Stem cell factor protects erythroid precursor cells from chemotherapeutic agents via up-regulation of BCL-2 family proteins

Synergistic immunotherapy targeting cancer-associated anemia: prospects of a combination strategy

Cancer-associated anemia promotes tumor progression, leads to poor quality of life in patients with cancer, and even obstructs the efficacy of immune checkpoint inhibitors therapy. However, the precise mechanism for cancer-associated anemia remains unknown and the feasible strategy to target cancer-associated anemia synergizing immunotherapy needs to be clarified. Here, we review the possible mechanisms of cancer-induced anemia regarding decreased erythropoiesis and increased erythrocyte destruction, and cancer treatment-induced anemia. Moreover, we summarize the current paradigm for cancer-associated anemia treatment. Finally, we propose some prospective paradigms to slow down cancer-associated anemia and synergistic the efficacy of immunotherapy. Video Abstract.

Tumor Immune Evasion Induced by Dysregulation of Erythroid Progenitor Cells Development

Cancer cells harness normal cells to facilitate tumor growth and metastasis. Within this complex network of interactions, the establishment and maintenance of immune evasion mechanisms are crucial for cancer progression. The escape from the immune surveillance results from multiple independent mechanisms. Recent studies revealed that besides well-described myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs) or regulatory T-cells (Tregs), erythroid progenitor cells (EPCs) play an important role in the regulation of immune response and tumor progression. EPCs are immature erythroid cells that differentiate into oxygen-transporting red blood cells. They expand in the extramedullary sites, including the spleen, as well as infiltrate tumors. EPCs in cancer produce reactive oxygen species (ROS), transforming growth factor β (TGF-β), interleukin-10 (IL-10) and express programmed death-ligand 1 (PD-L1) and potently suppress T-cells. Thus, EPCs regulate antitumor, antiviral, and antimicrobial immunity, leading to immune suppression. Moreover, EPCs promote tumor growth by the secretion of growth factors, including artemin. The expansion of EPCs in cancer is an effect of the dysregulation of erythropoiesis, leading to the differentiation arrest and enrichment of early-stage EPCs. Therefore, anemia treatment, targeting ineffective erythropoiesis, and the promotion of EPC differentiation are promising strategies to reduce cancer-induced immunosuppression and the tumor-promoting effects of EPCs.

BCL-XL expression is essential for human erythropoiesis and engraftment of hematopoietic stem cells

The anti-apoptotic BCL-2 proteins (BCL-2, BCL-XL, MCL-1, A1, BCL-W) counteract apoptotic signals emerging during development and under stress conditions, and are thus essential for the survival of every cell. While the “BCL-2 addiction” of different cell types is well described in mouse models, there is only limited information available on the role of different anti-apoptotic BCL-2 proteins in a given human cell type. Here we characterize the role of BCL-XL for survival and function of human hematopoietic cells, with the aim to predict hematological side effects of novel BCL-XL-inhibiting BH3-mimetics and to identify hematological malignancies potentially responsive to such inhibitors. Earlier clinical studies have shown that the combined BCL-2/BCL-XL/BCL-W inhibitor, Navitoclax (ABT-263) induces severe thrombocytopenia caused by direct platelet demise and counteracted by increased megakaryopoiesis. In contrast, murine studies have reported important contribution of BCL-XL to survival of late erythroid cells and megakaryocytes. Using lentiviral knockdown, we show that the roles of BCL-XL for human hematopoietic cells are much more pronounced than expected from murine data and clinical trials. Efficient genetic or chemical BCL-XL inhibition resulted in significant loss of human erythroid cells beginning from very early stages of erythropoiesis, and in a reduction of megakaryocytes. Most importantly, BCL-XL deficient human hematopoietic stem cells and multipotent progenitors were reduced in numbers, and they showed a severely impaired capacity to engraft in mice during xenotransplantation. BCL-XL deficiency was fully compensated by BCL-2 overexpression, however, loss of its antagonist BIM did not result in any rescue of human erythroid or stem and progenitor cells. We thus conclude that novel and specific BCL-XL inhibitors might be efficient to treat malignancies of erythroid or megakaryocytic origin, such as polycythemia vera, acute erythroid leukemia, essential thrombocytosis or acute megakaryocytic leukemia. At the same time, it can be expected that they will have more severe hematological side effects than Navitoclax.

Protective effects of cytokine combinations against the apoptotic activity of glucocorticoids on CD34+ hematopoietic stem/progenitor cells

Haematopoietic stem cells can self-renew and produce progenitor cells, which have a high proliferation capacity. Chemotherapeutic drugs are toxic to normal cells as well as cancer cells, and glucocorticoids (GCs), which are essential drugs for many chemotherapeutic protocols, efficiently induce apoptosis not only in malignant cells but also in normal haematopoietic cells. Studies have shown that haematopoietic cytokines can prevent the apoptosis induced by chemotherapy and decrease the toxic effects of these drugs. However, the apoptosis induction mechanism of GCs in CD34⁺ haematopoietic cells and the anti-apoptotic effects of cytokines have not been well elucidated. In this study, we investigated the apoptotic effects of GCs on CD34⁺, a haematopoietic stem/progenitor cell (HSPC) population, and demonstrated the protective effects of haematopoietic cytokines. We used a cytokine cocktail containing early-acting cytokines, namely, interleukin-3 (IL-3), thrombopoietin, stem cell factor and flt3/flk2 ligand, and dexamethasone and prednisolone were used as GCs. Apoptotic mechanisms were assessed by immunohistochemical staining and quantified using H-scoring. Dexamethasone and prednisolone induced apoptosis in CD34⁺ HSPCs. GC treatment caused a significant increase in apoptotic Fas, caspase-3, cytochrome c and Bax, but a significant decrease in anti-apoptotic Bcl-2. Furthermore, as expected, cytokines caused a significant decrease in all apoptotic markers and a significant increase in Bcl-2. Thus, our findings suggest that CD34⁺ HSPCs are an extremely sensitive target for GCs and that cytokines protect these cells from GC-induced apoptosis.

