Ju In Eom

Constitutive phosphorylation of Akt/PKB protein in acute myeloid leukemia: its significance as a prognostic variable.

Constitutive phosphorylation of Akt/PKB protein in acute myeloid leukemia: its significance as a prognostic variable

Protein kinase CK2α as an unfavorable prognostic marker and novel therapeutic target in acute myeloid leukemia

Introduction: Protein kinase CK2 is implicated in cellular proliferation and transformation. However, the clinical and biological significances of CK2 have not been elucidated in acute myeloid leukemia (AML). Experimental Design: We evaluated the biological significances of catalytic subunit of CK2 (CK2α) expression in leukemia cell lines and primary leukemic blasts obtained from AML patients. Results: In this study, the expression of CK2α was elevated in a substantial proportion of AML. In AML patients with normal karyotype, the disease-free survival and overall survival rates were significantly lower in the CK2α-high compared with the CK2α-low AML cases (P = 0.0252 and P = 0.0392, respectively). An induced overexpression of CK2α increased the levels of Ser473 phosphorylated (p)-Akt/protein kinase B (PKB), p-PDK1, pFKHR, p-BAD, Bcl-2, Bcl-xL, Mcl-1, and XIAP. Treatment of U937 cell line and primary AML blasts with selective CK2 inhibitor, tetrabromobenzotriazole or apigenin, reduced the levels of these molecules in a dose-dependent manner. CK2α small interfering RNA treatment also resulted in a down-regulation of p-Akt/PKB and Bcl-2 in U937 cells. Apigenin-induced cell death was preferentially observed in the CK2α-high leukemia cell lines, HL-60 and NB4, which was accompanied by cytoplasmic release of SMAC/DIABLO and proteolytic cleavage of procaspase-9, procaspase-3, procaspase-8, and poly(ADP)ribose polymerase. An induced overexpression of CK2α potentially enhanced the sensitivity of U937 cells to the apigenin-induced cell death. Apigenin-induced cell death was significantly higher in CK2α-high AML compared with CK2α-low AML (P < 0.0001) or normal bone marrow samples (P < 0.0001). Conclusion: These findings strongly suggest protein kinase CK2α as an unfavorable prognostic marker and novel therapeutic target in AML.

Cytoplasmic Mislocalization of p27Kip1 Protein Is Associated with Constitutive Phosphorylation of Akt or Protein Kinase B and Poor Prognosis in Acute Myelogenous Leukemia

Cyclin-dependent kinase inhibitor p27Kip1 functions at the nuclear level by binding to cyclin E/cyclin-dependent kinase-2. It was shown that Akt or protein kinase B (Akt/PKB)-dependent phosphorylation of p27Kip1 led to the cytoplasmic mislocalization of p27Kip1, suggesting the potential abrogation of its activity. Here, we evaluated the localization of p27Kip1 protein in leukemic blasts in relation to Akt/PKB phosphorylation and clinical outcomes in acute myelogenous leukemia (AML). Western blot analysis of the nuclear and cytoplasmic fractions revealed a heterogenous localization pattern of p27Kip1 in AML. Cytoplasmic mislocalization of p27Kip1 was significantly associated with the constitutive serine473 Akt/PKB phosphorylation in AML cells (P < 0.05). Transfection of U937 cells with an expression construct encoding the constitutively active form of Akt/PKB resulted in a remarkable increase in the levels of cytoplasmic p27Kip1. Whereas the transfection of U937 cells with a construct encoding dominant-negative Akt/PKB resulted in a recovery of nuclear localization of p27Kip1. Both the disease-free survival and overall survival are significantly shorter in AML cases with high cytoplasmic to nuclear ratio of p27Kip1 localization compared with the cases with low cytoplasmic to nuclear ratio (P = 0.0353, P = 0.0023, respectively). Multivariate analysis indicated that the cytoplasmic to nuclear ratio of p27Kip1 localization was an independent prognostic variable for both disease-free survival and overall survival (P = 0.043, P = 0.008, respectively). These findings additionally extend our understanding of the role of p27Kip1 in AML, and buttress the case of p27Kip1 mislocalization as a prognostic indicator and Akt/PKB/p27Kip1 pathway as a ready target for antileukemia therapy.

