Cell cycle regulators and hematopoiesis

A comprehensive review of computational cell cycle models in guiding cancer treatment strategies

This article reviews the current knowledge and recent advancements in computational modeling of the cell cycle. It offers a comparative analysis of various modeling paradigms, highlighting their unique strengths, limitations, and applications. Specifically, the article compares deterministic and stochastic models, single-cell versus population models, and mechanistic versus abstract models. This detailed analysis helps determine the most suitable modeling framework for various research needs. Additionally, the discussion extends to the utilization of these computational models to illuminate cell cycle dynamics, with a particular focus on cell cycle viability, crosstalk with signaling pathways, tumor microenvironment, DNA replication, and repair mechanisms, underscoring their critical roles in tumor progression and the optimization of cancer therapies. By applying these models to crucial aspects of cancer therapy planning for better outcomes, including drug efficacy quantification, drug discovery, drug resistance analysis, and dose optimization, the review highlights the significant potential of computational insights in enhancing the precision and effectiveness of cancer treatments. This emphasis on the intricate relationship between computational modeling and therapeutic strategy development underscores the pivotal role of advanced modeling techniques in navigating the complexities of cell cycle dynamics and their implications for cancer therapy.

Autophagy Inhibition-induced Cytosolic DNA Sensing Combined with Differentiation Therapy Induces Irreversible Myeloid Differentiation in Leukemia Cells

Accumulating evidence indicates that various oncogenic mutations interfere with normal myeloid differentiation of leukemogenic cells during the early process of acute myeloid leukemia (AML) development. Differentiation therapy is a therapeutic strategy capable of terminating leukemic expansion by reactivating the differentiation potential; however, the plasticity and instability of leukemia cells counteract the establishment of treatments aimed at irreversibly inducing and maintaining their differentiation states. On the basis of our previous observation that autophagy inhibitor treatment induces the accumulation of cytosolic DNA and activation of cytosolic DNA-sensor signaling selectively in leukemia cells, we herein examined the synergistic effect of cytosolic DNA-sensor signaling activation with conventional differentiation therapy on AML. The combined treatment succeeded in inducing irreversible differentiation in AML cell lines. Mechanistically, cytosolic DNA was sensed by absent in melanoma 2 (AIM2), a cytosolic DNA sensor. Activation of the AIM2 inflammasome resulted in the accumulation of p21 through the inhibition of its proteasomal degradation, thereby facilitating the myeloid differentiation. Importantly, the combined therapy dramatically reduced the total leukemia cell counts and proportion of blast cells in the spleens of AML mice. Collectively, these findings indicate that the autophagy inhibition-cytosolic DNA-sensor signaling axis can potentiate AML differentiation therapy.

SIGNIFICANCE

Clinical effects on AML therapy are closely associated with reactivating the normal myeloid differentiation potential in leukemia cells. This study shows that autophagosome formation inhibitors activate the cytosolic DNA-sensor signaling, thereby augmenting conventional differentiation therapy to induce irreversible differentiation and cell growth arrest in several types of AML cell lines.

Cone photoreceptor phosphodiesterase PDE6H inhibition regulates cancer cell growth and metabolism, replicating the dark retina response

BACKGROUND

PDE6H encodes PDE6γ', the inhibitory subunit of the cGMP-specific phosphodiesterase 6 in cone photoreceptors. Inhibition of PDE6, which has been widely studied for its role in light transduction, increases cGMP levels. The purpose of this study is to characterise the role of PDE6H in cancer cell growth.

METHODS

From an siRNA screen for 487 genes involved in metabolism, PDE6H was identified as a controller of cell cycle progression in HCT116 cells. Role of PDE6H in cancer cell growth and metabolism was studied through the effects of its depletion on levels of cell cycle controllers, mTOR effectors, metabolite levels, and metabolic energy assays. Effect of PDE6H deletion on tumour growth was also studied in a xenograft model.

RESULTS

PDE6H knockout resulted in an increase of intracellular cGMP levels, as well as changes to the levels of nucleotides and key energy metabolism intermediates. PDE6H knockdown induced G1 cell cycle arrest and cell death and reduced mTORC1 signalling in cancer cell lines. Both knockdown and knockout of PDE6H resulted in the suppression of mitochondrial function. HCT116 xenografts revealed that PDE6H deletion, as well as treatment with the PDE5/6 inhibitor sildenafil, slowed down tumour growth and improved survival, while sildenafil treatment did not have an additive effect on slowing the growth of PDE6γ'-deficient tumours.

CONCLUSIONS

Our results indicate that the changes in cGMP and purine pools, as well as mitochondrial function which is observed upon PDE6γ' depletion, are independent of the PKG pathway. We show that in HCT116, PDE6H deletion replicates many effects of the dark retina response and identify PDE6H as a new target in preventing cancer cell proliferation and tumour growth.

CgTNF-2 promotes the proliferation of haemocytes by regulating the expressions of CgRunx and cell cycle related genes in the Pacific oyster Crassostrea gigas

A TNF-α family member, CgTNF-2, was previously identified from the oyster Crassostrea gigas to involve in the antibacterial response. In the present study, the role of CgTNF-2 in mediating the proliferation of haemocytes was further explored. The mRNA expression of CgTNF-2 in granulocytes was significantly higher than that in semi-granulocytes and agranulocytes, and the percentages of CgTNF-2 antibody labeled cells in agranulocytes, semi-granulocytes and granulocytes were 19.15%, 40.25% and 94.07%, respectively. After the treatment with rCgTNF-2, the percentage of EdU⁺ cells in haemocytes increased significantly (1.77-fold, p < 0.05) at 6 h compared with that in rGST-treated group, and the mRNA expressions of CgRunx, CgCyclin A, CgCDK2 and CgCDC45 in haemocytes all increased significantly (p < 0.05), which were 1.94-fold, 2.13-fold, 1.97-fold, 1.76-fold of that in rGST-treated group, respectively. Meanwhile, the protein abundance of CgRunx and CgCyclin A in the haemocytes of oysters in the rCgTNF-2-treated group increased, and the percentage of PI⁺ haemocytes in S phase also increased significantly (2.19-fold, p < 0.05) compared with that in rGST-treated group. These results collectively confirmed that CgTNF-2 was highly expressed in granulocytes and involved in the proliferation of haemocytes by regulating the expressions of CgRunx and cell cycle related genes in C. gigas.

Efficient terminal erythroid differentiation requires the APC/C cofactor Cdh1 to limit replicative stress in erythroblasts

The APC/C-Cdh1 ubiquitin ligase complex drives proteosomal degradation of cell cycle regulators and other cellular proteins during the G1 phase of the cycle. The complex serves as an important modulator of the G1/S transition and prevents premature entry into S phase, genomic instability, and tumor development. Additionally, mounting evidence supports a role for this complex in cell differentiation, but its relevance in erythropoiesis has not been addressed so far. Here we show, using mouse models of Cdh1 deletion, that APC/C-Cdh1 activity is required for efficient terminal erythroid differentiation during fetal development as well as postnatally. Consistently, Cdh1 ablation leads to mild but persistent anemia from birth to adulthood. Interestingly, loss of Cdh1 seems to affect both, steady-state and stress erythropoiesis. Detailed analysis of Cdh1-deficient erythroid populations revealed accumulation of DNA damage in maturing erythroblasts and signs of delayed G2/M transition. Moreover, through direct assessment of replication dynamics in fetal liver cells, we uncovered slow fork movement and increased origin usage in the absence of Cdh1, strongly suggesting replicative stress to be the underlying cause of DNA lesions and cell cycle delays in erythroblasts devoid of Cdh1. In turn, these alterations would restrain full maturation of erythroblasts into reticulocytes and reduce the output of functional erythrocytes, leading to anemia. Our results further highlight the relevance of APC/C-Cdh1 activity for terminal differentiation and underscore the need for precise control of replication dynamics for efficient supply of red blood cells.

