Leukemic blasts program bone marrow adipocytes to generate a protumoral microenvironment

Despite currently available therapies most patients diagnosed with acute myeloid leukemia (AML) die of their disease. Tumor-host interactions are critical for the survival and proliferation of cancer cells; accordingly, we hypothesise that specific targeting of the tumor microenvironment may constitute an alternative or additional strategy to conventional tumor-directed chemotherapy. Since adipocytes have been shown to promote breast and prostate cancer proliferation, and because the bone marrow adipose tissue (MAT) accounts for up to 70% of bone marrow volume in adult humans, we examined the adipocyte-leukaemia cell interactions to determine if they are essential for the growth and survival of AML. Using in-vivo and in-vitro models of AML we show that bone marrow adipocytes from the tumor microenvironment support the survival and proliferation of malignant cells from patients with AML. We show that AML blasts alter metabolic processes in adipocytes to induce phosphorylation of hormone-sensitive lipase and consequently activate lipolysis, which then enables the transfer of fatty acids from adipocytes to AML blasts. In addition, we report that fatty acid binding protein-4 (FABP4) mRNA is up-regulated in adipocytes and AML when in co-culture. FABP4 inhibition using FABP4 shRNA knockdown or a small molecule inhibitor prevents AML proliferation on adipocytes. Moreover, knockdown of FABP4 increases survival in Hoxa9/Meis1-driven AML model. Finally, knockdown of carnitine palmitoyltransferase IA (CPT1A) in an AML patient-derived xenograft model improves survival. Here we report the first description of AML programming bone marrow adipocytes to generate a pro-tumoral microenvironment

The B-cell antigen receptor signals through a preformed transducer module of SLP65 and CIN85

The Slp65 adaptor molecule is important for B-cell receptor signalling. Here, the interactomes of SLP65 in resting and activated B cells are resolved by mass spectrometry. A number of SLP65 interacting partners, including CIN85, continuously associate with SLP65 in a stimulation-independent manner. CIN85 recruits SLP65 to the membrane and it is required for SLP65 phosphorylation

Drug-perturbation-based stratification of blood cancer

As new generations of targeted therapies emerge and tumor genome sequencing discovers increasingly comprehensive mutation repertoires, the functional relationships of mutations to tumor phenotypes remain largely unknown. Here, we measured ex vivo sensitivity of 246 blood cancers to 63 drugs alongside genome, transcriptome, and DNA methylome analysis to understand determinants of drug response. We assembled a primary blood cancer cell encyclopedia data set that revealed disease-specific sensitivities for each cancer. Within chronic lymphocytic leukemia (CLL), responses to 62% of drugs were associated with 2 or more mutations, and linked the B cell receptor (BCR) pathway to trisomy 12, an important driver of CLL. Based on drug responses, the disease could be organized into phenotypic subgroups characterized by exploitable dependencies on BCR, mTOR, or MEK signaling and associated with mutations, gene expression, and DNA methylation. Fourteen percent of CLLs were driven by mTOR signaling in a non-BCR-dependent manner. Multivariate modeling revealed immunoglobulin heavy chain variable gene (IGHV) mutation status and trisomy 12 as the most important modulators of response to kinase inhibitors in CLL. Ex vivo drug responses were associated with outcome. This study overcomes the perception that most mutations do not influence drug response of cancer, and points to an updated approach to understanding tumor biology, with implications for biomarker discovery and cancer care.Peer reviewe

SAMHD1 is a biomarker for cytarabine response and a therapeutic target in acute myeloid leukemia.

The nucleoside analog cytarabine (Ara-C) is an essential component of primary and salvage chemotherapy regimens for acute myeloid leukemia (AML). After cellular uptake, Ara-C is converted into its therapeutically active triphosphate metabolite, Ara-CTP, which exerts antileukemic effects, primarily by inhibiting DNA synthesis in proliferating cells. Currently, a substantial fraction of patients with AML fail to respond effectively to Ara-C therapy, and reliable biomarkers for predicting the therapeutic response to Ara-C are lacking. SAMHD1 is a deoxynucleoside triphosphate (dNTP) triphosphohydrolase that cleaves physiological dNTPs into deoxyribonucleosides and inorganic triphosphate. Although it has been postulated that SAMHD1 sensitizes cancer cells to nucleoside-analog derivatives through the depletion of competing dNTPs, we show here that SAMHD1 reduces Ara-C cytotoxicity in AML cells. Mechanistically, dGTP-activated SAMHD1 hydrolyzes Ara-CTP, which results in a drastic reduction of Ara-CTP in leukemic cells. Loss of SAMHD1 activity-through genetic depletion, mutational inactivation of its triphosphohydrolase activity or proteasomal degradation using specialized, virus-like particles-potentiates the cytotoxicity of Ara-C in AML cells. In mouse models of retroviral AML transplantation, as well as in retrospective analyses of adult patients with AML, the response to Ara-C-containing therapy was inversely correlated with SAMHD1 expression. These results identify SAMHD1 as a potential biomarker for the stratification of patients with AML who might best respond to Ara-C-based therapy and as a target for treating Ara-C-refractory AML

