Respecifying human iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells with a single factor.

Derivation of human hematopoietic stem cells (HSCs) from induced pluripotent stem cells (iPSCs) offers considerable promise for cell therapy, disease modeling, and drug screening. However, efficient derivation of functional iPSC-derived HSCs with in vivo engraftability and multilineage potential remains challenging. Here, we demonstrate a tractable approach for respecifying iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells (HSPCs) through transient expression of a single transcription factor, MLL-AF4 These induced HSPCs (iHSPCs) derived from iPSCs are able to fully reconstitute the human hematopoietic system in the recipient mice without myeloid bias. iHSPCs are long-term engraftable, but they are also prone to leukemic transformation during the long-term engraftment period. On the contrary, primary HSPCs with the same induction sustain the long-term engraftment without leukemic transformation. These findings demonstrate the feasibility of activating the HSC network in human iPSC-derived blood cells through expression of a single factor and suggest iHSPCs are more genomically instable than primary HSPCs, which merits further attention.

Nuclear FGFR2 Interacts with the MLL-AF4 Oncogenic Chimera and Positively Regulates HOXA9 Gene Expression in t(4;11) Leukemia Cells.

The chromosomal translocation t(4;11) marks an infant acute lymphoblastic leukemia associated with dismal prognosis. This rearrangement leads to the synthesis of the MLL-AF4 chimera, which exerts its oncogenic activity by upregulating transcription of genes involved in hematopoietic differentiation. Crucial for chimera's aberrant activity is the recruitment of the AF4/ENL/P-TEFb protein complex. Interestingly, a molecular interactor of AF4 is fibroblast growth factor receptor 2 (FGFR2). We herein analyze the role of FGFR2 in the context of leukemia using t(4;11) leukemia cell lines. We revealed the interaction between MLL-AF4 and FGFR2 by immunoprecipitation, western blot, and immunofluorescence experiments; we also tested the effects of FGFR2 knockdown, FGFR2 inhibition, and FGFR2 stimulation on the expression of the main MLL-AF4 target genes, i.e., HOXA9 and MEIS1. Our results show that FGFR2 and MLL-AF4 interact in the nucleus of leukemia cells and that FGFR2 knockdown, which is associated with decreased expression of HOXA9 and MEIS1, impairs the binding of MLL-AF4 to the HOXA9 promoter. We also show that stimulation of leukemia cells with FGF2 increases nuclear level of FGFR2 in its phosphorylated form, as well as HOXA9 and MEIS1 expression. In contrast, preincubation with the ATP-mimetic inhibitor PD173074, before FGF2 stimulation, reduced FGFR2 nuclear amount and HOXA9 and MEIS1 transcript level, thereby indicating that MLL-AF4 aberrant activity depends on the nuclear availability of FGFR2. Overall, our study identifies FGFR2 as a new and promising therapeutic target in t(4;11) leukemia.

[Leukemogenic pathway of infant leukemia with MLL fusion].

Acute lymphoblastic leukemia (ALL) in infants remains an intractable and difficult-to-treat leukemia as compared to other pediatric ALLs, for which considerable progress has been achieved in terms of treatment outcomes in recent years. The leukemic cells in infants with ALL frequently carry chromosome translocations involving 11q23, resulting in the rearrangement and fusion of the MLL (KMT2A) gene. Among many MLL fusion genes, MLL-AF4 (KMT2A-AFF1) fusion is characteristically observed in infants with ALL, representing a hallmark of poor prognosis. In MLL-AF4-positive infants with ALL, first leukemic cells with MLL-AF4 were generated in utero. Analysis of several murine and human leukemia models revealed that the target cells for tumorigenesis by MLL-AF4 were not the hematopoietic progenitor cells of the bone marrow, but the early hematopoietic progenitor cells present in the fetal liver during the embryonic period and possibly the undifferentiated cells prior to the commitment to hematopoietic cells in the fetus. Elucidation of the leukemogenic process of infant ALL with MLL-AF4 may lead to early, pre-symptomatic diagnosis of leukemia, resulting in the improvement of prognosis and prevention of the onset of ALL in infants.

