Establishment of a cell line with AML1-MTG8, TP53, and TP73 abnormalities from acute myelogenous leukemia

The Epigenetic Landscape of Meningiomas

Epigenetic changes have been found to be increasingly important in tumor development and progression. These alterations can be present in tumors such as meningiomas in the absence of any gene mutations and alter gene expression without affecting the sequence of the DNA itself. Some examples of these alterations that have been studied in meningiomas include DNA methylation, microRNA interaction, histone packaging, and chromatin restructuring. In this chapter we will describe in detail each of these mechanisms of epigenetic modification in meningiomas and their prognostic significance.

RCSD1-ABL1-positive B lymphoblastic leukemia is sensitive to dexamethasone and tyrosine kinase inhibitors and rapidly evolves clonally by chromosomal translocations

Recently, RCSD1 was identified as a novel gene fusion partner of the ABL1 gene. The RCSD1 gene, located at 1q23, is involved in t(1;9)(q23;q34) translocation in acute B lymphoblastic leukemia. Here we describe RCSD1-ABL1-positive B-cell acute lymphoblastic leukemia (ALL) followed by rapid clonal evolution exhibiting three rare reciprocal translocations. We performed breakpoint analysis of the transcript expressed by the RCSD1-ABL1 fusion gene. RT-PCR and sequence analyses detected transcription of a single RCSD1-ABL1 fusion gene variant, which had breakpoints in exon 3 of RCSD1 and exon 4 of ABL1. The RCSD1 portion of the RCSD1-ABL1 fusion transcript consists of exons 1, 2, and 3. Tyrosine kinase inhibitors, imatinib and dasatinib, coadministered with dexamethasone achieved transient clinical effects in the present RCSD1-ABL1-positive ALL. However, leukemic cells rapidly became refractory to this treatment following the subsequent development of three additional reciprocal chromosomal translocations, t(5;16)(q33;q24), dic(18;20)(p11.2;q11.2) and t(10;19)(q24;p13.3). The present RCSD1-ABL1-positive ALL may represent a state of high chromosomal instability.

p53 signaling in response to increased DNA damage sensitizes AML1-ETO cells to stress-induced death

Chromosomal translocation (8;21) is present in 10% to 15% of patients with acute myeloid leukemia. Expression of the AML1-ETO (AE) fusion protein alone is not sufficient to induce leukemia, but the nature of the additional genetic alterations is unknown. It is unclear whether AE facilitates acquisition of these cooperating events. We show that AE down-regulates genes involved in multiple DNA repair pathways, potentially through a mechanism involving direct binding at promoter elements, and increases the mutation frequency in vivo. AE cells display increased DNA damage in vitro and have an activated p53 pathway. This results in increased basal apoptosis and enhanced sensitivity to DNA damaging agents. Intriguingly, microarray data indicate that t(8;21) patient samples exhibit decreased expression of DNA repair genes and increased expression of p53 response genes compared with other acute myeloid leukemia (AML) patient samples. Inhibition of the p53 pathway by RNAi increases the resistance of AE cells to DNA damage. We thus speculate that AML1-ETO may facilitate accumulation of genetic alterations by suppressing endogenous DNA repair. It is possible that the superior outcome of t(8;21) patients is partly due to an activated p53 pathway, and that loss of the p53 response pathway is associated with disease progression.

Hypermethylation of the putative tumor-suppressor genes DCC, p51/63 and O6-methylguanine-DNA methyltransferase (MGMT) and loss of their expressions in cell lines of hematological malignancies

Alterations and defective expression of three putative tumor-suppressor genes, the deleted in colorectal cancer (DCC), p51, and O(6)-methylguanine-DNA methyltransferase (MGMT), have been demonstrated in many cancers. However, it is not known whether the defective expression of each of these genes is independent or whether it reflects a specific methylation abnormality. Here, we investigated the expression of the DCC, p51 and MGMT genes and the methylation status of the 5' flanking CpG region in 17 cell lines established from hematological malignancies. The reverse transcriptase-polymerase chain reaction method showed DCC expression to be absent in 13 of the 17 cell lines and showed expression of both p51 and MGMT to be absent in 5 of the 17 cell lines. The methylation patterns were analyzed with methylation-specific polymerase chain reaction (MSP) of the 5'flanking region of the DCC and p51 genes and the promoter region of the MGMT gene. Although unmethylated patterns of the CpG region in the DCC, p51, and MGMT genes were observed in all 11 normal controls, abnormal methylation patterns of these genes were found even in many cell lines expressing these genes. A hypermethylation pattern was detected for the CpG region of MGMT and p51 in cells that did not express these genes. In contrast, a hypermethylation pattern was not always detected for the CpG region of DCC in cells with reduced DCC expression. The results of this study indicate that in many hematological cell lines, the DCC, p51, and MGMT genes have been abnormally methylated in the CpG region. Hypermethylation of these three genes may be independent events in each cell line.

