The promyelocytic leukaemia gene PML is a pleiotropic tumour suppressor. We have recently demonstrated that PML opposes mTOR-HIF1α-VEGF signalling in hypoxia. To determine the relevance of PML-mTOR antagonism in tumourigenesis, we have intercrossed Pml null mice with Tsc2 heterozygous mice, which develop kidney cysts and carcinomas exhibiting mTOR upregulation. We find that combined inactivation of Pml and Tsc2 results in aberrant TORC1 activity both in pre-tumoural kidneys as well as in kidney lesions. Such increase correlates with a marked acceleration in tumour progression, impacting on both the biology and histology of kidney carcinomas. Also, Pml inactivation decreases the rate of loss of heterozygosity (LOH) for the wt Tsc2 allele. Interestingly, however, aberrant TORC1 activity does not accelerate renal cystogenesis in Tsc2/Pml mutants. Our data demonstrate that activation of mTOR is critical for tumour progression, but not for tumour initiation in the kidney.

PTEN encodes a lipid phosphatase that is underexpressed in many cancers owing to deletions, mutations or gene silencing. PTEN dephosphorylates phosphatidylinositol (3,4,5)-triphosphate, thereby opposing the activity of class I phosphatidylinositol 3-kinases that mediate growth- and survival-factor signalling through phosphatidylinositol 3-kinase effectors such as AKT and mTOR. To determine whether continued PTEN inactivation is required to maintain malignancy, here we generate an RNA interference-based transgenic mouse model that allows tetracycline-dependent regulation of PTEN in a time- and tissue-specific manner. Postnatal Pten knockdown in the haematopoietic compartment produced highly disseminated T-cell acute lymphoblastic leukaemia. Notably, reactivation of PTEN mainly reduced T-cell leukaemia dissemination but had little effect on tumour load in haematopoietic organs. Leukaemia infiltration into the intestine was dependent on CCR9 G-protein-coupled receptor signalling, which was amplified by PTEN loss. Our results suggest that in the absence of PTEN, G-protein-coupled receptors may have an unanticipated role in driving tumour growth and invasion in an unsupportive environment. They further reveal that the role of PTEN loss in tumour maintenance is not invariant and can be influenced by the tissue microenvironment, thereby producing a form of intratumoral heterogeneity that is independent of cancer genotype.

JAK1 is a critical effector of pro-inflammatory cytokine signaling and plays important roles in immune function, while abnormal JAK1 activity has been linked to immunological and neoplastic diseases. Specific functions of JAK1 in the context of hematopoiesis, and specifically within hematopoietic stem cells (HSCs), have not clearly been delineated. Here, we show that conditional Jak1 loss in HSCs reduces their self-renewal and markedly alters lymphoid/myeloid differentiation in vivo. Jak1-deficient HSCs exhibit decreased competitiveness in vivo and are unable to rescue hematopoiesis in the setting of myelosuppression. They exhibit increased quiescence, an inability to enter the cell cycle in response to hematopoietic stress, and a marked reduction in cytokine sensing, including in response to type I interferons and IL-3. Moreover, Jak1 loss is not fully rescued by expression of a constitutively active Jak2 allele. Together, these data highlight an essential role for Jak1 in HSC homeostasis and stress responses.

New anticancer drugs that target oncogenic signaling molecules have greatly improved the treatment of certain cancers. However, resistance to targeted therapeutics is a major clinical problem and the redundancy of oncogenic signaling pathways provides back-up mechanisms that allow cancer cells to escape. For example, the AKT and PIM kinases produce parallel oncogenic signals and share many molecular targets, including activators of cap-dependent translation. Here, we show that PIM kinase expression can affect the clinical outcome of lymphoma chemotherapy. We observe the same in animal lymphoma models. Whereas chemoresistance caused by AKT is readily reversed with rapamycin, PIM-mediated resistance is refractory to mTORC1 inhibition. However, both PIM- and AKT-expressing lymphomas depend on cap-dependent translation, and genetic or pharmacological blockade of the translation initiation complex is highly effective against these tumors. The therapeutic effect of blocking cap-dependent translation is mediated, at least in part, by decreased production of short-lived oncoproteins including c-MYC, Cyclin D1, MCL1, and the PIM1/2 kinases themselves. Hence, targeting the convergence of oncogenic survival signals on translation initiation is an effective alternative to combinations of kinase inhibitors.

