Transforming growth factor-beta1 transcriptionally activates CD34 and prevents induced differentiation of TF-1 cells in the absence of any cell-cycle effects

Marine derived macrolide bryostatin 4 inhibits the TGF-β signaling pathway against acute erythroleukemia

PURPOSE

Acute erythroleukemia (AEL) is a rare and highly aggressive subtype of acute myeloid leukemia (AML) with an extremely poor prognosis when treated with available drugs. Therefore, new investigational agents capable of inducing remission are urgently required.

METHODS

Bioinformatics analysis, western blot and qRT-PCR were used to reveal the potential biological mechanism of bryostatin 4 (B4), an antineoplastic macrolide derived from the marine bryozoan Bugula neritina. Then, in vivo experiments were conducted to evaluate the role of transforming growth factor (TGF)-β signaling in the progression of AEL.

RESULTS

Our results revealed that the proliferation of K562 cells and TF-1 cells was significantly inhibited by B4 at IC50 values of 37 nM and 52 nM, respectively. B4 inhibited TGF-β signaling and its downstream pathway targets, particularly the phosphorylation of Smad2, Smad3, Ras, C-RAF, ERK1/2, and MEK. B4 also played an important role in cell invasion and migration in K562 cells and TF-1 cells by reducing the protein levels of the mesenchymal cell marker vimentin. Moreover, Flow cytometry and western blot analyses demonstrated that B4 induced apoptosis and initiated G0/G1 phase arrest by modulating mitochondrial dysfunction and cyclin-dependent kinase (CDK) expression.

CONCLUSION

These findings indicated that B4 could inhibit the proliferation, migration, invasion, and TGF-β signaling pathways of AEL cells, thus suggesting that B4 possesses therapeutic potential as a treatment for AEL.

Early Microglial Changes Associated with Diabetic Retinopathy in Rats with Streptozotocin-Induced Diabetes

Although morphological changes in microglia have been reported to be associated with diabetic retinopathy, little is known about the early changes in the microglia and macrophages during the progression of this condition. The present study was aimed at characterizing retinal microglial activation in the early stages of experimental diabetic retinopathy. Toward this end, a model of diabetic retinopathy was generated by intraperitoneally injecting male Sprague-Dawley rats with streptozotocin. No apparent histological changes were observed during the early stages of experimental diabetic retinopathy. However, at 4 to 16 weeks after the onset of diabetes, the retinas from diabetic rats exhibited higher density of microglia than those from age-matched normal controls, with microglial density peaking at 12 weeks. In particular, the proportion of the activated microglia increased significantly in the diabetic rats, specifically in the nerve fiber and ganglion cell layers, whereas it decreased in the inner plexiform layer within 12 weeks. Furthermore, the resident retinal microglial cells were activated immediately after diabetes induction, peaked at 12 weeks, and remained for up to 16 weeks after disease onset. Thus, experimental diabetic retinopathy causes gradual hypoxia and neuroinflammation, followed by the activation of microglia and the migration of macrophages. The distribution and density of retinal microglial activation changed typically with the progression of the disease in early-stage diabetic rats.

The Impact of Age and Gender on Hematopoietic Stem Cells and Immune Contexture of the Bone Marrow Microenvironment

Hematopoietic stem cells (HSCs) are a rare population of cells that reside mainly in the bone marrow and are capable of generating and fulfilling the entire hematopoietic system upon differentiation. Thirty-six healthy donors, attending the HSCT center to donate their bone marrow, were categorized according to their age into child (0-12 years), adolescence (13-18 years), and adult (19-59 years) groups, and gender into male and female groups. Then, the absolute number of HSCs and mature immune cells in their harvested bone marrow was investigated. Here, we report that the absolute cell number can vary considerably based on the age of the healthy donor, and the number of both HSCs and immune cells declines with advancing age. The gender of the donor (male or female) did not have any impact on the number of the HSCs and immune cells in the bone marrow. In conclusion, since the number of HSCs plays a pivotal role in the clinical outcome of allogeneic HSC transplantations, identifying a younger donor regardless the gender is critical.

