人类恶性肿瘤中染色体17p13.3区带的杂合性丢失

人类恶性肿瘤中经常发生染色体染合性丢失,从而丢失抑癌基因的某一个等基因。人类１７号染色本特别是该色体的１７ｐ１３．３区带,在多种肿瘤中都存在着染色的体杂支失。     

Loss of heterozygosity studies in tumors from families with breast-ovarian cancer syndrome

A gene (BRCA1) predisposing for familial breast and ovarian cancer has been mapped to chromosome band 17q12-21. Based on the observation that ovarian tumors from families with breast and ovarian cancer lose the wild-type allele in the region for the BRCA1 locus, it has been suggested that the gene functions as a tumor suppressor gene. We have studied chromosomal deletions in the BRCA1 region in seven breast tumors, three ovarian tumors, one bladder cancer, and one colon cancer from patients in six families with breast-ovarian cancer, in order to test the hypothesis of the tumor suppressor mechanism at this locus. We have found a low frequency of loss of heterozygosity at this region, and our results do not support the idea that BRCA1 is a tumor suppressor gene. Alternatively, the disease segregating in these families is linked to one or more different loci.     

Loss of heterozygosity on chromosome 10 in human glioblastoma multiforme

Recessive mutations, revealed by loss of the wild-type allele, have been associated with the development of a variety of cancers in children and adults. Polymorphic chromosome 10 markers were used to screen paired tumor and lymphocyte DNA samples in 13 patients with glioblastoma multiforme. Ten patients showed loss of constitutional heterozygosity in the tumor samples. This finding suggests that a recessive gene involved in the development of glioblastoma multiforme is present on chromosome 10.     

Loss of heterozygosity of the p53 gene and deregulated expression of its mRNA and protein in human brain tumors

Tumor-specific alterations at the p53 gene locus were analyzed in 40 human brain tumor samples. Gliomas were more prevalent in young males and meningiomas in old females. Structural changes at the intron 1 region of the p53 gene were analyzed in these tumors by Southern blotting. Among the 40 tumors, 33 were informative and 21 of these (63.6%) informative cases showed loss of heterozygosity (LOH). This is the first report showing LOH at the intron 1 region of p53 gene in human brain tumors. The level of p53 mRNA, p53 protein and Ser 392 phosphorylated p53 protein were also analyzed in all tumor samples. Normal sized p53 mRNA and protein were present in all the tumor samples; however, their levels were 1.5- to 4-fold higher compared to the control suggesting deregulated p53 pathway in these tumors. No correlation was found between LOH status and the levels of p53 mRNA and protein. In all high-grade glioblastomas majority of the p53 protein existed as Ser 392 phosphorylated form as compared to low-grade gliomas. In addition, the percentage of Ser 392 phosphorylated form of p53 protein was lower in meningiomas and other brain tumor types irrespective of tumor grade. These results suggest involvement of Ser 392 phosphorylated form of p53 protein during the later stages of glioma development. These results also indicate that deregulation of p53 gene could occur at various steps in p53 pathway and suggest an overall deregulation of p53 gene in most brain tumor types.     

Loss of heterozygosity by SCRaMbLEing

Genetic variation drives phenotypic evolution within populations. Genetic variation can be divided into different forms according to the size of genomic changes. However, study of large-scale genomic variation such as structural variation and aneuploidy is still limited and mainly based on the static, predetermined feature of individual genomes. Here, using SCRaMbLE,different levels of loss of heterozygosity(LOH) events including short-range LOH, long-range LOH and whole chromosome LOH were detected in evolved strains. By contrast, using rapid adaptive evolution, aneuploidy was detected in the adaptive strains. It was further found that deletion of gene GLN3, long-range LOH in the left arm of synthetic chromosome Ⅹ, whole chromosome LOH of synthetic chromosome Ⅹ, and duplication of chromosome Ⅷ(trisomy) lead to increased rapamycin resistance in synthetic yeast. Comparative analysis of genome stability of evolved strains indicates that the aneuploid strain has a higher frequency of degeneration than the SCRaMbLEd strain. These findings enrich our understanding of genetic mechanism of rapamycin resistance in yeast, and provide valuable insights into yeast genome architecture and function.     