Molecular processes involved in B cell acute lymphoblastic leukaemia.

B cell leukaemia is one of the most frequent malignancies in the paediatric population, but also affects a significant proportion of adults in developed countries. The majority of infant and paediatric cases initiate the process of leukaemogenesis during foetal development (in utero) through the formation of a chromosomal translocation or the acquisition/deletion of genetic material (hyperdiploidy or hypodiploidy, respectively). This first genetic insult is the major determinant for the prognosis and therapeutic outcome of patients. B cell leukaemia in adults displays similar molecular features as its paediatric counterpart. However, since this disease is highly represented in the infant and paediatric population, this review will focus on this demographic group and summarise the biological, clinical and epidemiological knowledge on B cell acute lymphoblastic leukaemia of four well characterised subtypes: t(4;11) MLL-AF4, t(12;21) ETV6-RUNX1, t(1;19) E2A-PBX1 and t(9;22) BCR-ABL1.

CDKN1A-mediated responsiveness of MLL-AF4-positive acute lymphoblastic leukemia to Aurora kinase-A inhibitors.

Overexpression of Aurora kinases is largely observed in many cancers, including hematologic malignancies. In this study, we investigated the effects and molecular mechanisms of Aurora kinase inhibitors in acute lymphoblastic leukemia (ALL). Western blot analysis showed that both Aurora-A and Aurora-B are overexpressed in ALL cell lines and primary ALL cells. Both VE-465 and VX-680 effectively inhibited Aurora kinase activities in nine ALL cell lines, which exhibited different susceptibilities to the inhibitors. Cells sensitive to Aurora kinase inhibitors underwent apoptosis at an IC50 of ∼10-30 nM and displayed a phenotype of Aurora-A inhibition, whereas cells resistant to Aurora kinase inhibitors (with an IC50 more than 10 µM) accumulated polyploidy, which may have resulted from Aurora-B inhibition. Drug susceptibility of ALL cell lines was not correlated with the expression level or activation status of Aurora kinases. Interestingly, RS4;11 and MV4;11 cells, which contain the MLL-AF4 gene, were both sensitive to Aurora kinase-A inhibitors treatment. Complementary DNA (cDNA) microarray analysis suggested that CDKN1A might govern the drug responsiveness of ALL cell lines in a TP53-independent manner. Most importantly, primary ALL cells with MLL-AF4 and CDKN1A expression were sensitive to Aurora kinase inhibitors. Our study suggests CDKN1A could be a potential biomarker in determining the drug responsiveness of Aurora kinase inhibitors in ALL, particularly in MLL-AF4-positive patients.

Gene Expression Network and Circ_0008012 Promote Progression in MLL/AF4 Positive Acute Lymphoblastic Leukemia.

BACKGROUND: Acute lymphoblastic leukemia with MLL/AF4 rearrangement remains a major hurdle to improving outcomes. Gene network and circRNAs have been found to participate in tumorigenesis, while their roles in leukemia still need to be explored. Recent patents have shown that circRNAs exhibit the markers for the children ALL, although the target and related mechanism remain to be elucidated. OBJECTIVE: This study aims to explore the possible targets and mechanisms of ALL with MLLAF4 rearrangement. METHODS: We first generated a gene network focusing on MLL-AF4 rearrangement. Cell viability was determined with Cell Counting Kit-8 assay. The cell apoptosis was tested by the Annexin V/PI assay. The RNA-protein complexes were analyzed by qRT-PCR, and the pathway proteins were analyzed by western blot. RESULTS: This gene network was associated with biological processes, such as nucleic acid metabolism and immunity, indicating its key role in inflammation. We found that circ_0008012 was upregulated in MLL/AF4 ALL cells and regulated cell proliferation and apoptosis. Further computed simulation and RIP showed that IKKß was the strongest protein in the NF-κB pathway binding with circ_0008012. As a result, possible regulation of circ_0008012 is suggested by binding IKKß in the IKKα:IKKß:IKKγ compound, which then phosphorylates IκB and activates NF- κB:p65:p300 compound in cell nucleus, thereby leading to leukemia. CONCLUSION: We identified a gene network for MLL/AF4 ALL. Moreover, circ_0008012 may be a therapeutic target for this subtype of ALL.

