Disease relevance of THPO

• However, the biologic effects of TPO on human acute myeloblastic leukemia (AML) cells are largely unknown [1].
• Here, we show that TPO, interleukin-3 (IL-3) and, at least in short-term assays, also interferon gamma (IFN gamma) induced proliferation in acute myeloid leukemia (AML-M7)-derived M-07e cells [2].
• Identification of TPO, the c-Mpl ligand, as the primary physiologic regulator of megakaryocyte and platelet development offers important promise for treatment of thrombocytopenia [3].
• To study whether IFN interferes with hepatic thrombopoietin (TPO) synthesis, we used the human hepatoma cell line HepG2 [4].
• To understand the mechanism of the transient thrombocytosis in preterm infants we firstly evaluated a correlation between platelet counts and thrombopoietin (TPO) levels in preterm infants and next c-mpl mRNA levels on platelets in healthy preterm infants longitudinally during a half-year of life [5].

High impact information on THPO

• We derived an intragenic CA marker for the human THPO gene and performed linkage analysis in fourteen informative meioses in this family [6].
• RESULTS: In the 38 patients who received MGDF after chemotherapy, the median nadir platelet count was 188,000 per cubic millimeter (range, 68,000 to 373,000), as compared with 111,000 per cubic millimeter (range, 21,000 to 307,000) in 12 patients receiving placebo (P = 0.013) [7].
• CONCLUSIONS: MGDF has potent stimulatory effects on platelet production in patients with chemotherapy-induced thrombocytopenia [7].
• METHODS: We conducted a randomized, double-blind, placebo-controlled dose-escalation study of MGDF in 53 patients with lung cancer who were treated with carboplatin and paclitaxel [7].
• The patients were randomly assigned in blocks of 4 in a 1:3 ratio to receive either placebo or MGDF (0.03, 0.1, 0.3, 1.0, 3.0, or 5.0 microg per kilogram of body weight per day), injected subcutaneously [7].

Chemical compound and disease context of THPO

• The role of the GABA transporter in acute toxicity in chick retina due to metabolic inhibition was investigated by the use of several substrate (nipecotic acid, THPO) and nonsubstrate (SKF 89976A, NO711) GABA transport inhibitors [8].
• Impaired TPO-mediated platelet protein tyrosine phosphorylation was a consistent observation in patients with PV as well as those with idiopathic myelofibrosis (IMF), in contrast to patients with essential thrombocytosis, chronic myelogenous leukemia, secondary erythrocytosis, iron deficiency anemia, hemochromatosis, or normal volunteers [9].
• Plasma concentrations of the most potent megakaryocytopoietic cytokines, thrombopoietin (TPO) and interleukin-6 (IL-6), and the platelet activation marker P-selectin were evaluated in 24 patients with autoimmune thrombocytopenic purpura (ATP) who responded to conventional steroid treatment, at diagnosis and after steroid-induced recovery [10].
• Peripheral blood mononuclear cells from patients with ET, or secondary (reactive) thrombocytosis (2 degrees T), or healthy volunteers were grown in strictly serum-free agarose culture containing interleukin 3 (IL-3) and all-trans-retinoic acid, with various concentrations of PEG-rHu megakaryocyte growth and development factor (MGDF) [11].
• Despite severe hepatic dysfunction, serum TPO levels were initially normal and increased during hospitalization in acetaminophen-induced ALF, but did not prevent the development of thrombocytopenia [12].

Biological context of THPO

• Thrombopoietin (TPO) is a recently identified growth factor that regulates megakaryocytopoiesis [13].
• TPO stimulated this tyrosine phosphorylation in a time-dependent manner, reaching a maximum in 5 minutes [13].
• In contrast, TPO, in the presence of exogenous fibrinogen, induced concentration-dependent platelet aggregation, which was blocked by the soluble c-Mpl receptor [13].
• MKs reached a ploidy of 32N and 64N in the presence of TPO [14].
• Moreover, because adhesive interactions are known to modulate hematopoiesis, we studied whether hTPO might alter such interactions between human bone marrow (BM) megakaryocytes and human BM stromal fibroblasts [15].

Anatomical context of THPO

• Human megakaryocyte progenitor development was potentiated by hTPO alone and further augmented in the presence of the early-acting cytokines (IL-3) or kit ligand/stem cell factor (KL/SCF) [15].
• To further confirm the relationship between CpG demethylation and expression of GPVI in primary cells, we treated human cord blood cells with TPO [16].
• Moreover, we show that the combination of IL-16 plus TPO induces the generation of tolerogenic DCs, able to induce an anergic state in T cells that persists when T cells are rechallenged with immunogenic DCs [17].
• In this study we investigate the regulation of GPVI expression and show that thrombopoietin induces its expression in the megakaryocytic cell line UT-7/TPO [18].
• Interestingly, TPO markedly augmented the EE for committed progenitors, including CFU-GM, erythroid burst-forming units (BFU-E), and CFU-Mix, in the presence of SCF + IL-3 or FL + IL-3 [19].