Loss of heterozygosity on chromosome 11 in sporadic gastrinomas

Summary Gastrinomas are pancreatic endocrine neoplasms that arise either sporadically or are inherited as part of the multiple endocrine neoplasia type I syndrome (MEN I). Loss of heterozygosity (LOH) in the region flanking the MEN I gene at chromosome 11q13 has been documented in a few sporadic and familial pancreatic endocrine tumors, but not previously in sporadic gastrinomas. It has therefore been suggested that gastrinomas develop by a mechanism different from other tumors associated with the MENI syndsrome. We report LOH on chromosome 11 in 5 of 11 sporadic gastrinomas. Four of these tumors have LOH for markers flanking the MEN I region. Molecular evaluation of segments of chromosomes 3, 13, and 17 known to contain cloned or putative tumor suppressor genes fail to show LOH except at one locus in one tumor. These data suggest that a tumor suppressor DNA segment exists at 11q13 that may be involved in the development of sporadic gastrinomas.     

Loss of heterozygosity and the origin of meningioma

Summary In some human tumors, loss of particular genes manifested indirectly by loss of heterozygosity for specific RFLPs seems to uncover either heterozygous deletions leading to a gene dosis effect or homozygous deletions due to a silent allele at the corresponding locus, both causing the loss of regulatory functions (antioncogenes suppressor genes). Meningioma, a benign human tumor derived from the coverings of brain and spinal cord, is associated with complete loss, rarely deletion, of one chromosome 22. About 60% of meningiomas exhibit monosomy 22 in all or part of cells; however, about 40% display a normal karyotype. Comparison of constitutional and tumor genomes from 12 patients showed loss of heterozygosity on 22 in three cases, suggesting the involvement of events at the DNA level.     

Loss of heterozygosity and DNA damage repair in Saccharomyces cerevisiae

Loss of heterozygosity (LOH) of tumor suppressor genes is a crucial step in the development of sporadic and hereditary cancer. Understanding how LOH events arise may provide an opportunity for the prevention or early intervention of cancer development. In an effort to investigate the source of LOH events, we constructed MATalphacan1Delta::LEU2 and MATa CAN1 haploid yeast strains and examined canavanine-resistance mutations in a MATa CAN1/MATalphacan1Delta::LEU2 heterozygote formed by mating UV-irradiated and nonirradiated haploids. An increase in LOH was observed when the irradiated CAN1 haploid was mated with nonirradiated can1Delta::LEU2, while reversed irradiation only marginally increased LOH. In the rad51Delta background, allelic crossover type LOH increased following UV irradiation but not gene conversion. In the rad52Delta background, neither type of LOH increased. The chromosome structure following LOH and the requirement for Rad51 and Rad52 proteins indicated the involvement of gene conversion, allelic crossover and break-induced replication. We argued that LOH events could have occurred during the repair of double-strand breaks on a functional (damaged) but not nonfunctional (undamaged) chromosome through recombination.     

Loss of heterozygosity in hypotriploid cell cultures from testicular tumours

Summary We have established cell lines with a hypotriploid chromosome number from four testicular tumours. Each line had at least one Y chromosome and most of the informative centromere and enzyme markers were heterozygous implying that the tumours originated from germ cells before the first meiotic division. The small metacentric marker chromosome (i12p), specific for testicular tumours, was present in all tumour cell lines and up to three copies were found in some lines. Rearrangements of chromosome 1 and 11 were each found in three out of four tumours. The rearrangements of chromosome 1 all resulted in duplication of 1q and deletion of short-arm material from the same chromosome giving loss of heterozygosity for enzyme markers on 1p. Loss of satellite material from chromosome 13 and the centromere region of chromosome 9 were found in single cases. This study shows that even where the chromosome number of tumour cells is near triploid, regions of the genome can be deleted. The chromosomes most frequently involved in rearrangements, 1, 11, and 12 all contain sites of ras oncogenes and it is suggested that loss of normal alleles could result in homozygosity for mutant oncogenes which may play a part in tumour progression.     

