Loss Of IKZF1 Function Mediates Resistance Towards Glucocorticoid-Induced Apoptosis

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3865-3865
Author(s):  
Jorn Havinga ◽  
Laurensia Yuniati ◽  
Marc Demkes ◽  
Dorette van Ingen Schenau ◽  
Roland P. Kuiper ◽  
...  
Keyword(s):  
Gene Expression ◽  
Prognostic Factor ◽  
Transcriptional Activation ◽  
Lymphoblastic Leukemia ◽  
Luciferase Reporter ◽  
Human Leukemia ◽  
Wild Type ◽  
Gene Deletions ◽  
Expression Levels ◽  
Induced Apoptosis

Abstract Background Glucocorticoids (GCs) such as prednisolone and dexamethasone are critical components of multi-agent chemotherapy regimens used in the treatment of acute lymphoblastic leukemia (ALL). Children with ALL are stratified into risk groups based on diagnostic features (i.e. age and cytogenetics) and therapy response. It has been established that the initial response to prednisolone is a major prognostic factor. Moreover, at relapse, de novo or acquired resistance to GCs is common and represents an important determinant in treatment failure. Recent studies performed by us and others have identified IKZF1 gene deletions and mutations as an independent prognostic factor that predicts prognosis and treatment outcome of children with B cell precursor ALL (BCP-ALL). These monoallelic IKZF1 gene deletions either affect the whole gene or may result in expression of dominant-negative IKZF1 isoforms due to intragenic deletions. However, it has not been established whether loss of IKZF1 function directly impacts the response to glucocorticoids. Results We examined whether haplodeficiency for Ikzf1 gene expression in mouse lymphocytes affects glucocorticoid-induced apoptosis. Splenocytes from Ikzf1+/- knockout mice were activated with lipopolysaccharide (LPS) and treated with increasing concentrations of either prednisolone or dexamethasone for 48 hours. B-lymphocytes haplodeficient for IKZF1 showed a significantly enhanced survival after treatment with GCs compared to wild type cells, as measured in an MTS assay and by AnnexinV staining. In case of prednisolone, the inhibitory concentration (IC50) was about ∼200-fold higher in the Ikzf1+/- splenocytes as compared to the wild-type cells. Gene expression analysis revealed that Ikzf1+/- splenocytes displayed lower overall expression levels as well as diminished transcriptional activation of several glucocorticoid receptor (GR)-induced target genes (i.e. Sgk1, Irs2, Zfp36L2). Furthermore, in luciferase reporter assays we established that IKZF1 overexpression enhances GR-mediated transcriptional activation in response to prednisolone. Finally, lentivirus-mediated IKZF1-shRNA expression in Nalm6 cell line, which reduces endogenous IKZF1 protein levels to around 50%, inhibits prednisolone and dexamethasone-induced apoptosis, demonstrating that also in human leukemia cells reduced IKZF1 expression levels protect against GC-induced cell death. In conclusion, our data provide evidence that loss of IKZF1 function mediates resistance to glucocorticoid-induced apoptosis, which may contribute to the poor outcome of IKZF1-deleted BCP-ALL. Disclosures: No relevant conflicts of interest to declare.

ERG Deletions Define a Novel Subtype of B-Progenitor Acute Lymphoblastic Leukemia.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 691-691 ◽  
Author(s):  
Charles G. Mullighan ◽  
Christopher B. Miller ◽  
Xiaoping Su ◽  
Ina Radtke ◽  
James Dalton ◽  
...  
Keyword(s):  
Gene Expression ◽  
Acute Lymphoblastic Leukemia ◽  
Gene Expression Profile ◽  
Expression Profile ◽  
Lymphoblastic Leukemia ◽  
Luciferase Reporter ◽  
The Novel ◽  
Wild Type ◽  
Cytogenetic Abnormalities ◽  
Novel Gene

