Reduced expression of TGF β1RII in agnogenic myeloid metaplasia is not due to mutation or methylation

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.

Epigenetic therapy in myeloproliferative neoplasms: evidence and perspectives

The classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), which include polycythaemia vera, essential thrombocythaemia and primary myelofibrosis, originate from a stem cell-derived clonal myeloproliferation that manifests itself with variable haematopoietic cell lineage involvement; they are characterized by a high degree of similarities and the chance to transform each to the other and to evolve into acute leukaemia. Their molecular pathogenesis has been associated with recurrent acquired mutations in janus kinase 2 (JAK2) and myeloproliferative leukemia virus oncogene (MPL). These discoveries have simplified the diagnostic approach and provided a number of clues to understanding the phenotypic expression of MPNs; furthermore, they represented a framework for developing and/or testing in clinical trials small molecules acting as tyrosine kinase inhibitors. On the other hand, evidence of abnormal epigenetic gene regulation as a mechanism potentially contributing to the pathogenesis and the phenotypic diversity of MPNs is still scanty; however, study of epigenetics in MPNs represents an active field of research. The first clinical trials with epigenetic drugs have been completed recently, whereas others are still ongoing; results have been variable and at present do not allow any firm conclusion. Novel basic and translational information concerning epigenetic gene regulation in MPNs and the perspectives for therapy will be critically addressed in this review.

Enhanced histone deacetylase enzyme activity in primary myelofibrosis

We measured histone deacetylase (HDAC) activity in 17 patients with primary myelofibrosis (PMF); 19 with other myeloproliferative neoplasm (MPN) and 16 normal volunteers. Significantly elevated HDAC levels were shown in patients with PMF compared with other MPN patients and normal volunteers (p<0.05). Sixteen patients with PMF were also studied for correlation between JAK2 mutation status and HDAC levels; no significant correlation was found. We further correlated HDAC levels with clinical features in PMF: there was no correlation with WBC, platelet counts, Hb levels or degree of bone marrow fibrosis, but HDAC levels were correlated to the degree of splenomegaly. This suggests that HDAC may be recruited as essential thrombocythemia or polycythemia vera progresses into myelofibrosis or PMF progresses into more advanced stage. We then used the qRT-PCR cycle threshold (CT) method to study which HDACs were elevated in PMF. The results showed that, in general, Class 1 HDACs were elevated (HDAC1,2,8) except HDAC3, Class II HDACs were depressed (HDAC4,5) except HDAC6 and 10, and Class III HDACs were generally elevated. The current study may form the basis for using HDAC inhibitor in the treatment of patients with PMF and may implicate a possible role of HDAC in the association of pathogenesis of PMF.

Epigenetic Targeting of Transforming Growth Factor β Receptor II and Implications for Cancer Therapy

The transforming growth factor (TGF) β signaling pathway is involved in many cellular processes including proliferation, differentiation, adhesion, motility and apoptosis. The loss of TGFβ signaling occurs early in carcinogenesis and its loss contributes to tumor progression. The loss of TGFβ responsiveness frequently occurs at the level of the TGFβ type II receptor (TGFβRII) which has been identified as a tumor suppressor gene (TSG). In keeping with its TSG role, the loss of TGFβRII expression is frequently associated with high tumor grade and poor patient prognosis. Reintroduction of TGFβRII into tumor cell lines results in growth suppression. Mutational loss of TGFβRII has been characterized, particularly in a subset of colon cancers with DNA repair enzyme defects. However, the most frequent cause of TGFβRII silencing is through epigenetic mechanisms. Therefore, re-expression of TGFβRII by use of epigenetic therapies represents a potential therapeutic approach to utilizing the growth suppressive effects of the TGFβ signaling pathway. However, the restoration of TGFβ signaling in cancer treatment is challenging because in late stage disease, TGFβ is a pro-metastatic factor. This effect is associated with increased expression of the TGFβ ligand. In this Review, we discuss the mechanisms associated with TGFβRII silencing in cancer and the potential usefulness of histone deacetylase (HDAC) inhibitors in reversing this effect. The use of HDAC inhibitors may provide a unique opportunity to restore TGFβRII expression in tumors as their pleiotropic effects antagonize many of the cellular processes, which mediate the pro-metastatic effects associated with increased TGFβ expression.

Hypermethylation of CXCR4 promoter in CD34+ cells from patients with primary myelofibrosis

Constitutive mobilization of CD34(+) cells in patients with primary myelofibrosis (PMF) has been attributed to proteolytic disruption of the CXCR4/SDF-1 axis and reduced CXCR4 expression. We document here that the number of circulating CD34(+)/CXCR4(+) cells in PMF patients, as well as the cellular CXCR4 expression, was directly related to CXCR4 mRNA level and that reduced CXCR4 mRNA level was not due to SDF-1-induced downregulation. To address whether epigenetic regulation contributes to defective CXCR4 expression, we studied the methylation status of the CXCR4 promoter using methylation-specific polymerase chain reaction and methylation-specific sequencing in the JAK2V617F-positive HEL cell line and in CD34(+) cells. We found that CD34(+) cells from PMF patients, unlike those from normal subjects, presented hypermethylation of CXCR4 promoter CpG island 1. Following incubation with the demethylating agent 5-Aza-2'-deoxycytidine (5-AzaD), the percentage of PMF CD34(+) cells expressing CXCR4 increased 3-10 times, whereas CXCR4 mRNA level increased approximately 4 times. 5-AzaD-treated PMF CD34(+) cells displayed almost complete reversal of CpG1 island 1 hypermethylation and showed enhanced migration in vitro in response to SDF-1. These data point to abnormal methylation of the CXCR4 promoter as a mechanism contributing to constitutive migration of CD34(+) cells in PMF. Disclosure of potential conflicts of interest is found at the end of this article.