Upregulation of Dicer is more frequent in monoclonal gammopathies of undetermined significance than in multiple myeloma patients and is associated with longer survival in symptomatic myeloma patients

Evaluation of the clinical significance of RNase III enzyme DROSHA in pediatrics acute lymphocytic leukemia

Acute lymphocytic leukemia (ALL) is one of the subtypes of leukemia; it is one of the leading causes of malignancy and morbidity and childhood mortality. This study examined the dysregulation of DROSHA and its clinical implications in ALL. In the case-control investigation, we have included 140 samples, consisting of 70 peripheral whole blood samples diagnosed with ALL and 70 age and sex-matched healthy children, to assess the level of expression of DROSHA mRNA between two groups. Quantitative Real-Time PCR was used to establish the level of DROSHA gene expression in the patients and controls. The results revealed that DROSHA was overexpressed in patients compared with controls (p < 0.001). There were no major differences between DROSHA expression and demographic factors and clinicopathological parameters (p > 0.001). The finding of the study revealed that DROSHA expression in ALL patients is significantly up-regulated; which is suggesting that may be served as a critical role in the pathogenesis of ALL. Also, DROSHA will possibly be utilized as a novel therapeutic target for ALL patients within the future.

Epigenetic Aberrations in Multiple Myeloma

Simple Summary

Multiple Myeloma (MM) is a blood cancer characterized by an uncontrolled growth of cells named plasma cells, within the bone marrow. Patients with MM may present with anemia, bone lesions and kidney impairment. Several studies have been performed in order to provide an explanation to how this tumor may develop. Among them, the so called “epigenetic modifications” certainly represent important players that have been shown to support MM development and disease progression. The present article aims to summarize the current knowledge in the specific are of “epigenetics” in MM.

Abstract

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by proliferation of clonal plasma cells within the bone marrow. Several advances in defining key processes responsible for MM pathogenesis and disease progression have been made; and dysregulation of epigenetics, including DNA methylation and histone modification, has emerged as a crucial regulator of MM pathogenesis. In the present review article, we will focus on the role of epigenetic modifications within the specific context of MM.

Roles of noncoding RNAs in drug resistance in multiple myeloma

Despite the administration of new effective drugs in recent years, relapse and drug resistance are still the main obstacles in multiple myeloma (MM) treatment, making MM an incurable disease. To overcome drug resistance in MM, it is critical to understand the underlying mechanisms of malfunctioning gene expression and develop novel targeted therapies. During the past few decades, with the discovery and characterization of noncoding RNAs (ncRNAs), the landscape of dysregulated ncRNAs of cancers as well as their biological and pathobiological functions in tumorigenesis and drug resistance have been recognized. Studies about ncRNAs improved the understanding of variations of drug response among individuals at a level distinguished from genetic polymorphism, and provided with new orientations for targeted therapies. In this review, we will summarize the emerging impact and underlying molecular mechanisms of the most relevant classes of ncRNAs in drug resistance of MM, and discuss the potential as well as strategies of treating ncRNAs as therapeutic targets.

The Role and Function of microRNA in the Pathogenesis of Multiple Myeloma

Recently, attention has been drawn to the role of non-coding regions of the genome in cancer pathogenesis. MicroRNAs (miRNAs) are small non-coding RNAs with 19–25 bases of length that control gene expression by destroying messenger RNA or inhibiting its translation. In multiple myeloma (MM), the expression of several miRNAs, such as miR-15a and miR-16, is markedly decreased and their target genes upregulated, suggesting their role as tumor-suppressing miRNAs. In contrast, miRNAs such as miR-21 and miR-221 are highly expressed and function as oncogenes (oncomiRs). In addition, several miRNAs, such as those belonging to the miR-34 family, are transcriptional targets of p53 and mediate its tumor-suppressive functions. Many miRNAs are associated with drug resistance, and the modulation of their expression or activity might be explored to reverse it. Moreover, miRNA expression patterns in either MM cells or serum exosomes have been shown to be good prognostic markers. miRNA regulation mechanisms have not been fully elucidated. Many miRNAs are epigenetically controlled by DNA methylation and histone modification, and others regulate the expression of epigenetic modifiers, indicating that miRNA and other epigenetic effectors are part of a network. In this review, we outlined the roles of miRNAs in MM and their potential to predict MM prognosis and develop novel therapies.

