Telomerase activity in cell lines and lymphoma originating from Bloom syndrome.

Bloom syndrome (BS) is characterized by premature aging and high predisposition to various types of cancer. BLM is the causative gene for BS. BLM functions as a DNA helicase in the direction of 3' to 5' and small subsets of telomeres colocalize with BLM protein. We investigated telomerase activity and telomere repeat length in the cells from BS patients. In Epstein-Barr-virus (EBV) transformed lymphoblastoid cell lines and lymphoma cells from BS patients, telomerase activity was detected as in the control and compared. The metastatic tumor from BS patient, which had a 9-bp deletion of p53 DNA showed the strongest telomerase activity. Telomere repeat length in BS cells showed that there is no large difference compared with normal cells. Collectively, the results show that the BLM gene is not a major structural and regulatory factor in maintaining telomere repeat length and telomerase activity.     

No evidence of replication error phenotype in primary gastric lymphoma of mucosa-associated lymphoid tissue

Replication error (RER) phenotype, caused by deficiency of DNA mismatch repair genes and revealed by widespread microsatellite instability, has been detected in subsets of a wide variety of solid tumors, but rarely in lymphomas in general. So far, the involvement of RER phenotype in the pathogenesis of gastric lymphoma of mucosa-associated lymphoid tissue (MALT) type has not been conclusively established. We therefore examined 9 microsatellite loci on 5 chromosomes [D2S123, D3S11, D3S1261, D3S1262, D3S1265, D6S262, D18S59, a CTTT(T) repeat in intron 20 of RB1 gene and a CA repeat in p53 locus] in 33 cases of primary gastric MALT lymphoma for evidence of microsatellite instability by polymerase chain reaction using primers end-labeled with [γ-³³P] ATP. Although novel-length allele was observed in 7 of 33 cases (21.2%), none of these 7 cases showed changes in more than one locus. RER phenotype was scored as positive in a case when more than 1 of the 9 examined microsatellite loci showed length alterations. Accordingly, none of the 33 cases had a RER phenotype. This result suggests that the pathogenesis of gastric MALT lymphoma does not involve RER phenotype. It is consistent with the general observations in lymphomas, but is highly in contrast to a previous report showing more than 50% of MALT lymphomas with the RER phenotype. Int. J. Cancer 76:635–638, 1998.© 1998 Wiley-Liss, Inc.     

Management of malignant lymphoma in two siblings with Bloom's syndrome

Treatment of the malignant neoplasms which develop in patients with chromosome fragile syndrome, such as Bloom's syndrome (BS), requires extremely careful planning of the chemotherapy regime because of the excessive chemosensitivity of patients with such syndromes. Two siblings with BS developed B cell-type non-Hodgkin's lymphoma in the third decade of their lives. In both cases a 3-bp homozygous deletion of the BLM gene was detected. Since the lymphoma of the older brother was nasopharyngeal in origin, he was administrated radiation therapy as the primary treatment. However, hepatic metastasis was detected and this was the cause of his death. A 9-bp deletion in exon 7 of the p53 gene was detected in the metastatic lymphoma. His younger sister developed a lymphoma of abdominal lymph node in origin. She received a half dose of the drugs used in the acute lymphoblastic leukemia treatment without radiation, and twenty months after the diagnosis of her lymphoma she continues to be in complete remission and free of treatment complications. The p53 gene mutation was not detected in her lymphoma. These results suggest that radiation therapy and the radiation dose for the treatment for lymphoma in patients with BS should be carefully considered.     

