Bryan King

Contrasting roles of histone 3 lysine 27 demethylases in acute lymphoblastic leukaemia.

T-cell acute lymphoblastic leukaemia (T-ALL) is a haematological malignancy with a dismal overall prognosis, including a relapse rate of up to 25%, mainly because of the lack of non-cytotoxic targeted therapy options. Drugs that target the function of key epigenetic factors have been approved in the context of haematopoietic disorders, and mutations that affect chromatin modulators in a variety of leukaemias have recently been identified; however, ‘epigenetic’ drugs are not currently used for T-ALL treatment. Recently, we described that the polycomb repressive complex 2 (PRC2) has a tumour-suppressor role in T-ALL. Here we delineated the role of the histone 3 lysine 27 (H3K27) demethylases JMJD3 and UTX in T-ALL. We show that JMJD3 is essential for the initiation and maintenance of T-ALL, as it controls important oncogenic gene targets by modulating H3K27 methylation. By contrast, we found that UTX functions as a tumour suppressor and is frequently genetically inactivated in T-ALL. Moreover, we demonstrated that the small molecule inhibitor GSKJ4 (ref. 5) affects T-ALL growth, by targeting JMJD3 activity. These findings show that two proteins with a similar enzymatic function can have opposing roles in the context of the same disease, paving the way for treating haematopoietic malignancies with a new category of epigenetic inhibitors.

CXCL12-Producing Vascular Endothelial Niches Control Acute T Cell Leukemia Maintenance

The role of the microenvironment in T cell acute lymphoblastic leukemia (T-ALL), or any acute leukemia, is poorly understood. Here we demonstrate that T-ALL cells are in direct, stable contact with CXCL12-producing bone marrow stroma. Cxcl12 deletion from vascular endothelial, but not perivascular, cells impeded tumor growth, suggesting a vascular niche for T-ALL. Moreover, genetic targeting of Cxcr4 in murine T-ALL after disease onset led to rapid, sustained disease remission, and CXCR4 antagonism suppressed human T-ALL in primary xenografts. Loss of CXCR4 targeted key T-ALL regulators, including the MYC pathway, and decreased leukemia initiating cell activity in vivo. Our data identify a T-ALL niche and suggest targeting CXCL12/CXCR4 signaling as a powerful therapeutic approach for T-ALL.

TET1 is a tumor suppressor of hematopoietic malignancy

The methylcytosine dioxygenase TET1 (‘ten-eleven translocation 1’) is an important regulator of 5-hydroxymethylcytosine (5hmC) in embryonic stem cells. The diminished expression of TET proteins and loss of 5hmC in many tumors suggests a critical role for the maintenance of this epigenetic modification. Here we found that deletion of Tet1 promoted the development of B cell lymphoma in mice. TET1 was required for maintenance of the normal abundance and distribution of 5hmC, which prevented hypermethylation of DNA, and for regulation of the B cell lineage and of genes encoding molecules involved in chromosome maintenance and DNA repair. Whole-exome sequencing of TET1-deficient tumors revealed mutations frequently found in non-Hodgkin B cell lymphoma (B-NHL), in which TET1 was hypermethylated and transcriptionally silenced. Our findings provide in vivo evidence of a function for TET1 as a tumor suppressor of hematopoietic malignancy.

Genomic analysis identifies new drivers and progression pathways in skin basal cell carcinoma

Basal cell carcinoma (BCC) of the skin is the most common malignant neoplasm in humans. BCC is primarily driven by the Sonic Hedgehog (Hh) pathway. However, its phenotypic variation remains unexplained. Our genetic profiling of 293 BCCs found the highest mutation rate in cancer (65 mutations/Mb). Eighty-five percent of the BCCs harbored mutations in Hh pathway genes (PTCH1, 73% or SMO, 20% (P = 6.6 × 10−8) and SUFU, 8%) and in TP53 (61%). However, 85% of the BCCs also harbored additional driver mutations in other cancer-related genes. We observed recurrent mutations in MYCN (30%), PPP6C (15%), STK19 (10%), LATS1 (8%), ERBB2 (4%), PIK3CA (2%), and NRAS, KRAS or HRAS (2%), and loss-of-function and deleterious missense mutations were present in PTPN14 (23%), RB1 (8%) and FBXW7 (5%). Consistent with the mutational profiles, N-Myc and Hippo-YAP pathway target genes were upregulated. Functional analysis of the mutations in MYCN, PTPN14 and LATS1 suggested their potential relevance in BCC tumorigenesis.

