Expression of p15(ink4b) gene during megakaryocytic differentiation of normal and myelodysplastic hematopoietic progenitors

p15Ink4b Loss of Expression by Promoter Hypermethylation Adds to Leukemogenesis and Confers a Poor Prognosis in Acute Promyelocytic Leukemia Patients

PURPOSE

The p15^Ink4b gene exerts its influence as an inhibitor of cyclin-dependent kinases and is frequently associated with hematological malignancies. Inactivation of this gene through DNA methylation has been found to be the most prevalent epigenetic alteration reported, with a high frequency in all French-American-British subtypes of acute myeloid leukemias, including acute promyelocytic leukemia (APL). In this study,we investigated the prognostic significance of p15 gene promoter hypermethylation and its expression in APL patients of Kashmir (North India).

MATERIALS AND METHODS

p15 gene promoter hypermethylation was conducted by methylation-specific polymerase chain reaction, while its subsequent expression analysiswas carried out by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Of the 37 patients, 16 (43.2%) were found to have methylated p15 genes. Of these 16 cases, seven (43.8%) were methylated partially and nine (56.2%) were found to have complete methylation. Moreover, nine of the 37 patients (24.3%) who presented with leukocytosis at their baseline had complete p15 gene methylation as well (p < 0.05). Semiquantitative RT-PCR showed a complete loss of p15 expression in nine patients with complete methylation coupled with leukocytosis (p=0.031), while seven patients with partial methylation showed decreased p15 expression. Six patients relapsed during the maintenance phase of treatment and were found to have a completely methylated p15 gene and no p15 mRNA.

CONCLUSION

Complete methylation and loss of p15 gene expression causes susceptibility to relapse and decreased survival in APL patients. Thus, p15 promoter hypermethylation is a prospective prognostic indicator and a reliable clinical aid in assessment of patients with APL.

miR-125b modulates megakaryocyte maturation by targeting the cell-cycle inhibitor p19INK4D

A better understanding of the mechanisms involved in megakaryocyte maturation will facilitate the generation of platelets in vitro and their clinical applications. A microRNA, miR-125b, has been suggested to have important roles in the self-renewal of megakaryocyte-erythroid progenitors and in platelet generation. However, miR-125b is also critical for hematopoietic stem cell self-renewal. Thus, the function of miR-125b and the complex signaling pathways regulating megakaryopoiesis remain to be elucidated. In this study, an attentive examination of the endogenous expression of miR-125b during megakaryocyte differentiation was performed. Accordingly, the differentiation of hematopoietic stem cells requires the downregulation of miR-125b, whereas megakaryocyte determination and maturation synchronize with miR-125b accumulation. The overexpression of miR-125b improves megakaryocytic differentiation of K562 and UT-7 cells. Furthermore, stage-specific overexpression of miR-125b in primary cells demonstrates that miR-125b mediates an enhancement of megakaryocytic differentiation after megakaryocyte determination, the stage at which megakaryocytes are negative for the expression of the hematopoietic progenitor marker CD34. The identification of miR-125b targets during megakaryopoiesis was focused on negative regulators of cell cycle because the transition of the G1/S phase has been associated with megakaryocyte polyploidization. Real-time PCR, western blot and luciferase reporter assay reveal that p19^INK4D is a direct target of miR-125b. P19^INK4D knockdown using small interfering RNA (siRNA) in megakaryocyte-induced K562 cells, UT-7 cells and CD61⁺ promegakaryocytes results in S-phase progression and increased polyploidy, as well as improved megakaryocyte differentiation, similarly to the effects of miR-125b overexpression. P19^INK4D overexpression reverses these effects, as indicated by reduced expression of megakaryocyte markers, G1-phase arrest and polyploidy decrease. P19^INK4D knockdown in miR-125b downregulated cells or p19^INK4D overexpression in miR-125b upregulated cells rescued the effect of miR-125b. Taken together, these findings suggest that miR-125b expression positively regulates megakaryocyte development since the initial phases of megakaryocyte determination, and p19^INK4D is one of the key mediators of miR-125b activity during the onset of megakaryocyte polyploidization.

