BCL‐2 expression by leukaemic blasts in a SCID mouse model of biphenotypic leukaemia associated with the t(4;ll)(q21;q23) translocation

The chromosomal translocation t(4;11) marks infant acute lymphoblastic leukemia associated with a particularly dismal prognosis. The leukemogenic role of the corresponding fusion gene MLL-AF4 is not well understood. We show that transient inhibition of MLL-AF4 expression with small interfering RNAs impairs the proliferation and clonogenicity of the t(4; 11 IntroductionChromosomal aberrations giving rise to fusion genes are observed for many different leukemias. 1 Such tumor-specific oncogenes would be promising targets for new therapeutic approaches with improved specificity if these oncogenes were important for maintaining the leukemic phenotype. However, in contrast to the development of leukemia, a central role for leukemic persistence has only been established for a minority of fusion genes.The mixed-lineage leukemia (MLL) gene located on chromosome 11 band q23 is involved in numerous chromosomal aberrations associated with human leukemia. 2 The most prevalent among those is the translocation t(4;11)(q21;q23), which fuses MLL with the AF4 gene located on chromosome 4 band q21. [3][4][5] This translocation is the hallmark of a high-risk acute lymphoblastic leukemia (ALL) with a particularly poor prognosis in infants. 6 The wild-type MLL gene is a member of the trithorax family and encodes for a 430-kDa protein, which is proteolytically processed into 2 fragments of 300 and 180 kDa heterodimerizing with each other. [7][8][9][10] The MLL protein has a complex structure that includes an AT hook domain for A-T base-pair-rich DNA binding, a metallothionein domain showing homology to DNA methyltransferase, and methyl-binding domain protein 1 (MBD1), a plant homeodomain (PHD) containing zinc fingers and a Su(var)3-9, enhancer of zeste, trithorax (SET) histone methyl transferase domain. 2 MLL and at least some of its leukemic derivatives are involved in mechanisms controlling HOX gene transcription. [11][12][13][14] Moreover, the HOX genes HOXA7 and HOXA9 in combination with the homeotic gene MEIS1 are necessary for the transformation induced by several different MLL fusion genes. 15-17 Such a crucial role has not yet been reported for MLL-AF4. Nevertheless, expression levels of several HOX genes and of MEIS1 are raised in both primary t(4;11) ALL and t(4;11) leukemic cell lines. [18][19][20][21] The AF4 gene encodes a serine/proline-rich protein containing a nuclear localization signal and a guanosine triphosphate (GTP)-binding domain. It localizes to the nucleus 22 and is probably involved in the control of gene transcription. Whereas homozygous inactivation of MLL is embryonally lethal, 23 AF4-deficient mice exhibit imperfect T-cell development and modest alterations in B-cell development. 24 The t(4;11) translocation generates 2 fusion genes, AF4MLL and MLL-AF4. The significance of either fusion gene for leukemogenesis is currently not completely understood. AF4MLL has recently been shown to interfere with ubiquitin-mediated ALL-1 fused gene from chromosome 4 (AF4) degradation and to transform murine embryonic fi...

mentioning

confidence: 69%

Targeting MLL-AF4 with short interfering RNAs inhibits clonogenicity and engraftment of t(4;11)-positive human leukemic cells

Thomas¹,

Geßner²,

Vornlocher³

et al. 2005

“…SEMK2 was originally derived from a 5-year-old girl at relapse 15 and was kindly provided by Dr Scott Armstrong (Dana-Farber Cancer Institute). BEL-1 was a generous gift from Dr Ruoping Tang (University Laboratory, Paris).…”

Section: Leukemia Cell Linesmentioning

confidence: 99%

Specific promoter methylation identifies different subgroups of MLL-rearranged infant acute lymphoblastic leukemia, influences clinical outcome, and provides therapeutic options