Troglitazone inhibits hepatic oval cell proliferation by inducing cell cycle arrest through Hippo/YAP pathway regulation

Hepatic oval cells have strong proliferation and differentiation capabilities and are activated when chronic liver injury occurs or when liver function is severely impaired. Peroxisome proliferation-activated receptors (PPARs) are ligand-dependent, sequence-specific nuclear transcription factors. PPARγ is closely related to liver diseases (such as liver cancer, liver fibrosis and non-alcoholic fatty liver disease). As the main effector downstream of the Hippo signaling pathway, YAP can activate the hepatic progenitor cell program, and different expression or activity levels of YAP can determine different liver cell fates. We found that troglitazone (TRO), a classic PPARγ activator, can inhibit the growth of hepatic oval cells, and flow cytometry results showed that TRO inhibited the growth of WB-F344 cells by arresting the cells in the G_0/1 phase. Western blot results also confirmed changes in G_0/1 phase-related protein expression. Further experiments showed that PPARγ agonists induced hepatic oval cell proliferation inhibition and cell cycle G_0/1 phase arrest through the Hippo/YAP pathway. Our experiment demonstrated, for the first time, the relationship between PPARγ and the Hippo/YAP pathway in liver oval cells and revealed that PPARγ acts as a negative regulator of liver regeneration by inhibiting the proliferation of oval cells.

INTS11 regulates hematopoiesis by promoting PRC2 function

INTS11, the catalytic subunit of the Integrator (INT) complex, is crucial for the biogenesis of small nuclear RNAs and enhancer RNAs. However, the role of INTS11 in hematopoietic stem and progenitor cell (HSPC) biology is unknown. Here, we report that INTS11 is required for normal hematopoiesis and hematopoietic-specific genetic deletion of Ints11 leads to cell cycle arrest and impairment of fetal and adult HSPCs. We identified a novel INTS11-interacting protein complex, Polycomb repressive complex 2 (PRC2), that maintains HSPC functions. Loss of INTS11 destabilizes the PRC2 complex, decreases the level of histone H3 lysine 27 trimethylation (H3K27me3), and derepresses PRC2 target genes. Reexpression of INTS11 or PRC2 proteins in Ints11-deficient HSPCs restores the levels of PRC2 and H3K27me3 as well as HSPC functions. Collectively, our data demonstrate that INTS11 is an essential regulator of HSPC homeostasis through the INTS11-PRC2 axis.

Small molecule-mediated modulation of ubiquitination and neddylation improves HSC function ex vivo

Hematopoietic stem cells (HSCs) are particularly characterized by their quiescence and self-renewal. Cell cycle regulators tightly control quiescence and self-renewal capacity. Studies suggest that modulation of ubiquitination and neddylation could contribute to HSC function via cyclin-dependent kinase inhibitors (CDKIs). S-phase kinase-associated protein 2 (SKP2) is responsible for ubiquitin-mediated proteolysis of CDKIs. Here, we modulated overall neddylation and SKP2-associated ubiquitination in HSCs by using SKP2-C25, an SKP2 inhibitor, and MLN4924 (Pevonedistat) as an inhibitor of the NEDD8 system. Treatments of SKP2-C25 and MLN4924 increased both murine and human stem and progenitor cell (HSPC) compartments. This is associated with the improved quiescence of murine HSC by upregulation of p27 and p57 CDKIs. A colony-forming unit assay showed an enhanced in vitro self-renewal potential post inhibition of ubiquitination and neddylation. In addition, MLN4924 triggered the mobilization of bone marrow HSPCs to peripheral blood. Intriguingly, MLN4924 treatment could decrease the proliferation of murine bone marrow mesenchymal stem cells or endothelial cells. These findings shed light on the contribution of SKP2, and associated ubiquitination and neddylation in HSC maintenance, self-renewal, and expansion.

LIGHT/LTβR signaling regulates self-renewal and differentiation of hematopoietic and leukemia stem cells

The production of blood cells during steady-state and increased demand depends on the regulation of hematopoietic stem cell (HSC) self-renewal and differentiation. Similarly, the balance between self-renewal and differentiation of leukemia stem cells (LSCs) is crucial in the pathogenesis of leukemia. Here, we document that the TNF receptor superfamily member lymphotoxin-β receptor (LTβR) and its ligand LIGHT regulate quiescence and self-renewal of murine and human HSCs and LSCs. Cell-autonomous LIGHT/LTβR signaling on HSCs reduces cell cycling, promotes symmetric cell division and prevents primitive HSCs from exhaustion in serial re-transplantation experiments and genotoxic stress. LTβR deficiency reduces the numbers of LSCs and prolongs survival in a murine chronic myeloid leukemia (CML) model. Similarly, LIGHT/LTβR signaling in human G-CSF mobilized HSCs and human LSCs results in increased colony forming capacity in vitro. Thus, our results define LIGHT/LTβR signaling as an important pathway in the regulation of the self-renewal of HSCs and LSCs.

Cell cycle dynamics in the reprogramming of cellular identity

Reprogramming of cellular identity is fundamentally at odds with replication of the genome: cell fate reprogramming requires complex multidimensional epigenomic changes, whereas genome replication demands fidelity. In this review, we discuss how the pace of the genome's replication and cell cycle influences the way daughter cells take on their identity. We highlight several biochemical processes that are pertinent to cell fate control, whose propagation into the daughter cells should be governed by more complex mechanisms than simple templated replication. With this mindset, we summarize multiple scenarios where rapid cell cycle could interfere with cell fate copying and promote cell fate reprogramming. Prominent examples of cell fate regulation by specific cell cycle phases are also discussed. Overall, there is much to be learned regarding the relationship between cell fate reprogramming and cell cycle control. Harnessing cell cycle dynamics could greatly facilitate the derivation of desired cell types.

Genetically engineered drug rhCNB induces apoptosis and cell cycle arrest in both gastric cancer cells and hepatoma cells

Objectives

Calcineurin B (CNB) is a regulatory subunit of calcineurin, and it has antitumor activity. In this study, we aimed to investigate the effect of recombinant human calcineurin B (rhCNB) on the proliferation of gastric cancer cells and hepatoma cells both in vitro and in vivo.

Materials and methods

Cell viability and cell proliferation were detected by MTT and BrdU assay. Flow cytometry, Western blot and immunohistochemistry were performed to determine rhCNB-induced apoptosis and cell cycle arrest. The antitumor activities of rhCNB were observed in mice tumor models.

Results

We demonstrated that rhCNB inhibits the proliferation of gastric cancer cells and hepatoma cells both in vitro and in vivo. We showed that the inhibition of cell proliferation by rhCNB is associated with apoptosis and cell cycle arrest in both tumor cell lines. Furthermore, we indicated that rhCNB promotes p53 protein expression, a potent proapoptotic factor. Meanwhile, we also exhibited that rhCNB decreases the expression of both cyclin B1 and CDK1 proteins, two proteins associated with G₂/M arrest.

Conclusion

Together, these findings suggest that rhCNB markedly inhibits tumor growth and provides guidance for its drug development.

