镜观察

作者应用抗ｐ５３单克隆抗体Ｐａｂ１８０１（Ａｂ２美国癌基因公司产品）对３８例手术切除的胃癌组织及癌旁胃粘膜的冰冻切片标本进行ｐ５３突变蛋白表达的检测,并进一步用胶体全免疫电镜技术对ｐ５３突变蛋白的分布特征进行观察。结果：３８例胃癌组织中,２４例有ｐ５３突变蛋白高表达,阳性率６３．２％。在对应的癌旁胃粘膜中１０例为ｐ５３的弱表达,正常组织无表达。伴有淋巴结转移的２３例胃癌标本中,１８例ｐ５３高表达（７８．３％）。免疫电镜结果表现,ｐ５３蛋白主要分布于核内染色质中,胞浆中有散在的阳性区,但以核膜周边为主,紧靠核膜。本研究结果提承胃癌的发生及其肿瘤的生物学行为与抑癌基因ｐ５３的突变密切相关,ｐ５３突变蛋白可能是通过对ＤＮＡ复制的影响而参与肿瘤的形成。     

Mutation analysis of p53, K-ras, and BRAF genes in colorectal cancer progression

Gene mutations in APC, K-ras, and p53 are thought to be essential events for colorectal cancer development. Recent data seem to indicate that K-ras and p53 mutations rarely co-exist in the same tumor, indicating that these alterations do not represent a synergistic evolutionary pathway. Moreover, an inverse relation between K-ras gene activation and BRAF mutations has been demonstrated, suggesting alternative pathways for colorectal cancer transformation. To reconstruct the chronological modulation of these gene mutations during cell transformation and colorectal cancer progression, mutations of p53, K-ras, and BRAF genes were analyzed by Single Strand Conformation Polymorphism (SSCP) or sequencing analysis in 100 colorectal cancer samples, evenly distributed among different Dukes' stages. We found mutations in p53, K-ras, and BRAF genes in 35%, 30%, and 4% of tumors, respectively, and observed a minimal or no co-presence of these gene alterations. Moreover, the frequency of molecular p53 mutations increased as tumor stage increased, suggesting an important role for this gene in the progression of colorectal cancer. Conversely, K-ras or BRAF genes were not related to tumor stage or location. These data seem to indicate the absence of a co-presence of the genes, highlighting the possibility of multiple pathways for colorectal tumor progression. Moreover, mutations in p53, K-ras, and BRAF are not present in about one-third of colorectal cancers and therefore other gene mutations need to be investigated to better understand molecular mechanisms at the basis of cell transformation and the progression of colorectal cancer.     

散发性大肠癌组织及粪便脱落细胞p53蛋白的检测

为了解大肠癌组织及粪便脱落细胞中 p5 3蛋白表达对大肠癌诊断的临床意义 ,采用 S- P法对 38例大肠癌患者的癌组织及其中的 30例患者的粪便脱落细胞 p5 3蛋白进行检测。大肠癌组织中 p5 3蛋白阳性表达率为 39.47% (15 / 38) ,p5 3蛋白阳性与癌组织的分化程度及是否存在淋巴结转移均无相关性 (P>0 .0 5 )。粪便脱落细胞 p5 3蛋白阳性表达率为 36 .6 7%(11/ 30 ) ,脱落细胞与相应患者的癌组织中的 p5 3表达一致率为 83.33% (2 5 / 30 )。表明粪便中脱落细胞 p5 3蛋白的表达忠实反映了相应癌组织的 p5 3突变情况 ,对其检测有望成为大肠癌诊断及筛查的无创分子途径。同时表明粪便中脱落细胞核保持了肿瘤抗原决定簇的主要结构及生物特征 ,进行免疫细胞化学检测是可行的 ,为进行脱落细胞核其它肿瘤标志物或其它生物研究奠定了可行性的基础     

Frequent alteration of MLL3 frameshift mutations in microsatellite deficient colorectal cancer

Background

MLL3 is a histone 3- lysine 4 methyltransferase with tumor-suppressor properties that belongs to a family of chromatin regulator genes potentially altered in neoplasia. Mutations in MLL3 were found in a whole genome analysis of colorectal cancer but have not been confirmed by a separate study.

