Intrinsic Retinoic Acid Receptor α-Cyclin-Dependent Kinase-Activating Kinase Signaling Involves Coordination of the Restricted Proliferation and Granulocytic Differentiation of Human Hematopoietic Stem Cells

Potentially functional variants in nucleotide excision repair pathway genes predict platinum treatment response of Chinese ovarian cancer patients

Acquired platinum resistance impedes successful treatment of epithelial ovarian cancer (EOC), and this resistance may be associated with inherited DNA damage-repair response. In the present study, we performed a two-phase analysis to assess associations between 8191 single-nucleotide polymorphisms within 127 genes of nucleotide excision repair pathway from a genome-wide association study dataset and platinum treatment response in 803 Han Chinese EOC patients. As a result, we identified that platinum-based chemotherapeutic response was associated with two potentially functional variants MNAT1 rs2284704 T>C [TC + CC versus TT, adjusted odds ratio (OR) = 0.89, 95% confidence interval (CI) = 0.83-0.95 and P = 0.0005] and HUS1B rs61748571 A>G (AG + GG versus AA, OR = 1.10, 95% CI = 1.03-1.18 and P = 0.005). Compared with the prediction model for clinical factors only, models incorporating HUS1B rs61748571 [area under the curve (AUC) 0.652 versus 0.672, P = 0.026] and the number of unfavorable genotypes (AUC 0.652 versus 0.668, P = 0.040) demonstrated a significant increase in the AUC. Further expression quantitative trait loci analysis suggested that MNAT1 rs2284704 T>C significantly influenced mRNA expression levels of MNAT1 (P = 0.003). These results indicated that MNAT1 rs2284704 T>C and HUS1B rs61748571 A>G may serve as potential biomarkers for predicting platinum treatment response of Chinese EOC patients, once validated by further functional studies.

Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy

Neutrophils form an essential part of innate immunity against infection. Cancer chemotherapy-induced neutropenia (CCIN) is a condition in which the number of neutrophils in a patient's bloodstream is decreased, leading to increased susceptibility to infection. Granulocyte colony-stimulating factor (GCSF) has been the only approved treatment for CCIN over two decades. To date, CCIN-related infection and mortality remain a significant concern, as neutrophils generated in response to administered GCSF are functionally immature and cannot effectively fight infection. This review summarizes the molecular regulatory mechanisms of neutrophil granulocytic differentiation and innate immunity development, dissects the biology of GCSF in myeloid expansion, highlights the shortcomings of GCSF in CCIN treatment, updates the recent advance of a selective retinoid agonist that promotes neutrophil granulocytic differentiation, and evaluates the benefits of developing GCSF biosimilars to increase access to GCSF biologics versus seeking a new mode to fundamentally advance GCSF therapy for treatment of CCIN.

KLF4 functions as an oncogene in promoting cancer stem cell-like characteristics in osteosarcoma cells

Despite more effective chemotherapy combined with limb-salvage surgery for the osteosarcoma treatment, survival rates for osteosarcoma patients have stagnated over the past three decades due to the poor prognosis. Osteosarcoma cancer stem cells (OSCs) are responsible for the growth and metastasis of osteosarcoma. The existence of OSCs offers a theoretical explanation for therapeutic failures including tumor recurrence, metastasis, and drug resistance. Understanding the pathways that regulate properties of OSCs may shed light on mechanisms that lead to osteosarcoma and suggest better modes of treatment. In this study, we showed that the expression level of Kruppel-like factor 4 (KLF4) is highly associated with human osteosarcoma cancer stemness. KLF4-overexpressed osteosarcoma cells displayed characteristics of OSCs: increased sphere-forming potential, enhanced levels of stemness-associated genes, great chemoresistance to adriamycin and CDDP, as well as more metastasis potential. Inversely, KLF4 knockdown could reduce colony formation in vitro and inhibit tumorigenesis in vivo, supporting an oncogenic role for KLF4 in osteosarcoma pathogenesis. Furthermore, KLF4 was shown to activate the p38 MAPK signaling pathway to promote cancer stemness. Altogether, our studies uncover an essential role for KLF4 in regulation of OSCs and identify KLF4-p38 MAPK axis as a potential therapeutic target for osteosarcoma treatment.

Alcohol abuse and disorder of granulopoiesis

Granulocytes are the major type of phagocytes constituting the front line of innate immune defense against bacterial infection. In adults, granulocytes are derived from hematopoietic stem cells in the bone marrow. Alcohol is the most frequently abused substance in human society. Excessive alcohol consumption injures hematopoietic tissue, impairing bone marrow production of granulocytes through disrupting homeostasis of granulopoiesis and the granulopoietic response. Because of the compromised immune defense function, alcohol abusers are susceptible to infectious diseases, particularly septic infection. Alcoholic patients with septic infection and granulocytopenia have an exceedingly high mortality rate. Treatment of serious infection in alcoholic patients with bone marrow inhibition continues to be a major challenge. Excessive alcohol consumption also causes diseases in other organ systems, particularly severe alcoholic hepatitis which is life threatening. Corticosteroids are the only therapeutic option for improving short-term survival in patients with severe alcoholic hepatitis. The existence of advanced alcoholic liver diseases and administration of corticosteroids make it more difficult to treat serious infection in alcoholic patients with the disorder of granulopoieis. This article reviews the recent development in understanding alcohol-induced disruption of marrow granulopoiesis and the granulopoietic response with the focus on progress in delineating cell signaling mechanisms underlying the alcohol-induced injury to hematopoietic tissue. Efforts in exploring effective therapy to improve patient care in this field will also be discussed.