Loss of TG-Interacting Factor 1 decreases survival in mouse models of myeloid leukaemia

TG‐Interacting Factor 1 (Tgif1) affects proliferation and differentiation of myeloid cells and regulates self‐renewal of haematopoietic stem cells (HSCs). To determine its impact on leukaemic haematopoiesis, we induced acute or chronic myeloid leukaemias (AML or CML) in mice by enforced expression of MLL‐AF9 or BCR‐ABL, respectively, in Tgif1^+/+ or Tgif1^−/− haematopoietic stem and progenitor cells (HSPCs) and transplanted them into syngeneic recipients. We find that loss of Tgif1 accelerates leukaemic progression and shortens survival in mice with either AML or CML. Leukaemia‐initiating cells (LICs) occur with higher frequency in AML among mice transplanted with MLL‐AF9‐transduced Tgif1^−/− HSPCs than with Tgif1^+/+ BMCs. Moreover, AML in mice generated with Tgif1^−/− HSPCs are chemotherapy resistant and relapse more rapidly than those whose AML arose in Tgif1^+/+ HSPCs. Whole transcriptome analysis shows significant alterations in gene expression profiles associated with transforming growth factor‐beta (TGF‐beta) and retinoic acid (RA) signalling pathways because of Tgif1 loss. These findings indicate that Tgif1 has a protective role in myeloid leukaemia initiation and progression, and its anti‐leukaemic contributions are connected to TGF‐beta‐ and RA‐driven functions.

Hydroxyurea-induced senescent peripheral blood mesenchymal stromal cells inhibit bystander cell proliferation of JAK2V617F-positive human erythroleukemia cells

Hydroxyurea (HU) is a nonalkylating antineoplastic agent used in the treatment of hematological malignancies. HU is a DNA replication stress inducer, and as such, it may induce a premature senescence-like cell phenotype; however, its repercussion on bystander cell proliferation has not been revealed so far. Our results indicate that HU strongly inhibited peripheral blood mesenchymal stromal cells (PBMSC) proliferation by cell cycle arrest in S phase, and that, consequently, PBMSC acquire senescence-related phenotypical changes. HU-treated PBMSC display increased senescence-associated β-galactosidase levels and p16^INK4 expression, as well as DNA damage response and genotoxic effects, evidenced by expression of γH2A.X and micronuclei. Moreover, HU-induced PBMSC senescence is mediated by increased reactive oxygen species (ROS) levels, as demonstrated by the inhibition of senescence markers in the presence of ROS scavenger N-acetylcysteine and NADPH oxidase inhibitor Apocynin. To determine the HU-induced bystander effect, we used the JAK2V617F-positive human erythroleukemia 92.1.7 (HEL) cells. Co-culture with HU-induced senescent PBMSC (HU-S-PBMSC) strongly inhibited bystander HEL cell proliferation, and this effect is mediated by both ROS and transforming growth factor (TGF)-β expression. Besides induction of premature senescence, HU educates PBMSC toward an inhibitory phenotype of HEL cell proliferation. Finally, our study contributes to the understanding of the role of HU-induced PBMSC senescence as a potential adjuvant in hematological malignancy therapies.

The Transforming Growth Factor Beta 1/SMAD Signaling Pathway Involved in Human Chronic Myeloid Leukemia

Transforming growth factor beta 1 (TGF-β1) is the prototypic member of a large family of structurally related pleiotropic-secretedcytokines. The TGF-β1/SMAD signaling pathway usually participates in a wide range of cellular processes such as growth, proliferation, differentiation and apoptosis. Upon binding onTGF-β1, the dimerized TGF-β type II receptors recruit and phosphorylate the TGF-β type I receptors, which phosphorylate the receptor-regulated SMAD (SMAD2 and SMAD3) presented by the SMAD anchor for receptor activation.

The phosphorylated receptor-regulated SMAD form heterologous complexes with the common-mediator SMAD (SMAD4) and subsequently translocate into the nucleus, where they interact with other transcription factors to regulate the expression of target genes. This multi-functional signaling pathway modulated by various elements with complex mechanisms at different levels is also inevitably involved in cancer. We herein present data on the role of the TGF-β1/SMAD signaling pathway in human chronic myeloid leukemia and explain the potent biological effects of TGF-β1 on leukemia cells. The paper is based on a review of articles selected from Cancerline and Medline data bases.

The constitutively active tyrosine kinase produced by the specific Bcr-Abl fusion gene on the Philadelphia chromosome can enhance the resistance of malignant cells to TGF-β1-induced growth inhibition and apoptosis, which contributes to enhancement of proteasomal degradation of p27. However, overexpression of the EVI1 gene, which is also caused by Bcr-Abl, can recruit the C-terminal binding protein and histone deacetylase to prevent the MH2 domain on SMAD3. The later is essential for transcription activation on target genes and leads to blockage of the TGF-β1/SMAD signaling pathway.