Abstract In a previous gene expression profiling study of acute lymphoblastic leukemia (ALL), we identified a novel subtype of B-progenitor ALL (4.9% of 284 cases) with a unique gene expression profile, aberrant expression of CD2 and the absence of recurring cytogenetic abnormalities (Cancer Cell2002;1:133). Efforts to identify rearrangement or mutation of many of the top-ranked genes in the novel expression signature failed to identify a causative lesion. To further investigate the genetic basis of this subtype, we performed integrated genomic analysis of 277 ALL cases. Affymetrix 250k Sty and Nsp SNP microarrays were used in all cases, and Affymetrix U133A gene expression profiles were obtained on 183 of the cases. Unsupervised clustering of gene expression data identified 16 cases of the novel subtype, including all of the 14 previously defined cases. Remarkably, focal mono-allelic deletions of the ETS family member ERG (v-ets erythroblastosis virus E26 oncogene homolog) were detected by genome-wide copy number analysis in 11/16 (69%) of the novel cases, but not in any other ALL subtype. Extensive analysis failed to reveal evidence of translocations involving the altered ERG allele, indicating that these are intragenic deletions limited to ERG. The ERG deletions involved a subset of exons (ERG isoform 1 exons 3–7 or 3–9) resulting in the expression of internally deleted ERG transcripts with altered reading frames predicted to produce a prematurely truncated N-terminal protein fragment. However, using an alternative translational start site 5′ to exon 10, the transcripts also encode a ∼28kDa C-terminal ERG fragment that contains the entire C-terminal ETS DNA-binding and transactivation domains, but lacks all N-terminal domains. Importantly, western blot analysis of primary leukemic blasts revealed expression of only the 28kDa C-terminal ERG protein, along with full length ERG expressed from the retained wild type allele. Remarkably, the C-terminal ERG protein was also detected in 4 of 5 novel ALL cases that lacked detectable ERG deletions, but not in any other ALL subtype. In luciferase reporter assays, this aberrant ERG protein acts as a competitive inhibitor of wild type ERG. Analysis of a second cohort of 35 B-progenitor ALL cases lacking recurring cytogenetic abnormalities identified two cases with ERG deletions and a third expressing the aberrant ERG protein, all of which had the novel gene expression profile. Sequencing of ERG in 252 ALL cases identified only one case with an ERG mutation that resulted in a frameshift in the ETS domain. This case did not share the novel signature nor express the aberrant C-terminal ERG protein. Finally, in an analysis of 37 acute leukemia cell lines, the B-progenitor ALL line NALM-6 was found to harbor a focal, internally truncating ERG deletion, expressed the aberrant ERG protein, and shared the novel gene expression profile, thus identifying it as a model of this novel ALL subtype. These data establish focal ERG deletions as the genetic lesion underlying a novel subtype of ALL, and have expanded the genetic mechanisms that lead to the dysregulation of ERG from chromosomal translocations that result in enhanced transcriptional activity, to deletions that generate dominant negative forms of the transcription factor.

scholarly journals The role of microRNA-572 in the proliferation and chemotherapeutic treatment of prostate cancer

2021 ◽  
Vol 49 (5) ◽  
pp. 030006052110143
Author(s):  
Mingcui Zang ◽  
Xun Guo ◽  
Manqiu Chen
Keyword(s):  
Prostate Cancer ◽  
Luciferase Reporter ◽  
Migration And Invasion ◽  
Prostate Tumorigenesis ◽  
Expression Levels ◽  
Matrigel Invasion ◽  
Tensin Homolog ◽  
Docetaxel Treatment ◽  
Induced Apoptosis