Loss of heterozygosity and K-ras gene mutations in gastric cancer

In order to identify relevant genetic lesions in gastric carcinoma, we searched for tumor suppressor gene inactivation and K-ras gene mutations by analyzing tumor and control DNAs from 34 patients. These were from an epidemiologically defined area of Italy characterized by one of the world's highest incidences of stomach cancer. Allele losses were investigated by the Southern blotting procedure at 16 polymorphic loci on 11 different chromosomes. Our data demonstrate that chromosomal regions 5q, 11p, 17p and 18q are frequently deleted, and that 7q and 13q chromosome arms are also involved, although at a lower frequency. Loss of heterozygosity (LOH) at region 11p was not found during other surveys carried out on patients of different geographic origins. No specific combination of allelic losses could be recognized in the samples analyzed, the only exception being that tumors with 17p allelic loss also showed LOH on the 18q region. When matching frequent LOH events and the stage of progression of the tumors, we observed a trend of association between advanced stages and allelic losses on 17p and 18q chromosome arms. The analysis of K-ras, carried out by the polymerase chain reaction and denaturing gradient gel electrophoresis, demonstrated transforming mutations in only 3 out of 32 cases. Colorectal tumorigenesis proceeds by the accumulation of genetic alterations, including K-ras mutations and inactivation of tumor suppressor genes on the 5q, 17p and 18q regions. Our data indicate that, although gastric and colorectal neoplasias share common genetic alterations, they probably progress through different pathways.     

Loss of heterozygosity on chromosome 5 in Iranian esophageal cancer patients

There is a high incidence of esophageal squamous cell carcinoma (ESCC) in Iran. Non-functionality of some tumor suppressor genes has been reported in esophageal cancer. Loss of heterozygosity on chromosome 5 has also been reported in esophageal carcinomas. We assessed loss of heterozygosity along a region of the long arm of chromosome 5 (5q), from 5q23.1 to 5q23.2, by PCR amplifying DNA fragments of tumor tissues from patients with ESCC and their corresponding normal samples. The PCR products were electrophoresed on 6% non-denaturing polyacrylamide gels, and band intensity was shown by silver staining. Of 40 patients with ESCC, 27, 25 and 36% of informative cases showed allelic losses at microsatellite markers D5S1384, D5S1478 and D5S1505, respectively. Two of the 40 patients studied had microsatellite instability at marker D5S1384. Based on the fact that loss of heterozygosity with more than 22% incidence for a specific marker cannot be regarded as a random event, we add support to previous reports concerning the presence of tumor suppressor genes in this chromosome region and that they affect esophageal cancer development. According to the data in NCBI UniSTS, the PCR product size of human DNA with primers of the D5S1505 marker ranges from 243 to 275 bp, containing about 20 repeats of the TAGA tetranucleotide, while the amplicon size of one allele of one of our cases was 207 bp, with about 10 repeats of the TAGA tetranucleotide, which would be the shortest sequence reported so far.     

Loss of heterozygosity on 17p in human breast carcinomas: defining the smallest common region of deletion

The marker D17S5, mapping to the short arm of chromosome 17, was recently reported by us and others to undergo frequent heterozygous deletion in human primary breast carcinomas, implicating the presence of a tumor suppressor gene in this region. To narrow down the location of this gene more precisely, we have performed a deletion-mapping study in an extended series of 78 breast carcinomas, using nine polymorphic markers for the short arm and two polymorphic markers for the long arm of chromosome 17. Partial allele losses on 17p were observed in nine cases, which, taken together, suggest that the target gene for the deletions maps to the region extending between the markers D17S5 (17p13.3) and D17S67 (17p12).     

