B-cell chronic lymphocytic leukemia (B-CLL) is the most common human leukemia in the world. Deregulation of the TCL1 oncogene is a causal event in the pathogenesis of the aggressive form of this disease as was verified by using animal models. To study the mechanism of Tcl1 regulation in CLL, we carried out microRNA expression profiling of three types of CLL: indolent CLL, aggressive CLL, and aggressive CLL showing 11q deletion. We identified distinct microRNA signatures corresponding to each group of CLL. We further determined that Tcl1 expression is regulated by miR-29 and miR-181, two microRNAs differentially expressed in CLL. Expression levels of miR-29 and miR-181 generally inversely correlated with Tcl1 expression in the CLL samples we examined. Our results suggest that Tcl1 expression in CLL is, at least in part, regulated by miR-29 and miR-181 and that these microRNAs may be candidates for therapeutic agents in

B-cell chronic lymphocytic leukemia (B-CLL), the most common leukemia in the Western world, occurs in two forms, aggressive (showing for the most part high ZAP-70 expression and unmutated IgH V H ) and indolent (showing low ZAP-70 expression and mutated IgH V H ). We found that miR-29a is up-regulated in indolent human B-CLL as compared with aggressive B-CLL and normal CD19 + B cells. To study the role of miR-29 in B-CLL, we generated Eμ-miR-29 transgenic mice overexpressing miR-29 in mouse B cells. Flow cytometric analysis revealed a markedly expanded CD5 + population in the spleen of these mice starting at 2 mo of age, with 85% (34/40) of miR-29 transgenic mice exhibiting expanded CD5 + B-cell populations, a characteristic of B-CLL. On average, 50% of B cells in these transgenic mice were CD5 positive. At 2 y of age the mice showed significantly enlarged spleens and an increase in the CD5 + B-cell population to ∼100%. Of 20 Eμ-miR-29 transgenic mice followed to 24-26 mo of age, 4 (20%) developed frank leukemia and died of the disease. These results suggest that dysregulation of miR-29 can contribute to the pathogenesis of indolent B-CLL.mouse models | microRNA C hronic lymphocytic leukemia (CLL) is the most common human leukemia, accounting for ∼30% of all cases (1), with ∼10,000 new cases observed each year in the United States. Characteristically, CLL is a disease of elderly people, with the incidence increasing linearly with each decade above age 40 y (1, 2). It is known that this disease is characterized by the clonal expansion of CD5 + B cells (2).MicroRNAs, representing between 1% and 3% of all eukaryotic genes, are a class of endogenous noncoding RNAs, 19-25 nt in size, which regulate gene expression at the transcriptional or translational level (3). Approximately half of human microRNAs are located at fragile sites and genomic regions involved in alterations in cancers (4), and alteration of microRNA expression profiles occurs in most cancers, suggesting that individual microRNAs could function as tumor suppressors or oncogenes (5).The 13q14 deletion is the most common CLL aberration and is detected by cytogenetic analysis in approximately half of the cases (6). Analysis of a deletion at 13q14.3 led to the discovery of two physically linked microRNAs, miR-15a and miR-16-1, as targets of these deletions (7). Consequently, miR-15a and miR-16-1 expression is reduced in the majority of CLL cases (7), and further studies indicated that miR-15a/miR-16-1 negatively regulate Bcl2 expression (8). These findings indicated that microRNAs play important roles in CLL and that down-regulation of miR-15/16 and subsequent Bcl2 up-regulation contribute to CLL pathogenesis (7). Because miR-15/16 was identified as a tumor suppressor in indolent CLL, the microRNA expression profile in CLL has been studied extensively, and a signature profile was reported describing 13 microRNAs that differentiate aggressive and indolent CLL (4).We and others observed that miRNA-29 expression is downregulated in aggressive CLL as compared ...

