TPO/Mpl Studies in Agnogenic Myeloid Metaplasia
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TPO/Mpl Studies in Agnogenic Myeloid Metaplasia Kirugaval C Hemavathy, Kathir Suppiah, Gazala Hashmi, Allan D Novetsky and Jen C Wang* Address: Division of Hematology/Oncology, Department of Medicine, Maimonides Medical Center, Brooklyn, New York, USA Email: Kirugaval C Hemavathy - [email protected]; Kathir Suppiah - [email protected]; Gazala Hashmi - [email protected]; Allan D Novetsky - [email protected]; Jen C Wang* - [email protected] * Corresponding author
Published: 03 February 2005 Cell Communication and Signaling 2005, 3:4
doi:10.1186/1478-811X-3-4
Received: 17 November 2004 Accepted: 03 February 2005
This article is available from: http://www.biosignaling.com/content/3/1/4 © 2005 Hemavathy et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: Agnogenic myeloid metaplasia (AMM) is one of the Philadelphia chromosome negative myeloproliferative disorder and is diagnosed by hyperplasia of atypical megakaryocytes, hepatosplenomegaly, extramedullary hematopoiesis and bone marrow fibrosis. Fibrosis is considered to be a secondary consequence of enhanced levels of fibrogenic growth factors such as TGF β1, bFGF and PDGF produced by enhanced numbers of megakaryocytes, while the primary cause is considered to be the enhanced proliferation of a defective stem cell. We have previously reported that thrombopoietin (TPO) is elevated in patients with AMM. Others have reported that Mpl protein is decreased in these patients. Since TPO is essential for the development of megakaryocytes, and Mpl protein is the receptor for TPO, we extended the study of TPO/Mpl to in vitro and in vivo cell culture systems to better understand the mechanism that leads to reduced Mpl protein in AMM patients. Results: Plasma TPO levels were significantly elevated and Mpl protein levels were significantly reduced in AMM patients in concordance with previous studies. Platelet Mpl transcripts in AMM were however similar to those in controls. We also cloned Mpl cDNA from AMM patients and tested for their ability to make functional proteins in vitro and in the in vivo system of 293 T human embryonic kidney cells. Their expression including the glycosylated forms was similar to those from the controls. We also measured the level of translation initiation factor, eIF4E and found it to be increased in patients with AMM demonstrating that the reduced Mpl protein may not be due to translation defects. Conclusions: Our studies using the in vitro and in vivo systems further confirm that reduced Mpl protein levels are not due to defects in its transcription/translation. Reduced Mpl protein could be due to its increased internalisation owing to enhanced plasma TPO or in vivo intrinsic defects in patients with AMM.
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