Defining the fetal origin of MLL-AF4 infant leukemia highlights specific fatty acid requirements.

Infant MLL-AF4-driven acute lymphoblastic leukemia (ALL) is a devastating disease with dismal prognosis. A lack of understanding of the unique biology of this disease, particularly its prenatal origin, has hindered improvement of survival. We perform multiple RNA sequencing experiments on fetal, neonatal, and adult hematopoietic stem and progenitor cells from human and mouse. This allows definition of a conserved fetal transcriptional signature characterized by a prominent proliferative and oncogenic nature that persists in infant ALL blasts. From this signature, we identify a number of genes in functional validation studies that are critical for survival of MLL-AF4+ ALL cells. Of particular interest are PLK1 because of the readily available inhibitor and ELOVL1, which highlights altered fatty acid metabolism as a feature of infant ALL. We identify which aspects of the disease are residues of its fetal origin and potential disease vulnerabilities.

circRNA circAF4 functions as an oncogene to regulate MLL-AF4 fusion protein expression and inhibit MLL leukemia progression.

BACKGROUND: Circular RNAs (circRNAs) represent a type of endogenous noncoding RNAs that are generated by back-splicing events and favor repetitive sequences. Recent studies have reported that cancer-associated chromosomal translocations could juxtapose distant complementary repetitive intronic sequences, resulting in the aberrant formation of circRNAs. However, among the reported fusion genes, only a small number of circRNAs were found to originate from fusion regions during gene translocation. We question if circRNAs could also originate from fusion partners during gene translocation. METHODS: Firstly, we designed divergent primers for qRT-PCR to identify a circRNA circAF4 in AF4 gene and investigated the expression pattern in different types of leukemia samples. Secondly, we designed two small interfering RNAs specially targeting the back-spliced junction point of circAF4 for functional studies. CCK8 cell proliferation and cell cycle assay were performed, and a NOD-SCID mouse model was used to investigate the contribution of circAF4 in leukemogenesis. Finally, luciferase reporter assay, AGO2 RNA immunoprecipitation (RIP), and RNA Fluorescent in Situ Hybridization (FISH) were performed to confirm the relationship of miR-128-3p, circAF4, and MLL-AF4 expression. RESULTS: We discovered a circRNA, named circAF4, originating from the AF4 gene, a partner of the MLL fusion gene in MLL-AF4 leukemia. We showed that circAF4 plays an oncogenic role in MLL-AF4 leukemia and promotes leukemogenesis in vitro and in vivo. More importantly, knockdown of circAF4 increases the leukemic cell apoptosis rate in MLL-AF4 leukemia cells, while no effect was observed in leukemia cells that do not carry the MLL-AF4 translocation. Mechanically, circAF4 can act as a miR-128-3p sponge, thereby releasing its inhibition on MLL-AF4 expression. We finally analyzed most of the MLL fusion genes loci and found that a number of circRNAs could originate from these partners, suggesting the potential roles of fusion gene partner-originating circRNAs (named as FP-circRNAs) in leukemia with chromosomal translocations. CONCLUSION: Our findings demonstrate that the abnormal elevated expression of circAF4 regulates the cell growth via the circAF4/miR-128-3p/MLL-AF4 axis, which could contribute to leukemogenesis, suggesting that circAF4 may be a novel therapeutic target of MLL-AF4 leukemia.

MLL-Rearranged Acute Leukemia with t(4;11)(q21;q23)-Current Treatment Options. Is There a Role for CAR-T Cell Therapy?