Some studies have indicated that certain therapeutic agents applied in clinical treatment can inhibit proliferation and promote differentiation of leukemia cells by way of modulation of the TGF-β1/SMAD signal pathway. For example, arsenic trioxide can promote specific degradation of the AML1/MDS1/EVI1 oncoprotein and inhibit the proliferation of leukemia cells. However, specific histone deacetylase inhibitors can interrupt the effect of histone deacetylase to alleviate EVI1-mediated suppression of TGF-β1/SMAD signaling. The tyrosine kinase inhibitor in the target therapy of chronic myeloid leukemia can effectively inhibit the tyrosine kinase activity of Bcr-Abl and induce suppression on the TGF-β1/SMAD signaling pathway.

The TGF-β1/SMAD signaling pathway plays an important role in chronic myeloid leukemia cells and leads the leukemia cells to growth inhibition, differentiation and apoptosis. The positive influence of the TGF-β1/SMAD signaling pathway in chronic myeloid leukemia is fairly significant, and its potential effects in clinical treatment will bring about definite benefits.

Since it is a complex signaling pathway widely involved in many aspects of cellular activities, further study and comprehensive analysis of the TGF-β1/SMAD signaling pathway are imperative and will have a guiding significance in research and clinical applications. It is an exciting area for future research. Free full text available at www.tumorionline.it

Brain Transforming Growth Factor-β Resists Hypertension Via Regulating Microglial Activation

BACKGROUND AND PURPOSE

Hypertension is the major risk factor for stroke. Recent work unveiled that hypertension is associated with chronic neuroinflammation; microglia are the major players in neuroinflammation, and the activated microglia elevate sympathetic nerve activity and blood pressure. This study is to understand how brain homeostasis is kept from hypertensive disturbance and microglial activation at the onset of hypertension.

METHODS

Hypertension was induced by subcutaneous delivery of angiotensin II, and blood pressure was monitored in conscious animals. Microglial activity was analyzed by flow cytometry and immunohistochemistry. Antibody, pharmacological chemical, and recombinant cytokine were administered to the brain through intracerebroventricular infusion. Microglial depletion was performed by intracerebroventricular delivering diphtheria toxin to CD11b-diphtheria toxin receptor mice. Gene expression profile in sympathetic controlling nucleus was analyzed by customized qRT-PCR array.

RESULTS

Transforming growth factor-β (TGF-β) is constitutively expressed in the brains of normotensive mice. Removal of TGF-β or blocking its signaling before hypertension induction accelerated hypertension progression, whereas supplementation of TGF-β1 substantially suppressed neuroinflammation, kidney norepinephrine level, and blood pressure. By means of microglial depletion and adoptive transfer, we showed that the effects of TGF-β on hypertension are mediated through microglia. In contrast to the activated microglia in established hypertension, the resting microglia are immunosuppressive and important in maintaining neural homeostasis at the onset of hypertension. Further, we profiled the signature molecules of neuroinflammation and neuroplasticity associated with hypertension and TGF-β by qRT-PCR array.

CONCLUSIONS

Our results identify that TGF-β-modulated microglia are critical to keeping brain homeostasis responding to hypertensive disturbance.

CD34 expression modulates tube-forming capacity and barrier properties of peripheral blood-derived endothelial colony-forming cells (ECFCs)

Endothelial colony-forming cells (ECFC) are grown from circulating CD34⁺ progenitors present in adult peripheral blood, but during in vitro expansion part of the cells lose CD34. To evaluate whether the regulation of CD34 characterizes the angiogenic phenotypical features of PB-ECFCs, we investigated the properties of CD34⁺ and CD34⁻ ECFCs with respect to their ability to form capillary-like tubes in 3D fibrin matrices, tip-cell gene expression, and barrier integrity. Selection of CD34⁺ and CD34⁻ ECFCs from subcultured ECFCs was accomplished by magnetic sorting (FACS: CD34⁺: 95 % pos; CD34⁻: 99 % neg). Both fractions proliferated at same rate, while CD34⁺ ECFCs exhibited higher tube-forming capacity and tip-cell gene expression than CD3⁴⁻ cells. However, during cell culture CD34⁻ cells re-expressed CD34. Cell-seeding density, cell–cell contact formation, and serum supplements modulated CD34 expression. CD34 expression in ECFCs was strongly suppressed by newborn calf serum. Stimulation with FGF-2, VEGF, or HGF prepared in medium supplemented with 3 % albumin did not change CD34 mRNA or surface expression. Silencing of CD34 with siRNA resulted in strengthening of cell–cell contacts and increased barrier function of ECFC monolayers as measured by ECIS. Furthermore, CD34 siRNA reduced tube formation by ECFC, but did not affect tip-cell gene expression. These findings demonstrate that CD34⁺ and CD34⁻ cells are different phenotypes of similar cells and that CD34 (1) can be regulated in ECFC; (2) is positively involved in capillary-like sprout formation; (3) is associated but not causally related to tip-cell gene expression; and (4) can affect endothelial barrier function.