Tumor predisposition in mice mutant for p63 and p73: evidence for broader tumor suppressor functions for the p53 family

p63 and p73 are functionally and structurally related to the tumor suppressor p53. However, their own role in tumor suppression is unclear. Given the p53-like properties of p63 and p73, we tested whether they are involved in tumor suppression by aging mice heterozygous for mutations in all p53 family genes and scored for spontaneous tumors. We show here that p63+/-;p73+/- mice develop spontaneous tumors. Loss of p63 and p73 can also cooperate with loss of p53 in tumor development. Mice heterozygous for mutations in both p53 and p63 or p53 and p73 displayed higher tumor burden and metastasis compared to p53+/- mice. These findings provide evidence for a broader role for the p53 family than has been previously reported.

FISH analysis of hematological neoplasias with 1p36 rearrangements allows the definition of a cluster of 2.5 Mb included in the minimal region deleted in 1p36 deletion syndrome

Rearrangements in the distal region of the short arm of chromosome 1 are recurrent aberrations in a broad spectrum of human neoplasias. However, neither the location of the breakpoints (BP) on 1p36 nor the candidate genes have been fully determined. We have characterized, by fluorescence in situ hybridization (FISH), the BP in 26 patients with hematological neoplasias and 1p36 rearrangements in the G-banding karyotype. FISH allowed a better characterization of all samples analyzed. Nine cases (35%) showed reciprocal translocations, 15 (58%) unbalanced rearrangements, and two (7%) deletions. We describe two new recurrent aberrations. In 18 of the 26 cases analyzed the BP were located in band 1p36, which is 25.5 Mb long. In 14 of these 18 cases (78%) and without distinction between myeloid and lymphoid neoplasias, the BP clustered in a 2.5 Mb region located between 1p36.32 and the telomere. Interestingly, this region is contained in the 10.5 Mb cluster on 1p36.22-1pter defined in cases with 1p36 deletion syndrome. The 2.5 Mb region, located on 1p36.32-1pter, has a higher frequency of occurrence of tandem repeats and segmental duplications larger than 1 kb, when compared with the 25.5 Mb of the complete 1p36 band. This could explain its proneness for involvement in chromosomal rearrangements in hematological neoplasias.

Characterization of the recurrent translocation t(1;1)(p36.3;q21.1-2) in non-Hodgkin lymphoma by multicolor banding and fluorescence in situ hybridization analysis

Aberrations of chromosomal bands 1p36 and 1q11-q23 are among the most common chromosomal alterations in non-Hodgkin lymphoma (NHL). In this study, 16 cases of NHL showing recurrent unbalanced translocation t(1;1)(p36;q11-23) by G-band analysis were selected for further analysis. To delineate the exact breakpoints, multicolor band analysis for chromosome 1 (M-BAND1), and locus-specific fluorescence in situ hybridization (LS-FISH) using human genome designated BAC clones were performed. In all but one dicentric case, the breakpoint was determined to involve chromosomal bands 1p36.3 and 1q21.1-2. LS-FISH analysis for the TP73, MEL1, SKI, and CASP9 loci at 1p36, and the loci IRTA1, IRTA2, BCL9, AF1Q, JTB, and MUC1 at 1q21, verified the MBAND1 results and further delineated the breakpoints. In band 1p36, two hybridization patterns were observed, one involving deletions of MEL1, TP73, and SKI, but not CASP9, and the second involving a breakpoint telomeric to TP73. In region 1q21, four hybridization patterns were observed, the first involving duplication/translocation of all five genes; the second involving duplication/translocation of BCL9, AF1Q, JTB, and MUC1; the third involving duplication/translocation of AF1Q, JTB, and MUC1; and the fourth with a breakpoint telomeric to MUC1. Using an alpha-satellite probe for chromosome 1 (D1Z5), centromeric involvement in the unbalanced translocation t(1;1)(p36.3;q21.1-2) was excluded in all but the one dicentric case, that is, dic(1;1)(p36.3;q10). In conclusion, deletion of 1p36 and duplication of 1q21 through formation of an unbalanced translocation t(1;1)(p36.3;q21.1-2) is a non-random event in NHL, suggesting a deletion-duplication mechanism involved in lymphoma progression and justifying further systematic research.