MNAT1 is overexpressed in colorectal cancer and mediates p53 ubiquitin-degradation to promote colorectal cancer malignance

BACKGROUND

MNAT1 (menage a trois 1, MAT1), a cyclin-dependent kinase-activating kinase (CAK) complex, high expresses in various cancers and is involved in cancer pathogenesis. However, mechanisms underlying its regulation in carcinogenesis are unclear.

METHODS

The tissue microarray of colorectal cancer (CRC) was used to evaluate MNAT1 expressions in CRC tissues using immunohistochemistry, CRC cell lines were also detected MNAT1 expression using Western-blotting. MNAT1 and shMNAT1 vectors were constructed, and transfected into CRC cells. Cell growths of the transfected cells were observed using MTT and colony formation. The affects of MNAT1 on p53 expression were analyzed using Western-blotting and Real-time PCR. Immunoprecipitation assay was used to analyze the interaction p53 and MNAT1, and Western-blotting was used to test the effects of MNAT1 on p53 downstream molecules. The apoptosis of CRC cells with MNAT1 or shMNAT1 were analyzed using flow cytometry. BABL/c athymic nude mice were used to observe the effect of MNAT1 on CRC cell growth in vivo.

RESULTS

MNAT1 was found to be overexpressed in CRC tissues and cells, and MNAT1 expressions in CRC tissue samples were associated with CRC carcinogenesis and poor patient outcomes. MNAT1-knockin increased CRC cell growth and colony formation, and MNAT1-knockdown dramatically decreased cell motility and invasion. MNAT1 physically interacted with p53, MNAT1 also increased the interaction of MDM2 with p53. Strikingly, MNAT1 mediated p53 ubiquitin-degradation. MNAT1 shortened p53 half-life, and ectopic MNAT1 expression decreased p53 protein stability. Moreover, MNAT1 induced RAD51 and reduced p21, cleaved-caspase3, cleaved-PARP and BAX expression. MNAT1 inhibited CRC cell apoptosis. shMANT1 decreased tumor growths in nude mice following p53 increase.

CONCLUSION

MNAT1 binds to p53, mediates p53 ubiquitin-degradation through MDM2, increases cell growth and decreases cell apoptosis, and finally promotes CRC malignance. MNAT1 binding to p53 and mediating p53 ubiquitin-degradation axis represents a novel molecular joint in the p53 pathway.

Am80-GCSF synergizes myeloid expansion and differentiation to generate functional neutrophils that reduce neutropenia-associated infection and mortality

Neutrophils generated by granulocyte colony‐stimulating factor (GCSF) are functionally immature and, consequently, cannot effectively reduce infection and infection‐related mortality in cancer chemotherapy‐induced neutropenia (CCIN). Am80, a retinoic acid (RA) agonist that enhances granulocytic differentiation by selectively activating transcription factor RA receptor alpha (RARα), alternatively promotes RA‐target gene expression. We found that in normal and malignant primary human hematopoietic specimens, Am80‐GCSF combination coordinated proliferation with differentiation to develop complement receptor‐3 (CR3)‐dependent neutrophil innate immunity, through altering transcription of RA‐target genes RARβ_2,C/EBPε, CD66,CD11b, and CD18. This led to generation of functional neutrophils capable of fighting infection, whereas neutralizing neutrophil innate immunity with anti‐CD18 antibody abolished neutrophil bactericidal activities induced by Am80‐GCSF. Further, Am80‐GCSF synergy was evaluated using six different dose‐schedule‐infection mouse CCIN models. The data demonstrated that during “emergency” granulopoiesis in CCIN mice undergoing transient systemic intravenous bacterial infection, Am80 effect on differentiating granulocytic precursors synergized with GCSF‐dependent myeloid expansion, resulting in large amounts of functional neutrophils that reduced infection. Importantly, extensive survival tests covering a full cycle of mouse CCIN with perpetual systemic intravenous bacterial infection proved that without causing myeloid overexpansion, Am80‐GCSF generated sufficient numbers of functional neutrophils that significantly reduced infection‐related mortality in CCIN mice. These findings reveal a differential mechanism for generating functional neutrophils to reduce CCIN‐associated infection and mortality, providing a rationale for future therapeutic approaches.