Integrated Systems Biology Approach Identifies Novel Maternal and Placental Pathways of Preeclampsia

Preeclampsia is a disease of the mother, fetus, and placenta, and the gaps in our understanding of the complex interactions among their respective disease pathways preclude successful treatment and prevention. The placenta has a key role in the pathogenesis of the terminal pathway characterized by exaggerated maternal systemic inflammation, generalized endothelial damage, hypertension, and proteinuria. This sine qua non of preeclampsia may be triggered by distinct underlying mechanisms that occur at early stages of pregnancy and induce different phenotypes. To gain insights into these molecular pathways, we employed a systems biology approach and integrated different "omics," clinical, placental, and functional data from patients with distinct phenotypes of preeclampsia. First trimester maternal blood proteomics uncovered an altered abundance of proteins of the renin-angiotensin and immune systems, complement, and coagulation cascades in patients with term or preterm preeclampsia. Moreover, first trimester maternal blood from preterm preeclamptic patients in vitro dysregulated trophoblastic gene expression. Placental transcriptomics of women with preterm preeclampsia identified distinct gene modules associated with maternal or fetal disease. Placental "virtual" liquid biopsy showed that the dysregulation of these disease gene modules originates during the first trimester. In vitro experiments on hub transcription factors of these gene modules demonstrated that DNA hypermethylation in the regulatory region of ZNF554 leads to gene down-regulation and impaired trophoblast invasion, while BCL6 and ARNT2 up-regulation sensitizes the trophoblast to ischemia, hallmarks of preterm preeclampsia. In summary, our data suggest that there are distinct maternal and placental disease pathways, and their interaction influences the clinical presentation of preeclampsia. The activation of maternal disease pathways can be detected in all phenotypes of preeclampsia earlier and upstream of placental dysfunction, not only downstream as described before, and distinct placental disease pathways are superimposed on these maternal pathways. This is a paradigm shift, which, in agreement with epidemiological studies, warrants for the central pathologic role of preexisting maternal diseases or perturbed maternal-fetal-placental immune interactions in preeclampsia. The description of these novel pathways in the "molecular phase" of preeclampsia and the identification of their hub molecules may enable timely molecular characterization of patients with distinct preeclampsia phenotypes.

The genetic and molecular pathogenesis of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) comprise a diverse group of clonal and malignant myeloid disorders characterized by ineffective hematopoiesis, resultant peripheral cytopenias, and a meaningful increased risk of progression to acute myeloid leukemia. A wide array of recurring genetic mutations involved in RNA splicing, histone manipulation, DNA methylation, transcription factors, kinase signaling, DNA repair, cohesin proteins, and other signal transduction elements has been identified as important substrates for the development of MDS. Cytogenetic abnormalities, namely those characterized by loss of genetic material (including 5q- and 7q-), have also been strongly implicated and may influence the clonal architecture which predicts such mutations and may provoke an inflammatory bone marrow microenvironment as the substrate for clonal expansion. Other aspects of the molecular pathogenesis of MDS continue to be further elucidated, predicated upon advances in gene expression profiling and the development of new, and improved high-throughput techniques. More accurate understanding of the genetic and molecular basis for the development of MDS directly provides additional opportunity for treatment, which to date remains limited. In this comprehensive review, we examine the current understanding of the molecular pathogenesis and pathophysiology of MDS, as well as review future prospects which may enhance this understanding, treatment strategies, and hopefully outcomes.

The cyclin-dependent kinase 2 (CDK2) mediates hematopoiesis through G1-to-S transition in Chinese mitten crab Eriocheir sinensis

Cyclin-dependent kinases (CDKs), a family of cell cycle-related serine/threonine kinases, participate in various biological processes, and play crucial roles in the innate immunity. In the present study, a CDK2 (designed as EsCDK2) with a serine/threonine protein kinase catalytic domain was identified from Chinese mitten crab (Eriocheir sinensis). The full-length cDNA sequence of EsCDK2 was of 2405 bp with an open reading frame (ORF) of 909 bp. EsCDK2 shared 66%-81% sequence similarities with previously identified CDK2s. It was clustered with the CDK2 from Penaeus monodon in the invertebrate branch of the phylogenetic tree. The mRNA transcripts of EsCDK2 were highly expressed in hematopoietic tissue (HPT) and gonad, while lower in hemocytes, heart, gills, and muscle. EsCDK2 protein distributed in both cytoplasm and nucleus of HPT cells. The expression of EsCDK2 mRNA in HPT was significantly up-regulated and peaked at 3 h post stimulations with Aeromonas hydrophila (2.31-fold, p < 0.05) and Lipopolysaccharide (LPS) (2.02-fold, p < 0.05). After exsanguination, the total hemocyte counts (THC) decreased significantly to 0.42 × 10⁷/ml (0.39-fold, p < 0.05) at 0.5 h, then returned to a normal level at 6 h, while the mRNA expression of EsCDK2 in HPT cells was up-regulated at the early phase from 0.5 h to 6 h. After injection of EsCDK2-dsRNA, the mRNA expression level of EsCDK2 in HPT and THC both decreased to 0.53-fold (p < 0.01) and 0.78-fold (p < 0.05) at 24 h, respectively, and the percentage of new-born hemocytes in HPT also decreased significantly from 37.7% to 16.3% (0.43-fold, p < 0.01). After knocking down of EsCDK2, THC decreased dramatically at 6 h (0.65-fold, p < 0.01) post exsanguination, while returned normal at 6 h in PBS group. After interference of EsCDK2 mRNA expression, the percentage of G0-G1 phase cells significantly increased to 85.01% (1.26-fold, p < 0.01), while S phase and G2-M phase cells significantly decreased to 7.92% (0.46-fold, p < 0.01) and 7.07% (0.43-fold, p < 0.01) respectively, indicating that the cell cycle of HPT cells arrested at G1 phase. These results collectively demonstrated that EsCDK2 participated in the regeneration of hemocytes or hematopoiesis by regulating the transition from G1 to S phase in the cell cycle, and involves in the innate immune responses of E. sinensis.

Long-Term Hematopoietic Engraftment of Congenic Amniotic Fluid Stem Cells After in Utero Intraperitoneal Transplantation to Immune Competent Mice

Clinical success of in utero transplantation (IUT) using allogeneic hematopoietic stem cells (HSCs) has been limited to fetuses that lack an immune response to allogeneic cells due to severe immunological defects, and where transplanted genetically normal cells have a proliferative or survival advantage. Amniotic fluid (AF) is an autologous source of stem cells with hematopoietic potential that could be used to treat congenital blood disorders. We compared the ability of congenic and allogeneic mouse AF stem cells (AFSC) to engraft the hematopoietic system of time-mated C57BL/6J mice (E13.5). At 4 and 16 weeks of age, multilineage donor engraftment was higher in congenic versus allogeneic animals. In vitro mixed lymphocyte reaction confirmed an immune response in the allogeneic group with higher CD4 and CD8 cell counts and increased proliferation of stimulated lymphocytes. IUT with congenic cells resulted in 100% of donor animals having chimerism of around 8% and successful hematopoietic long-term engraftment in immune-competent mice when compared with IUT with allogeneic cells. AFSCs may be useful for autologous cell/gene therapy approaches in fetuses diagnosed with congenital hematopoietic disorders.