Comparative study of autophagy inhibition by 3MA and CQ on Cytarabine‑induced death of leukaemia cells

BACKGROUND

As the molecular mechanisms of Cytarabine,one of the most important drugs used in the leukaemia’s treatment, are only partially understood and the role of autophagy on leukaemia development and treatment is only recently being investigated, in this study, by using Chloroquine (CQ) and 3-methyladenine (3MA) as autophagy inhibitors, we aim to evaluate the contribution of an autophagic mechanism to Cytarabine (AraC)-induced death of HL60 leukaemia cells.

METHODS

Trypan blue exclusion and AnnexinV/PI assays were used to evaluate HL60 cell death under AraC treatment in the presence or absence of 3MA and CQ. Western blotting and immunofluorescence experiments were performed to show the involvement of apoptosis and autophagy protein expressions. Phenotypic characterization of HL60-treated cells was performed by using immunophenotyping. Clonogenic assays were applied to analyse clonal function of HL60-treated cells.

RESULTS

We observed that although autophagy inhibition by 3MA, but not CQ, increased the death of HL60 AraC cells after 24 h of treatment, no significant differences between AraC and AraC + 3MA-treated groups were observed by using clonogenic assay. In addition, increased number of immature (CD34(+)/CD38(−)Lin(−/low)) HL60 cells was found in AraC and AraC-3MA groups when compared with control untreated cells.

CONCLUSIONS

Although AraC anti-leukaemia effects could be potentiated by 3MA autophagy inhibition after 24 h of exposure, leukaemia cell resistance, the main causes of treatment failure, is also promoted by autophagy initial stage impairment by 3MA, denoting the complex role of autophagy in leukaemia cells’ response to chemotherapy.

STAT3-mediated astrogliosis protects myelin development in neonatal brain injury

OBJECTIVE

Pathological findings in neonatal brain injury associated with preterm birth include focal and/or diffuse white matter injury (WMI). Despite the heterogeneous nature of this condition, reactive astrogliosis and microgliosis are frequently observed. Thus, molecular mechanisms by which glia activation contribute to WMI were investigated.

METHODS

Postmortem brains of neonatal brain injury were investigated to identify molecular features of reactive astrocytes. The contribution of astrogliosis to WMI was further tested in a mouse model in genetically engineered mice.

RESULTS

Activated STAT3 signaling in reactive astrocytes was found to be a common feature in postmortem brains of neonatal brain injury. In a mouse model of neonatal WMI, conditional deletion of STAT3 in astrocytes resulted in exacerbated WMI, which was associated with delayed maturation of oligodendrocytes. Mechanistically, the delay occurred in association with overexpression of transforming growth factor (TGF)β-1 in microglia, which in healthy controls decreased with myelin maturation in an age-dependent manner. TGFβ-1 directly and dose-dependently inhibited the maturation of purified oligodendrocyte progenitors, and pharmacological inhibition of TGFβ-1 signaling in vivo reversed the delay in myelin development. Factors secreted from STAT3-deficient astrocytes promoted elevated TGFβ-1 production in cultured microglia compared to wild-type astrocytes.

INTERPRETATION

These results suggest that myelin development is regulated by a mechanism involving crosstalk between microglia and oligodendrocyte progenitors. Reactive astrocytes may modify this signaling in a STAT3-dependent manner, preventing the pathological expression of TGFβ-1 in microglia and the impairment of oligodendrocyte maturation.

Interleukin-21 induces the differentiation of human umbilical cord blood CD34-lineage- cells into pseudomature lytic NK cells

Background

Umbilical cord blood (UCB) is enriched with transplantable CD34⁺ cells. In addition to CD34-expressing haematopoietic stem cells (HSC), human UCB contains a rare population of CD34^-lineage^- cells endowed with the ability to differentiate along the T/NK pathway in response to interleukin (IL)-15 and a stromal cell support. IL-21 is a crucial regulator of NK cell function, whose influence on IL-15-induced differentiation of CD34^-lineage^- cells has not been investigated previously. The present study was designed and conducted to address whether IL-21 might replace the stromal cell requirements and foster the IL-15-induced NK differentiation of human UCB CD34^-lineage^- cells.