Levetiracetam enhances the temozolomide effect on glioblastoma stem cell proliferation and apoptosis

Background

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor in which cancer cells with stem cell-like features, called cancer stem cells (CSCs), were identified. Two CSC populations have been previously identified in GBM, one derived from the GBM area called enhanced lesion (GCSCs) and the other one from the brain area adjacent to the tumor margin (PCSCs) that greatly differ in their growth properties and tumor-initiating ability. To date the most effective chemotherapy to treat GBM is represented by alkylating agents such as temozolomide (TMZ), whose activity can be regulated by histone deacetylases (HDACs) inhibitors through the modulation of O6-methylguanine-DNA methyltransferase (MGMT) expression. Levetiracetam (LEV), a relatively new antiepileptic drug, modulates HDAC levels ultimately silencing MGMT, thus increasing TMZ effectiveness. However, an improvement in the therapeutic efficacy of TMZ is needed.

Methods

Cell proliferation was investigated by BrdU cell proliferation assay and by Western Blot analysis of PCNA expression. Apoptosis was evaluated by Western Blot and Immunofluorescence analysis of the cleaved Caspase-3 expression. MGMT and HDAC4 expression was analyzed by Western Blotting and Immunofluorescence. Statistical analysis was performed using the Student's t test and Mann-Whitney test.

Results

Here we evaluated the effect of TMZ on the proliferation rate of the IDH-wildtype GCSCs and PCSCs derived from six patients, in comparison with the effects of other drugs such as etoposide, irinotecan and carboplatin. Our results demonstrated that TMZ was less effective compared to the other agents; hence, we verified the possibility to increase the effect of TMZ by combining it with LEV. Here we show that LEV enhances the effect of TMZ on GCSCs proliferation (being less effective on PCSCs) by decreasing MGMT expression, promoting HDAC4 nuclear translocation and activating apoptotic pathway.

Conclusions

Although further studies are needed to determine the exact mechanism by which LEV makes GBM stem cells more  sensitive to TMZ, these results suggest that the clinical therapeutic efficacy of TMZ in GBM might be enhanced by the combined treatment with LEV.

PI3K-Akt Signal Transduction Molecules Maybe Involved in Downregulation of Erythroblasts Apoptosis and Perifosine Increased Its Apoptosis in Chronic Mountain Sickness

Background

Chronic mountain sickness (CMS) has a higher incidence in the plateau region. The one of its principal characters is excessive erythrocytosis. The PI3K-Akt pathway plays an important role in the process of erythropoiesis, and could downregulate apoptosis by regulating apoptosis-related molecules. In this paper, we explored the change in apoptosis of erythroblasts and the effect of the PI3K-Akt signal pathway on erythroblasts apoptosis in CMS.

Material/Methods

A total of 22 CMS and 20 non-CMS participants were involved in this study. Bone marrow mononuclear cells were cultured and treated with celecoxib and perifosine in vitro for 72 hours. The apoptotic rate, the mRNA expressions of Akt, Bcl-xl, and caspase-9, and the protein expressions of Akt, p-Akt, Bcl-xl, and caspase-9 were determined by flow cytometry, quantitative RT-PCR, and western-blot technique.

Results

The apoptotic rate of cultured erythroblasts was lower in the CMS group than in the non-CMS group. It was increased after perifosine intervention. The mRNA and protein expressions of Akt and Bcl-xl were higher and caspase-9 was lower in the CMS group than the non-CMS group. Perifosine induced decreased Bcl-xl mRNA and proteins and p-Akt proteins, and increased caspase-9 mRNA and proteins in vitro. In the CMS group, the hemoglobin concentration was correlated with apoptotic rate negatively and with Bcl-xl mRNA positively in erythroblasts; the erythroblasts apoptotic rate was negatively associated with the Akt mRNA and Bcl-xl mRNA.

Conclusion

The erythroblasts apoptosis was downregulated and the PI3K-Akt signal pathway appeared to be involved in the mechanism of decreased erythroblasts apoptosis in CMS.

Analysis of POU5F1, c-Kit, PLAP, AP2γ and SALL4 in gonocytes of patients with cryptorchidism

Cryptorchidism is a risk factor for the development of testicular germ cell tumors (TGCTs). The most common type of TGCT in cryptorchidism is seminoma. The intratubular germ cell neoplasia unclassified (ITGCNU) is a histological pattern preceding the development of seminomas and non-seminomas. It was suggested that in patients with cryptorchidism, the gonocytes remained undifferentiated with pluripotent abilities expressing proteins like POU domain class 5 transcription factor 1 (POU5F1), tyrosine kinase receptor c-Kit, placental-like alkaline phosphatase (PLAP), the transcription factor AP2γ and sal-like protein 4 (SALL4) that confer to the gonocytes this ability and therefore make them susceptible to develop ITGCNU. The aim of the present study was to determine if the gonocytes of patients with cryptorchidism express POU5F1, c-Kit, PLAP, AP2γ and SALL4 proteins after their differentiation period. Based on this, we evaluated samples of testicular tissue from newborns to 16-year old subjects with or without cryptorchidism in search of POU5F1, c-Kit, PLAP, AP2γ and SALL4 using immunocytochemical method, the results of which were validated by RT-PCR. The results showed that control subjects witnessed a down-regulation in the expression of these five proteins in the first year of life, which eventually disappeared. On the other hand, it was determined that 21.6% (8/37) of the patients with cryptorchidism continued to express, at least, one of the proteins analyzed in this study after the second year of life. And only 5.4% (2/37) of the patients were positive to the five markers. These data sustain the proposed hypothesis that in cryptorchid patients, ITGCNU arises from gonocytes that fail in their differentiation process to spermatogonia with conservation of the proteins (POU5F1, c-Kit, PLAP, AP2γ and SALL4) that maintain pluripotency and undifferentiated characteristics and which are responsible for making the gonocytes susceptible to malignancy. However, we cannot guarantee that these patients present neoplastic transformation.