Various Signaling Pathways in Multiple Myeloma Cells and Effects of Treatment on These Pathways

Multiple myeloma (MM) results from malignancy in plasma cells and occurs at ages > 50 years. MM is the second most common hematologic malignancy after non-Hodgkin lymphoma, which constitutes 1% of all malignancies. Despite the great advances in the discovery of useful drugs for this disease such as dexamethasone and bortezomib, it is still an incurable malignancy owing to the development of drug resistance. The tumor cells develop resistance to apoptosis, resulting in greater cell survival, and, ultimately, develop drug resistance by changing the various signaling pathways involved in cell proliferation, survival, differentiation, and apoptosis. We have reviewed the different signaling pathways in MM cells. We reached the conclusion that the most important factor in the drug resistance in MM patients is caused by the bone marrow microenvironment with production of adhesion molecules and cytokines. Binding of tumor cells to stromal cells prompts cytokine production of stromal cells and launches various signaling pathways such as Janus-activated kinase/signal transduction and activator of transcription, Ras/Raf/MEK/mitogen-activated protein kinase, phosphatidyl inositol 3-kinase/AKT, and NF-KB, which ultimately lead to the high survival rate and drug resistance in tumor cells. Thus, combining various drugs such as bortezomib, dexamethasone, lenalidomide, and melphalan with compounds that are not common, including CTY387, LLL-12, OPB31121, CNTO328, OSI-906, FTY720, triptolide, and AV-65, could be one of the most effective treatments for these patients.

The downregulation of c-Myc and its target gene hTERT is associated with the antiproliferative effects of baicalin on HL-60 cells

Baicalin is a flavonoid compound isolated from Scutellaria baicalensis, a Chinese traditional medicinal herb, and is used as an anti-inflammatory, antibacterial, anxiolytic and hepatoprotective drug. Accumulating evidence has demonstrated that baicalin exhibits potent antitumor properties by suppressing cell growth, arresting cell cycle progression and inducing differentiation or apoptosis in leukemia cell lines. However, whether or not the extrinsic pathway is involved in baicalin-induced apoptosis of leukemia cells and the mechanisms underlying the antitumor activity of baicalin remain unclear. In the present study, the effect of baicalin on the expression of caspase-8, Fas cell surface death receptor (Fas) and Fas ligand in HL-60 cells was assessed, and it was demonstrated that the Fas-mediated extrinsic pathway was also involved in baicalin-triggered cell apoptosis, in addition to the intrinsic pathway. Furthermore, baicalin was able to inhibit the proliferation of HL-60 cells by arresting the cell cycle at the G₀/G₁ phase, and by down-regulating Myc proto-oncogene protein (c-Myc) along with its target gene, human telomerase reverse transcriptase. In summary, the results of the present study demonstrated that baicalin was able to inhibit the growth of HL-60 cells through blockade of the G₀/G₁ phase of the cell cycle, and significantly induce the apoptosis of cells by activating the intrinsic and extrinsic pathways. The inhibition of HL-60 cell growth was also demonstrated to be mediated by telomerase inhibition through suppression of c-Myc. The results of the present study highlight the possibility of baicalin as a promising regimen for the treatment of AML.

A Novel Glycogen Synthase Kinase-3 Inhibitor Optimized for Acute Myeloid Leukemia Differentiation Activity

Standard therapies used for the treatment of acute myeloid leukemia (AML) are cytotoxic agents that target rapidly proliferating cells. Unfortunately, this therapeutic approach has limited efficacy and significant toxicity and the majority of AML patients still die of their disease. In contrast to the poor prognosis of most AML patients, most individuals with a rare subtype of AML, acute promyelocytic leukemia, can be cured by differentiation therapy using regimens containing all-trans retinoic acid. GSK3 has been previously identified as a therapeutic target in AML where its inhibition can lead to the differentiation and growth arrest of leukemic cells. Unfortunately, existing GSK3 inhibitors lead to suboptimal differentiation activity making them less useful as clinical AML differentiation agents. Here, we describe the discovery of a novel GSK3 inhibitor, GS87. GS87 was discovered in efforts to optimize GSK3 inhibition for AML differentiation activity. Despite GS87's dramatic ability to induce AML differentiation, kinase profiling reveals its high specificity in targeting GSK3 as compared with other kinases. GS87 demonstrates high efficacy in a mouse AML model system and unlike current AML therapeutics, exhibits little effect on normal bone marrow cells. GS87 induces potent differentiation by more effectively activating GSK3-dependent signaling components including MAPK signaling as compared with other GSK3 inhibitors. GS87 is a novel GSK3 inhibitor with therapeutic potential as a differentiation agent for non-promyelocytic AML. Mol Cancer Ther; 15(7); 1485-94. ©2016 AACR.

Defective endomitosis during megakaryopoiesis leads to thrombocytopenia in Fanca-/- mice

Fanconi anemia (FA) is an inherited chromosomal instability syndrome that is characterized by progressive bone marrow failure. One of the main causes of morbidity and mortality in FA is a bleeding tendency, resulting from low platelet counts. Platelets are the final products of megakaryocyte (MK) maturation. Here, we describe a previously unappreciated role of Fanconi anemia group A protein (Fanca) during the endomitotic process of MK differentiation. Fanca deficiency leads to the accumulation of MKs with low nuclear ploidy and to decreased platelet production. We show, for the first time, that Fanca(-/-) mice are characterized by limited number and proliferative capacity of MK progenitors. Defective megakaryopoiesis of Fanca(-/-) cells is associated with the formation of nucleoplasmic bridges and increased chromosomal instability, indicating that inaccurate endoreplication and karyokinesis occur during MK polyploidization. Sustained DNA damage forces Fanca(-/-) MKs to enter a senescence-like state. Furthermore, inhibition of the Rho-associated kinase, a regulator of cytokinesis, improves the polyploidization of Fanca(-/-) MKs but greatly increases their genomic instability and diminishes their differentiation potential, supporting the notion that accumulation of DNA damage through endomitotic cycles affects MK maturation. Our study indicates that Fanca expression during endomitosis is crucial for normal megakaryopoiesis and platelet production.

Conditional and inducible transgene expression in endothelial and hematopoietic cells using Cre/loxP and tetracycline-off systems

In the present study, the tetracycline-off and Cre/loxP systems were combined to gain temporal and spatial control of transgene expression. Mice were generated that carried three transgenes: Tie2-tTA, tet-O-Cre and either the ZEG or ZAP reporter. Tie2-tTA directs expression of tetracycline-controlled transactivator (tTA) in endothelial and hematopoietic cells under the control of the Tie2 promoter. Tet-O-Cre produces Cre recombinase from a minimal promoter containing the tet-operator (tetO). ZEG or ZAP contains a strong promoter and a loxP-flanked stop sequence, followed by an enhanced green fluorescence protein (EGFP) or human placental alkaline phosphatase (hPLAP) reporter. In the presence of tetracycline, the tTA transactivator produced by Tie-2-tTA is disabled and Cre is not expressed. In the absence of tetracycline, the tTA binds tet-O-Cre to drive the expression of Cre, which recombines the loxP sites of the ZEG or ZAP transgene and results in reporter gene expression. In the present study, the expression of the ZEG or ZAP reporter genes in embryos and adult animals with and without tetracycline treatment was examined. In the presence of tetracycline, no reporter gene expression was observed. When tetracycline was withdrawn, Cre excision was activated and the reporter genes were detected in endothelial and hematopoietic cells. These results demonstrate that this system may be used to bypass embryonic lethality and access adult phenotypes.

A molecular signaling map and its application

Cancer research over the past decades has revealed a number of molecular, biochemical, and cellular events that reflect progressive transformation of normal human cells into their malignant derivatives. These findings help to better understand the complexity of human tumorigenesis. In our study, molecular information is organized to chart a comprehensive map of the signaling network for human cancer. It includes transcriptional and translational regulation and diverse feedback-control loops. It is demonstrated that applying this signaling network map allows predicting the effect of targeted therapy before it can be applied into practice to reduce clinical trial risks. Hence, the proposed map with prognosticating potential effect might become part of drug discovery programs for targeted therapy. Applied in individual patient care it helps to reduce the current reliance of cancer treatment on chemotherapies with low therapeutic indices. This study also demonstrates that continuing elucidation of tumorigenesis will not only need heterotypic organ culture systems in vitro and increasingly refined animal models in vivo, but also computationally calculable virtual cell models in silico.