Objective MicroRNAs (miRNAs) regulate prostate tumorigenesis and progression by involving different molecular pathways. In this study, we examined the role of miR-572 in prostate cancer (PCa). Methods The proliferation rates of LNCaP and PC-3 PCa cells were studied using MTT assays. Transwell migration and Matrigel invasion assays were performed to evaluate cell migration and invasion, respectively. Protein expression levels were examined using western blotting. Docetaxel-induced apoptosis was evaluated by Caspase-Glo3/7 assays. The putative miR-572 binding site in the phosphatase and tensin homolog (PTEN) 3ʹ untranslated region (3ʹ UTR) was assessed with dual-luciferase reporter assays. Additionally, miR-572 expression levels in human PCa tissues were examined by qRT-PCR assays. Results Upregulation of miR-572 promoted proliferation, migration, and invasion of PCa cells. Overexpression of miR-572 decreased sensitivity of PCa cells to docetaxel treatment by reducing docetaxel-induced apoptosis. MiR-572 can regulate migration and invasion in PCa cells. Furthermore, miR-572 could regulate expression of PTEN and p-AKT in PCa cells by directly binding to the PTEN 3ʹ UTR. MiR-572 expression levels were increased in human PCa tissues and associated with PCa stage. Conclusions miR-572 displayed essential roles in PCa tumor growth and its expression level may be used to predict docetaxel treatment in these tumors.

DNA-binding and transcriptional regulatory properties of hepatic leukemia factor (HLF) and the t(17;19) acute lymphoblastic leukemia chimera E2A-HLF

1994 ◽  
Vol 14 (9) ◽  
pp. 5986-5996
Author(s):  
S P Hunger ◽  
R Brown ◽  
M L Cleary
Keyword(s):  
Dna Binding ◽  
Binding Site ◽  
Dna Sequences ◽  
Transcriptional Activation ◽  
Binding Sites ◽  
Lymphoblastic Leukemia ◽  
Consensus Sequence ◽  
Reporter Genes ◽  
Wild Type ◽  
Basic Leucine Zipper

The t(17;19) translocation in acute lymphoblastic leukemias results in creation of E2A-hepatic leukemia factor (HLF) chimeric proteins that contain the DNA-binding and protein dimerization domains of the basic leucine zipper (bZIP) protein HLF fused to a portion of E2A proteins with transcriptional activation properties. An in vitro binding site selection procedure was used to determine DNA sequences preferentially bound by wild-type HLF and chimeric E2A-HLF proteins isolated from various t(17;19)-bearing leukemias. All were found to selectively bind the consensus sequence 5'-GTTACGTAAT-3' with high affinity. Wild-type and chimeric HLF proteins also bound closely related sites identified previously for bZIP proteins of both the proline- and acidic amino acid-rich (PAR) and C/EBP subfamilies; however, E2A-HLF proteins were significantly less tolerant of certain deviations from the HLF consensus binding site. These differences were directly attributable to loss of an HLF ancillary DNA-binding domain in all E2A-HLF chimeras and were further exacerbated by a zipper mutation in one isolate. Both wild-type and chimeric HLF proteins displayed transcriptional activator properties in lymphoid and nonlymphoid cells on reporter genes containing HLF or C/EBP consensus binding sites. But on reporter genes with nonoptimal binding sites, their transcriptional properties diverged and E2A-HLF competitively inhibited activation by wild-type PAR proteins. These findings establish a spectrum of binding site-specific transcriptional properties for E2A-HLF which may preferentially activate expression of select subordinate genes as a homodimer and potentially antagonize expression of others through heteromeric interactions.

