癌基因与抑癌基因的表达研究进展

肿瘤的发生发展本质上是细胞原癌基因的激活和抑癌基因的失活造成的.癌基因和抑癌基因的研究对探索肿瘤发病机制,寻找预防和治疗肿瘤的新措施具有重要意义.本文较全面地介绍了癌基因和抑癌基因的种类以及它们对细胞的调控作用和致癌、抑癌的分子机制,特别是总结了近年来癌基因及抑癌基因的研究进展.     

基因在儿童急性淋巴细胞白血病中异常表达的特点

目的:研究转录因子基因BCL6、KLF5及核仁蛋白基因NCL在急性淋巴细胞白血病(acute lymphoblastic leukemia,ALL)患儿骨髓细胞中的表达情况及其在不同疾病状态下的表达特点。方法:选取北京儿童医院2004年1月至2005年12月住院ALL患儿100例,另取由于骨骼畸形而在北京儿童医院进行外科手术的5例非ALL患儿作对照;以基因芯片检测ALL患儿骨髓细胞中异常表达基因,GeXP多重基因表达分析系统检测BCL6、KLF5、NCL基因在另外选取的10例配对ALL患儿初诊及缓解期的表达变化。结果:基因芯片筛查发现,在100例各亚型ALL标本中,BCL6和KLF5mRNA表达均下调,NCLmRNA表达均上调。BCL6和KLF5mRNA在10例ALL初诊患儿骨髓细胞中表达较低,完全缓解后表达升高(0.380±0.16vs0.850±0.10,0.074±0.021vs0.228±0.049;均P<0.01);NCLmRNA在ALL初诊患儿骨髓细胞中表达较高,完全缓解后表达降低(0.234±0.054vs0.151±0.055,P<0.01)。在10例配对患者儿中,TEL-AML1阳性及E2A-PBX1阳性组患儿的初诊及缓解期骨髓细胞中,该3个基因在两组中的表达变化趋势一致。结论:ALL患儿骨髓细胞中BCL6、KLF5基因在初诊时表达下调、在临床缓解后表达上调,NCL基因初诊时上调、临床缓解后下调;该3个基因似可作为白血病的分子标志物及效疗的监测指标。     

BCL6、KLF5、NCL基因在儿童急性淋巴细胞白血病中异常表达的特点

目的:研究转录因子基因BCL6、KLF5及核仁蛋白基因NCL在急性淋巴细胞白血病(acute lymphoblastic leukemia,ALL)患儿骨髓细胞中的表达情况及其在不同疾病状态下的表达特点。方法:选取北京儿童医院2004年1月至2005年12月住院ALL患儿100例,另取由于骨骼畸形而在北京儿童医院进行外科手术的5例非ALL患儿作对照;以基因芯片检测ALL患儿骨髓细胞中异常表达基因,GeXP多重基因表达分析系统检测BCL6、KLF5、NCL基因在另外选取的10例配对ALL患儿初诊及缓解期的表达变化。结果:基因芯片筛查发现,在100例各亚型ALL标本中,BCL6和KLF5mRNA表达均下调,NCLmRNA表达均上调。BCL6和KLF5mRNA在10例ALL初诊患儿骨髓细胞中表达较低,完全缓解后表达升高(0.380±0.16vs0.850±0.10,0.074±0.021vs0.228±0.049;均P<0.01);NCLmRNA在ALL初诊患儿骨髓细胞中表达较高,完全缓解后表达降低(0.234±0.054vs0.151±0.055,P<0.01)。在10例配对患者儿中,TEL-AML1阳性及E2A...     

Aberrant methylation in promoter-associated CpG islands of multiple genes in acute lymphoblastic leukemia

Methylation profile was analyzed in 10 childhood acute lymphoblastic leukemia (ALL) and nine adult ALL cases. Four genes (p15, p16, RARbeta, FHIT) had methylation in both diseases, four genes (p14, Rb, MLH1, DAPK) showed no methylation in both diseases, and the two genes (APC, RIZ) demonstrated methylation only in adult ALL. Methylation of the RARbeta was more frequent in adult ALL than that in childhood ALL (p=0.01). The number of patients with methylation of multiple genes was higher in adult ALL than that in childhood ALL (p=0.006). Moreover, overall frequency of methylation was higher in adult ALL than that in childhood ALL (p=0.01).     