Retinoic acid signaling and neuronal differentiation

The identification of neurological symptoms caused by vitamin A deficiency pointed to a critical, early developmental role of vitamin A and its metabolite, retinoic acid (RA). The ability of RA to induce post-mitotic, neural phenotypes in various stem cells, in vitro, served as early evidence that RA is involved in the switch between proliferation and differentiation. In vivo studies have expanded this "opposing signal" model, and the number of primary neurons an embryo develops is now known to depend critically on the levels and spatial distribution of RA. The proneural and neurogenic transcription factors that control the exit of neural progenitors from the cell cycle and allow primary neurons to develop are partly elucidated, but the downstream effectors of RA receptor (RAR) signaling (many of which are putative cell cycle regulators) remain largely unidentified. The molecular mechanisms underlying RA-induced primary neurogenesis in anamniote embryos are starting to be revealed; however, these data have been not been extended to amniote embryos. There is growing evidence that bona fide RARs are found in some mollusks and other invertebrates, but little is known about their necessity or functions in neurogenesis. One normal function of RA is to regulate the cell cycle to halt proliferation, and loss of RA signaling is associated with dedifferentiation and the development of cancer. Identifying the genes and pathways that mediate cell cycle exit downstream of RA will be critical for our understanding of how to target tumor differentiation. Overall, elucidating the molecular details of RAR-regulated neurogenesis will be decisive for developing and understanding neural proliferation-differentiation switches throughout development.

Isolation and characterization of stem cells from human central nervous system malignancies

Central Nervous System (CNS) tumors include some of the most invasive and lethal tumors in humans. The poor prognosis in patients with CNS tumors is ascribed to their invasive nature. After the description of a stem cell-like cohort in hematopoietic cancers, tumor stem cells (TSCs) have been isolated from a variety of solid tumors, including brain tumors. Further research has uncovered the crucial role these cells play in the initiation and propagation of brain tumors. More importantly, TSCs have also been shown to be relatively resistant to conventional cytotoxic therapeutics, which may also account for the alarmingly high rate of CNS tumor recurrence. In order to elucidate prospective therapeutic targets it is imperative to study these cells in detail and to accomplish this, we need to be able to reliably isolate and characterize these cells. This chapter will therefore, provide an overview of the methods used to isolate and characterize stem cells from human CNS malignancies.

Human ALDH1B1 polymorphisms may affect the metabolism of acetaldehyde and all-trans retinaldehyde--in vitro studies and computational modeling

PURPOSE

To elucidate additional substrate specificities of ALDH1B1 and determine the effect that human ALDH1B1 polymorphisms will have on substrate specificity.

METHODS

Computational-based molecular modeling was used to predict the binding of the substrates propionaldehyde, 4-hydroxynonenal, nitroglycerin, and all-trans retinaldehyde to ALDH1B1. Based on positive in silico results, the capacity of purified human recombinant ALDH1B1 to metabolize nitroglycerin and all-trans retinaldehyde was explored. Additionally, metabolism of 4-HNE by ALDH1B1 was revisited. Databases queried to find human polymorphisms of ALDH1B1 identified three major variants: ALDH1B1*2 (A86V), ALDH1B1*3 (L107R), and ALDH1B1*5 (M253V). Computational modeling was used to predict the binding of substrates and of cofactor (NAD(+)) to the variants. These human polymorphisms were created and expressed in a bacterial system and specific activity was determined.

RESULTS

ALDH1B1 metabolizes (and appears to be inhibited by) nitroglycerin and has favorable kinetics for the metabolism of all-trans retinaldehyde. ALDH1B1 metabolizes 4-HNE with higher apparent affinity than previously described, but with low throughput. Recombinant ALDH1B1*2 is catalytically inactive, whereas both ALDH1B1*3 and ALDH1B1*5 are catalytically active. Modeling indicated that the lack of activity in ALDH1B1*2 is likely due to poor NAD(+) binding. Modeling also suggests that ALDH1B1*3 may be less able to metabolize all-trans retinaldehyde and that ALDH1B1*5 may bind NAD(+) poorly.

CONCLUSIONS

ALDH1B1 metabolizes nitroglycerin and all-trans-retinaldehyde. One of the three human polymorphisms, ALDH1B1*2, is catalytically inactive, likely due to poor NAD(+) binding. Expression of this variant may affect ALDH1B1-dependent metabolic functions in stem cells and ethanol metabolism.