Low-dose decitabine promotes megakaryocyte maturation and platelet production in healthy controls and immune thrombocytopenia

Impaired megakaryocyte maturation and insufficient platelet production have been shown to participate in the pathogenesis of immune thrombocytopenia (ITP). Our previous study demonstrated that low expression of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) in megakaryocytes contributed to impaired platelet production in ITP. Decitabine (DAC), a demethylating agent, is known to promote cell differentiation and maturation at low doses. However, whether decitabine is potential in promoting megakaryocyte maturation and platelet release in ITP is unclear. In this study, we evaluated the effect of DAC on megakaryocyte maturation and platelet release in the presence of ITP plasma that has been shown to cause impaired megakaryocyte maturation and platelet production. We observed that low-dose DAC (10 nM) could significantly increase the number of mature polyploid (≥ 4N) megakaryocytes in cultures with plasma from healthy controls and more than one-half of ITP patients in vitro. Furthermore, the number of platelets released from these megakaryocytes significantly increased compared with those untreated with DAC. In these megakaryocytes, DAC significantly enhanced TRAIL expression via decreasing its promoter methylation status. These findings demonstrate that low-dose DAC can promote megakaryocyte maturation and platelet production and enhance TRAIL expression in megakaryocytes in healthy controls and ITP. The potential therapeutic role of low-dose DAC may be beneficial for thrombocytopenic disorders.

Azacytidine (Vidaza(R)) in the treatment of myelodysplastic syndromes

The myelodysplastic syndromes (MDS) are a heterogeneous group of disorders that manifest as bone marrow failure with the risk of life threatening infections and bleeding. A third of these patients may transform to acute leukemia. Age and co-morbidities have limited treatment in the majority to supportive care with a minority of patients eligible for the only curative modality to date, allogeneic stem cell transplantation. The advent of targeted therapy has increased the repertoire of therapeutic options. In particular the methyl transferase inhibitor 5 Azacytidine, that targets epigenetic changes in MDS, has been shown to be effective in up to 60% of patients in a Phase III randomized controlled trial comparing it with best supportive care and has been licensed by the US Food and Drug Administration for use in all subtypes of MDS. It has been shown to prolong time to leukemic transformation (21 vs 12 months with 3% transforming to leukemia p=0.0001) and is the only disease-modifying drug. Patients with monosomy 7, trisomy 8, and diploid chromosomes appear to particularly benefit with the former deriving sustained remissions. As an outpatient therapy, with an acceptable side effect profile, treatment with Azacytidine needs to be considered in all MDS patients who are eligible for treatment.

The effect of decitabine on megakaryocyte maturation and platelet release

Thrombocytopenia is a common feature of myelodysplastic syndromes (MDS). 5-aza-2'-deoxycytidine (decitabine) has been used to treat MDS with an approximately 20% response rate in thrombocytopenia. However, the mechanism of how decitabine increases platelet count is not clear. In this study, we investigated the effect of decitabine on megakaryocyte maturation and platelet release in the mouse. The effect of decitabine on megakaryocyte maturation was studied in an in vitro megakaryocyte differentiation model utilising mouse bone marrow cells and mouse megakaryoblastic cell line L8057. Decitabine (2.5 μM) is able to induce L8057 cells to differentiate into a megakaryocyte-like polyploidy cells with positive markers of acetylcholinesterase and αIIb integrin (CD41). Higher expression of αIIb integrin was also found in primary mouse bone marrow cells and human cord blood CD34+ cells cultured with both thrombopoietin and decitabine as compared to thrombopoietin alone. In addition, we noted a 30% platelet count increase in Balb/c mice 12 hours after the injection of decitabine at a clinically relevant dose (15 mg/m2), suggesting a rapid platelet release from the spleen or bone marrow. Our data suggest that decitabine increases platelet counts by enhancing platelet release and megakaryocyte maturation.

High-level CD34 expression on megakaryocytes independently predicts an adverse outcome in patients with myelodysplastic syndromes

Expression of CD34 on mature-appearing megakaryocytes can be seen in various intrinsic bone marrow (BM) disorders as well as reactive bone marrows. In this study we investigate the clinical significance of CD34+ megakaryocytes in myelodysplastic syndromes (MDSs). Expression of CD34 on megakaryocytes was assessed on BM biopsies obtained from 202 patients with MDS. High-level (≥20%) CD34 expression on megakaryocytes was found in BM of 29 patients (14%). The expression of CD34 on megakaryocytes is correlated with severe cytopenia, higher numbers of myeloblasts, more frequent and higher risk cytogenetic abnormalities, and a shorter overall survival. Multivariate analysis indicated that the expression of CD34 on megakaryocytes could be a strong and an independent poor prognostic factor in MDS, with a hazard ratio of 2.53.

