Homozygous deletions of p16/MTS1 gene are frequent but mutations are infrequent in childhood T-cell acute lymphoblastic leukemia

Fifty-six primary childhood T-cell acute lymphoblastic leukemia (T-ALL) samples and 17 T-ALL cell lines were examined for mutations and homozygous deletions of the p16/MTS1 gene using polymerase chain reaction single-strand conformation polymorphism and Southern blot analysis. Homozygous deletions were found in 22 primary samples (39%) and in 10 cell lines (59%). In contrast, mutations including small deletions and/or insertions were identified in only 4 primary samples (7%) and in 2 cell lines (12%). Mutations included samples (7%) and in 2 cell lines (12%). Mutations included one nonsense mutation at codon 72, one missense mutation at codon 58, one deletion (29 bp from codon 52-61), one insertion (7 bp into codon 50), and two deletion/insertions (codon 63 and intron 1). Four of the six mutations caused subsequent stop codon and presumably produced truncated p16 protein. Our results suggest that p16 gene alterations are involved in the development of T- ALLs and that the inactivation of the p16 gene occurs mainly through homozygous deletions rather than mutations.     

p16 gene homozygous deletions in acute lymphoblastic leukemia

The p16 protein is a cyclin inhibitor encoded by a gene located in 9p21, which may have antioncogenic properties, and is inactivated by homozygous p16 gene deletion or, less often, point mutation in several types of solid tumors often associated to cytogenetic evidence of 9p21 deletion. We looked for homozygous deletion and point mutation of the p16 gene in acute lymphoblastic leukemia (ALL), where 9p21 deletion or rearrangement are also nonrandom cytogenetic findings. Other hematologic malignancies including acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), chronic lymphocytic leukemia (CLL), and myeloma were also studied. Homozygous deletion of the p16 gene was seen in 9 of the 63 (14%) ALL analyzed, including 6/39 precursor B-ALL, 3/12 T-ALL, and 0/12 Burkitt's ALL. Three of the 7 ALL with 9p rearrangement (including 3 of the 5 patients where this rearrangement was clearly associated to 9p21 monosomy) had homozygous deletion compared to 5 of the 55 patients with normal 9p (the last patient with homozygous deletion was not successfully karyotyped). Single stranded conformation polymorphism analysis of exons 1 and 2 of the p16 gene was performed in 88 cases of ALL, including the 63 patients analyzed by Southern blot. Twenty-six of the cases had 9p rearrangement, associated to 9p21 monosomy in at least 12 cases. A missense point mutation, at codon 49 (nucleotide 164), was seen in only 1 of the 88 patients. No homozygous deletion and no point mutation of the p16 gene was seen in AML, MDS, CLL, and myeloma. Homozygous deletion of interferon alpha genes (situated close to p16 gene in 9p21) was seen in only 3 of the 9 ALL patients with p16 gene homozygous deletion, and none of the ALL without p16 gene homozygous deletion. Our findings suggest that homozygous deletion of the p16 gene is seen in about 15% of ALL cases, is not restricted to cases with cytogenetically detectable 9p deletion, and could have a pathogenetic role in this malignancy. On the other hand, p16 point mutations are very rare in ALL, and we found no p16 homozygous deletions or mutations in the other hematologic malignancies studied.     

Homozygous deletions of p16 in human gastric adenocarcinoma

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Genetic analysis of p53 and RB1 tumor-suppressor genes in blast crisis of chronic myeloid leukemia

Summary We have investigated the involvement of the p53 and RB1 tumor-suppressor genes in 26 cases of chronic myeloid leukemia (CML) blast crisis, including 17 myeloid, eight lymphoid, and one megakaryoblastic crisis. The presence of p53 mutations in exons 5 through 9 was tested by the PCR-single-strand conformation polymorphism (SSCP) assay, followed by PCR-direct sequencing; in addition, loss of heterozygosity (LOH) at 17p13, the site of the p53 gene, was assayed by Southern blot. Given the variability of the mechanisms of inactivation of the RB1 gene in human tumors, a combination of Southern blot and mutational analysis by PCR-SSCP was used. p53 mutations were restricted to one case of myeloid blast crisis, showing a CGCTGC (ArgCys) mutation at codon 283; two additional cases displayed LOH at 17p13 in the absence of p53 mutations. No molecular lesions of the RB1 gene were detected in any of the cases analyzed. These data indicate that inactivation of p53 and RB1 is a rare event in the molecular pathogenesis of CML acute transformation.     