Methods and Results

We analyzed mutations of coding region and promoter methylation in MLL3 using 126 cases of colorectal cancer. We found two isoforms of MLL3 and DNA sequencing revealed frameshift and other mutations affecting both isoforms of MLL3 in colorectal cancer cells and 19 of 134 (14%) primary colorectal samples analyzed. Moreover, frameshift mutations were more common in cases with microsatellite instability (31%) both in CRC cell lines and primary tumors. The largest isoform of MLL3 is transcribed from a CpG island-associated promoter that has highly homology with a pseudo-gene on chromosome 22 (psiTPTE22). Using an assay which measured both loci simultaneously we found prominent age related methylation in normal colon (from 21% in individuals less than 25 years old to 56% in individuals older than 70, R = 0.88, p<0.001) and frequent hypermethylation (83%) in both CRC cell lines and primary tumors. We next studied the two loci separately and found that age and cancer related methylation was solely a property of the pseudogene CpG island and that the MLL3 loci was unmethylated.

Conclusions

We found that frameshift mutations of MLL3 in both CRC cells and primary tumor that were more common in cases with microsatellite instability. Moreover, we have shown CpG island-associated promoter of MLL3 gene has no DNA methylation in CRC cells but also primary tumor and normal colon, and this region has a highly homologous of pseudo gene (psiTPTE22) that was age relate DNA methylation.     

Low levels of p27 in association with deregulated p53-pRb protein status enhance tumor proliferation and chromosomal instability in non-small cell lung carcinomas

BACKGROUND: Down-regulation or overexpression of the cyclin-dependent kinase inhibitor p27 have been observed in a range of malignancies, including lung cancer. To further elucidate the role of the molecule in tumor growth regulation, we evaluated p27 expression in a series of non-small cell lung carcinomas (NSCLCs), and examined its relation with histology, kinetic parameters, ploidy, and overall survival. We extended our investigation into the association of p27 levels with the presence of Ki-ras mutations, as well as with the expression status of p53 and pRb in tumor cells. MATERIAL AND METHODS: p27, p53, and pRb status were immunohistochemically evaluated in a total of 69 NSCLCs. In situ assays were employed to assess the kinetic parameters (Ki-67 immunohistochemistry for proliferation index, Tdt-mediated dUTP nick end labeling assay for apoptotic index). The ploidy status of the tumors was assessed after staining nuclei with the Feulgen procedure, and the presence of Ki-ras mutations was examined by restriction fragment length polymorphisms. All possible associations were assessed with a series of statistical methods. RESULTS: Immunoreactivity for p27 was observed in the entire series of specimens, with the mean percentage of positive cells being 33%. Adenocarcinomas (AdCs) exhibited higher p27 levels compared to squamous cell carcinomas (SqCCs) (p < 0.01). An inverse correlation was established between p27 expression and proliferation index (PI) (r = -0.834, p < 0.01) but not with apoptotic index (AI), whereas aneuploid tumors were characterized by lower p27 levels than diploid ones (p < 0.01). No difference in p27 immunostaining was observed with regard to the presence of Ki-ras mutations, whereas aberrant p53 and/or pRb expression patterns were associated with p27 underexpression (p < 0.01 for p53 status, p < 0.05 regarding pRb levels, and p < 0.01 for a combined deregulation of both proteins). Two or more alterations in the p27/p53/pRb protein network (i.e., p27 levels lower than the estimated mean value, overexpressed p53, and/or aberrant pRb) were associated with increased PI and aneuploidy (p < 0.001 and p < 0.01, respectively). A powerful trend was found between p27 expression and overall survival (p = 0.066). CONCLUSIONS: Our findings confirm the heterogeneity between AdCs and SqCCs, and are suggestive of an increased proliferative activity in NSCLCs underexpressing p27. Furthermore, our analysis supports the concept of p27 forming a functionally compact network with p53 and pRb, which is actively involved in the regulation of cellular proliferation and chromosomal stability.     

p16基因甲基化状态与散发性大肠癌的相关性研究

为探讨p1 6基因甲基化状态与散发性大肠癌发生发展的关系 ,用甲基化特异性的聚合酶链反应 (methylati omspecificPCR ,MSP)结合测序检测散发性大肠癌及相应癌旁组织p1 6基因甲基化状态。研究发现p1 6基因在散发性大肠癌中甲基化率为 2 8 9% (1 3 4 5 ) ,有 8例癌及癌旁组织都发生了甲基化 ;有淋巴结及远处转移的甲基化率为5 0 % (8 1 6 ) ,高于无转移的甲基化率 2 0 8(5 2 4 ) (P <0 0 5 )。p1 6基因高甲基化是散发性大肠癌中常见的分子改变之一 ,大肠癌中p1 6基因高甲基化可能发生在癌变早期并与大肠癌的恶性进展有相关性     

