The fifth epidermal growth factor-like region of thrombomodulin exerts cytoprotective function and prevents SOS in a murine model.

The present study found that the fifth epidermal growth factor-like domain of thrombomodulin (TME5) possesses the cytoprotective function in association with an increase in levels of anti-apoptotic myeloid cell leukemia-1 protein in an activated protein C-independent manner in human umbilical vein endothelial cells (HUVECs). Importantly, TME5 counteracted calcineurin inhibitor-induced vascular permeability and successfully prevented monocrotaline-induced sinusoidal obstruction syndrome (SOS) in a murine model. Taken together, TME5 may be useful for preventing or treating lethal complications that develop after hematopoietic stem cell transplantation such as SOS and thrombotic microangiopathy in which endothelial cell damage has a role.

Thrombomodulin blocks calcineurin inhibitor-induced vascular permeability via inhibition of Src/VE-cadherin axis.

Recombinant human soluble thrombomodulin (rTM) counteracted capillary leakage and alleviated edema in individuals with sinusoidal obstruction syndrome and engraftment syndrome after hematopoietic stem cell transplantation. We previously showed that rTM increased levels of antiapoptotic protein Mcl-1 and protected endothelial cells from calcineurin inhibitor cyclosporine A (CsA)-induced apoptosis. However, the molecular mechanisms by which rTM enhances barrier function in vascular endothelial cells remain unknown. Here we show that exposure of vascular endothelial EA.hy926 cells to CsA induced phosphorylation of Src/vascular endothelial cadherin (VE-cadherin) and translocation of VE-cadherin from cell surface to cytoplasm, resulting in an increase in vascular permeability. In addition, CsA increased production of inflammatory cytokines, including interleukin (IL)-1ß and IL-6, associated with an increase in nuclear levels of nuclear factor-κB (NF-κB) which also enhanced vascular permeability. Importantly, the fourth and fifth regions of epidermal growth factor-like domain of TM (TME45) attenuated CsA-induced p-Src/VE-cadherin and vascular permeability in parallel with a decrease in nuclear levels of NF-κB and cytokine production in EA.hy926 cells. In conclusion, TM, especially TME45, maintains vascular integrity, at least in part, via Src signaling.

Comprehensive mutational analysis of primary and relapse acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a subtype of myeloid leukemia characterized by differentiation block at the promyelocyte stage. Besides the presence of chromosomal rearrangement t(15;17), leading to the formation of PML-RARA (promyelocytic leukemia-retinoic acid receptor alpha) fusion, other genetic alterations have also been implicated in APL. Here, we performed comprehensive mutational analysis of primary and relapse APL to identify somatic alterations, which cooperate with PML-RARA in the pathogenesis of APL. We explored the mutational landscape using whole-exome (n=12) and subsequent targeted sequencing of 398 genes in 153 primary and 69 relapse APL. Both primary and relapse APL harbored an average of eight non-silent somatic mutations per exome. We observed recurrent alterations of FLT3, WT1, NRAS and KRAS in the newly diagnosed APL, whereas mutations in other genes commonly mutated in myeloid leukemia were rarely detected. The molecular signature of APL relapse was characterized by emergence of frequent mutations in PML and RARA genes. Our sequencing data also demonstrates incidence of loss-of-function mutations in previously unidentified genes, ARID1B and ARID1A, both of which encode for key components of the SWI/SNF complex. We show that knockdown of ARID1B in APL cell line, NB4, results in large-scale activation of gene expression and reduced in vitro differentiation potential.

The novel function of CD82 and its impact on BCL2L12 via AKT/STAT5 signal pathway in acute myelogenous leukemia cells.

