Mutations of the Notch1 gene in T-cell acute lymphoblastic leukemia: analysis in adults and children

Adipocyte-mediated epigenomic instability in human T-ALL cells is cytotoxic and phenocopied by epigenetic-modifying drugs

The world’s population with obesity is reaching pandemic levels. If current trends continue, it is predicted that there will be 1.5 billion people with obesity by 2030. This projection is alarming due to the association of obesity with numerous diseases including cancer, with recent studies demonstrating a positive association with acute myeloid leukemia (AML) and B cell acute lymphoblastic leukemia (B-ALL). Interestingly, several epidemiological studies suggest the converse relationship may exist in patients with T cell acute lymphoblastic leukemia (T-ALL). To determine the relationship between obesity and T-ALL development, we employed the diet-induced obesity (DIO) murine model and cultured human T-ALL cells in adipocyte-conditioned media (ACM), bone marrow stromal cell-conditioned media, stromal conditioned media (SCM), and unconditioned media to determine the functional impact of increased adiposity on leukemia progression. Whereas only 20% of lean mice transplanted with T-ALL cells survived longer than 3 months post-inoculation, 50%–80% of obese mice with leukemia survived over this same period. Furthermore, culturing human T-ALL cells in ACM resulted in increased histone H3 acetylation (K9/K14/K18/K23/K27) and methylation (K4me3 and K27me3) posttranslational modifications (PTMs), which preceded accelerated cell cycle progression, DNA damage, and cell death. Adipocyte-mediated epigenetic changes in human T-ALL cells were recapitulated with the H3K27 demethylase inhibitor GSK-J4 and the pan-HDAC inhibitor vorinostat. These drugs were also highly cytotoxic to human T-ALL cells at low micromolar concentrations. In summary, our data support epidemiological studies demonstrating that adiposity suppresses T-ALL pathogenesis. We present data demonstrating that T-ALL cell death in adipose-rich microenvironments is induced by epigenetic modifications, which are not tolerated by leukemia cells. Similarly, GSK-J4 and vorinostat treatment induced epigenomic instability and cytotoxicity profiles that phenocopied the responses of human T-ALL cells to ACM, which provides additional support for the use of epigenetic modifying drugs as a treatment option for T-ALL.

NICD3 regulates the expression of MUC5AC and MUC2 by recruiting SMARCA4 and is involved in the differentiation of mucinous colorectal adenocarcinoma

Adenocarcinoma is the most prevalent histological subtype of colorectal cancer (CRC), with mucinous colorectal adenocarcinoma (MCA) being a unique form. Although the mucinous subtype is known to elicit a worse response to chemotherapy and immunotherapy than the nonmucinous subtype, its pathogenesis remains poorly understood. Neurogenic locus notch homolog protein 3 (NOTCH3), a member of the NOTCH subfamilies, is highly expressed in CRC. In the past three decades, many studies have been performed evaluating the biological role of NOTCH3 in CRC. However, the precise activities of NOTCH3 in MCA, as well as the mechanisms involved in its transcriptional control, are yet to be elucidated. Our finding showed that the critical transcriptional regulatory factor transcription activator BRG1 (SMARCA4) directly binds to the intracellular domain of NOTCH3 to control transcriptional regulation. Moreover, RNA‐sequencing results indicated a common targeting effect on the transcriptional activity of mucin‐5AC (MUC5AC) and mucin‐2 (MUC2) in CRC cells by NOTCH3 and SMARCA4. Furthermore, NOTCH3 was found to control the expressions of MUC5AC and MUC2 in a SMARCA4‐dependent manner. MUC5AC and MUC2, which encode two secreted mucins, are located on chromosome 11p15.5, and are linked to the development of MCA. This finding suggests that the interaction between NOTCH3 and SMARCA4 may be involved in MCA differentiation by jointly targeting MUC5AC and MUC2. Patients with MCA are often treated in accordance with CRC guidelines. Determining the relationship between NOTCH3 and SMARCA4 by demonstrating their interactions in the pathophysiology of MCA could provide novel therapeutic targets and help identify potential prognostic markers for MCA.

Next generation DNA sequencing of atypical choroid plexus papilloma of brain: Identification of novel mutations in a female patient by Ion Proton

Choroid plexus papilloma (CPP) is a rare benign tumor of the central nervous system that is usually confined to the cerebral ventricles. According to the World Health Organization, CPP corresponds to a grade I atypical CPP (a-CPP); however, it can become more aggressive and reach grade II, which can rarely undergo malignant transformation into a choroid plexus carcinoma (grade III). To the best of our knowledge, identification of these tumors mutations by next generation DNA sequencing (NGS) has not been yet reported. In the present study, NGS analysis of an a-CPP case was performed. Data were analyzed using Advaita Bioinformatics i-VariantGuide and Ion Reporter 5.6 programs. The results from NGS identified 12 novel missense mutations in the following genes: NOTCH1, ATM, STK36, MAGI1, DST, RECQL4, NUMA1, THBS1, MYH11, MALT1, SMARCA4 and CDH20. The PolyPhen score of six variants viz., DST, RECQL4, NUMA1, THBS1, MYHI1 and SMARCA4 were high, which suggested these variants represents pathogenic variants. Two novel insertions that caused frameshift were also found. Furthermore, two novel nonsense mutations and 14 novel intronic variants were identified in this tumor. The novel missense mutation detected in ATM gene was situated in c.5808A>T; p. (Leu1936Phe) in exon 39, and a known ATM mutation was in c.5948A>G; p. (Asn1983Ser). These novel mutations had not been reported in previous database. Subsequently, the quality statistics of these variants, including allele coverage, allele ratio, P-value, Phred quality score, sequencing coverage, PolyPhen score and alleles frequency was performed. For all variants, P-value was highly significant and the Phred quality score was high. In addition, the results from sequencing coverage demonstrated that 97.02% reads were on target and that 97.88% amplicons had at least 500 reads. These findings may serve at determining new strategies to distinguish the types of choroid plexus tumor, and at developing novel targeted therapies. Development of NGS technologies in the Kingdom of Saudi Arabia may be used in molecular pathology laboratories.