Angiogenesis and p53 and H-ras mutations in pancreatic ductal adenocarcinoma

OBJECTIVE: To evaluate the correlation of angiogenesis and p53 and H-ras mutations with prognostic factors and proliferative activity assessed with Ki-67 protein expression by studying archival tissues from 24 patients with primary pancreatic ductal adenocarcinoma. STUDY DESIGN: Vascular structures were labeled immunohistochemically using factor VIII-related antigen. Vascular surface density (VSD) and microvessel number (NVES) were assessed by stereology. The tissues were also analyzed with the immunohistochemical method for the expression of proteins, including p53, H-ras and Ki-67. RESULTS: Statistical analysis revealed that tumors with greater NVES and VSD values significantly correlated with occurrence of metastases, higher proliferative activity, poorer histologic differentiation and greater tumor size. p53 Mutations were found in 11 cases (45.8%). However, only three cases (12.5%), all negative for p53 mutations, showed H-ras mutations. p53 Mutation-positive tumors exhibited a statistically significant correlation with occurrence of metastases and higher proliferative activity, whereas H-ras mutations did not show such a correlation. CONCLUSION: Angiogenesis might have a role in predicting prognosis in pancreatic carcinomas, and p53 mutations might be acquired in later stages associated with metastatic progression and higher proliferative activity. Although H-ras mutations were rare in the present study, they might play a role in a different carcinogenic pathway excluding p53 mutations.     

Human Papillomavirus and Cystic Node Metastasis in Oropharyngeal Cancer and Cancer of Unknown Primary Origin

The clinical significance of human papillomavirus (HPV) in neck node metastasis from cancer of unknown primary (CUP) is not well established. We aimed to address the relationship of HPV status between node metastasis and the primary tumor, and also the relevance of HPV status regarding radiographically detected cystic node metastasis in head and neck squamous cell carcinoma (HNSCC) and CUP. HPV DNA was examined in 68 matched pairs of node metastasis and primary tumor, and in node metastasis from 27 CUPs. In surgically treated CUPs, p16 was examined immunohistochemically. When tonsillectomy proved occult tonsillar cancer in CUP, HPV DNA and p16 were also examined in the occult primary. Cystic node metastasis on contrast-enhanced computed tomography scans was correlated with the primary site and HPV status in another series of 255 HNSCCs and CUPs with known HPV status. Node metastasis was HPV-positive in 19/37 (51%) oropharyngeal SCCs (OPSCCs) and 10/27 (37%) CUPs, but not in non-OPSCCs. Fluid was collected from cystic node metastasis using fine needle aspiration in two OPSCCs and one CUP, and all fluid collections were HPV-positive. HPV status, including the presence of HPV DNA, genotype, and physical status, as well as the expression pattern of p16 were consistent between node metastasis and primary or occult primary tumor. Occult tonsillar cancer was found more frequently in p16-positive CUP than in p16-negative CUP (odds ratio (OR), 39.0; 95% confidence interval (CI), 1.4–377.8; P = 0.02). Radiographically, cystic node metastasis was specific to OPSCC and CUP, and was associated with HPV positivity relative to necrotic or solid node metastasis (OR, 6.2; 95% CI, 1.2–45.7; P = 0.03). In conclusion, HPV status remains unchanged after metastasis. The occult primary of HPV-positive CUP is most probably localized in the oropharynx. HPV status determined from fine needle aspirates facilitates the diagnosis of cystic node metastasis.     

Efficient introduction of specific TP53 mutations into mouse embryonic fibroblasts and embryonic stem cells

This protocol describes a rapid, precise method for generating sets of embryonic stem (ES) cells or mouse embryonic fibroblasts (MEFs) harboring point mutations in the p53 tumor suppressor gene (officially known as Trp53). The strategy uses cells from the Trp53 (p53-null) 'platform' mouse, which allows site-specific integration of plasmid DNA into the Trp53 locus. Simple PCR protocols identify correctly targeted clones and immunoblots verify re-expression of the protein. We also present protocol modifications needed for efficient recovery of MEF clones expressing p53 constructs that retain wild-type function, including growth at low (3%) oxygen and transient downregulation of p53 regulators to forestall cell senescence of primary MEFs. A library of cell lines expressing various p53 mutants derived from the same population of primary fibroblasts or platform ES cells can be acquired and screened in less than 1 month.     

