Decrease of Smad4 gene expression in patients with essential thrombocythaemia may cause an escape from suppression of megakaryopoiesis by transforming growth factor-beta1

The role of TGFβ in hematopoiesis and myeloid disorders

The role of transforming growth factor-β (TGFβ) signaling in embryological development and tissue homeostasis has been thoroughly characterized. Its canonical downstream cascade is well known, even though its true complexity and other non-canonical pathways are still being explored. TGFβ signaling has been described as an important pathway involved in carcinogenesis and cancer progression. In the hematopoietic compartment, the TGFβ pathway is an important regulator of proliferation and differentiation of different cell types and has been implicated in the pathogenesis of a diverse variety of bone marrow disorders. Due to its importance in hematological diseases, novel inhibitors of this pathway are being developed against a number of hematopoietic disorders, including myelodysplastic syndromes (MDS). In this review, we provide an overview of the TGFβ pathway, focusing on its role in hematopoiesis and impact on myeloid disorders. We will discuss therapeutic interventions with promising results against MDS.

Bone marrow fibrosis in primary myelofibrosis: pathogenic mechanisms and the role of TGF-β

Primary myelofibrosis (PMF) is a Philadelphia chromosome negative myeloproliferative neoplasm (MPN) with adverse prognosis and is associated with bone marrow fibrosis and extramedullary hematopoiesis. Even though the discovery of the Janus kinase 2 (JAK2), thrombopoietin receptor (MPL) and calreticulin (CALR) mutations have brought new insights into the complex pathogenesis of MPNs, the etiology of fibrosis is not well understood. Furthermore, since JAK2 inhibitors do not lead to reversal of fibrosis further understanding of the biology of fibrotic process is needed for future therapeutic discovery. Transforming growth factor beta (TGF-β) is implicated as an important cytokine in pathogenesis of bone marrow fibrosis. Various mouse models have been developed and have established the role of TGF-β in the pathogenesis of fibrosis. Understanding the molecular alterations that lead to TGF-β mediated effects on bone marrow microenvironment can uncover newer therapeutic targets against myelofibrosis. Inhibition of the TGF-β pathway in conjunction with other therapies might prove useful in the reversal of bone marrow fibrosis in PMF.

Involvement of TGFβ1 in autocrine regulation of proplatelet formation in healthy subjects and patients with primary myelofibrosis

Megakaryocytes release platelets into the bloodstream by elongating proplatelets. In this study, we showed that human megakaryocytes constitutively release Transforming Growth Factor β1 and express its receptors. Importantly, Transforming Growth Factor β1 downstream signaling, through SMAD2/3 phosphorylation, was shown to be active in megakaryocytes extending proplatelets, indicating a type of autocrine stimulation on megakaryocyte development. Furthermore, inactivation of Transforming Growth Factor β1 signaling, by the receptor inhibitors SB431542 and Stemolecule ALK5 inhibitor, determined a significant decrease in proplatelet formation. Recent studies indicated a crucial role of Transforming Growth Factor β1 in the pathogenesis of primary myelofibrosis. We demonstrated that primary myelofibrosis-derived megakaryocytes expressed increased levels of bioactive Transforming Growth Factor β1; however, higher levels of released Transforming Growth Factor β1 did not lead to enhanced activation of downstream pathways. Overall, these data propose Transforming Growth Factor β1 as a new element in the autocrine regulation of proplatelet formation in vitro. Despite the increase in Transforming Growth Factor β1 this mechanism seems to be preserved in primary myelofibrosis.

The complex regulation of TGF-β in cardiovascular disease

Transforming growth factor β (TGF-β1) is a pleiotropic cytokine with many and complex effects in cell and tissue physiology. This is made possible by a very complex and interwoven signaling system, whose regulation continues to be the focus of a growing line of research. This complex regulation translates to a key role in cardiovascular physiology, hemostasis, and the blood–vessel interface. In accordance with this, the TGF-β1 pathway appears to be deregulated in related disorders, such as atherosclerotic vascular disease and myeloproliferative syndromes. It is expected that the growing amount of experimental and clinical research will yield medical advances in the applications of knowledge of the TGF-β1 pathway to diagnosis and therapeutics.

