ETNK1 mutations induce a mutator phenotype that can be reverted with phosphoethanolamine

Recurrent somatic mutations in ETNK1 (Ethanolamine-Kinase-1) were identified in several myeloid malignancies and are responsible for a reduced enzymatic activity. Here, we demonstrate in primary leukemic cells and in cell lines that mutated ETNK1 causes a significant increase in mitochondrial activity, ROS production, and Histone H2AX phosphorylation, ultimately driving the increased accumulation of new mutations. We also show that phosphoethanolamine, the metabolic product of ETNK1, negatively controls mitochondrial activity through a direct competition with succinate at mitochondrial complex II. Hence, reduced intracellular phosphoethanolamine causes mitochondria hyperactivation, ROS production, and DNA damage. Treatment with phosphoethanolamine is able to counteract complex II hyperactivation and to restore a normal phenotype.

Pro-inflammatory cytokines favor the emergence of ETV6-RUNX1-positive pre-leukemic cells in a model of mesenchymal niche

ETV6-RUNX1 (E/R) fusion gene, arising in utero from translocation t(12;21)(p13:q22), is the most frequent alteration in childhood acute lymphoblastic leukemia (ALL). However, E/R is insufficient to cause overt leukemia since it generates a clinically silent pre-leukemic clone which persists in the bone marrow but fails to out-compete normal progenitors. Conversely, pre-leukemic cells show increased susceptibility to transformation following additional genetic insults. Infections/inflammation are the most accredited triggers for mutations accumulation and leukemic transformation in E/R⁺ pre-leukemic cells. However, precisely how E/R and inflammation interact in promoting leukemia is still poorly understood. Here we demonstrate that IL6/TNFα/ILβ pro-inflammatory cytokines cooperate with BM-MSC in promoting the emergence of E/R⁺ Ba/F3 over their normal counterparts by differentially affecting their proliferation and survival. Moreover, IL6/TNFα/ILβ-stimulated BM-MSC strongly attract E/R⁺ Ba/F3 in a CXCR2-dependent manner. Interestingly, E/R-expressing human CD34⁺ IL7R⁺ progenitors, a putative population for leukemia initiation during development, were preserved in the presence of BM-MSC and IL6/TNFα/ILβ compared to their normal counterparts. Finally, the extent of DNA damage increases within the inflamed niche in both control and E/R-expressing Ba/F3, potentially leading to transformation in the apoptosis-resistant pre-leukemic clone. Overall, our data provide new mechanistic insights into childhood ALL pathogenesis.

Daily Onset of Light and Darkness Differentially Controls Hematopoietic Stem Cell Differentiation and Maintenance

Hematopoietic stem and progenitor cells (HSPCs) tightly couple maintenance of the bone marrow (BM) reservoir, including undifferentiated long-term repopulating hematopoietic stem cells (LT-HSCs), with intensive daily production of mature leukocytes and blood replenishment. We found two daily peaks of BM HSPC activity that are initiated by onset of light and darkness providing this coupling. Both peaks follow transient elevation of BM norepinephrine and TNF secretion, which temporarily increase HSPC reactive oxygen species (ROS) levels. Light-induced norepinephrine and TNF secretion augments HSPC differentiation and increases vascular permeability to replenish the blood. In contrast, darkness-induced TNF increases melatonin secretion to drive renewal of HSPCs and LT-HSC potential through modulating surface CD150 and c-Kit expression, increasing COX-2/αSMA+ macrophages, diminishing vascular permeability, and reducing HSPC ROS levels. These findings reveal that light- and darkness-induced daily bursts of norepinephrine, TNF, and melatonin within the BM are essential for synchronized mature blood cell production and HSPC pool repopulation.

