CHROMOSOME 3 MAY HARBOR MULTIPLE TUMOR SUPPRESSOR GENES ASSOCIATED WITH PRIMARY GLIOBLASTOMA MULTIFORME

Objective: To investigate whether deletion of chromosome 3 is involved in the carcinogenesis of primary glioblastoma multiforme (GBM) and to localize the possible common deletion region in the aforementioned chromosome. Methods: PCR based microsatellite polymorphism analyses were performed to detect loss of heterozygosity (LOH). Twenty-three loci on chromosome 3 were examined in 20 cases of GBM. Fluorescence-labeled primers and Perkin Elmer 377 DNA Sequencer were applied. Results: 50% informative cases of GBM displayed LOH on chromosome 3. 50% of informative cases displayed LOH on 3q and 35% on 3p. 25.6% of informative loci showed LOH in our series, in which frequent LOH were observed in the chromosomal region from loci D3S1614 (42.9%) to D3S1565 (35.3%) on 3q24–27 and at loci D3S1569 (35.3%) on 3q22–23 and D3S1289 (33.3%) on 3p14.1–14.3. Conclusion: Loss of genetic material on chromosome 3 may play an important part in the tumorigenesis of GBM. The chromosomal regions from loci D3S1614 to D3S1565 on 3q24–27 and at loci D3S1569 on 3q22–23 and D3S1289 on 3p14.1–14.3 are potential sites for novel tumor suppressor genes associated with GBM.

CHROMOSOME 17P MAY HARBOR MULTIPLE TUMOR SUPPRESSOR GENES ASSOCIATED WITH PRIMARY GLIOBLASTOMA MULTIFORME

Objective: To investigate whether deletion of chromosome 17 is involved in the carcinogenesis of primary glioblastoma multiforme and to localize the possible common deletion region in the aforementioned chromosome. Methods: Polymerase chain reaction-based microsatellite analysis was used to assess loss of heterozygosity (LOH) on chromosome 17 in 20 primary glioblastoma multiforme (GBM). Fifteen fluorescent dye-labeled polymorphic markers were used. Results: Thirteen of twenty (65%) GBM displayed LOH on at least one marker of chromosome 17p. Two tumors showed either LOH or non-informativeness on all markers tested. The most frequent LOH was observed at loci including D17s799 (53.3%), D17s1852 (53.8%), D17s938 (63.20/o), D17s831 (55.6%). The loci D17s831 (on 17p13) and D17s799–D17s1852 (17p11.2–p12) are distal and proximal to p53 respectively. The frequencies of LOH at all loci examined on chromosome 17q were relatively low (<30%). None of informative loci exhibited microsatellite instability in this study. Conclusion: Loss of genetic material on chromosome 17p may play an important role in the pathogenesis of GBM. Besides the well-known TSG p53 on 17p, other unknown TSCs associated with GBM may be present on the chromosomal regions 17p13 and 17p11.2–p12, which are distal and proximal to p53 respectively.

A preliminary study on the loss of heterozygosity at 17p13 in gastric and colorectal cancers

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Frequent loss of heterozygosity at 8p22 chromosomal region in diffuse type of gastric cancer

AIM: To study the loss of heterozygosity (LOH) at 8p21-23 locus in diffuse gastric cancer.METHODS: To evaluate the involvement of this region in gastric cancer, we used eight microsatellite markers covering two Mb of mentioned region, to perform a high-resolution analysis of allele loss in 42 cases of late diffuse gastric adenocarcinoma.RESULTS: Six of these STS makers: D8S1149, D8S1645, D8S1643, D8S1508, D8S1591, and D8S1145 showed 36%, 28%, 37%, 41%, 44% and 53% LOH, respectively.CONCLUSION: A critical region of loss, close to the NAT2 locus and relatively far from FEZ1 gene currently postulated as tumor suppressor gene in this region.