Two novel mutations in Gli-similar 3 in patients with congenital hypothyroidism and thyroid dysgenesis

2021 ◽  
Author(s):  
Jie Lan ◽  
Chunhui Sun ◽  
Xinping Liang ◽  
Ruixin Ma ◽  
Yuhua Ji ◽  
...  
Keyword(s):  
Congenital Hypothyroidism ◽  
Transcriptional Activation ◽  
Luciferase Assay ◽  
Expression Vectors ◽  
Luciferase Reporter ◽  
Dominant Negative Effect ◽  
Wild Type ◽  
Thyroid Dysgenesis ◽  
Type Protein ◽  
Wild Type Protein

Abstract Background: Thyroid dysgenesis (TD) is the main cause of congenital hypothyroidism (CH). As variants of the transcription factor Gli-similar 3 (GLIS3) have been associated with CH and GLIS3 is one of candidate genes of TD, we screened and characterized GLIS3 mutations in Chinese patients with CH and TD.Methods: To detect mutations, we sequenced all GLIS3 exons in the peripheral blood genomic DNA isolated from 50 patients with TD and 100 healthy individuals. Wild-type and mutant expression vectors of Glis3 were constructed. Quantitative real-time PCR, western blotting, and double luciferase assay were performed to investigation the effect of the mutations on GLIS3 protein function and transcriptional activation.Results: Two novel heterozygous missense mutations, c.2710G>A (p.G904R) and c.2507C>A (p.P836Q), were detected in two unrelated patients. Functional studies revealed that p.G904R expression was 59.95% lower and p.P836Q was 31.23% lower than wild-type GLIS3 mRNA expression. The p.G904R mutation also resulted in lower GLIS3 protein expression compared with that encoded by wild-type GLIS3. Additionally, the luciferase reporter assay revealed that p.G904R mediated impaired transcriptional activation compared with the wild-type protein (p < 0.05) but did not have a dominant-negative effect on the wild-type protein.Conclusions: We for the first time screened and characterized the function of GLIS3 mutations in Chinese individuals with CH and TD. Our study not only broadens the GLIS3 mutation spectrum, but also provides further evidence that GLIS3 defects cause TD.

scholarly journals MDM2 Suppresses p73 Function without Promoting p73 Degradation

1999 ◽  
Vol 19 (5) ◽  
pp. 3257-3266 ◽  
Author(s):  
Xiaoya Zeng ◽  
Lihong Chen ◽  
Christine A. Jost ◽  
Ruth Maya ◽  
David Keller ◽  
...  
Keyword(s):  
Transcriptional Activation ◽  
Feedback Loop ◽  
Human Lung ◽  
Activation Function ◽  
Wild Type ◽  
Mdm2 Protein ◽  
Induced Apoptosis ◽  
P53 Inactivation

ABSTRACT The newly identified p53 homolog p73 can mimic the transcriptional activation function of p53. We investigated whether p73, like p53, participates in an autoregulatory feedback loop with MDM2. p73 bound to MDM2 both in vivo and in vitro. Wild-type but not mutant MDM2, expressed in human p53 null osteosarcoma Saos-2 cells, inhibited p73- and p53-dependent transcription driven by the MDM2 promoter-derived p53RE motif as measured in transient-transfection and chloramphenicol acetyltransferase assays and also inhibited p73-induced apoptosis in p53-null human lung adenocarcinoma H1299 cells. MDM2 did not promote the degradation of p73 but instead disrupted the interaction of p73, but not of p53, with p300/CBP by competing with p73 for binding to the p300/CBP N terminus. Both p73α and p73β stimulated the expression of the endogenous MDM2 protein. Hence, MDM2 is transcriptionally activated by p73 and, in turn, negatively regulates the function of this activator through a mechanism distinct from that used for p53 inactivation.

scholarly journals DNA-binding and transcriptional regulatory properties of hepatic leukemia factor (HLF) and the t(17;19) acute lymphoblastic leukemia chimera E2A-HLF.

