An important mediator of cytokine signaling implicated in regulation of hematopoiesis is the PI3K/protein kinase B (PKB/c-Akt) signaling module. Constitutive activation of this signaling module has ...been observed in a large group of leukemias. Because activation of this signaling pathway has been demonstrated to be sufficient to induce hematologic malignancies and is thought to correlate with poor prognosis and enhanced drug resistance, it is considered to be a promising target for therapy. A high number of pharmacologic inhibitors directed against either individual or multiple components of this pathway have already been developed to improve therapy. In this review, the safety and efficacy of both single and dual-specificity inhibitors will be discussed as well as the potential of combination therapy with either inhibitors directed against other signal transduction molecules or classic chemotherapy.
Hematopoietic stem cell transplantation is the most powerful treatment modality for a large number of hematopoietic malignancies, including leukemia. Successful hematopoietic recovery after ...transplantation depends on homing of hematopoietic stem cells to the bone marrow and subsequent lodging of those cells in specific niches in the bone marrow. Migration of hematopoietic stem cells to the bone marrow is a highly regulated process that requires correct regulation of the expression and activity of various molecules including chemoattractants, selectins and integrins. This review will discuss recent studies that have extended our understanding of the molecular mechanisms underlying adhesion, migration and bone marrow homing of hematopoietic stem cells.
Translocation t(12;21), resulting in the ETV6-RUNX1 (or TEL-AML1) fusion protein, is present in 25% of pediatric patients with B-cell precursor acute lymphoblastic leukemia and is considered a first ...hit in leukemogenesis. A targeted therapy approach is not available for children with this subtype of leukemia. To identify the molecular mechanisms underlying ETV6-RUNX1-driven leukemia, we performed gene expression profiling of healthy hematopoietic progenitors in which we ectopically expressed ETV6-RUNX1. We reveal an ETV6-RUNX1-driven transcriptional network that induces proliferation, survival and cellular homeostasis. In addition, Vps34, an important regulator of autophagy, was found to be induced by ETV6-RUNX1 and up-regulated in ETV6-RUNX1-positive leukemic patient cells. We show that induction of Vps34 was transcriptionally regulated by ETV6-RUNX1 and correlated with high levels of autophagy. Knockdown of Vps34 in ETV6-RUNX1-positive cell lines severely reduced proliferation and survival. Inhibition of autophagy by hydroxychloroquine, a well-tolerated autophagy inhibitor, reduced cell viability in both ETV6-RUNX1-positive cell lines and primary acute lymphoblastic leukemia samples, and selectively sensitized primary ETV6-RUNX1-positive leukemia samples to L asparaginase. These findings reveal a causal relationship between ETV6-RUNX1 and autophagy, and provide pre-clinical evidence for the efficacy of autophagy inhibitors in ETV6-RUNX1-driven leukemia.
The cellular targets of primary mutations and malignant transformation remain elusive in most cancers. Here, we show that clinically and genetically different subtypes of acute lymphoblastic leukemia ...(ALL) originate and transform at distinct stages of hematopoietic development. Primary ETV6-RUNX1 (also known as TEL-AML1) fusions and subsequent leukemic transformations were targeted to committed B-cell progenitors. Major breakpoint BCR-ABL1 fusions (encoding P210 BCR-ABL1) originated in hematopoietic stem cells (HSCs), whereas minor BCR-ABL1 fusions (encoding P190 BCR-ABL1) had a B-cell progenitor origin, suggesting that P190 and P210 BCR-ABL1 ALLs represent largely distinct tumor biological and clinical entities. The transformed leukemia-initiating stem cells in both P190 and P210 BCR-ABL1 ALLs had, as in ETV6-RUNX1 ALLs, a committed B progenitor phenotype. In all patients, normal and leukemic repopulating stem cells could successfully be separated prospectively, and notably, the size of the normal HSC compartment in ETV6-RUNX1 and P190 BCR-ABL1 ALLs was found to be unaffected by the expansive leukemic stem cell population.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Bone marrow homeostasis is controlled by a series of complex cell fate decisions that determine whether hematopoietic stem and progenitor cells divide, differentiate or die. Exquisite control of the ...stem cell niche is crucial for the correct maintenance of blood cell production, allowing inductive external signals to modulate stem cell self-renewal or increased production of specific blood cell lineages. Since the first bone marrow transplantation more than 40 years ago, research has been focused on understanding the molecular processes regulating hematopoietic stem cell function. While our appreciation of the transcriptional regulators of hematopoiesis has developed considerably, the role of specific intracellular signal transduction modules remains surprisingly undefined. One such module includes phosphatidylinostiol 3-kinase (PI3K) and protein kinase B (PKB/c-akt). The identification and cloning of PI3K and PKB in the early 1990s has resulted in the publication of a large body of literature providing evidence for a crucial role of these molecules in the regulation of proliferation, apoptosis and differentiation. This review will focus on recent studies that have extended our understanding of how PI3K-PKB can regulate the complex process of hematopoiesis.