Alveolar proteinosis associated with chronic myeloid leukemia

The association of pulmonary alveolar proteinosis with hematologic malignancy is well known. The prognosis, in this peculiar setting, is poor. Yet, few patients have been treated in due time. We report a case of pulmonary alveolar proteinosis associated with chronic granulocytic leukemia. The evolution was fatal in spite of intensive treatment.     

非小细胞肺癌中MTAP与p16纯合缺失与突变分析

目的研究非小细胞肺癌中MTAP与p16纯合性缺失与点突变发生频率,探讨MTAP与肺癌的相关性。方法提取44例原发性非小细胞肺癌标本(21例腺癌和23例鳞癌)的基因组DNA;设计MTAP、p16基因外显子及其参照基因MTAP的引物,以基因组DNA为模板,进行PCR扩增,通过SSCP分析基因点突变现象,通过PCR-ELISA分析基因纯合性缺失现象。结果SSCP方法分析发现在44例原发性肺癌标本中,p16和MTAP没有点突变现象;PCR-ELISA分析发现p16基因的纯合性缺失频率为6.8%,MTAP的纯合性缺失频率9.1%,统计学分析表明二基因之间的缺失频率无显著性差异,但二者均与非小细胞肺癌显著相关。结论与p16类似,MTAP纯合性缺失是原发性非小细胞肺癌中发生的重要事件之一,有其肿瘤生物学基础。     

Philadelphia-chromosome-negative chronic myelogenous leukemia with lymphoid stem cell blastic transformation

A patient is described who had blastic transformation of Ph1 negative chronic myelogenous leukemia (Ph1 - CML). Characterization of the leukemic cells revealed a population with a lymphoid stem cell phenotype (cALL-, TdT+, Ia+, cIgM-). This particular phenotype may be responsible for the refractoriness to vincristine and prednisone and the rapid downhill course.     

Double Ph-positive megakaryoblastic transformation of chronic myeloid leukemia

A 64-yr-old Japanese man presented with mild anemia, leukocytosis, and thrombocytosis in November 1999. A diagnosis of chronic myeloid leukemia was made with a positive Ph chromosome, and interferon alpha treatment was started, 6 million units a day. Two years later, in October 2001, the patient developed leukocytosis, an increased LDH level, and large blasts with basophilic cytoplasm with cytoplasmic projections appeared in the peripheral blood. Bone marrow aspiration revealed increased blasts (59.6%). These blasts were negative on peroxidase stain, positive on acid phosphatase, and weakly positive on alpha naphthyl butyrate esterase stain and periodic acid-Schiff stain. Immunohistochemical staining with monoclonal antibodies revealed that these blasts were strongly positive with anti-CD41 (glycoprotein IIb/IIIa), weakly positive with CD7, CD33, and CD34, and negative with other monoclonal antibodies. A diagnosis of megakaryoblastic transformation from chronic myeloid leukemia was therefore made. Two-color fluorescence in situ hybridization (FISH) for portions of the major-bcr and abl genes from bone marrow cells revealed two fused signals in 90.6% and one fused signal in 5.8% of 106 cells. A cytogenetic study revealed that bone marrow cells were 69, XYY, +6, -7, +8, -9, t(9;22)(q34;q11), +11, +13, -15, -16, dic(17;18)(p11;p11), -18, +19, +21, der(22)t(9;22) in six of nine examined cells. These findings confirmed that these megakaryoblasts originated from megakaryocytes of the chronic myeloid leukemia clone.     

Hypercalcemia associated with blast crisis of chronic myeloid leukemia

We describe a patient with CML who developed hypercalcemia in his course of blast crisis. A 25-years-old man was diagnosed as CML with priapism in April 1985, and controlled with BHAC-DVP, VMP, busulfan therapy. In December 1987, he readmitted to our hospital with abdominal pain. Investigations at that time showed: white blood cell count 11600/microliters (blast cells 9%); hemoglobin 8.4 g/microliters; platelets 19.0 X 10(4)/microliters; serum calcium 13.2 mg/dl; BUN 44 mg/dl; creatinine 2.7 mg/dl. Treatment with predonine, 6-MP and vincristine was begun. But serum calcium level rose gradually up to 16.5 mg/dl. So we tried middle dose Ara-c therapy, serum calcium decreased to 6.8 mg/dl. At once he was in a chronic phase, but he relapsed and died of heart failure. Necropsy showed extensive leukemic blast-cell infiltration of the bone marrow, liver, spleen, lung, and kidney. The cause of hypercalcemia in our case was suspected of local osteolytic hypercalcemia, because multiple bone destruction was found.     