Postnatal Notch1 activation induces T‑cell malignancy in conditional and inducible mouse models

The Notch1 signaling pathway is essential for hematopoietic development. However, the effects of postnatal activation of Notch1 signaling on hematopoietic system is not yet fully understood. We previously generated ZEG‑IC‑Notch1 transgenic mice that have a floxed β‑geo/stop signal between a CMV promoter and intracellular domain of Notch1 (IC‑Notch1). Constitutively active IC‑Notch1 is silent until the introduction of Cre recombinase. In this study, endothelial/hematopoietic specific expression of IC‑Notch1 in double transgenic ZEG‑IC‑Notch1/Tie2‑Cre embryos induced embryonic lethality at E9.5 with defects in vascular system but not in hematopoietic system. Inducible IC‑Notch1 expression in adult mice was achieved by using tetracycline regulated Cre system. The ZEG‑IC‑Notch1/Tie2‑tTA/tet‑O‑Cre triple transgenic mice survived embryonic development when maintained on tetracycline. Post‑natal withdrawal of tetracycline induced expression of IC‑Notch1 transgene in hematopoietic cells of adult mice. The triple transgenic mice displayed extensive T‑cell infiltration in multiple organs and T‑cell malignancy of lymph nodes. In addition, the protein levels of p53 and alternative reading frame (ARF) were decreased in lymphoma‑like neoplasms from the triple transgenic mice while their mRNA expression remained unchanged, suggesting that IC‑Notch1 might repress ARF‑p53 pathway by a post‑transcriptional mechanism. This study demonstrated that activation of constitutive Notch1 signaling after embryonic development alters adult hematopoiesis and induces T‑cell malignancy.

Inactivation of Rb and E2f8 synergizes to trigger stressed DNA replication during erythroid terminal differentiation

Rb is critical for promoting cell cycle exit in cells undergoing terminal differentiation. Here we show that during erythroid terminal differentiation, Rb plays a previously unappreciated and unorthodox role in promoting DNA replication and cell cycle progression. Specifically, inactivation of Rb in erythroid cells led to stressed DNA replication, increased DNA damage, and impaired cell cycle progression, culminating in defective terminal differentiation and anemia. Importantly, all of these defects associated with Rb loss were exacerbated by the concomitant inactivation of E2f8. Gene expression profiling and chromatin immunoprecipitation (ChIP) revealed that Rb and E2F8 cosuppressed a large array of E2F target genes that are critical for DNA replication and cell cycle progression. Remarkably, inactivation of E2f2 rescued the erythropoietic defects resulting from Rb and E2f8 deficiencies. Interestingly, real-time quantitative PCR (qPCR) on E2F2 ChIPs indicated that inactivation of Rb and E2f8 synergizes to increase E2F2 binding to its target gene promoters. Taken together, we propose that Rb and E2F8 collaborate to promote DNA replication and erythroid terminal differentiation by preventing E2F2-mediated aberrant transcriptional activation through the ability of Rb to bind and sequester E2F2 and the ability of E2F8 to compete with E2F2 for E2f-binding sites on target gene promoters.

Enhancement of baicalin by hexamethylene bisacetamide on the induction of apoptosis contributes to simultaneous activation of the intrinsic and extrinsic apoptotic pathways in human leukemia cells

Hexamethylene bisacetamide (HMBA) and natural flavanoid baicalin both exert potent antileukemic activity. However, there is currently no data on the anti-leukemic effects of baicalin in combination with HMBA. In the present study, we demonstrated that the combination of baicalin and HMBA synergistically inhibited the proliferation of acute myeloid leukemia (AML) cell lines. In addition, a slight G0/G1 phase arrest and significant apoptosis were observed. The combination treatment triggered apoptosis through the intrinsic pathway, which involved loss of MMP, decreased Bcl‑2/Bax ratio and Bcl‑XL/Bax ratio, caspase‑9 activation, as well as through the extrinsic pathway mediated by Fas and caspase‑8 activation. On the other hand, combination of baicalin and HMBA showed little toxic effect on peripheral blood mononuclear cells from healthy volunteers. Our results raise the possibility that the novel combination of baicalin and HMBA may be a promising regimen for the treatment of AML.

The nucleotide sugar UDP-glucose mobilizes long-term repopulating primitive hematopoietic cells

Hematopoietic stem progenitor cells (HSPCs) are present in very small numbers in the circulating blood in steady-state conditions. In response to stress or injury, HSPCs are primed to migrate out of their niche to peripheral blood. Mobilized HSPCs are now commonly used as stem cell sources due to faster engraftment and reduced risk of posttransplant infection. In this study, we demonstrated that a nucleotide sugar, UDP-glucose, which is released into extracellular fluids in response to stress, mediates HSPC mobilization. UDP-glucose-mobilized cells possessed the capacity to achieve long-term repopulation in lethally irradiated animals and the ability to differentiate into multi-lineage blood cells. Compared with G-CSF-mobilized cells, UDP-glucose-mobilized cells preferentially supported long-term repopulation and exhibited lymphoid-biased differentiation, suggesting that UDP-glucose triggers the mobilization of functionally distinct subsets of HSPCs. Furthermore, co-administration of UDP-glucose and G-CSF led to greater HSPC mobilization than G-CSF alone. Administration of the antioxidant agent NAC significantly reduced UDP-glucose-induced mobilization, coinciding with a reduction in RANKL and osteoclastogenesis. These findings provide direct evidence demonstrating a potential role for UDP-glucose in HSPC mobilization and may provide an attractive strategy to improve the yield of stem cells in poor-mobilizing allogeneic or autologous donors.

Positive feedback between PU.1 and the cell cycle controls myeloid differentiation

Regulatory gene circuits with positive-feedback loops control stem cell differentiation, but several mechanisms can contribute to positive feedback. Here, we dissect feedback mechanisms through which the transcription factor PU.1 controls lymphoid and myeloid differentiation. Quantitative live-cell imaging revealed that developing B cells decrease PU.1 levels by reducing PU.1 transcription, whereas developing macrophages increase PU.1 levels by lengthening their cell cycles, which causes stable PU.1 accumulation. Exogenous PU.1 expression in progenitors increases endogenous PU.1 levels by inducing cell cycle lengthening, implying positive feedback between a regulatory factor and the cell cycle. Mathematical modeling showed that this cell cycle-coupled feedback architecture effectively stabilizes a slow-dividing differentiated state. These results show that cell cycle duration functions as an integral part of a positive autoregulatory circuit to control cell fate.