An interstitial deletion on chromosome 4q12 resulting in the formation of the FIP1L1-PDGFRA fusion protein is involved in the pathogenesis of imatinib-sensitive chronic eosinophilic leukemia. The ...molecular mechanisms underlying the development of disease are largely undefined. Human CD34(+) hematopoietic progenitor cells were used to investigate the role of FIP1L1-PDGFRA in modulating lineage development. FIP1L1-PDGFRA induced both proliferation and differentiation of eosinophils, neutrophils, and erythrocytes in the absence of cytokines, which could be inhibited by imatinib. Whereas expression of FIP1L1-PDGFRA in hematopoietic stem cells and common myeloid progenitors induced the formation of multiple myeloid lineages, expression in granulocyte-macrophage progenitors induced only the development of eosinophils, neutrophils, and myeloblasts. Deletion of amino acids 30 to 233 in the FIP1L1 gene FIP1L1(1-29)-PDGFRA gave rise to an intermediate phenotype, exhibiting a dramatic reduction in the number of erythrocytes. FIP1L1-PDGFRA and FIP1L1(1-29)-PDGFRA both induced the activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) in myeloid progenitors, whereas signal transducers and activators of transcription 5 (STAT5) and protein kinase B/c-akt were only activated by FIP1L1-PDGFRA. Dominant-negative STAT5 partially inhibited FIP1L1-PDGFRA-induced colony formation, whereas combined inhibition of phosphatidylinositol-3-kinase and ERK1/2 significantly reversed FIP1L1-PDGFRA-induced colony formation. Taken together, these results suggest that expression of FIP1L1-PDFGRA in human hematopoietic progenitors induce a myeloproliferative phenotype via activation of multiple signaling molecules including phosphatidylinositol-3-kinase, ERK1/2, and STAT5.
Dendritic cells (DCs) are composed of different subsets that exhibit distinct functionality in the induction and regulation of immune responses. The myeloid DC subsets, including interstitial DCs and ...Langerhans cells (LCs), develop from CD34+ hematopoietic progenitors via direct DC precursors or monocytes. The molecular mechanisms regulating DC development are still largely unknown and mostly studied in mice. Phosphatidylinositol 3-kinase (PI3K) regulates multiple processes in myeloid cells. This study investigated the role of PI3K signaling in the development of human CD34-derived myeloid DCs. Pharmacologic inhibition of PI3K or one of its downstream targets mTOR reduced interstitial DC and LC numbers in vitro. Increased activity of this signaling module by introduction of constitutively active protein kinase B (PKB/c-Akt) increased the yields of human DC precursors in vitro as well as in transplanted beta2-microglobulin-/- NOD/SCID mice in vivo. Signaling inhibition during differentiation did not affect the acquisition of a DC phenotype, whereas proliferation and survival strongly depended on intact PI3K-PKB-mTOR signaling. Interestingly, however, this pathway became redundant for survival regulation upon terminal differentiation, which was associated with an altered expression of apoptosis regulating genes. Although dispensable for costimulatory molecule expression, the PI3K-PKB-mTOR signaling module was required for other important processes associated with DC function, including Ag uptake, LPS-induced cytokine secretion, CCR7 expression, and T cell stimulation. Thus, PI3K-PKB-mTOR signaling plays a crucial role in the development of functional CD34-derived myeloid DCs. These findings could be used as a strategy to manipulate DC subset distribution and function to regulate immunity.