The Potential Roles of Long Noncoding RNAs (lncRNA) in Glioblastoma Development

Long noncoding RNA (lncRNA) may contribute to the initiation and progression of tumor. In this study, we first systematically compared lncRNA and mRNA expression between glioblastoma and paired normal brain tissues using microarray data. We found 27 lncRNA and 82 mRNA significantly upregulated in glioblastoma, as well as 198 lncRNA and 285 mRNA significantly downregulated in glioblastoma. We identified 138 coexpressed lncRNA-mRNA pairs from these differentially expressed lncRNA and genes. Subsequent pathway analysis of the lncRNA-paired genes indicated that EphrinB-EPHB, p75-mediated signaling, TNFα/NF-κB, and ErbB2/ErbB3 signaling pathways might be altered in glioblastoma. Specifically, lncRNA RAMP2-AS1 had significant decrease of expression in glioblastoma tissues and showed coexpressional relationship with NOTCH3, an important tumor promoter in many neoplastic diseases. Our follow up experiment indicated that (i) an overexpression of RAMP2-AS1 reduced glioblastoma cell proliferation in vitro and also reduced glioblastoma xenograft tumors in vivo; (ii) NOTCH3 and RAMP2-AS1 coexpression rescued the inhibitory action of RAMP2-AS1 in glioblastoma cells; and (iii) RNA pull-down assay revealed a direct interaction of RAMP2-AS1 with DHC10, which may consequently inhibit, as we hypothesize, the expression of NOTCH3 and its downstream signaling molecule HES1 in glioblastoma. Taken together, our data revealed that lncRNA expression profile in glioblastoma tissue was significantly altered; and RAMP2-AS1 might play a tumor suppressive role in glioblastoma through an indirect inhibition of NOTCH3 Our results provided some insights into understanding the key roles of lncRNA-mRNA coregulation in human glioblastoma and the mechanisms responsible for glioblastoma progression and pathogenesis. Mol Cancer Ther; 15(12); 2977-86. ©2016 AACR.

Aberrant Wnt Signaling in Leukemia

The Wnt signaling pathway is essential in the development and homeostasis of blood and immune cells, but its exact role is still controversial and is the subject of intense research. The malignant counterpart of normal hematopoietic cells, leukemic (stem) cells, have hijacked the Wnt pathway for their self-renewal and proliferation. Here we review the multiple ways dysregulated Wnt signaling can contribute to leukemogenesis, both cell autonomously as well as by changes in the microenvironment.

Prolyl-isomerase Pin1 controls Notch3 protein expression and regulates T-ALL progression

Deregulated Notch signaling is associated with T-cell Acute Lymphoblastic Leukemia (T-ALL) development and progression. Increasing evidence reveals that Notch pathway has an important role in the invasion ability of tumor cells, including leukemia, although the underlying molecular mechanisms remain mostly unclear. Here, we show that Notch3 is a novel target protein of the prolyl-isomerase Pin1, which is able to regulate Notch3 protein processing and to stabilize the cleaved product, leading to the increased expression of the intracellular domain (N3_IC), finally enhancing Notch3-dependent invasiveness properties. We demonstrate that the combined inhibition of Notch3 and Pin1 in the Notch3-overexpressing human leukemic TALL-1 cells reduces their high invasive potential, by decreasing the expression of the matrix metalloprotease MMP9. Consistently, Pin1 depletion in a mouse model of Notch3-induced T-ALL, by reducing N3_IC expression and signaling, impairs the expansion/invasiveness of CD4⁺CD8⁺ DP cells in peripheral lymphoid and non-lymphoid organs. Notably, in in silico gene expression analysis of human T-ALL samples we observed a significant correlation between Pin1 and Notch3 expression levels, which may further suggest a key role of the newly identified Notch3-Pin1 axis in T-ALL aggressiveness and progression. Thus, combined suppression of Pin1 and Notch3 proteins may be exploited as an additional target therapy for T-ALL.

Genetic mutational profiling analysis of T cell acute lymphoblastic leukemia reveal mutant FBXW7 as a prognostic indicator for inferior survival

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplasm for which there are currently no adequate biomarkers for developing risk-adapted therapeutic regimens to improve the treatment outcome. In this prospective study of 83 Chinese patients (54 children and 29 adults) with de novo T-ALL, we analyzed mutations in 11 T-ALL genes: NOTCH1, FBXW7, PHF6, PTEN, N-RAS, K-RAS, WT1, IL7R, PIK3CA, PIK3RA, and AKT1. NOTCH1 mutations were identified in 51.9 and 37.9 % of pediatric and adult patients, respectively, and these patients showed improved overall survival (OS) and event-free survival (EFS). The FBXW7 mutant was present in 25.9 and 6.9 % of pediatric and adult patients, respectively, and was associated with inferior OS and EFS in pediatric T-ALL. Multivariate analysis revealed that mutant FBXW7 was an independent prognostic indicator for inferior EFS (hazard ratio [HR] 4.38; 95 % confidence interval [CI] 1.15-16.71; p = 0.03) and tended to be associated with reduced OS (HR 2.81; 95 % CI 0.91-8.69; p = 0.074) in pediatric T-ALL. Mutant PHF6 was present in 13 and 20.7 % of our childhood and adult cohorts, respectively, while PTEN mutations were noted in 11.1 % of the pediatric patients. PTEN and NOTCH1 mutations were almost mutually exclusive, while IL7R and WT1 mutations were rare in pediatric T-ALL and PTPN11 and AKT1 mutations were infrequent in adult T-ALL. This study revealed differences in the mutational profiles of pediatric and adult T-ALL and suggests mutant FBXW7 as an independent prognostic indicator for inferior survival in pediatric T-ALL.

Notch signaling activation in pediatric low-grade astrocytoma

Pilocytic astrocytoma (PA) is the most common primary brain tumor in children; various signaling pathways have been implicated in its biology. The Notch signaling pathway has been found to play a role in the development, stem cell biology, and pathogenesis of several cancers, but its role in PA has not been investigated. We studied alterations in Notch signaling components in tumor tissue from 18 patients with PA and 4 with other low-grade astrocytomas to identify much needed therapeutic targets. We found that Notch pathway members were overexpressed at the mRNA (NOTCH1, NOTCH2, HEY1, HEY2) and protein (HES1) levels in PAs at various anatomic sites compared with non-neoplastic brain samples. These changes were not associated with specific BRAF alterations. Inhibiting the Notch pathway in the pediatric low-grade astrocytoma cell lines Res186 and Res259 using either RNA interference or a γ-secretase inhibitor resulted in variable, but significant, reduction in cell growth and migration. This study suggests a potential role for Notch signaling in pediatric low-grade astrocytoma tumorigenesis and that Notch signaling may be a viable pathway therapeutic target.