MiR-19b and miR-20a suppress apoptosis, promote proliferation and induce tumorigenicity of multiple myeloma cells by targeting PTEN

Multiple myeloma (MM) is a common hematological malignancy that is often associated with osteolytic lesions, anemia and renal impairment. Deregulation of miRNA has been implicated in the pathogenesis of MM. It was found in our study that miR-19b and miR-20a as members of crucial oncogene miR-17-92 cluster were differentially expressed between patients with MM and normal controls by genechip microarray, and this result was further confirmed in sera of patients with MM by qRT-PCR. The functional effect of miR-19b/20a was analyzed and results showed that miR-19b/20a promoted cell proliferation and migration, inhibited cell apoptosis and altered cell cycle in MM cells. PTEN protein expression was reduced after transfection of miR-19b/20a, suggesting that PTEN was a direct target of miR-19b/20a. In addition, over-expression of miR-19b/20a reversed the anti-proliferation and pro-apoptosis effect of PTEN in MM cells. Finally, our in vivo experiment demonstrated that lentivirus-mediated delivery of miR-20a promoted tumor growth in murine xenograft model of MM, which provide evidence that miR-20a inhibitor exerts therapeutic activity in preclinical models and supports a framework for the development of miR-19b/20a-based treatment strategies for MM patients.

Factors Regulating microRNA Expression and Function in Multiple Myeloma

Intensive research has been undertaken during the last decade to identify the implication of microRNAs (miRNAs) in the pathogenesis of multiple myeloma (MM). The expression profiling of miRNAs in MM has provided relevant information, demonstrating different patterns of miRNA expression depending on the genetic abnormalities of MM and a key role of some miRNAs regulating critical genes associated with MM pathogenesis. However, the underlying causes of abnormal expression of miRNAs in myeloma cells remain mainly elusive. The final expression of the mature miRNAs is subject to multiple regulation mechanisms, such as copy number alterations, CpG methylation or transcription factors, together with impairment in miRNA biogenesis and differences in availability of the mRNA target sequence. In this review, we summarize the available knowledge about the factors involved in the regulation of miRNA expression and functionality in MM.

Role of Dicer as a prognostic predictor for survival in cancer patients: a systematic review with a meta-analysis

Objective

The role of Dicer in the prognosis of cancer patients remains controversial. This systematic review is attempted to assess the influence of Dicer as a prognostic predictor for survival in diverse types of cancers.

Methods

Studies were selected as candidates if they published an independent evaluation of Dicer expression level together with the correlation with prognosis in cancers. Random-effect model was applied in this meta-analysis. Heterogeneity between studies was assessed by Q-statistic with P < 0.10 to be statistically significant. Publication bias was investigated using funnel plot and test with Begg's and Egger's test. P < 0.05 was regarded as statistically significant.

Results

24 of 44 articles revealed low Dicer status as a predictor of poor prognosis. The aggregate result of overall survival (OS) indicated that low Dicer expression level resulted in poor clinical outcomes, and subgroup of IHC and RT-PCR method both revealed the same result. Overall analysis of progression-free survival (PFS) showed the same result as OS, and both the two subgroups divided by laboratory method revealed positive results. Subgroup analysis by tumor types showed low dicer levels were associated with poor prognosis in ovarian cancer (HR = 1.93, 95% CI: 1.19-3.15), otorhinolaryngological tumors (HR = 2.39, 95% CI: 1.70-3.36), hematological malignancies (HR = 2.45, 95% CI: 1.69-3.56) and neuroblastoma (HR = 4.03, 95% CI: 1.91-8.50).

Conclusion

Low Dicer status was associated with poor prognosis in ovarian cancer, otorhinolaryngological tumors and ematological malignancies. More homogeneous studies with high quality are needed to further confirm our conclusion and make Dicer a useful parameter in clinical application.