Hyperoside, a flavonoid compound, inhibits proliferation and stimulates osteogenic differentiation of human osteosarcoma cells

Osteosarcoma, one of the most common malignant bone tumours, is generally considered a differentiation disease caused by genetic and epigenetic disruptions in the terminal differentiation of osteoblasts. Novel therapies based on the non-cytotoxic induction of cell differentiation-responsive pathways could represent a significant advance in treating osteosarcoma; however, effective pharmaceuticals to induce differentiation are lacking. In the present study, we investigated the effect of hyperoside, a flavonoid compound, on the osteoblastic differentiation of U2OS and MG63 osteosarcoma cells in vitro. Our results demonstrated that hyperoside inhibits the proliferation of osteosarcoma cells by inducing G₀/G₁ arrest in the cell cycle, without causing obvious cell death. Cell migration assay further suggested that hyperoside could inhibit the invasion potential of osteosarcoma cells. Additionally, osteopontin and runt-related transcription factor 2 protein levels and osteocalcin activation were upregulated dramatically in hyperoside-treated osteosarcoma cells, suggesting that hyperoside may stimulates osteoblastic differentiation in osteosarcoma cells. This differentiation was accompanied by the activation of transforming growth factor (TGF)-β and bone morphogenetic protein-2, suggesting that the hyperoside-induced differentiation involves the TGF-β signalling pathway. To our knowledge, this study is the first to evaluate the differentiation effect of hyperoside in osteosarcoma cells and assess the possible potential for hyperoside treatment as a future therapeutic approach for osteosarcoma differentiation therapy.

The lost intrinsic fragmentation of MAT1 protein during granulopoiesis promotes the growth and metastasis of leukemic myeloblasts

MAT1, an assembly factor and targeting subunit of both cyclin-dependent kinase-activating kinase (CAK) and general transcription factor IIH (TFIIH) kinase, regulates cell cycle and transcription. Previous studies show that expression of intact MAT1 protein is associated with expansion of human hematopoietic stem cells (HSC), whereas intrinsically programmed or retinoic acid (RA)-induced MAT1 fragmentation accompanies granulocytic differentiation of HSC or leukemic myeloblasts. Here we determined that, in humanized mouse microenvironment, MAT1 overexpression resisted intrinsic MAT1 fragmentation to sustain hematopoietic CD34+ cell expansion while preventing granulopoiesis. Conversely, we mimicked MAT1 fragmentation in vitro and in a mouse model by overexpressing a fragmented 81-aa MAT1 polypeptide (pM9) that retains the domain for assembling CAK but cannot affix CAK to TFIIH-core. Our results showed that pM9 formed ΔCAK by competing with MAT1 for CAK assembly to mimic MAT1 fragmentation-depletion of CAK. This resulting ΔCAK acted as a dominant negative to inhibit the growth and metastasis of different leukemic myeloblasts, with or without RA resistance, by concurrently suppressing CAK and TFIIH kinase activities to inhibit cell cycle and gene transcription. These findings suggest that the intrinsically programmed MAT1 expression and fragmentation regulate granulopoiesis by inversely coordinating CAK and TFIIH activities, whereas pM9 shares a mechanistic resemblance with MAT1 fragmentation in suppressing myeloid leukemogenesis.

β-Escin inhibits NNK-induced lung adenocarcinoma and ALDH1A1 and RhoA/Rock expression in A/J mice and growth of H460 human lung cancer cells

Lung cancer is the leading cause of cancer-related deaths. β-Escin, a triterpene saponin isolated from horse chestnut seeds, was tested for inhibition of lung adenoma and adenocarcinoma induced by the tobacco carcinogen 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female A/J mice; and its possible mode of action was evaluated using the H460 human lung cancer cell line. At 6 weeks of age, 35 mice were fed AIN-76A-modified diet, and one week later, lung tumors were induced with a single intraperitoneal (i.p.) injection of 10 μmol NNK/mouse. Three weeks after the NNK treatment, groups of mice were fed either control or experimental diets containing 500 ppm for 20 weeks (10 control, 5 β-escin) or 36 weeks (15 control, 5 β-escin) and evaluated for lung tumor via histopathologic methods. Administration of 500 ppm β-escin significantly suppressed lung tumor (adenoma + adenocarcinoma) formation by more than 40% (P < 0.0015) at 20 weeks and by 53.3% (P < 0.0001) at 37 weeks. β-Escin inhibited NNK-induced lung adenocarcinoma formation by 65% (P < 0.001) at 20 weeks and by 53% (P < 0.0001) at 37 weeks. Immunohistochemical analysis revealed that lung tumors from mice exposed to β-escin showed significantly reduced aldehyde dehydrogenase (ALDH)1A1 and phospho-Akt (p-Akt) expression when compared with those in mice fed control diet. Aldefluor assay for ALDH revealed that among H460 lung cancer cells treated with different concentrations of β-escin (0-40 μmol/L), the subpopulation of cells with elevated ALDH activity was inhibited significantly. Our findings suggest that β-escin inhibits tobacco carcinogen-induced lung tumor formation by modulating ALDH1A1-positive cells and RhoA/Rock signaling.