Programmed cell death 4 (Pdcd4) is a tumor suppressor protein that interacts with eukaryotic initiation factor 4A and inhibits protein synthesis. Pdcd4 also suppresses the transactivation of activator protein-1 (AP-1)-responsive promoters by c-Jun. The Akt (protein kinase B) serine/ threonine kinase is a key mediator of phosphoinositide 3-kinase pathway involved in the regulation of cell proliferation, survival, and growth.

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B-cell chronic lymphocytic leukemia (CLL) is the most common human leukemia. 13q14 deletions are most common chromosomal alterations in CLL. We previously reported that miR-15/16 is a target of 13q14 deletions and plays a tumor suppressor role by targeting BCL2. Because DLEU7 is located near miR-15/16 and is also positioned within a minimal deleted region, we investigated whether DLEU7 could also play a tumor suppressor role. Recent studies of transgenic mouse models demonstrated the importance of the nuclear factor-B (NF-B) pathway in CLL. To examine the possible role of DLEU7 in CLL, we investigated the effect of DLEU7 expression on NF-B and nuclear factor of activated T cells (NFAT) activity. We found that DLEU7 functions as a potent NF-B and NFAT inhibitor by physically interacting and inhibiting TACI and IntroductionChronic lymphocytic leukemia (CLL) lymphocytes have mature appearance and the B220 ϩ CD5 ϩ phenotype. 1,2 Several chromosomal aberrations occur frequently in CLL cases, including 13q deletions (ϳ 50%), 11q23 deletions (18%), trisomy 12 (12%), and 17p deletions (7%). 3 The 13q14 deletion is the most common B-CLL aberration and is seen by cytogenetics in approximately half of the cases. 3 13q14 is seen predominantly in the indolent form of CLL and is associated with low levels of ZAP70 expression and mutated variable region genes of immunoglobulins. 4 Analysis of an approximately 30-kb deletion at 13q14.3 and chromosomal breakpoint mapping of translocation t(2:13)(q32;q14) led to the discovery of 2 physically linked microRNAs, miR-15a and miR-16-1, as targets of these deletions. 5 Furthermore, both, miR-15a and miR-16-1 were reduced in expression in most CLL cases, 5 and further studies indicated that miR-15a/miR-16-1 negatively regulate Bcl2 expression. 6 These findings indicated that down-regulation of miR-15/16 and subsequent Bcl2 up-regulation contribute to CLL pathogenesis. 5 A high-resolution map of 13q14 deletions using 171 CLL samples was recently reported. 7 These data indicated that the minimal deleted region, in addition to miR-15/16, also contains the DLEU7 gene ( Figure 1A). 7 DLEU7 was previously identified as a candidate tumor suppressor gene at 13q14. 8 It encodes a 221-amino acid protein with no homology to known proteins. No mutations in DLEU7 were found in 45 CLL samples, although the DLEU7 promoter was methylated in 61% of CLL. 8 Since DLEU7 is the only protein-coding gene located within the minimal deleted region at 13q14, we investigated whether DLEU7 can function as a tumor suppressor. Methods CLL samples and real-time PCR experimentsA total of 25 CLL samples were obtained after informed consent from patients diagnosed with CLL from the CLL Research Consortium. Research was performed with the approval of the Institutional Review Board of Ohio State University. Briefly, blood was obtained from patients with CLL, and lymphocytes were isolated through Ficoll/Hypaque gradient centrifugation (Amersham Biosciences) and processed for RNA extraction by using the standard TRIzol met...