DNA methyltransferase and histone deacetylase inhibitors in the treatment of myelodysplastic syndromes

The recently approved drugs 5-azacitidine (5AC) and 5-aza-2'-deoxyazacytidine (DAC) are in wide clinical use for the treatment of myelodysplastic syndrome (MDS) of all types and chronic myelomonocytic leukemia (CMML). These agents were developed based upon an understanding of the importance of epigenetic changes in malignancy, and they have been evaluated in randomized clinical trials, which demonstrate response rates between 20% and 40% in patients for whom no previous standard of care was available. As understanding of the epigenetic changes characteristic of the malignant phenotype improves, we are able to target other regulators of chromatin conformation that contribute to aberrant gene transcription and dysregulated cell growth. The histone deacetylase (HDAC) inhibitors belong to one class of therapeutics developed using this paradigm. Although responses using HDAC inhibitors alone in MDS have been modest, robust preclinical data drive clinical trials in which they are utilized in combination with DNA methyltransferase (DNMT) inhibitors. Combination therapy offers the possibility of hematologic improvement and remission to myelodysplastic patients with previously untreatable disease.

P19INK4D links endomitotic arrest and megakaryocyte maturation and is regulated by AML-1

The molecular mechanisms that regulate megakaryocyte (MK) ploidization are poorly understood. Using MK differentiation from primary human CD34(+) cells, we observed that p19(INK4D) expression was increased both at the mRNA and protein levels during ploidization. p19(INK4D) knockdown led to a moderate increase (31.7% +/- 5%) in the mean ploidy of MKs suggesting a role of p19(INK4D) in the endomitotic arrest. This increase in ploidy was associated with a decrease in the more mature MK population (CD41(high)CD42(high)) at day 9 of culture, which was related to a delay in differentiation. Inversely, p19(INK4D) overexpression in CD34(+) cells resulted in a decrease in mean ploidy level associated with an increase in CD41 and CD42 expression in each ploidy class. Confirming these in vitro results, bone marrow MKs from p19(INK4D) KO mice exhibited an increase in mean ploidy level from 18.7N (+/- 0.58N) to 52.7N (+/- 12.3N). Chromatin immunoprecipitation assays performed in human MKs revealed that AML-1 binds in vivo the p19(INK4D) promoter. Moreover, AML-1 inhibition led to the p19(INK4D) down-regulation in human MKs. These results may explain the molecular link at the transcriptional level between the arrest of endomitosis and the acceleration of MK differentiation.

Loss of the tumor suppressor p15Ink4b enhances myeloid progenitor formation from common myeloid progenitors

OBJECTIVE

The tumor suppressor p15Ink4b (Ink4b) is a cell-cycle inhibitor that is inactivated in a high percentage of acute myeloid leukemia and myeloid dysplasia syndrome cases. Despite this, the role of Ink4b in hematopoiesis remains unclear. Here we examined the role of Ink4b in blood cell formation using Ink4b-deficient (Ink4b(-/-)) mice.

METHODS

We compared the bone marrow (BM) of Ink4b(-/-) and wild-type mice using flow cytometric, colony-forming unit and competitive repopulating assays (CRA). The proliferation, differentiation, self-renewal, and apoptosis of progenitor cells were further compared by in vitro and in vivo methods.

RESULTS

BM from Ink4b(-/-) mice contained increased numbers of granulocyte-monocyte progenitors and Gr-1(+) cells and showed a competitive advantage over wild-type cells in myeloid cell formation by CRA. Ink4b(-/-) progenitors did not demonstrate increased proliferation, self-renewing potential, or reduced apoptosis. Instead, Ink4b(-/-) common myeloid progenitors (CMPs) showed increased myeloid progenitor formation concomitant with reduced erythroid potential.

CONCLUSIONS

This work establishes a role for Ink4b in regulating the differentiation of CMPs and indicates that loss of Ink4b enhances the formation of myeloid progenitors.