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

Retinoic acid represses invasion and stem cell phenotype by induction of the metastasis suppressors RARRES1 and LXN

The mouse haematopoietic stem cell (SC) regulator Latexin (LXN) is the only known homologue of the retinoic acid receptor responder 1 (RARRES1) gene. Both genes lie adjacent on chromosome 3 and differ mostly by the presence of a transmembrane domain in RARRES1. Despite their homology, it is not known whether they possess similar regulatory mechanisms, cellular localization and function. Here, we identified RARRES1 and LXN as highly significantly downregulated genes in human prostate SCs, whose expression was induced by the pro-differentiation agent all-trans retinoic acid (atRA). AtRA induced expression in the most differentiated cells compared with the SC fraction, suggesting that this subpopulation was less responsive to atRA. Small interfering RNA suppression of RARRES1 and LXN enhanced the SC properties of primary prostate cultures, as shown by a significant increase in their colony-forming ability. Expression of both RARRES1 and LXN was co-ordinately repressed by DNA methylation in prostate cancer cell lines and inhibition of RARRES1 and LXN increased the invasive capacity of primary prostate cultures, which also fully rescued an inhibitory effect induced by atRA. Moreover, we showed that RARRES1 and LXN reside within different sub-cellular compartments, providing evidence that RARRES1 is not a plasma membrane protein as previously supposed but is located primarily in the endoplasmic reticulum; whereas LXN was detected in the nucleus of prostate epithelial cells. Thus, LXN and RARRES1 are potential tumour suppressor genes, which are co-ordinately regulated, SC-silenced genes functioning to suppress invasion and colony-forming ability of prostate cancer cells; yet the proteins reside within different sub-cellular compartments.

Retinoid agonist Am80-enhanced neutrophil bactericidal activity arising from granulopoiesis in vitro and in a neutropenic mouse model

Despite advances in the therapeutic use of recombinant granulocyte colony-stimulating factor (G-CSF) to promote granulopoiesis of human hematopoietic stem cells (HSCs), neutropenia remains one of the most serious complications of cancer chemotherapy. We discovered that retinoid agonist Am80 (tamibarotene) is more potent than G-CSF in coordinating neutrophil differentiation and immunity development. Am80-induced neutrophils (AINs) either in vitro or in neutropenic mouse model displayed strong bactericidal activities, similar to those of human peripheral blood neutrophils (PBNs) or mouse peripheral blood neutrophils (MPBNs) but markedly greater than did G-CSF–induced neutrophils (GINs). In contrast to GINs but similar to PBNs, the enhanced bacterial killing by AINs accompanied both better granule maturation and greater coexpression of CD66 antigen with the integrin β2 subunit CD18. Consistently, anti-CD18 antibody neutralized Am80-induced bactericidal activities of AINs. These studies demonstrate that Am80 is more effective than G-CSF in promoting neutrophil differentiation and bactericidal activities, probably through coordinating the functional interaction of CD66 with CD18 to enhance the development of neutrophil immunity during granulopoiesis. Our findings herein suggest a molecular rationale for developing new therapy against neutropenia using Am80 as a cost-effective treatment option.

Human osteosarcoma CD49f(-)CD133(+) cells: impaired in osteogenic fate while gain of tumorigenicity

The biological relationships among self-renewal, tumorigenicity, and lineage differentiation of human osteosarcoma-initiating cells (OSIC) remain elusive, making it difficult to identify and distinguish OSIC from osteosarcoma-forming cells (OSFC) for developing OSIC-targeted therapies. Using a new inverse lineage tracking strategy coupled with serial human-to-mouse xenotransplantation, we identified a subpopulation of osteosarcoma cells with OSIC-like properties and sought to distinguish them from their progeny, OSFC. We found that serial transplantation of cells from different osteosarcoma cell lines and primary osteosarcoma tissues progressively increased the CD49f⁺ subpopulation composing the bulk of the osteosarcoma mass. These CD49f⁺ cells displayed characteristics of OSFC: limited in vivo tumorigenicity, weak lineage differentiation, more differentiated osteogenic feature, and greater chemo-sensitivity. By contrast, their parental CD49f⁻CD133⁺ cells had an inhibited osteogenic fate, together with OSIC-like properties of self-renewal, strong tumorigenicity, and differentiation to CD49f⁺ progeny. Hence, the CD49f⁻CD133⁺ phenotype appears to identify OSIC-like cells that possess strong tumorigenicity correlated with an impaired osteogenic fate and the ability to initiate tumor growth through generation of CD49f⁺ progeny. These findings advance our understanding of OSIC-like properties and, for the first time, provide a much-needed distinction between OSIC and OSFC in this cancer.