Loss of chromosome 9p21 and decreased p16 expression correlate with malignant gastrointestinal stromal tumor

AIM: To investigate loss of heterozygosity (LOH) of chromosome 9p21 and the prognostic relevance of p16 expression in gastrointestinal stromal tumor (GIST). METHODS: Fifty-one GIST patients (30 men and 21 women; median age 59 years; range 29-80 years) treated surgically within a 10-year period were grouped by aggressive behavior risk (17 with very low and low, 14 intermediate, and 20 high risk). GISTs were characterized immunohistochemically and evaluated for LOH of 9p21 by microsatellite analysis at D9S1751, D9S1846, D9S942, and D9S1748. LOH of 9p21 and immunohistochemicalexpression of p16 protein encoded at 9p21 were correlated with clinicopathological parameters, and the prognostic significance of p16 alterations was evaluated. RESULTS: Thirty-one (63.3%) cases showed LOH with at least one microsatellite marker. LOH frequency was 37.0% at D9S1751, 37.5% at D9S1846, 42.1% at D9S942, and 24.2% at D9S1748. There was a higher LOH frequency of D9S942 in high-risk than in non-highrisk tumors (P < 0.05, χ 2 = 4.47). Gender, age, tumor size and site were not correlated with allelic loss. Ninety percent (18/20) of the GIST patients in the high risk group showed LOH with at least one of the 9p21 markers, while 57.1% (8/14) in the intermediate risk group and 33.3% (5/15) in the very low and low risk groups, respectively (P < 0.05, χ 2 = 12.16). Eight (28.5%) of 31 patients with LOH and 1 (5.6%) of 18 patients without LOH died of the disease during the follow-up period. Loss of p16 protein expression occurred in 41.2%, but in 60% of the high risk group and 23.5% of the very low and low risk groups (P < 0.05, χ 2 = 4.98). p16 loss was associated with poor prognosis (P < 0.05, χ 2 = 4.18): the 3and 5-year overall survival rates were 84.8% and 70.8% for p16-negative and 100% and 92.0% for p16-positive patients, respectively. CONCLUSION: LOH at 9p21 appears to play an important role in GIST progression; decreased p16 expression in GIST is highly predictive of poor outcome.

Refined mapping of loss of heterozygosity on 1q31.1-32.1 in sporadic colorectal carcinoma

AIM: To explore precise deleted regions and screen the candidate tumor suppressor genes related to sporadic colorectal carcinoma. METHODS: Six markers on 1q31.1-32.1 were chosen. These polymorphic microsatellite markers in 83 colorectal cancer patients tumor and normal DNA were analyzed via PCR. PCR products were electrophoresed on an ABI 377 DNA sequencer. Genescan 3.1 and Genotype 2.1 software were used for Loss of heterozygosity (LOH) scanning and analysis. Comparison between LOH frequency and clinicopathological factors was performed by χ2 test. RESULTS: 1q31.1-32.1 exhibited higher LOH frequency in colorectal carcinoma. The average LOH frequency of 1q31.1-32.1 was 23.0%, with the highest frequency of 36.7% (18/49) at D1S2622, and the lowest of 16.4% (11/67) at D1S412, respectively. A minimal region of frequent deletion was located within a 2 cM genomic segment at D1S413-D1S2622 (1q31.3-32.1). There was no significant association between LOH of each marker on 1q31.1-32.1 and the clinicopathological data (patient sex, age, tumor size, growth pattern or Dukes stage), which indicated that on 1q31.1-32.1, LOH was a common phenomenon in all kinds of sporadic colorectal carcinoma. CONCLUSION: Through our refined deletion mapping,the critical and precise deleted region was located within 2 cM chromosomal segment encompassing 2 loci (D1S413, D1S2622). No significant association was found between LOH and clinicopathologic features in 1q31.1-32.1.

Are there tumor suppressor genes on chromosome 4p in sporadic colorectal carcinoma?