The ubiquitin ligase Huwe1 regulates the maintenance and lymphoid commitment of hematopoietic stem cells

Hematopoietic stem cells (HSCs) are dormant in the bone marrow and can be activated in response to diverse stresses to replenish all blood cell types. Here we identify the ubiquitin ligase Huwe1 as a crucial regulator of HSC functions via its post-translational control of N-myc. We found Huwe1 to be essential for HSC self-renewal, quiescence and lymphoid fate specification. Using a novel fluorescent fusion allele (MycnM), we observed that N-myc expression was restricted to the most immature, multipotent stem and progenitor populations. N-myc was upregulated in response to stress or upon loss of Huwe1, leading to increased proliferation and stem cell exhaustion. Mycn depletion reversed most of these phenotypes in vivo, suggesting that the attenuation of N-myc by Huwe1 is essential to reestablish homeostasis following stress.Hematopoietic stem cells (HSCs) are dormant in the bone marrow and can be activated in response to diverse stresses to replenish all blood cell types. We identified the ubiquitin ligase Huwe1 as a crucial regulator of HSC function via its post-translational control of the oncoprotein N-myc (encoded by Mycn). We found Huwe1 to be essential for HSC self-renewal, quiescence and lymphoid-fate specification in mice. Through the use of a fluorescent fusion allele (MycnM), we observed that N-myc expression was restricted to the most immature, multipotent stem and progenitor populations. N-myc expression was upregulated in response to stress or following loss of Huwe1, which led to increased proliferation and stem-cell exhaustion. Mycn depletion reversed most of these phenotypes in vivo, which suggested that the attenuation of N-myc by Huwe1 is essential for reestablishing homeostasis following stress.

Erratum: TET1 is a tumor suppressor of hematopoietic malignancy

Nat. Immunol. 16, 653–662 (2015); published online 13 April 2015; corrected after print 17 June 2015 In the version of this article initially published, labels reading “5hmC gain” were incorrectly included below the plots in Figure 6e, and the plot at right was mislabeled above (as “loss”). The plotat left should have a single label above reading “5hmC loss” and the plot at right should have a single label above reading “5hmC gain.

Abstract A06: The chemokine receptor CXCR4 is essential for the maintenance of T cell acute lymphoblastic leukemia.

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy arising in immature T cell progenitors. Despite improved survival rates, relapse remains a major therapeutic obstacle and intensive treatment regimens expose T-ALL patients to serious long-term side-effects. Hence more effective, less toxic treatment options are required. While the localization of leukemia cells determines the course of disease, little is known about T-ALL migration. Upon profiling chemokine receptor expression by T-ALL cells, we observed high surface levels of the CXCL12 receptor, CXCR4. Intravital imaging revealed that T-ALL cells are in direct contact with CXCL12-producing bone marrow stromal cells in vivo. Genetic targeting of CXCR4 in T-ALL cells resulted in a marked reduction of leukemia burden and significantly prolonged survival. Moreover, disruption of CXCR4 signaling with a small molecule inhibitor severely impaired T-ALL progression in mouse and human xenograft models of the disease. We found that CXCR4 promotes c-Myc expression, which is required in leukemia initiating cells. Given the relatively subtle role for CXCR4 in normal developing T cells, CXCR4 inhibition to our knowledge has not been proposed as a therapy for T cell malignancies. Our data strongly suggest that targeting CXCR4 could be a promising strategy for combating T-ALL. Citation Format: Lauren A. Pitt, Anastasia N. Tikhonova, Thomas Trimarchi, Bryan King, Hai Hu, Yixiao Gong, Aris Tsirigos, Marta Sanchez-Martin, Dan R. Littman, Adolfo Ferrando, Sean J. Morrison, David R. Fooksman, Iannis Aifantis, Susan Schwab. The chemokine receptor CXCR4 is essential for the maintenance of T cell acute lymphoblastic leukemia. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr A06.

Abstract A07: Characterizing the specific oncogenic and tumor suppressor roles of H3K27me3 epigenetic modulators in T cell leukemia

T cell acute lymphoblastic leukemia (T-ALL) is an immature hematopoietic malignancy driven mainly by oncogenic activation of NOTCH1 signaling. In a recently published work, we identified and characterized a tumor suppressor role for the Polycomb Repressive Complex 2 (PRC2), that was underlined through the identification of loss-of-function mutations and deletions of members of the PRC2 complex in 25% of the patients with T cell leukemia. Further inhibition of PRC2 action in T cell leukemia comes through competition with master oncogenes, such as Notch1, for chromatin binding. Extending our work on the H3K27me3 mark, we now show that the activity of the corresponding H3K27me3 demethylases is also very important for the initiation, progression and maintenance of the disease. More specifically, transcriptional data analysis and exome sequencing of primary T-ALL samples demonstrates a significant correlation between levels and mutational status of these demethylases and major oncogenic pathways in leukemia. Functionally, genomic ablation of these epigenetic modulators as well as targeting with a specific-recently produced and characterized-inhibitor-GSKJ4, leads to apoptosis and cell cycle arrest of T-ALL lines in vitro and in vivo, accompanied by major epigenetic and transcriptional changes at specific anti-apoptotic, oncogenic and metabolic genes. Furthermore, genetic ablation of these epigenetic modulators leads to slower initiation of the disease in a classic mouse model of leukemia with highly improved survival rates. In light of recent developments of novel epigenetic inhibitors against these molecules, these findings pave the way to specific pharmacological targeting of T cell leukemia. Citation Format: Panagiotis Ntziachristos, Aris Tsirigos, Thomas Trimarchi, Evangelia Loizou, Xu Luyao, Pieter Van Vlierberghe, Bryan King, Grant Welstead, Charles Mullighan, Rudolf Jaenisch, Adolfo Ferrando, Iannis Aifantis. Characterizing the specific oncogenic and tumor suppressor roles of H3K27me3 epigenetic modulators in T cell leukemia. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr A07.