MicroRNAs are frequently deregulated in cancer. Here we show that miR-22 is upregulated in myelodysplastic syndrome (MDS) and leukemia and its aberrant expression correlates with poor survival. To explore its role in hematopoietic stem cell function and malignancy, we generated transgenic mice conditionally expressing miR-22 in the hematopoietic compartment. These mice displayed reduced levels of global 5-hydroxymethylcytosine (5-hmC) and increased hematopoietic stem cell self-renewal accompanied by defective differentiation. Conversely, miR-22 inhibition blocked proliferation in both mouse and human leukemic cells. Over time, miR-22 transgenic mice developed MDS and hematological malignancies. We also identify TET2 as a key target of miR-22 in this context. Ectopic expression of TET2 suppressed the miR-22-induced phenotypes. Downregulation of TET2 protein also correlated with poor clinical outcomes and miR-22 overexpression in MDS patients. Our results therefore identify miR-22 as a potent proto-oncogene and suggest that aberrations in the miR-22/TET2 regulatory network are common in hematopoietic malignancies.

The IGF receptor type 1 (IGF-1R) pathway is frequently deregulated in human tumors and has become a target of interest for anti-cancer therapy.

The PML tumor suppressor controls key pathways for growth suppression, induction of apoptosis, and cellular senescence. PML loss occurs frequently in human tumors through unknown posttranslational mechanisms. Casein kinase 2 (CK2) is oncogenic and frequently upregulated in human tumors. Here we show that CK2 regulates PML protein levels by promoting its ubiquitin-mediated degradation dependent on direct phosphorylation at Ser517. Consequently, PML mutants that are resistant to CK2 phosphorylation display increased tumor-suppressive functions. In a faithful mouse model of lung cancer, we demonstrate that Pml inactivation leads to increased tumorigenesis. Furthermore, CK2 pharmacological inhibition enhances the PML tumor-suppressive property in vivo. Importantly, we found an inverse correlation between CK2 kinase activity and PML protein levels in human lung cancer-derived cell lines and primary specimens. These data identify a key posttranslational mechanism that controls PML protein levels and provide therapeutic means toward PML restoration through CK2 inhibition.

Nuclear exclusion of the PTEN (phosphatase and tensin homologue deleted in chromosome 10) tumour suppressor has been associated with cancer progression. However, the mechanisms leading to this aberrant PTEN localization in human cancers are currently unknown. We have previously reported that ubiquitinylation of PTEN at specific lysine residues regulates its nuclear-cytoplasmic partitioning. Here we show that functional promyelocytic leukaemia protein (PML) nuclear bodies co-ordinate PTEN localization by opposing the action of a previously unknown PTEN-deubiquitinylating enzyme, herpesvirus-associated ubiquitin-specific protease (HAUSP, also known as USP7), and that the integrity of this molecular framework is required for PTEN to be able to enter the nucleus. We find that PTEN is aberrantly localized in acute promyelocytic leukaemia, in which PML function is disrupted by the PML-RARalpha fusion oncoprotein. Remarkably, treatment with drugs that trigger PML-RARalpha degradation, such as all-trans retinoic acid or arsenic trioxide, restore nuclear PTEN. We demonstrate that PML opposes the activity of HAUSP towards PTEN through a mechanism involving the adaptor protein DAXX (death domain-associated protein). In support of this paradigm, we show that HAUSP is overexpressed in human prostate cancer and is associated with PTEN nuclear exclusion. Thus, our results delineate a previously unknown PML-DAXX-HAUSP molecular network controlling PTEN deubiquitinylation and trafficking, which is perturbed by oncogenic cues in human cancer, in turn defining a new deubiquitinylation-dependent model for PTEN subcellular compartmentalization.