1994 ◽  
Vol 14 (9) ◽  
pp. 5986-5996 ◽  
Author(s):  
S P Hunger ◽  
R Brown ◽  
M L Cleary
Keyword(s):  
Dna Binding ◽  
Binding Site ◽  
Dna Sequences ◽  
Transcriptional Activation ◽  
Binding Sites ◽  
Lymphoblastic Leukemia ◽  
Consensus Sequence ◽  
Reporter Genes ◽  
Wild Type ◽  
Basic Leucine Zipper

The t(17;19) translocation in acute lymphoblastic leukemias results in creation of E2A-hepatic leukemia factor (HLF) chimeric proteins that contain the DNA-binding and protein dimerization domains of the basic leucine zipper (bZIP) protein HLF fused to a portion of E2A proteins with transcriptional activation properties. An in vitro binding site selection procedure was used to determine DNA sequences preferentially bound by wild-type HLF and chimeric E2A-HLF proteins isolated from various t(17;19)-bearing leukemias. All were found to selectively bind the consensus sequence 5'-GTTACGTAAT-3' with high affinity. Wild-type and chimeric HLF proteins also bound closely related sites identified previously for bZIP proteins of both the proline- and acidic amino acid-rich (PAR) and C/EBP subfamilies; however, E2A-HLF proteins were significantly less tolerant of certain deviations from the HLF consensus binding site. These differences were directly attributable to loss of an HLF ancillary DNA-binding domain in all E2A-HLF chimeras and were further exacerbated by a zipper mutation in one isolate. Both wild-type and chimeric HLF proteins displayed transcriptional activator properties in lymphoid and nonlymphoid cells on reporter genes containing HLF or C/EBP consensus binding sites. But on reporter genes with nonoptimal binding sites, their transcriptional properties diverged and E2A-HLF competitively inhibited activation by wild-type PAR proteins. These findings establish a spectrum of binding site-specific transcriptional properties for E2A-HLF which may preferentially activate expression of select subordinate genes as a homodimer and potentially antagonize expression of others through heteromeric interactions.

scholarly journals The Effect and Mechanism of KLF7 in the TLR4/NF-κB/IL-6 Inflammatory Signal Pathway of Adipocytes

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Meixiu Zhang ◽  
Cuizhe Wang ◽  
Jinxiu Wu ◽  
Xiaodan Ha ◽  
Yuchun Deng ◽  
...  
Keyword(s):  
Protein Expression ◽  
Signaling Pathway ◽  
Transcriptional Activation ◽  
Inflammatory Cytokine ◽  
Luciferase Reporter ◽  
Signal Pathways ◽  
High Concentration ◽  
Inflammatory Signaling ◽  
Expression Levels ◽  
Mrna And Protein Expression

Objective. To investigate the role and possible molecular mechanism of Krüppel-like factor 7 (KLF7) in the TLR4/NF-κB/IL-6 inflammatory signaling pathway activated by free fatty acids (FFA). Methods. The mRNA and protein expression levels of KLF7 and the factors of TLR4/NF-κB/IL-6 inflammatory signal pathways were detected by qRT-PCR and Western blotting after cell culture with different concentrations of palmitic acid (PA). The expression of KLF7 or TLR4 in adipocytes was upregulated or downregulated; after that, the mRNA and protein expression levels of these key factors were detected. KLF7 expression was downregulated while PA stimulated adipocytes, and then the mRNA and protein expressions of KLF7/p65 and downstream inflammatory cytokine IL-6 were detected. The luciferase reporter assay was used to determine whether KLF7 had a transcriptional activation effect on IL-6. Results. (1) High concentration of PA can promote the expression of TLR4, KLF7, and IL-6 in adipocytes. (2) TLR4 positively regulates KLF7 expression in adipocytes. (3) KLF7 positively regulates IL-6 expression in adipocytes. (4) PA promotes IL-6 expression via KLF7 in adipocytes. (5) KLF7 has a transcriptional activation on IL-6. Conclusion. PA promotes the expression of the inflammatory cytokine IL-6 by activating the TLR4/KLF7/NF-κB inflammatory signaling pathway. In addition, KLF7 may directly bind to the IL-6 promoter region and thus activate IL-6.