Microsatellite Instability and k-ras, p53 Mutations in Thyroid Lymphoma

Patho-epidemiological studies showed that thyroid lymphoma (TL) arises in inflammatory lesions of chronic lymphocytic thyroiditis (CLTH). Replication error (RER) is found in inflammatory lesions and associated cancer, suggesting that chronic inflammation could be a risk factor for neoplastic development through causing RER. To clarify whether RER is involved in the pathogenesis of TL, we examined the microsatellite instability (MSI) in 9 cases with CLTH and 19 with TL, including 10 diffuse large B-cell lymphoma (DLBL), 4 follicle center cell lymphoma, 3 marginal zone B-cell lymphoma of extranodal (MALT) type, and 2 lymphoplasmacytic type. Sixteen distinct microsatellite repeats were analyzed. Mutations of p53 and k- ras genes were also examined. When alterations at 2 or more microsatellite loci were judged as positive, only 5 DLBL cases exhibited MSI. The frequency of MSI in DLBL was significantly higher than that in other types of TL and CLTH ( P < 0.05). Four of 19 cases (21.1%) showed point mutation of the k- ras gene. The k- ras mutations occurred in the cases with DLBL with RER, and four of five cases with RER had a k- ras mutation, indicating a close association between RER and k- ras mutation. p53 mutations were not found in the CLTH. Two of 19 TL cases showed mutations of p53 gene. There was no significant association between RER and p53 mutation. These findings indicate that genomic instability contributes to the progression of TL from low grade to high grade, but not to the development of low grade lymphoma in CLTH lesions.     

Microsatellite instability and k-ras, p53 mutations in thyroid lymphoma.

Patho-epidemiological studies showed that thyroid lymphoma (TL) arises in inflammatory lesions of chronic lymphocytic thyroiditis (CLTH). Replication error (RER) is found in inflammatory lesions and associated cancer, suggesting that chronic inflammation could be a risk factor for neoplastic development through causing RER. To clarify whether RER is involved in the pathogenesis of TL, we examined the microsatellite instability (MSI) in 9 cases with CLTH and 19 with TL, including 10 diffuse large B-cell lymphoma (DLBL), 4 follicle center cell lymphoma, 3 marginal zone B-cell lymphoma of extranodal (MALT) type, and 2 lymphoplasmacytic type. Sixteen distinct microsatellite repeats were analyzed. Mutations of p53 and k-ras genes were also examined. When alterations at 2 or more microsatellite loci were judged as positive, only 5 DLBL cases exhibited MSI. The frequency of MSI in DLBL was significantly higher than that in other types of TL and CLTH (P < 0.05). Four of 19 cases (21.1%) showed point mutation of the k-ras gene. The k-ras mutations occurred in the cases with DLBL with RER, and four of five cases with RER had a k-ras mutation, indicating a close association between RER and k-ras mutation. p53 mutations were not found in the CLTH. Two of 19 TL cases showed mutations of p53 gene. There was no significant association between RER and p53 mutation. These findings indicate that genomic instability contributes to the progression of TL from low grade to high grade, but not to the development of low grade lymphoma in CLTH lesions.     

The mtDNA Microsatellite Instability Indicated the Prognosis of Chinese Patients with Non-Hodgkin’s Lymphoma

This study aimed to investigate the relationship and diagnostic potential between microsatellite instability (MSI) caused by a 9-bp GGGGGTAGA insertion/deletion in mitochondrial DNA (mtDNA) at position 8272 and clinical features in Chinese patients diagnosed with non-Hodgkin’s lymphoma. The 9-bp GGGGGTAGA insertion/deletion in the non-d-loop area of the mitochondrial DNA at the 8272 locus was detected by PCR in 139 non-Hodgkin’s lymphoma patient samples. GGGGGTAGA insertion/deletion was found in a total of 16 cases (11.5%), including nine T cell lymphoma and seven B cell lymphoma cases. The 5-year survival rate was 33.3% in patients with non-Hodgkin’s lymphoma and MSI, and was 26.7% in non-Hodgkin’s lymphoma patients lacking MSI. In B-cell lymphoma, the 5-year survival rate was 42.9% in patients harboring the 9-bp insertion/deletion, and was 36.8% in patients lacking MSI. In T-cell lymphoma, the 5-year survival rate was 55.6% in patients with the 9-bp insertion/deletion, and was 16.4% in patients lacking MSI (p < 0.05). The difference between 5-year survival rates was statistically significant only in T-cell lymphoma patients. In conclusion, the mtDNA GGGGGTAGA indel/variation at position 8272 can be used as an independent prognostic marker for T-cell lymphoma.     

Molecular analysis of mucosa-associated lymphoid tissue (MALT) lymphoma of ocular adnexa.