Role of tumor suppressor p53 and micro-RNA interplay in multiple myeloma pathogenesis

The molecular mechanisms underlying dysregulated wild type (wt) p53 in multiple myeloma (MM) have been subjects of intense investigation for years. Indeed, correlation of rarely occurring TP53 gene mutations or deletions with adverse clinical outcomes in MM patients is strongly established, while in majority of cases wtp53 seems to be non-functional or dysregulated bearing a high clinical impact. Interestingly, findings from recent investigations show that micro-RNAs (miRNAs) may contribute to suppression of wtp53 in MM, as they are now known to function as key regulatory elements in the p53 network. This area is shedding new light on understanding the biologic effects of dysregulated p53 in MM pathogenesis especially drug resistance. miRNAs such as miR-125b (oncomiR) or miR-34a (tumor suppressor-miR) can be negative or positive regulators of wtp53 function, respectively, with specific effects on MM cell viability. On the other hand, our knowledge of miRNA interaction with mutant (mt) p53 in MM, which is rather related to disease progression and resistance to therapy, is limited which demands in-depth exploration. Here, we will put forward the current knowledge on miRNA-p53 interaction in MM and its role in MM pathogenesis including drug resistance. We will also highlight the pre-clinical approaches for therapeutic application of miRNAs targeting p53 pathway.

Epigenetics in multiple myeloma: From mechanisms to therapy

Multiple myeloma (MM) is a tumor of antibody producing plasmablasts/plasma cells that resides within the bone marrow (BM). In addition to the well-established role of genetic lesions and tumor-microenvironment interactions in the development of MM, deregulated epigenetic mechanisms are emerging as important in MM pathogenesis. Recently, MM sequencing and expression projects have revealed that mutations and copy number variations as well as deregulation in the expression of epigenetic modifiers are characteristic features of MM. In the past decade, several studies have suggested epigenetic mechanisms via DNA methylation, histone modifications and non-coding RNAs as important contributing factors in MM with impacts on disease initiation, progression, clonal heterogeneity and response to treatment. Herein we review the present view and knowledge that has accumulated over the past decades on the role of epigenetics in MM, with focus on the interplay between epigenetic mechanisms and the potential use of epigenetic inhibitors as future treatment modalities for MM.

miRNAs in multiple myeloma--a survival relevant complex regulator of gene expression

Purpose

microRNAs regulate gene-expression in biological and pathophysiological processes, including multiple myeloma. Here we address i) What are the number and magnitude of changes in miRNA-expression between normal plasma cells and myeloma- or MGUS-samples, and the latter two? ii) What is the biological relevance and how does miRNA-expression impact on gene-expression? iii) Is there a prognostic significance, and what is its background?

Experimental design

Ninety-two purified myeloma-, MGUS-, normal plasma cell- and myeloma cell line-samples were investigated using miChip-arrays interrogating 559 human miRNAs. Impact on gene-expression was assessed by Affymetrix DNA-microarrays in two cohorts of myeloma patients (n = 677); chromosomal aberrations were assessed by iFISH, survival for 592 patients undergoing up-front high-dose chemotherapy.

Results

Compared to normal plasma cells, 67/559 miRNAs (12%) with fold changes of 4.6 to −3.1 are differentially expressed in myeloma-, 20 (3.6%) in MGUS-samples, and three (0.5%) between MGUS and myeloma. Expression of miRNAs is associated with proliferation, chromosomal aberrations, tumor mass, and gene expression-based risk-scores. This holds true for target-gene signatures of regulated mRNAs. miRNA-expression confers prognostic significance for event-free and overall survival, as do respective target-gene signatures.

Conclusions

The myeloma-miRNome confers a pattern of small changes of individual miRNAs impacting on gene-expression, biological functions, and survival.

MicroRNAs in multiple myeloma and related bone disease

MicroRNAs (miRNAs) are short non coding RNAs aberrantly expressed in solid and hematopoietic malignancies where they play a pivotal function as post-transcriptional regulators of gene expression. Recent reports have unveiled a central role of miRNAs in multiple myeloma onset and progression and preclinical findings are progressively disclosing their potential therapeutic value as drugs or targets. In this review, we provide the basic insights of miRNA biology and function, showing how these molecules are extensively dysregulated in malignant plasma cells (PC) and related microenvironment, thus favoring clone survival and proliferation. We here describe how these critical activities have recently been evaluated to design miRNA-based therapies against multiple myeloma cells and its surrounding microenvironment.