Results

CD34^-lineage^- cells were maintained in liquid culture with Flt3-L and SCF, with the addition of IL-15 and IL-21, either alone or in combination. Cultures were established in the absence of feeder cells or serum supplementation. Cytokine-treated cells were used to evaluate cell surface phenotype, expression of molecular determinants of lymphoid/NK cell differentiation, secretion of IFN-γ, GM-CSF, TNF-α and CCL3/MIP-1α, and cytolytic activity against NK-sensitive tumour cell targets. CD34^-lineage^- cells proliferated vigorously in response to IL-15 and IL-21 but not to IL-21 alone, and up-regulated phosphorylated Stat1 and Stat3 proteins. CD34^-lineage^- cells expanded by IL-21 in combination with IL-15 acquired lymphoid morphology and killer-cell immunoglobulin-like receptor (KIR)^-CD56⁺CD16^-/+ phenotype, consistent with pseudo-mature NK cells. IL-21/IL-15-differentiated cells expressed high levels of mRNA for Bcl-2, GATA-3 and Id2, a master switch required for NK-cell development, and harboured un-rearranged TCRγ genes. From a functional standpoint, IL-21/IL-15-treated cells secreted copious amounts of IFN-γ, GM-CSF and CCL3/MIP-1α, and expressed cell surface CD107a upon contact with NK-sensitive tumour targets, a measure of exocytosis of NK secretory granules.

Conclusion

This study underpins a novel role for IL-21 in the differentiation of pseudo-mature lytic NK cells in a synergistic context with IL-15, and identifies a potential strategy to expand functional NK cells for immunotherapy.

CD34 expression by hair follicle stem cells is required for skin tumor development in mice

The cell surface marker CD34 marks mouse hair follicle bulge cells, which have attributes of stem cells, including quiescence and multipotency. Using a CD34 knockout (KO) mouse, we tested the hypothesis that CD34 may participate in tumor development in mice because hair follicle stem cells are thought to be a major target of carcinogens in the two-stage model of mouse skin carcinogenesis. Following initiation with 200 nmol 7,12-dimethylbenz(a)anthracene (DMBA), mice were promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 20 weeks. Under these conditions, CD34KO mice failed to develop papillomas. Increasing the initiating dose of DMBA to 400 nmol resulted in tumor development in the CD34KO mice, albeit with an increased latency and lower tumor yield compared with the wild-type (WT) strain. DNA adduct analysis of keratinocytes from DMBA-initiated CD34KO mice revealed that DMBA was metabolically activated into carcinogenic diol epoxides at both 200 and 400 nmol. Chronic exposure to TPA revealed that CD34KO skin developed and sustained epidermal hyperplasia. However, CD34KO hair follicles typically remained in telogen rather than transitioning into anagen growth, confirmed by retention of bromodeoxyuridine-labeled bulge stem cells within the hair follicle. Unique localization of the hair follicle progenitor cell marker MTS24 was found in interfollicular basal cells in TPA-treated WT mice, whereas staining remained restricted to the hair follicles of CD34KO mice, suggesting that progenitor cells migrate into epidermis differently between strains. These data show that CD34 is required for TPA-induced hair follicle stem cell activation and tumor formation in mice.

Effects of histamine on immunophenotype and notch signaling in human HL-60 leukemia cells

Surface molecules are important biomarkers for cell proliferation and differentiation and play important roles in cell function and cell interaction. Notch is a transmembrane receptor that regulates developmental processes and cell-fate decision. Histamine is used as an adjunct to immunotherapy in myelogenous leukemia, and regulates hematopoietic cell development. Thus, we investigated the effects of histamine on immunophenotype and Notch signaling in human HL-60 leukemia cells. Histamine (0.1-10 microM) inhibited the colony-forming efficiency of HL-60 cells in a dose-dependent fashion and shifted the growth curve to the right. HL-60 cells were treated with histamine 0.1-1.0 microM for 6 days, and surface molecules were analyzed by flow cytometry. Histamine decreased CD49d positive cells by 74% while increasing CD31 positive cells by 53% as compared to controls. Histamine did not affect the expression of CD11b, CD14, CD34, CD44, CD54, CD49e, and CD62L. To examine Notch signaling in histamine-induced immunophenotype alterations in HL-60 cells, total RNA was isolated, purified, and subjected to real-time RT-PCR analysis. The expressions of Notch1, Notch4, the ligands Jagged1, Delta4, and the downstream hairy enhancer of split 1 gene (HES1) were not significantly altered by histamine. In summary, this study demonstrated that histamine inhibited HL-60 cell growth and regulated immunophenotypes of CD49d and CD31. These effects are not mediated through the Notch signaling.