Lymphomas of mucosa-associated lymphoid tissue (MALT) are a distinct subgroup of extranodal B-cell non-Hodgkin's lymphomas. Most studies have failed to demonstrate the clonal rearrangement of BCL-1, BCL-2 or c-MYC genes for MALT lymphomas. Further, alteration of the p53 gene is rarely demonstrated in low-grade MALT lymphomas, but can be detected in high-grade disease. Lymphomas of the ocular adnexa represent approximately eight percent of all extranodal lymphomas, most of which are MALT lymphomas, but few studies had explored the alterations of BCL-1, BCL-2, c-MYC and p53 genes specifically for ocular MALT lymphomas. We investigated the changes to BCL-1, BCL-2, c-MYC and p53 genes in these lymphomas for Taiwanese patients. Clonal rearrangement for immunoglobulin heavy-chain (IgH), BCL-1, BCL-2, c-MYC and p53 genes was examined for 16 cases of ocular MALT lymphoma. Restriction-length polymorphism and polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) of the DNA, corresponding to exons 5 through 9, followed by DNA sequencing, were utilized to analyze the possible mutations of the p53 gene for these tumors. Thirteen of the cases revealed rearranged IgH genes using Southern blotting or PCR. No rearrangement of BCL-1, BCL-2, c-MYC or p53 genes was discovered, with point mutation of the p53 gene in one case. As for other types of MALT lymphomas, BCL-1, BCL-2 and c-MYC genes are not implicated in the pathogenesis of the ocular sub-group. Although alteration of the p53 gene is rare for low-grade ocular MALT lymphoma, its role in disease progression merits further research.     

Disrupted p53 function as predictor of treatment failure and poor prognosis in B- and T-cell non-Hodgkin's lymphoma.

Mutation of the p53 gene has been associated with treatment failure and poor outcome in various malignancies. It has been suggested that immunohistochemical analysis of p53 and p21Waf1, a downstream target, can be used to screen for p53 gene mutations. We determined the value of immunohistochemical screening for p53 gene mutations as a prognostic marker in a population-based group of B- and T-cell non-Hodgkin's lymphomas (NHLs). On the basis of p53 gene mutation status and immunohistochemically detected p53 and p21Waf1 expression in 34 lymphomas, we established an immunophenotype (delta p53) correlating with p53 gene mutation. The immunohistochemical analysis was extended to encompass 199 lymphomas from a population-based registry and was correlated with clinical parameters. Delta p53 showed 100% concordance with p53 gene mutation and was detected in 42 cases (21%). Multivariate analysis of advanced stage lymphomas showed that delta p53 was independently associated with treatment failure (relative risk, 3.8; P = 0.001). Delta p53 predicted poor survival when analyzing all patients (P = 0.0001), as well as B-cell (P = 0.04) and T-cell NHL (P = 0.000002). In multivariate analysis, delta p53 (relative risk, 2.2; P = 0.001) maintained prognostic significance. The impact on prognosis of delta p53 was highly significant in the low-intermediate-risk group (P = 0.00002). Comparing survival of the aggressive lymphoma patients in this group showed that the 8 delta p53 patients died within 1 year, whereas the median survival of the 28 non-delta p53 patients was 36 months. These results suggest that immunohistochemically assessed p53 status may predict treatment response and outcome in B- and T-cell NHL patients.     