Pax5 Haploinsufficiency Cooperates with BCR-ABL1 to Induce Acute Lymphoblastic Leukemia

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 293-293 ◽  
Author(s):  
ChristoPher B Miller ◽  
Charles G Mullighan ◽  
Xiaoping Su ◽  
Jing Ma ◽  
Michael Wang ◽  
...  
Keyword(s):  
Gene Expression ◽  
Transcription Factors ◽  
Acute Lymphoblastic Leukemia ◽  
B Cell ◽  
Point Mutation ◽  
Copy Number ◽  
Lymphoblastic Leukemia ◽  
Wild Type ◽  
Lymphoid Development ◽  
B Lymphoid

Abstract Genes regulating B lymphoid development are somatically mutated in over 40% of B-progenitor acute lymphoblastic leukemia (ALL) cases, with the most common targets being the transcription factors PAX5, IKZF1 (encoding Ikaros), and EBF1. Notably, BCR-ABL1 ALL is characterized by a high frequency of mutations of IKZF1 (85%), PAX5 (55%), and CDKN2A/B (encoding INK4/ARF, 55%), suggesting that these lesions cooperate with BCR-ABL1 in lymphoid leukemogenesis. To examine cooperativity between Pax5 haploinsufficiency and BCR-ABL1, we transplanted Pax5+/+ and Pax5+/− bone marrow cells transduced with MSCV-GFP-IRES-p185 BCR-ABL1 retrovirus into lethally irradiated wild-type C57BL6 recipient mice. Mice transplanted with BCR-ABL1 transduced Pax5+/− marrow developed B progenitor cell ALL with significantly higher penetrance and decreased latency when compared to animals transplanted with BCR-ABL1 transduced Pax5+/+ marrow (median survival 36 vs. 60 days, P=0.0003). The latency of tumor onset was further decreased in the presence of Arf haploinsufficiency (Pax5+/+Arf+/+ 60 days, Pax5+/−Arf+/+ 36 days, Pax5+/−Arf+/− 21 days, P&lt;0.0001). All leukemias were of B cell lineage and were transplantable to secondary recipients. In addition, Southern blot analysis revealed the Pax5+/−Arf+/+ leukemias to be monoclonal, where as the Pax5+/−Arf+/− leukemias were oligoclonal. Importantly, the Pax5+/− leukemias exhibited a more immature B cell immunophenotype than Pax5 wild type leukemias. Moreover, a proportion of the Pax5+/− leukemias (19%) exhibited a very immature early pro B cell immunophenotype (Cd19−, Bp1−), suggesting the possibility of acquired lesions in other key regulators of normal B cell differentiation. To explore this possibility and to identify the total complement of genetic lesions required to generate overt leukemia, we performed genome-wide copy number analysis on 30 murine leukemias (15 Pax5+/+, 15 Pax5+/−) using a custom CGH microarray (Agilent) that interrogated 477,000 autosomal loci, including 18,000 probes covering 20 genes encoding B lymphoid transcription factors and genes targeted by recurring copy number abnormalities (CNAs) in human BCR-ABL1 ALL (Bcl11a, Cdkn2a, Ebf1, Ikzf1, Ikzf2, Ikzf3, Il7r, Lef1, Mdm2, Mef2c, Myb, Pax5, Pten, Rb1, Sfpi1, Sox4, Stat5a, Tcf3, Tcf4, and Trp53). This analysis identified focal recurring CNAs in multiple genes including Cdkn2a/b, Ebf1, Ikzf1, Ikzf2, Ikzf3, and Pax5, each of which is a target of mutation in human B-ALL. Overall, there were on average 3.5 CNAs in Pax5+/+ leukemias versus 0.7 CNAs in Pax5+/− leukemias. Genomic resequencing was also performed on Pax5 and revealed three missense mutations in the DNA binding paired domain (R38H, P80R and G85R), one of which (P80R) is the most common PAX5 point mutation in human B-ALL. All three point mutations are predicted to impair DNA binding of Pax5. Interestingly, the majority of the pro-B cell leukemias that arose in the Pax5+/−Arf+/+ animals were found to harbor mutations (CNAs or point mutation) of the retained Pax5 allele, consistent with the immature immunophenotype. To further explore the relationship between our murine model and human BCR-ABL1 ALL, we performed gene expression profiling of Pax5+/+ and Pax5+/− leukemias and compared their signatures to those of human BCR-ABL1 ALL and stage-specific murine B lymphoid developmental signatures using gene set enrichment analysis (GSEA). This analysis identified significant similarity between murine and human BCR-ABL1 leukemias, thus providing further evidence that this model closely recapitulates human BCR-ABL1 ALL. Notably, Pax5+/− leukemias, or Pax5+/+ leukemias that acquired additional mutations of B-lymphoid regulators exhibited a less mature gene expression profile than leukemias lacking B-lymphoid regulatory mutations. These data indicate that loss of Pax5 contributes to leukemogenesis, that additional genomic alterations in genes regulating B lymphoid development and cell cycle regulators/tumor suppressors (Arf) are frequent events in BCR-ABL1 acute lymphoblastic leukemia, and that these lesions result in impaired B-lymphoid maturation in B-ALL. The genetic complexity of BCR-ABL1 ALL is likely to have important therapeutic implications for this poor prognosis subtype of leukemia.

