Patogeneza nowotworów układu chłonnego

Lymphocyte development is a complex and multistep process that leads to generation of a repertoire of cells endowed with specific receptors and capable of recognizing and responding to antigens. The B- (BCR) and T-cell (TCR) receptors are generated as a result of immunoglobulin or TCR gene re­arrangements that involve DNA double strand breaks. The DNA editing processes occurring in de­veloping lymphocytes predispose cells to primary translocations and oncogenic mutations, followed by additional aberrations accumulating in the background of these primary lesions. Arising typical, recurrent genetic abnormalities are a diagnostic feature of certain lymphoid malignancies. Genetic and epigenetic lesions accumulating within cells lead to deregulated signaling pathways and un­controlled cell proliferation, resistance to apoptosis and metabolic changes. Transformed cells retain some features of their normal counterparts, such as reliance on tonic BCR signaling and signals delivered by microenvironment. In the current manuscript, we provide a concise review of common pathogenic mechanisms in lymphoid tumors and their biological implications.Limfopoeza to złożony proces fizjologiczny, którego celem jest stworzenie repertuaru komórek ze swoistymi receptorami zdolnymi do odpowiedzi na antygeny. Powstanie receptora B-komórkowego (BCR) lub T-komórkowego (TCR) następuje wskutek rearanżacji genów immunoglobulinowych lub genów TCR, zachodzących z udziałem reakcji obejmujących powstanie podwójnych pęknięć DNA. Procesy edycji DNA BCR i TCR predysponują limfocyty do nabywania translokacji i mutacji o charakterze onkogennym stanowiących tło dla akumulacji kolejnych zaburzeń. Aberracje gene­tyczne to częsty mechanizm patogenetyczny i w związku z tym są jednym z kryteriów diagnostycz­nych nowotworów układu chłonnego. Konsekwencją genetycznych nieprawidłowości jest zaburzenie aktywności układów sygnałowych i kluczowych funkcji biologicznych, takich jak cykl komórkowy, apoptoza i metabolizm. Stransformowane komórki zachowują niektóre z cech swoich prawidłowych odpowiedników, na przykład zależność od tonicznego sygnału BCR i zdolność do interakcji z ich naturalnym mikrośrodowiskiem, stanowiącym źródło sygnałów wspierających wzrost nowotworu. W niniejszej pracy przedstawiono najistotniejsze i najczęstsze mechanizmy patogenezy nowotworów układu chłonnego oraz ich biologiczne konsekwencje

Zaburzenia mechanizmów epigenetycznych w ostrej białaczce szpikowej

Epigenetic regulation influences gene expression without changing the nucleotide sequence of the deoxyribonucleic acid (DNA). The most important epigenetic mechanisms include DNA methylation, modifications of histone proteins and non-coding RNAs. The dysregulation of the above mentioned processes plays a significant role in the pathogenesis of acute myeloid leukemia (AML). Mutations in the genes that are essential for epigenetic regulations are common in 70% of patients with AML. The most frequent mutations involve the DNMT3A, TET2, IDH1/2 and ASXL1 genes. Their presence or absence may constitute a vital prognostic factor in the future as well as become a potential basis for targeted therapies. The present paper manifests the importance of epigenetic alterations in the development of acute myeloid leukemia and their impact on the course of the disease. The article also discusses some possibilities for the use of epigenetic modifications in the AML therapy.Regulacja epigenetyczna wpływa na ekspresję genów, nie zmieniając zapisu sekwencji nukleo­tydowej kwasu deoksyrybonukleinowego (DNA). Mechanizmy epigenetyczne obejmują zmiany struktury chromatyny wskutek metylacji DNA i modyfikacji białek histonowych oraz regulację ekspresji genów poprzez niekodujące cząsteczki kwasu rybonukleinowego. Nieprawidłowy przebieg powyższych procesów odgrywa istotną rolę w patogenezie ostrej białaczki szpikowej (AML). Mutacje genów kodujących regulatory epigenetyczne występują u 70% chorych z AML i najczęściej dotyczą genów DNMT3A, TET2, IDH1/2 oraz ASXL1. Obecność lub brak mutacji w wymienionych ge­nach może stanowić w przyszłości ważny czynnik prognostyczny oraz potencjalny punkt uchwytu dla terapii celowanych. W poniższym artykule omówiono znaczenie zaburzeń epigenetycznych w rozwoju AML, ich wpływ na przebieg choroby oraz możliwość wykorzystania w terapii

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

<div><p>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 <i>in vitro</i> 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.</p></div

Primer sequences used for MEK1 mutagenesis.