Interleukin-5 enhances the migration and invasion of bladder cancer cells via ERK1/2-mediated MMP-9/NF-κB/AP-1 pathway: involvement of the p21WAF1 expression

Inflammatory cytokines may be a critical component of epithelial cancer progression. We examined the role of interleukin (IL)-5 in the migration of bladder cancer cells. The expression of IL-5 and its receptor IL-5Rα was enhanced in patients with muscle invasive bladder cancers (MIBC), and then it was detected in bladder cancer cell lines 5637 and T-24. IL-5 increased migration and MMP-9 expression via activation of transcription factors NF-κB and AP-1, and induced activation of ERK1/2 and Jak-Stat signaling in both cells. Treatment with ERK1/2 inhibitor U0126 significantly inhibited induction of migration, MMP-9 expression, and activation of NF-κB and AP-1 in IL-5-treated cells. However, none of the Jak inhibitors affected the IL-5-induced migration of bladder cancer cells. Moreover, gene knockdown for IL-5Rα, using siRNA transfection, suppressed migration, ERK1/2 activation, MMP-9 expression, as well as the binding activation of NF-κB and AP-1 in IL-5-treated bladder cancer cells. Similar results were observed in βc siRNA (si-βc) transfected cells. Unexpectedly, IL-5 treatment resulted in significant induction of p21WAF1 in both cell lines. The p21WAF1-specific small interfering RNA inhibited IL-5-induced cell migration, ERK activity, MMP-9 expression, and activation of NF-κB and AP-1 in bladder cancer cells. The effects of IL-5-induced cell responses were confirmed by transfection of IL-5 gene, which demonstrated that p21WAF1 participates in the induction of cell migration, leading to an increase in ERK1/2-mediated MMP-9 expression through activation of NF-κB and AP-1 in IL-5-treated bladder cancer cells. These unexpected results provide a theoretical basis for the therapeutic targeting of IL-5 in bladder cancer.

Investigational cell cycle inhibitors in clinical trials for bladder cancer

INTRODUCTION

Cancer-related cell cycle defects are often mediated by alterations in activity of diverse cell cycle regulators. The development of cell cycle inhibitors has undergone a gradual evolution, and new investigational drugs have been extensively tested as a single agent or combination with conventional chemotherapeutic drugs.

AREAS COVERED

This review covers a broad perspective of how the cell cycle is deregulated in bladder cancer and discusses the clinical trials of cell cycle inhibitors.

EXPERT OPINION

Although diverse cell cycle inhibitors have been considered as relevant drug candidates for cancer therapy owing to their potential role in restoring control of the cell cycle, these inhibitors have not been yet widely tested in human bladder cancer. Numerous studies already reported that deregulation of cell cycle controls has been commonly observed in bladder cancer cells, thus warranting clinical trials of these inhibitors in advanced bladder cancer patients. In addition, nonmuscle invasive bladder cancer (NMIBC) and muscle invasive bladder cancer (MIBC) show different clinical and molecular biological characteristics, although ∼ 10 - 20% of NMIBC will progress to MIBC. Therefore, adequate cell cycle inhibitors have to be chosen for bladder cancer treatment based on the different genetic features between NMIBC and MIBC related to cell cycle regulators.

Tetramethylpyrazine potentiates arsenic trioxide activity against HL-60 cell lines

The objective of this study was to evaluate the effects of tetramethylpyrazine (TMP) in combination with arsenic trioxide (As2O3) on the proliferation and differentiation of HL-60 cells. The HL-60 cells were treated with 300 µg/mL TMP, 0.5 µM As2O3, and 300 µg/mL TMP combined with 0.5 µM As2O3, respectively. The proliferative inhibition rates were determined with MTT. Differentiation was detected by the nitroblue tetrazolium (NBT) reduction test, Wright's staining and the distribution of CD11b and CD14. Flow cytometry was used to analyze cell cycle distribution. RT-PCR and Western blot assays were employed to detect the expressions of c-myc, p27, CDK2, and cyclin E1. Combination treatment had synergistic effects on the proliferative inhibition rates. The rates were increased gradually after the combination treatment, much higher than those treated with the corresponding concentration of As2O3 alone. The cells exhibited characteristics of mature granulocytes and a higher NBT-reducing ability, being a 2.6-fold increase in the rate of NBT-positive ratio of HL-60 cells within the As2O3 treatment versus almost a 13-fold increase in the TMP + As2O3 group. Cells treated with both TMP and As2O3 expressed far more CD11b antigens, almost 2-fold compared with the control group. Small doses of TMP potentiate As2O3-induced differentiation of HL-60 cells, possibly by regulating the expression and activity of G0/G1 phase-arresting molecules. Combination treatment of TMP with As2O3 has significant synergistic effects on the proliferative inhibition of HL-60 cells.

Cyclin dependent kinase inhibitors differentially modulate synergistic cytokine responsiveness of hematopoietic progenitor cells

Cyclin dependent kinase inhibitors (CDKIs) influence proliferation of hematopoietic progenitor cells (HPCs), but little is known of how they influence proliferative responsiveness of HPCs to colony stimulating factors (CSFs), alone and in combination with other hematopoietically active factors, such as the potent co-stimulating cytokine stem cell factor (SCF), or inhibition by myelosuppressive chemokines. Using mice with deletions in p18(INK4c), p21(CIP1/WAF1), or p27(KIP1) genes, and in mice with double gene deletions for either p18/p21 or p18/p27, we determined effects of absence of these CDKIs and their interactions on functional HPC numbers in vivo, and HPC proliferative responsiveness in vitro. There is a decrease in bone marrow HPC proliferation in p18(-/-) mice commensurate with decreased numbers of HPC, suggesting a positive role for p18 on HPC in vivo, similar to that for p21. These positive effects of p18 dominate negative effects of p27 gene deletion. Moreover, the CDKIs differentially regulate responsiveness of granulocyte macrophage (GM) progenitors to synergistic cell proliferation in response to GM-CSF plus SCF, which is considered important for normal hematopoiesis. Responsiveness of HPCs to inhibition by myelosuppressive chemokines is directly related to the capacity of HPCs to respond to synergistic stimulation, and their cell cycle status. P18(INK4c) gene deletion rescued the loss of chemokine suppression of synergistic proliferation due to deletion of p21(CIP1/WAF1). These findings underscore the complex interplay of cell cycle regulators in HPC, and demonstrate that loss of one can sometimes be compensated by loss of another CDKI in both, a pro- or anti-proliferative context.

Physiological relevance of cell cycle kinases

The basic biology of the cell division cycle and its control by protein kinases was originally studied through genetic and biochemical studies in yeast and other model organisms. The major regulatory mechanisms identified in this pioneer work are conserved in mammals. However, recent studies in different cell types or genetic models are now providing a new perspective on the function of these major cell cycle regulators in different tissues. Here, we review the physiological relevance of mammalian cell cycle kinases such as cyclin-dependent kinases (Cdks), Aurora and Polo-like kinases, and mitotic checkpoint regulators (Bub1, BubR1, and Mps1) as well as other less-studied enzymes such as Cdc7, Nek proteins, or Mastl and their implications in development, tissue homeostasis, and human disease. Among these functions, the control of self-renewal or asymmetric cell division in stem/progenitor cells and the ability to regenerate injured tissues is a central issue in current research. In addition, many of these proteins play previously unexpected roles in metabolism, cardiovascular function, or neuron biology. The modulation of their enzymatic activity may therefore have multiple therapeutic benefits in human disease.

Mathematical study on kinetics of hematopoietic stem cells--theoretical conditions for successful transplantation

Numerous haematological diseases occur due to dysfunctions during homeostasis processes of blood cell production. Haematopoietic stem cell transplantation (HSCT) is a therapeutic option for the treatment of haematological malignancy and congenital immunodeficiency. Today, HSCT is widely applied as an alternative method to bone marrow transplantation; however, HSCT can be a risky procedure because of potential side effects and complications after transplantations. Although an optimal regimen to achieve successful HSCT while maintaining quality of life is to be developed, even theoretical considerations such as the evaluations of successful engraftments and proposals of clinical management strategies have not been fully discussed yet. In this paper, we construct and investigate mathematical models that describe the kinetics of hematopoietic stem cell self-renewal and granulopoiesis under the influence of growth factors. Moreover, we derive theoretical conditions for successful HSCT, primarily on the basis of the idea that the basic reproduction number R (0) represents a threshold condition for a population to successfully grow in a given steady-state environment. Successful engraftment of transplanted haematopoietic stem cells (HSCs) is subsequently ensured by employing a concept of dynamical systems theory known as 'persistence'. On the basis of the implications from the modelling study, we discuss how the conditions derived for a successful HSCT are used to link to experimental studies.