Stumpel

Schneider

Roon

et al. 2009

142

137

MLL-rearranged infant acute lymphoblastic leukemia (ALL) remains the most aggressive type of childhood leukemia, displaying a unique gene expression profile. Here we hypothesized that this characteristic gene expression signature may have been established by potentially reversible epigenetic modifications. To test this hypothesis, we used differential methylation hybridization to explore the DNA methylation patterns underlying MLLrearranged ALL in infants. The obtained results were correlated with gene expression data to confirm gene silencing as a result of promoter hypermethylation. Distinct promoter CpG island methylation patterns separated different genetic subtypes of MLL-rearranged ALL in infants. MLL translocations t(4;11) and t(11;19) characterized extensively hypermethylated leukemias, whereas t(9;11)-positive infant ALL and infant ALL carrying wildtype MLL genes epigenetically resembled normal bone marrow. Furthermore, the degree of promoter hypermethylation among infant ALL patients carrying t(4; 11) or t(11;19) appeared to influence relapse-free survival, with patients displaying accentuated methylation being at high relapse risk. Finally, we show that the demethylating agent zebularine reverses aberrant DNA methylation and effectively induces apoptosis in MLLrearranged ALL cells. Collectively these data suggest that aberrant DNA methylation occurs in the majority of MLLrearranged infant ALL cases and guides clinical outcome. Therefore, inhibition of aberrant DNA methylation may be an important novel therapeutic strategy for MLL-rearranged ALL in infants. (Blood. 2009;114:5490-5498) IntroductionAlthough long-term survival rates in childhood acute lymphoblastic leukemia (ALL) exceed 80%, 1 the survival chances of infants (Ͻ 1 year of age) still range between 20% and 50%. 2 Approximately 80% of infants with ALL carry chromosomal translocations involving the MLL (mixed lineage leukemia) gene, 3 fusing the N-terminal portion of the MLL gene to the C-terminal region of one of its translocation partner genes. The most frequent MLL translocations among infant ALL patients are t(4;11), t(11;19), and t(9;11), 2,4 giving rise to the fusion proteins MLL-AF4, MLL-ENL, and MLL-AF9. These chimeric MLL fusion proteins exhibit pronounced transforming capacities 5 and independently contribute to an unfavorable prognosis. 2,6 As a member of the trithorax gene family, MLL is involved in transcriptional regulation. 7 Therefore, structural alterations of this gene may be expected to affect its function, presumably leading to transcriptional deregulation. Not surprisingly, in recent gene expression profiling studies, 8,9 the authors characterized MLL-rearranged ALL as a unique type of leukemia that is genetically clearly separable from other ALL subtypes. Because epigenetic modifications affect gene expression patterns, 10 we hypothesized that the specific gene expression profiles associated with MLL-rearranged infant ALL may well be driven by epigenetic changes, which recently have been established to play important role...

“…The SEMK2 represents a B-lineage MLL-rearranged ALL cell line, 21 and MV4-11 is an MLL-rearranged acute myeloid leukemia (AML) cell line. Both cell lines harbor MLL translocation t(4;11) and are highly resistant to prednisolone in vitro.…”

Section: Cell Line Culturementioning

confidence: 99%

Association of high-level MCL-1 expression with in vitro and in vivo prednisone resistance in MLL-rearranged infant acute lymphoblastic leukemia

Stam

Boer

Schneider

et al. 2010

MLL-rearranged acute lymphoblastic leukemia (ALL) represents an unfavorable type of leukemia that often is highly resistant to glucocorticoids such as prednisone and dexamethasone. Because response to prednisone largely determines clinical outcome of pediatric patients with ALL, overcoming resistance to this drug may be an important step toward improving prognosis. Here, we show how gene expression profiling identifies high-level MCL-1 expression to be associated with prednisolone resistance in MLL-rearranged infant ALL, as well as in more favorable types of childhood ALL. To validate this observation, we determined MCL-1 expression with quantitative reverse transcription-polymerase chain reaction in a cohort of MLL-rearranged infant ALL and pediatric noninfant ALL samples and confirmed that high-level MCL-1 expression is associated with prednisolone resistance in vitro. In addition, MCL-1 expression appeared to be significantly higher in MLL-rearranged infant patients who showed a poor response to prednisone in vivo compared with prednisone good responders. Finally, downregulation of MCL-1 in prednisoloneresistant MLL-rearranged leukemia cells by RNA interference, to some extent, led to prednisolone sensitization. Collectively, our findings suggest a potential role for MCL-1 in glucocorticoid resistance in MLL-rearranged infant ALL, but at the same time strongly imply that highlevel MCL-1 expression is not the sole mechanism providing resistance to these drugs. (Blood. 2010;115:1018-1025) IntroductionAcute lymphoblastic leukemia (ALL) in infants (ie, children Ͻ 1 year of age) is characterized by an exceptionally high incidence (ϳ 80% of the cases) of chromosomal translocations affecting the MLL gene. 1,2 These chromosomal abnormalities, believed to be initiating events in leukemogenesis, usually involve reciprocal translocations fusing the N-terminal portion of the MLL gene to the C-terminal region of one of its translocation partner genes, of which more than 50 have been described. 3,4 The presence of MLL rearrangements represents the most important independent predictor of an adverse outcome. 1,5 Although current therapies for pediatric ALL in general result in long-term survival in more than 80% of the cases, these therapies fail in more than 50% of infants diagnosed with MLL-rearranged ALL. 1 A major obstacle hampering successful treatment results in MLL-rearranged infant ALL is cellular resistance to several drugs used in the treatment of ALL. In vitro studies showed that MLL-rearranged infant ALL cells are particularly highly resistant to prednisolone, 6 the spearhead drug of ALL treatment regimes. Moreover, approximately 30% of the infant patients with MLLrearranged ALL show a poor prednisone response in vivo, defined as the presence of at least 1000 leukemic blasts/L after a 7-day window of prednisone monotherapy. 1,7 In contrast, among children older than 1 year of age (noninfants) diagnosed with ALL, less than 10% of the patients show a poor in vivo response to prednisone. 8 Both in vitro prednisolone...