Notch and NF-kB signaling pathways regulate miR-223/FBXW7 axis in T-cell acute lymphoblastic leukemia

Notch signaling deregulation is linked to the onset of several tumors including T-cell acute lymphoblastic leukemia (T-ALL). Deregulated microRNA (miRNA) expression is also associated with several cancers, including leukemias. However, the transcriptional regulators of miRNAs, as well as the relationships between Notch signaling and miRNA deregulation, are poorly understood. To identify miRNAs regulated by Notch pathway, we performed microarray-based miRNA profiling of several Notch-expressing T-ALL models. Among seven miRNAs, consistently regulated by overexpressing or silencing Notch3, we focused our attention on miR-223, whose putative promoter analysis revealed a conserved RBPjk binding site, which was nested to an NF-kB consensus. Luciferase and chromatin immunoprecipitation assays on the promoter region of miR-223 show that both Notch and NF-kB are novel coregulatory signals of miR-223 expression, being able to activate cooperatively the transcriptional activity of miR-223 promoter. Notably, the Notch-mediated activation of miR-223 represses the tumor suppressor FBXW7 in T-ALL cell lines. Moreover, we observed the inverse correlation of miR-223 and FBXW7 expression in a panel of T-ALL patient-derived xenografts. Finally, we show that miR-223 inhibition prevents T-ALL resistance to γ-secretase inhibitor (GSI) treatment, suggesting that miR-223 could be involved in GSI sensitivity and its inhibition may be exploited in target therapy protocols.

Therapeutic targeting of NOTCH signaling ameliorates immune-mediated bone marrow failure of aplastic anemia

Notch1 signaling sustains the proinflammatory behavior of Th1 cells, implicated in the development of aplastic anemia in humans and mice.

Severe aplastic anemia (AA) is a bone marrow (BM) failure (BMF) disease frequently caused by aberrant immune destruction of blood progenitors. Although a Th1-mediated pathology is well described for AA, molecular mechanisms driving disease progression remain ill defined. The NOTCH signaling pathway mediates Th1 cell differentiation in the presence of polarizing cytokines, an action requiring enzymatic processing of NOTCH receptors by γ-secretase. Using a mouse model of AA, we demonstrate that expression of both intracellular NOTCH1^IC and T-BET, a key transcription factor regulating Th1 cell differentiation, was increased in spleen and BM-infiltrating T cells during active disease. Conditionally deleting Notch1 or administering γ-secretase inhibitors (GSIs) in vivo attenuated disease and rescued mice from lethal BMF. In peripheral T cells from patients with untreated AA, NOTCH1^IC was significantly elevated and bound to the TBX21 promoter, showing NOTCH1 directly regulates the gene encoding T-BET. Treating patient cells with GSIs in vitro lowered NOTCH1^IC levels, decreased NOTCH1 detectable at the TBX21 promoter, and decreased T-BET expression, indicating that NOTCH1 signaling is responsive to GSIs during active disease. Collectively, these results identify NOTCH signaling as a primary driver of Th1-mediated pathogenesis in AA and may represent a novel target for therapeutic intervention.

Inhibition of ADAM-17 more effectively down-regulates the Notch pathway than that of γ-secretase in renal carcinoma

BACKGROUND

Our study is to research the effect of inhibited ADAM-17 expression through the Notch pathway in renal carcinoma.

METHODS

Immunohistochemistry and western blot were used to examine the expression of ADAM-17 protein in renal cancer tissues. Proliferation and cell invasion of 786-o cells, as well as OS-RC-2 cells, after treatment with two different inhibitors of the Notch pathway, were examined by CCK-8 assay and Transwell assay, respectively. 786-o cell apoptosis was measured using the FCM test.

RESULTS

ADAM-17 was highly expressed in RCC tissues. Compared with blocking γ-secretase, a known mechanism of impairing Notch, blockade of ADAM-17 more effectively down-regulated the expressions of Notch1 and HES-1 proteins. Similarly, we found that the ADAM-17 inhibitor, Marimastat, could more efficiently reduce renal cell proliferation and invasive capacity in comparison with the γ-secretase inhibitor DAPT when used at the same dose. Similar results were obtained when apoptosis of 786-o was measured.

CONCLUSION

Compared with γ-secretase, inhibition of ADAM-17 expression more effectively inhibits Notch pathway-mediated renal cancer cell proliferation and invasion. ADAM-17 may be a new target for future treatment of renal carcinoma.

Complementary genomic screens identify SERCA as a therapeutic target in NOTCH1 mutated cancer

Notch1 is a rational therapeutic target in several human cancers, but as a transcriptional regulator, it poses a drug discovery challenge. To identify Notch1 modulators, we performed two cell-based, high-throughput screens for small-molecule inhibitors and cDNA enhancers of a NOTCH1 allele bearing a leukemia-associated mutation. Sarco/endoplasmic reticulum calcium ATPase (SERCA) channels emerged at the intersection of these complementary screens. SERCA inhibition preferentially impairs the maturation and activity of mutated Notch1 receptors and induces a G0/G1 arrest in NOTCH1-mutated human leukemia cells. A small-molecule SERCA inhibitor has on-target activity in two mouse models of human leukemia and interferes with Notch signaling in Drosophila. These studies "credential" SERCA as a therapeutic target in cancers associated with NOTCH1 mutations.

Differential requirements for Wnt and Notch signaling in hematopoietic versus thymic niches

All blood cells are derived from multipotent stem cells, the so-called hematopoietic stem cells (HSCs), that in adults reside in the bone marrow. Most types of blood cells also develop there, with the notable exception of T lymphocytes that develop in the thymus. For both HSCs and developing T cells, interactions with the surrounding microenvironment are critical in regulating maintenance, differentiation, apoptosis, and proliferation. Such specialized regulatory microenvironments are referred to as niches and provide both soluble factors as well as cell-cell interactions between niche component cells and blood cells. Two pathways that are critical for early T cell development in the thymic niche are Wnt and Notch signaling. These signals also play important but controversial roles in the HSC niche. Here, we review the differences and similarities between the thymic and hematopoietic niches, with particular focus on Wnt and Notch signals, as well as the latest insights into regulation of these developmentally important pathways.

