Chun Shik Park

Sulforaphane Induces Cell Cycle Arrest and Apoptosis in Acute Lymphoblastic Leukemia Cells

Acute lymphoblastic leukemia (ALL) is the most common hematological cancer in children. Although risk-adaptive therapy, CNS-directed chemotherapy, and supportive care have improved the survival of ALL patients, disease relapse is still the leading cause of cancer-related death in children. Therefore, new drugs are needed as frontline treatments in high-risk disease and as salvage agents in relapsed ALL. In this study, we report that purified sulforaphane, a natural isothiocyanate found in cruciferous vegetables, has anti-leukemic properties in a broad range of ALL cell lines and primary lymphoblasts from pediatric T-ALL and pre-B ALL patients. The treatment of ALL leukemic cells with sulforaphane resulted in dose-dependent apoptosis and G2/M cell cycle arrest, which was associated with the activation of caspases (3, 8, and 9), inactivation of PARP, p53-independent upregulation of p21CIP1/WAF1, and inhibition of the Cdc2/Cyclin B1 complex. Interestingly, sulforaphane also inhibited the AKT and mTOR survival pathways in most of the tested cell lines by lowering the levels of both total and phosphorylated proteins. Finally, the administration of sulforaphane to the ALL xenograft models resulted in a reduction of tumor burden, particularly following oral administration, suggesting a potential role as an adjunctive agent to improve the therapeutic response in high-risk ALL patients with activated AKT signaling.

The Cytosolic Protein G0S2 Maintains Quiescence in Hematopoietic Stem Cells

Bone marrow hematopoietic stem cells (HSCs) balance proliferation and differentiation by integrating complex transcriptional and post-translational mechanisms regulated by cell intrinsic and extrinsic factors. We found that transcripts of G0/G1 switch gene 2 (G0S2) are enriched in lineage− Sca-1+ c-kit+ (LSK) CD150+ CD48− CD41− cells, a population highly enriched for quiescent HSCs, whereas G0S2 expression is suppressed in dividing LSK CD150+ CD48− cells. Gain-of-function analyses using retroviral expression vectors in bone marrow cells showed that G0S2 localizes to the mitochondria, endoplasmic reticulum, and early endosomes in hematopoietic cells. Co-transplantation of bone marrow cells transduced with the control or G0S2 retrovirus led to increased chimerism of G0S2-overexpressing cells in femurs, although their contribution to the blood was reduced. This finding was correlated with increased quiescence in G0S2-overexpressing HSCs (LSK CD150+ CD48−) and progenitor cells (LS−K). Conversely, silencing of endogenous G0S2 expression in bone marrow cells increased blood chimerism upon transplantation and promoted HSC cell division, supporting an inhibitory role for G0S2 in HSC proliferation. A proteomic study revealed that the hydrophobic domain of G0S2 interacts with a domain of nucleolin that is rich in arginine-glycine-glycine repeats, which results in the retention of nucleolin in the cytosol. We showed that this cytosolic retention of nucleolin occurs in resting, but not proliferating, wild-type LSK CD150+ CD48− cells. Collectively, we propose a novel model of HSC quiescence in which elevated G0S2 expression can sequester nucleolin in the cytosol, precluding its pro-proliferation functions in the nucleolus.

Krüppel-like factor 4 (KLF4) promotes the survival of natural killer cells and maintains the number of conventional dendritic cells in the spleen

The development and survival of NK cells rely on a complex, spatiotemporal gene expression pattern regulated by specific transcription factors in NK cells and tissue‐specific microenvironments supported by hematopoietic cells. Here, we show that somatic deletion of the KLF4 gene, using inducible and lineage‐specific cre‐transgenic mice, leads to a significant reduction of NK cells (NK1.1+ TCR‐β−) in the blood and spleen but not in the BM, liver, or LNs. Functional and immunophenotypic analyses revealed increased apoptosis of CD27+/− CD11b+ NK cells in the spleen of KLF4‐deficient mice, although remaining NK cells were able to lyse tumor target cells and produce IFN‐γ. A normal recovery of adoptively transferred KLF4‐deficient NK cells in WT hosts suggested that the survival defect was not intrinsic of NK cells. However, BM chimeras using KLF4‐deficient mice as donors indicated that reduced survival of NK cells depended on BM‐derived hematopoietic cells in the spleen. The number of CD11chi DCs, which are known to support NK cell survival, was reduced significantly in the spleen of KLF4‐deficient mice, likely a result of a lower number of precDC progenitor cells in this tissue. Taken together, our data suggest that the pluripotency‐associated gene KLF4 is required for the maintenance of DCs in the spleen and consequently, survival of differentiated NK cells in this tissue.