Mutation analysis of mitotic checkpoint genes (hBUB1 and hBUBR1) and microsatellite instability in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a neoplasm of T-lymphocytes, and human T-cell lymphotropic virus type-I (HTLV-I) is etiologically considered as the causative virus of ATLL. The karyotypes of ATLL are very complex in both number and structure, although no specific karyotype abnormalities have been identified. HTLV-I is thought to integrate its provirus into random sites in host chromosomal DNA and induces chromosomal instability. The BUB gene is a component of the mitotic checkpoint in budding yeast. Recently, human homologues of the BUB were identified and mutant alleles of hBUB1 and hBUBR1 were detected in two colorectal tumor cell lines, which showed microsatellite instability (MIN). In vitro, BUB proteins form a complex of monomers. These proteins interact with the human MAD1 gene product, a target of the HTLV-1 tax oncogene. We examined the role of checkpoint gene in the chromosomal abnormalities of ATLL by investigating mutations of hBUB1 and hBUBR1, and MIN of replication errors of BAX, insulin-like growth factor, and transforming growth factor beta type II. We analyzed ten cases with ATLL and eight B-cell lymphomas (five diffuse large cell lymphomas, three follicular lymphomas). Complex chromosomal abnormalities were detected in ATLL, while B-cell lymphomas showed only simple or minimal chromosomal abnormalities. Significant mutations/deletion of hBUB1 or hBUBR1 were detected in four of ten cases with ATLL, including two heterozygous point mutations, one homozygous point mutation, and one with a 47 bp deletion. In contrast, only one of eight B-cell lymphomas showed nonsense mutation of hBUBR1. None of the ATLL and B-cell lymphomas showed MIN. In the multistage process of leukemogenesis of ATLL, our findings indicate that mutations of mitotic checkpoint genes may play an important role in the induction of complex chromosomal abnormalities.     

Histopathologic features and expression of Bcl-2 and p53 proteins in primary gastric lymphomas

The aim of this study is to present a histopathologic and immunohistochemical analysis of primary gastric lymphomas which were reclassified according to the concept of mucosa associated lymphoid tissue (MALT). The resected specimens from 41 patients with primary gastric lymphoma were investigated retrospectively. Immunohistochemical study was done to analyze the immunophenotype and bcl-2 and p53 proteins expression. Twenty three of the cases had tumors mainly located in the antrum. Histologically, 12 were low grade and 20 were high grade B-cell lymphoma of MALT, 9 other B-cell nonHodgkin's lymphomas. Helicobacter pylori was identified in 72% of the cases. According to Musshoff's modification, most of the MALT lymphoma cases had stage I or II disease. There was significant difference between low and high grade cases, in respect to depth of invasion in gastric wall. Immunohistochemically, the neoplastic cells in all MALT lymphomas expressed B-cell phenotype. Bcl-2 protein was found to be expressed in 59% and p53 protein expression was detected in 72% of cases. Among the B-cell lymphoma of MALT, bcl-2 positivity decreased and p53 positivity increased significantly as the histological grade advanced. So, an inverse correlation was observed between the expression of bcl-2 and p53. In conclusion, most primary gastric lymphomas are low or high grade B-cell MALT lymphomas and appear to arise in MALT acquired as a reaction to Helicobacter pylori infection. Expression of bcl-2 and p53 in gastric lymphomas may be associated with transformation from low-grade to high-grade disease.     

SV40 and p53 as team players in childhood lymphoproliferative disorders

Simian virus 40 (SV40) is known to be potently oncogenic and can induce several types of tumours, such as lymphoma. p53 was discovered as a cellular partner of the SV40 large T-antigen, the oncoprotein of this virus. There have not been many studies on SV40 and p53 in lymphomas and the ones that exist, are controversial. A comparison of these two components in lymphoma has not been reported previously. We examined 91 lymphomas [60 B-cell non-Hodgkin's lymphomas (B-NHLs), 19 B-cell acute lymphoblastic leukemias (B-ALLs), 7 B-cell precursor acute lymphoblastic leukemias and 5 T-cell acute lymphoblastic leukemias] for the presence of SV40. Overall, 40 samples from 12 B-NHL/19 B-ALL patients were additionally investigated for p53 mutation in the hot-spot exons 5 to 8. Overall, we found 62/91 lymphomas to be SV40-positive, among them 16/19 B-ALLs and 38/60 B-NHLs. SV40 was absent in 147 of the 149 blood control samples. We found 11 p53 mutations in 19 B-ALL patients: 5 in exon 5 (codons 132, 141, 143, 155 and 181), 4 in exon 7 (codons 236, 238 and 248), 2 in exon 8 (codon 273). In B-NHL patients we found p53-mutations in 9/12 samples: 6 of these in 3 lymph nodes (LNs). One LN harboured 3 different p53 mutations: Exon 5 (codon 132), exon 6 (codon 213) and exon 8 (codon 288). Another LN showed 2 different p53 mutations: Exon 6 (codon 213) and exon 8 (codon 285). Except for 1 nonsense mutation in an LN of a B-NHL patient, all 20 mutations were missense mutations, 2 were homozygous, both found in B-NHL-samples, and one of these (codon 175) is known to cause the global denaturation of p53. All occur in the DNA-binding domain of p53. All specimens showing a p53 mutation, were SV40-positive. p53 mutaions found in LNs of B-NHL patients harbour high SV40 copy numbers. Our data strongly support an important role for SV40, as well as a strong association of SV40 and p53 in childhood lympho-proliferative disorders.     