Notch signaling expands a pre-malignant pool of T-cell acute lymphoblastic leukemia clones without affecting leukemia-propagating cell frequency

NOTCH1 pathway activation contributes to the pathogenesis of over 60% of T-cell acute lymphoblastic leukemia (T-ALL). While Notch is thought to exert the majority of its effects through transcriptional activation of Myc, it also likely has independent roles in T-ALL malignancy. Here, we utilized a zebrafish transgenic model of T-ALL, where Notch does not induce Myc transcription, to identify a novel Notch gene expression signature that is also found in human T-ALL and is regulated independently of Myc. Cross-species microarray comparisons between zebrafish and mammalian disease identified a common T-ALL gene signature, suggesting that conserved genetic pathways underlie T-ALL development. Functionally, Notch expression induced a significant expansion of pre-leukemic clones; however, a majority of these clones were not fully transformed and could not induce leukemia when transplanted into recipient animals. Limiting-dilution cell transplantation revealed that Notch signaling does not increase the overall frequency of leukemia-propagating cells (LPCs), either alone or in collaboration with Myc. Taken together, these data indicate that a primary role of Notch signaling in T-ALL is to expand a population of pre-malignant thymocytes, of which a subset acquire the necessary mutations to become fully transformed LPCs.

Prognostic implications of NOTCH1 and FBXW7 mutations in adult acute T-lymphoblastic leukemia

BACKGROUND

NOTCH1 mutations have been associated with a favorable outcome in pediatric acute T-lymphoblastic leukemia. However, the results of studies on the prognostic significance of NOTCH1 mutations in adult T-lymphoblastic leukemia remain controversial.

DESIGN AND METHODS

Here we have investigated the prognostic impact of mutations in the NOTCH1 pathway, in particular, the NOTCH1 and FBXW7 genes, in a large cohort of adult patients with T-lymphoblastic leukemia (n=126). We determined the occurrence of mutations in NOTCH1 and FBXW7 by DNA amplification and direct sequencing of polymerase chain reaction products.

RESULTS

Mutations were identified in 57% and 12% of the NOTCH1 and FBXW7 genes, respectively. The characteristics of patients carrying NOTCH1 and/or FBXW7 (NOTCH1-FBXW7) mutations were similar to those with wild-type genes. Patients with NOTCH1-FBXW7 mutations more often showed a thymic immunophenotype (p=0.001). In the overall cohort, no significant differences were seen in the complete remission or event-free survival rates between patients with mutated or wild-type NOTCH1-FBXW7 (p=0.39).

CONCLUSIONS

NOTCH1 and FBXW7 mutations were not predictive of outcome in the overall cohort of adult patients with T-lymphoblastic leukemia, but there was a trend towards a favorable prognostic impact of NOTCH1-FBXW7 mutations in the small subgroup of patients with low-risk ERG/BAALC expression status. Our findings further confirm the high frequency of NOTCH1 mutations in adult T-lymphoblastic leukemia.

Zebrafish models for cancer

First established as a valuable vertebrate model system for studying development, zebrafish have emerged as an attractive animal system for modeling human cancers. Major technical advances have been essential for the generation of zebrafish cancer models relevant to human diseases. These models develop tumors in various organ sites that bear striking resemblance to human malignances, both histologically and genetically. Thus, the focus of cancer research in zebrafish has transcended the need to validate zebrafish as a viable model organism to study cancer biology. With the significant advantages of in vivo imaging, the power of forward genetics, well-established high efficiency for transgenesis, and ease of transplantation, further exploration of the zebrafish cancer models not only will generate unique insights into underlying mechanisms of cancer but will also provide platforms useful for drug discovery.

NOTCH and phosphatidylinositide 3-kinase/phosphatase and tensin homolog deleted on chromosome ten/AKT/mammalian target of rapamycin (mTOR) signaling in T-cell development and T-cell acute lymphoblastic leukemia

Activating mutations in NOTCH1 consitute the most prominent genetic abnormality in T-cell acute lymphoblastic leukemia (T-ALL). However, most T-ALL cell lines with NOTCH1 mutations are resistant to treatment with γ-secretase inhibitors (GSIs). The spotlight is now shifting to the phosphatidylinositide 3-kinase (PI3K)/phosphatase and tensin homolog deleted on chromosome ten (PTEN)/AKT/mammalian target of rapamycin (mTOR) pathway as another key potential target. These two signaling routes are deregulated in many types of cancer. In this review we discuss these two pathways with respect to their signaling mechanisms, functions during T-cell development, and their mutual roles in the development of T-ALL.

Notch3 activation promotes invasive glioma formation in a tissue site-specific manner

Although Notch signaling has been widely implicated in neoplastic growth, direct evidence for in vivo initiation of neoplasia by the pathway in murine models has been limited to tumors of lymphoid, breast, and choroid plexus cells. To examine tumorigenic potential in the eye and brain, we injected retroviruses encoding activated forms of Notch1, Notch2, or Notch3 into embryonic mice. Interestingly, the majority of animals infected with active Notch3 developed proliferative lesions comprised of pigmented ocular choroid cells, retinal and optic nerve glia, and lens epithelium. Notch3-induced lesions in the choroid, retina, and optic nerve were capable of invading adjacent tissues, suggesting that they were malignant tumors. Although Notch3 activation induced choroidal tumors in up to 67% of eyes, Notch1 or Notch2 activation never resulted in such tumors. Active forms of Notch1 and Notch2 did generate a few small proliferative glial nodules in the retina and optic nerve, whereas Notch3 was 10-fold more efficient at generating growths, many of which were large invasive gliomas. Expression of active Notch1/Notch3 chimeric receptors implicated the RBPjk-association molecule and transactivation domains of Notch3 in generating choroidal and glial tumors, respectively. In contrast to our findings in the optic nerve and retina, introduction of active Notch receptors, including Notch3, into the brain never caused glial tumors. Our results highlight the differential ability of Notch receptor paralogs to initiate malignant tumor formation, and suggest that glial precursors of the optic nerve, but not the brain, are susceptible to transformation by Notch3.