Blocking p55PIK signaling inhibits proliferation and induces differentiation of leukemia cells

p55PIK, a regulatory subunit of phosphatidylinositol 3-kinases, promotes cell cycle progression by interacting with cell cycle modulators such as retinoblastoma protein (Rb) via its unique amino-terminal 24 amino-acid residue (N24). Overexpression of N24 specifically inhibits these interactions and leads to cell cycle arrest. Herein, we describe the generation of a fusion protein (Tat transactivator protein (TAT)-N24) that contains the protein transduction domain and N24, and examined its effects on the proliferation and differentiation of leukemia cells. TAT-N24 not only blocks cell proliferation but remarkably induces differentiation of leukemia cells in vitro and in vivo. Systemically administered TAT-N24 also significantly decreases growth of leukemia cell tumors in animal models. Furthermore, overexpression of p55PIK in leukemia cells leads to increased proliferation; however, TAT-N24 blocks this effect and concomitantly induces differentiation. There is significant upregulation of p55PIK mRNA and protein expression in leukemia cells from patients. TAT-N24 inhibits cell cycle progression and induces differentiation of bone marrow cells derived from patients with several different types of leukemia. These results show that cell-permeable N24 peptide induces leukemia cell differentiation and suggest that p55PIK may be a novel drug target for the treatment of hematopoetic malignancies.

Retinoid-regulated FGF8f secretion by osteoblasts bypasses retinoid stimuli to mediate granulocytic differentiation of myeloid leukemia cells

Signaling from the human hematopoietic stem cell (HSC) niche formed by osteoblastic cells regulates hematopoiesis. We previously found that retinoic acid receptor alpha (RARα), a transcription factor activated by retinoic acid (RA), mediates both granulocytic and osteoblastic differentiation. This effect depends on decreased phosphorylation of serine 77 of RARα (RARαS77) by the cyclin-dependent kinase-activating kinase (CAK) complex, a key cell-cycle regulator. In this article, we report that, by suppressing CAK phosphorylation of RARα, RA induces FGF8f to mediate osteosarcoma U2OS cell differentiation in an autocrine manner. By contrast, paracrine FGF8f secreted into osteoblast-conditioned medium by U2OS cells transduced with FGF8f or a phosphorylation-defective RARαS77 mutant, RARαS77A, bypasses RA stimuli to cross-mediate granulocytic differentiation of different types of human leukemic myeloblasts and normal primitive hematopoietic CD34(+) cells, possibly through modulating mitogen-activated protein kinase (MAPK) pathways. Further experiments using recombinant human FGF8f (rFGF8f) stimuli, antibody neutralization, and peptide blocking showed that paracrine FGF8f is required for mediating terminal leukemic myeloblast differentiation. These studies indicate a novel regulatory mechanism of granulocytic differentiation instigated by RA from the HSC niche, which links loss of CAK phosphorylation of RARα with paracrine FGF8f-mediated MAPK signaling to mediate leukemic myeloblast differentiation in the absence of RA. Therefore, these findings provide a compelling molecular rationale for further investigation of paracrine FGF8f regulation, with the intent of devising HSC niche-based FGF8f therapeutics for myeloid leukemia, with or without RA-resistance.

The role of human aldehyde dehydrogenase in normal and cancer stem cells

Normal stem cells and cancer stem cells (CSCs) share similar properties, in that both have the capacity to self-renew and differentiate into multiple cell types. In both the normal stem cell and cancer stem cell fields, there has been a great need for a universal marker that can effectively identify and isolate these rare populations of cells in order to characterize them and use this information for research and therapeutic purposes. Currently, it would appear that certain isoenzymes of the aldehyde dehydrogenase (ALDH) superfamily may be able to fulfill this role as a marker for both normal and cancer stem cells. ALDH has been identified as an important enzyme in the protection of normal hematopoietic stem cells, and is now also widely used as a marker to identify and isolate various types of normal stem cells and CSCs. In addition, emerging evidence suggests that ALDH1 is not only a marker for stem cells, but may also play important functional roles related to self-protection, differentiation, and expansion. This comprehensive review discusses the role that ALDH plays in normal stem cells and CSCs, with focus on ALDH1 and ALDH3A1. Discrepancies in the functional themes between cell types and future perspectives for therapeutic applications will also be discussed.

Inhibition of all-trans-retinoic acid-induced proteasome activation potentiates the differentiating effect of retinoid in acute myeloid leukemia cells

All-trans retinoic acid (ATRA) is nowadays considered to be the sole efficient agent for differentiation-based therapy in leukemia; however, the mechanisms of ATRA's biological effects remain largely unknown. Here we first reported that ATRA-induced myeloid leukemia differentiation was accompanied with the increased level of ubiquitin-protein conjugates and the upregulation of proteasome activity. To explore the functional role of the activated proteasome in retinoic acid (RA) signaling, the effects of proteasome inhibitors on RA-induced cell differentiation were determined. Our results demonstrated that inhibition of ATRA-elevated proteasome activity obviously promoted the myeloid maturation program triggered by ATRA, suggesting that the overactivated proteasome is not beneficial for ATRA's effects. Further studies demonstrated that the synergistic differentiating effects of ATRA and proteasome inhibitors might be associated with the protection of retinoic acid receptor alpha (RARα) from degradation by the ubiquitin-proteasome pathway (UPP). Moreover, the accumulated RARα was able to enhance the transcription of its target gene, which might also contribute to the enhanced differentiation of leukemia cells. Together, by linking the UPP to ATRA-dependent signaling, our data provide a novel insight into studying the mechanisms of ATRA-elicited cellular effects and imply the possibility of combination of ATRA and proteasome inhibitors in leukemia therapy.