Phosphatase and tensin homologue phosphorylation in the C-terminal regulatory domain is frequently observed in acute myeloid leukaemia and associated with poor clinical outcome

Summary. Phosphorylation of PTEN (phosphatase and tensin homologue) affects PTEN protein stability and function. In this study, phosphorylated PTEN (pPTEN) was observed in 45 (73·8%) of 61 cases with acute myeloid leukaemia (AML). Phosphorylation of Akt and its downstream molecules [FKHR; Forkhead (Drosophila) homologue 1; and GSK‐3β; glycogen synthase kinase 3 beta] was significantly associated with pPTEN (P < 0·001). The complete remission rates were not different with respect to pPTEN, but overall survival was significantly shorter in patients with pPTEN (P < 0·05). Constitutive PTEN phosphorylation may add insight into the molecular pathogenesis of AML, and may be a new parameter for an unfavourable outcome.

Constitutive phosphorylation of FKHR transcription factor as a prognostic variable in acute myeloid leukemia

The transcription factor FKHR, which is controlled by Akt-PKB signaling, is involved in regulating cell cycle progression and cell death. In this study, the phosphorylation of FKHR was observed in 45 (73.8%) of 61 patients with acute myeloid leukemia (AML). The phosphorylation of Akt-PKB was found to be significantly associated with phospho-FKHR (P<0.001). Patients with phospho-FKHR had a significantly shorter overall survival than those without (P<0.05). In conclusion, the constitutive phosphorylation of FKHR was observed in the majority of AML, and the detection of phospho-FKHR might provide a new tool for identifying AML patients with an unfavorable outcome.

Myeloperoxidase Expression as a Potential Determinant of Parthenolide-Induced Apoptosis in Leukemia Bulk and Leukemia Stem Cells

Given that parthenolide (PTL) is an effective antileukemic agent, identifying molecular markers that predict response to PTL is important. We evaluated the role of myeloperoxidase (MPO) in determining the sensitivity of leukemia cells to PTL-induced apoptosis. In this study, the level of PTL-induced generation of reactive oxygen species (ROS) and apoptosis was significantly higher in the MPO-high leukemia cell lines compared with the MPO-low leukemia cell lines. Pretreatment of MPO-high leukemia cells with a MPO-specific inhibitor, 4-aminobenzoic acid hydrazide, or a MPO-specific small interfering RNA (siRNA) abrogated the PTL-induced ROS generation and apoptosis, indicating that MPO plays a crucial role in PTL-induced apoptosis in leukemia cells. PTL-induced apoptosis was accompanied by down-regulation of nuclear factor-κB, Bcl-xL, Mcl-1, X-linked inhibitor of apoptosis protein, and survivin and selectively observed in primary acute myeloid leukemia (AML) cells expressing higher levels of MPO (≥50%) while sparing both AML cells with lower MPO and normal CD34-positive (CD34+) normal bone marrow cells. The extent of PTL-induced apoptosis of the CD34+CD38− cell fraction was significantly greater in the MPO-high AML cases, compared with the MPO-low AML (P < 0.01) and normal CD34+ marrow cells (P < 0.01). Nonobese diabetic/severe combined immunodeficient human leukemia mouse model also revealed that PTL preferentially targets the MPO-high AML cells. Our data suggest that MPO plays a crucial role in determining the susceptibility of leukemia cells to PTL-induced apoptosis. PTL can be considered a promising leukemic stem cell-targeted therapy for AML expressing high levels of MPO.

Serum microRNA-21 as a potential biomarker for response to hypomethylating agents in myelodysplastic syndromes.

Identification of biomarkers that predict responses to hypomethylating agents (HMAs) will allow optimal strategies for epigenetic therapy in myelodysplastic syndromes (MDS) to be established. Serum miR-21 was quantitatively measured in 58 MDS patients treated with HMAs and 14 healthy controls. Serum miR-192 was an internal control, and diagnostic performance was evaluated according to receiver operating characteristics (ROCs). ROC analysis indicated that serum miR-21 levels differentiated responders from non-responders with an area under the curve of 0.648 (95% confidence, 0.49 to 0.72). The baseline level of serum miR-21 was significantly lower in the responder group than in the non-responder group (P = 0.041). The overall response rate (ORR) of the high miR-21 group was significantly lower than that of the low miR-21 group (41.2 vs. 73.2%, P = 0.021). Progression-free survival (PFS) was significantly inferior in the high group versus the low group (14.0 vs. 44.5 months, P = 0.001). Multivariate analyses revealed that the initial serum miR-21 level (P = 0.001) and circulating blasts (P = 0.007) were prognostic factors for PFS. Serum miR-21 level was significantly associated with ORR and PFS in MDS patients treated with HMAs. Although validation with a large prospective study is required, serum miR-21 is a potential biomarker of epigenetic therapy in MDS patients.

