[TGF-beta and platelet].
In the present paper, we investigated the pathophysiological implication of TGF-beta from megakaryocytes or megakaryoblasts in the development of myelofibrosis. In the bone marrow of myelofibrosis, proliferation of megakaryocytes is often noticed. We therefore investigated the TGF-beta expression in the bone marrow megakaryocytes from 12 chronic myeloproliferative disorder patients with myelofibrosis by immunohistochemical analysis. About all the specimen showed strong positivity for TGF-beta. In order to examine whether megakaryoblasts produce TGF-beta, we then measured TGF-beta activity in the conditioned medium (CM) of megakaryoblasts from a patient with acute megakaryoblastic leukemia who had profound myelofibrosis. The CM showed strong collagen synthesis stimulating activity which was nullified by addition of anti TGF-beta antibody. Since TGF-beta exists as latent form in platelets, TGF-beta was considered to be altered from active to latent form during megakaryocytes differentiation. In this context, MEG-01, a megakaryoblastic cell line which produces active TGF-beta was underwent differentiation to produce platelet-like bleb with TPA treatment. During the differentiation, MEG-01 showed the decrease of active TGF-beta production and increase of latent TGF-beta together with the production of LTBP. These results suggest that megakaryoblasts produce active TGF-beta and may may cause myelofibrosis, while more differentiated megakaryocytes produce latent TGF-beta. Mechanism by which megakaryoblast escape from negative autocrine of active TGF-beta was also investigated. MEG-01 was found to express mutated p53 which is considered to be responsible for impaired signal transduction of TGF-beta.
Department of Internal Medicine, Sapporo Medical University.
K
K
Kogawa
Y
Y
Mogi
K
K
Morii
R
R
Takimoto
Y
Y
Niitsu
D001792:Blood Platelets / Q000166:cytology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism; D055728:Primary Myelofibrosis / Q000209:etiology* / Q000473:pathology; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000502:physiology
D016212:Transforming Growth Factor beta