Patryk Górniak

Role of 657del5 NBN mutation and 7p12.2 (IKZF1), 9p21 (CDKN2A), 10q21.2 (ARID5B) and 14q11.2 (CEBPE) variation and risk of childhood ALL in the Polish population.

Recent studies have shown that SNPs mapping to 7p12.2 (IKZF1), 9p21 (CDKN2A), 10q21.2 (ARID5B), and 14q11.2 (CEBPE) and carrier status for recessively inherited Nijmegen Breakage syndrome (NBS) influence childhood acute lymphoblastic leukemia (ALL) risk. To examine these relationship, we analysed 398 ALL cases and 731 controls from Poland. Statistically significant association between genotype at 7p12.2 (IKZF1), 10q21.2 (ARID5B) and the NBS associated locus, 8q21.3 (NBN) and ALL risk was found; odds ratios (ORs), 1.34 (P=0.002), 1.33 (P=0.003), and 1325.21 (P=0.0028), respectively. These data provide further insights into the biological basis of ALL highlighting the existence of both common and rare disease susceptibility variants.

FOXO1 activation is an effector of SYK and AKT inhibition in tonic BCR signal-dependent diffuse large B-cell lymphomas.

Inhibition of spleen tyrosine kinase (SYK) in tonic B-cell receptor (BCR) signal-dependent diffuse large B-cell lymphomas (DLBCLs) inhibits cellular proliferation, decreases cholesterol biosynthesis, and triggers apoptosis, at least in part via a mechanism involving decreased activity of phosphatidylinositol 3-kinase/AKT axis. Because forkhead box O1 (FOXO1) is a major effector of this pathway, we investigated the role of FOXO1 in toxicity of BCR pathway inhibition. Inhibition of SYK in DLBCL cells with tonic BCR signaling decreased phospho-AKT and phospho-FOXO1 levels and triggered FOXO1-driven gene expression. Introduction of constitutively active FOXO1 mutant triggered cell cycle arrest and apoptosis, indicating that increased FOXO1 activity is toxic to these DLBCL cells. Depletion of FOXO1 with short hairpin RNA led to almost complete resistance to chemical SYK inhibitor R406, demonstrating that FOXO1 is also required for R406-induced cell death. FOXO1 in these cells is also involved in regulation of expression of the critical master regulator of cholesterol biosynthesis, SREBP1. Because HRK is the key effector of SYK inhibition, we characterized a mechanism linking FOXO1 activation and HRK induction that involves caspase-dependent cleavage of HRKs transcriptional repressor DREAM. Because AKT in lymphoma cells can be regulated by other signals than BCR, we assessed the combined effects of the AKT inhibitor MK-2206 with R406 and found markedly synergistic FOXO1-dependent toxicity. In primary DLBCLs, FOXO1 expression was present in 80% of tumors, correlated with SYK activity, and was associated with longer overall survival. These results demonstrate that FOXO1 is required for SYK and AKT inhibitor-induced toxicity.

FOXO1 is a TXN- and p300-dependent sensor and effector of oxidative stress in diffuse large B-cell lymphomas characterized by increased oxidative metabolism

Molecular profiling has led to identification of subtypes of diffuse large B-cell lymphomas (DLBCLs) differing in terms of oncogenic signaling and metabolic programs. The OxPhos-DLBCL subtype is characterized by enhanced mitochondrial oxidative phosphorylation. As increased oxidative metabolism leads to overproduction of potentially toxic reactive oxygen species (ROS), we sought to identify mechanisms responsible for adaptation of OxPhos cells to these conditions. Herein, we describe a mechanism involving the FOXO1–TXN–p300 redox-dependent circuit protecting OxPhos-DLBCL cells from ROS toxicity. We identify a BCL6-dependent transcriptional mechanism leading to relative TXN overexpression in OxPhos cells. We found that OxPhos cells lacking TXN were uniformly more sensitive to ROS and doxorubicin than control cells. Consistent with this, the overall survival of patients with high TXN mRNA expression, treated with doxorubicin-containing regimens, is significantly shorter than of those with low TXN mRNA expression. TXN overexpression curtails p300-mediated FOXO1 acetylation and its nuclear translocation in response to oxidative stress, thus attenuating FOXO1 transcriptional activity toward genes involved in apoptosis and cell cycle inhibition. We also demonstrate that FOXO1 knockdown in cells with silenced TXN expression markedly reduces ROS-induced apoptosis, indicating that FOXO1 is the major sensor and effector of oxidative stress in OxPhos-DLBCLs. These data highlight dynamic, context-dependent modulation of FOXO1 tumor-suppressor functions via acetylation and reveal potentially targetable vulnerabilities in these DLBCLs.