AIM: To study the candidate tumor suppressor genes (TSG) on chromosome 4p by detecting the high frequency of loss of heterozygosity (LOH) in sporadic colorectal carcinoma in Chinese patients.METHODS: Seven fluorescent labeled polymorphic microsatellite markers were analyzed in 83 cases of colorectal carcinoma and matched normal tissue DNA by PCR. PCR products were eletrophoresed on an ABI 377 DNA sequencer. Genescan 3.7 and Genotype 3.7 software were used for LOH scanning and analysis. The same procedure was performed by the other six microsatellite markers spanning D4S3013 locus to make further detailed deletion mapping. Comparison between LOH frequency and clinicopathological factors was performed by χ2 test.RESULTS: Data were collected from all informative loci. The average LOH frequency on 4p was 24.25%, and 42.3% and 35.62% on D4S405 and D4S3013 locus, respectively. Adjacent markers of D4S3013 displayed a low LOH frequency (< 30%) by detailed deletion mapping. Significant opposite difference was observed between LOH frequency and tumor diameter on D4S412 and D4S1546 locus (0% vs 16.67%, P = 0.041; 54.55% vs 11.11%, P = 0.034, respectively). On D4S403 locus, LOH was significantly associated with tumor gross pattern (11.11%, 0, 33.33%, P = 0.030). No relationship was detected on other loci compared with clinicopathologial features.CONCLUSION: By deletion mapping, two obvious high frequency LOH regions spanning D4S3013 (4p15.2) and D4S405 (4p14) locus are detected. Candidate TSG, which is involved in carcinogenesis and progression of sporadic colorectal carcinoma on chromosome 4p, may be located between D4S3017 and D4S2933 (about 1.7 cm).

Tumor suppress genes screening analysis on 4q in sporadic colorectal carcinoma

AIM: To search candidate tumor suppressor genes (TSGs) on chromosome 4q through detecting high loss of heterozygosity (LOH) regions in sporadic colorectal carcinoma in Chinese patients. METHODS: Thirteen fluorescent labeled polymorphic microsatellite markers were analyzed in 83 cases of colorectal carcinoma and matched normal tissue DNA by polymerase chain reaction (PCR). PCR products were eletrophoresed on an ABI 377 DNA sequencer. Genescan 3.7 and Genotype 3.7 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological factors were performed by χ2 test. RESULTS: Data were collected on all informative loci. The average LOH frequency on 4q was 28.56%. The D4S2915 locus showed highest LOH frequency (36.17%). Two obvious deletion regions were detected: one between D4S3000 and D4S2915 locus (4q12-21.1), another flanked by D4S407 and D4S2939 locus (4q25-31.1). None case showed complete deletion of 4q, most cases displayed interstitial deletion pattern solely. Furthermore, compared with clinicopathological features, a significant relationship was observed between LOH frequencies on D4S3018locus. In tumors larger than 5 cm in diameter, LOH frequency was significantly higher than tumors that were less than 5 cm (56% vs 13.79%, P = 0.01). On D4S1534 locus, LOH was significantly associated with liver metastasis (80% vs 17.25%, P = 0.012). No relationship was detected on other locus compared with clinicopathologial features. CONCLUSION: By high resolution deletion mapping, two high frequency regions of LOH (4q12-21.1 and 4q25-31.1) were detected, which may contribute to locate TSGs on chromosome 4q involved in carcinogenesis and progression of sporadic colorectal carcinoma.

Analysis on chromosome 8 heterozygosity loss in humanprostate carcinoma and high grade prostaticintraepithelial neoplasia