Aldehyde dehydrogenase 1B1 (ALDH1B1) is a potential biomarker for human colon cancer

Aldehyde dehydrogenases (ALDHs) belong to a superfamily of NAD(P)+-dependent enzymes, which catalyze the oxidation of endogenous and exogenous aldehydes to their corresponding acids. Increased expression and/or activity of ALDHs, particularly ALDH1A1, have been reported to occur in human cancers. It is proposed that the metabolic function of ALDH1A1 confers the "stemness" properties to normal and cancer stem cells. Nevertheless, the identity of ALDH isozymes that contribute to the enhanced ALDH activity in specific types of human cancers remains to be elucidated. ALDH1B1 is a mitochondrial ALDH that metabolizes a wide range of aldehyde substrates including acetaldehyde and products of lipid peroxidation (LPO). In this study, we immunohistochemically examined the expression profile of ALDH1A1 and ALDH1B1 in human adenocarcinomas of colon (N=40), lung (N=30), breast (N=33) and ovary (N=33) using an NIH tissue array. The immunohistochemical expression of ALDH1A1 or ALDH1B1 in tumor tissues was scored by their intensity (scale=1-3) and extensiveness (% of total cancer cells). Herein we report a 5.6-fold higher expression score for ALDH1B1 in cancerous tissues than that for ALDH1A1. Remarkably, 39 out of 40 colonic cancer specimens were positive for ALDH1B1 with a staining intensity of 2.8±0.5. Our study demonstrates that ALDH1B1 is more profoundly expressed in the adenocarcinomas examined in this study relative to ALDH1A1 and that ALDH1B1 is dramatically upregulated in human colonic adenocarcinoma, making it a potential biomarker for human colon cancer.

Aldehyde dehydrogenase 1B1: molecular cloning and characterization of a novel mitochondrial acetaldehyde-metabolizing enzyme

Ethanol-induced damage is largely attributed to its toxic metabolite, acetaldehyde. Clearance of acetaldehyde is achieved by its oxidation, primarily catalyzed by the mitochondrial class II aldehyde dehydrogenase (ALDH2). ALDH1B1 is another mitochondrial aldehyde dehydrogenase (ALDH) that shares 75% peptide sequence homology with ALDH2. Recent population studies in whites suggest a role for ALDH1B1 in ethanol metabolism. However, to date, no formal documentation of the biochemical properties of ALDH1B1 has been forthcoming. In this current study, we cloned and expressed human recombinant ALDH1B1 in Sf9 insect cells. The resultant enzyme was purified by affinity chromatography to homogeneity. The kinetic properties of purified human ALDH1B1 were assessed using a wide range of aldehyde substrates. Human ALDH1B1 had an exclusive preference for NAD(+) as the cofactor and was catalytically active toward short- and medium-chain aliphatic aldehydes, aromatic aldehydes, and the products of lipid peroxidation, 4-hydroxynonenal and malondialdehyde. Most importantly, human ALDH1B1 exhibited an apparent K(m) of 55 μM for acetaldehyde, making it the second low K(m) ALDH for metabolism of this substrate. The dehydrogenase activity of ALDH1B1 was sensitive to disulfiram inhibition, a feature also shared with ALDH2. The tissue distribution of ALDH1B1 in C57BL/6J mice and humans was examined by quantitative polymerase chain reaction, Western blotting, and immunohistochemical analysis. The highest expression occurred in the liver, followed by the intestinal tract, implying a potential physiological role for ALDH1B1 in these tissues. The current study is the first report on the expression, purification, and biochemical characterization of human ALDH1B1 protein.

Retinoid-suppressed phosphorylation of RARalpha mediates the differentiation pathway of osteosarcoma cells

Although retinoic acid (RA) is a potent agent that coordinates inhibition of proliferation with differentiation of many cell types, RA-mediated signaling pathways in osteosarcoma cell differentiation are uncharacterized. In this study, we show that in human U2OS osteosarcoma cells, decreased phosphorylation of RA receptor alpha (RARalpha) by RA treatment or overexpressing a phosphorylation-defective mutant RARalphaS77A results in the inhibition of proliferation and induction of differentiation, and that U2OS cells transduced with RARalphaS77A suppresses tumor formation in nude mice. Moreover, using different human primary osteosarcoma cells and human mesenchymal stem cells for gene expression analysis, we found that either RA or RARalphaS77A induces many of the same differentiation response pathways and signaling molecules involved in U2OS cell differentiation. In addition, overexpression of the fibroblast growth factor 8f (FGF8f), one of the downstream targets induced by both RA and RARalphaS77A in U2OS cells, inhibits proliferation and induces expression of osteoblastic differentiation regulators. Hence, these data strongly suggest that RA-suppressed phosphorylation of RARalpha induces FGF8f expression to mediate differentiation response pathway in U2OS osteosarcoma cells.