Loss of heterozygosity for alleles on chromosome II in cervical carcinoma.

The HeLa cell (a cervical carcinoma cell line) tumor-suppressor gene has been localized to the long arm of chromosome 11 by molecular genetic studies of nontumorigenic and tumorigenic hybrids derived from normal chromosome 11 x HeLa cell fusions. In the present study, 33 primary cervical carcinoma samples were analyzed using chromosome 11-specific polymorphic DNA markers. The RFLP analysis indicated a somatic loss of chromosome 11 heterozygosity in 10 (30%) of the primary tumors. Preferential loss of the long arm of the chromosome was observed in two of the primary tumors. In addition, at least eight-fold amplification of sequences in the q13 region, including those coding for the fibroblast growth factor-related gene (int-2), was observed in one of the primary tumors. These results suggest a possible role for gene(s) localized to chromosome 11, possibly that localized to the long arm in the development and/or progression of cervical carcinomas.     

Loss of heterozygosity on chromosome 11p13 in primary bladder carcinoma

Although the occurrence of bladder cancer is common, the molecular events underlying the pathogenesis of this cancer remain ill-defined. A loss of heterozygosity (LOH) at specific chromosomal loci may predispose individuals to the development of bladder cancer but this has not been examined in detail. Furthermore, the role that deletion or inactivation of putative tumour suppressor genes might play in the genesis of bladder cancer has not been established. In this study, allelic deletion analysis on the short arm of chromosome 17 of patients with primary bladder tumours failed to show deletion at 17p13 (0/7), a region known to contain the p53 tumour suppressor gene. Chromosome 11p15 showed allelic deletion at the IGF2 locus (2/7: 29%) and the PTH locus (1/11: 9%). However, no deletion was observed at the CALCA locus (0/6). LOH at 11p13, a region containing the Wilm's tumour suppressor gene (WT1), was also studied. Analysis of LOH at 11p13 showed deletion at the CAT locus (13/18: 72%), the J/D11S414 locus (5/15: 33%), the WT1 locus (7/14: 50%) and the FSHB locus (6/16: 38%). The significance of these findings is discussed.     

Loss of NOTCH2 positively predicts survival in subgroups of human glial brain tumors

The structural complexity of chromosome 1p centromeric region has been an obstacle for fine mapping of tumor suppressor genes in this area. Loss of heterozygosity (LOH) on chromosome 1p is associated with the longer survival of oligodendroglioma (OD) patients. To test the clinical relevance of 1p loss in glioblastomas (GBM) patients and identifiy the underlying tumor suppressor locus, we constructed a somatic deletion map on chromosome 1p in 26 OG and 118 GBM. Deletion hotspots at 4 microsatellite markers located at 1p36.3, 1p36.1, 1p22 and 1p11 defined 10 distinct haplotypes that were related to patient survival. We found that loss of 1p centromeric marker D1S2696 within NOTCH2 intron 12 was associated with favorable prognosis in OD (P = 0.0007) as well as in GBM (P = 0.0175), while 19q loss, concomitant with 1p LOH in OD, had no influence on GBM survival (P = 0.918). Assessment of the intra-chromosomal ratio between NOTCH2 and its 1q21 pericentric duplication N2N (N2/N2N-test) allowed delineation of a consistent centromeric breakpoint in OD that also contained a minimally lost area in GBM. OD and GBM showed distinct deletion patterns that converged to the NOTCH2 gene in both glioma subtypes. Moreover, the N2/N2N-test disclosed homozygous deletions of NOTCH2 in primary OD. The N2/N2N test distinguished OD from GBM with a specificity of 100% and a sensitivity of 97%. Combined assessment of NOTCH2 genetic markers D1S2696 and N2/N2N predicted 24-month survival with an accuracy (0.925) that is equivalent to histological classification combined with the D1S2696 status (0.954) and higher than current genetic evaluation by 1p/19q LOH (0.762). Our data propose NOTCH2 as a powerful new molecular test to detect prognostically favorable gliomas.     