Objective: To analysis the chromosome 8 heterozygosity loss in human prostate carcinoma and high grade prostatic intraepithelial neoplasia. Methods: Pure DNA was obtained from prostate neoplasms and normal tissues by tissue microdissection. The chromosome 8 heterozygosity loss was detected by PCR based micro-satellite polymorphism analysis technique using 14 pairs of microsatellite primers in 10 samples of prostate carcinoma and 10 samples of high grade prostatic intraepithelial neoplasia. Results: There were different frequencies of chromosome 8 heterozygosity loss in 10 samples of prostate carcinoma. 8p23.1-p23.2 and p21-p22 were two high frequency heterozygosity loss regions. Chromosome 8 heterozygosity loss was detected in 3 samples of high grade prostatic intraepithelial neoplasia. Conclusion: There were high frequency heterozygosity loss regions on chromosome 8 of prostate carcinoma, located at 8p23.1-p23.2 and p21-p22. The high grade prostatic intraepithelial neoplasia and prostate carcinoma share the same allelic loss on 8p. Tumor suppressor genes located at these two regions may be potentially involved in the initiation and progression of prostate carcinoma.

Chromosome 14q may harbor multiple tumor suppressor genes in primary glioblastoma multiforme

OBJECTIVE: To evaluate whether deletion of chromosome 14q is involved in the carcinogenesis of primary glioblastoma multiforme and to identify possibly common deletion regions. METHJODS: Fourteen fluorescent dye-labeled polymorphic markers were used and polymerase chain reaction-based microsatellite analysis was employed to investigate loss of heterozygosity (LOH) on chromosome 14q in 20 primary glioblastoma multiforme (GBM). RESULTS: Ten of twenty (50%) GBM displayed LOH at one or more of the markers on chromosome 14q. Five tumors showed either LOH or non-informative on all markers tested. The most frequent LOH was observed at locus D14S65 (57.1%) on 14q32.1, and in the chromosomal region spanning from D14S63 (47.1%) to D14S74 (46.7%) on 14q23-31. None of the informative loci exhibited microsatellite instability. CONCLUSIONS: Allelic deletion on chromosome 14q plays an important role in the pathogenesis of GBM. Chromosomal regions at locus D14S65 on 14q32.1 and spanning from D14S63 to D14S74 on 14q23-31 may harbor multiple tumor suppressor genes associated with GBM.

Screening of tumor suppressor genes on 1q31.1-32.1 in Chinese patients with sporadic colorectal cancer

Background As a model for both multistep and multipathway carcinogenesis, colorectal neoplastic progression provides paradigms for researching both oncogenes and tumor suppressor genes （TSGs）. However, the mechanism of colorectal cancer （CRC） is not completely understood, and many genes may be involved in the colorectal carcinogenesis. The purpose of this study was to screen for the potential TSGs on chromosome 1q31.1-32.1 in Chinese patients with sporadic colorectal cancer, to explore whether colorectal cancer in the Chinese population has unique genetic alterations and determine whether other putative TSGs exist and contribute to colon carcinogenesis. Methods Six polymorphic microsatellite markers, at a density of approximately one marker in every 1.6 cM, were chosen for refined loss of heterozygosity （LOH） mapping of 1q31.1-32.1. Eighty-three colorectal cancer patients＇ tumor and normal DNA were analyzed via polymerase chain reaction （PCR） for these microsatellite markers. PCR products were eletrophoresed on an ABI 377 DNA sequencer. Genescan 3.1 and Genotype 2.1 software were used for LOH scanning and analysis. On the basis of refined LOH mapping results, we undertook a microarray-based expression screening to identify tumor association genes in 19 of the CRC cases. Results The average LOH frequency of 1q31.1-32.1 was 24.41%, with the highest frequency of 36.73% （18/49） at D1S2622, and the lowest of 16.42% （11/67） at D1S412. A minimal region of frequent deletion was located within a 2 cM genomic segment at D1S413-D1S2622. There was no significant association between LOH of any marker in the studied regions and the clinicopathological data （patient sex, age, tumor size, growth pattern, or Dukes stage）. On the basis of refined mapping results, we chose 25 genes located in the D1S413-D1S2622 （1q31.3-32.1） region and presented a microarray-based high throughput screening approach in 19 sporadic CRC cases to identify candidate CRC related tumor suppressor genes. This study found 4 significantly down-expressed genes, including CSRP1, LMOD1, PPP1R12B and CFHL3. There was no significant association between expression levels of CFHL3, CSRP1, LMOD1, PPP1R12B and the clinicopathological data. By database searching, CSRP1 was hypothesized to be a colorectal cancer related tumor suppressor gene. Conclusions Through detailed deletion mapping, we found that the 1q31.3-32.1 region might harbor one or more colorectal cancer related tumor suppressor gene（s）. And by microarray-based high-throughput screening of candidate genes located in this region and by subsequent database searching, we present the first evidence that CSRP1 might be involved in the progression of CRC.