Retinoic Acid-induced Cell Cycle Arrest of Human Myeloid Cell Lines

Retinoic acid-induced terminal differentiation of myeloid cells involves the sequential regulation of cell cycle regulatory genes, coordinating the process of differentiation with arrest in the G0/G1 phase of the cell cycle. In this review we have summarized changes in expression and activity of cell cycle regulatory proteins associated with retinoic acid induced-growth arrest in human myeloid cell lines. These changes involve: (i) an early down-regulation of c-Myc; (ii) up-regulation of p21CIP1 and p27KIP1 and, in some cases, p15INK4b or p18INK4c; (iii) down-regulation of cyclin E and cyclin D1/D3, and, at later stages, cyclin A and cyclin B; and (iv) decreased CDK activity and dephosphorylation of pRb.

PIM1 kinase is destabilized by ribosomal stress causing inhibition of cell cycle progression

PIM1 is a constitutively active serine/threonine kinase regulated by cytokines, growth factors and hormones. It has been implicated in the control of cell cycle progression and apoptosis and its overexpression has been associated with various kinds of lymphoid and hematopoietic malignancies. The activity of PIM1 is dependent on the phosphorylation of several targets involved in transcription, cell cycle and apoptosis. We have recently observed that PIM1 interacts with ribosomal protein (RP)S19 and cosediments with ribosomes. Defects in ribosome synthesis (ribosomal stress) have been shown to activate a p53-dependent growth arrest response. To investigate if PIM1 could have a role in the response to ribosomal stress, we induced ribosome synthesis alterations in TF-1 and K562 erythroid cell lines. We found that RP deficiency, induced by RNA interference or treatment with inhibitor of nucleolar functions, causes a drastic destabilization of PIM1. The lower level of PIM1 induces an increase in the cell cycle inhibitor p27(Kip1) and blocks cell proliferation even in the absence of p53. Notably, restoring PIM1 level by transfection causes a recovery of cell growth. Our data indicate that PIM1 may act as a sensor for ribosomal stress independently of or in concert with the known p53-dependent mechanisms.

The homeobox gene Hhex regulates the earliest stages of definitive hematopoiesis

The development and emergence of the hematopoietic stem cell involves a series of tightly regulated molecular events that are not well characterized. The hematopoietically expressed homeobox (Hhex) gene, a member of the homeobox gene family, is an essential regulator of embryogenesis and hematopoietic progenitor development. To investigate the role of Hhex in hematopoiesis we adapted a murine embryonic stem (ES) cell coculture system, in which ES cells can differentiate into CD41(+) and CD45(+) hematopoietic progenitors in vitro. Our results show that in addition to delayed hemangioblast development, Hhex(-/-) ES-derived progeny accumulate as CD41(+) and CD41(+)c-kit(+) cells, or the earliest definitive hematopoietic progenitors. In addition, Hhex(-/-) ES-derived progeny display a significantly reduced ability to develop into mature CD45(+) hematopoietic cells. The observed reduction in hematopoietic maturation was accompanied by reduced proliferation, because Hhex(-/-) CD41(+)CD45(-)c-kit(+) hematopoietic progenitors accumulated in the G(2) phase of the cell cycle. Thus, Hhex is a critical regulator of hematopoietic development and is necessary for the maturation and proliferation of the earliest definitive hematopoietic progenitors.

EKLF directly activates the p21WAF1/CIP1 gene by proximal promoter and novel intronic regulatory regions during erythroid differentiation

The switch from proliferation to differentiation during the terminal stages of erythropoiesis is a tightly controlled process that relies in part on transcription factor-mediated activation of cell cycle components. EKLF is a key transcription factor that is necessary for the initial establishment of the red cell phenotype. Here, we find that EKLF also plays a role during the subsequent differentiation process, as it induces p21(WAF1/CIP1) expression independent of p53 to regulate the changes in the cell cycle underlying erythroid maturation. EKLF activates p21 not only by directly binding to an EKLF site within a previously characterized GC-rich region in the p21 proximal promoter but also by occupancy at a novel, phylogenetically conserved region that contains consensus CACCC core motifs located downstream from the p21 TATA box. Our findings demonstrate that EKLF, likely in coordination with other transcription factors, directly contributes to the complex set of events that occur at the final erythroid cell divisions and accentuates terminal differentiation directly by activation of CDK inhibitors such as p21.

CD99 inhibits neural differentiation of human Ewing sarcoma cells and thereby contributes to oncogenesis

Ewing sarcoma (EWS) is an aggressive bone tumor of uncertain cellular origin. CD99 is a membrane protein that is expressed in most cases of EWS, although its function in the disease is unknown. Here we have shown that endogenous CD99 expression modulates EWS tumor differentiation and malignancy. We determined that knocking down CD99 expression in human EWS cell lines reduced their ability to form tumors and bone metastases when xenografted into immunodeficient mice and diminished their tumorigenic characteristics in vitro. Further, reduction of CD99 expression resulted in neurite outgrowth and increased expression of beta-III tubulin and markers of neural differentiation. Analysis of a panel of human EWS cells revealed an inverse correlation between CD99 and H-neurofilament expression, as well as an inverse correlation between neural differentiation and oncogenic transformation. As knockdown of CD99 also led to an increase in phosphorylation of ERK1/2, we suggest that the CD99-mediated prevention of neural differentiation of EWS occurs through MAPK pathway modulation. Together, these data indicate a new role for CD99 in preventing neural differentiation of EWS cells and suggest that blockade of CD99 or its downstream molecular pathway may be a new therapeutic approach for EWS.

PU.1 directly regulates cdk6 gene expression, linking the cell proliferation and differentiation programs in erythroid cells

Cell proliferation and differentiation are highly coordinated processes during normal development. Most leukemia cells are blocked from undergoing terminal differentiation and also exhibit uncontrolled proliferation. Dysregulated expression of transcription factor PU.1 is strongly associated with Friend virus-induced erythroleukemia. PU.1 inhibits erythroid differentiation by binding to and inhibiting GATA-1. PU.1 also may be involved in controlling proliferation of erythroid cells. We reported previously that the G(1) phase-specific cyclin-dependent kinase 6 (CDK6) also blocks erythroid differentiation. We now report that PU.1 directly stimulates transcription of the cdk6 gene in both normal erythroid progenitors and erythroleukemia cells, as well as in macrophages. We propose that PU.1 coordinates proliferation and differentiation in immature erythroid cells by inhibiting the GATA-1-mediated gene expression program and also by regulating expression of genes that control progression through the G(1) phase of the cell cycle, the period during which the decision to differentiate is made.

H4 histamine receptors mediate cell cycle arrest in growth factor-induced murine and human hematopoietic progenitor cells

The most recently characterized H4 histamine receptor (H4R) is expressed preferentially in the bone marrow, raising the question of its role during hematopoiesis. Here we show that both murine and human progenitor cell populations express this receptor subtype on transcriptional and protein levels and respond to its agonists by reduced growth factor-induced cell cycle progression that leads to decreased myeloid, erythroid and lymphoid colony formation. H4R activation prevents the induction of cell cycle genes through a cAMP/PKA-dependent pathway that is not associated with apoptosis. It is mediated specifically through H4R signaling since gene silencing or treatment with selective antagonists restores normal cell cycle progression. The arrest of growth factor-induced G1/S transition protects murine and human progenitor cells from the toxicity of the cell cycle-dependent anticancer drug Ara-C in vitro and reduces aplasia in a murine model of chemotherapy. This first evidence for functional H4R expression in hematopoietic progenitors opens new therapeutic perspectives for alleviating hematotoxic side effects of antineoplastic drugs.

