Epigenetic silencing of MIR203 in multiple myeloma

Aberrant microRNA expression in multiple myeloma

Multiple myeloma (MM) is a devastating disease with a complex biology, and in spite of improved survivability by novel treatment strategies over the last decade, MM is still incurable by current therapy. MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression at a post-transcriptional level. More than half of all protein coding genes are estimated to be controlled by miRNAs, and their expression is frequently deregulated in many diseases, including cancer. Recent studies have reported aberrant miRNA expression patterns in MM, and the function of individual miRNAs in MM has been investigated in detail in cell culture and animal models. Here, we review the current knowledge on the role of miRNAs in MM pathogenesis and discuss their potential as prognostic biomarkers and targets for treatment.

Non-coding RNA: a novel opportunity for the personalized treatment of multiple myeloma

INTRODUCTION

Increasing evidence indicates that non-coding RNAs (ncRNAs) are aberrantly expressed and/or functionally deregulated in hematological malignancies, including multiple myeloma. Harnessing these abnormalities by either replacing or inhibiting ncRNAs is emerging as novel therapeutic option.

AREAS COVERED

We review the recent remarkable advancement in the understanding of the biological functions of human ncRNAs in multiple myeloma, including the biogenesis, the mechanisms of expression, the relevance as biomarkers, and mostly, the therapeutic potential. Special emphasis is given to microRNAs, the best characterized class of ncRNAs.

EXPERT OPINION

An improved understanding of the role of ncRNAs in multiple myeloma would provide valuable information about key cancer-promoting pathways and might be highly useful for diagnostic and prognostic assessments. This knowledge might also lead to advancement in the management of multiple myeloma through the development of novel personalized ncRNA-based therapies.

Methylation of tumor suppressor microRNAs: lessons from lymphoid malignancies

miRNAs are a group of small noncoding RNAs measuring 19-25 nucleotides. Sequence-specific binding of miRNAs to the 3´ untranslated regions of target genes leads to translational repressions. Dysregulation of miRNA expression involved in cancer can be triggered by multiple mechanisms including aberrant DNA methylation of the miRNA gene promoter. Of note, DNA methylation of tumor suppressor miRNAs has been implicated in various human cancers. Moreover, miRNA silencing mediated by aberrant promoter DNA methylation can potentially be reversed by hypomethylating agents, and hence may pose a new therapeutic target in cancer. In this review, the authors will focus on the aberrant methylation of miRNAs in the pathogenesis of lymphoid malignancies including chronic lymphocytic leukemia, multiple myeloma and acute lymphoblastic leukemia.

Restoration of microRNA-214 expression reduces growth of myeloma cells through positive regulation of P53 and inhibition of DNA replication

MicroRNA have been demonstrated to be deregulated in multiple myeloma. We have previously reported that miR-214 is down-regulated in multiple myeloma compared to in normal plasma cells. The functional role of miR-214 in myeloma pathogenesis was explored by transfecting myeloma cell lines with synthetic microRNA followed by gene expression profiling. Putative miR-214 targets were validated by luciferase reporter assay. Ectopic expression of miR-214 reduced cell growth and induced apoptosis of myeloma cells. In order to identify the potential direct target genes of miR-214 which could be involved in the biological pathways regulated by this microRNA, gene expression profiling of the H929 myeloma cell line transfected with precursor miR-214 was carried out. Functional analysis revealed significant enrichment for DNA replication, cell cycle phase and DNA binding. miR-214 directly down-regulated the expression of PSMD10, which encodes the oncoprotein gankyrin, and ASF1B, a histone chaperone required for DNA replication, by binding to their 3'-untranslated regions. In addition, gankyrin inhibition induced an increase of P53 mRNA levels and subsequent up-regulation of CDKN1A (p21Waf1/Cip1) and BAX transcripts, which are direct transcriptional targets of p53. In conclusion, MiR-214 functions as a tumor suppressor in myeloma by positive regulation of p53 and inhibition of DNA replication.

Downregulation of specific miRNAs in hyperdiploid multiple myeloma mimics the oncogenic effect of IgH translocations occurring in the non-hyperdiploid subtype

Currently, multiple myeloma (MM) patients are broadly grouped into a non-hyperdiploid (nh-MM) group, highly enriched for IgH translocations, or into a hyperdiploid (h-MM) group, which is typically characterized by trisomies of some odd-numbered chromosomes. We compared the micro RNA (miRNA) expression profiles of these two groups and we identified 16 miRNAs that were downregulated in the h-MM group, relative to the nh-MM group. We found that target genes of the most differentially expressed miRNAs are directly involved in the pathogenesis of MM; specifically, the inhibition of hsa-miR-425, hsa-miR-152 and hsa-miR-24, which are all downregulated in h-MM, leads to the overexpression of CCND1, TACC3, MAFB, FGFR3 and MYC, which are the also the oncogenes upregulated by the most frequent IgH chromosomal translocations occurring in nh-MM. Importantly, we showed that the downregulation of these specific miRNAs and the upregulation of their targets also occur simultaneously in primary cases of h-MM. These data provide further evidence on the unifying role of cyclin D pathways deregulation as the key mechanism involved in the development of both groups of MM. Finally, they establish the importance of miRNA deregulation in the context of MM, thereby opening up the potential for future therapeutic approaches based on this molecular mechanism.