B Cell Receptor-Mediated Antigen Gathering Requires Ubiquitin Ligase Cbl and Adaptors Grb2 and Dok-3 to Recruit Dynein to the Signaling Microcluster

SummaryThe B cell receptor (BCR) mediates B cell antigen gathering and acquisition for presentation to T cells. Although the amount of antigen presentation to T cells determines the extent of B cell activation, the molecular mechanisms underlying antigen gathering remain unexplored. Here, through a combination of high-resolution imaging, genetics and quantitative mass spectrometry, we demonstrate that adaptors Grb2 and Dok-3, and ubiquitin ligase Cbl in signaling BCR microclusters mediate association with the microtubule motor dynein. Furthermore, we visualize the localization and movement of these microclusters on the underlying microtubule network. Importantly, disruption of this network or diminished dynein recruitment in Grb2-, Dok-3-, or Cbl-deficient B cells, does not influence microcluster formation or actin-dependent spreading, but abrogates directed movement of microclusters and antigen accumulation. Thus we identify a surprising but pivotal role for dynein and the microtubule network alongside Grb2, Dok-3, and Cbl in antigen gathering during B cell activation

Selective Inactivation of Cancer Drugs by SAMHD1 Provides a Molecular Rationale for Therapeutic Stratification in AML

Background: Nucleoside analog (NA) drugs are widely used to treat a variety of cancers, including acute myeloid leukemia (AML). With an essential role in regulating the cellular dNTP pool by degrading cellular nucleotides, SAMHD1 has the potential to decrease the cellular concentration of frequently prescribed NAs and thereby diminish their clinical efficacy in cancer therapy. Method: In this study, we used biochemical, structural, and cell based methods to examine the interaction of SAMHD1 with various AML cancer drugs, including cytarabine, cladribine, clofarabine, fludarabine, gemcitabine and the two DNA-hypomethylating agents (HMAs) decitabine and azacytidine. Results: We found that both the catalytic and the allosteric sites of SAMHD1 can bind NAs and that the SAMHD1 substrate specificity is regulated by 2′ sugar modifications of the nucleotide analogs. Cell culture, AML blasts and xenotransplantation models confirmed the crystallography findings that most of these drugs are affected by SAMHD1 activity, while some stay unaffected. In accordance with these data expression levels of SAMHD1 are correlating with survival parameters in patients treated with SAMHD1-dependent NAs. Conclusion: Taken together, these results establish SAMHD1 as a substrate-specific resistance factor that has promise as a predictive biomarker for drug stratification and a therapeutic target in nucleoside analog-based AML therapy. Conflict of interest: non

Oncogenic RAS commandeers amino acid sensing machinery to aberrantly activate mTORC1 in multiple myeloma

Oncogenic RAS mutations are common in multiple myeloma (MM), an incurable malignancy of plasma cells. However, the mechanisms of pathogenic RAS signaling in this disease remain enigmatic and difficult to inhibit therapeutically. We employ an unbiased proteogenomic approach to dissect RAS signaling in MM. We discover that mutant isoforms of RAS organize a signaling complex with the amino acid transporter, SLC3A2, and MTOR on endolysosomes, which directly activates mTORC1 by co-opting amino acid sensing pathways. MM tumors with high expression of mTORC1-dependent genes are more aggressive and enriched in RAS mutations, and we detect interactions between RAS and MTOR in MM patient tumors harboring mutant RAS isoforms. Inhibition of RAS-dependent mTORC1 activity synergizes with MEK and ERK inhibitors to quench pathogenic RAS signaling in MM cells. This study redefines the RAS pathway in MM and provides a mechanistic and rational basis to target this mode of RAS signaling. RAS mutations are commonly found in multiple myeloma (MM). Here, the authors show that oncogenic RAS mutations activate mTORC1 signalling in MM and combining mTORC1 and MEK/ERK inhibitors synergize to improve survival in preclinical models