The HVEM (TNFRSF14) receptor gene is among the most frequently mutated genes in germinal center lymphomas. We report that loss of HVEM leads to cell-autonomous activation of B cell proliferation and drives the development of GC lymphomas in vivo. HVEM-deficient lymphoma B cells also induce a tumor-supportive microenvironment marked by exacerbated lymphoid stroma activation and increased recruitment of T follicular helper (TFH) cells. These changes result from the disruption of inhibitory cell-cell interactions between the HVEM and BTLA (B and T lymphocyte attenuator) receptors. Accordingly, administration of the HVEM ectodomain protein (solHVEM(P37-V202)) binds BTLA and restores tumor suppression. To deliver solHVEM to lymphomas in vivo, we engineered CD19-targeted chimeric antigen receptor (CAR) T cells that produce solHVEM locally and continuously. These modified CAR-T cells show enhanced therapeutic activity against xenografted lymphomas. Hence, the HVEM-BTLA axis opposes lymphoma development, and our study illustrates the use of CAR-T cells as "micro-pharmacies" able to deliver an anti-cancer protein.

Despite recent advances, the myeloproliferative neoplasms (MPNs) are attended by considerable morbidity and mortality. Janus kinase (Jak) inhibitors such as ruxolitinib manage symptoms but do not substantially change the natural history of the disease. In this report, we show the effects of IMG-7289, an irreversible inhibitor of the epigenetically active lysine-specific demethylase 1 (LSD1) in mouse models of MPN. Once-daily treatment with IMG-7289 normalized or improved blood cell counts, reduced spleen volumes, restored normal splenic architecture, and reduced bone marrow fibrosis. Most importantly, LSD1 inhibition lowered mutant allele burden and improved survival. IMG-7289 selectively inhibited proliferation and induced apoptosis of JAK2 V617F cells by concomitantly increasing expression and methylation of p53, and, independently, the pro-apoptotic factor PUMA and by decreasing the levels of its antiapoptotic antagonist BCLXL. These data provide a molecular understanding of the disease-modifying activity of the LSD1 inhibitor IMG-7289 that is currently undergoing clinical evaluation in patients with high-risk myelofibrosis. Moreover, low doses of IMG-7289 and ruxolitinib synergize in normalizing the MPN phenotype in mice, offering a rationale for investigating combination therapy.

The Ten-eleven translocation (TET) enzymes regulate gene expression by promoting DNA demethylation and partnering with chromatin modifiers. TET2, a member of this family, is frequently mutated in hematological disorders. The contributions of TET2 in hematopoiesis have been attributed to its DNA demethylase activity, and the significance of its nonenzymatic functions has remained undefined. To dissect the catalytic and non-catalytic requirements of Tet2, we engineered catalytically inactive Tet2 mutant mice and conducted comparative analyses of Tet2 mutant and Tet2 knockout animals. Tet2 knockout mice exhibited expansion of hematopoietic stem and progenitor cells (HSPCs) and developed myeloid and lymphoid disorders, while Tet2 mutant mice predominantly developed myeloid malignancies reminiscent of human myelodysplastic syndromes. HSPCs from Tet2 knockout mice exhibited distinct gene expression profiles, including downregulation of Gata2. Overexpression of Gata2 in Tet2 knockout bone marrow cells ameliorated disease phenotypes. Our results reveal the non-catalytic roles of TET2 in HSPC homeostasis.

The tumor suppressor PTEN controls cell proliferation by regulating phosphatidylinositol-3-kinase (PI3K) activity, but the participation of PTEN in host defense against bacterial infection is less well understood. Anti-inflammatory PI3K-Akt signaling is suppressed in patients with cystic fibrosis (CF), a disease characterized by hyper-inflammatory responses to airway infection. We found that Ptenl-/- mice, which lack the NH2-amino terminal splice variant of PTEN, were unable to eradicate Pseudomonas aeruginosa from the airways and could not generate sufficient anti-inflammatory PI3K activity, similar to what is observed in CF. PTEN and the CF transmembrane conductance regulator (CFTR) interacted directly and this interaction was necessary to position PTEN at the membrane. CF patients under corrector-potentiator therapy, which enhances CFTR transport to the membrane, have increased PTEN amounts. These findings suggest that improved CFTR trafficking could enhance P. aeruginosa clearance from the CF airway by activating PTEN-mediated anti-bacterial responses and might represent a therapeutic strategy.