Collaboration of the Meningioma 1 (MN1) Oncogene with MLL-Fusions in Pediatric Leukemia

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3786-3786
Author(s):  
Ting Liu ◽  
Dragana Jankovic ◽  
Laurent Brault ◽  
Sabine Ehret ◽  
Vincenzo Rossi ◽  
...  
Keyword(s):  
Gene Expression ◽  
Acute Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Lymphoblastic Leukemia ◽  
Leukemia Cell ◽  
Leukemic Cells ◽  
Human Leukemia ◽  
Fusion Genes ◽  
Pediatric Leukemia ◽  
Acute Myeloid

Abstract Expression of meningioma 1 (MN1) has been proposed to be a negative prognostic marker in adult acute myeloid leukemia (AML). In pediatric leukemia, we found overexpression of MN1 in 53 of 88 cases: whereas no MN1 expression was detected in T-cell acute lymphoblastic leukemia (T-ALL), significant amounts of MN1 were found in immature B-cell ALL and most cases of infant leukemia. Interestingly, 17 of 19 cases harboring fusion genes involving the mixed-lineage leukemia (MLL-X) gene showed elevated MN1 expression. Lentiviral siRNA mediated MN1 knock-down resulted in cell cycle arrest and impaired clonogenic growth of 3 MLL-X-positive human leukemia cell lines overexpressing MN1 (THP-1, RS4;11, MOLM-13). In a mouse model of MLL-ENL-induced leukemia we found MN1 to be overexpressed as a consequence of provirus integration. Strikingly co-expression of MN1 with MLL-ENL resulted in significantly reduced latency for induction of an AML phenotype in mice suggesting functional cooperation. Immunophenotyping and secondary transplant experiments suggested that MN1 overexpression seems to expand the L-GMP cell population targeted by the MLL-ENL fusion. Gene expression profiling allowed defining a number of potential MN1 hematopoietic targets. Upregulation of CD34, FLT3, HLF, or DLK1 was validated in bone marrow transiently overexpressing MN1, in MN1-induced mouse acute myeloid leukemia, as well as in pediatric leukemias with elevated MN1 levels. Our work shows that MN1 is overexpressed in a significant fraction of pediatric acute leukemia, is essential for growth of leukemic cells, and that MN1 can act as a cooperating oncogene with MLL-ENL most probably through modification of a distinct gene expression program that leads to expansion of a leukemic progenitor population targeted by MLL-fusion genes.