Differentiation potential of o bombay human-induced pluripotent stem cells and human embryonic stem cells into fetal erythroid-like cells

Objective

There is constant difficulty in obtaining adequate supplies of blood components, as well as disappointing performance of "universal" red blood cells. Advances in somatic cell reprogramming of human-induced pluripotent stem cells (hiPSCs) have provided a valuable alternative source to differentiate into any desired cell type as a therapeutic promise to cure many human disease.

Materials and Methods

In this experimental study, we examined the erythroid differentiation potential of normal Bombay hiPSCs (B-hiPSCs) and compared results to human embryonic stem cell (hESC) lines. Because of lacking ABO blood group expression in B-hiPSCs, it has been highlighted as a valuable source to produce any cell type in vitro.

Results

Similar to hESC lines, hemangioblasts derived from B-hiPSCs expressed approximately 9% KDR⁺CD31⁺ and approximately 5% CD31⁺CD34⁺. In semisolid media, iPSC and hESC-derived hemangioblast formed mixed type of hematopoietic colony. In mixed colonies, erythroid progenitors were capable to express CD71⁺GPA⁺HbF⁺ and accompanied by endothelial cells differentiation.

Conclusion

Finally, iPS and ES cells have been directly induced to erythropoiesis without hemangioblast formation that produced CD71⁺HbF⁺ erythroid cells. Although we observed some variations in the efficiency of hematopoietic differentiation between iPSC and ES cells, the pattern of differentiation was similar among all three tested lines.

Kit transduced signals counteract erythroid maturation by MAPK-dependent modulation of erythropoietin signaling and apoptosis induction in mouse fetal liver

Signaling by the stem cell factor receptor Kit in hematopoietic stem and progenitor cells is functionally associated with the regulation of cellular proliferation, differentiation and survival. Expression of the receptor is downregulated upon terminal differentiation in most lineages, including red blood cell terminal maturation, suggesting that omission of Kit transduced signals is a prerequisite for the differentiation process to occur. However, the molecular mechanisms by which Kit signaling preserves the undifferentiated state of progenitor cells are not yet characterized in detail. In this study, we generated a mouse model for inducible expression of a Kit receptor carrying an activating mutation and studied its effects on fetal liver hematopoiesis. We found that sustained Kit signaling leads to expansion of erythroid precursors and interferes with terminal maturation beyond the erythroblast stage. Primary KIT(D816V) erythroblasts stimulated to differentiate fail to exit cell cycle and show elevated rates of apoptosis because of insufficient induction of survival factors. They further retain expression of progenitor cell associated factors c-Myc, c-Myb and GATA-2 and inefficiently upregulate erythroid transcription factors GATA-1, Klf1 and Tal1. In KIT(D816V) erythroblasts we found constitutive activation of the mitogen-activated protein kinase (MAPK) pathway, elevated expression of the src kinase family member Lyn and impaired Akt activation in response to erythropoietin. We demonstrate that the block in differentiation is partially rescued by MAPK inhibition, and completely rescued by the multikinase inhibitor Dasatinib. These results show that a crosstalk between Kit and erythropoietin receptor signaling cascades exists and that continuous Kit signaling, partly mediated by the MAPK pathway, interferes with this crosstalk.

Novel anti-apoptotic microRNAs 582-5p and 363 promote human glioblastoma stem cell survival via direct inhibition of caspase 3, caspase 9, and Bim

Glioblastoma is the most common and lethal primary brain tumor. Tumor initiation and recurrence are likely caused by a sub-population of glioblastoma stem cells, which may derive from mutated neural stem and precursor cells. Since CD133 is a stem cell marker for both normal brain and glioblastoma, and to better understand glioblastoma formation and recurrence, we looked for dys-regulated microRNAs in human CD133+ glioblastoma stem cells as opposed to CD133+ neural stem cells isolated from normal human brain. Using FACS sorting of low-passage cell samples followed by microRNA microarray analysis, we found 43 microRNAs that were dys-regulated in common in three separate CD133+ human glioblastomas compared to CD133+ normal neural stem cells. Among these were several microRNAs not previously associated with cancer. We then verified the microRNAs dys-regulated in glioblastoma using quantitative real time PCR and Taqman analysis of the original samples, as well as human GBM stem cell and established cell lines and many human specimens. We show that two candidate oncogenic microRNAs, miR-363 and miR-582-5p, can positively influence glioblastoma survival, as shown by forced expression of the microRNAs and their inhibitors followed by cell number assay, Caspase 3/7 assay, Annexin V apoptosis/fluorescence activated cell sorting, siRNA rescue of microRNA inhibitor treatment, as well as 3′UTR mutagenesis to show luciferase reporter rescue of the most successful targets. miR-582-5p and miR-363 are shown to directly target Caspase 3, Caspase 9, and Bim.

