Coexpression of Kit and the receptors for erythropoietin, interleukin 6 and GM-CSF on hemopoietic cells

Elevated CDKN1A (P21) mediates β-thalassemia erythroid apoptosis, but its loss does not improve β-thalassemic erythropoiesis

β-thalassemias are common hemoglobinopathies due to mutations in the β-globin gene that lead to hemolytic anemias. Premature death of β-thalassemic erythroid precursors results in ineffective erythroid maturation, increased production of erythropoietin (EPO), expansion of erythroid progenitor compartment, extramedullary erythropoiesis, and splenomegaly. However, the molecular mechanism of erythroid apoptosis in β-thalassemia is not well understood. Using a mouse model of β-thalassemia (Hbbth3/+), we show that dysregulated expression of the FOXO3 transcription factor is implicated in β-thalassemia erythroid apoptosis. In Foxo3-/-/Hbbth3/+ mice, erythroid apoptosis is significantly reduced, whereas erythroid cell maturation, and red blood cell and hemoglobin production are substantially improved even with elevated reactive oxygen species in double-mutant erythroblasts. However, persistence of elevated reticulocytes and splenomegaly suggests that ineffective erythropoiesis is not resolved in Foxo3-/-/Hbbth3/+. We found the cell cycle inhibitor Cdkn1a (cyclin-dependent kinase inhibitor p21), a FOXO3 target gene, is markedly upregulated in both mouse and patient-derived β-thalassemic erythroid precursors. Double-mutant p21/Hbbth3/+ mice exhibited embryonic lethality with only a fraction of mice surviving to weaning. Notably, studies in adult mice displayed greatly reduced apoptosis and circulating Epo in erythroid compartments of surviving p21-/-/Hbbth3/+ mice relative to Hbbth3/+ mice, whereas ineffective erythroid cell maturation, extramedullary erythropoiesis, and splenomegaly were not modified. These combined results suggest that mechanisms that control β-thalassemic erythroid cell survival and differentiation are uncoupled from ineffective erythropoiesis and involve a molecular network including FOXO3 and P21. Overall, these studies provide a new framework for investigating ineffective erythropoiesis in β-thalassemia.

Clinical significance of endothelial cell marker CD34 and mast cell marker CD117 in prostate adenocarcinoma

Prostate cancer is the second cause of cancer-related deaths in men and this is attributed to its aggressiveness and metastatic identity. Our objective was to evaluate the expression patterns of endothelial cell marker CD34 and mast cell marker CD117 in prostate adenocarcinoma (PCa) compared to benign prostate tissue and their relation to the clinicopathological features. A total of 90 prostate samples, including 45 PCa and 45 benign prostate tissues were immunohistochemically examined for the detection of CD34 and CD117 markers. The expression of these markers was also correlated with clinicopathological parameters. Significant overexpression of CD34 was found in PCa group compared to benign prostate tissues (P≤0.001). The expression of CD34 and CD117 in PCa with advanced Gleason score was more than PCa with early Gleason score (P=0.02 and P=0.005, respectively). A significant positive correlation was observed between CD34 expression and the level of total serum prostate specific antigen (sPSA) (P=0.006). In addition, CD34High/CD117High phenotype was frequently observed in PCa cases compared to benign prostate tissues (P≤0.001). There was a positive significant association between CD34High/CD117High phenotype with advanced Gleason score (P≤0.001) and total sPSA level (P=0.02). Our findings showed that increased expression of CD34 and CD117 markers confer tumor progression and aggressiveness on PCa. These molecules may be good candidates for targeted therapy of PCa patients.

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.

Heterozygous kit mutants with little or no apparent anemia exhibit large defects in overall hematopoietic stem cell function

OBJECTIVE

The evolutionarily conserved Kit receptor is vital for function of hematopoietic stem cells (HSC). Kit(W-41) (W-41) and Kit(W-42) (W-42) are single residue changes in the KIT intracellular phosphotransferase domain, while Kit(W-v) (W-v) is a single residue change in the ATP binding domain. This study tests how each mutation affects HSC function.

METHODS

Cells in mutant and C57BL/6J(+/+) blood and marrow were compared. Overall HSC function was measured by competitive repopulation. Functions of specific progenitor populations were tested with stage-specific competitive repopulation and standard colony-forming unit assays.

