TGF-β inhibits growth and induces apoptosis in leukemic B cell precursors

IntroductionFMS-like tyrosine kinase-3 (FLT3) has been shown to be mutated in about one-third of patients with acute myeloid leukemia (AML), representing one of the most frequently occurring mutations in this disease. 1,2 Until now, two distinct clusters of activating mutations are known: FLT3-internal tandem duplications (FLT3-ITDs) in the juxtamembrane (JM) domain in 20% to 25% of patients, and point mutations (PMs) in the tyrosine-kinase domain (FLT3-TKD) in 7% to 10% of patients. [3][4][5][6][7][8][9] Recently, the crystal structure of the autoinhibited form of FLT3 was resolved. 10 The structure conforms to the prototypical conformation common to other inactive kinases that have a "closed" activation loop, but the remarkable feature is the complete JM domain serving as a critical autoinhibitory loop and interacting with all key features of FLT3. This domain can be divided into three distinct parts: the JM binding motif (JM-B), JM switch motif (JM-S), and the zipper or linker peptide segment (JM-Z). According to that model, the JM-B region is nearly buried in the FLT3 structure. It serves as an autoinhibitory domain, which in an inactive state prevents the N lobe from rotating toward the C lobe of the tyrosine kinase domain (TKD) to generate the activated kinase fold.The cytoplasmatic juxtamembrane domain is highly conserved between different members of the class III receptor tyrosine kinase (RTK) family. A variety of tumors in animals and humans have been described that harbor activating mutations in the JM domain. [11][12][13][14] The most frequently occurring activating mutations in AML, FLT3-ITDs, occur primarily in the JM-Z domain. They represent a heterogenous group of mutations, where a fragment of the JM domain, varying in length from 2 to 204 nucleotides (nt), is duplicated and inserted in a direct head-to-tail orientation always maintaining the reading frame.Recently, we discovered a novel missense point mutation in the JM domain of FLT3 in the AML cell lines Mono-Mac (MM)-1 and MM-6, changing valine with alanine at position 592. 15 By performing a LightCycler (Roche, Mannheim, Germany) mutational screening of FLT3 in 785 AML patient samples, we were able to identify two other point mutations: F594L in two AML patients and Y591C in 1 AML patient. In addition, Stirewalt et al 16 found additional point mutations in the JM domain of FLT3 (V579A and F590GY591D) in AML patients by using single-stranded conformational polymorphism analyses (polymerase chain reaction [PCR]/SSCPs).Here, we have studied the functional significance of this new class of activating mutations in patients with AML: PMs that cluster in a 16-aa stretch of the JM domain (FLT3-JM-PMs).We could clearly demonstrate that FLT3 receptors harboring one of these JM point mutations, when expressed in Ba/F3 cells, Supported by a grant from the Deutsche Forschungsgemeinschaft (DFG Sp556/3-1) and the Deutsche Krebshilfe (10-1997-Sp2).Reprints: Karsten Spiekermann, Department of Medicine III, University Hospital Grosshadern, CCG "Leukemia," GSF...

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“…Determination of the DNA content of cell nuclei was performed by propidium iodide (PI) staining as described previously. 17 …”

Section: Apoptosis Analysismentioning

confidence: 99%

Point mutations in the juxtamembrane domain of FLT3 define a new class of activating mutations in AML

Reindl¹,

Bagrintseva²,

Vempati³

et al. 2006

Blood

109

113

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“…However, the leukemic B cell precursors were sensitive to exogenous TGF-␤; in vitro administration of TGF-␤ significantly reduced cell viability and enhanced apoptotic cell death of leukemic B cell precursors from ALL patients. 80 This sensitivity to TGF-␤ may be useful in the development of new therapeutic approaches, based on the hypothesis that administration of TGF-␤ to BCP-ALL patients may inhibit the uncontrolled proliferation of leukemic cells.…”

Section: Effects Of Tgf-␤ On Malignancies Of the Immune System Ie Leumentioning

confidence: 99%

Effects of TGF-β on the immune system: implications for cancer immunotherapy

1999

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Transforming growth factor-␤ (TGF-␤) is a potent regulator of numerous processes including hematopoiesis, cell proliferation, differentiation and activation. TGF-␤ has pleiotropic and profound effects on the immune system and on hematologic malignancies, ie leukemia. It is the most potent immunosuppressor described to date. Evidence exists that the immunosuppressive potential of TGF-␤ is an important promoter of malignant cell growth. This is partly caused by TGF-␤-induced interference with the generation of tumor-specific cytotoxic T lymphocytes, but also by TGF-␤-induced promotion of angiogenesis and tumor stroma formation. Until now, significant clinical responses have not been achieved with the current cancer immunotherapeutic approaches. One of the possible explanations for this failure is immunosuppression induced by tumor-derived TGF-␤. Here, several strategies to counteract the immunosuppressive effects of TGF-␤ and the current limitations of these strategies will be discussed. Knowledge of the mechanisms by which TGF-␤ interferes with the development of an anti-tumor response and of the strategies to counteract these immunosuppressive activities is crucial to improve the current cancer immunotherapeutic approaches.

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“…Although TGF-␤1 has classically been shown to arrest growth at the G 1 phase of the cell cycle (3), it has more recently been demonstrated to play an important role as an inducer of apoptosis in several cell types, including primary hepatocytes (4), hepatoma cell lines (5,6), prostate epithelial cancer cells (7), ovarian carcinoma (8), and leukemic cells (9). Although the down-regulation of Bcl-2 (8,10), induction of c-fos and c-jun genes (8), and the involvement of caspase family protease(s) (11,12) have each been postulated to play a role in TGF-␤1-mediated apoptosis, the signaling pathways of TGF-␤1-induced apoptosis are still largely unknown.…”

Section: Tgf-␤1mentioning

confidence: 99%

Cdc2 and Cdk2 Kinase Activated by Transforming Growth Factor-β1 Trigger Apoptosis through the Phosphorylation of Retinoblastoma Protein in FaO Hepatoma Cells

Choi¹,

Eom²,

Kang³

et al. 1999

Journal of Biological Chemistry

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TGF-β inhibits growth and induces apoptosis in leukemic B cell precursors

Abstract: The uncontrolled proliferation of malignant lymphoblasts is theIn contrast to the fast growing knowledge about the acti- pressing signals. One major candidate for growth arrest of nor-

Cited by 37 publications

References 7 publications

Point mutations in the juxtamembrane domain of FLT3 define a new class of activating mutations in AML

Point mutations in the juxtamembrane domain of FLT3 define a new class of activating mutations in AML

Effects of TGF-β on the immune system: implications for cancer immunotherapy

Cdc2 and Cdk2 Kinase Activated by Transforming Growth Factor-β1 Trigger Apoptosis through the Phosphorylation of Retinoblastoma Protein in FaO Hepatoma Cells

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