Patients with myeloproliferative neoplasms (MPNs) frequently progress to bone marrow failure or acute myeloid leukemia (AML), and mutations in epigenetic regulators such as the metabolic enzyme isocitrate dehydrogenase (IDH) are associated with poor outcomes. Here, we showed that combined expression of Jak2V617F and mutant IDH1R132H or Idh2R140Q induces MPN progression, alters stem/progenitor cell function, and impairs differentiation in mice. Jak2V617F Idh2R140Q-mutant MPNs were sensitive to small-molecule inhibition of IDH. Combined inhibition of JAK2 and IDH2 normalized the stem and progenitor cell compartments in the murine model and reduced disease burden to a greater extent than was seen with JAK inhibition alone. In addition, combined JAK2 and IDH2 inhibitor treatment also reversed aberrant gene expression in MPN stem cells and reversed the metabolite perturbations induced by concurrent JAK2 and IDH2 mutations. Combined JAK2 and IDH2 inhibitor therapy also showed cooperative efficacy in cells from MPN patients with both JAK2mut and IDH2mut mutations. Taken together, these data suggest that combined JAK and IDH inhibition may offer a therapeutic advantage in this high-risk MPN subtype.

Connecting specific cancer genotypes with phenotypes and drug responses constitutes the central premise of precision oncology but is hindered by the genetic complexity and heterogeneity of primary cancer cells. Here, we use patient-derived induced pluripotent stem cells (iPSCs) and CRISPR/Cas9 genome editing to dissect the individual contributions of two recurrent genetic lesions, the splicing factor SRSF2 P95L mutation and the chromosome 7q deletion, to the development of myeloid malignancy. Using a comprehensive panel of isogenic iPSCs-with none, one, or both genetic lesions-we characterize their relative phenotypic contributions and identify drug sensitivities specific to each one through a candidate drug approach and an unbiased large-scale small-molecule screen. To facilitate drug testing and discovery, we also derive SRSF2-mutant and isogenic normal expandable hematopoietic progenitor cells. We thus describe here an approach to dissect the individual effects of two cooperating mutations to clinically relevant features of malignant diseases.

GATA-1-dependent transcription is essential for erythroid differentiation and maturation. Suppression of programmed cell death is also thought to be critical for this process; however, the link between these two features of erythropoiesis has remained elusive. Here, we show that the POZ-Krüppel family transcription factor, LRF (also known as Zbtb7a/Pokemon), is a direct target of GATA1 and plays an essential antiapoptotic role during terminal erythroid differentiation. We find that loss of Lrf leads to lethal anemia in embryos, due to increased apoptosis of late-stage erythroblasts. This programmed cell death is Arf and p53 independent and is instead mediated by upregulation of the proapoptotic factor Bim. We identify Lrf as a direct repressor of Bim transcription. In strong support of this mechanism, genetic Bim loss delays the lethality of Lrf-deficient embryos and rescues their anemia phenotype. Thus, our data define a key transcriptional cascade for effective erythropoiesis, whereby GATA-1 suppresses BIM-mediated apoptosis via LRF.

Inhibition of the eIF4A RNA helicase with silvestrol and related compounds is emerging as a powerful anti-cancer strategy. We find that a synthetic silvestrol analogue (CR-1-31 B) has nanomolar activity across many cancer cell lines. It is especially active against aggressive MYC+/BCL2+ B cell lymphomas and this likely reflects the eIF4A-dependent translation of both MYC and BCL2. We performed a genome-wide CRISPR/Cas9 screen and identified mechanisms of resistance to this new class of therapeutics. We identify three negative NRF2 regulators (KEAP1, CUL3, CAND1) whose inactivation is sufficient to cause CR1-31-B resistance. NRF2 is known to alter the oxidation state of translation factors and cause a broad increase in protein production. We find that NRF2 activation particularly increases the translation of some eIF4A-dependent mRNAs and restores MYC and BCL2 production. We know that NRF2 functions depend on removal of sugar adducts by the frutosamine-3-kinase (FN3K). Accordingly, loss of FN3K results in NRF2 hyper-glycation and inactivation and resensitizes cancer cells to eIF4A inhibition. Together, our findings implicate NRF2 in the translation of eIF4A-dependent mRNAs and point to FN3K inhibition as a new strategy to block NRF2 functions in cancer.