Global transcription analysis of immature avian erythrocytic progenitors: from self-renewal to differentiation

The molecular mechanisms regulating the cell fate decision between self-renewal and differentiation/apoptosis in stem and progenitor cells are poorly understood. Here, we report the first comprehensive identification of genes potentially involved in the switch from self-renewal toward differentiation of primary, non-immortalized erythroid avian progenitor cells (T2EC cells). We used the Serial Analysis of Gene Expression (SAGE) technique in order to identify and quantify the genome fraction functionally active in a self-renewing versus a differentiating cell population. We generated two SAGE libraries and sequenced a total of 37,589 tags, thereby obtaining the first transcriptional profile characterization of a chicken cell. Tag identification was performed using a new relational database (Identitag) developed in the laboratory, which allowed a highly satisfactory level of identification. Among 123 differentially expressed genes, 11 were investigated further and for nine of them the differential expression was subsequently confirmed by real-time PCR. The comparison of tag abundance between the two libraries revealed that only a small fraction of transcripts was differentially expressed. The analysis of their functions argue against a prominent role for a master switch in T2EC cells decision-making, but are in favor of a critical role for coordinated small variations in a relatively small number of genes that can lead to essential cellular identity changes.

Differential activation of MAPK signaling pathways by TGF-beta1 forms the molecular mechanism behind its dose-dependent bidirectional effects on hematopoiesis

We have earlier reported that transforming growth factor-beta1 (TGF-beta1), a well-known inhibitor of hematopoiesis, stimulated colony formation from adult human bone marrow mononuclear cells (BM MNC) when used at low concentrations. We examined the possible molecular mechanism behind this bidirectional effect using CD34+ cells isolated from human BM for clonal assays and the KG1a cell line as a model system for analysis of proteins for signaling pathways by immunoblotting. We found that TGF-beta1 at low doses (picogram levels) stimulated the colony formation from CD34+ cells, indicating that these progenitors form the direct target of stimulatory action of TGF-beta1. CD34+ cells were found to be more sensitive to the TGF-beta1 concentration than the total MNC. We used the KG1a cell line as a model system for identification of mitogen-activated protein kinase (MAPK) and AKT signaling pathways involved in the process. Low doses strongly induced p44/42 MAPK phosphorylation, whereas high doses induced p38 activation. Use of specific p44/42 MAPK inhibitor PD 98059 in the colony assay abrogated the stimulatory effect of low TGF-beta1. On the other hand, use of p38 MAPK inhibitor SB 203580 along with low TGF-beta1 concentrations had a synergistic effect on stimulation of colony formation. Treatment of BM MNC with Anisomycin, which activates stress kinases, resulted in a dose-dependent inhibition of colony formation. This inhibition could not be rescued by stimulatory doses of TGF-beta1. Phosphorylation of AKT was found to occur in a dose-dependent way but declined slightly at the highest concentration used (10 ng/ml). Inhibition of the AKT pathway by LY 294002 strongly suppressed colony formation. These data indicate clearly that sustained activation of p44/42 MAPK perhaps forms the stimulatory signal induced by low TGF-beta1, whereas activation of p38 forms the inhibitory pathway.

Long-term expansion of human functional epidermal precursor cells: promotion of extensive amplification by low TGF-beta1 concentrations