G0S2 inhibits the proliferation of K562 cells by interacting with nucleolin in the cytosol

G0/G1 switch gene 2 (G0S2) is a basic protein with ill-defined function that inhibits the proliferation of hematopoietic stem cells. Herein, we show that treatment of K562 cells with 5-azacytidine (5-Aza) resulted in a 24-fold increase in G0S2 expression and a reduction in cell growth. Conversely, gene demethylation in the presence of G0S2-specific shRNA restored proliferation, further supporting an inhibitory role for G0S2 in cell proliferation. Elevated levels of G0S2 inhibited the division of K562 cells by sequestering the nucleolar phosphoprotein nucleolin in the cytosol. G0S2 inhibited the proliferation of leukemia cells in vivo in xenograft models. Collectively, our data identify a new mechanism that controls proliferation in K562 cells, suggesting a possible tumor suppressor function in leukemia cells.

Differential roles of KLF4 in the development and differentiation of CD8+ T cells

The transcription factor Krüppel-like factor 4 (KLF4) can activate or repress gene expression in a cell-context dependent manner. We have previously shown that KLF4 inhibits the proliferation of naïve CD8(+) T cells in vitro downstream of the transcription factor ELF4. In this work, we describe a novel role of KLF4 in the differentiation of CD8(+) T cells upon infection. Loss of KLF4 had minimal effect on thymic T cell development and distribution of mature T cells in the spleen, blood, and lymph nodes. KLF4-deficient naïve CD8(+) T cells also displayed normal homeostatic proliferation upon adoptive transfer into lymphopenic hosts. However, activation of KLF4-deficient naïve CD8(+) T cells by in vitro TCR crosslink and co-stimulation resulted in increased proliferation. Furthermore, naïve KLF4-deficient OT-I CD8(+) T cells generated increased numbers of functional memory CD8(+) T cells compared to wild type OT-I CD8(+) T cells co-injected in the same recipient in both primary and recall responses to Listeria monocytogenes-OVA. Collectively, our data demonstrate that KLF4 regulates differentiation of functional memory CD8(+) T cells while sparing development and homeostasis of naïve CD8(+) T cells.

Role of the reprogramming factor KLF4 in blood formation

Krüppel‐like factor 4 is a zinc finger protein with dual functions that can act as a transcriptional activator and repressor of genes involved in cell proliferation, differentiation, and apoptosis. Although most studies have focused on terminally differentiated epithelial cells, evidence suggests that Krüppel‐like factor 4 regulates the development and function of the myeloid and lymphoid blood lineages. The ability of Krüppel‐like factor 4 to dedifferentiate from somatic cells into pluripotent stem cells in cooperation with other reprogramming factors suggests its potential function in the preservation of tissue‐specific stem cells. Additionally, emerging interest in the redifferentiation of induced pluripotent stem cells into blood cells to correct hematologic deficiencies and malignancies warrants further studies on the role of Krüppel‐like factor 4 in steady‐state blood formation.

Genetic control of quiescence in hematopoietic stem cells

Cellular quiescence is a reversible cell cycle arrest that is poised to re-enter the cell cycle in response to a combination of cell-intrinsic factors and environmental cues. In hematopoietic stem cells, a coordinated balance between quiescence and differentiating proliferation ensures longevity and prevents both genetic damage and stem cell exhaustion. However, little is known about how all these processes are integrated at the molecular level. We will briefly review the environmental and intrinsic control of stem cell quiescence and discuss a new model that involves a protein-to-protein interaction between G0S2 and the phospho-nucleoprotein nucleolin in the cytosol.