Asparagine synthetase (ASNS) gene polymorphism is associated with the outcome of childhood acute lymphoblastic leukemia by affecting early response to treatment

The polymorphism of 14-bp tandem repeat sequence located in the ASNS gene probably acts as a transcriptional enhancer element and leads to higher expression of the gene in carriers of more than 2 repeats (>R2). We searched for an association with disease outcome in 264 children with ALL. A multivariate proportional hazard regression model adjusted for age at diagnosis (HR (95%CI)=1.05 (1.04-1.09)) and high-risk group (HR(95%CI)=3.47 (1.74-6.88)) revealed that R3 carriers with a poor response at day 15 had an increased risk of events, HR (95%CI)=2.72 (1.06-6.96). These results suggest a conditional interaction between the ASNS polymorphism and an early response to chemotherapy among pediatric patients with ALL.

Comparison of high‐resolution melting analysis with direct sequencing for the detection of recurrent mutations in DNA methyltransferase 3A and isocitrate dehydrogenase 1 and 2 genes in acute myeloid leukemia patients

Acute myeloid leukemia (AML) cells harbor frequent mutations in genes responsible for epigenetic modifications. Increasing evidence of clinical role of DNMT3A and IDH1/2 mutations highlights the need for a robust and inexpensive test to identify these mutations in routine diagnostic work‐up. Herein, we compared routinely used direct sequencing method with high‐resolution melting (HRM) assay for screening DNMT3A and IDH1/2 mutations in patients with AML. We show very high concordance between HRM and Sanger sequencing (100% samples for IDH2‐R140 and DNMT3‐R882 mutations, 99% samples for IDH1‐R132 and IDH2‐R172 mutations). HRM method reported no false‐negative results, suggesting that it can be used for mutations screening. Moreover, HRM displayed much higher sensitivity in comparison with DNA sequencing in all assessed loci. With Sanger sequencing, robust calls were observed when the sample contained 50% of mutant DNA in the background of wild‐type DNA. In marked contrast, the detection limit of HRM improved down to 10% of mutated DNA. Given the ubiquitous presence of wild‐type DNA background in bone marrow aspirates and clonal variations regarding mutant allele burden, these results favor HRM as a sensitive, specific, labor‐, and cost‐effective tool for screening and detection of mutations in IDH1/2 and DNMT3A genes in patients with AML.

MEK Inhibition Sensitizes Precursor B-Cell Acute Lymphoblastic Leukemia (B-ALL) Cells to Dexamethasone through Modulation of mTOR Activity and Stimulation of Autophagy.

Resistance to glucocorticosteroids (GCs) is a major adverse prognostic factor in B-ALL, but the molecular mechanisms leading to GC resistance are not completely understood. Herein, we sought to elucidate the molecular background of GC resistance in B-ALL and characterize the therapeutic potential of targeted intervention in these mechanisms. Using exploratory bioinformatic approaches, we found that resistant cells exhibited significantly higher expression of MEK/ERK (MAPK) pathway components. We found that GC-resistant ALL cell lines had markedly higher baseline activity of MEK and small-molecule MEK1/2 inhibitor selumetinib increased GCs-induced cell death. MEK inhibitor similarly increased in vitro dexamethasone activity in primary ALL blasts from 19 of 22 tested patients. To further confirm these observations, we overexpressed a constitutively active MEK mutant in GC-sensitive cells and found that forced MEK activity induced resistance to dexamethasone. Since recent studies highlight the role GC-induced autophagy upstream of apoptotic cell death, we assessed LC3 processing, MDC staining and GFP-LC3 relocalization in cells incubated with either DEX, SEL or combination of drugs. Unlike either drug alone, only their combination markedly increased these markers of autophagy. These changes were associated with decreased mTOR activity and blocked 4E-BP1 phosphorylation. In cells with silenced beclin-1 (BCN1), required for autophagosome formation, the synergy of DEX and SEL was markedly reduced. Taken together, we show that MEK inhibitor selumetinib enhances dexamethasone toxicity in GC-resistant B-ALL cells. The underlying mechanism of this interaction involves inhibition of mTOR signaling pathway and modulation of autophagy markers, likely reflecting induction of this process and required for cell death. Thus, our data demonstrate that modulation of MEK/ERK pathway is an attractive therapeutic strategy overcoming GC resistance in B-ALL patients.