We have previously introduced the concept of high proliferative potential-quiescent (HPP-Q) cells to refer to primitive human hematopoietic progenitors, on which transforming growth factor-beta1 (TGF-beta1) exerts a pleiotropic effect. TGF-beta1 confers to these slow-dividing cells a mitogenic receptor(low) phenotype and maintains immature properties by preventing differentiation and apoptosis. However, the effect of TGF-beta1 on long-term expansion has not yet been clearly demonstrated. Here, we describe the characterization of a human skin keratinocyte subpopulation, highly enriched for primitive epidermal precursors, on the basis of high adhesion capacity (Adh+++) and low expression of the epidermal growth factor receptor (Adh+++EGF-Rlow). In our standard culture condition without feeder cells, the mean estimated output for cells from an unfractionated population of primary foreskin keratinocytes was 10(7)-10(8), increasing to 10(12)-10(13) in cultures initiated with selected Adh+++EGF-Rlow precursors. Characterization of these cells revealed a hitherto unknown property of TGF-beta1: its addition at a very low concentration (10 pg/ml) in long-term cultures induces a very significant additional increase of expansion. In this optimized system, outputs obtained in cultures initiated with Adh+++EGF-Rlow cells repeatedly reached 10(16)-10(17) ( approximately 60 population doublings, approximately 4 x 10(18) keratinocytes produced per clonogenic cell present in the initial population). At the molecular level, this effect is associated with an increase in Smad1, Smad2 and Smad3 phosphorylation and an increase in alpha6 and beta1 integrin expression. No such effect could be observed on mature keratinocytes with low adhesion capacity (Adh-/+). We finally demonstrated that the progeny of Adh+++EGF-Rlow precursors after long-term expansion is still capable of generating a pluristratified epidermis in a model for skin reconstruction. In conclusion, after further characterizing the phenotype of primitive epidermal precursors, we demonstrated a new function of TGF-beta1, which is to promote undifferentiated keratinocyte amplification.

Identification of a novel subpopulation of human cord blood CD34-CD133-CD7-CD45+lineage- cells capable of lymphoid/NK cell differentiation after in vitro exposure to IL-15

The hemopoietic stem cell (HSC) compartment encompasses cell subsets with heterogeneous proliferative and developmental potential. Numerous CD34(-) cell subsets that might reside at an earlier stage of differentiation than CD34(+) HSCs have been described and characterized within human umbilical cord blood (UCB). We identified a novel subpopulation of CD34(-)CD133(-)CD7(-)CD45(dim)lineage (lin)(-) HSCs contained within human UCB that were endowed with low but measurable extended long-term culture-initiating cell activity. Exposure of CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs to stem cell factor preserved cell viability and was associated with the following: 1) concordant expression of the stem cell-associated Ags CD34 and CD133, 2) generation of CFU-granulocyte-macrophage, burst-forming unit erythroid, and megakaryocytic aggregates, 3) significant extended long-term culture-initiating cell activity, and 4) up-regulation of mRNA signals for myeloperoxidase. At variance with CD34(+)lin(-) cells, CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs maintained with IL-15, but not with IL-2 or IL-7, proliferated vigorously and differentiated into a homogeneous population of CD7(+)CD45(bright)CD25(+)CD44(+) lymphoid progenitors with high expression of the T cell-associated transcription factor GATA-3. Although they harbored nonclonally rearranged TCRgamma genes, IL-15-primed CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs failed to achieve full maturation, as manifested in their CD3(-)TCRalphabeta(-)gammadelta(-) phenotype. Conversely, culture on stromal cells supplemented with IL-15 was associated with the acquisition of phenotypic and functional features of NK cells. Collectively, CD34(-)CD133(-)CD7(-)CD45(dim)lin(-) HSCs from human UCB displayed an exquisite sensitivity to IL-15 and differentiated into lymphoid/NK cells. Whether the transplantation of CD34(-)lin(-) HSCs possessing T/NK cell differentiation potential may impact on immunological reconstitution and control of minimal residual disease after HSC transplantation for autoimmune or malignant diseases remains to be determined.

Transforming growth factor-beta signaling in normal and malignant hematopoiesis

Transforming growth factor-beta (TGF-beta) is perhaps the most potent endogenous negative regulator of hematopoiesis. The intracellular signaling events mediating the effects of TGF-beta are multiple, involving extensive crosstalk between Smad-dependent and MAP-kinase-dependent pathways. We are only beginning to understand the importance of the balance between these cascades as a determinant of the response to TGF-beta, and have yet to determine the roles that disruption in TGF-beta signaling pathways might play in leukemogenesis. This review summarizes current knowledge regarding the function of TGF-beta in normal and malignant hematopoiesis. The principal observations made by gene targeting studies in mice are reviewed, with an emphasis on how a disruption of this pathway in vivo can affect blood cell development and immune homeostasis. We overview genetic alterations that lead to impaired TGF-beta signaling in hematopoietic neoplasms, including the suppression of Smad-dependent transcriptional responses by oncoproteins such as Tax and Evi-1, and fusion proteins such as AML1/ETO. We also consider mutations in genes encoding components of the core cell cycle machinery, such as p27(Kip1) and p15(INK4A), and emphasize their impact on the ability of TGF-beta to induce G1 arrest. The implications of these observations are discussed, and opinions regarding important directions for future research on TGF-beta in hematopoiesis are provided.

