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Phorbol ester PMA induces expression of the thrombopoietin receptor MPL in leukemia cells
G Graf1, M Zaborski, H Quentmeier
1Department of Human and Animal Cell Cultures, DSMZ-German Collection of Microorganisms & Cell Cultures, Braunschweig, Germany.
Abstract:
Thrombopoietin (TPO) is a major regulator of megakaryocytopoiesis both in vivo and in vitro. TPO initiates its biological effects by binding to the c-MPL receptor, which is a member of the hematopoietin receptor superfamily. To define the regulation of the MPL receptor, six continuous human leukemia cell lines with megakaryocytic properties were treated with the phorbol ester 12-myristate 13-acetate (PMA), TPO and transforming growth factor (TGF)-beta 1, a cytokine known to possess inhibitory effects. We used Northern blotting and flow cytometry analysis to determine MPL mRNA and protein levels. An increase of MPL mRNA and protein expression was observed in 2/6 PMA-exposed cell lines. There is no evidence from this study that TPO or TGF-beta 1 cause any decrease or increase in MPL expression. MPL upregulation triggered by PMA was accompanied by signs of induced differentiation such as increase in CD41, CD42 and CD61 expression, increase in cell size and cessation of proliferation. These data demonstrate that MPL can be upregulated in differentiating megakaryocytic cells via stimulation of protein kinase C, the intracellular target of PMA and a key kinase in one of the second messenger signal transduction pathways. These findings further the understanding of the regulation of this molecule, a cytokine receptor that, together with its ligand TPO, appears to represent a crucial element in megakaryocytopoiesis.
Insights
Phorbol ester 12-myristate 13-acetate (PMA) upregulates the MPL receptor in differentiating megakaryocytic cells by activating protein kinase C. This study found no effect of TPO or TGF-beta 1 on MPL expression.
Area of Science:
- Hematology
- Molecular Biology
- Cell Biology
Background:
- Thrombopoietin (TPO) regulates megakaryocytopoiesis by binding to the c-MPL receptor.
- The c-MPL receptor is part of the hematopoietin receptor superfamily.
- Understanding MPL receptor regulation is crucial for megakaryopoiesis.
Purpose of the Study:
- To investigate the regulation of the MPL receptor in megakaryocytic cell lines.
- To determine the effects of PMA, TPO, and TGF-beta 1 on MPL expression.
- To elucidate the signaling pathways involved in MPL receptor regulation.
Main Methods:
- Treatment of six human leukemia cell lines with megakaryocytic properties with PMA, TPO, and TGF-beta 1.
- Analysis of MPL mRNA and protein levels using Northern blotting and flow cytometry.
- Assessment of cellular differentiation markers (CD41, CD42, CD61), cell size, and proliferation.
Main Results:
- PMA treatment led to increased MPL mRNA and protein expression in 2 out of 6 cell lines.
- TPO and TGF-beta 1 did not significantly alter MPL expression levels.
- PMA-induced MPL upregulation correlated with signs of megakaryocytic differentiation and proliferation cessation.
Conclusions:
- MPL receptor can be upregulated in differentiating megakaryocytic cells through protein kinase C activation by PMA.
- These findings highlight the role of protein kinase C in MPL regulation during megakaryopoiesis.
- The TPO-MPL axis is a critical regulator of megakaryocytopoiesis, with potential for further investigation into its modulation.