Detailed Deletion Mapping of Chromosome 9p21-22 in Nasopharyngeal Carcinoma

Objective: To further refine the extent of deletion on chromosome 9p21-22 in nasopharyngeal carcinoma (NPC) and provide evidence for discovering new tumor suppressor gene. Methods: Loss of heterozygosity (LOH) on chromosome 9p21-22 was analyzed in 25 paired blood and tumor samples by using 11 high-density microsatellite polymorphic markers. Results: 17 of 25 cases (68.0%) showed LOH at one or more loci. Higher frequencies of LOH were found at four loci: D9S161 (35.0%), D9S1678 (31.5%), D9S263 (33.3%) and D9S1853 (33.3%), where 6 cases had a contiguous stretch of allelic loss. Conclusion: The minimal common region of deletion might be defined between D9S161 and D9S1853 (estimated about 2.7 cM in extent) at 9p21.1, suggesting that inactivation of one or more tumor suppressor genes located in this region may be an important step in NPC.

瘤细胞纯度梯度体系及APC-LOH模型的建立和意义

建立了一个瘤细胞标本纯度参照体系,以降低标本不纯对抑癌基因杂合性缺失(LOH)研究的影响。根据代表不同纯度的标本中两个等位基因的配比推算纯合子/杂合子DNA的构成比及掺入量,进而构建了瘤细胞模拟纯度梯度体系,并以APC基因的LOH分析为例,在优化实验条件基础上建立了不同纯度瘤细胞的APC-LOH模型。结果表明,该APC-LOH检测系统至少能分析纯度低至60％的标本,优于其它文献提出的纯度要求(>70%)。结论是构建纯度梯度体系及抑癌基因LOH模型有利于提高及确定LOH检测系统的分辨能力。

精细定位和克隆9p21-22区域内鼻咽癌候选抑瘤基因

目的：进一步精细限定鼻咽癌９ｐ２１－２２区域等位基因杂合性丢失的频率和范围，筛选和克隆其共同缺失区内鼻咽癌相关的候选抑瘤基因。方法：应用１１个定位于 ９ｐ２１－２２区域的高密度微卫星位点，检测 ２５例低分化鼻咽癌患者的杂合性丢失，确定其共同缺失区；用ＲＴ－ＰＣＲ和Ｎｏｒｔｈｅｒｎ筛出在鼻咽癌细胞株ＨＮＥ１和鼻咽癌活检组织中表达下调的、定位于共同缺失区内的 ３’末端ＥＳＴｓ（Ｅｘｐｒｅｓｓ Ｓｅｑｕｅｎｃｅ Ｔａｇｓ）；采用 ＲＡＣＥ技术和生物信息学资源克隆出候选ＥＳＴ的全长ｃＤＮＡ。结果： ２５例患者中有１７例（６８％）存在一个或多个位点的杂合性丢失，其中Ｄ９ｓ１６１（３５．０％，７／２０），Ｄ９Ｓ１６７８（３１．５％，６／１９），Ｄ９Ｓ２６３（３．３％，６／１８）和Ｄ９Ｓ１８５３（３３．３％，７／２１）四个紧邻位点的丢失频率相对较高，并发现六位患者在该四个位点表现为连续性缺失；筛选Ｄ９Ｓ１６１－Ｄ９Ｓ１８５３区域内２５个代表新基因的３’末端ＥＳＴｓ序列，发现一个ＥＳＴ（ｄｂＥＳＴ：２０８８２５）在鼻咽癌细胞株ＨＮＥ１及７３％（１１／１５）的活检组织中表达降低， Ｍｕｌｔｉｐｌｅ Ｔｉｓｓｕｅ Ｎｏｒｔ