CDKN2B methylation status and isolated chromosome 7 abnormalities predict responses to treatment with 5-azacytidine

5-Azacytidine, a DNA methyl transferase inhibitor, is effective in patients with myelodysplastic syndromes (MDS). Whether responses to 5-Azacytidine are achieved by demethylation of key genes or by cytotoxicity is unclear. Of 34 patients with MDS or acute myeloid leukaemia (AML) treated with 5-Azacytidine, 7 achieved complete remissions (CR) (21%) and 6 achieved haematological improvement. All six had less than 5% bone marrow (BM) blasts at the time of haematological improvements (HI) (2 had pre-existing refractory anaemia (RA), 4 had refractory anaemia with excess blasts (RAEB)). A further patient with RAEB had blast reduction to less than 5% without HI. Five of the seven (71%) complete responders had chromosome 7 abnormalities. BM CR predicted longer overall survival (OS) (median 23 versus 9 months, P=0.015). Bisulphite genomic sequencing (BGS) of the CDKN2B (p15(INK4b)) promoter showed low level, heterogeneous pretreatment methylation (mean 12.2%) in 14/17 (82%) patients analysed. Lower baseline methylation occurred in responders (9.8% versus 16.2% in non-responders P=0.07). No response was seen in patients with >24% methylation, in whom p15(INK4b) mRNA was not expressed. 5-Azacytidine reduced CDKN2B methylation by mean 6.8% in 8/17 (47%) patients, but this did not correlate with response. At 75 mg/m(2), cell death (reduced BM cellularity (P=0.001) and increased apoptosis (P=0.02)) rather than demethylation of CDKN2B correlates with response. Patients with >24% methylation may benefit from alternative dosing or combination strategies.

Cyclin D-Cdk4 is regulated by GATA-1 and required for megakaryocyte growth and polyploidization

Endomitosis is a unique form of cell cycle used by megakaryocytes, in which the latter stages of mitosis are bypassed so that the cell can increase its DNA content and size. Although several transcription factors, including GATA-1 and RUNX-1, have been implicated in this process, the link between transcription factors and polyploidization remains undefined. Here we show that GATA-1-deficient megakaryocytes, which display reduced size and polyploidization, express nearly 10-fold less cyclin D1 and 10-fold increased levels of p16 compared with their wild-type counterparts. We further demonstrate that cyclin D1 is a direct GATA-1 target in megakaryocytes, but not erythroid cells. Restoration of cyclin D1 expression, when accompanied by ectopic overexpression of its partner Cdk4, resulted in a dramatic increase in megakaryocyte size and DNA content. However, terminal differentiation was not rescued. Of note, polyploidization was only modestly reduced in cyclin D1-deficient mice, likely due to compensation by elevated cyclin D3 expression. Finally, consistent with an additional defect conferred by increased levels of p16, inhibition of cyclin D-Cdk4 complexes with a TAT-p16 fusion peptide significantly blocked polyploidization of wild-type megakaryocytes. Together, these data show that GATA-1 controls growth and polyploidization by regulating cyclin D-Cdk4 kinase activity.

Epigenetics and chronic lymphocytic leukemia

The DNA methylation level in patients with chronic lymphocytic leukemia is generally lower than healthy individuals. Although DNA methylation is globally decreased, regional hypermethylation of gene promoters leads to gene silencing. Many of these genes have tumor suppressor phenotypes. Unlike mutations or deletions, hypermethylation is potentially reversible after inhibition with DNA methylation modulators. Myelodysplastic syndrome has been a model disease in which treatment of patients results in demethylation of specific genes. The story in patients with chronic lymphocytic leukemia is slowly unraveling as epigenetic modifications likely also play an important role. Ongoing clinical trials correlating clinical response to gene expression after treatment with DNA methylation inhibitors will ultimately allow us to better risk stratify and predict the subgroup of patients who will benefit from treatment with this class of drugs.

Effects of 5-aza-2'-deoxycytidine on proliferation, differentiation and p15/INK4b regulation of human hematopoietic progenitor cells

The demethylating agents 5-azacytidine and 5-aza-2'-deoxycytidine (DAC) have been shown to induce differentiation and inhibit growth of leukemic myeloid cells at low concentrations. However, the effect of DAC in changing the differentiation and proliferation behavior of normal human myeloid progenitors has rarely been investigated. Therefore, we established an in vitro model of normal hematopoietic differentiation, using CD34+ cells from mobilized peripheral blood, to study proliferation and colony formation, expression of several myeloid maturation markers and of the inhibitor of cyclin-dependent kinases p15/INK4b. Upon DAC treatment, cell growth was significantly decreased in a dose-dependent manner, without an increase in cytotoxicity. DAC treatment also resulted in a substantial increase of lysozyme-positive cells, which could be enhanced by G-CSF, a modest increase of myeloperoxidase+ and CD15+ cells, as well as an increase of colony-forming cells (CFU-GM) compared to control cells. p15/INK4b protein expression was strongly upregulated upon myeloid maturation, and additional DAC treatment did not change p15 expression or the methylation status of the p15 promoter at the noncytotoxic concentrations used. Taken together, these data indicate a role of DAC in changing myeloid progenitor cell expansion and differentiation. This model appears suitable also for global analyses of multiple differentially methylated genes.

