TLS-ERG Leukemia Fusion Protein Deregulates Cyclin-Dependent Kinase 1 and Blocks Terminal Differentiation of Myeloid Progenitor Cells

Abstract

TLS-ERG fusion protein is derived from the t(16;21) translocation found in human myeloid leukemia. Here, we show that retroviral transduction of TLS-ERG confers a growth advantage to L-G myeloid progenitor cells and blocks terminal differentiation. We found that the level of cyclin-dependent kinase 1 (Cdk1) protein was significantly decreased in controls but unchanged in TLS-ERG -expressing cells after granulocyte colony-stimulating factor treatment or interleukin-3 withdrawal. Injection of TLS-ERG -expressing L-G cells induced rapid development of a leukemia-like disease in syngeneic mice. Through site-directed mutagenesis, we showed that transformation and deregulation of Cdk1 by TLS-ERG require an intact ets DNA-binding domain within the fusion protein. Interestingly, treatment of TLS-ERG -expressing L-G cells with 5-aza-2 ¶-deoxycytidine (Decitabine) or trichostatin A resulted in down-regulation of Cdk1 and induction of terminal differentiation. To investigate whether Cdk1 deregulation is indeed responsible for transformation by TLS-ERG, we constructed lentiviral vectors for delivery of Cdk1 mutants and small interfering RNA (siRNA). Both dominant-negative inhibition and siRNA knockdown of Cdk1 were able to restore the ability of TLS-ERG -expressing L-G cells to undergo terminal differentiation. In addition, siRNA knockdown of Cdk1 in YNH-1 cells derived from a t(16;21) acute myelogenous leukemia patient also resulted in terminal differentiation. As restoration of terminal myeloid differentiation to TLS-ERG cells is dependent on cell cycle arrest, our findings suggest an important role for Cdk1 in cellular transformation and may be useful in the search for new treatments of TLS-ERG -associated myeloid leukemia. (Mol Cancer Res 2008;6(5):862 -72)

Targeting CDK1 promotes FLT3-activated acute myeloid leukemia differentiation through C/EBPα

“…While we believe that much of the activity of these inhibitors is through their effects on C/EBPα phosphorylation, our experiments do not rule out effects on other pathways as well. We also found that activation of the CDK1 pathway by FLT3ITD involves upregulation of cyclin B1 rather than upregulation of CDK1 itself (49). While these data suggest that cyclin B1 is involved in the activation of CDK1, we cannot rule out that other CDK1 regulators, such as Myt1 and cdc25c, could also be involved (41).…”

“…Higher expression levels of CDK1 were detected in leukemic cells with del(5q) (48). Also, a recent report described upregulation of CDK1 in leukemia with translocation liposarcoma/ETS-related gene (TLS-ERG) and attributed increased expression of CDK1 to the differentiation block (49). Similarly, we found that in AML with constitutively active FLT3 receptor, CDK1 can contribute to the maturation block by inhibiting function of the transcription factor C/EBPα, which is required for granulopoietic development.…”

Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection

“…pEGFP-UL27, pEGFP-UL27R233S, and pEGFP-UL27aa1-415 were generously provided by Morgan Hakki and Sunwen Chou (Oregon Health Sciences University) (29). The pLL3.7-CDK1AF-FLAG and pLL3.7 vectors were generously provided by Liu Yang (University of Washington) (51). Disruption of p21…”

“…For this experiment, U373 cells were serum starved in 0.5% serum for 24 h and then maintained in a low concentration of serum and transfected with a control vector or with a vector expressing a constitutively active CDK1 with a FLAG epitope (CDK1AF) (51). CDK1AF contains substitutions at threonine 14 and tyrosine 15, preventing inactivation.…”

Promotion and maintenance of leukemia by ERG

“…2,3 The FUS/TLS-ERG fusion protein is able to transform NIH3T3 cells and to block G-CSFinduced differentiation of the L-G mouse myeloid cell line, depending on the functions of the FUS/TLS part of the fusion. 2,6 Notwithstanding these activities, including its ability to enhance cell proliferation, the presence of the FUS/TLS-ERG gene itself is insufficient to initiate leukemia but requires additional cooperating genetic events. 7,8 Interestingly, the EWS-ERG fusion protein, in which another RNA-binding protein, EWS, is fused to the ETS domain of ERG, is able to induce leukemia when ectopically expressed in the T-cell compartment in mice, 9 although it is noteworthy that the fusion is associated with sarcomas, and not leukemia, in humans.…”