Wogonin induced differentiation and G1 phase arrest of human U-937 leukemia cells via PKCdelta phosphorylation

Wogonin, a natural monoflavonoid, has been shown to have tumor therapeutic potential in vitro and in vivo. Recently many studies have focused on the induction of apoptosis of tumor cells by wogonin. In this study, we found that wogonin could induce differentiation and G1 phase arrest of human U-937 leukemia cells. The growth of U-937 cells incubated with wogonin was inhibited in a time- and concentration-dependent manner. After treatment with wogonin, U-937 cells exhibited the characteristics of mature granulocytes, such as increased cytoplasmic-to-nuclear ratio, enhanced prominence of cytoplasmic granules, membrane ruffling, a higher NBT-reducing ability, and an increased expression of CD11b. Moreover, wogonin could induce G1 phase arrest and influenced the expression of associated proteins. For example, the expression of phorsphorylated protein kinase C (PKC) delta, p21 increased, while that of cyclin D1/cyclin-dependent kinase (CDK) 4, p-Rb decreased. The upregulation of p21 could be reversed by rottlerin, an inhibitor of PKCdelta. Taken together, wogonin induced U-937 cells to undergo granulocytic differentiation and G1 phase arrest via PKCdelta phosphorylation-induced upregulation of p21 proteins.

Essential roles of mgcRacGAP in multilineage differentiation and survival of murine hematopoietic cells

MgcRacGAP, a negative regulator for Rho family GTPases, has been shown to play important roles in cytokinesis using several cell lines. However, the physiological role of mgcRacGAP in multilineage hematopoietic development remains unclear. Here, we conditionally ablated mgcRacGAP in vivo to clarify this issue. As the result, we found that normal hematopoietic development including proliferation and survival requires mgcRacGAP. We also found that depletion of mgcRacGAP in hematopoietic cells results in a marked decrease in c-Kit(+)Sca-1(+)Lin(-) cells, suggesting that mgcRacGAP is required for the maintenance of the hematopoietic stem cells. In addition, B cells in which mgcRacGAP had been selectively ablated showed proliferation failure and fell into apoptosis. Taken together, mgcRacGAP is now shown to play a indispensable role in the development of hematopoietic cells in vivo.

Cdk2 is critical for proliferation and self-renewal of neural progenitor cells in the adult subventricular zone

We investigated the function of cyclin-dependent kinase 2 (Cdk2) in neural progenitor cells during postnatal development. Chondroitin sulfate proteoglycan (NG2)–expressing progenitor cells of the subventricular zone (SVZ) show no significant difference in density and proliferation between Cdk2^−/− and wild-type mice at perinatal ages and are reduced only in adult Cdk2^−/− mice. Adult Cdk2^−/− SVZ cells in culture display decreased self-renewal capacity and enhanced differentiation. Compensatory mechanisms in perinatal Cdk2^−/− SVZ cells, which persist until postnatal day 15, involve increased Cdk4 expression that results in retinoblastoma protein inactivation. A subsequent decline in Cdk4 activity to wild-type levels in postnatal day 28 Cdk2^−/− cells coincides with lower NG2⁺ proliferation and self-renewal capacity similar to adult levels. Cdk4 silencing in perinatal Cdk2^−/− SVZ cells abolishes Cdk4 up-regulation and reduces cell proliferation and self- renewal to adult levels. Conversely, Cdk4 overexpression in adult SVZ cells restores proliferative capacity to wild-type levels. Thus, although Cdk2 is functionally redundant in perinatal SVZ, it is important for adult progenitor cell proliferation and self-renewal through age-dependent regulation of Cdk4.

Differentiation is coupled to changes in the cell cycle regulatory apparatus of human embryonic stem cells

Mouse embryonic stem cells (mESC) exhibit cell cycle properties entirely distinct from those of somatic cells. Here we investigated the cell cycle characteristics of human embryonic stem cells (hESC). HESC could be sorted into populations based on the expression level of the cell surface stem cell marker GCTM-2. Compared to mESC, a significantly higher proportion of hESC (GCTM-2(+) Oct-4(+) cells) resided in G(1) and retained G(1)-phase-specific hypophosphorylated retinoblastoma protein (pRb). We showed that suppression of traverse through G(1) is sufficient to promote hESC differentiation. Like mESC, hESC expressed cyclin E constitutively, were negative for D-type cyclins, and did not respond to CDK-4 inhibition. By contrast, cyclin A expression was periodic in hESC and coincided with S and G(2)/M phase progression. FGF-2 acted solely to sustain hESC pluripotency rather than to promote cell cycle progression or inhibit apoptosis. Differentiation increased G(1)-phase content, reinstated cyclin D activity, and restored the proliferative response to FGF-2. Treatment with CDK-2 inhibitor delayed hESC in G(1) and S phase, resulting in accumulation of cells with hypophosphorylated pRb, GCTM-2, and Oct-4 and, interestingly, a second pRb(+) GCTM-2(+) subpopulation lacking Oct-4. We discuss evidence for a G(1)-specific, pRb-dependent restriction checkpoint in hESC closely associated with the regulation of pluripotency.

Transcriptional cross talk between the forkhead transcription factor forkhead box O1A and the progesterone receptor coordinates cell cycle regulation and differentiation in human endometrial stromal cells

Differentiation of human endometrial stromal cells (HESCs) into decidual cells is associated with induction of the forkhead transcription factor forkhead box O1A (FOXO1). We performed a genomic screen to identify decidua-specific genes under FOXO1 control. Primary HESCs were transfected with small interfering RNA targeting FOXO1 or with nontargeting control small interfering RNA before treatment with a cAMP analogue and the progestin, medroxyprogesterone acetate for 72 h. Total RNA was processed for whole genome analysis using high-density oligonucleotide arrays. We identified 3405 significantly regulated genes upon decidualization of HESCs, 507 (15.3%) of which were aberrantly expressed upon FOXO1 knockdown. Among the most up-regulated FOXO1-dependent transcriptional targets were WNT signaling-related genes (WNT4, WNT16 ), the insulin receptor (INSR), differentiation markers (PRL, IGFBP1, and LEFTY2), and the cyclin-dependent kinase inhibitor p57(Kip2) (CDKN1C). Analysis of FOXO1-dependent down-regulated genes uncovered several factors involved in cell cycle regulation, including CCNB1, CCNB2, MCM5, CDC2 and NEK2. Cell viability assay and cell cycle analysis demonstrated that FOXO1 silencing promotes proliferation of differentiating HESCs. Using a glutathione-S-transferase pull-down assay, we confirmed that FOXO1 interacts with progesterone receptor, irrespectively of the presence of ligand. In agreement, knockdown of PR disrupted the regulation of FOXO1 target genes involved in differentiation (IGFBP1, PRL, and WNT4) and cell cycle regulation (CDKN1, CCNB2 and CDC2) in HESCs treated with either cAMP plus medroxyprogesterone acetate or with cAMP alone. Together, the data demonstrate that FOXO1 engages in transcriptional cross talk with progesterone receptor to coordinate cell cycle regulation and differentiation of HESCs.