Significance of oncogenes and tumor suppressor genes in AML prognosis

Acute myeloid leukemia (AML) is a heterogeneous disorder among hematologic malignancies. Several genetic alterations occur in this disease, which cause proliferative progression, reducing differentiation and apoptosis in leukemic cells as well as increasing their survival. In the genetic study of AML, genetic translocations, gene overexpression, and mutations effective upon biology and pathogenesis of this disease have been recognized. Proto-oncogenes and tumor suppressor genes, which are important in normal development of myeloid cells, are involved in the regulation of cell cycle and apoptosis, undergo mutation in this type of leukemia, and are effective in prognosis of AML subtypes. This review deals with these genes, the assessment of which can be important in the diagnosis and prognosis of patients as well as therapeutic outcome.     

Jak3 expression and genomic sequence in pediatric acute lymphoblastic leukemia

Janus tyrosine kinase 3 (JAK3) is one of several key regulatory enzymes in B-cell precursors which is highly conserved between multiple species. The gene for Jak3 has been mapped to human chromosome 19p12-13.1 and encompasses 23 exons. Constitutively high levels of JAK3 activity may contribute to drug resistance and enhanced clonogenicity of leukemic B-cell precursors from children and infants with acute lymphoblastic leukemia (ALL). As part of a systematic effort to accurately determine the genomic sequence of Jak3 gene in normal and leukemic B-cell precursors, we sequenced a relatively short region of Jak3 spanning two introns, originally termed introns 10 and 11. This genomic sequence appeared in certain RT-PCR products from our analysis of Jak3 gene expression in pediatric, as well as infant, primary ALL cells. Unexpectedly, a gap in the original Jak3 genomic sequence was found in intron 10 across the sequence matching to an Alu element. Furthermore, the sequence obtained from intron 11 did not match at all to that previously reported, and the length of the intron was much larger than expected at 1.1 kb. Homology to Alu elements (three regions, 699 bp total) and a LINE2 element (one region, 189 bp total) were seen across the entire region covering exons 10-12 (2.1 kb total). Two potential single nucleotide polymorphisms (SNPs) were observed in intron 11. No apparent genomic mutation was found across this region in leukemic B-cell precursors from any of the ALL patients examined. This newly described sequence corrects the previous published genomic sequence from this region rather than identifying an insertion or translocation specific to these ALL cases. Our results significantly extend previous efforts to determine the genomic sequence of Jak3 and analyze its expression in childhood pro-B ALL and other forms of ALL.     

Osteonecrosis in pediatric patients with acute lymphoblastic leukemia

The authors report five pediatric patients with acute lymphoblastic leukemia (ALL) in whom symptomatic aseptic osteonecrosis developed on therapy. All patients had been on treatment with a modified BFM protocol and developed osteonecrosis in the maintenance phase of the protocol. The avascular necrosis was multifocal in all. The authors' data suggest that dexamethasone used in the reinduction phase of the protocol may be the responsible agent although no definite proof exists. Since only symptomatic patients are reported, the true frequency of this complication may be significantly higher.     

High expression of Myosin 1g in pediatric acute lymphoblastic leukemia

Acute Lymphoblastic Leukemia (ALL) is the most frequent cancer in pediatric population. Although the treatment has improved and almost 85% of the children are cured about 20% suffer relapse, therefore finding molecules that participate in the pathogenesis of the disease for the identification of relapse and patients at risk is an urgent unmet need. Class I myosins are molecular motors involved in membrane tension, endocytosis, phagocytosis and cell migration and recently they have been shown important for development and aggressiveness of diverse cancer types, however Myo1g an hematopoietic specific myosin has not been studied in cancer so far. We evaluated the expression of Myo1g by qRT-PCR, Immunocytochemistry and Immunofluorescence in a cohort of 133 ALL patients and correlated the expression at diagnosis and after treatment with clinical features and treatment outcomes. We found high expression levels of Myo1g in Peripheral Blood Mononuclear Cells (PBMCs) from patients with ALL at diagnosis and those levels decreased after complete remission; furthermore, we found an increase in Myo1g expression on patients with 9:22 translocation and those who relapse. This study show that Myo1g is over expressed in ALL and that may participate in the pathogenesis of the disease specially in high-risk patients.     