p53 Gene mutation and genetic instability in superficial multifocal esophageal squamous cell carcinoma

Tumor multicentricity is occasionally observed in esophageal squamous cell carcinoma (SCC). We studied five surgically resected superficial multifocal esophageal SCCs for p53 gene mutation and genetic instability, using DNA extracted from microdissected areas. A total of 38 target areas (TAs) were analyzed in SCC, dysplasia, basal cell hyperplasia (BCH) and normal squamous epithelium. Analysis of the replication error (RER) at 10 microsatellite loci showed microsatellite instability in all TAs, as well as in normal squamous epithelium. p53 gene mutation was identified in 28.9% (11/38 TAs). All cases showed a common missense mutation in exon 8 at codon 273 (CGT-->CAT, Arg-->His), which was DNA contact mutation in the S10 beta strand. In association with microsatellite alterations, 7 of 9 TAs with p53 mutation in exon 8 at codon 273 also showed loss of heterozygosity (LOH) of p53 gene. LOH of p53 gene was detected in 83.8% (31/37 TAs). LOH at D2S123 on 2p16 near MSH2 gene and at D3S1611 on 3p22 near MLH1 gene was detected in 65.4% (17/26) and 71.4% (10/14) TAs, respectively. Frequencies of LOH at p53 and D2S123 were similar in non-cancerous areas and SCCs. LOH of p53 and D2S123 were found in 50% (5/10 TAs) of non-cancerous areas and 60% (9/15 TAs) of SCCs. Our results suggest that genetic instability induces esophageal tumor multicentricity, and that p53 gene contact mutation together with LOH are early events of the multistage carcinogenesis of multifocal primary esophageal SCC.     

Helicobacter pylori eradication therapy for high-grade mucosa-associated lymphoid tissue lymphomas of the stomach with analysis of p53 and K-ras alteration and microsatellite instability

Recent studies have shown that 70-80% of low-grade mucosa-associated lymphoid tissue (MALT) lymphomas regress in response to eradication of Helicobacter pylori (H. pylori). However, there are no reports on whether gastric high-grade MALT lymphomas regress after H. pylori eradication. We performed H. pylori eradication therapy in 4 patients with stage I, high-grade MALT lymphoma after obtaining their informed consent. H. pylori infection was observed in all 4 patients. The patients were treated with proton-pump inhibitor-based eradication therapy for 1 or 2 weeks, and then underwent endoscopic examination and biopsy sampling. H. pylori eradication was achieved in all 4 patients. Six months after eradication treatment, 2 patients showed complete regression of the lymphoma and 2 patients showed no change. The 2 patients with non-responding lymphoma were then treated with an additional chemotherapy (CHOP regimen), whereupon the tumors completely regressed. These patients, followed-up at least 18 months after eradication treatment, showed no recurrence. We also examined genetic alteration of the p53 and K-ras genes and microsatellite instability in these high-grade MALT lymphomas. One patient with a tumor that showed no change after H. pylori eradication, had a loss of heterozygosity of the p53 gene. No other genetic alterations were detected among the patients. Our results indicate that the eradication of H. pylori may be effective not only for patients with low-grade MALT lymphoma but also for patients with high-grade MALT lymphoma. The treatment may be efficacious as a first-line therapy for patients with high-grade MALT lymphoma. However, our sample size was limited and further studies are needed to clarify the issue.     