<p>Primer sequences used for MEK1 mutagenesis.</p

Serine biosynthesis pathway supports MYC-miR-494-EZH2 feed-forward circuit necessary to maintain metabolic and epigenetic reprogramming of burkitt lymphoma cells

Burkitt lymphoma (BL) is a rapidly growing tumor, characterized by high anabolic requirements. The MYC oncogene plays a central role in the pathogenesis of this malignancy, controlling genes involved in apoptosis, proliferation, and cellular metabolism. Serine biosynthesis pathway (SBP) couples glycolysis to folate and methionine cycles, supporting biosynthesis of certain amino acids, nucleotides, glutathione, and a methyl group donor, S-adenosylmethionine (SAM). We report that BLs overexpress SBP enzymes, phosphoglycerate dehydrogenase (PHGDH) and phosphoserine aminotransferase 1 (PSAT1). Both genes are controlled by the MYC-dependent ATF4 transcription factor. Genetic ablation of PHGDH/PSAT1 or chemical PHGDH inhibition with NCT-503 decreased BL cell lines proliferation and clonogenicity. NCT-503 reduced glutathione level, increased reactive oxygen species abundance, and induced apoptosis. Consistent with the role of SAM as a methyl donor, NCT-503 decreased DNA and histone methylation, and led to the re-expression of ID4, KLF4, CDKN2B and TXNIP tumor suppressors. High H3K27me3 level is known to repress the MYC negative regulator miR-494. NCT-503 decreased H3K27me3 abundance, increased the miR-494 level, and reduced the expression of MYC and MYC-dependent histone methyltransferase, EZH2. Surprisingly, chemical/genetic disruption of SBP did not delay BL and breast cancer xenografts growth, suggesting the existence of mechanisms compensating the PHGDH/PSAT1 absence in vivo

Schematic diagram showing a postulated mechanism of MEK inhibition—induced sensitization to GCs via modulation of autophagy.

<p>Schematic diagram showing a postulated mechanism of MEK inhibition—induced sensitization to GCs via modulation of autophagy.</p

Overexpression of a constitutively active MEK1 mutant (MEK-Q56P) in GC-sensitive RS4;11 cells induces resistance to DEX.

<p>(A) RS4;11 cells were retrovirally transduced with MEK-Q56P or empty control. Cells were lysed and ERK1/2 phoshorylation status was assessed by immunoblotting. (B-C) Control cells and MEK-Q56P—transduced cells were incubated with DEX (0.05, 2 or 30 μg/ml) for 72h. Thereafter, cell death was assessed by annexinV/PI staining and flow cytometry analysis. Absolute, averaged numbers of apoptotic cells in two independent experiments are indicated in (C). Error bars represent SD. P value was calculated using Student’s t-test.</p

BCN1 knockdown reduces SEL-mediated sensitization to DEX.

<p>(A) SEMK2 cells were retrovirally transduced with BCN1-specific shRNA or scrambled control (SCR). After selection of stable transfectants, BCN1 knockdown was confirmed by western blot. (B,C) Cells with BCN1 knockdown or control cells were incubated with DEX, (0.05 μg/ml or 2 μg/ml) in the presence or absence of MEK1/2 inhibitor, selumetinib (SEL, 200 nM) for 72h. Apoptosis was assessed by annexinV/PI staining followed by flow cytometry analysis. Representative dot-plots from FACS analysis are shown in B; averaged results from 3 independent experiments with SD are indicated in (C) Statistical difference in responses between mock- and shBCN1-transduced cells were determined using 2-sided Student’s t-test. (D) Beclin-1 expression in cells treated with DEX, SEL or their combination. SEMK2 cells were incubated for 24 h with DEX (0.05 μg/ml), SEL (200 nM) or combination of DEX+SEL and BCN1 expression level was assessed by western blot.</p