Decitabine in Myelodysplastic Syndromes

Myelodysplastic syndromes (MDS) are a heterogenous group of hematopoietic stem cell disorders that are multifactorial in their etiology. Aberrant DNA hypermethylation is now thought to be involved in MDS, as numerous tumor-suppressor genes have been identified that are silenced in these patients. Thus, the use of DNA methyltransferase inhibitors, such as 5-aza-2'-deoxycytidine (decitabine, Dacogen, MGI Pharma Inc, Bloomington, MN), for reversal of this process appears to be a rational intervention that may influence the course of the disease. Several phase I/II studies have been conducted using a low-dose schedule of decitabine in MDS patients. Based on these studies, decitabine appears to be effective and generally well tolerated, especially in those patients with worse prognostic indicators. Recent results of a phase III study also confirmed that patients treated with decitabine compared to standard supportive care had higher overall response rates and longer time to AML transformation. Decitabine appears to be a promising new therapy for the treatment of MDS; however, defining the optimal dosing schedule and exploring the possible use in combination with other agents such as the histone deacetylase inhibitors need further evaluation.

Methylation status of the p15 and p16 genes in paediatric myelodysplastic syndrome and juvenile myelomonocytic leukaemia

Aberrant DNA methylation is frequently observed in adults with myelodysplastic syndrome (MDS), and is recognized as a critical event in the disease's pathogenesis and progression. This is the first report to investigate the methylation status of p15 and p16, cell cycle regulatory genes, in children with MDS (n = 9) and juvenile myelomonocytic leukaemia (JMML; n = 18) by using a methylation-specific polymerase chain reaction. The frequency of p15 hypermethylation in paediatric MDS was 78% (7/9), which was comparable to that in adult MDS. In contrast, p15 hypermethylation in JMML was a rare event (17%; 3/18). In JMML, clinical and laboratory characteristics including PTPN11 mutations and aberrant colony formation were not different between the three patients with hypermethylated p15 and the others. Aberrant methylation of p16 was not detected in children with either MDS or JMML. Since p15 and p16 genes were unmethylated in two children with JMML, in whom the disease had progressed with an increased number of blasts, a condition referred to as blastic crisis, we infer that the aberrant methylation of these genes is not responsible for the progression of JMML. The results suggest that demethylating agents may be effective in most children with MDS and a few patients with JMML.

p15 mRNA expression detected by real-time quantitative reverse transcriptase-polymerase chain reaction correlates with the methylation density of the gene in adult acute leukemia

Cyclin-dependent kinase inhibitor p15 is frequently inactivated by either methylation or deletion in patients with acute leukemia. To examine pathologic and clinical significance of the p15 gene inactivation, we established a quantitative assay of p15 mRNA expression in the bone marrow cells by real-time quantitative reverse transcriptase-polymerase chain reaction. p15 mRNA expression in 14 patients with precursor B-cell acute lymphoblastic leukemia (PBC-ALL) well correlated with status of deletion and methylation in the p15 gene analyzed by Southern blotting. Furthermore, two patients with PBC-ALL and 11 acute myeloblastic leukemia (AML) were quantitatively examined for p15 gene methylation using bisulfite genomic sequencing. The data showed that p15 mRNA expression significantly correlated with the CpG island methylation density. Among 108 AML patients, p15 mRNA expression was significantly lower in the myeloid lineage (M1, M2, M3) than the monocytic lineage (M4, M5) (P = 0.0019). Above all, the majority of M3 patients showed low p15 expression compared with M1 and M2 patients (P = 0.029). These observations suggest that quantitative analysis of p15 mRNA will be useful to evaluate transcriptional repression of the p15 gene caused by various degrees of methylation.

Epigenetic Inactivation of Tumor Suppressor Genes in Hematologic Malignancies

A number of genetic alterations are involved in the development of hematologic malignancies. These alterations include the activation of oncogenes by chromosomal translocation or gene amplification and the inactivation of tumor suppressor genes by gene deletion or mutations. Recently, epigenetic change has been proven to be another important means of inactivating tumor suppressor genes in tumor cells, and hypermethylation of promoter DNA is one of the most important mechanisms. In hematologic malignancies, many kinds of tumor suppressor genes and candidate suppressor genes are epigenetically inactivated. Inactivation of tumor suppressor genes usually occurs in a disease-specific manner and plays important roles in the development and progression of the disease. Some of these alterations have clinical effects on treatment results or the prognoses of the patients.