Previous small series have suggested that acute myeloid leukemia with t(8;16) is a distinct morphologic and clinical entity associated with poor prognosis. We describe 18 patients with t(8;16) AML, including their clinical, cytomorphologic, immunophenotypic and cytogenetic features. Half of the patients had extramedullary disease, most commonly leukemia cutis, which often preceded bone marrow involvement and six had therapy-related AML. Patients with t(8;16) AML commonly present with clinical and pathological features that mimic APL, with promyelocytes and promyeloblast-like cells and coagulopathy in most patients. Several patients also presented with marrow histiocytes with hemophagocytosis and erythrophagocytosis. Comprehensive molecular analysis for co-occurring genetic alterations revealed a somatic mutation in RUNX1 in 1 of 6 t(8;16) patients with no known AML mutation in the remaining five t(8;16) patients. This suggests that the t(8;16) translocation could be sufficient to induce hematopoietic cell transformation to AML without acquiring other genetic alteration. These data further support classifying t(8;16) AML as a clinically and molecularly defined subtype of AML marked by characteristic clinical and cytomorphologic features that mimic APL, and is associated with very poor survival.

Aberrant Skp2 signaling has been implicated as a driving event in tumorigenesis. Although the underlying molecular mechanisms remain elusive, cytoplasmic Skp2 correlates with more aggressive forms of breast and prostate cancers. Here, we report that Skp2 is acetylated by p300 at K68 and K71, which is a process that can be antagonized by the SIRT3 deacetylase. Inactivation of SIRT3 leads to elevated Skp2 acetylation, which leads to increased Skp2 stability through impairment of the Cdh1-mediated proteolysis pathway. As a result, Skp2 oncogenic function is increased, whereby cells expressing an acetylation-mimetic mutant display enhanced cellular proliferation and tumorigenesis in vivo. Moreover, acetylation of Skp2 in the nuclear localization signal (NLS) promotes its cytoplasmic retention, and cytoplasmic Skp2 enhances cellular migration through ubiquitination and destruction of E-cadherin. Thus, our study identifies an acetylation-dependent regulatory mechanism governing Skp2 oncogenic function and provides insight into how cytoplasmic Skp2 controls cellular migration.

Insights into cancer genetics can lead to therapeutic opportunities. By cross-referencing chromosomal changes with an unbiased genetic screen we identify the ephrin receptor A7 (EPHA7) as a tumor suppressor in follicular lymphoma (FL). EPHA7 is a target of 6q deletions and inactivated in 72% of FLs. Knockdown of EPHA7 drives lymphoma development in a murine FL model. In analogy to its physiological function in brain development, a soluble splice variant of EPHA7 (EPHA7(TR)) interferes with another Eph-receptor and blocks oncogenic signals in lymphoma cells. Consistent with this drug-like activity, administration of the purified EPHA7(TR) protein produces antitumor effects against xenografted human lymphomas. Further, by fusing EPHA7(TR) to the anti-CD20 antibody (rituximab) we can directly target this tumor suppressor to lymphomas in vivo. Our study attests to the power of combining descriptive tumor genomics with functional screens and reveals EPHA7(TR) as tumor suppressor with immediate therapeutic potential.

Genetic and functional studies underscore the central role of JAK/STAT signaling in myeloproliferative neoplasms (MPNs). However, the mechanisms that mediate transformation in MPNs are not fully delineated, and clinically utilized JAK inhibitors have limited ability to reduce disease burden or reverse myelofibrosis. Here we show that MPN progenitor cells are characterized by marked alterations in gene regulation through differential enhancer utilization, and identify nuclear factor κB (NF-κB) signaling as a key pathway activated in malignant and non-malignant cells in MPN. Inhibition of BET bromodomain proteins attenuated NF-κB signaling and reduced cytokine production in vivo. Most importantly, combined JAK/BET inhibition resulted in a marked reduction in the serum levels of inflammatory cytokines, reduced disease burden, and reversed bone marrow fibrosis in vivo.