Aberrant methylation of candidate tumor suppressor genes in neuroblastoma

CpG island hypermethylation has been recognized as an alternative mechanism for tumor suppressor gene inactivation. In this study, we performed methylation-specific PCR (MSP) to investigate the methylation status of 10 selected tumor suppressor genes in neuroblastoma. Seven of the investigated genes (CD44, RASSF1A, CASP8, PTEN, ZMYND10, CDH1, PRDM2) showed high frequencies (> or =30%) of methylation in 33 neuroblastoma cell lines. In 42 primary neuroblastoma tumors, the frequencies of methylation were 69%, CD44; 71%, RASSF1A; 56%, CASP8; 25%, PTEN; 15%, ZMYND10; 8%, CDH1; and 0%, PRDM2. Furthermore, CASP8 and CDH1 hypermethylation was significantly associated with poor event-free survival. Meta-analysis of 115 neuroblastoma tumors demonstrated a significant correlation between CASP8 methylation and MYCN amplification. In addition, there was a correlation between ZMYND10 methylation and MYCN amplification. The MSP data, together with optimized mRNA re-expression experiments (in terms of concentration and time of treatment and use of proper reference genes) further strengthen the notion that epigenetic alterations could play a significant role in NB oncogenesis. This study thus warrants the need for a global profiling of gene promoter hypermethylation to identify genome-wide aberrantly methylated genes in order to further understand neuroblastoma pathogenesis and to identify prognostic methylation markers.     

Aberrant methylation in promoter-associated CpG islands of multiple genes in relapsed childhood acute lymphoblastic leukemia

Methylation profile was analyzed in nine cases of relapsed childhood acute lymphoblastic leukemia (ALL) for p14, p15, p16, Rb, MGMT, APC, hMLH1, RARbeta, RIZ, DAPK, and FHIT genes by using methylation specific polymerase chain reaction (MSP) analysis. Frequency of methylation in each gene was: MGMT, 56%; RARbeta, 44%; and p16, 22%, respectively. None of the p14, p15, Rb, APC, hMLH1, RIZ, DAPK, and FHIT genes were hypermethylated. Five (56%) of 9 cases showed methylation of at least one gene. All of the samples with hypermethylation in p16 and MGMT gene at relapse, had already acquired the change at the time of initial diagnosis. Interestingly, three of 4 cases with RARbeta gene methylation at relapse did not have methylation of this gene at the time of initial presentation. These results suggest that hypermethylation might be involved in the relapse of childhood ALL.     

Aberrant DNA methylation in pediatric patients with acute lymphocytic leukemia

BACKGROUND: Aberrant methylation of promoter-associated cystosine-guanine (CpG) islands is an epigenetic modification of DNA frequently observed in adult patients with acute lymphocytic leukemia (ALL). This epigenetic modification has been associated with gene silencing, malignant transformation, and aging. It is not known whether there are epigenetic differences between pediatric patients and adult patients with ALL. METHODS: To investigate the methylation characteristics of pediatric patients with ALL and to determine whether DNA methylation can explain prognostic or biologic differences between pediatric and adult patients, the authors analyzed the methylation status of 7 promoter-associated CpG islands in 16 pediatric patients with ALL and compared them with the methylation characteristics of a cohort of adult patients with ALL. The genes analyzed included the estrogen receptor gene (ER), multidrug resistance gene 1 (MDR1), p15, C-ABL, CD10, p16, and p73. RESULTS: The mean methylation densities of ER, MDR1, CD10, p15, and C-ABL were 25.4%, 16.4%, 5.23%, 4.24%, and 4%, respectively. P16 was methylated in 11.7% of patients, and p73 was methylated in 17.6% of patients. One patient (6.2%) had methylation of 0 genes, 15 patients (93.7%) had methylation of >/= 1 gene, and 4 patients (25%) had methylation of 3-4 genes. Methylation of all these genes was < 2% (or methylation specific polymerase chain reaction negative) in nonneoplastic tissues. A significant inverse correlation was observed between methylation of CD10 and CD10 expression. No differences were observed between the methylation characteristics of pediatric patients and adult patients. CONCLUSIONS: The results indicate that DNA methylation is common in pediatric patients with ALL and that methylation of the genes studied does not account for prognostic differences between pediatric patients and adult patients with ALL.     

Urolithiasis in pediatric patients with acute lymphoblastic leukemia.

We evaluated the incidence, timing, and consequences of urolithiasis in children with acute lymphoblastic leukemia (ALL). A total of 20 patients with urolithiasis were identified from 2095 patients with ALL treated at St Jude Children's Research Hospital on consecutive protocols between 1968 and 1998. For remission induction therapy, all patients received daily prednisone; continuation chemotherapy regimens differed by protocol with some including pulses of prednisone or dexamethasone and others no glucocorticoid. Patients with urolithiasis were older at diagnosis of ALL than those without urolithiasis (median age, 7.5 vs 5.0 years; P=0.03) and less likely to be black (P=0.03) than white or Hispanic, but sex and treatment era did not differ. Presenting symptoms included abdominal or flank pain, hematuria, and dysuria. All stones analyzed biochemically were calcium stones. The incidence of urolithiasis after completion of therapy was 1.8 per 10 000 person-years. Compared to this baseline rate, the relative risk of urolithiasis was 45 (P<0.01) during induction therapy, 22 (P<0.01) during continuation therapy with glucocorticoids, and 5.1 (P>0.05) during continuation therapy without glucocorticoids. Urolithiasis occurred 4.5 times more often during continuation treatment with glucocorticoids than without (P<0.05). Seven patients (35%) had recurrent urolithiasis. Patients with ALL are at risk of developing calcium renal stones during chemotherapy, especially when a glucocorticoid is included.     