The effects of 5-aza-2′-deoxycytidine (Decitabine) on the platelet count in patients with intermediate and high-risk myelodysplastic syndromes

5-Aza-2'-deoxycytidine, a DNA-hypomethylating agent, can induce clinical remissions in patients with high-risk myelodysplastic syndromes (MDS). During treatment an increase in platelet count is frequently the first positive event to be seen. In this study, we analyzed the platelet response of patients with high-risk MDS on low-dose 5-aza-2'-deoxycytidine therapy. We evaluated 162 from the 170 patients entered in three consecutive Phase II studies. One hundred twenty-six of them were thrombocytopenic at start of the therapy. All patients had an IPSS risk score of Intermediate I or higher. A rise in platelet count preceded a good trilineage response. In 58% of the thrombocytopenic patients a platelet response was already seen after one cycle of therapy. During therapy 69% of the patients with a low platelet count showed a response. Due to disease progression the final response rate was 63% in thrombocytopenic patients. No correlation was found between the platelet response and either the presence or absence of an adequate number of megakaryocytes or serum thrombopoietin levels. However, platelet response strongly predicted for overall survival (P < 0.0001). 5-Aza-2'-deoxycytidine has a clinically significant, often long lasting, effect on the platelet count in a substantial number of high-risk MDS patients.

The Hematopoietic Stem Cell in Myelodysplasia

The mechanisms underlying hematopoietic stem cell or progenitor cell abnormalities in myelodysplastic syndromes (MDSs) remain poorly characterized. Current evidence exists for multiple intrinsic and extrinsic influences upon the stem cell in these disorders. These influences are outlined in this review and include: stem cell characteristics in MDSs, as compared with those in acute myelogenous leukemia; the role of increased apoptosis; the role of signaling pathway abnormalities; the influences of immune modulation; and the effect of stromal cells and stromal cell cytokine production. Despite numerous studies that have examined these factors, how they converge to produce a situation in which accelerated proliferation and accelerated death occur simultaneously remains largely an unexplored area. It is anticipated that future studies that focus on well-characterized and purified progenitor populations in these disorders will elucidate the process by which ineffective hematopoiesis results from the influences of stem cell abnormalities versus abnormalities in the stem cell's microenvironmental and immunologic milieu.

Smad expression in human atherosclerotic lesions: evidence for impaired TGF-beta/Smad signaling in smooth muscle cells of fibrofatty lesions

OBJECTIVE

Transforming growth factor-beta (TGF-beta) has been implicated in the pathogenesis of human atherosclerosis but its actions during lesion progression are poorly understood. Smad2, Smad3, and Smad4 proteins are signaling molecules by which TGF-beta modulates gene transcription. Our objective was to define the actions of TGF-beta during lesion progression in humans by examining the expression of Smads in relation to TGF-beta-mediated responses.

METHODS AND RESULTS

Immunohistochemistry and reverse-transcription polymerase chain reaction demonstrated Smad2, Smad3, and Smad4 expression in macrophages of fibrofatty lesions and their upregulation after differentiation of monocytes to macrophages. The major Smad splice variants expressed by the macrophages were those that are transcriptionally most active. Macrophages also expressed cyclin inhibitors whose expression is induced via Smad proteins. The cytoplasmic location of p21(Waf1) suggests it may protect macrophages from apoptosis. Smooth muscle cells (SMCs) within the fibrofatty lesions did not express the Smad proteins or the cyclin inhibitors. SMCs of fibrous plaques expressed all 3 Smad proteins.

CONCLUSIONS

In human atherosclerotic lesions, the actions of TGF-beta appear restricted to SMCs in fibrous plaques and macrophages in fatty streaks/fibrofatty lesions. The lack of key TGF-beta signaling components in SMCs of fibrofatty lesions indicates impaired ability of these cells to initiate TGF-beta-mediated Smad-dependent transcriptional responses.