The T-cell leukemia/lymphoma 1 (TCL1) oncogene is a target of chromosomal translocations and inversions at 14q31.2, and its rearrangement in T cells causes T-cell prolymphocytic leukemias. TCL1 dysregulation in B cells is responsible for the development of an aggressive form of chronic lymphocytic leukemia (CLL), the most common human leukemia. We have IntroductionThe T-cell leukemia/lymphoma 1 (TCL1) gene maps to chromosome 14q31.2 and is involved in chromosomal translocations and inversions in T-cell prolymphocytic leukemia (T-PLL). It is also dysregulated in several B-cell malignancies, including B-cell chronic lymphocytic leukemia (B-CLL) and in germ cell tumors, such as seminoma and dysgerminoma. 1,2 Normally, Tcl1 protein is expressed in early embryos and fetal tissues, germ cells, and early T and B cells. [3][4][5] We previously showed that aggressive human CLLs overexpress Tcl1 6 and that transgenic mice expressing TCL1 in B cells developed an aggressive form of CLL. 7,8 These previous studies demonstrated that Tcl1 up-regulation is critical in the pathogenesis of the aggressive form of human CLL. Tcl1 is also known to be a coactivator of the Akt oncoprotein 9 and of the NF-B transcription pathway. 10 Despite efforts to clarify the molecular mechanisms of Tcl1 oncogenic function, the identification of specific pathways through which Tcl1 modulates oncogenic functions has been elusive. This was mainly because Tcl1 interacting proteins could not be identified by conventional methods aimed to isolate protein-protein complexes, with the exception of Akt, a protein unlikely to play a significant role in B-cell malignancies. 10,11 The ATM (ataxia-telangiectasia mutated) gene, located at chromosome 11q22.3, 12 is responsible for a rare disorder called ataxia-telangiectasia (AT), an autosomal recessive disease characterized by progressive cerebellar degeneration, variable immunodeficiency, genomic instability, and susceptibility to cancer, especially lymphoid malignancies. [12][13][14] ATM is thought to be a tumor suppressor gene because DNA double-strand breaks caused by ionizing radiation or chemicals result in rapid Atm autophosphorylation and activation, leading to checkpoint activation and phosphorylation of substrates that regulate cell-cycle progression, DNA repair, recombination, transcription, and cell death. 12,15 Atm is a Ser/Thr kinase responsible for the phosphorylation of many substrates, including p53, Nbs1, Chk2, H2A.X, Mdm2, 4E-BP1, and IB␣. IB␣ is an inhibitor of NF-B, a transcription factor involved in a variety of hematologic and solid tumor malignancies. 16 IB␣ 17-21 phosphorylation leads to its degradation followed by activation of NF-B. Atm has a carboxy-terminal sequence with significant homology to the catalytic domain of phosphatidylinositol-3-OH kinase (PI3K). 15 AKT is a downstream target of PI3K and interacts directly with Tcl1. 22 ATM biallelic loss in AT leads to chromosomal translocations and inversions at 14q31.2, resulting in Tcl1 overexpression in AT patients. Preleukemic and ...

Our data provide support for a link between I-131 thyroid dose and generation of carcinogenic gene fusions, the predominant mechanism of thyroid cancer associated with radiation exposure from the Chernobyl accident.

B-cell chronic lymphocytic leukemia (B-CLL) is the most common adult leukemia. Deregulation of the T-cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. We recently reported that levels of TCL1 expression in B-CLL are regulated by miR-29 and miR-181 that target 3′ UTR of TCL1. To determine whether treatment with microRNAs targeting TCL1 can inhibit B-CLL in mice, we generated TCL1 transgenic mice using a construct containing the 3′ and 5′ UTRs of TCL1 under B-cell-specific Eμ promoter (Eμ-TCL1FL). At the age of 16–20 months, these mice showed B-CLL-like disease. Immunophenotyping revealed accumulation of CD5 + CD23 + B220 + population in spleens and lymph nodes. Our results show that CD5 + CD23 + B-cell populations from Eμ-TCL1FL mice actively proliferate and show significantly increased levels of phospho-Akt. El-TCL1FL mice showed immunological abnormalities similar to human B-CLL, including hypoimmunoglobulinemia, abnormal levels of cytokines and impaired immune response. These findings revealed biochemical and immunological similarities between Tcl1-driven B-CLL in mice and human B-CLL.