The aim of this study was to explore the biological functions of a tetraspanin family protein CD82 expressed aberrantly in chemotherapy-resistant CD34(+)/CD38(-) acute myelogenous leukemia (AML) cells. Microarray analysis of patient-isolated CD34(+)/CD38(-) AML cells revealed that the levels of anti-apoptotic protein BCL2L12 were downregulated after CD82 depletion by specific short hairpin RNA (shRNA). Western blot analysis indicated that BCL2L12 was aberrantly expressed in patient-isolated AML cells and AML cell lines. Furthermore, CD82 blockade by a specific antibody downregulated BCL2L12 in parallel with dephosphorylation of signal transducer and activator of transcription 5 (STAT5) and AKT, whereas pharmacological inhibition of STAT5 and AKT activation decreased BCL2L12 expression in leukemia cells. In addition, shRNA-mediated downregulation of BCL2L12 increased the levels of cleaved caspase-3 and suppressed proliferation of leukemia cells, impairing their engraftment in immunodeficient mice. Taken together, our results indicate that CD82 regulated BCL2L12 expression via STAT5A and AKT signaling and stimulated proliferation and engrafting of leukemia cells, suggesting that CD82 and BCL2L12 may be promising therapeutic targets in AML.

Thrombomodulin alleviates murine GVHD in association with an increase in the proportion of regulatory T cells in the spleen.

Recombinant human soluble thrombomodulin (rTM), a potent anticoagulant, has been used for the treatment of disseminated intravascular coagulation in Japan since 2008. Interestingly, rTM possesses anti-inflammatory and cytoprotective functions. This study examined whether rTM alleviates GVHD in a murine hematopoietic SCT (HSCT) model. Use of rTM significantly improved the survival of mice on day 28 of transplantation (survival rate 70% in rTM - treated mice vs 35% in control, P<0.05) in association with a significant decrease in plasma levels of IL-6, IFN-γ and high-mobility group B1 DNA-binding protein on day 7 of HSCT. Intriguingly, the proportion of regulatory T cells in the spleen was significantly increased in rTM-treated mice on day 7 of transplantation compared with control diluent-treated mice. In addition, elevated plasma levels of TM and fibrin/fibrinogen degradation product were noted in HSCT-recipient mice, suggesting coagulopathy caused by endothelial cell damage in this GVHD model. The use of rTM potently decreased these levels. Importantly, rTM did not hamper the anti-GVL and engraftment of hematopoietic cells. Taken together, the use of rTM may prevent GVHD and serve as a potential therapeutic strategy to improve clinical outcomes in individuals who receive HSCT.

Imatinib causes epigenetic alterations of PTEN gene via upregulation of DNA methyltransferases and polycomb group proteins.

We have recently reported the possible imatinib-resistant mechanism; long-term exposure of leukemia cells to imatinib downregulated levels of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) via hypermethylation of its promoter region (Leukemia 2010; 24: 1631). The present study explored the molecular mechanisms by which imatinib caused methylation on the promoter region of this tumor suppressor gene in leukemia cells. Real-time reverse transcription PCR found that long-term exposure of chronic eosinophilic leukemia EOL-1 cells expressing FIP1L1/platelet-derived growth factor receptor-α to imatinib induced expression of DNA methyltransferase 3A (DNMT3A) and histone-methyltransferase enhancer of zeste homolog 2 (EZH2), a family of polycomb group, thereby increasing methylation of the gene. Immunoprecipitation assay found the increased complex formation of DNMT3A and EZH2 proteins in these cells. Moreover, chromatin immunoprecipitation assay showed that amounts of both DNMT3A and EZH2 proteins bound around the promoter region of PTEN gene were increased in EOL-1 cells after exposure to imatinib. Furthermore, we found that levels of DNMT3A and EZH2 were strikingly increased in leukemia cells isolated from individuals with chronic myelogenous leukemia (n=1) and Philadelphia chromosome-positive acute lymphoblastic leukemia (n=2), who relapsed after treatment with imatinib compared with those isolated at their initial presentation. Taken together, imatinib could cause drug-resistance via recruitment of polycomb gene complex to the promoter region of the PTEN and downregulation of this gene's transcripts in leukemia patients.

Long-term exposure of leukemia cells to multi-targeted tyrosine kinase inhibitor induces activations of AKT, ERK and STAT5 signaling via epigenetic silencing of the PTEN gene.