Epigenetics in Multiple Myeloma

Multiple myeloma is characterized by clonal proliferation of plasma cells within the bone marrow resulting in anemia, lytic bone lesions, hypercalcemia, and renal impairment. Despite advanced in our understanding of this complex disease in recent years, it is still considered an incurable malignancy. This is, in part, due to the highly heterogenous genomic and phenotypic nature of the disease, which is to date incompletely understood. It is clear that a deeper level of knowledge of the biological events underlying the development of these diseases is needed to identify new targets and generate effective novel therapies. MicroRNAs (miRNAs), which are single strand, 20-nucleotide, noncoding RNA's, are key regulators of gene expression and have been reported to exert transcriptional control in multiple myeloma. miRNAs are now recognized to play a role in many key areas such as cellular proliferation, differentiation, apoptosis and stress response. Substantial advances have been made in recent years in terms of our understanding of the biological role of miRNAs in a diverse range of hematological and solid malignancues, In multiple myeloma these advances have yielded new information of prognostic and diagnostic relevance which have helped to shed light on epigenetic regulation in this disease.

Aberrant Levels of miRNAs in Bone Marrow Microenvironment and Peripheral Blood of Myeloma Patients and Disease Progression

The bone marrow (BM) microenvironment of multiple myeloma (MM) is reported to play a role in the biology of disease. In this study, we found that the extracellular BM microenvironment in MM contains a unique miRNA signature detectable by miRNA microarray and quantitative real-time PCR, which is partially represented in the peripheral blood. Eleven miRNAs were significantly decreased in both BM and serum of MM patients in comparison with controls. Evaluation of these miRNAs in plasma of a separate cohort of MM patients and controls confirmed significantly aberrant levels of let-7a, let-7b, let-7i, miR-15b, miR-16, and miR-20a in both serum and plasma. We then studied the myeloma precursor diseases and found that a subset of the MM miRNAs exhibited aberrant expression in monoclonal gammopathy of undetermined significance and smoldering myeloma. miRNA analysis of enriched CD138(+) plasma cells from MM and monoclonal gammopathy of undetermined significance found that most of the validated MM BM signature miRNAs were significantly decreased in MM plasma cells. Gene expression profiling indicated that multiple targets of the decreased miRNAs found increased expression in MM plasma cells, including ATF2, HRAS, HDAC4, TGFB1, TGFBR1, and mitogen-activated protein kinases. The findings suggest that these miRNAs are detectable in aberrant levels in the peripheral blood of patients with plasma cell proliferation and may play a role in aberrant plasma cell proliferation and disease progression.

MicroRNAs in B-cells: from normal differentiation to treatment of malignancies

MicroRNAs (miRNAs) are small non-coding RNAs that play important post-transcriptional regulatory roles in a wide range of biological processes. They are fundamental to the normal development of cells, and evidence suggests that the deregulation of specific miRNAs is involved in malignant transformation due to their function as oncogenes or tumor suppressors. We know that miRNAs are involved in the development of normal B-cells and that different B-cell subsets express specific miRNA profiles according to their degree of differentiation. B-cell-derived malignancies contain transcription signatures reminiscent of their cell of origin. Therefore, we believe that normal and malignant B-cells share features of regulatory networks controlling differentiation and the ability to respond to treatment. The involvement of miRNAs in these processes makes them good biomarker candidates. B-cell malignancies are highly prevalent, and the poor overall survival of patients with these malignancies demands an improvement in stratification according to prognosis and therapy response, wherein we believe miRNAs may be of great importance. We have critically reviewed the literature, and here we sum up the findings of miRNA studies in hematological cancers, from the development and progression of the disease to the response to treatment, with a particular emphasis on B-cell malignancies.