Inhibitors of DNA methylation in the treatment of hematological malignancies and MDS

DNA methylation abnormalities have recently emerged as one of the most frequent molecular changes in hematopoietic neoplasms. Since methylation and transcriptional status are inversely correlated, the hypermethylation of genes involved in cell-cycle control and apoptosis could have a pathogenetic role in the development of cancer. In particular, high-risk myelodysplastic syndromes (MDS) and secondary leukemias show a high prevalence of tumor suppressor gene hypermethylation. The progression of chronic myeloproliferative diseases and of myelodysplastic syndromes, as well as that of lymphoproliferative diseases, is associated with an increased methylation rate, pointing to a role for hypermethylation of critical promoter regions in the transformation to more aggressive phenotypes. In the same line, a significantly worse prognosis has been shown for patients with hypermethylation of several genes compared to that of patients with unmethylated genes. For these reasons, the use of irreversible DNA methyltransferase inhibitors, such as 5-azacytidine and Decitabine, appears to be a promising option for the treatment of MDS and acute myeloid leukemia. In clinical trials, Azacytidine results in a significantly higher response rate, improved quality of life, reduced risk of leukemic transformation, and improved survival compared to supportive care. Similarly, Decitabine showed favorable results, promising response rates, a good nonhematologic toxicity profile, and a trend for better survival compared to intensive chemotherapy, particularly in older patients. The synergistic effect of histone deacetylase inhibitors, including phenylbutyrate (PB), in reactivating silenced genes encouraged clinical studies on the combination of PB and demethylating agents in hematological diseases, characterized by p15 silencing. The sequential administration of a "first generation" demethylating agent and HDAC inhibitors gave preliminary evidence of a reduced methylation of target genes, as also described with Decitabine. Clinical trials are still ongoing, and preliminary data indicate for the first time that the natural history of MDS may be changed by a non-intensive treatment, characterized by an outstanding toxicity profile.

Epigenetic targets in hematopoietic malignancies

Frequent genetic alterations in hematopoietic neoplasias (chromosomal translocations, point mutations, etc.) have provided biologic targets for the development of effective novel therapies. A rapidly increasing body of knowledge provides evidence also for multiple epigenetic alterations in these disorders, which can complement or even precede genetic aberrations. Gene inactivation ('silencing') of tumor suppressor and growth inhibitory genes (e.g. the cyclin-dependent kinase inhibitors p16, p15, p21) is frequently mediated by DNA methylation of gene promoters. The acetylation state of histones (functionally linked to the DNA methylation state by the methylcytosine binding protein 2, recruiting histone deacetylases) provides a second major epigenetic silencing mechanism. Therapeutic reversal strategies are being developed for acute leukemias, myelodysplastic syndromes and malignant lymphomas. Since the discovery of the DNA methyltransferase (Dnmt) inhibitory activity of two azanucleosides (5-azacytidine, 5-aza-2'-deoxycytidine/decitabine) even at doses with minimal nonhematologic toxicity, both have been clinically studied in several myeloid neoplasias, particularly in elderly patients unable to tolerate aggressive treatment. Further development of agents counteracting aberrant methylation is directed at more targeted approaches, for example, antisense molecules against Dnmts. Histone deacetylases (HDACs) can be inhibited by numerous compounds (sodium phenylbutyrate, valproic acid, novel compounds such as depsipeptide), which have entered the clinical arena in similar indications as Dnmt inhibitors. Impressive effects of HDAC inhibition in acute promyelocytic leukemia models (PML/RARA expression) translate the finding of HDAC recruitment by this chimeric transcription factor to its target genes. The recent discovery of recruitment by PML/RARA also of Dnmt activity to the retinoic acid receptor-beta promoter makes it an interesting candidate for Dnmt inhibitors. Studies combining a 're-expressor' strategy with inhibitors of Dnmts and HDACs are underway. Thus, resensitization to biological agents such as retinoids, colony-stimulating factors and other differentiation inducers may be envisioned.

Methylation of p15INK4B is common, is associated with deletion of genes on chromosome arm 7q and predicts a poor prognosis in therapy-related myelodysplasia and acute myeloid leukemia

The p14(ARF), p15(INK4B), and p16(INK4A) genes are important negative cell-cycle regulators often inactivated by deletions, mutations, or hypermethylation in malignancy. Hypermethylation of the three genes was studied in 81 patients with therapy-related myelodysplasia (t-MDS) or acute myeloid leukemia (t-AML) by methylation-specific PCR, and p15 methylation additionally by bisulfite genomic sequencing. In all, 55 patients disclosed p15 methylation, five patients showed p16 methylation, whereas p14 methylation was not observed. Methylation of p15 was closely associated with deletion or loss of chromosome arm 7q (P=0.0006). In t-MDS, the p15 methylation frequency and the p15 methylation density both increased significantly by stage (P=0.004 and 0.0002), and p15 methylation frequency increased with an increasing percentage of myeloblasts in the bone marrow (P=0.006). In a two-variable Cox model including the percentage of myeloblasts, p15 methylation was an independent prognostic factor (P=0.005). Methylation of p15 was less common in t-AML of subtype M5 than in other FAB subtypes (P=0.03). Methylation of p15 was unrelated to type of previous therapy, to latent period from start of therapy, to platelet count, and to p53 mutations. Inactivation of p15 and deletion of genes on chromosome arm 7q possibly cooperate in leukemogenesis.