RESULTS

Bone marrow cells from these Kit mutants are severely defective at reconstituting peripheral blood lineages and bone marrow of irradiated recipients, when compared to +/+ control marrow. These defects increased with time. Marrow from W-41/+ and W-v/+ functions similarly but better than marrow from W-41/W-41 and W-42/+, to repopulate the erythroid and lymphoid lineages. Long-term (LT) and short-term (ST) HSC from W-v/+, W-41/W-41, and W-42/+ are more defective at reconstituting bone marrow than LT- and ST-HSC from W-41/+ and +/+. Common myeloid progenitor (CMP) cells from W-42/+ and W-41/W-41 are more defective at producing spleen colonies than CMP from W-v/+ and W-41/+.

CONCLUSION

Heterozygous Kit mutants with little or no apparent anemia exhibit surprisingly large defects in overall HSC function. Multiplying the fractional defects in LT-HSC, ST-HSC, and CMP can account for overall effects of W-v/+, but does not completely account for the defects observed with W-41/+, W-42/+, and W-41/W-41.

The alpha subunit of the granulocyte-macrophage colony-stimulating factor receptor interacts with c-Kit and inhibits c-Kit signaling

The cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) regulates hematopoiesis and the function of mature host defense cells through the GM-CSF receptor (GMR), which is composed of alpha (alphaGMR) and beta (betaGMR) subunits. Stem cell factor is another important hematopoietic cytokine that signals through c-Kit, a receptor tyrosine kinase, and regulates hematopoietic stem cell maintenance and erythroid development. Like other cytokine receptors, GMR and c-Kit are generally deemed as independent adaptor molecules capable of transducing cytokine-specific signals. We found that the alphaGMR directly interacts with c-Kit and that the interaction is mediated by the cytoplasmic domains. Furthermore, alphaGMR inhibited c-Kit auto-phosphorylation induced by the ligand stem cell factor. Consistent with the inhibitory effect, the expression of alphaGMR was suppressed in cells whose viability was dependent on c-Kit signaling. In contrast, the alternatively spliced alpha2 isoform of the alphaGMR could not inhibit c-Kit signaling, providing a rationale for the existence of the alpha2 isoform. Our results suggest that in addition to having the commonly appreciated roles in cytokine signal transduction, the receptors alphaGMR and c-Kit could interact to coordinate their signal initiation.

Multilevel Regulation of IL-6R by IL-6-sIL-6R Fusion Protein According to the Primitiveness of Peripheral Blood-Derived CD133+Cells

Interleukin-6 (IL-6) and its soluble receptor (sIL-6R) are major factors for maintenance and expansion of hematopoietic stem cells (HSCs). Sensitivity of HSCs to IL-6 has been previously studied, in part by measuring the expression of IL-6R on the membrane (mIL-6R). Several studies have described the regulation of cell surface expression of IL-6R by several cytokines, but the role of glycoprotein 130 activation has not yet been investigated. In this study, CD133(+) cells were purified from adult peripheral blood and were precultured in the absence or presence of 5-fluorouracil (5-FU) for selection of quiescent HSCs. Cells were cultured with continuous or pulsed stimulations of an IL-6-sIL-6R fusion protein (hyperinterleukin-6 [HIL-6]) to 1) detect mIL-6R by flow cytometry, 2) assess mIL-6R and sIL-6R RNAs by reverse transcription-polymerase chain reaction, 3) measure sIL-6R in supernatants by enzyme-linked immunosorbent assay, 4) analyze cell-cycle status, and 5) perform long-term culture-initiating cell assays. The level of mIL-6R(-) cells was preserved by 5-FU incubation. HIL-6 increased steady-state mIL-6R RNA and expression rate on HSCs, independently of treatment with 5-FU. Enhanced production of sIL-6R was observed with short pulses of HIL-6 on CD133(+) 5-FU-pretreated cells. This overproduction of sIL-6R was abrogated by tumor necrosis factor-alpha protease inhibitor-1, an inhibitor of a disintegrin and metalloprotease proteases, suggesting the shedding of mIL-6R. This phenomenon was mediated through the phosphatidylinositol-3'-kinase pathway and was involved in the maintenance of primitive HSCs. In conclusion, expression and production of IL-6R are tightly regulated and stage specific. We assume that sIL-6R produced by shedding should be involved in autocrine and paracrine loops in the HSC microenvironment.