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

LYL1 degradation by the proteasome is directed by a N-terminal PEST rich site in a phosphorylation-independent manner

Background

The Lymphoblastic leukemia 1 (LYL1) gene is a proto-oncogenic transcription factor found upregulated in patients with T-cell acute lymphoblastic leukemia (T-cell ALL). Initially, the upregulation was described to be as a result of a translocation. However, further studies revealed that transcriptional upregulation of LYL1could also occur without translocations. In addition, post-translational mechanisms, such as protein degradation could influence LYL1 expression as well.

Methodology/Principal Findings

In this study, we considered possible post-translational regulation of Lyl1, and investigated fundamental mechanisms governing LYL1 degradation in cell-based culture assays. We identify a PEST sequence motif located in the N-terminus of LYL1, which determines the efficiency of LYL1 degradation by the proteasome. The absence of the PEST degradation site leads to accumulation or upregulation of LYL1. We also show that LYL1 is phosphorylated by MAPK at S₃₆, and determined that proteasomal degradation of LYL1 occurs in a phosphorylation-independent manner.

Conclusions/Significance

Understanding LYL1 degradation is a step forward not only towards deciphering the normal function and regulation of LYL1, but could suggest post-translational mechanisms for upregulation of LYL1 that may contribute to its oncogenic role.

Overexpression of human CAP10-like protein 46 KD in T-acute lymphoblastic leukemia and acute myelogenous leukemia

AIMS

We earlier identified a novel gene human CAP10-like protein 46 KD (hCLP46) from human acute myelogenous leukemia (AML) transformed from myelodysplastic syndrome CD34(+) cells, but the function of this gene remains unclear. In this study, a real-time polymerase chain reaction-based assay was developed to quantify expression of hCLP46 in the peripheral blood of AML and T-acute lymphoblastic leukemia (T-ALL) primary samples and in six leukemic cell lines. Also, we investigated expression of CDKN2A/B and the apoptosis in U937 cells when hCLP46 is downregulated in vitro.

RESULTS

Our findings showed that hCLP46 was overexpressed in AML, T-ALL, and the leukemic cell lines. Suppressing hCLP46 overexpression had no effect on expression of CDKN2A/B and apoptosis of U937 cells.

CONCLUSION

Considering that hCLP46 has the capability of modifying the Notch pathway, our finding adds weight to the importance of Notch signaling in hematopoiesis and suggests that overexpression of hCLP46 might be an early event in the pathogenesis of AML and T-ALL.

Dual antitumor mechanisms of Notch signaling inhibitor in a T-cell acute lymphoblastic leukemia xenograft model

Constitutive activation of Notch signaling is required for the proliferation of a subgroup of human T-cell acute lymphoblastic leukemias (T-ALL). Previous in vitro studies have demonstrated the therapeutic potential of Notch signaling inhibitors for treating T-ALL. To further examine this possibility, we applied a gamma-secretase inhibitor (GSI) to T-ALL xenograft models. Treatment of established subcutaneous tumors with GSI resulted in partial or complete regression of tumors arising from four T-ALL cell lines that were also sensitive to GSI in vitro. To elucidate the mechanism of action, we transduced DND-41 cells with the active form of Notch1 (aN1), which conferred resistance to in vitro GSI treatment. Nevertheless, in vivo treatment with GSI induced a partial but significant regression of subcutaneous tumors that developed from aN1-transduced DND-41 cells, whereas it induced complete regression of tumors that developed from mock-transduced DND-41 cells. These findings indicate that the remarkable efficacy of GSI might be attributable to dual mechanisms, directly via apoptosis of DND-41 cells through the inhibition of cell-autonomous Notch signaling, and indirectly via disturbance of tumor angiogenesis through the inhibition of non-cell-autonomous Notch signaling.

Hes1 immortalizes committed progenitors and plays a role in blast crisis transition in chronic myelogenous leukemia

Hairy enhancer of split 1 (Hes1) is a basic helix-loop-helix transcriptional repressor that affects differentiation and often helps maintain cells in an immature state in various tissues. Here we show that retroviral expression of Hes1 immortalizes common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) in the presence of interleukin-3, conferring permanent replating capability on these cells. Whereas these cells did not develop myeloproliferative neoplasms when intravenously administered to irradiated mice, the combination of Hes1 and BCR-ABL in CMPs and GMPs caused acute leukemia resembling blast crisis of chronic myelogenous leukemia (CML), resulting in rapid death of the recipient mice. On the other hand, BCR-ABL alone caused CML-like disease when expressed in c-Kit-positive, Sca-1-positive, and lineage-negative hematopoietic stem cells (KSLs), but not committed progenitors CMPs or GMPs, as previously reported. Leukemic cells derived from Hes1 and BCR-ABL-expressing CMPs and GMPs were more immature than those derived from BCR-ABL-expressing KSLs. Intriguingly, Hes1 was highly expressed in 8 of 20 patients with CML in blast crisis, but not in the chronic phase, and dominant negative Hes1 retarded the growth of some CML cell lines expressing Hes1. These results suggest that Hes1 is a key molecule in blast crisis transition in CML.

NOTCH1mutations are rare in acute myeloid leukemia

Mutations in the NOTCH1 gene were investigated in 12 primary acute myeloid leukemia (AML) cell samples and eight AML cell lines. Mutations in the genomic DNA were screened using a nested PCR-SSCP analysis and confirmed by direct sequencing. A missense mutation, Pro2439Leu (7316C/T), was found in the PEST domain in one primary AML case. This mutation was different from those previously reported for T-cell acute lymphoblastic leukemia, in which more than half the cases had the mutations. This mutation was not detected in his sample in complete remission, which indicated that the mutation was not a single nucleotide polymorphism. The sample with the mutation expressed the intracellular Notch1 fragment by immunoblotting and HES1 mRNA by reverse transcription-polymerase chain reaction. This is the first paper to present an AML case with NOTCH1 mutation. The precise role of the mutation is to be determined.