鼻咽癌全基因组杂合性缺失分析

目的:分析鼻咽癌(nasopharyngealcarcinoma,NPC)全基因组染色体杂合性缺失(lossofheterozygosity,LOH),定位NPC发生高频率LOH的区域,为定位NPC相关基因提供分子遗传学依据。方法:用PCR微卫星多态性分析(335个位点)技术检测98例NPC肿瘤基因组DNA等位基因缺失。结果:在22对染色体中,19对染色体在所选取位点中有至少1个位点LOH频率≥30%,3对染色体(15号、20号和22号)无LOH频率大于30%的位点;在335个位点中,4个位点LOH频率≥60%,其中3个在3号染色体,1个在9号染色体;5个位点LOH频率介于50%～59%,其中3个在3号染色体,5号和11号染色体各1个位点;22个位点LOH频率介于40%～49%,52个位点LOH频率介于30%～39%;252个位点LOH频率低于30%,提示为背景缺失;LOH频率≥30%的位点主要集中于12个染色体臂,分布于:1p36-34,3p24-26,3p14-21,3q25-27,4q35-31,5q15-21和5q32-33,8p22-23,9p21-23和9q33-34,11p12-14,11q13-23,13q13-14和13q31-32,14q11-13,14q23-24,14q32。本研究新报道在染色体区带1p,5q和19q等发生高频率LOH,LOH精细图谱提示这些区域内可能存在与NPC相关的TSG。结论:NPC肿瘤细胞在多染色体区带发生高频率LOH是常见的分子事件,提示在这些缺失区,可能存在与NPC发生、发展过程中起重要作用的肿瘤抑制基因。

鼻咽癌组织中GNAT1基因的表达、杂合性丢失及甲基化分析

背景与目的:在鼻咽癌中,染色体3p21.3为高频缺失区,杂合性丢失(lossofheterozygosity,LOH)分析和功能学研究都表明3p21.3区存在与鼻咽癌相关的抑瘤基因。GNAT1基因也定位于3p21.3,但在鼻咽癌中未见关于GNAT1基因的研究报道。本研究旨在探讨GNAT1基因在鼻咽癌组织中的表达、LOH及甲基化情况。方法:应用逆转录-聚合酶链式反应(reversetranscriptionpolymerasechainreaction,RT-PCR)方法检测了33例鼻咽癌组织和15例慢性鼻咽炎组织中GNAT1基因的表达,并通过微卫星分析技术和甲基化特异性聚合酶链式反应(methylation-specificpolymerasechainreaction,MSP)分析GNAT1基因LOH和启动子区甲基化情况。结果:GNAT1基因在慢性鼻咽炎组织中均稳定表达,而在72.7%(24/33)的鼻咽癌组织中表达下调或缺失,显著低于慢性鼻咽炎组织(100%,15/15)(P=0.022);LOH分析显示鼻咽癌组织中GNAT1基因的杂合性丢失率为15%(3/20),且LOH与基因表达存在相关性(P=0.016);甲基化分析发现在100%的鼻咽癌组织和80%慢性鼻咽炎组织中存在GNAT1基因启动子区高甲基化。结论:GNAT1基因在鼻咽癌组织中表达下调或缺失,这一现象与GNAT1基因的LOH存在相关性,而与3p21.3区基因启动子区CpG岛的甲基化可能无关。GNAT1基因的甲基化可能不是鼻咽癌的发病机制。