Analysis for microsatellite instability and mutations of the DNA mismatch repair gene hMLH1 in familial gastric cancer

We examined 30 gastric-cancer patients with a varying degree of family history of stomach cancer and/or synchronous gastric tumors for microsatellite instability. We observed microsatellite instability at at least 1 of 8 loci tested in tumors of 14/30 patients; of these 14, 8 had single locus alterations and 6 had alterations at at least half of the 8 loci. Among the patients with microsatellite instability at >=4 loci, 3 patients showed a strong familial clustering of gastric cancer. Mutation analysis of the DNA mismatch repair gene hMLH1 on paired non-tumorous and tumor DNA from 10 patients 6 with microsatellite instability at 24 loci and 4 with an alteration at one locus, revealed a novel missense mutation, present in the normal and tumor DNA of one patient with microsatellite instability at multiple loci in his tumor. His family history of cancer included one second-degree relative affected with gastric cancer. These data suggest that germline mutations in the hMLH1 gene occur in some gastric-cancer patients and that in the majority of cases microsatellite instability in gastric tumors may be due to defects in other genes responsible for DNA replication fidelity than the hMLH1. © 1996 Wiley-Liss, Inc.     

p53 Mutation in B-Cell Lymphoid Neoplasms with Reference to Oncogene Rearrangements Associated with Chromosomal Translocations

We investigated mutations of the p53 tumor suppressor gene in B-cell lymphoid neoplasms with reference to oncogene rearrangements associated with specific chromosomal translocations. These included 15 patients with a BCL1/PRAD1 gene rearrangement and/or PRAD1 overexpression, 45 with a BCL2 rearrangement, 2 with a BCL3 rearrangement, 24 with a BCL6 rearrangement, and 6 with both BCL2 and BCL6 rearrangements. Thirty-six patients lacked detectable oncogene rearrangements. Genomic DNA was isolated from involved tissues or leukemic cells obtained at diagnosis and/or at relapse, and established cell lines. Polymerase chain reaction-mediated single-strand conformation polymorphism analysis and direct sequencing were performed to analyze abnormalities of the p53 gene. We detected p53 gene alterations in 18 of 128 patients, representing 21 of the total 151 materials analyzed. In the total of 66 patients with an oncogene rearrangement studied at diagnosis, only one had a mutation; however, 6 of 37 patients studied at relapse showed p53 mutations. Sequential analysis revealed that the p53 mutation was closely associated with transformation from follicular lymphoma to large cell lymphoma, exclusively in BCL2 -positive lymphoma cases. Two of 13 mutations observed in oncogene rearrangement-positive cases and cell lines were transitions at CpG dinucleotides. In contrast, the relationship between p53 mutations and clinical behavior in oncogene rearrangement-negative cases was variable; 5 patients including one with indolent follicular lymphoma were positive for p53 mutation at initial presentation, and 2 of the 5 showed prolonged disease-free survival. Our findings suggest that p53 alteration exhibits diverse functions in the development and progression of B-cell tumors related to the presence or absence of oncogene rearrangement, and that chemotherapy-related influences may be involved in the occurrence of progression-associated p53 mutations.     

Mutations found in cell‐free DNAs of patients with malignant lymphoma at remission can derive from clonal hematopoiesis

Cell‐free DNA (cfDNA) analysis to detect circulating tumor DNA has been focused on monitoring malignant lymphomas. However, clonal hematopoiesis of indeterminate potential (CHIP)‐associated mutations can also be detected by cfDNA analysis. Our aim is to investigate the origin of mutations detected in cfDNA among B‐cell lymphoma patients. MYD88/CD79B, DNMT3A, and TP53 were chosen as genes of interest, representing each of the following categories: lymphoma driver genes, CHIP‐related genes, and genes shared between lymphoma and CHIP. Seventy‐five B‐cell lymphoma patients were included in this retrospective study. Serum cfDNAs at time of complete metabolic response (CMR) were sequenced for TP53 (N = 75) and DNMT3A (N = 49). MYD88 p.L265P and CD79B p.Y196C/H mutations were analyzed in diffuse large B‐cell lymphoma (DLBCL) patients whose tumor samples were available (N = 29). Two and seven mutations in TP53 and DNMT3A, respectively, were detected in cfDNA at CMR. These mutations were detected in either bone marrow mononuclear cells (BMMC) or PBMC. Although four DNMT3A mutations were also detected in tumors, median variant allele frequencies in the tumors (<1.0%) were significantly lower than those in both BMMC (6.1%) and serum (5.2%) obtained before the therapy. Conversely, five MYD88 and three CD79B mutations detected in tumors were confirmed in cfDNA before therapy, but not in BMMC nor in cfDNA at CMR. Thus, all TP53 and DNMT3A mutations detected in cfDNA at remission seemed to originate from CHIP rather than from residual disease. Results of liquid biopsy should be carefully interpreted, especially in genes shared between lymphomas and CHIP.     