Aconitum C₂₀-diterpenoid alkaloid derivatives regulate the growth and differentiation of cord blood derived human hematopoietic stem/progenitor cells

The pharmacological activity of Aconitum alkaloids depends on their fundamental structure. While C₁₉-norditerpenoid alkaloids present significant toxicity to the central nervous system, C₂₀-diterpenoid alkaloids have reduced toxicities. However, there is little information regarding the precise pharmacological properties of C₂₀-diterpenoid alkaloids. C₂₀-diterpenoid alkaloid derivatives have explicit structure-activity relationships targeting various tumor cells, which depend on the C11-substrate. However, the present study showed that C6-derivatives additively or synergistically sustained proliferation of CD34⁺ hematopoietic stem/progenitor cells derived from the placental/umbilical cord blood. It revealed that identical structures belonging to C₂₀-diterpenoid alkaloids surprisingly have opposing proliferative effects depending on the derivatization sites (C6 versus C11).

The Notch2-Jagged1 interaction mediates stem cell factor signaling in erythropoiesis

Stem cell factor (SCF), the ligand for the c-kit receptor, is essential for the production of red blood cells during development and stress erythropoiesis. SCF promotes erythroblast proliferation and survival, while delaying erythroid differentiation through mechanisms that are largely unknown. In cultures of primary human differentiating erythroblasts, we found that SCF induces an increase in the expression of Notch2, a member of the Notch family implicated in the control of cell growth and differentiation. Functional inhibition of either Notch or its ligand Jagged1 inhibited the effects of SCF on erythroid cell expansion. SCF also induced the expression of Hes-1 and GATA-2, which may contribute to transduce Notch2 signals in response to SCF. Transduction of primary erythroid precursors with a dominant-negative Notch2 mutant inhibited both basal and SCF-mediated erythroblast expansion, and counteracted the effects of SCF on erythroblast differentiation. These findings provide a clue to understand the effects of increased proliferation and delayed differentiation elicited by SCF on the erythroid compartment and indicate Notch2 as a new player in the regulation of red cell differentiation.

Experimental Models of Acute Renal Failure and Erythropoietin: What Evidence of a Direct Effect?

The kidney can achieve a structural and functional recovery after the damage induced by ischemia and reperfusion. This is due to the regeneration of epithelial tubular cells, the intervention of immature cells mainly localized in the medulla, and a small number of bone marrow-derived stem cells. In many instances, however, recovery is delayed or does not occur at all. The mechanisms allowing the renal cells to de-differentiate still need to be clarified in order to find a therapeutic approach that can amplify this ability and then stop the fibroid involution and the progression toward renal failure. Several authors have hypothesized a protective effect of EPO against ischemic and cytotoxic renal damage and observed that patients precociously treated with EPO showed a slower progression of renal failure. EPO has been demonstrated to have proliferative and anti-apoptotic effects in ischemia-reperfusion models in the brain and cell cultures. Moreover, EPO can mobilize stem cells and increase the plasmatic levels and the renal expression of VEGF. These effects seem to be dose-dependent and could be due to the activation of signal transduction systems, like Jak and STAT. In the presence of high doses of exogenous EPO or during the treatment with long-acting EPO-like molecules, non-specific receptors may be activated through a low-affinity link. Further investigations are needed to determine new therapeutic applications for EPO and other analogous hormones. Very long-acting molecules or molecules with cyto-protective but no erythropoietic effect may represent useful tools in the study of the molecular mechanisms underlying EPO's action and may have a rapid and safe therapeutic application.

Interferon Alpha 2b as Maintenance Therapy Improves Outcome In Follicular Lymphoma

The role of interferon alpha as maintenance therapy in follicular lymphoma (FL) remains unsolved. We started a controlled clinical trial to assess if interferon alpha 2b could improve outcome, measured with event free survival (EFS) and overall survival (OS) in patients with FL in complete remission after chemotherapy based anthracyclines and adjuvant radiotherapy to sites of initial bulky disease. Three hundred and eighty four patients in complete response after 6 cycles of CEOP-Bleo (cyclophosphamide, epirubicin, vincristine, prednisone and bleomycin, at standard doses), and adjuvant radiotherapy when necessary, were randomized to received Interferon alpha 2b, three times a week for 1 year or no treatment (control group). Median follow up was 9.8 years (range 7.0-15 years); actuarial curves showed that EFS was 64% (95% confidence interval (CI) 56-71%) in patients treated with interferon that was statistically significant to patients in the control group: 35% (95% CI: 28-43%) (p<.01). OS was also statistically significant: 81% in patients treated with interferon (95% CI: 74-93%) and 57% (95% CI: 50-63%) in the control group (p<.001). Toxicity was mild, all patients received the planned dose of interferon on time. The use of aggressive chemotherapy and maintenance therapy with interferon alpha 2b in follicular lymphoma improved outcome; more than 60% of patients remain alive free of disease at longer follow-up.

Activity of the BH3 mimetic ABT-737 on polycythemia vera erythroid precursor cells

An increased expression of antiapoptotic molecules is often found in malignant cells, where it contributes to their clonal expansion by conferring an improved survival ability. We found that erythroid precurors derived from patients with polycythemia vera (PV) with medium and high JAK2V617F mutation rates often express elevated levels of the antiapoptotic molecules Bcl-2 and Bcl-XL (5 of 12 patients with 3 to 7 times Bcl-2 and 3 of 12 patients with 4 to 7 times Bcl-XL than average normal controls) and are more resistant to myelosuppressive drugs than normal erythroblasts. ABT-737, a small-molecule inhibitor of Bcl-2, Bcl-XL, and Bcl-W, induced apoptosis preferentially in JAK2V617F-high PV erythroid precursors as compared with JAK2V617F-low or normal erythroblasts. ABT-737 inhibited also the proliferation of PV erythroblasts and interfered with the formation of endogenous erythroid colonies by PV hematopoietic progenitors. Altogether, these results suggest that small-molecule inhibitors of Bcl-2/Bcl-XL may be used in the treatment of patients with PV with high JAK2V617F allele burden.