Gain-of-function mutations and copy number increases of Notch2 in diffuse large B-cell lymphoma

Signaling through the Notch1 receptor has a pivotal role in early thymocyte development. Gain of Notch1 function results in the development of T-cell acute lymphoblastic leukemia in a number of mouse experimental models, and activating Notch1 mutations deregulate Notch1 signaling in the majority of human T-cell acute lymphoblastic leukemias. Notch2, another member of the Notch gene family, is preferentially expressed in mature B cells and is essential for marginal zone B-cell generation. Here, we report that 5 of 63 (approximately 8%) diffuse large B-cell lymphomas, a subtype of mature B-cell lymphomas, have Notch2 mutations. These mutations lead to partial or complete deletion of the proline-, glutamic acid-, serine- and threonine-rich (PEST) domain, or a single amino acid substitution at the C-terminus of Notch2 protein. Furthermore, high-density oligonucleotide microarray analysis revealed that some diffuse large B-cell lymphoma cases also have increased copies of the mutated Notch2 allele. In the Notch activation-sensitive luciferase reporter assay in vitro, mutant Notch2 receptors show increased activity compared with wild-type Notch2. These findings implicate Notch2 gain-of-function mutations in the pathogenesis of a subset of B-cell lymphomas, and suggest broader roles for Notch gene mutations in human cancers.

Candidate Genes on Chromosome 9q33-34 Involved in the Progression of Childhood Ependymomas

Purpose

The molecular pathogenesis of pediatric ependymoma remains unclear. Our study was designed to identify genetic changes implicated in ependymoma progression.

Patients and Methods

We characterized 59 ependymoma samples (33 at diagnosis and 26 at relapse) using array-comparative genomic hybridization (aCGH). Specific chromosomal imbalances were confirmed by fluorescent in situ hybridization, and candidate genes were assessed by real-time quantitative polymerase chain reaction (qPCR), immunohistochemistry, sequencing, and in vitro functional studies.

Results

aCGH analysis revealed a significant increase in genomic imbalances on relapse compared with diagnosis, such as gain of 9qter and 1q (54% v 21% and 12% v 0%, respectively) and loss of 6q (27% v 6%). Supervised tumor classification showed that gain of 9qter was associated with tumor recurrence, age older than 3 years, and posterior fossa location. Using a candidate-gene strategy, we found an overexpression of two potential oncogenes at the locus 9qter: Tenascin-C and Notch1. Moreover, Notch pathway analysis (qPCR) revealed overexpression of Notch ligands, receptors, and target genes (Hes-1, Hey2, and c-Myc), and downregulation of Notch repressor Fbxw7. We confirmed by immunohistochemistry the overexpression of Tenascin-C and Hes-1. We detected Notch1 missense mutations in 8.3% of the tumors (only in the posterior fossa location and in case of 9q33-34 gain). Furthermore, inhibition of Notch pathway with a γ-secretase inhibitor impaired the growth of ependymoma stem cell cultures.

Conclusion

The activation of the Notch pathway and Tenascin-C seem to be important events in ependymoma progression and may represent future targets for therapy. We report, to our knowledge for the first time, recurrent oncogenic mutations in pediatric posterior fossa ependymomas.

NOTCH inhibition and glucocorticoid therapy in T-cell acute lymphoblastic leukemia

Inhibition of NOTCH1 signaling with gamma-secretase inhibitors (GSIs) has been proposed as a molecularly targeted therapy in T-cell acute lymphoblastic leukemia (T-ALL). However, GSIs seem to have limited antileukemic activity in human T-ALL and are associated with severe gastrointestinal toxicity resulting from inhibition of NOTCH signaling in the gut. Inhibition of NOTCH1 signaling in glucocorticoid-resistant T-ALL restored glucocorticoid sensitivity and co-treatment with glucocorticoids inhibited GSI-induced gut toxicity. Thus, combination therapies with GSIs plus glucocorticoids may offer a new opportunity for the use of anti-NOTCH1 therapies in human T-ALL.

NOTCH inhibition and glucocorticoid therapy in T-cell acute lymphoblastic leukemia

Inhibition of NOTCH1 signaling with gamma-secretase inhibitors (GSIs) has been proposed as a molecularly targeted therapy in T-cell acute lymphoblastic leukemia (T-ALL). However, GSIs seem to have limited antileukemic activity in human T-ALL and are associated with severe gastrointestinal toxicity resulting from inhibition of NOTCH signaling in the gut. Inhibition of NOTCH1 signaling in glucocorticoid-resistant T-ALL restored glucocorticoid sensitivity and co-treatment with glucocorticoids inhibited GSI-induced gut toxicity. Thus, combination therapies with GSIs plus glucocorticoids may offer a new opportunity for the use of anti-NOTCH1 therapies in human T-ALL.

FBXW7 and NOTCH1 mutations in childhood T cell acute lymphoblastic leukaemia and T cell non-Hodgkin lymphoma

Mutation analysis of FBXW7 and NOTCH1 genes was performed in 55 T cell acute lymphoblastic leukaemia (T-ALL) and 14 T cell non-Hodgkin lymphoma (T-NHL) patients who were treated on the Japan Association of Childhood Leukaemia Study (JACLS) protocols ALL-97 and NHL-98. FBXW7 and/or NOTCH1 mutations were found in 22 (40.0%) of 55 T-ALL and 7 (50.0%) of 14 T-NHL patients. FBXW7 mutations were found in 8 (14.6%) of 55 T-ALL and 3 (21.4%) of 14 T-NHL patients, and NOTCH1 mutations in 17 (30.9%) of 55 T-ALL and 6 (42.9%) of 14 T-NHL patients. Three (5.4%) T-ALL and two (1.4%) T-NHL patients had mutations in both FBXW7 and NOTCH1. FBXW7 mutations included one insertion, one deletion, one deletion/insertion and nine missense mutations. NOTCH1 mutations were detected in the heterodimerization domain (HD) in 15 cases, in the PEST domain in seven cases, and in both the HD and PEST domains in one case. Five-year event-free survival and overall survival for patients with FBXW7 and/or NOTCH1 mutations were 95.5% (95% CI, 71.9-99.4%) and 100% respectively, suggesting that T-ALL patients with FBXW7 and/or NOTCH1 mutation represent a good prognosis compared to those without FBXW7 and/or NOTCH1 mutations (63.6%, P = 0.007 and 78.8%, P = 0.023, respectively).