AMPK–ULK1-Mediated Autophagy Confers Resistance to BET Inhibitor JQ1 in Acute Myeloid Leukemia Stem Cells

Purpose: Bromodomain and extraterminal domain (BET) inhibitors are promising epigenetic agents for the treatment of various subsets of acute myeloid leukemia (AML). However, the resistance of leukemia stem cells (LSC) to BET inhibitors remains a major challenge. In this study, we evaluated the mechanisms underlying LSC resistance to the BET inhibitor JQ1. Experimental Design: We evaluated the levels of apoptosis and autophagy induced by JQ1 in LSC-like leukemia cell lines and primary CD34+CD38− leukemic blasts obtained from AML cases with normal karyotype without recurrent mutations. Results: JQ1 effectively induced apoptosis in a concentration-dependent manner in JQ1-sensitive AML cells. However, in JQ1-resistant AML LSCs, JQ1 induced little apoptosis and led to upregulation of beclin-1, increased LC3-II lipidation, formation of autophagosomes, and downregulation of p62/SQSTM1. Inhibition of autophagy by pharmacologic inhibitors or knockdown of beclin-1 using specific siRNA enhanced JQ1-induced apoptosis in resistant cells, indicating that prosurvival autophagy occurred in these cells. Independent of mTOR signaling, activation of the AMPK (pThr172)/ULK1 (pSer555) pathway was found to be associated with JQ1-induced autophagy in resistant cells. AMPK inhibition using the pharmacologic inhibitor compound C or by knockdown of AMPKα suppressed autophagy and promoted JQ1-induced apoptosis in AML LSCs. Conclusions: These findings revealed that prosurvival autophagy was one of the mechanisms involved in the resistance AML LSCs to JQ1. Targeting the AMPK/ULK1 pathway or inhibition of autophagy could be an effective therapeutic strategy for combating resistance to BET inhibitors in AML and other types of cancer. Clin Cancer Res; 23(11); 2781–94. ©2016 AACR.

Aurora-A kinase inhibition enhances the cytosine arabinoside-induced cell death in leukemia cells through apoptosis and mitotic catastrophe

Aurora-A (Aur-A) is a centrosome-associated serine/threonine kinase that is overexpressed in various cancers and potentially correlated with chemoresistance. In the Ara-C-sensitive leukemia cell lines, silencing of Aur-A by small interfering RNA transfection led to a significant increase in the Ara-C-induced cell death rate through induction of mitochondria-mediated, caspase-dependent apoptosis. In contrast, combined treatment of the Ara-C-resistant leukemia cell lines with Aur-A siRNA and Ara-C remarkably enhanced the cell death rate via non-caspase-dependent mitotic catastrophe. Taken together, Aur-A inhibition was an effective treatment for both the Ara-C-sensitive and resistant leukemia cells by increasing apoptosis and mitotic catastrophe, respectively.

Targeting AMPK-ULK1-mediated autophagy for combating BET inhibitor resistance in acute myeloid leukemia stem cells

ABSTRACT Bromodomain and extraterminal domain (BET) inhibitors are promising epigenetic agents for the treatment of various subsets of acute myeloid leukemia (AML). However, the resistance of leukemia stem cells (LSCs) to BET inhibitors remains a major challenge. In this study, we evaluated the mechanisms underlying LSC resistance to the BET inhibitor JQ1. We evaluated the levels of apoptosis and macroautophagy/autophagy induced by JQ1 in LSC-like leukemia cell lines and primary CD34+ CD38− leukemic blasts obtained from AML cases with normal karyotype without recurrent mutations. JQ1 effectively induced apoptosis in a concentration-dependent manner in JQ1-sensitive AML cells. However, in JQ1-resistant AML LSCs, JQ1 induced little apoptosis and led to upregulation of BECN1/Beclin 1, increased LC3 lipidation, formation of autophagosomes, and downregulation of SQSTM1/p62. Inhibition of autophagy by pharmacological inhibitors or knockdown of BECN1 using specific siRNA enhanced JQ1-induced apoptosis in resistant cells, indicating that prosurvival autophagy occurred in these cells. Independent of MTOR signaling, activation of the AMPK (p-Thr172)-ULK1 (p-Ser555) pathway was found to be associated with JQ1-induced autophagy in resistant cells. AMPK inhibition using the pharmacological inhibitor compound C or by knockdown of PRKAA/AMPKα suppressed autophagy and promoted JQ1-induced apoptosis in AML LSCs. These findings revealed that prosurvival autophagy was one of the mechanisms involved in the resistance of AML LSCs to JQ1. Targeting the AMPK-ULK1 pathway or inhibition of autophagy could be an effective therapeutic strategy for combating resistance to BET inhibitors in AML and other types of cancer.