Cannabis-induced cytotoxicity in leukemic cell lines: the role of the cannabinoid receptors and the MAPK pathway

Δ9-Tetrahydrocannabinol (THC) is the active metabolite of cannabis. THC causes cell death in vitro through the activation of complex signal transduction pathways. However, the role that the cannabinoid 1 and 2 receptors (CB1-R and CB2-R) play in this process is less clear. We therefore investigated the role of the CB-Rs in mediating apoptosis in 3 leukemic cell lines and performed microarray and immunoblot analyses to establish further the mechanism of cell death. We developed a novel flow cytometric technique of measuring the expression of functional receptors and used combinations of selective CB1-R and CB2-R antagonists and agonists to determine their individual roles in this process. We have shown that THC is a potent inducer of apoptosis, even at 1 × IC50 (inhibitory concentration 50%) concentrations and as early as 6 hours after exposure to the drug. These effects were seen in leukemic cell lines (CEM, HEL-92, and HL60) as well as in peripheral blood mononuclear cells. Additionally, THC did not appear to act synergistically with cytotoxic agents such as cisplatin. One of the most intriguing findings was that THC-induced cell death was preceded by significant changes in the expression of genes involved in the mitogen-activated protein kinase (MAPK) signal transduction pathways. Both apoptosis and gene expression changes were altered independent of p53 and the CB-Rs.

Different steroids co-regulate long-term expansion versus terminal differentiation in primary human erythroid progenitors

Outgrowth, long-term self-renewal, and terminal maturation of human erythroid progenitors derived from umbilical cord blood in serum-free medium can be modulated by steroid hormones. Homogeneous erythroid cultures, as characterized by flow cytometry and dependence on a specific mixture of physiologic proliferation factors, were obtained within 8 days from a starting population of mature and immature mononuclear cells. Due to previous results in mouse and chicken erythroblasts, the proliferation-promoting effect of glucocorticoids was not unexpected. Surprisingly, however, androgen had a positive effect on the sustained expansion of human female but not male erythroid progenitors. Under optimal conditions, sustained proliferation of erythroid progenitors resulted in a more than 10(9)-fold expansion within 60 days. Terminal erythroid maturation was significantly improved by adding human serum and thyroid hormone (3,5,3'-triiodothyronine [T3]) to the differentiation medium. This resulted in highly synchronous differentiation of the cells toward enucleated erythrocytes within 6 days, accompanied by massive size decrease and hemoglobin accumulation to levels comparable to those in peripheral blood erythrocytes. Thus, obviously, different ligand-activated nuclear hormone receptors massively influence the decision between self-renewal and terminal maturation in the human erythroid compartment.

Effect of haemopoietic growth factors on cancer cell lines and their role in chemosensitivity

The recombinant growth factors (GFs) erythropoietin (Epo) and granulocyte-macrophage colony stimulating factor (GM-CSF) have important roles in the management of cancer patients. However, the effects of these GFs at a cellular level are not well understood. We examined the effect of GFs alone, and in combination with cytotoxic chemotherapy, in a panel of seven cell lines. Flow cytometric analysis showed varying levels of receptor expression, which correlated with phosphorylated MAPK expression. Additionally, there were also concomitant increases in BCL-2 protein levels in those cells with high levels of MAPK activation. Although culturing cells with Epo or GM-CSF did not alter cell viability by themselves, GF pretreatment in cell lines expressing higher receptor levels resulted in a reduced magnitude of cell kill following exposure to cytotoxic IC50 concentrations of cisplatin. Subsequent co-culture with either the MEK inhibitor U0126 or the GM-CSF antagonist E21R negated this induced resistance to cytotoxic chemotherapy, confirming the importance of the GF receptor as well as MAPK in mediating these effects. These results suggest that the use of GFs during chemotherapy may be detrimental in those cancers expressing higher levels of the specific receptor. Conversely, our results also suggest that GFs are safe to use in chemotherapeutic regimens if the cancer cells do not overexpress the particular receptor.