Fetal hemoglobin chemical inducers for treatment of hemoglobinopathies

The switch from fetal ((G)gamma and (A)gamma) to adult (beta and delta) globin gene expression occurs at birth, leading to the gradual replacement of HbF with HbA. Genetic regulation of this switch has been studied for decades, and the molecular mechanisms underlying this developmental change in gene expression have been in part elucidated. The understanding of the developmental regulation of gamma-globin gene expression was paralleled by the identification of a series of chemical compounds able to reactivate HbF synthesis in vitro and in vivo in adult erythroid cells. Reactivation of HbF expression is an important therapeutic option in patients with hemoglobin disorders, such as sickle cell anemia and beta-thalassemia. These HbF inducers can be grouped in several classes based on their chemical structures and mechanisms of action. Clinical studies with some of these agents have shown that they were effective, in a part of patients, in ameliorating the clinical condition. The increase in HbF in response to these drugs varies among patients with beta-thalassemia and sickle cell disease due to individual genetic determinants.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor affects fate determination of human gonocytes in vitro

The stem cell factor (SCF), binding its tyrosine kinase receptor c-Kit, has been shown to play essential roles in the proliferation, differentiation, and survival of germline cells. However, few reports are available about the effect of SCF on the development of human gonocytes within the fetal testis. The objective of this study was to investigate whether SCF affects the biological behaviors of human gonocytes before or after they enter the mitotic arrest stage. Employing an organ culture system, we observed that addition of exogenous SCF could influence the morphology of human gonocytesin vitro. Moreover, SCF was able to trigger the colony formation of round gonocytes, which were characterized positive for alkaline phosphatase activity, Oct-4, SSEA-4, and c-Kit as well. We found that SCF exerted actions in a dose- and age-dependent manner, although the stimulatory effect lasted no more than 14 days. We also showed that SCF played a role in suppressing the apoptosis of human gonocytes. Blocking of SCF signaling with either phosphatidylinositol 3-kinase or mitogen-activated protein kinase inhibitor resulted in similar apoptotic features as well as the SCF-withdrawal cultures. Taken together, we report that SCF acts as a potent regulator in the fate determination of human gonocytes. Our studies should form the basis forin vitrostudies and facilitate investigation of the molecular mechanisms underlying this unique stage.

Effective erythropoiesis and HbF reactivation induced by kit ligand in beta-thalassemia

In human beta-thalassemia, the imbalance between alpha- and non-alpha-globin chains causes ineffective erythropoiesis, hemolysis, and anemia: this condition is effectively treated by an enhanced level of fetal hemoglobin (HbF). In spite of extensive studies on pharmacologic induction of HbF synthesis, clinical trials based on HbF reactivation in beta-thalassemia produced inconsistent results. Here, we investigated the in vitro response of beta-thalassemic erythroid progenitors to kit ligand (KL) in terms of HbF reactivation, stimulation of effective erythropoiesis, and inhibition of apoptosis. In unilineage erythroid cultures of 20 patients with intermedia or major beta-thalassemia, addition of KL, alone or combined with dexamethasone (Dex), remarkably stimulated cell proliferation (3-4 logs more than control cultures), while decreasing the percentage of apoptotic and dyserythropoietic cells (<5%). More important, in both thalassemic groups, addition of KL or KL plus Dex induced a marked increase of gamma-globin synthesis, thus reaching HbF levels 3-fold higher than in con-trol cultures (eg, from 27% to 75% or 81%, respectively, in beta-thalassemia major). These studies indicate that in beta-thalassemia, KL, alone or combined with Dex, induces an expansion of effective erythropoiesis and the reactivation of gamma-globin genes up to fetal levels and may hence be considered as a potential therapeutic agent for this disease.

Chemotherapy-induced thrombocytopenia derives from the selective death of megakaryocyte progenitors and can be rescued by stem cell factor

Thrombocytopenia is a common side effect of chemotherapy, responsible for increased risk of bleeding and delay of treatment schedules in cancer patients. It is currently unknown how chemotherapeutic agents affect platelet production and whether the platelet precursors megakaryocytes represent a direct target of cytotoxic drugs. We investigated the effects of chemotherapeutic agents on primary megakaryocytes by using a culture system that recapitulates in vitro human megakaryopoiesis and found that cytotoxic drugs predominantly destroyed megakaryocytic progenitors at early stages of differentiation. Immature megakaryocytes could be protected from chemotherapeutic agents by the cytokine stem cell factor (SCF), which binds the c-kit receptor expressed on hematopoietic stem and progenitor cells. In chemotherapy-treated megakaryocytes, SCF activated Akt, neutralized the mitochondrial apoptotic machinery, and inhibited caspase activity. Interfering with Akt activation abrogated the antiapoptotic effects of SCF, whereas exogenous expression of constitutively active Akt inhibited drug-induced apoptosis of primary megakaryocytes, indicating the Akt pathway as primarily responsible for SCF-mediated protection of megakaryocyte progenitors. These results indicate apoptosis of megakaryocyte progenitors as a major cause of chemotherapy-induced thrombocytopenia and suggest that SCF may be used to prevent platelet loss in cancer patients with c-kit-negative tumors.