A unique spectrum of p53 mutations in B-cell chronic lymphocytic leukemia distinct from that of other lymphoid malignancies

The spectrum and pattern of p53 mutations detected in 42 cases of B-cell chronic lymphocytic leukemia (B-CLL) were analyzed, and several interesting features were noted. Codon 209 in the p53 gene may be a new hot-spot for p53 mutation in B-CLL disease. Four of the 42 (10%) reported B-CLL p53 mutations occurred at codon 209 versus none in 214 cases of other lymphoid malignancies screened for p53 mutations (P = 0.0006). Transversion mutations predominated at codon 273 rather than the transition mutations that are known to occur at this CpG site. Four of six (67%) B-CLL cases had transversions at codon 273 compared with two of 17 (12%) of all other lymphoid tumors examined (P = 0.02). In addition, over 65% of the p53 mutations detected in B-CLL showed a strand bias for p53 mutations on the untranscribed DNA strand. This feature of DNA strand bias is notable in cancers of the lung, esophagus, and head and neck, which may result from high exposure to carcinogens. This spectrum of p53 mutations in B-CLL together with the high frequency of transversion mutations and DNA strand bias may implicate environmental carcinogens associated with p53 gene damage in some B-CLL patients. © 1995 Wiley- Liss, Inc.     

Bloom's syndrome protein response to ultraviolet-C radiation and hydroxyurea-mediated DNA synthesis inhibition

Bloom's syndrome (BS) arises through mutations in both copies of the BLM gene that encodes a RecQ 3'-5' DNA helicase. BS patients are predisposed to developing all the cancers that affect the general population, and BS cells exhibit marked genetic instability. We showed recently that BLM protein contributes to the cellular response to ionizing radiation by acting as downstream ATM kinase effector. We now show that following UVC treatment, BLM-deficient cells exhibit a reduction in the number of replicative cells, a partial escape from the G2/M cell cycle checkpoint, and have an altered p21 response. Surprisingly, we found that hydroxyurea-treated BLM-deficient cells exhibit an intact S phase arrest, proper recovery from the S phase arrest, and intact p53 and p21 responses. We also show that the level of BLM falls sharply in response to UVC radiation. This UVC-induced reduction in BLM does not require a functional ATM gene and does not result from a subcellular compartment change. Finally, we demonstrate that exposure to UVC and hydroxyurea treatment both induce BLM phosphorylation via an ATM-independent pathway. These results are discussed in the light of their potential physiological significance with regard to the role of BLM in the cellular pathways activated by UVC radiation or HU-mediated inhibition of DNA synthesis.     

Missense mutation of the hMSH6 and p53 genes in sporadic urothelial transitional cell carcinoma

Functional defects in DNA mismatch repair genes have been shown to be associated mainly with hereditary human malignancies. We examined genomic DNA from 88 sporadic transitional cell carcinomas (TCCs) of the urinary tract for mutations in hMSH6 gene by polymerase chain reaction and direct sequencing analysis. Mutational status of p53 gene was also studied as a potential target of genetic instability secondary to hMSH6 dysfunction. A total of 5 cases (5.7%: 5/88) displayed hMSH6 mutations all consisted of transition and located in exon 4, including three cases with missense mutation and two without change of corresponding amino acid. These three tumors with hMSH6 missense mutation had no microsatellite instability with five microsatellite markers tested. p53 gene mutations were detected in 22 cases (25.0%: 22/88). No tumors with p53 mutation had any hMSH6 missense mutations. Compared to the cases without hMSH6 alterations, the three patients with hMSH6 alterations had more frequent additional primary cancer (P<0.05). These findings provide the first in vivo evidence for the type of alterations and frequency of possible involvement of the hMSH6 mutations in sporadic type urothelial TCCs.