CD34, CD117, and actin expression in phyllodes tumor of the breast

BACKGROUND

This study investigated the immunophenotypic patterns of CD34, CD117 (a product of the c-kit proto-oncogene), and actin (HHF35) in benign and malignant phyllodes tumors (PTs). We correlated the expression of CD34, CD117, and actin with histopathological grade.

MATERIALS AND RESULTS

We analyzed 19 cases (7 benign and 12 malignant cases) of PTs using immunohistochemical analysis. Six of 7 benign PT stromal lesions stained positively for CD34, while only 3 of 12 cases of malignant PT were focally CD34 positive (P = 0.0106). Only 1 of the 7 benign PTs stromal lesions expressed CD117. Nine of the malignant PTs were composed CD117-positive fibroblasts. This result demonstrated that CD117 expression is associated with the malignant potential of PTs (P = 0. 0106). Actin (HHF-35) expression was found in 8 of 12 cases of malignant PTs (P = 0.027), but in only 1 of 7 cases of benign PTs. Actin expression was significantly (P = 0.04) correlated to frequent mitotic activity (>5 mitoses per 10 high-power fields). The immunophenotypic markers were not related to tumor size. Additionally, we sequenced part of the juxtamembrane region of the c-kit proto-oncogene and found point mutations in two malignant PTs.

CONCLUSION

Our results demonstrated that expression of CD34 was associated with benign PTs, while CD117 and actin were preferentially expressed in malignant PTs. Our results implied that these immunohistological markers might be used for the histopathological grading of PTs.

Protein kinase C alpha controls erythropoietin receptor signaling

Protein kinase C (PKC) is implied in the activation of multiple targets of erythropoietin (Epo) signaling, but its exact role in Epo receptor (EpoR) signal transduction and in the regulation of erythroid proliferation and differentiation remained elusive. We analyzed the effect of PKC inhibitors with distinct modes of action on EpoR signaling in primary human erythroblasts and in a recently established murine erythroid cell line. Active PKC appeared essential for Epo-induced phosphorylation of the Epo receptor itself, STAT5, Gab1, Erk1/2, AKT, and other downstream targets. Under the same conditions, stem cell factor-induced signal transduction was not impaired. LY294002, a specific inhibitor of phosphoinositol 3-kinase, also suppressed Epo-induced signal transduction, which could be partially relieved by activators of PKC. PKC inhibitors or LY294002 did not affect membrane expression of the EpoR, the association of JAK2 with the EpoR, or the in vitro kinase activity of JAK2. The data suggest that PKC controls EpoR signaling instead of being a downstream effector. PKC and phosphoinositol 3-kinase may act in concert to regulate association of the EpoR complex such that it is responsive to ligand stimulation. Reduced PKC-activity inhibited Epo-dependent differentiation, although it did not effect Epo-dependent "renewal divisions" induced in the presence of Epo, stem cell factor, and dexamethasone.

Myeloproliferative disorder and leukaemia in mice induced by different classes of constitutive mutants of the human IL-3/IL-5/GM-CSF receptor common beta subunit

Several constitutively active mutant forms of the common beta subunit of the human IL-3, IL-5 and GM-CSF receptors (hbetac), which enable it to signal in the absence of ligand, have recently been described. Two of these, V449E and I374N, are amino acid substitutions in the transmembrane and extracellular regions of hbetac, respectively. A third, FIDelta, contains a 37 amino acid duplication in the extracellular domain. We have shown previously that when expressed in primary murine haemopoietic cells, the extracellular mutants confer factor-independence on cells of the neutrophil and monocyte lineages only, whereas V449E does so on all cell types of the myeloid and erythroid compartments. To study the in vivo effects and leukaemic potential of these mutants, we have expressed all three in mice by bone marrow reconstitution using retrovirally infected donor cells. Expression of the extracellular mutants leads to an early onset, chronic myeloproliferative disorder marked by elevations in the neutrophil, monocyte, erythrocyte and platelet lineages. In contrast, expression of V449E leads to an acute leukaemia-like syndrome of anaemia, thrombocytopaenia and blast cell expansion. These data support the possibility that activating mutations in hbetac are involved in haemopoietic disorders in man.