Pleiotropic role of histone deacetylases in the regulation of human adult erythropoiesis

Histone acetylation and deacetylation play fundamental roles in transcriptional regulation. We investigated the role of histone deacetylases (HDACs) in human adult haematopoiesis, using the structurally distinct HDAC inhibitors FK228 (depsipeptide) and Trichostatin A. When CD34+ cells were cultured with interleukin (IL)-3 or stem cell factor (SCF) + IL-3, FK228 (0.5 ng/ml) specifically enhanced the generation of immature erythroid cells with a CD36+ glycophorin A (GPA)low phenotype. In semisolid cultures, FK228 promoted the formation of erythroid colonies by CD34+ cells with IL-3 and SCF + IL-3. Furthermore, upon exposure to FK228, CD34+ cell-derived CD36+ GPA- cells were induced to form erythroid colonies with IL-3 alone. Conversely, FK228 inhibited the generation of CD36+ GPAhigh relatively mature erythroid cells from CD34+ cells in the presence of erythropoietin (EPO) and SCF + EPO. FK228 suppressed the EPO-mediated survival of CD36+ GPAlow/- and CD36+ GPAhigh cells and induced their apoptosis. Similar effects were observed for trichostatin A in the generation of erythroid cells in IL-3- and EPO-containing cultures. These data suggest that HDACs negatively regulate the IL-3-mediated growth of early erythroid precursors by suppressing their responsiveness to IL-3, while playing an important role in EPO-mediated differentiation and survival of erythroid precursors. Our data revealed that HDACs have diverse functions in human adult erythropoiesis.

Stem cell factor expression, mast cells and inflammation in asthma

The Kit ligand SCF or stem cell factor (SCF) is a multipotent growth factor, acting as an important growth factor for human mast cells. SCF induces chemotaxis and survival of the mast cell, as well as proliferation and differentiation of immature mast cells from CD34(+) progenitors. Additionally, SCF enhances antigen-induced degranulation of human lung-derived mast cells, and induces a mast cell hyperplasia after subcutaneous administration. SCF expression increases in the airways of asthmatic patients, and this is reversed after treatment with glucocorticoids. A role for SCF may thus be hypothesized in diseases associated with a local increase in the number and/or activation of mast cells, as occurring in the airways in asthma. SCF will be reviewed as a potential therapeutic target in asthma, to control the regulation of mast cell number and activation. We here report the main pathways of SCF synthesis and signalling, and its potential role on airway function and asthma.

The survival of differentiating embryonic stem cells is dependent on the SCF-KIT pathway

The stem cell factor (SCF)-KIT signal transduction pathway plays a role in the proliferation, differentiation and survival of a range of stem and progenitor cell types but little is known about its function in embryonic stem (ES) cells. We generated ES cells carrying a null allele of Kit as well as a knock-in allele that encodes an SCF-independent hybrid KIT receptor that can be activated by the FKBP binding drug, AP20187. KIT null ES cells die when induced to differentiate upon withdrawal of leukaemia inhibitory factor in monolayer culture. This phenotype is recapitulated in wild-type ES cells treated with a KIT-neutralising antibody and reversed in mutant cells by activation of the hybrid KIT receptor. Differentiating KIT null ES cells exhibit elevated levels of DNA laddering and reduced BCL2 expression, indicative of apoptosis. We conclude that mouse ES cell differentiation in vitro is dependent on the SCF-KIT pathway contrasting with the apparently normal differentiation of KIT null inner cell mass or epiblast cells in vivo. This discrepancy could be explained by the presence of compensatory signals in the embryo or it could lend support to the idea of a phenotypic relationship between ES cells and early germ cells.

Enhancement of growth and survival and alterations in Bcl-family proteins in beta-thalassemic erythroid progenitors by novel short-chain fatty acid derivatives

Accelerated apoptosis of erythroid progenitors is a characteristic of beta-thalassemia which presents a significant barrier to definitive therapeutic approaches utilizing induction of endogenous fetal globin gene expression. gamma-globin gene expression may not be inducible in, or may not be able to rescue, erythroid cells in which programmed cell death is initiated early in erythroblast development. In this report, short-chain fatty acid derivatives (SCFADs) which induce fetal globin gene expression were tested for their ability to promote proliferation and survival of erythroid progenitors cultured from beta-thalassemic subjects, and of cytokine-dependent erythroid cell lines. Certain SCFADs promoted thalassemic Bfu-e growth and cytokine-independent growth and survival of erythroid cell lines. A 40-80% increase in erythroid Bfu-e colony number was observed in cultures established with any of five mitogenic SCFADs, compared to control or butyrate-treated cultures from the same subjects. Immunoblot analysis demonstrated that these same SCFADs also regulated the expression of specific protein inhibitors of apoptosis. Anti-apoptotic ratios of the proteins Bcl-xL/Bcl-xS in thalassemic Bfu-e were increased by 30-120% with exposure to the SCFDs, compared to the ratios in the same cells cultured under control conditions. Similar anti-apoptotic increases in Mcl-1L/Mcl-1S ratios were induced by the SCFADs. These findings suggest that select fetal globin-inducing SCFADs which enhance proliferation of beta-thalassemia progenitors may enhance survival of these progenitors by altering levels of Bcl-family protein members. This combination of effects should enhance erythroid cell survival in the beta-thalassemia syndromes, allowing fetal globin gene expression to be induced more effectively than currently available, growth-suppressing, fetal globin-inducing agents, such as the butyrates or chemotherapeutic agents.