The relationship of the active and latent forms of TGF-β1 with marrow fibrosis in essential thrombocythemia and primary myelofibrosis

The aim of this study was to perform an immunohistochemical analysis from 100 megakaryocytes per sample, analyzing positivity and intensity levels of anti-LAP human TGF-β1 (or Latent TGF-β1) and anti-TGF-β1 (or Active TGF-β1) antibodies from 18 essential thrombocythemia (ET) and 38 primary myelofibrosis (PMF) patients (being 19 pre-fibrotic and 19 fibrotic). Six bone marrow donor biopsies were used as controls. Fibrosis in bone marrow biopsies (BMB) was evaluated according to the European Consensus. The average fibrosis grade differed between each group (P=0.001 or P=0.003). Latent TGF-β1 values differed significantly between pre-fibrotic (P=0.018) and fibrotic (P=0.031) groups when compared with the control group. The high immunoexpression level of Latent TGF-β1 in the megakaryocytes from patients with myelofibrosis, which was not observed in patients with essential thrombocythemia, may be associated with the development of bone marrow fibrosis.

Consistent up-regulation of Stat3 Independently of Jak2 mutations in a new murine model of essential thrombocythemia

Janus-activated kinase 2 (JAK2) mutations are common in myeloproliferative disorders; however, although they are detected in virtually all polycythemia vera patients, they are found in approximately 50% of essential thrombocythemia (ET) patients, suggesting that converging pathways/abnormalities underlie the onset of ET. Recently, the chromosomal translocation 3;21, leading to the fusion gene AML1/MDS1/EVI1 (AME), was observed in an ET patient. After we forced the expression of AME in the bone marrow (BM) of C57BL/6J mice, all the reconstituted mice died of a disease with symptoms similar to ET with a latency of 8 to 16 months. Peripheral blood smears consistently showed an elevated number of dysplastic platelets with anisocytosis, degranulation, and giant size. Although the AME-positive mice did not harbor Jak2 mutations, the BM of most of them had significantly higher levels of activated Stat3 than the controls. With combined biochemical and biological assays we found that AME binds to the Stat3 promoter leading to its up-regulation. Signal transducers and activators of transcription 3 (STAT3) analysis of a small group of ET patients shows that in about half of the patients, there is STAT3 hyperactivation independently of JAK2 mutations, suggesting that the hyperactivation of STAT3 by JAK2 mutations or promoter activation may be a critical step in development of ET.

Henoch-Schonlein Purpura with thrombocythaemia: an abnormality in Smad4 expression?

We discuss a patient with Henoch-Schonlein Purpura (HSP) and a thrombocythaemia which was diagnosed as a coincidental Essential Thrombocythaemia. We suggest that deficiencies in Smad4 expression may allow for escape thrombocythaemia under the influence of the high levels of TGF-beta found in HSP. With normal Smad4 expression TGF-beta provides inhibition of thrombocyte proliferation. While this needs further elucidation, it could lead to a new approach to classification and management of HSP.

Thrombopoietin levels increased in patients with severe acute respiratory syndrome

Hematological changes in patients with Severe Acute Respiratory Syndrome (SARS) are common and frequently include thrombocytopenia. Using a ELISA method, we found an increase in thrombopoietin (TPO) levels in the plasma of convalesced SARS patients (290 ± 53 pg/ml) and active SARS patients (251 ± 23 pg/ml) comparing to that from normal control patients (228 ± 17 pg/ml). In addition, the plasma from active SARS patients had an inhibitory effect on CFU-MK formation, which could be neutralized by anti-TGF-β antibodies. In the experiment to determine whether SARS-CoV can directly infect hematopoietic stem cells and megakaryocytic cells, incubation of the cells with SARS-CoV did not show active infection. Our findings of increased TPO levels in the plasma of SARS patients provide a possible explanation for the genesis of thrombocytosis, which frequently develops from thrombocytopenia in SARS patients.

Expression of the CUB domain containing protein 1 (CDCP1) gene in colorectal tumour cells

Expression of CUB domain containing protein 1 (CDCP1) is upregulated in carcinoma cells. We quantitated CDCP1 gene expression in matched normal colon and tumour tissue and compared the level of expression to other genes upregulated in colorectal tumourigenesis. Furthermore, we show that the CDCP1 gene generates two transcripts which are co-expressed in normal and matched tumour tissue as well as in the majority of cell lines analysed. However, intracellular localisation studies revealed that only one of these transcripts encodes a protein that is localised to the cell surface.