Cross-talk between tumor and endothelial cells involving the Notch3-Dll4 interaction marks escape from tumor dormancy

The Notch ligand Dll4 has a recognized role during both physiologic and tumor angiogenesis, as it contributes to regulate Notch activity in endothelial cells (EC). The effects of Dll4 on Notch signaling in tumor cells expressing Notch receptors remain, however, largely unknown. Here, we report that escape of human T-cell acute lymphoblastic leukemia (T-ALL) cells or colorectal cancer cells from dormancy is associated with Dll4 expression in the tumor microenvironment and increased Notch3 signaling in tumor cells. Dll4 was expressed at early time points during the angiogenic process, and its expression preceded perfusion of the newly established vessels. Treatment of EC with angiogenic factors induced Dll4 expression and increased Notch3 activation in cocultured T-ALL cells. Neutralization of Dll4 greatly reduced EC-mediated activation of Notch 3 signaling in T-ALL cells and blocked tumorigenesis. Moreover, silencing Notch3 by RNA interference had marked antiproliferative and proapoptotic effects on T-ALL cells in vitro and reduced tumorigenicity in vivo. Our results elucidate a novel mechanism by which a direct interplay between endothelial and tumor cells promotes survival and triggers tumor growth.

Notch1 is a frequent mutational target in chemically induced lymphoma in mouse

Activating Notch1 mutations have been reported in human T-lineage acute lymphoblastic leukemia (T-ALL) and lymphomas from genetically modified mice. We report that Notch1 is a prevalent and major mutational target in chemically induced mouse lymphoma. The regions of the gene that are frequently mutated are the heterodimerization domain and the N-terminal ligand-binding region, important for protein stability, and the polypeptide rich in proline, glutamate, serine and threonine (PEST) domains, which is critical for protein degradation. Another gene, CDC4, is also involved in Notch1 degradation and shows frequent mutations. Mutations in the heterodimerization and the ligand-binding regions may cause ligand-independent signaling, whereas mutations preventing protein degradation result in accumulation of intracellular Notch1. We analyzed 103 chemical-induced mouse lymphomas for mutations in the Notch1 gene using single strand conformation analysis (SSCA) and DNA sequencing. Genetic alterations resulting in premature truncation of Notch1 were identified in 28 tumors, whereas 8 revealed alterations in the heterodimerization and 16 harbored deletions in the ligand-binding region. Dideoxycytidine-induced lymphomas displayed the highest frequency of Notch1 mutations (49%), whereas in butadiene- and phenolphthalein-induced tumors showed lower frequencies (26 and 10%, respectively). In total, 26 novel and 3 previously reported mutations were detected. This report shows that Notch1 is a prevalent and major mutational target for 2',3'-dideoxycytidine and butadiene-induced lymphoma.

Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells

Notch signaling is involved in tumorigenesis, but its role in B-chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor-kappa B (NF-kappaB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the gamma-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-kappaB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.

NOTCH1 mutation can be an early, prenatal genetic event in T-ALL

NOTCH1 mutations are common in T-lineage acute lymphoblastic leukemia (T-ALL). Twin studies and retrospective screening of neonatal blood spots provide evidence that fusion genes and other chromosomal abnormalities associated with pediatric leukemias can originate prenatally. Whether this is also the case for NOTCH1 mutations is unknown. Eleven cases of T-ALL were screened for NOTCH1 mutations and 4 (36%) had mutations in either the heterodimerization (HD) or proline glutamic acid/serine/threonine (PEST) domains. Of these 4, 3 could be amplified by mutation-specific polymerase chain reaction primers. In one of these 3, with the highest sensitivity, NOTCH1 mutation was detected in neonatal blood spots. In this patient, the blood spot was negative for SIL-TAL1 fusion, present concomitant with NOTCH1 mutation, in the diagnostic sample. We conclude that NOTCH1 can be an early or initiating event in T-ALL arising prenatally, to be complemented by a postnatal SIL-TAL1 fusion.

Detection of NOTCH1 mutations in adult T-cell leukemia/lymphoma and peripheral T-cell lymphoma

We analyzed NOTCH1 gene mutation in 53 adults with mature T-cell leukemia/lymphoma: 21 patients with adult T-cell leukemia (ATL), 25 with T-cell non-Hodgkin's lymphoma (T-NHL), and 7 with T-cell prolymphocytic leukemia. We detected a nonsense mutation, C7249T (resulting in Q2417X, where X is a termination codon) in the PEST domain of NOTCH1 in an ATL patient and detected a 3-bp deletion (positions 7234-7236) that resulted in deletion of a proline codon at codon 2412 in the PEST domain of NOTCH1 in a patient with a T-NHL, peripheral T-cell lymphoma-unspecified (PTCL-u). We also analyzed the expression of NOTCH1 target genes (HES1, CCND1, and MYC), all of which were expressed in the sample of the PTCL-u patient with the NOTCH1 mutation, but found only MYC to be expressed in the sample from the ATL patient. These findings suggest that nonsense mutation in the PEST domain in the ATL case was associated with NOTCH1 signaling through a pathway different from that for T-cell acute lymphoblastic leukemia (T-ALL). Although NOTCH1 mutation occurs infrequently in mature T-cell leukemia/lymphoma, NOTCH1 may be involved in leukemogenesis associated with various forms of T-cell leukemia/lymphoma rather than only with T-ALL.

Notch signaling in development and cancer

Notch is an evolutionarily conserved local cell signaling mechanism that participates in a variety of cellular processes: cell fate specification, differentiation, proliferation, apoptosis, adhesion, epithelial-mesenchymal transition, migration, and angiogenesis. These processes can be subverted in Notch-mediated pathological situations. In the first part of this review, we will discuss the role of Notch in vertebrate central nervous system development, somitogenesis, cardiovascular and endocrine development, with attention to the mechanisms by which Notch regulates cell fate specification and patterning in these tissues. In the second part, we will review the molecular aspects of Notch-mediated neoplasias, where Notch can act as an oncogene or as a tumor suppressor. From all these studies, it becomes evident that the outcome of Notch signaling is strictly context-dependent and differences in the strength, timing, cell type, and context of the signal may affect the final outcome. It is essential to understand how Notch integrates inputs from other signaling pathways and how specificity is achieved, because this knowledge may be relevant for future therapeutic applications.