Personalized immunotherapy for the treatment of non-Hodgkin's lymphoma: a promising approach

The efficacy of immunotherapeutic strategies for the treatment of lymphoid malignancies has been demonstrated in recent years. In patients with B-cell lymphomas, particularly indolent lymphoma, the use of passive immunotherapy, such as the anti-CD20 monoclonal antibody rituximab, has made an impressive impact on patient outcome. Personalized immunotherapy, a method that triggers the immune system to mount a response against tumor cells, has shown promising results in early clinical trials in hematologic malignancies. This therapeutic modality appears safe, with the most common adverse events being transient, local reactions at the site of injection. Furthermore, personalized immunotherapy has the potential to generate immunologic memory, which could provide prolonged remission. Currently, 3 large phase III studies are evaluating the efficacy and safety of personalized immunotherapy in patients with follicular lymphoma. It is hoped that the results of these studies will lead to the incorporation of this promising approach into the standard treatment of patients with lymphoma.

Neuroprotection by stem cell factor in rat cortical neurons involves AKT and NFκB

Stem cell factor (SCF) is a highly expressed cytokine in the central nervous system. In the present study, we demonstrate a neuroprotective role for SCF and its tyrosine kinase receptor, c-kit, against camptothecin-induced apoptosis and glutamate excitotoxicity in rat cortical neurons. This protection was blocked by pharmacological or molecular inhibition of either the MEK/ERK or PI3K/Akt signaling pathways. The importance of these pathways was further confirmed by the activation of both ERK, in a MEK-dependent manner, and Akt, via PI3K. Activation of Akt increased the binding of the p50 and p65 subunits of NFkappaB, which was also important for neuroprotection. Akt inhibition prevented NFkappaB binding, suggesting a role for Akt in SCF-induced NFkappaB. Pharmacological inhibition of NFkappaB or dominant negative IkappaB also prevented neuroprotection by SCF. SCF up-regulated the anti-apoptotic genes, bcl-2 and bcl-xL in an NFkappaB-dependent manner. Together, these findings demonstrate a neuroprotective role for SCF in cortical neurons, an effect that was mediated by Akt and ERK, as well as NFkappaB-mediated gene transcription. SCF represents a novel therapeutic target in the treatment of neurodegenerative disease.

PECAM-1, apoptosis and CD34+ precursors

Apoptosis is a physiological process that controls tissue homeostasis, in combination with survival signals delivered by distinct receptors that bind hormones, growth factors or extracellular matrix components. The extrinsic pathway of apoptosis is due to the triggering of death receptors and the activation of the caspase cascade; the intrinsic pathway is due to withdrawal of growth factors and mainly related to mitochondrial metabolism. The choice between survival or apoptosis, which is the result of such different integrated environmental signals, is crucial for the maintainance of bone marrow reservoir of hematopoietic precursors (HPC). CD34+ HPC can receive multiple survival signals during homing and maturation, due to different interactions with adhesion molecules expressed on endothelial and bone marrow stromal cells, proteins of the extracellular matrix and chemokines or growth factors. Among them, the signal delivered via platelet endothelial cell adhesion molecule-1 (PECAM-1) seems to contribute to the resistance of this cell population to starvation, and it is related to the maintainance of mitochondrial metabolism. Indeed, this molecule, originally described as an adhesion receptor belonging to the immunoglobulin superfamily, capable of homophilic and heterophilic interactions, turned out to be a signalling molecule, containing an immunoreceptor tyrosine-based inhibitory motifs (ITIM) within its cytoplasmic domain. In particular, it has been shown that PECAM-1 binds to different kinases and phosphatases, including the phosphatidylinositide-3-kinase that phosphorylates Akt, which, in turn can upregulate transcription and function of antiapoptotic proteins, such as Bcl-2 and Bcl-x or A1, responsible for the rescue from mitochondrial apoptosis. The possible role of PECAM-1 engagement in the prevention of starvation-induced apoptosis of HPC precursors and in the maintainance of their survival is discussed.

Antibody-targeted therapy: a paradigm of innovative treatment strategies in indolent and aggressive B-cell non-Hodgkin lymphoma

PURPOSE OF REVIEW

This review outlines the principles of treatment of indolent and aggressive B-cell lymphoma based on current knowledge on the classification of hematologic malignancies and the rationale to implement new antibody-targeted immunotherapeutic approaches.

RECENT FINDINGS

An update is provided on the use of antibody-targeted therapies in clinical trials, with emphasis on new, emerging strategies of immunotherapy in B-cell non-Hodgkin lymphoma.

SUMMARY

The success of immune-mediated therapies has encouraged studies on antibody-targeted therapy in B-cell non-Hodgkin lymphoma. Promising new approaches combine classical dose-intense chemotherapy with "tumor-specific" antibody targeting during several phases of the disease. The safety and efficacy of anti-CD20 in the treatment of indolent and aggressive B-cell non-Hodgkin lymphoma at any stage of disease, either as a single agent or as part of multimodality regimes, as an unconjugated antibody or as radioimmunoconjugate have changed dramatically our treatment strategies. Increasing insights into basic molecular biology and immunology of B-cell non-Hodgkin lymphoma may identify subgroups of patients categorized in current classification systems who may benefit from tailored approaches with new modality antibody-targeted therapy in near future.