Evaluating gene expression profiling by quantitative polymerase chain reaction to develop a clinically feasible test for outcome prediction in multiple myeloma

The gene expression profiles (GEPs) of 96 selected genes were analysed by real-time quantitative polymerase chain reaction (qPCR) with a TaqMan low-density array card in isolated tumour plasma cells (PCs) from 157 newly diagnosed multiple myeloma (MM) patients. This qPCR-based GEP correctly classified cases following the Translocation-cyclin D classification. Classic prognostic parameters and qPCR-based GEP predicted MM patient outcome and, although multivariate analyses revealed that cytogenetic risk (standard vs. high risk) was the variable that most strongly predicted prognosis, GEP added significant information for risk stratification. Considering only the standard risk cytogenetic patients, multivariate analyses revealed that high β2-microglobulin, low CDKN1A and high SLC19A1 gene expression levels independently predicted a short time-to-progression (TTP), while high International Staging System stage, low CDKN2B and high TBRG4 gene expression predicted poor overall survival (OS). A gene expression risk score enabled the division of standard risk patients into two groups with different TTPs (83% vs. 38% at 3 years, P < 0·0001) and OS rates (88% vs. 61% at 5 years; P = 0·003). This study demonstrates that quantitative PCR is a robust, accurate and feasible technique for implementing in the daily routine as a surrogate for GEP-arrays.

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.

Promises and challenges of MicroRNA-based treatment of multiple myeloma

MicroRNAs (miRNAs) recently emerged with a key role in multiple myeloma (MM) pathophysiology and are considered important regulators of MM cell growth and survival. Since miRNAs can act either as oncogenes or tumour suppressors, the potential of targeting the miRNA network arises as a novel therapeutic approach for human cancer. Potential strategies based on miRNA therapeutics basically rely on miRNA inhibition or miRNA replacement approaches and take benefit respectively from the use of antagomirs or synthetic miRNAs as well as from lipid-based nanoparticles which allow an efficient miRNA-delivery. The availability of experimental in vivo platforms which recapitulate the growth of MM cells within the specific human bone marrow microenvironment in immunocompromised mice (SCID-hu and SCID-synth-hu) provides powerful systems for development of miRNA-based therapeutics in MM. Preliminary findings on the anti-MM activity of synthetic miRNAs in such experimental models offer a proof-of-principle that miRNA therapeutics is a promising opportunity for this still incurable disease representing the rationale for a new venue of investigation in this specific field.

MicroRNAs and Glucocorticoid-Induced Apoptosis in Lymphoid Malignancies

The initial response of lymphoid malignancies to glucocorticoids (GCs) is a critical parameter predicting successful treatment. Although being known as a strong inducer of apoptosis in lymphoid cells for almost a century, the signaling pathways regulating the susceptibility of the cells to GCs are only partly revealed. There is still a need to develop clinical tests that can predict the outcome of GC therapy. In this paper, I discuss important parameters modulating the pro-apoptotic effects of GCs, with a specific emphasis on the microRNA world comprised of small players with big impacts. The journey through the multifaceted complexity of GC-induced apoptosis brings forth explanations for the differential treatment response and raises potential strategies for overcoming drug resistance.

Clinicopathological and prognostic significance of the microRNA processing enzyme DICER1 mRNA expression in colorectal cancer patients

The cytoplasmic ribonuclease DICER1 is one of the key enzymes in microRNA (miRNA) processing, essential for the production of mature miRNA. The effect of DICER1 expression in tumor cells on the prognosis of patients with several cancers has been examined with controversial results in various cancer types. In particular, the clinical significance of DICER1 expression in colorectal cancer (CRC) patients has yet to be determined. The aim of this study was to evaluate the correlation between the DICER1 mRNA levels and the clinicopathological characteristics and prognostic significance in CRC patients. Tumor and normal adjacent tumor tissues from 260 patients with CRC (Dukes' stage A: 40 cases, Dukes' B: 68 cases, Dukes' C: 88 cases and Dukes' D: 64 cases) were examined. The DICER1 mRNA levels were measured using the TaqMan real-time reverse transcription polymerase chain reaction (RT-PCR) method. The expression levels of DICER1 mRNAs showed a significant decrease in CRC tissues as compared to normal ones (P=0.039). A statistically significant association was observed between DICER1 mRNA expression and tumor size, depth of invasion, lymph node metastasis, lymphatic invasion and Dukes' stage. In Kaplan-Meier survival curve analysis, overall survival (OS) and disease-free survival (DFS) rates of patients with a low DICER1 mRNA expression were significantly worse compared to patients with a high DICER1 mRNA expression (OS P<0.001; DFS P<0.001). In the Cox multivariate analysis, DICER1 mRNA expression in CRC tissues was identified as an independent prognostic factor for OS [hazard ratio (HR), 0.30; 95% confidence interval (CI), 0.13-0.64; P=0.001] and DFS (HR, 0.23; 95% CI, 0.10-0.48; P=0.001). This study demonstrated that a reduced DICER1 mRNA expression is associated with poor prognosis in CRC patients.