Loss of CAK phosphorylation of RAR{alpha} mediates transcriptional control of retinoid-induced cancer cell differentiation

Although the role of the classic retinoic acid (RA)-induced genomic pathway in cancer cell differentiation is well recognized, the underlying mechanisms remain to be dissected. Retinoic acid receptor alpha (RARalpha) is a transcription factor activated by RA, and its serine 77 (RARalphaS77) is the main residue phosphorylated by the cyclin-dependent kinase (CDK)-activating kinase (CAK) complex. We report here that in both human myeloid leukemia and mouse embryonic teratocarcinoma stem cells, either RA-suppressed CAK phosphorylation of RARalpha or mutation of RARalphaS77 to alanine (RARalphaS77A) coordinates CAK-dependent G(1) arrest with cancer cell differentiation by transactivating RA-target genes. Both hypophosphorylated RARalpha and RARalphaS77A reduce binding to retinoic acid-responsive elements (RARE) in the promoters of RA-target genes while stimulating gene transcription. The enhanced transactivation and reduced RARalpha-chromatin interaction are accompanied by RARalpha dissociation from the transcriptional repressor N-CoR and are association with the coactivator NCoA-3. Such effects of decreased CAK phosphorylation of RARalphaS77 on mediating RA-dependent transcriptional control of cancer cell differentiation are examined correspondingly in both RA-resistant myeloid leukemia and embryonic teratocarcinoma stem RARalpha(-/-) cells. These studies demonstrate, for the first time, that RA couples G(1) arrest to transcriptional control of cancer cell differentiation by suppressing CAK phosphorylation of RARalpha to release transcriptional repression.-Wang, A., Alimova, I. N., Luo, P. Jong, A., Triche, T. J., Wu, L. Loss of CAK phosphorylation of RARalpha mediates transcriptional control of retinoid-induced cancer cell differentiation.

Delineating liver events in trichloroethylene-induced autoimmune hepatitis

Exposure to the environmental pollutant trichloroethylene (TCE) has been linked to autoimmune disease development in humans. Chronic (32-week) low-level exposure to TCE has been shown to promote autoimmune hepatitis in association with CD4(+) T cell activation in autoimmune-prone MRL+/+ mice. MRL+/+ mice are usually thought of as a model of systemic lupus rather than an organ-specific disease such as autoimmune hepatitis. Consequently, the present study examined gene expression and metabolites to delineate the liver events that skewed the autoimmune response toward that organ in TCE-treated mice. Female MRL+/+ mice were treated with 0.5 mg/mL TCE in their drinking water. The results showed that TCE-induced autoimmune hepatitis could be detected in as little as 26 weeks. TCE exposure also generated a time-dependent increase in the number of antibodies specific for liver proteins. The gene expression correlated with the metabolite analysis to show that TCE upregulated the methionine/homocysteine pathway in the liver after 26 weeks of exposure. The results also showed that TCE exposure altered the expression of selective hepatic genes associated with immunity and inflammation. On the basis of these results, future mechanistic studies will focus on how alterations in genes associated with immunity and inflammation, in conjunction with protein alterations in the liver, promote liver immunogenicity in TCE-treated MRL+/+ mice.

Drug resistance is dramatically restored by hedgehog inhibitors in CD34+ leukemic cells

Aberrant reactivation of hedgehog (Hh) signaling has been described in a wide variety of human cancers and in cancer stem cells. However, the contribution of Hh signaling to leukemic cell regulation has remained unclear. In this study, we assessed the possibility that Hh pathway activation contributes to the survival and drug resistance of cluster of differentiation (CD)34+ leukemia cells. Hh signaling in leukemic cell lines and primary leukemic cells was screened by reverse transcription - polymerase chain reaction (RT-PCR) and a Hh signaling reporter assay. We found that Hh signaling is active in several human acute myeloid leukemia (AML) cells, especially primary CD34+ leukemic cells and cytokine-responsive CD34+ cell lines such as Kasumi-1, Kasumi-3 and TF-1. These CD34+ cells express the downstream effectors glioma-associated oncogene homolog (GLI)1 or GLI2, indicative of active Hh signaling. Moreover, inhibition of Hh signaling with the naturally derived Smoothened antagonist cyclopamine, endogenous Hh inhibitor hedgehog-interacting protein or anti-hedgehog neutralizing antibody induced apoptosis after 48 h of exposure, although these CD34+ cell lines exhibited resistance to cytarabine (Ara-C). In contrast, cyclopamine failed to affect growth or survival in U937 and HL-60 cell lines that lack expression of Hh receptor components, confirming that the effect of Hh inhibition is specific. Furthermore, combination with 10 microM cyclopamine significantly reduced drug resistance of CD34+ cell lines and primary CD34+ leukemic cells to Ara-C. These results suggest that aberrant Hh pathway activation is a feature of some CD34+ myeloid leukemic cells and Hh inhibitors may have a therapeutic role in the treatment of AML.