The MLL (mixed-lineage leukemia) gene, located on chromosome 11q23, is involved in chromosomal translocations in a subtype of acute leukemia, which represents approximately 10% of acute lymphoblastic leukemia and 2.8% of acute myeloid leukemia cases. These translocations form fusions with various genes, of which more than 80 partner genes for MLL have been identified. The most recurrent fusion partner in MLL rearrangements (MLL-r) is AF4, mapping at chromosome 4q21, accounting for approximately 36% of MLL-r leukemia and particularly prevalent in MLL-r acute lymphoblastic leukemia (ALL) cases (57%). MLL-r leukemia is associated with a sudden onset, aggressive progression, and notoriously poor prognosis in comparison to non-MLL-r leukemias. Despite modern chemotherapeutic interventions and the use of hematopoietic stem cell transplantations, infants, children, and adults with MLL-r leukemia generally have poor prognosis and response to these treatments. Based on the frequency of patients who relapse, do not achieve complete remission, or have brief event-free survival, there is a clear clinical need for a new effective therapy. In this review, we outline the current therapy options for MLL-r patients and the potential application of CAR-T therapy.

Analysis of clinical characteristics and prognosis of newly-treated acute lymphoblastic leukemia patients with MLL-AF4 fusion gene-positive / 白血病·淋巴瘤

Objective:To investigate the development of MLL-AF4 fusion gene-positive in newly-treated acute lymphoblastic leukemia (ALL) and to analyze the clinical characteristics and prognosis of patients with MLL-AF4 fusion gene-positive ALL.Methods:The clinical data of 455 patients with primary newly-treated ALL from February 2010 to February 2021 in Zhumadian Central Hospital were retrospectively analyzed. Fluorescence in situ hybridization was used to detect the presence of MLL gene rearrangement, and multiplexed nested reverse transcription polymerase chain reaction was used to detect the development of MLL-AF4 fusion gene-positive, and to compare the clinical characteristics and prognosis of patients with positive and negative MLL-AF4 fusion gene.Results:Among 455 patients with primary newly-treated ALL, 30 cases (6.6%) were positive for MLL gene rearrangement, including 21 positive for MLL-AF4 fusion gene (MLL-AF4 positive group), 6 cases positive for MLL-ENL fusion gene, 2 cases positive for MLL-AF9 fusion gene, and 1 case positive for MLL-AF10 fusion gene. A total of 60 ALL patients without any detection of fusion gene during the same period were randomly selected as the MLL-AF4-negative group. The proportion of those with hepatomegaly or splenomegaly, central nervous system (CNS) invasion, and the median peripheral blood leukocyte count and median peripheral blood na?ve cells absolute value in the MLL-AF4-positive group were higher than those in the MLL-AF4-negative group (all P < 0.05). The complete remission rates on day 15 of chemotherapy were 81.0% (17/21) and 90.0% (54/60), respectively in the MLL-AF4-positive group and MLL-AF4-negative group ( χ2 = 0.49, P = 0.484), and the cumulative relapse rates of 3 months were 38.1% (8/21) and 13.3% (8/60), respectively in the MLL-AF4-positive group and MLL-AF4-negative group ( χ2 = 4.56, P = 0.033). The overall survival in the MLL-AF4-positive group was worse than that in the MLL-AF4-negative group ( χ2 = 5.93, P = 0.015). Conclusions:Patients with MLL-AF4 fusion gene-positive ALL have a higher tumor load, a higher recurrence rate, a lower overall survival rate, and a poorer prognosis compared with negative patients at the initial diagnosis.

MLL-AF4 Spreading Identifies Binding Sites that Are Distinct from Super-Enhancers and that Govern Sensitivity to DOT1L Inhibition in Leukemia.