Hypermethylation of GpG islands in the promoter region of p15(INK4b) in acute promyelocytic leukemia represses p15(INK4b) expression and correlates with poor prognosis

We evaluated the methylation status of p15 gene in a series of 65 patients with newly diagnosed acute promyelocytic leukemia (APL) receiving homogeneous treatment. Moreover, in 32 of them, the methylation status of p15 gene was correlated to the p15 m-RNA expression. In total, 31 patients had no p15 methylation (U group). An abnormal methylation pattern was found in 34 patients: in seven of these patients only methylated DNA was detected (M group), while in the remaining 27 patients (M/U group), both methylated and unmethylated DNA were amplified. Patients from M group showed a higher incidence of relapses and a lower disease-free survival (DSF) with respect to patients from U and M/U groups (29, 64 and 79% at 5 years for M, U/M and U patients, respectively, P=0.03), while p15 methylation had no impact on overall survival. The p15 expression was detectable in all patients with unmethylated DNA, in none of patients with fully methylated DNA and in 60% of patients with partially methylated DNA. The DFS estimate at 5 years for p15-negative patients was significantly lower than that of p15-positive patients (P=0.03). These data confirm that the presence of p15 methylation negatively influences the prognosis of APL, mainly when it represses the p15 gene transcription.

Possible involvement of hMLH1, p16(INK4a) and PTEN in the malignant transformation of endometriosis

Endometriosis is a common gynecologic disease, which generally follows a benign course. Notwithstanding, several clinical and histologic studies as well as molecular data show that endometriosis could be a precursor of sporadic endometrioid and clear cell carcinomas at extrauterine loci. Several reports have implicated alterations of the hMLH1 and p16(ink4a) (p16) genes, in particular hypermethylation of the promoter region, and of the PTEN gene, principally genetic mutations, in endometrial and ovarian cancers and have indicated that these alterations are already present in precancer conditions. In this report, we analyzed the methylation status of hMLH1 and p16 and the protein expression of PTEN and hMLH1 in 46 cases of endometriosis stages III and IV to better define the possible involvement of these genes in the malignant transformation of endometriosis. We found abnormal methylation of hMLH1 in 4 of the 46 cases (8.6%). In addition, these cases had no detectable hMLH1 protein expression. Regarding patients with hMLH1 alterations, 2 were classified as stage IV and 2 showed coexistent endometriosis and carcinoma. Only 1 case of endometriosis (2.17%), classified as atypical, showed abnormal methylation of p16. Reduced PTEN protein expression was detected in 7 of 46 cases (15.21%): 5 were clinically classified as stage IV, and the other 2 presented both cancer and hypermethylated hMLH1. Our preliminary study suggests that reduced expression of both hMLH1 and PTEN may be involved in the malignant evolution of endometriosis and should be used as markers of neoplastic transformation in aggressive endometriosis with elevated tumor markers.

Effect of etafenone on total and regional myocardial blood flow

The distribution of blood flow to the subendocardial, medium and subepicardial layers of the left ventricular free wall was studied in anaesthetized dogs under normoxic (A), hypoxic (B) conditions and under pharmacologically induced (etafenone) coronary vasodilation (C). Regional myocardial blood flow was determined by means of the particle distribution method. In normoxia a transmural gradient of flow was observed, with the subendocardial layers receiving a significantly higher flow rate compared with the subepicardial layers. In hypoxia induced vasodilation this transmural gradient of flow was persistent. In contrast a marked redistribution of regional flow was observed under pharmacologically induced vasodilation. The transmural gradient decreased. In contrast to some findings these experiments demonstrate that a considerable vasodilatory capacity exists in all layers of the myocardium and can be utilized by drugs. The differences observed for the intramural distribution pattern of flow under hypoxia and drug induced vasodilation support the hypothesis that this pattern reflects corresponding gradients of regional myocardial metabolism.