Downregulated Dicer expression predicts poor prognosis in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the western world. Alterations in microRNAs (miRNAs) expression have been proposed to play a role in CLL pathogenesis. Dicer and Drosha are the main regulators of miRNA biogenesis, and deregulation of their expression has been indicated as a possible cause of miRNA alterations observed in various cancers. To investigate the role of Dicer and Drosha in CLL, we assessed the expression of Dicer and Drosha and their correlation with other prognostic factors, including Binet stages, immunoglobulin heavy chain variable gene (IGHV) mutation status, TP53 mutation status, ZAP-70 protein and CD38 expression level in 165 CLL patients by using real-time polymerase chain reaction methods. Patients with unmutated IGHV genes had significantly lower expression of Dicer than patients with IGHV mutations. The lower expression level of Dicer was also significantly associated with higher level of CD38 and ZAP-70, and more aggressive Binet stage. We also analyzed Dicer expression in different cytogenetic subgroups. Lower Dicer level was found in patients with unfavorable cytogenetic aberrations (deletion in 17p13 or 11q22.3) in contrast to higher level in good risk cytogenetics (deletion in 13q14 as the sole abnormality). Furthermore, the lower expression of Dicer in CLL shows a strong association with shorter overall survival (OS) (P = 0.0046) as well as with reduced treatment free survival (TFS) (P = 0.0006). By contrast, no differences in the expression of Drosha among these groups of patients were observed. Our data suggest that Dicer expression may play an important role in the progression and prognosis of CLL.

Demethylation of the FCER1G promoter leads to FcεRI overexpression on monocytes of patients with atopic dermatitis

BACKGROUND

Overexpression of the high-affinity receptor for immunoglobulin E on atopic monocytes and dendritic cells is known to contribute to the pathogenesis of atopic dermatitis (AD). However, it remains unclear what is the underlying mechanism of FcεRI deregulation. It has been speculated that epigenetic deregulation may play a role.

METHODS

Global DNA methylation levels of monocytes from 10 AD patients and 10 healthy controls were measured using a global DNA methylation kit. Bisulfite sequencing was performed to determine the methylation status of the FCER1G promoter region. FcεRIγ mRNA and FcεRI protein levels were detected by real-time RT-PCR, Western blotting, and flow cytometry, respectively. Patch methylation and the demethylating agent, 5-azacytidine, were used to determine the functional significance of methylation changes on FcεRI expression.

RESULTS

Monocytes from AD patients show a global hypomethylation, as well as a locus-specific hypomethylation at FCER1G promoter, as compared to healthy controls. Furthermore, this hypomethylation of FCER1G is inversely correlated with its expression. Patch methylation in combination with luciferase reporter assay confirmed the direct relationship between methylation and expression. Moreover, treating healthy monocytes with 5-azacytidine caused a reduction in methylation levels and an induction in FcεRIγ transcription and surface expression of FcεRI.

CONCLUSION

Demethylation of specific regulatory elements within the FCER1G locus contributes to FcεRI overexpression on monocytes from patients with AD.

MicroRNAs: New Players in Multiple Myeloma

MicroRNAs (miRNAs) are short non-coding RNAs that play critical roles in numerous cellular processes through post-transcriptional regulating functions. The aberrant role of miRNAs has been reported in a number of hematopoietic malignancies including multiple myeloma (MM). In this review we summarize the current knowledge on roles of miRNAs in the pathogenesis of MM.