Understanding the underlying molecular mechanisms of defined cancers is crucial for effective personalized therapies. Translocations of the mixed-lineage leukemia (MLL) gene produce fusion proteins such as MLL-AF4 that disrupt epigenetic pathways and cause poor-prognosis leukemias. Here, we find that at a subset of gene targets, MLL-AF4 binding spreads into the gene body and is associated with the spreading of Menin binding, increased transcription, increased H3K79 methylation (H3K79me2/3), a disruption of normal H3K36me3 patterns, and unmethylated CpG regions in the gene body. Compared to other H3K79me2/3 marked genes, MLL-AF4 spreading gene expression is downregulated by inhibitors of the H3K79 methyltransferase DOT1L. This sensitivity mediates synergistic interactions with additional targeted drug treatments. Therefore, epigenetic spreading and enhanced susceptibility to epidrugs provides a potential marker for better understanding combination therapies in humans.

Development Refractoriness of MLL-Rearranged Human B Cell Acute Leukemias to Reprogramming into Pluripotency.

Induced pluripotent stem cells (iPSCs) are a powerful tool for disease modeling. They are routinely generated from healthy donors and patients from multiple cell types at different developmental stages. However, reprogramming leukemias is an extremely inefficient process. Few studies generated iPSCs from primary chronic myeloid leukemias, but iPSC generation from acute myeloid or lymphoid leukemias (ALL) has not been achieved. We attempted to generate iPSCs from different subtypes of B-ALL to address the developmental impact of leukemic fusion genes. OKSM(L)-expressing mono/polycistronic-, retroviral/lentiviral/episomal-, and Sendai virus vector-based reprogramming strategies failed to render iPSCs in vitro and in vivo. Addition of transcriptomic-epigenetic reprogramming "boosters" also failed to generate iPSCs from B cell blasts and B-ALL lines, and when iPSCs emerged they lacked leukemic fusion genes, demonstrating non-leukemic myeloid origin. Conversely, MLL-AF4-overexpressing hematopoietic stem cells/B progenitors were successfully reprogrammed, indicating that B cell origin and leukemic fusion gene were not reprogramming barriers. Global transcriptome/DNA methylome profiling suggested a developmental/differentiation refractoriness of MLL-rearranged B-ALL to reprogramming into pluripotency.

Expression of MLL-AF4 or AF4-MLL fusions does not impact the efficiency of DNA damage repair.

The most frequent rearrangement of the human MLL gene fuses MLL to AF4 resulting in high-risk infant B-cell acute lymphoblastic leukemia (B-ALL). MLL fusions are also hallmark oncogenic events in secondary acute myeloid leukemia. They are a direct consequence of mis-repaired DNA double strand breaks (DNA-DSBs) due to defects in the DNA damage response associated with exposure to topoisomerase-II poisons such as etoposide. It has been suggested that MLL fusions render cells susceptible to additional chromosomal damage upon exposure to etoposide. Conversely, the genome-wide mutational landscape in MLL-rearranged infant B-ALL has been reported silent. Thus, whether MLL fusions compromise the recognition and/or repair of DNA damage remains unanswered. Here, the fusion proteins MLL-AF4 (MA4) and AF4-MLL (A4M) were CRISPR/Cas9-genome edited in the AAVS1 locus of HEK293 cells as a model to study MLL fusion-mediated DNA-DSB formation/repair. Repair kinetics of etoposide- and ionizing radiation-induced DSBs was identical in WT, MA4- and A4M-expressing cells, as revealed by flow cytometry, by immunoblot for γH2AX and by comet assay. Accordingly, no differences were observed between WT, MA4- and A4M-expressing cells in the presence of master proteins involved in non-homologous end-joining (NHEJ; i.e.KU86, KU70), alternative-NHEJ (Alt-NHEJ; i.e.LigIIIa, WRN and PARP1), and homologous recombination (HR, i.e.RAD51). Moreover, functional assays revealed identical NHEJ and HR efficiency irrespective of the genotype. Treatment with etoposide consistently induced cell cycle arrest in S/G2/M independent of MA4/A4M expression, revealing a proper activation of the DNA damage checkpoints. Collectively, expression of MA4 or A4M does neither influence DNA signaling nor DNA-DSB repair.

Instructive Role of MLL-Fusion Proteins Revealed by a Model of t(4;11) Pro-B Acute Lymphoblastic Leukemia.

