RESUMO
Agnogenic myeloid metaplasia (AMM) is characterized by bone marrow fibrosis and enhanced proliferation of megakaryocytes and CD34+ cells. We have analyzed the factors that could lead to reduced expression of TGF beta1RII in CD34+ cells of AMM patients. Our results demonstrate absence of mutations in the coding region and the promoter of this gene and absence of CpG methylation of its promoter in AMM patients. Further studies on transcriptional regulation of TGF beta1RII involving its cis-regulatory elements, the interacting transcription factors and their association with HDAC will provide valuable information on the pathogenesis of AMM and are under current investigation.
Assuntos
Metilação de DNA , Regulação da Expressão Gênica/genética , Mutação , Mielofibrose Primária/metabolismo , Receptores de Fatores de Crescimento Transformadores beta/biossíntese , Proliferação de Células , Ilhas de CpG , Feminino , Histona Desacetilases/metabolismo , Humanos , Masculino , Megacariócitos/metabolismo , Megacariócitos/patologia , Mielofibrose Primária/genética , Mielofibrose Primária/patologia , Regiões Promotoras Genéticas , Proteínas Serina-Treonina Quinases , Receptor do Fator de Crescimento Transformador beta Tipo II , Receptores de Fatores de Crescimento Transformadores beta/genética , Fatores de Transcrição/metabolismo , Transcrição GênicaRESUMO
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 beta1, 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.