Phosphorylation of Nrf2 at Ser40 by protein kinase C in response to antioxidants leads to the release of Nrf2 from INrf2, but is not required for Nrf2 stabilization/accumulation in the nucleus and transcriptional activation of antioxidant response element-mediated NAD(P)H:quinone oxidoreductase-1 gene expression

The antioxidant response element (ARE) and transcription factor Nrf2 regulate basal expression and antioxidant induction of NAD(P)H:quinone oxidoreductase-1 (NQO1) and other detoxifying genes. Under normal conditions, Nrf2 is targeted for proteasomal degradation by INrf2. Oxidative stress causes release of Nrf2 from INrf2. Nrf2 translocates to the nucleus, binds to the ARE, and activates gene expression. In this study, we demonstrate that protein kinase C (PKC) plays a significant role in the regulation of ARE-mediated NQO1 gene expression and induction in response to t-butylhydroquinone. Treatment of HepG2 cells with the PKC inhibitors staurosporine and calphostin C repressed ARE-mediated induction of a luciferase reporter as well as that of the endogenous NQO1 gene. Similar experiments with inhibitors of MEK/ERK, p38, phosphatidylinositol 3-kinase, and tyrosine kinases failed to repress ARE-mediated gene expression. The PKC inhibitor staurosporine blocked the nuclear translocation of Nrf2, suggesting that Nrf2 might be the target for PKC regulation. A Prosite search revealed the presence of seven putative PKC sites in mouse Nrf2. The PKC site at Ser40 is conserved among species and lies in the Neh2 domain, which interacts with INrf2. We demonstrate that phosphorylation of Ser40 is necessary for Nrf2 release from INrf2, but is not required for Nrf2 stabilization/accumulation in the nucleus and transcriptional activation of ARE-mediated NQO1 gene expression. A peptide that competes with endogenous Nrf2 for INrf2 binding was able to induce ARE activity more effectively than t-butylhydroquinone, and Nrf2 that accumulated in the nucleus as a result was not phosphorylated.

Transforming growth factor-beta1 causes transcriptional activation of CD34 and preserves haematopoietic stem/progenitor cell activity

Stem/progenitor cells endowed with in vitro and in vivo haematopoietic activity express the surface protein CD34. Transforming growth factor beta1 (TGF-beta1) is one of the soluble molecules that regulate cell cycle and differentiation of haematopoietic cells, but has pleiotropic activities depending on the state of responsiveness of the target cells. It has previously been shown that TGF-beta1 maintains human CD34+ haematopoietic progenitors in an undifferentiated state, independently of any cell cycle effect. Here, we have shown that TGF-beta1 upregulates the human CD34, an effect that was evident in primary stem/progenitor cells (CD34+lin-) both at the transcriptional and protein levels, and was not associated with any relevant effect on cell growth. The presence of TGF-beta1 influenced differentiation, maintaining primary CD34+/Lin- in an undifferentiated state. This effect was associated with Smad activation and with a dramatic decrease in p38 phosphorylation. Moreover, blocking p38 phosphorylation by the SB202190 inhibitor increased CD34 RNA levels but did not enhance CD34 protein expression in CD34+/Lin- cells, suggesting that modulation of multiple signalling pathways is necessary to reproduce TGF-beta1 effects. These data establish the role that TGF-beta1 has in the modulation of the CD34 stem/progenitor protein and stem/progenitor functions, providing important clues for understanding haematopoietic development and a potential tool for the modulation of human haematopoiesis.

Semiquantitative RT-PCR analysis to assess the expression levels of multiple transcripts from the same sample

We describe a semiquantitative RT-PCR protocol optimized in our laboratory to extract RNA from as little as 10,000 cells and to measure the expression levels of several target mRNAs from each sample. This procedure was optimized on the human erythroleukemia cell line TF-1 but was successfully used on primary cells and on different cell lines. We describe the detailed procedure for the analysis of Bcl-2 levels. Aldolase A was used as an internal control to normalize for sample to sample variations in total RNA amounts and for reaction efficiency. As for all quantitative techniques, great care must be taken in all optimization steps: the necessary controls to ensure a rough quantitative (semi-quantitative) analysis are described here, together with an example from a study on the effects of TGF-beta1 in TF-1 cells.