结直肠癌mP53 和PCNA 表达的相关性及临床意义

目的:探讨结直肠癌中突变型P53基因(mP53)和增殖细胞核抗原(PCNA)表达的相关性及临床意义。方法:应用免疫组化二步法,检测60例结直肠癌组织及20例正常肠粘膜中mP53、PCNA的表达,结合临床病理资料进行统计分析。结果:60例结直肠癌中mP53阳性表达率65.0%,PCNA阳性表达率78.3%,20例正常肠粘膜中mP53、PCNA表达均为阴性(P<0.05)。mP53和PCNA阳性表达率在低分化组、浆膜层浸润组、淋巴结转移组均较高(P均<0.05)。mP53和PCNA表达呈正相关(r=0.58,P<0.05)。结论:mP53和PCNA在结直肠癌中表达均增高,二者与结直肠癌病理学分级、浸润深度和淋巴结转移有关,可作为判断结直肠癌预后的参考指标。     

Comparative study of the expression of Rb and p53 genes in human colorectal cancers,colon carcinoma cell lines and synchronized human fibroblasts

We have compared the expression of the retinoblastoma (Rb) and p53 genes in normal human fibroblasts, colon carcinoma cell lines, matched pairs of colorectal tumor tissues and adjacent normal mucosa and in synchronized human diploid fibroblast cell line W138. The increased expression of Rb and p53 RNA was observed in a majority of colorectal cancers in comparison to adjacent normal mucosa and is accompanied by proportional increase in the expression of histone H3 gene. The Rb and p53 RNA levels varied significantly between the various colon carcinoma cell lines. However, we found that the expression of Rb and p53 RNA is regulated differently in cell cycle synchronized normal human fibroblasts. The Rb mRNA level did not change with the position in the cell cycle and did not differ significantly whether the cells were serum deprived or in 10% serum. But p53 mRNA expression follows the same pattern as histone H3 mRNA.     

Lifestyle factors and Ki-ras mutations in colon cancer tumors

Heterogeneity in colon tumors implies that environmental, lifestyle, or genetic factors influence the type of mutations seen in tumors. In this study we evaluate the association between previously identified risk factors for colon cancer and Kirsten-ras (Ki-ras) mutations in tumors. The presence of Ki-ras mutations in codons 12 and 13 were determined in a population-based case-control study of colon cancer. Participants were between 30 and 79 years of age at time of diagnosis and include both men and women. Questionnaire data were used to obtain information on lifestyle factors. Valid study data and Ki-ras mutational status were available from 1428 cases of colon cancer, data from 2410 controls were available for comparative purposes. Participants with Ki-ras mutations were more likely to have proximal rather than distal tumors. Cigarette smoking, use of aspirin and/or NSAIDs, use of vitamin/mineral supplements, and consumption of caffeine were associated with both Ki-ras+ and Ki-ras- tumors; the associations were not confounded by dietary intake or other lifestyle factors. Among men, but not among women, those with low levels of physical activity were more likely to have a tumor with a Ki-ras mutation than one without a Ki-ras mutation. However, among women, those with a larger BMI were more likely to have a Ki-ras mutation in their tumor. Given the limited information available on what causes Ki-ras mutations, the information generated from this study indicates that these factors previously associated with colon cancer work through other disease pathways.     

Have p53 gene mutations and protein expression a different biological significance in colorectal cancer?*

p53 alterations are considered the most common genetic events in many types of neoplasms, including colorectal carcinoma (CRC). These alterations include mutations of the gene and/or overexpression of the protein. The aim of our study was to assess whether in 160 patients undergoing resective surgery for primary operable CRC there was an association between p53 mutations and protein overexpression and between these and other biological variables, such as cell DNA content (DNA-ploidy) and S-phase fraction (SPF), and the traditional clinicopathological variables. p53 mutations, identified by PCR-SSCP-sequencing analysis, were found in 68/160 patients (43%) and positive staining for p53 protein, detected with the monoclonal antibody DO-7, was present in 48% (77/160) of the cases, with agreement of 57% (91/160). In particular, a significant association was found between increased p53 expression and genetic alterations localized in the conserved regions of the gene or in the L3 DNA-binding domain and the specific type of mutation. Furthermore, both overexpression of p53 and mutations in the conserved areas of the gene were found more frequently in distal than in proximal CRCs, suggesting that they might be "biologically different diseases." Although p53 mutations in conserved areas were associated with flow cytometric variables, overexpression of p53 and mutations in its L3 domain were only related respectively to DNA-aneuploidy and high SPF. These data may reflect the complex involvement of p53 in the different pathways regulating cell-cycle progression. In conclusion, the combination of the mutational status and immunohistochemistry of p53, and flow cytometric data may provide an important insight into the biological features of CRCs.