Polymorphism in IKZF1 gene affects age at onset of childhood acute lymphoblastic leukemia

Abstract Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, characterized by a peak of incidence between 2 and 5 years. Since recently conducted genome-wide association (GWA) studies revealed that the common low-penetrance susceptibility allele at 7p12.2 (IKZF1 gene) confers an increased risk of pediatric ALL, we investigated whether the risk allele at rs4132601 also coexists with well-established prognostic factors, among 508 Polish pediatric patients with newly diagnosed ALL. Additionally, to verify whether the risk allele is favored by somatic tumor evolution, we examined the incidence of IKZF1 deletions in leukemic clones derived from 153 previously genotyped cases of pediatric ALL. Results of the analysis provide statistically significant support for an association between the rs4132601 polymorphic site and age at diagnosis of childhood ALL (p = 0.04). No association between allele variant and occurrence of IKZF1 deletions was found. These data provide further evidence of a biological role of gene variants in the development of ALL.

MiR-17-92 represses PTPROt and PP2A phosphatases and amplifies tonic BCR signaling in DLBCL cells.

B-cell receptor (BCR) signaling plays a pivotal role in the pathogenesis of diffuse large B-cell lymphoma (DLBCL) and targeting the BCR pathway is a highly promising therapeutic strategy in this malignancy. The oncogenic microRNA miR-17-92 modulates multiple cellular processes such as survival, proliferation, apoptosis, angiogenesis, and BCR signaling. In the present study, we identified new targets of miR-17-92, PTPROt (protein phosphatase, receptor type O, truncated) and PP2A (protein phosphatase 2A) phosphatases, which regulate the activity of spleen tyrosine kinase (SYK) and AKT, critical components of BCR signal transduction in DLBCL cells. Introduction of miR-17-92 into DLBCL cells dampened the expression of the PTPROt and PP2A regulatory subunits PPP2R2A (protein phosphatase 2, regulatory subunit B, alpha) and PPP2R5E (protein phosphatase 2, regulatory subunit B, epsilon isoform) and increased the magnitude of SYK and AKT phosphorylation upon BCR ligation. Finally, we found that miR-17-92 expression modulates response to inhibitors of BCR signaling because downregulation of miR-17-92 increased SYK inhibitor-mediated toxicity in DLBCL cells. Our study reveals novel posttranscriptional regulatory pathways that contribute to the deregulation of BCR signaling and modulate SYK inhibitor activity in DLBCL.

Microenvironment‐induced PIM kinases promote CXCR4‐triggered mTOR pathway required for chronic lymphocytic leukaemia cell migration

Lymph node microenvironment provides chronic lymphocytic leukaemia (CLL) cells with signals promoting their survival and granting resistance to chemotherapeutics. CLL cells overexpress PIM kinases, which regulate apoptosis, cell cycle and migration. We demonstrate that BCR crosslinking, CD40 stimulation, and coculture with stromal cells increases PIMs expression in CLL cells, indicating microenvironment‐dependent PIMs regulation. PIM1 and PIM2 expression at diagnosis was higher in patients with advanced disease (Binet C vs. Binet A/B) and in those, who progressed after first‐line treatment. In primary CLL cells, inhibition of PIM kinases with a pan‐PIM inhibitor, SEL24‐B489, decreased PIM‐specific substrate phosphorylation and induced dose‐dependent apoptosis in leukaemic, but not in normal B cells. Cytotoxicity of SEL24‐B489 was similar in TP53‐mutant and TP53 wild‐type cells. Finally, inhibition of PIM kinases decreased CXCR4‐mediated cell chemotaxis in two related mechanisms‐by decreasing CXCR4 phosphorylation and surface expression, and by limiting CXCR4‐triggered mTOR pathway activity. Importantly, PIM and mTOR inhibitors similarly impaired migration, indicating that CXCL12‐triggered mTOR is required for CLL cell chemotaxis. Given the microenvironment‐modulated PIM expression, their pro‐survival function and a role of PIMs in CXCR4‐induced migration, inhibition of these kinases might override microenvironmental protection and be an attractive therapeutic strategy in this disease.

Increased expression of E3 ubiquitin ligases targeting p53 in CLL patients with wild-type TP53 exhibits associations with clinical features of the disease.

Patryk Gorniak, Bozena Budziszewska, Bartosz Pula, Maja Wasylecka, Katarzyna Borg, Grazyna Nowak, Hanna Makuch-Lasica, Ewa Lech-Maranda, Krzysztof Warzocha and Przemyslaw Juszczynski Department of Diagnostic Hematology, Institute of Hematology and Transfusion Medicine, Warsaw, Poland; Department of Hematology, Institute of Hematology and Transfusion Medicine, Warsaw, Poland; Department of Hematology and Transfusion Medicine, Centre of Postgraduate Medical Education, Warsaw, Poland