Imatinib induces complete molecular response in patients with chronic myeloid leukemia (CML) and chronic eosinophilic leukemia (CEL). However, development of resistance to imatinib has emerged as an important clinical problem for molecular-targeted therapy in CML and CEL. In this study, we have established the imatinib-resistant CEL EOL-1 sub-lines (designated as EOL-1R) by culturing cells with increasing concentrations of imatinib for 6 months. Interestingly, EOL-1R cells showed epigenetic silencing of the phosphatase and tensin homolog deleted on chromosome ten (PTEN) gene. Exposure of EOL-1R cells to imatinib failed to dephosphorylate AKT, ERK and STAT5, although PDGFRalpha was effectively inactivated. The forced expression of PTEN negatively regulated these signal pathways and sensitized EOL-1R cells to imatinib. Notably, hypermethylation of the promoter region of the PTEN gene in association with the downregulation of this gene's transcripts was identified in imatinib-resistant leukemia cells isolated from individuals with CEL, CML and Philadelphia-positive acute lymphoblastic leukemia. In addition, anti-epigenetic agents restored PTEN expression, resulting in the sensitization of EOL-1R cells to imatinib. Taken together, epigenetic silence of PTEN is one of the mechanisms that cause drug resistance in individuals with leukemia after exposure to imatinib. Anti-epigenetic agents may be useful for overcoming drug resistance in such a case.

A novel treatment strategy targeting polo-like kinase 1 in hematological malignancies.

Polo-like kinase1 (PLK1) belongs to the family of serine/threonine kinases and plays an important role in centrosome maturation, bipolar spindle formation, and cytokinesis during mitosis. We found in this study that PLK1 was aberrantly highly expressed in a variety of human leukemia cell lines (n=20), as well as, freshly isolated leukemia cells from individuals with acute myelogenous leukemia (n=50) and acute lymphoblastic leukemia (n=15) compared with bone marrow mononuclear cells from healthy volunteers (n=13) (acute myelogenous leukemia, P=0.016; acute lymphoblastic leukemia, P=0.008), as measured by real-time RT-PCR. Downregulation of PLK1 by a small interfering RNA in NB4 acute myelogenous leukemia cells inhibited their proliferation. GW843682X is a novel selective PLK1 inhibitor. The compound-induced growth inhibition, caused accumulation of cells in the G2/M phase of the cell cycle and mediated apoptosis of human leukemia cells. Pre-treatment of cells with the caspase inhibitor Z-VAD-FMK attenuated the action of GW843682X in leukemia cells, indicating the involvement of the caspase pathway in the PLK1 inhibitor-mediated apoptosis. Furthermore, we found that the PLK1 inhibitor synergistically potentiated the growth inhibition and apoptosis of leukemia cells when combined with tubulin-depolymerizing agent vincristine. Taken together, targeting PLK1 may be a promising treatment strategy for individuals with leukemia.

Blockade of mTOR signaling potentiates the ability of histone deacetylase inhibitor to induce growth arrest and differentiation of acute myelogenous leukemia cells.

This study found that MS-275, a novel synthetic benzamide histone deacetylase inhibitor (HDACI), blocked Akt/mammalian target of rapamycin (mTOR) signaling in acute myelogenous leukemia (AML) HL60 and acute promyelocytic leukemia (APL) NB4 cells, as assessed by decreased levels of the phosphorylated (p)-Akt, p-p70 ribosomal S6 kinase (p70S6K) and p-S6K by western blot analysis. Interestingly, further inactivation of mTOR by rapamycin analog RAD001 (everolimus) significantly enhanced MS-275-mediated growth inhibition and apoptosis of these cells in parallel with enhanced upregulation of p27(kip1) and downregulation of c-Myc. In addition, RAD001 potentiated the ability of MS-275 to induce differentiation of HL60 and NB4 cells, as measured by the expression of CD11b cell surface antigens, as well as reduction of nitroblue tetrazolium. Importantly, RAD001 potentiated the ability of MS-275 to induce the expression of the myeloid differentiation-related transcription factor, CCAAT enhancer-binding protein-epsilon, in these cells in association with enhanced acetylation of histone H3 on its promoter. Furthermore, RAD001 (5 mg/kg) significantly enhanced the effects of MS-275 (10 mg/kg) to inhibit proliferation of HL60 tumor xenografts in nude mice without adverse effects. Taken together, concomitant administration of an HDACI and an mTOR inhibitor may be a promising treatment strategy for the individuals with a subset of human leukemia.