抑癌基因甲基化在肾细胞癌研究中的新进展

抑癌基因启动子高度甲基化被认为是除突变和缺失以外的抑癌基因功能失活的关键机制,在肿瘤的发生和发展中起重要作用,已成为目前肿瘤病因学基础研究的热点.肾细胞癌是泌尿系统最常见的恶性肿瘤之一,近年来也有许多文献报道了肾细胞癌中抑癌基因的异常甲基化情况.肾细胞癌临床发病隐匿,出现症状时多为晚期,肾细胞癌相关基因异常甲基化检测有望为肾癌的早期无创诊断提供新的途径.针对肾癌对放、化疗效果均不敏感的特点,改变DNA甲基转移酶活性和抑癌基因甲基化状况可作为肾细胞癌辅助治疗的一种新思路.本文对抑癌基因甲基化与肾细胞癌关系的研究进展作一综述,介绍DNA甲基化在肿瘤发生过程中的作用及机理;总结近7年来肾细胞癌中抑癌基因甲基化的研究情况和肾细胞癌独特的甲基化谱,并着重介绍了新近报道的HOXB13,HAI2/SPINT2,CDH1,CTNNG/JUP四个基因启动子异常甲基化与肾细胞癌的关系;阐述DNA甲基化研究对肾细胞癌的临床意义.     

Differential miRNA expression in childhood acute lymphoblastic leukemia and association with clinical and biological features

The present study aimed to analyze the expression profile of the microRNAs previously described as associated with childhood ALL, miR-92a, miR-100, miR-125a-5p, miR-128a, miR-181b, miR-196b and let-7e, and their association with biological/prognostic features in 128 consecutive samples of childhood acute lymphoblastic leukemia (ALL) by quantitative real-time PCR. A significant association was observed between higher expression levels of miR-196b and T-ALL, miR-100 and patients with low white blood cell count at diagnosis and t(12;21) positive ALL. These findings suggest a potential activity of these microRNAs in pediatric ALL biology.     

Whole-exome sequencing of pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL), the most common malignant disorder in childhood, is typically associated with numerical chromosomal aberrations, fusion genes or small focal deletions, thought to represent important pathogenetic events in the development of the leukemia. Mutations, such as single nucleotide changes, have also been reported in childhood ALL, but these have only been studied by sequencing a small number of candidate genes. Herein, we report the first unbiased sequencing of the whole exome of two cases of pediatric ALL carrying the ETV6/RUNX1 (TEL/AML1) fusion gene (the most common genetic subtype) and corresponding normal samples. A total of 14 somatic mutations were identified, including four and seven protein-altering nucleotide substitutions in each ALL. Twelve mutations (86%) occurred in genes previously described to be mutated in other types of cancer, but none was found to be recurrent in an extended series of 29 ETV6/RUNX1-positive ALLs. The number of single nucleotide mutations was similar to the number of copy number alterations as detected by single nucleotide polymorphism arrays. Although the true pathogenetic significance of the mutations must await future functional evaluations, this study provides a first estimate of the mutational burden at the genetic level of t(12;21)-positive childhood ALL.     

Classical oncogenes and tumor suppressor genes: a comparative genomics perspective

We have curated a reference set of cancer- related genes and reanalyzed their sequences in the light of molecular information and resources that have become available since they were first cloned. Homology studies were carried out for human oncogenes and tumor suppressors, compared with the complete proteome of the nematode, Caenorhabditis elegans, and partial proteomes of mouse and rat and the fruit fly, Drosophila melanogaster. Our results demonstrate that simple, semi-automated bioinformatics approaches to identifying putative functionally equivalent gene products in different organisms may often be misleading. An electronic supplement to this article provides an integrated view of our comparative genomics analysis as well as mapping data, physical cDNA resources and links to published literature and reviews, thus creating a "window" into the genomes of humans and other organisms for cancer biology.