Abstract 3385: ETNK1 mutations promote ROS production and DNA damage through increased mitochondrial activity

Atypical chronic myeloid leukemia (aCML) is a clonal disorder belonging to the myelodysplastic/myeloproliferative syndromes. About 13% of aCML cases carry somatic mutations in ETNK1 gene, encoding for H243Y, N244S, and G245V substitutions. We previously showed that ETNK1 mutations cause a decreased catalytic activity of the enzyme. Despite this evidence however, their oncogenic role remained largely unexplained. Since ETNK1 activity is essential for the synthesis of phosphatidylethanolamine (PE) and given that PE is one of the most abundant phospholipids in the inner membrane of mitochondria, we focused our attention on mitochondrial activity. In order to characterize the oncogenic effect of ETNK1 variants we generated CRISPR/Cas9 clones carrying heterozygous N244S mutation and homozygous ETNK1 deletion (KO cells) on the 293 Flp-In™ cell-line. Both N244S and KO cells showed a significant increase in mitochondrial activity (1.78 and 2.13 fold increase, respectively; p= 0.0096 and p=0.0050) compared to WT, as assessed by MitoTracker™ Red. In line with this finding, electron microscopy revealed a significant modification in mitochondria morphology for N244S and KO cells, changing from an elongated, tubular shape to a round, swollen one. ATP (1.67 and 1.68 fold; p<0.0001; ATPlite Luminescence Assay System) and ROS production (1.66 and 1.74 fold increase; p<0.0001; CellROX™ Green Reagent) were similarly increased. Histone H2AX phosphorylation (γ-H2AX) analysis revealed a higher number of foci in N244S and KO cells (2.60±0.22 and 2.89±0.27; p<0.0001) compared to WT (0.56±0.08). A similar increase in γ-H2AX (3.6 fold; p=0.0037) was present in primary samples from aCML patients carrying ETNK1 mutation compared to ETNK1-WT ones.

In line with these data, a higher mutation rate was detected in N244S and KO cells (8.09*10-7±9.6*10-8 and 8.20*10-7±1.28*10-7; p=0.0060 and p=0.0264) compared to WT (2.98*10-7±8.2*10-8) by 6-thioguanine assay.

The reconstruction of the hierarchy of somatic mutations in ETNK1-mutated aCML patients revealed that ETNK1 variants invariably occur very early in the evolution history of the aCML patients.

Taken together, our results show that impairment of ETNK1 function causes an increase in mitochondrial activity, which in turn leads to increased ROS production driving the accumulation of DNA mutations. Since the characterization of aCML subclonal architecture indicates ETNK1 mutations as a very early event in the history of the disease, we hypothesize that ETNK1 could contribute to the onset of aCML through the activation of a mutant phenotype, which in turn would accelerate the accumulation of further oncogenic mutations.

Citation Format: Diletta Fontana, Mario Mauri, Antonio Niro, Luca Massimino, Mayla Bertagna, Giovanni Zambrotta, Mario Bossi, Stefania Citterio, Barbara Crescenzi, Giovanni Signore, Vincenzo Piazza, Cristina Mecucci, Guido Cavaletti, Delphine Rea, Carlo Gambacorti-Passerini, Rocco Piazza. ETNK1 mutations promote ROS production and DNA damage through increased mitochondrial activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3385.

Cutaneous Side-effects of Immunomodulators in MS

Local skin reactions to subcutaneous injections of interferon beta (IFNB) or glatiramer acetate (GA) in multiple sclerosis (MS) are frequent, while severe cutaneous toxicity is rare. Both IFNB and GA are immunomodulatory drugs that have excellent safety profiles and are currently used for treatment of MS. They are administered by SC injection every other day for IFNB-1b, three times a week for IFNB-1a or daily for 20 mg for GA. The most common adverse effects, which occur in approximately 20-60% of patients, include pain, inflammation and induration at the injection sites. Another adverse effect is frank panniculitis followed by localized lipoatrophy at the injection sites, which has been described in half of the patients receiving GA injections but is also described with Subcutaneous IFNB-1b. No guidelines have yet been established for the treatment of skin reactions, which is a frequent point for discussion between neurologists and dermatologists. In addition, no treatment has been found for established lipoatrophy. The prevention and management of cutaneous side-effects include patient education, regular examination and manual palpation of all injection sites. Non-steroid antiinflammatory gels, local corticosteroids or endermology can help patients to resolve side-effects and to continue immunomodulatory treatment.