Inactivation of KLF4 promotes T-cell acute lymphoblastic leukemia and activates the MAP2K7 pathway.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with a high incidence of relapse in pediatric ALL. Although most T-ALL patients exhibit activating mutations in NOTCH1, the cooperating genetic events required to accelerate the onset of leukemia and worsen disease progression are largely unknown. Here, we show that the gene encoding the transcription factor KLF4 is inactivated by DNA methylation in children with T-ALL. In mice, loss of KLF4 accelerated the development of NOTCH1-induced T-ALL by enhancing the G1-to-S transition in leukemic cells and promoting the expansion of leukemia-initiating cells. Mechanistically, KLF4 represses the gene encoding the kinase MAP2K7. Our results showed that in murine and pediatric T-ALL, loss of KLF4 leads to aberrant activation of MAP2K7 and of the downstream effectors JNK and ATF2. As a proof-of-concept for the development of a targeted therapy, administration of JNK inhibitors reduced the expansion of leukemia cells in cell-based and patient-derived xenograft models. Collectively, these data uncover a novel function for KLF4 in regulating the MAP2K7 pathway in T-ALL cells, which can be targeted to eradicate leukemia-initiating cells in T-ALL patients.

G0S2 modulates homeostatic proliferation of naïve CD8 + T cells and inhibits oxidative phosphorylation in mitochondria

Since its discovery, diverse functions have been attributed to the G0/G1 switch gene 2 (G0S2), from lipid metabolism to control of cell proliferation. Our group showed for the first time that G0S2 promotes quiescence in hematopoietic stem cells by interacting with and retaining nucleolin around the nucleus. Herein, we report the role of G0S2 in the differentiation and function of CD8+ T cells examined in mice with an embryonic deletion of the G0s2 gene. G0S2 expression in naïve CD8+ T cells decreased immediately after T‐cell receptor activation downstream of the mitogen‐activated protein kinase, calcium/calmodulin, phosphatidylinositol 3′‐kinase and mammalian target of rapamycin pathways. Surprisingly, G0S2‐null naïve CD8+ T cells displayed increased basal and spare respiratory capacity that was not associated with increased mitochondrial biogenesis but with increased phosphorylation of AMP‐activated protein kinase α. Naïve CD8+ T cells showed increased proliferation in response to in vitro activation and in vivo lymphopenia; however, naïve CD8+ T cells expressing the OT‐1 transgene exhibited normal differentiation of naïve cells to effector and memory CD8+ T cells upon infection with Listeria monocytogenes in a wild‐type or a G0s2‐null environment, with increased circulating levels of free fatty acids. Collectively, our results suggest that G0S2 inhibits energy production by oxidative phosphorylation to fine‐tune proliferation in homeostatic conditions.

Abstract LB-181: KLF4 suppresses T-cell acute lymphoblastic leukemia by inhibiting the stress kinase MAP2K7 pathway

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with the highest incidence of relapse of any pediatric ALL. A minimal two-hit model of leukemogenesis suggests that an initial genetic driver transforms hematopoietic progenitor cells into LICs, whereas a secondary genetic alteration would endow LICs with proliferative and survival advantages. Although most T-ALL patients exhibit activating mutations in NOTCH1 , the cooperating genetic events required to accelerate onset of leukemia and worsen disease progression are largely unknown. Here, we show that low levels of the transcription factor KLF4 in children with T-ALL were associated with methylation of its promoter. Consistent with a tumor suppressor function, loss of KLF4 accelerated the development of NOTCH1-induced T-ALL in mice by enhancing the G1-to-S transition and promoting the expansion of leukemia-initiating cells that are responsible for chemoresistance and relapses. Mechanistically, KLF4 represses the gene encoding the kinase MAP2K7, and thus loss of KLF4 activates MAP2K7 and downstream effector JNK both in murine model of T-ALL and lymphoblasts from pediatric patients with T-ALL. Furthermore, pharmacological inhibition of JNK reduced leukemia burden in a xenograft model of human T-ALL and small molecule inhibitors exhibited anti-leukemic properties in patient-derived xenograft cells. In summary, our findings demonstrate a novel tumor suppressor function of KLF4 in a T-ALL mouse model and in pediatric T-ALL and support a model of leukemia inhibition by repression of the stress kinase MAP2K7 and its downstream targets JNK, c-JUN, and ATF2. In addition, our study provides proof-of-principle pre-clinical data supporting JNK inhibition as a potential targeted therapy for T-ALL and prompts future studies in high-risk T-ALL patients with refractory and relapsed disease. Citation Format: Ye Shen, Chun Shik Park, Koramit Suppipat, Toni-Ann Mistretta, Monica Puppi, Terzah Horton, Karen Rabin, Daniel Lacorazza. KLF4 suppresses T-cell acute lymphoblastic leukemia by inhibiting the stress kinase MAP2K7 pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-181.