Induction of stem cell factor/c-Kit/slug signal transduction in multidrug-resistant malignant mesothelioma cells

Malignant mesothelioma (MM) is strongly resistant to conventional chemotherapy by unclear mechanisms. We and others have previously reported that cytokine- and growth factor-mediated signal transduction is involved in the growth and progression of MM. Here, we identified a pathway that involves stem cell factor (SCF)/c-Kit/Slug in mediating multidrug resistance of MM cells. When we compared gene expression profiles between five MM cells and their multidrug-resistant (MM DX) sublines, we found that MM DX cells expressed both SCF and c-Kit and had higher mRNA levels of Slug. Knockdown of c-Kit or Slug expression with their respective small interfering RNA sensitized MM DX cells to the induction of apoptosis by different chemotherapeutic agents, including doxorubicin, paclitaxel, and vincristine. Transfection of c-Kit in parental MM cells in the presence of SCF up-regulated Slug and increased resistance to the chemotherapeutic agents. Moreover, MM cells expressing Slug showed a similar increased resistance to the chemotherapeutic agents. These results indicate that induction of Slug by autocrine production of SCF and c-Kit activation plays a key role in conferring a broad spectrum chemoresistance on MM cells and reveal a novel signal transduction pathway for pharmacological or genetic intervention of MM patients.

Two-phase culture in Diamond Blackfan anemia: localization of erythroid defect

The erythroid defect in Diamond Blackfan anemia (DBA) is known to be intrinsic to the stem cell, but its molecular pathophysiology remains obscure. Using a 2-phase liquid erythroid culture system, we have demonstrated a consistent defect in DBA, regardless of clinical severity, including 3 first-degree relatives with normal hemoglobin levels but increased erythrocyte adenosine deaminase activity. DBA cultures were indistinguishable from controls until the end of erythropoietin (Epo)-free phase 1, but failed to demonstrate the normal synchronized wave of erythroid expansion and terminal differentiation on exposure to Epo. Dexamethasone increased Epo sensitivity of erythroid progenitor cells, and enhanced erythroid expansion in phase 2 in both normal and DBA cultures. In DBA cultures treated with dexamethasone, Epo sensitivity was comparable to normal, but erythroid expansion remained subnormal. In clonogenic phase 2 cultures, the number of colonies did not significantly differ between normal cultures and DBA, in the presence or absence of dexamethasone, and at both low and high Epo concentrations. However, colonies were markedly smaller in DBA under all conditions. This suggests that the Epo-triggered onset of terminal maturation is intact in DBA, and the defect lies down-stream of the Epo receptor, influencing survival and/or proliferation of erythroid progenitors.

Apoptotic mechanisms in the control of erythropoiesis

Erythropoiesis is a complex multistep process encompassing the differentiation of hemopoietic stem cells to mature erythrocytes. The steps involved in this complex differentiation process are numerous and involve first the differentiation to early erythoid progenitors (burst-forming units-erythroid, BFU-E), then to late erythroid progenitors (colony-forming units-erythroid) and finally to morphologically recognizable erythroid precursors. A key event of late stages of erythropoiesis is nuclear condensation, followed by extrusion of the nucleus to produce enucleated reticulocytes and finally mature erythrocytes. During the differentiation process, the cells became progressively sensitive to erythropoietin that controls both the survival and proliferation of erythroid cells. A normal homeostasis of the erythropoietic system requires an appropriate balance between the rate of erythroid cell production and red blood cell destruction. Growing evidences outlined in the present review indicate that apoptotic mechanism play a relevant role in the control of erythropoiesis under physiologic and pathologic conditions. Withdrawal of erythropoietin or stimulation of death receptors such as Fas or TRAIL-Rs leads to activation of a subset of caspase-3, -7 and -8, which then cleave the transcription factors GATA-1 and TAL-1 and trigger apoptosis. In addition, there is evidence that a number of caspases are physiologically activated during erythroid differentiation and are functionally required for erythroid maturation. Several caspase substrates are cleaved in differentiating cells, including the protein acinus whose activation by cleavage is required for chromatin condensation. The studies on normal erythropoiesis have clearly indicated that immature erythroid precursors are sensitive to apoptotic triggering mediated by activation of the intrinsic and extrinsic apoptotic pathways. These apoptotic mechanisms are frequently exacerbated in some pathologic conditions, associated with the development of anemia (ie, thalassemias, multiple myeloma, myelodysplasia, aplastic anemia). The considerable progress in our understanding of the apoptotic mechanisms underlying normal and pathologic erythropoiesis may offer the way to improve the treatment of several pathologic conditions associated with the development of anemia.

Role of RB and RB2/P130 genes in marrow stromal stem cells plasticity

Marrow stromal cells (MSCs) are stem-like cells having a striking somatic plasticity. In fact, besides differentiating into mesenchymal lineages (bone, cartilage, and fat), they are capable of differentiating into neurons and astrocytes in vitro and in vivo. The RB and RB2/P130 genes, belonging to the retinoblastoma gene family, play a key role in neurogenesis, and for this reason, we investigated their role in neural commitment and differentiation of MSCs. In MSCs that were either uncommitted or committed toward neural differentiation, we ectopically expressed RB and RB2/P130 genes and analyzed their role in regulating the cell cycle, apoptosis and differentiation. In uncommitted MSCs, the activity of RB and RB2/P130 appeared limited to negatively regulating cell cycle progression, having no role in apoptosis and differentiation (toward either mesenchymal or neural lineages). On the other hand, in MSCs committed toward the neural phenotype, both RB and RB2/P130 reduced cell proliferation rate and affected the apoptotic process. RB protected differentiating cells from programmed cell death. On the contrary, RB2/P130 increased the percentage of cells in apoptosis. All of these activities were accomplished mainly in an HDAC-independent way. The retinoblastoma genes also influenced differentiation in neural committed MSCs. RB2/P130 contributes mainly to the induction of generic neural properties, while RB triggers cholinergic differentiation. These differentiating activities are HDAC-dependent. Our research shows that there is a critical temporal requirement for the RB genes during neuronal differentiation of MSCs: they are not required for cell commitment but play a role in the maturation process. For the above reasons, RB and RB2/P130 may have a role in neural differentiation but not in neural determination.