Role of transforming growth factor-beta in hematologic malignancies

The transforming growth factor-beta (TGF-beta) signaling pathway is an essential regulator of cellular processes, including proliferation, differentiation, migration, and cell survival. During hematopoiesis, the TGF-beta signaling pathway is a potent negative regulator of proliferation while stimulating differentiation and apoptosis when appropriate. In hematologic malignancies, including leukemias, myeloproliferative disorders, lymphomas, and multiple myeloma, resistance to these homeostatic effects of TGF-beta develops. Mechanisms for this resistance include mutation or deletion of members of the TGF-beta signaling pathway and disruption of the pathway by oncoproteins. These alterations define a tumor suppressor role for the TGF-beta pathway in human hematologic malignancies. On the other hand, elevated levels of TGF-beta can promote myelofibrosis and the pathogenesis of some hematologic malignancies through their effects on the stroma and immune system. Advances in the TGF-beta signaling field should enable targeting of the TGF-beta signaling pathway for the treatment of hematologic malignancies.

Role of transforming growth factor-beta1-smad signal transduction pathway in patients with hepatocellular carcinoma

AIM: To explore the role of transforming growth factor-beta1 (TGF-β1)-smad signal transduction pathway in patients with hepatocellular carcinoma.

METHODS: Thirty-six hepatocellular carcinoma specimens were obtained from Qidong Liver Cancer Institute and Department of Pathology of the Second Affiliated Hospital of Nanjing Medical University. All primary antibodies (polyclonal antibodies) to TGF-β1, type II Transforming growth factor-beta receptor (TβR-II), nuclear factor-kappaB (NF-κB), CD34, smad4 and smad7,secondary antibodies and immunohistochemical kit were purchased from Zhongshan Biotechnology Limited Company (Beijing, China). The expressions of TGF-β1, TβR-II, NF-κB, smad4 and smad7 proteins in 36 specimens of hepatocellular carcinoma (HCC) and its adjacent tissue were separately detected by immunohistochemistry to observe the relationship between TGF-β1 and TβR-II, between NF-κB and TGF-β1, between smad4 and smad7 and between TGF-β1 or TβR-IIand microvessel density (MVD). MVD was determined by labelling the vessel endothelial cells with CD34.

RESULTS: The expression of TGF-β1, smad7 and MVD was higher in HCC tissue than in adjacent HCC tissue (P<0.01, P <0.05, P <0.01 respectively). The expression of TβR-IIand smad4 was lower in HCC tissue than in its adjacent tissue (P <0.01, P <0.05 respectively). The expression of TGF-β1 protein and NF-κB protein was consistent in HCC tissue. The expression of TGF-β1 and MVD was also consistent in HCC tissue. The expression of TβR-IIwas negatively correlated with that of MVD in HCC tissue.

CONCLUSION: The expressions of TGF-β1, TβR-II, NF-κB, smad4 and smad7 in HCC tissue, which are major up and down stream factors of TGF-β1-smad signal transduction pathway , are abnormal. These factors are closely related with MVD and may play an important role in HCC angiogenesis. The inhibitory action of TGF-β1 is weakened in hepatic carcinoma cells because of abnormality of TGF-β1 receptors (such as TβR-II) and postreceptors (such as smad4 and smad7). NF-κB may cause activation and production of TGF-β1.

Involvement of transforming growth factor-β and thrombopoietin in the pathogenesis of myelodysplastic syndrome with myelofibrosis

We investigated the cause of myelofibrosis and proliferation of megakaryocytes in myelodysplastic syndrome with myelofibrosis (MDS-MF (+)). Plasma-transforming growth factor-beta1 (PTGF-beta1) concentrations closely correlated with myelofibrosis grade in MDS-MF (+) and were higher than those in idiopathic myelofibrosis (IMF), essential thrombocythemia (ET), idiopathic thrombocytopenic purpura (ITP), MDS-without MF (MDS-MF (-)) or healthy volunteers (HV). Peripheral blood mononuclear cells from MDS-MF (+) patients expressed more TGF-beta1 mRNA than those from IMF, MDS-MF (-) or HV. When we immunostained bone marrow specimens of MDS-MF (+) for TGF-beta, the intensity of blasts was apparently higher than that of megakaryocytes, while in MDS-MF (-), megakaryocytes were immunostained with a similar intensity as that in MDS-MF (+), but blasts were negative for staining. In IMF, megakaryocytes, monocytes and small mononuclear cells representing CD34+ cells were all similarly stained with a much lower intensity than that of blasts in MDS-MF (+). The number of bone marrow megakaryocytes were increased the most in MDS-MF (+), followed by ET, ITP, MDS-MF (-) and NHL and correlated with plasma thrombopoietin (TPO) levels or with plasma TGF-beta1 levels, respectively, in each disease. Thus, in MDS-MF (+), both myelofibrosis and the increased megakaryocytes were ascribed to overproduction of TGF-beta1 from blasts.