Homozygous deletions of the p15 (MTS2) and p16 (CDKN2/MTS1) genes in adult T-cell leukemia

Adult T-cell leukemia (ATL) is associated with prior infection with human T-cell leukemia virus type I (HTLV-I). Twenty to 40 years often elapse from viral infection to overt ATL, suggesting that other genetic events must occur to produce frank leukemia. The p15 (MTS2) and p16 (CDKN2/MTS1) genes located on chromosome 9p have been implicated as candidate tumor-suppressor genes in several types of tumors. We examined for alterations of these genes in ATL using Southern blot and polymerase chain reaction-single-strand conformation polymorphism analyses. Both p15 and p16 genes were homozygously deleted in 4 of 23 acute/lymphomatous ATL (17%). An additional 3 (13%) and 4 (17%) acute/lymphomatous samples had hemizygous deletions in at least one exon of p15 and p16, respectively. One of 14 chronic ATL samples had a homozygously deleted p16 gene and another had a hemizygous deletion of p16. Neither homozygous nor hemizygous deletions of the p15 gene were found in chronic ATL. In total, 10 of 37 (27%) ATL samples had loss of the p15 and/or p16 genes. No point mutations of the p15 and p16 genes were found. The ATL patient with a homozygously deleted p16 in the chronic phase rapidly progressed to acute ATL and died within 6 months of the initial diagnosis. One instructive patient had no detectable deletion of the p15 and p16 genes during the chronic phase of ATL but had a homozygous deletions of both genes when she progressed to acute ATL. Our results suggest an association of p15/p16 deletions with development of acute ATL.     

Mucosa-associated lymphoid tissue type lymphoma of the gallbladder associated with acute myeloid leukemia.

We describe a patient with mucosa-associated lymphoid tissue (MALT) type lymphoma of the gallbladder who developed concurrent acute myeloid leukemia (M2). She was admitted because of progressive jaundice and underwent cholecystectomy. Histologic examination of the gallbladder showed diffuse proliferation of atypical lymphoid cells and a formed lymphoepithelial lesion. Because of progressive thrombocytopenia, a bone marrow tap was performed 25 days after the operation. Bone marrow contained 65.5% blasts, and was positive for peroxidase, CD33 and HLA-DR, and negative for lymphoid markers. We discuss the rare association of these disorders.     

Frequent deletions of JARID2 in leukemic transformation of chronic myeloid malignancies

Chronic myeloproliferative neoplasms (MPN) and myelodysplastic syndromes (MDS) have an inherent tendency to progress to acute myeloid leukemia (AML). Using high-resolution SNP microarrays, we studied a total of 517 MPN and MDS patients in different disease stages, including 77 AML cases with previous history of MPN (N = 46) or MDS (N = 31). Frequent chromosomal deletions of variable sizes were detected, allowing the mapping of putative tumor suppressor genes involved in the leukemic transformation process. We detected frequent deletions on the short arm of chromosome 6 (del6p). The common deleted region on 6p mapped to a 1.1-Mb region and contained only the JARID2 gene--member of the polycomb repressive complex 2 (PRC2). When we compared the frequency of del6p between chronic and leukemic phase, we observed a strong association of del6p with leukemic transformation (P = 0.0033). Subsequently, analysis of deletion profiles of other PRC2 members revealed frequent losses of genes such as EZH2, AEBP2, and SUZ12; however, the deletions targeting these genes were large. We also identified two patients with homozygous losses of JARID2 and AEBP2. We observed frequent codeletion of AEBP2 and ETV6, and similarly, SUZ12 and NF1. Using next generation exome sequencing of 40 patients, we identified only one somatic mutation in the PRC2 complex member SUZ12. As the frequency of point mutations in PRC2 members was found to be low, deletions were the main type of lesions targeting PRC2 complex members. Our study suggests an essential role of the PRC2 complex in the leukemic transformation of chronic myeloid disorders.     

Chromosome 3q21 abnormalities associated with hyperactive thrombopoiesis in acute blastic transformation of chronic myeloid leukemia

Two patients with acute blastic transformation of chronic myeloid leukemia (CML) associated with strikingly elevated platelet counts showed abnormalities of chromosome 3q in addition to the standard Philadelphia (Ph1) chromosome translocation. The first patient had an inversion of chromosome 3 (q21q26) cytologically identical to an inversion 3 previously reported in de novo acute megakaryoblastic leukemia, and the second patient showed a translocation between chromosome 3q and the chromosome 9 homologue not involved in the Ph1 translocation, [t(3;9)(q21;q34)]. Previous studies had incriminated either 3q21 or 3q26 as the locus for a regulatory thrombopoietic gene, but the current study suggests that 3q21 is the relevant site.