The t(4;11)(q21;q23) fuses mixed-lineage leukemia (MLL) to AF4, the most common MLL-fusion partner. Here we show that MLL fused to murine Af4, highly conserved with human AF4, produces high-titer retrovirus permitting efficient transduction of human CD34+ cells, thereby generating a model of t(4;11) pro-B acute lymphoblastic leukemia (ALL) that fully recapitulates the immunophenotypic and molecular aspects of the disease. MLL-Af4 induces a B ALL distinct from MLL-AF9 through differential genomic target binding of the fusion proteins leading to specific gene expression patterns. MLL-Af4 cells can assume a myeloid state under environmental pressure but retain lymphoid-lineage potential. Such incongruity was also observed in t(4;11) patients in whom leukemia evaded CD19-directed therapy by undergoing myeloid-lineage switch. Our model provides a valuable tool to unravel the pathogenesis of MLL-AF4 leukemogenesis.

Identificación de alteraciones moleculares en pacientes Venezolanos con diagnóstico de leucemia linfoblástica aguda / Identification of molecular alterations in Venezuelan patients with acute lymphoblastic leukemia diagnosis

La Leucemia Linfoblástica Aguda (LLA) es la neoplasia más frecuente en edad pediátrica. En los últimos años, entre el 15 y 20% de los pacientes fracasan en el tratamiento. Conocimientos en citogenética y biología molecular repercuten de manera importante en la determinación del pronóstico y del esquema de tratamiento adecuado. En Venezuela existe un conocimiento limitado en cuanto a la genética molecular de esta alteración onco-hematológica. El objetivo del trabajo fue evaluar las alteraciones genéticas más frecuentes en pacientes venezolanos con diagnóstico clínico de leucemia linfoblástica aguda. Se realizó un estudio transversal, descriptivo y prospectivo de 2006 a 2014, en el que se evaluaron las translocaciones ETV6/RUNX1, MLL/AF4, TCF3/PBX1, BCR/ABL1, así como las mutaciones en los genes PAX5 y FLT3 mediante el uso de diferentes tipos de PCR. Ciento treinta pacientes con diagnóstico clínico de leucemia linfocítica aguda fueron incluidos en el estudio. Se identificaron alteraciones moleculares en 56 pacientes (43,1%), en los que observamos la presencia de una o varias alteraciones en conjunción en un mismo paciente. Las alteraciones identificadas fueron t(12;21) (11,5%), t(4;11) (8,5%), t(1;19) (10%), t(9;22) (20,8%), ITD-FLT3 (14,8%), mutación P80S (4,2%) y S77del (4,2%) en el gen PAX5. La prevalencia de BCR/ ABL, es una de las más altas que ha sido descrita hasta ahora en casos de LLA donde la mayor parte de la población está conformada por pacientes pediátricos. Estos resultados representan el primer estudio molecular de la LLA en Venezuela, sentando las bases para el diagnóstico y seguimiento de la enfermedad en su población.

Acute Lymphoblastic Leukemia (ALL) is the most common neoplasm in pediatric age. In recent years, between 15 and 20% of patients failed in their treatments. Knowledge on cytogenetics and molecular biology has an important impact on the determination of the prognosis and the appropriate treatment scheme. In Venezuela there is limited knowledge regarding the molecular genetics of this onco-hematological alteration. The aim of this work was to evaluate the most frequent genetic alterations in Venezuelan patients with a clinical diagnosis of acute lymphoblastic leukemia. A cross-sectional, descriptive and prospective study was carried out from 2006 to 2014, in which the translocations ETV6/RUNX1, MLL/AF4, TCF3/PBX1, BCR/ABL1, as well as mutations in the PAX5 and FLT3 genes were evaluated through the use of different types of PCR. One hundred and thirty patients with a clinical diagnosis of acute lymphocytic leukemia were included in the study. Molecular alterations were identified in 56 patients (43.1%), in which we observed the presence of one or several alterations in conjunction in the same patient. The alterations identified were t(12; 21) (11.5%), t(4; 11) (8.5%), t(1; 19) (10%), t(9; 22) (20.8%), ITD-FLT3 (14.8%), P80S mutation (4.2%) and S77del (4.2%) in the PAX5 gene. The prevalence of BCR/ABL is one of the highest described so far in cases of ALL where most of the population is made up of pediatric patients. These results represent the first molecular study of ALL in Venezuela, laying the foundations for the diagnosis and monitoring of the disease in its population.