NOTCH1-induced T-cell leukemia in transgenic zebrafish

Activating mutations in the NOTCH1 gene have been found in about 60% of patients with T-cell acute lymphoblastic leukemia (T-ALL). In order to study the molecular mechanisms by which altered Notch signaling induces leukemia, a zebrafish model of human NOTCH1-induced T-cell leukemia was generated. Seven of sixteen mosaic fish developed a T-cell lymphoproliferative disease at about 5 months. These neoplastic cells extensively invaded tissues throughout the fish and caused an aggressive and lethal leukemia when transplanted into irradiated recipient fish. However, stable transgenic fish exhibited a longer latency for leukemia onset. When the stable transgenic line was crossed with another line overexpressing the zebrafish bcl2 gene, the leukemia onset was dramatically accelerated, indicating synergy between the Notch pathway and the bcl2-mediated antiapoptotic pathway. Reverse transcription-polymerase chain reaction analysis showed that Notch target genes such as her6 and her9 were highly expressed in NOTCH1-induced leukemias. The ability of this model to detect a strong interaction between NOTCH1 and bcl2 suggests that genetic modifier screens have a high likelihood of revealing other genes that can cooperate with NOTCH1 to induce T-ALL.

NOTCH1 mutations in T-cell acute lymphoblastic leukemia: prognostic significance and implication in multifactorial leukemogenesis

PURPOSE

NOTCH signaling pathway is essential in T-cell development and NOTCH1 mutations are frequently present in T-cell acute lymphoblastic leukemia (T-ALL). To gain insight into its clinical significance, NOTCH1 mutation was investigated in 77 patients with T-ALL.

EXPERIMENTAL DESIGN

Detection of NOTCH1 mutation was done using reverse transcription-PCR amplification and direct sequencing, and thereby compared according to the clinical/biological data of the patients.

RESULTS

Thirty-two mutations were identified in 29 patients (with dual mutations in 3 cases), involving not only the heterodimerization and proline/glutamic acid/serine/threonine domains as previously reported but also the transcription activation and ankyrin repeat domains revealed for the first time. These mutations were significantly associated with elevated WBC count at diagnosis and independently linked to short survival time. Interestingly, the statistically significant difference of survival according to NOTCH1 mutations was only observed in adult patients (>18 years) but not in pediatric patients (< or = 18 years), possibly due to the relatively good overall response of childhood T-ALL to the current chemotherapy. NOTCH1 mutations could coexist with HOX11, HOX11L2, or SIL-TAL1 expression. The negative effect of NOTCH1 mutation on prognosis was potentiated by HOX11L2 but was attenuated by HOX11.

CONCLUSION

NOTCH1 mutation is an important prognostic marker in T-ALL and its predictive value could be even further increased if coevaluated with other T-cell-related regulatory genes. NOTCH pathway thus acts combinatorially with oncogenic transcriptional factors on T-ALL pathogenesis.

Establishment of a novel B-cell lymphoma cell line with suppressed growth by gamma-secretase inhibitors

A novel lymphoma cell line, designated TMD8 was established from cells of a patient with diffuse large B-cell lymphoma. TMD8 cells expressed HES1 mRNA, suggesting constitutive activation of Notch signaling. TMD8 cells expressed normal-sized Notch1 protein, and showed no mutations in the NOTCH1 gene. Cell growth was suppressed by gamma-secretase inhibitors (GSI). It was reported that GSI suppressed growth of T-cell acute lymphoblastic leukemia (T-ALL) cell lines, which frequently had NOTCH1 mutations. In addition to T-ALL, TMD8 is another unique cell line sensitive to GSI, and is useful to study effects of GSI in molecular targeting therapy.

Notch and Wnt signaling in T-lymphocyte development and acute lymphoblastic leukemia

Many acute lymphoblastic leukemias can be considered as malignant counterparts of cells in the various stages of normal lymphoid development in bone marrow and thymus. T-cell development in the thymus is an ordered and tightly controlled process. Two evolutionary conserved signaling pathways, which were first discovered in Drosophila, control the earliest steps of T-cell development. These are the Notch and Wnt-signaling routes, which both are deregulated in several types of leukemias. In this review we discuss both pathways, with respect to their signaling mechanisms, functions during T-cell development and their roles in development of leukemias, especially T-cell acute lymphoblastic leukemia.

A new recurrent 9q34 duplication in pediatric T-cell acute lymphoblastic leukemia

Over the last decade, genetic characterization of T-cell acute lymphoblastic leukemia (T-ALL) has led to the identification of a variety of chromosomal abnormalities. In this study, we used array-comparative genome hybridization (array-CGH) and identified a novel recurrent 9q34 amplification in 33% (12/36) of pediatric T-ALL samples, which is therefore one of the most frequent cytogenetic abnormalities observed in T-ALL thus far. The exact size of the amplified region differed among patients, but the critical region encloses approximately 4 Mb and includes NOTCH1. The 9q34 amplification may lead to elevated expression of various genes, and MRLP41, SSNA1 and PHPT1 were found significantly expressed at higher levels. Fluorescence in situ hybridization (FISH) analysis revealed that this 9q34 amplification was in fact a 9q34 duplication on one chromosome and could be identified in 17-39 percent of leukemic cells at diagnosis. Although this leukemic subclone did not predict for poor outcome, leukemic cells carrying this duplication were still present at relapse, indicating that these cells survived chemotherapeutic treatment. Episomal NUP214-ABL1 amplification and activating mutations in NOTCH1, two other recently identified 9q34 abnormalities in T-ALL, were also detected in our patient cohort. We showed that both of these genetic abnormalities occur independently from this newly identified 9q34 duplication.

Recent insights into the role of Notch signaling in tumorigenesis

Members of the Notch family of transmembrane receptors play an important role in cell fate determination. Over the past decade, a role for Notch in the pathogenesis of hematologic and solid malignancies has become apparent. Numerous cellular functions and microenvironmental cues associated with tumorigenesis are modulated by Notch signaling, including proliferation, apoptosis, adhesion, epithelial-to-mesenchymal transition, and angiogenesis. It is becoming increasingly evident that Notch signaling can be both oncogenic and tumor suppressive. This review highlights recent findings regarding the molecular and functional aspects of Notch-mediated neoplastic transformation. In addition, cellular mechanisms that potentially explain the complex role of Notch in tumorigenesis are discussed.