Caspase-9: A Candidate Susceptibility Factor for Murine Alkylator-Induced Leukemia.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1273-1273
Author(s):  
Yedda Li ◽  
Patrick Cahan ◽  
Masayo Izumi ◽  
Timothy Graubert
Keyword(s):  
Gene Expression ◽  
Progenitor Cells ◽  
Copy Number ◽  
Genetic Factors ◽  
The Novel ◽  
Caspase 9 ◽  
Hematopoietic Stem ◽  
Exon 2 ◽  
Expression Levels ◽  
Induced Apoptosis

Abstract Abstract 1273 Poster Board I-295 Therapy-related acute myeloid leukemia (tAML) is caused by exposure to chemotherapies and radiotherapies and has a poor prognosis. To better understand the genetic factors involved in secondary leukemogenesis, we studied alkylator-induced leukemias in murine models. We performed genome-wide mRNA profiling and found that differential expression of apoptosis-related genes was correlated with strain-dependent differences in tAML susceptibility. To identify genetic variants associated with these gene expression changes, we examined copy number variants (CNVs), differences in the DNA copy number of genomic regions greater than one kilobase in length, across 20 different inbred murine genomes. Our studies indicate that CNVs are a major contributor to natural variation among inbred laboratory mouse strains, and our array-based expression data show that the presence of certain CNVs correlates with differences in apoptotic gene expression. One CNV identified on murine chromosome 4 is correlated with altered Caspase-9 (Casp9) expression levels in murine hematopoietic stem/progenitor cells. Casp9 is a gene downstream from extrinsic and intrinsic death-inducing signals crucial for the initiation of cellular apoptosis, and we propose that it may be an important factor that influences tAML susceptibility. Sequencing the CNV region confirmed in two tAML susceptible strains (DBA/2J and PL/J) the presence of a 1,705 bp CNV loss in Casp9 intron 6. In these strains, Casp9 expression is undetectable in flow sorted kit+/lineage- (KL) hematopoietic stem/progenitor cells as measured by microarray profiling, and confirmed in independent samples by qRT-PCR using assays targeting Casp9 exons 2-3 or exons 8-9. Full-length Casp9 cDNA clones could be isolated from mRNA libraries prepared from KL cells, but 35% of the transcripts isolated from DBA/2J and PL/J mice were a novel isoform lacking exon 2 that results in a frameshift and an early stop codon in exon 4. This premature translation termination codon is predicted to trigger nonsense-mediated mRNA decay, leading to the degradation of the novel isoform and thus preventing its translation. This mechanism may account for the low Casp9 expression levels in DBA/2J and PL/J mice. In addition, Casp9 cDNA sequencing also identified an unusually high SNP density in exon 2 for the full-length isoforms in these strains. At least two of the six SNPs result in the formation of putative exonic splice enhancers (ESE), sequences that enhance the splicing of the exon in which they reside. The presence of these novel ESEs could explain the excision of exon 2 and the creation of the novel Casp9 isoform in DBA/2J and PL/J mice. We hypothesize that cells with relatively low Casp9 expression would be more resistant to alkylator-induced apoptosis. Cells that fail to undergo apoptosis after genotoxic stress may be more likely to accumulate mutations and initiate leukemias. Preliminary data from flow cytometric apoptosis assays (by Annexin V staining) in flow sorted KL bone marrow cells after treatment with ENU, an alkylating agent, suggest that PL/J cells may be more resistant to ENU-induced apoptosis, compared to C57BL/6J cells with normal Casp9 expression (5.3±1.4% vs. 9.7±1.8% post-ENU AnnexinV+ cells, respectively). These results suggest that differences in Casp9 expression levels may play a role in influencing individual susceptibility to tAML, and that inherited genetic factors may explain the observed expression differences. Ultimately, our understanding of the role that genetics plays in determining susceptibility to secondary leukemias may allow us to define a process by which individuals who are more susceptible can be successfully identified and screened from potential treatments that are known to induce these cancers. Disclosures No relevant conflicts of interest to declare.

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