DNA methylation and microRNA dysregulation in cancer

DNA methylation plays a key role in the silencing of numerous cancer-related genes, thereby affecting a number of vital cellular processes, including the cell cycle checkpoint, apoptosis, signal transduction, cell adhesion and angiogenesis. Also widely altered in human malignancies is the expression of microRNAs (miRNAs), a class of small noncoding RNAs that act as posttranscriptional regulators of gene expression. Furthermore, emerging evidence now supports the idea that DNA methylation is crucially involved in the dysregulation of miRNAs in cancer. This is in part the result of technological advances that enable more comprehensive analysis of miRNA expression profiles and the epigenome in cancer cells, which has led to the identification of a number of epigenetically regulated miRNAs. As with protein-coding genes, it appears that miRNA genes involved in regulating cancer-related pathways are silenced in association with CpG island hypermethylation. In addition, methylation in CpG island shore regions and DNA hypomethylation also appear to contribute to miRNA dysregulation in cancer. Aberrant DNA methylation of miRNA genes is a potentially useful biomarker for detecting cancer and predicting its outcome. Moreover, re-expression of miRNAs and the replacement of tumor suppressive miRNAs using miRNA mimics or expression vectors could be effective approaches to cancer therapy.

MicroRNAs in Acute Myeloid Leukemia and Other Blood Disorders

Common blood disorders include hematopoietic cell malignancies or leukemias and plasma cell dyscrasia, all of which have associated microRNA abnormalities. In this paper, we discuss several leukemias including acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL) and identify altered microRNAs and their targets. Immune disorders with altered blood levels of antibodies include autoimmune disorders, such as systemic lupus erythematosus (SLE) with associated anti-self-autoantibodies and immunoglobulin A nephropathy (IgAN) also have related microRNA abnormalities. The alterations in microRNAs may serve as therapeutic targets in these blood disorders.

Methylation of miR-34a, miR-34b/c, miR-124-1 and miR-203 in Ph-negative myeloproliferative neoplasms

Background

MicroRNA (miR) miR-34a, -34b/c, -124-1 and -203 are tumor suppressor miRs implicated in carcinogenesis.

Methods

We studied DNA methylation of these miRs in Philadelphia-negative (Ph-ve) myeloproliferative neoplasms (MPNs). Methylation-specific PCR (MSP), verified by direct sequencing of the methylated MSP products, was performed in cell lines, normal controls and diagnostic marrow samples of patients with MPNs.

Results

Methylation of these miRs was absent in the normal controls. miR-34b/c were homozygously methylated in HEL cells but heterozygously in MEG-01. In HEL cells, homozygous miR-34b/c methylation was associated with miR silencing, and 5-aza-2'-deoxycytidine treatment led to re-expression of both miR-34b and miR-34c, consistent with that both miRs are under the regulation of the same promoter CpG island. miR-34a was heterozygously methylated in MEG-01 and K-562. miR-203 was completely unmethylated in K-562 and SET-2 but no MSP amplification was found in both HEL and MEG-01, suggestive of miR deletion. In primary samples, four each had miR-34b/c and -203 methylation, in which two had concomitant methylation of miR-34b/c and -203. miR-34a was methylated in one patient and none had methylation of miR-124-1. Seven patients (15.6%) had methylation of at least one of the four miRs. miR methylation did not correlate with clinical parameters, disease complications or JAK2 V617F mutation.

Conclusion

This is the first report of miR hypermethylation in MPNs. miR-203 hypermethylation is not specific to Ph+ve leukemias but also present in Ph-ve MPNs. miR-34b/c methylation was associated with reversible miR silencing. There was no correlation of miR methylation with clinical demographic data or outcome.

Epigenetic inactivation of the MIR34B/C in multiple myeloma

We postulated that MIR34B/C, a direct transcriptional target of TP53, might be inactivated by promoter hypermethylation in multiple myeloma (MM). MIR34B/C promoter methylation was studied in 8 normal marrow controls, 8 MM cell lines, 95 diagnostic, and 23 relapsed/progressed MM samples by methylation-specific PCR. MIR34B/C was methylated in 6 (75.0%) MM cell lines but not normal controls. 5-Aza-2'-deoxycytidine led to MIR34B/C promoter demethylation and MIR34B reexpression. Moreover, restoration of MIR34B led to reduced cellular proliferation and enhanced apoptosis of myeloma cells. In primary samples, methylation of MIR34B/C occurred in 5.3% at diagnosis and 52.2% at relapse/disease progression (P < .001). In 12 MM patients with paired samples at diagnosis and relapse/progression, MIR34B/C methylation was acquired in 6 at relapse/progression. In conclusion, MIR34B/C is a tumor suppressor in myeloma. Hypermethylation of MIR34B/C is tumor-specific. Frequent MIR34B/C hypermethylation during relapse/progression but not at diagnosis implicated a role of MIR34B/C hypermethylation in myeloma relapse/progression.