Associations of THPO with chemical compounds

• A fraction of the TPO-dependent platelet attachment to a collagen-coated surface was insensitive to treatment with prostaglandin E1 [13].
• AG490, a specific inhibitor for Jak2, and LY294002, a specific inhibitor for phosphatidylinositol (PI) 3-kinase, reduced the protein level of Bcl-xL in UT-7/TPO cells, accompanied by an increase in the ratio of apoptotic cells [20].
• MATERIALS AND METHODS: Mks were generated from mobilized peripheral blood (PB) CD34+ cells from normal donors in serum-free medium with TPO, IL-3, and Flt3-ligand at 20% and 5% O2 [21].
• Glucose uptake was significantly raised by elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) with thapsigargin, this effect being additive to the activation induced by cytokines (SCF, GM-CSF and TPO) and hydrogen peroxide [22].
• To clarify them further, we used a human megakaryoblastic cell line, Meg-J, which showed prominant polyploidization and augmented platelet glycoprotein (GP) Ib expression after incubation with thrombopoietin (TPO, c-mpl ligand) and K252a (an indolocarbasole derivative) [23].

Physical interactions of THPO

• A reporter assay with various lengths of Bcl-x gene promoter revealed that both Stat- and nuclear factor kappa B-binding sites are prerequisites for TPO-induced promoter activity [20].
• We found that TPO did not activate phospholipase C in human platelets and was unable to restore ADP-induced phospholipase C activation upon blockade of the G(q)-coupled P2Y1 receptor [24].
• The role of the chemokine binding stromal-derived factor 1 (SDF-1) in normal human megakaryopoiesis at the cellular and molecular levels and its comparison with that of thrombopoietin (TPO) have not been determined [25].
• Additionally, TPO-induced the tyrosine phosphorylation and DNA-binding activity of STAT3 [26].

Enzymatic interactions of THPO

• STAT5 was a major component of this DNA-binding complex, and STAT5 was tyrosine phosphorylated in response to TPO [26].

Regulatory relationships of THPO

• Inhibition of TPO-induced MEK or mTOR activity induces opposite effects on the ploidy of human differentiating megakaryocytes [27].
• In a serum-free liquid culture, thrombopoietin (TPO) selectively stimulated the growth of megakaryocytic cells from CD34-positive cord blood cells [28].
• The abolishment of NF-E2 p45 with NF-E2 antisense oligomers inhibited TPO plus K252a-induced polyploidization [23].
• It is noteworthy that the differentiative effect of EPO in TF-1/c-mpl cells was associated with an increase in GATA-1 transcripts which was totally suppressed by TPO [29].
• Inhibition of erythroid differentiation and induction of megakaryocytic differentiation by thrombopoietin are regulated by two different mechanisms in TPO-dependent UT-7/c-mpl and TF-1/c-mpl cell lines [29].

Other interactions of THPO

• Furthermore, when UT-7/EPO-Mpl cells, which stably express human C-myeloproliferative leukemia virus ligand (c-Mpl), were treated with TPO, demethylation of the GP6 promoter was induced [16].
• Altogether, our results are in line with a model in which binding of TPO to the TPO receptor (mpl) could activate the rapamycin-sensitive PI3K-AKT-mTOR-p70S6K pathway and its downstream targets in promoting megakaryocytic cell polyploidization [27].
• The expansion efficiency (EE) of FL for each progenitor was inferior to that of SCF in the presence of various cytokines, except TPO [19].
• We cultured these cells long term (> 6 months) in the continuous presence of TPO (omitting GM-CSF) [30].
• Our results are consistent with previous mechanistic studies and suggest that TPO and IL-6 may be active mediators of platelet production [31].

Analytical, diagnostic and therapeutic context of THPO

• The median value of TPO in AML/MDS patients during diagnosis was 150.6 pg/ml and increased significantly during chemotherapy (median: 828 pg/ml; p < 0.05) but then decreased following complete remission (median: 221.4 pg/ml) [31].
• To evaluate hematopoiesis-supporting activity, CB CD34+ cells were expanded in cocultures with USSC and BMMSC or in the presence of Flt3-L, SCF, and TPO [32].
• In order to test the hypothesis that c-mpl, c-mpl ligand pathway is involved in the spontaneous growth of megakaryocyte progenitors, we investigated mRNA expressions of c-mpl and TPO in cells grown in serum-free liquid culture using RT-PCR [33].
• The effect of TPO on platelet function, both alone and in combination with other hematopoietic growth factors, adenosine diphosphate (ADP), and epinephrine, was investigated using fluorescent-labeled antibodies to the activation-dependent antigen CD62 (P-selectin) and flow cytometry [34].
• A human TPO cDNA was isolated by PCR from kidney mRNA [35].

References