The clinical use of chromatin-modulating drugs, such as histone deacetylase inhibitors, for the treatment of bone marrow failure and hematopoietic malignancies has increased dramatically over the ...last few years. Nonetheless, little is currently known concerning their effects on myelopoiesis.
We utilized an ex vivo differentiation system in which umbilical cord blood-derived CD34(+) cells were treated with trichostatin A, sodium butyrate and valproic acid to evaluate the effect of histone deacetylase inhibitor treatment on myeloid lineage development, colony-forming potential, proliferation, and terminal neutrophil differentiation.
Trichostatin A treatment modestly reduced progenitor proliferation, while sodium butyrate and valproic acid resulted in concentration-dependent effects on proliferation and apoptosis. Addition of valproic acid uniquely stimulated CD34(+) proliferation. Sodium butyrate treatment inhibited terminal neutrophil differentiation both quantitatively and qualitatively. Addition of 100 microM valproic acid resulted in increased numbers of mature neutrophils with a block in differentiation at increasing concentrations. Sodium butyrate and valproic acid treatment resulted in increased acetylation of histones 3 and 4 while trichostatin A, sodium butyrate and valproic acid had differential effects on the acetylation of non-histone proteins.
Individual histone deacetylase inhibitors had specific effects on cell fate decisions during myeloid development. These data provide novel insights into the effects of histone deacetylase inhibitors on the regulation of normal hematopoiesis, which is of importance when considering utilizing these compounds for the treatment of myeloid malignancies and bone marrow failure syndromes.
Signal transducer and activator of transcription 5 (STAT5) activity is induced by a plethora of cytokines and growth factors resulting in transcriptional activation of specific target genes. STAT5 ...plays an important role in a variety of cellular processes, including proliferation, differentiation, and apoptosis. Aberrant regulation of STAT5 has been observed in solid tumors as well as in patients with either chronic or acute myeloid leukemia. Kinase inhibitors are currently being developed to negatively regulate STAT5 activity for clinical purposes.
Hematopoiesis is a highly regulated process resulting in the formation of all blood lineages. Aberrant regulation of phosphatidylinositol-3-kinase (PI3K) signaling has been observed in hematopoietic ...malignancies, suggesting that regulated PI3K signaling is critical for regulation of blood cell production. An ex vivo differentiation system was used to investigate the role of PI3K and its downstream effector, protein kinase B (PKB/c-akt) in myelopoiesis. PI3K activity was essential for hematopoietic progenitor survival. High PKB activity was found to promote neutrophil and monocyte development, while, conversely, reduction of PKB activity was required to induce optimal eosinophil differentiation. In addition, transplantation of β2-microglobulin (−/−) NOD/SCID mice with CD34+ cells ectopically expressing constitutively active PKB resulted in enhanced neutrophil and monocyte development, whereas ectopic expression of dominant-negative PKB induced eosinophil development in vivo. Inhibitory phosphorylation of C/EBPα on Thr222/226 was abrogated upon PKB activation in hematopoietic progenitors. Ectopic expression of a nonphosphorylatable C/EBPα mutant inhibited eosinophil differentiation ex vivo, whereas neutrophil development was induced, demonstrating the importance of PKB-mediated C/EBPα phosphorylation in regulation of granulopoiesis. These results identify an important novel role for PKB in regulation of cell fate choices during hematopoietic lineage commitment.
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