原发性肝癌9号染色体等位基因杂合性丢失研究

目的：对广东地区37例肝癌染色体9p的9个位点进行微卫星多态性分析，明确这些位点染色体等位基因杂合性丢失（LOH）的情况，定位该区域可能存在的与肝癌有关的肿瘤抑制基因。方法：对所取位点用PCR法进行微卫星多态性分析并确定发生LOH的位点；结果：30例（80.80％）在至少一个位点发生LOH，其中LOH频率最高的位点是D9554（60．60％），LOH频率高于50％的位点有位于9p21带的1FNA，D9S1747和D9S1752，6例在所有能够提供信息的位点均发生LOH，7例在所有9个位点均未发生LOH。提示本地区肝癌染色体9P缺失的区域主要位于D9554（9p24），和DgS1752，D9S1747，1FNA（9p21）。结论：本研究首次发现肝癌在染色体9p24区发生高频率LOH，染色体9p21区也发生高频率LOH，提示在染色体9p24和9p21区域可能存在多个与肝癌相关的肿瘤抑制基困。

肺癌癌前病变中的分子生物学异常事件

近二十年来,我国肺癌的发病率迅速上升,到目前为止,肺癌的发病率和死亡率已居肿瘤之首。早期诊断是提高肺癌5年生存率的关键。本文拟对肺癌发生中的早期遗传学事件加以概述,其中主要有p53的突变,p16启动子区的异常甲基化,3p、8p、9p、5q的杂合性缺失等,以期寻找肺癌发生中的生物标记,为肺癌的诊断和治疗提供理论参考。

中国儿童急性淋巴细胞性白血病染色体6q16.3～21区域候选肿瘤抑制基因的定位与鉴定

为了克隆儿童急性淋巴细胞性白血病(ALL)候选肿瘤抑制基因,首先选取分布于6q16.3～21上的11个多态性微卫星标记,对139例中国儿童ALL标本进行杂合性缺失(LOH)分析.分析显示32%的患者存在至少一个位点的LOH,且高频缺失区位于D6S1709～D6S301之间,大小为2cM.各位点LOH与白细胞总数、病态细胞数有显著性相关(P<0.05),与年龄、性别、形态学分型和免疫学分型无显著相关(P>0.05).进一步在高频缺失区域内,采用定位候选克隆策略、生物信息学技术及RT-PCR技术筛选、鉴定与儿童ALL相关的候选肿瘤抑制基因及其cDNA片段.在D6S1709～D6S301之间筛选到一个在儿童ALL细胞中低表达的EST(GenBank登录号:AA403058),与正常外周血单个核细胞比较,在15例ALL患者中有10例表达下调(P<0.05).采用数字化差异表达分析显示,位于6q16.3～21区域内的AMD1基因、PPIL6基因和WASF1基因在肿瘤组织中的表达丰度要低于正常组织(P<0.05).上述结果为进一步在6q16.3～21区域克隆肿瘤抑制基因提供了线索.

SEMA3B基因在鼻咽癌组织中的表达、杂合性丢失和甲基化分析

SEMA3B基因定位于鼻咽癌高频缺失区域3p21.3上,最近被证明具有抑瘤基因的功能.分析了鼻咽癌组织中SEMA3B基因的表达、杂合性丢失(LOH)和甲基化情况.首先应用逆转录-聚合酶链式反应(RT-PCR)方法检测了33例鼻咽癌组织和15例慢性鼻咽炎组织中SEMA3B基因的表达,结果显示75.8%(25/33)鼻咽癌组织中SEMA3B基因表达缺失或下调,显著低于慢性鼻咽炎组织中的表达(P=0.001).进一步选取3个微卫星位点D3S1568、D3S1621和D3S4597分析了20例鼻咽癌组织中SEMA3B基因LOH的情况,结果表明3个位点的丢失率分别为10%、20%和15%,总的丢失率为45%,统计分析发现LOH与基因表达之间存在明显相关(P=0.023).最后,采用甲基化特异性PCR方法分析了SEMA3B基因启动子区甲基化,结果发现在100%的鼻咽癌组织和73.3%的慢性鼻咽炎组织中检测到SEMA3B基因启动子区高甲基化.由此得出结论,SEMA3B基因在鼻咽癌组织中表达缺失或下调,LOH是引起其表达异常的原因之一.