Loss of PTEN expression in neuroendocrine pancreatic tumors

PTEN (phosphatase and tensin homologue deleted from chromosome 10) is a well established tumor suppressor gene, which was cloned to chromosome 10q23. PTEN plays an important role in controlling cell growth, apoptosis, cell adhesion, and cell migration. In various studies, a genetic change as well as loss of PTEN expression by different carcinomas has been described. To date, the role of PTEN as a differentiation marker for neuroendocrine tumors (NET) and for the loss of PTEN expression is still unknown. It is assumed that loss of PTEN expression is important for tumor progression of NETs. We hypothesize that PTEN might be used as a new prognostic marker. We report 38 patients with a NET of the pancreas. Tumor tissues were surgically resected, fixed in formalin, and embedded in paraffin. PTEN expression was evaluated by immunohistochemistry and was correlated with several clinical and pathological parameters of each individual tumor. After evaluation of our immunohistochemistry data using a modified Remmele Score, a widely accepted method for categorizing staining results for reports and statistical evaluation, staining results of PTEN expression were correlated with the clinical and pathological parameters of each individual tumor. Our data demonstrates a significant difference in survival with existence of lymph node or distant metastases. Negative patients show a significant better survival compared with positive patients. Furthermore, we show a significant difference between PTEN expression and WHO or TNM classification. Taken together, our data shows a positive correlation between WHO classification and the new TNM classification of NETs, and loss of PTEN expression as well as survival. These results strongly implicate that PTEN might be helpful as a new prognostic factor.     

Analysis of Loss of heterozygosity and immunohistochemistry in BRCA1 gene in sporadic breast cancers

BRCA1 is a tumour suppressor gene (TSG), which predisposes cancer to both breast and ovary. The primary objective of the present study is to ascertain the involvement of BRCA1 gene in the pathogenesis of sporadic breast cancer women in Chennai (South India) by analysing its protein expression by immunohistochemistry (IHC) and loss of heterozygosity (LOH) for confirmation of the involvement of TSG in the study population. We found down regulation of BRCA1 protein (54%) in IHC and it was correlated with the clinicopathological parameters of the patients. We found near significant correlation (P < 0.063) between BRCA1 protein expression and clinicopathological parameters. We found 30% LOH in our study and it was also correlated with the clinicopathological parameters. No correlation was found between LOH and clinicopathological parameters. Though we found no correlation, the results revealed in this study support the involvement of BRCA1 TSG in the pathogenesis of sporadic breast cancer women in Chennai (South India).     

Loss of heterozygosity atBRCA1/2 loci in hereditary and sporadic ovarian cancers

Loss of heterozygosity atBRCA1/2 loci in breast and ovarian tumors is a suggested risk factor for germlineBRCA1/2 mutation status. We evaluated the presence of losses of selected microsatellite markers localized on chromosomes 17 and 13q in hereditary and sporadic ovarian tumors. 151 consecutive primary ovarian tumors (including 21 withBRCA1/2 mutations and 130 without the mutations) were screened for loss of heterozygosity at loci on chromosomes 17 and 13q. Losses of heterozygosity of at least one microsatellite marker localized on chromosomes 17 and 13q were revealed in 123 (81.5%) and 104 (68.9%) tumors, respectively. Losses of all informative markers on chromosomes 17 and 13 occurred in 30 (19.9%) and 31 (20.5%) tumors, respectively. There was no difference in the frequency of losses atBRCA1 intragenic markers (D17S855 and D17S1323) between BRCA1-positive and BRCA1-negative patients. The frequency of losses on chromosome 17 was higher in high-grade than in low-grade carcinomas. Loss of heterozygosity on chromosomes 17 and 13q is a frequent phenomenon in both hereditary and sporadic ovarian cancers. The frequency of losses atBRCA1 intragenic markers in the ovarian tumor tissue is not strongly related to the presence ofBRCA1 germline mutations.