MLL-Rearranged Acute Lymphoblastic Leukemias Activate BCL-2 through H3K79 Methylation and Are Sensitive to the BCL-2-Specific Antagonist ABT-199.

Targeted therapies designed to exploit specific molecular pathways in aggressive cancers are an exciting area of current research. Mixed Lineage Leukemia (MLL) mutations such as the t(4;11) translocation cause aggressive leukemias that are refractory to conventional treatment. The t(4;11) translocation produces an MLL/AF4 fusion protein that activates key target genes through both epigenetic and transcriptional elongation mechanisms. In this study, we show that t(4;11) patient cells express high levels of BCL-2 and are highly sensitive to treatment with the BCL-2-specific BH3 mimetic ABT-199. We demonstrate that MLL/AF4 specifically upregulates the BCL-2 gene but not other BCL-2 family members via DOT1L-mediated H3K79me2/3. We use this information to show that a t(4;11) cell line is sensitive to a combination of ABT-199 and DOT1L inhibitors. In addition, ABT-199 synergizes with standard induction-type therapy in a xenotransplant model, advocating for the introduction of ABT-199 into therapeutic regimens for MLL-rearranged leukemias.

MicroRNA-205 downregulates mixed-lineage-AF4 oncogene expression in acute lymphoblastic leukemia.

Myeloid/lymphoid or mixed-lineage AF4 acute lymphoblastic leukemia (MLL-AF4 ALL) is a pediatric leukemia that occurs rarely in adults. MLL-AF4 ALL is typically characterized by the presence of chromosomal translocation (t(4;1l)(q21;q23)), leading to expression of MLL-AF4 fusion protein. Although MLL-AF4 fusion protein triggers a molecular pathogenesis and hematological presentations that are unique to leukemias, the precise role of this oncogene in leukemogenesis remains unclear. Previous studies have indicated that microRNAs (miRs) might modulate the expression of MLL-AF4 ALL fusion protein, thereby suggesting the involvement of miR in progression or suppression of MLL-AF4 ALL. We have previously demonstrated that miR-205 negatively regulates transcription of an MLL-AF4 luciferase reporter. Here, we report that exogenous expression of miR-205 in MLL-AF4 human cell lines (RS4;11 and MV4-11) inversely regulates the expression of MLL-AF4 at both messenger RNA (mRNA) and protein level. Furthermore, miR-205 significantly induced apoptosis in MLL-AF4 cells as evidenced by Annex in V staining using fluorescence-activated cell sorting (FACS) analysis. The proliferative capacity of leukemic cells was suppressed by miR-205. The addition of an miR-205 inhibitor was able to restore the observed effects. In conclusion, these findings demonstrate that miR-205 may have potential value as a novel therapeutic agent in the treatment of MLL-AF4 ALL.

The biological advance in acute lymphoblastic leukemia of t (4;11) in infants / 临床儿科杂志

Infant acute lymphoblastic leukemia B (B-ALL) accounts for 10% of childhood ALL. Eighty percent of infant B-ALL was caused byMLL gene rearrangement (MLL-r). The overall survival rate of ALL was less than 35% in infants with MLL-r. Among infant ALL with MLL-r, infants with positivefusion geneMLL-AF4 (MA4) formed by chromosome t (4;11) had even poor prognosis. Studies in monozygotic twins and archived blood spot at birth had veriifed that fusion gene MA4 originated from antenatal. Whole genome sequencing found that t (4;11) alone might be sufifcient to spawn leukemia. This paper is going to summarize the advances in biological characteristics such as clinical features, cellular origin, genomics and disease models of normalMLL gene and infant B-ALL withMA4.