Aberrant gene promoter methylation marking disease progression in multiple myeloma

Cereblon Enhancer Methylation and IMiD Resistance in Multiple Myeloma

Cereblon is the direct binding target of the immunomodulatory drugs that are commonly used to treat Multiple Myeloma, the second most frequent hematologic malignancy. Patients respond well to initial IMiD treatment but virtually all develop drug resistance over time with the underlying mechanisms poorly understood. We identified a yet undescribed DNA hypermethylation in an active intronic CRBN enhancer. Differential hypermethylation in this region was found increased in healthy plasma cells, but more pronounced in IMiD refractory MM. Methylation significantly correlated with decreased CRBN expression levels. DNTMi in vitro experiments induced CRBN enhancer demethylation and sensitizing effects on Lenalidomide treatment were observed in two MM cell lines. Thus, we provide first evidence that aberrant CRBN DNA methylation is a novel mechanism of IMiD resistance in Multiple Myeloma and may predict IMiD response prior treatment.

Role of microRNAs in Diagnosis, Prognosis and Management of Multiple Myeloma

Multiple myeloma (MM) is a cancerous bone disease characterized by malignant transformation of plasma cells in the bone marrow. MM is considered to be the second most common blood malignancy, with 20,000 new cases reported every year in the USA. Extensive research is currently enduring to validate diagnostic and therapeutic means to manage MM. microRNAs (miRNAs) were shown to be dysregulated in MM cases and to have a potential role in either progression or suppression of MM. Therefore, researchers investigated miRNAs levels in MM plasma cells and created tools to test their impact on tumor growth. In the present review, we discuss the most recently discovered miRNAs and their regulation in MM. Furthermore, we emphasized utilizing miRNAs as potential targets in the diagnosis, prognosis and treatment of MM, which can be useful for future clinical management.

Frequent upregulation of G9a promotes RelB-dependent proliferation and survival in multiple myeloma

Background

Multiple myeloma is an incurable hematological malignancy characterized by a heterogeneous genetic and epigenetic landscape. Although a number of genetic aberrations associated with myeloma pathogenesis, progression and prognosis have been well characterized, the role of many epigenetic aberrations in multiple myeloma remain elusive. G9a, a histone methyltransferase, has been found to promote disease progression, proliferation and metastasis via diverse mechanisms in several cancers. A role for G9a in multiple myeloma, however, has not been previously explored.

Methods

Expression levels of G9a/EHMT2 of multiple myeloma cell lines and control cells Peripheral Blood Mononuclear Cells (PBMCs) were analyzed. Correlation of G9a expression and overall survival of multiple myeloma patients were analyzed using patient sample database. To further study the function of G9a in multiple myeloma, G9a depleted multiple myeloma cells were built by lentiviral transduction, of which proliferation, colony formation assays as well as tumorigenesis were measured. RNA-seq of G9a depleted multiple myeloma with controls were performed to explore the downstream mechanism of G9a regulation in multiple myeloma.

Results

G9a is upregulated in a range of multiple myeloma cell lines. G9a expression portends poorer survival outcomes in a cohort of multiple myeloma patients. Depletion of G9a inhibited proliferation and tumorigenesis in multiple myeloma. RelB was significantly downregulated by G9a depletion or small molecule inhibition of G9a/GLP inhibitor UNC0642, inducing transcription of proapoptotic genes Bim and BMF. Rescuing RelB eliminated the inhibition in proliferation and tumorigenesis by G9a depletion.

Conclusions

In this study, we demonstrated that G9a is upregulated in most multiple myeloma cell lines. Furthermore, G9a loss-of-function analysis provided evidence that G9a contributes to multiple myeloma cell survival and proliferation. This study found that G9a interacts with NF-κB pathway as a key regulator of RelB in multiple myeloma and regulates RelB-dependent multiple myeloma survival. G9a therefore is a promising therapeutic target for multiple myeloma.

Frequent methylation of the tumour suppressor miR-1258 targeting PDL1: implication in multiple myeloma-specific cytotoxicity and prognostification

miR-1258 is localised to the first intron of ZNF385B at chromosome 2q31.3. miR-1258 promoter methylation was studied in 147 samples including 10 normal buffy coat, eight normal bone marrow plasma cells, 16 human myeloma cell lines (HMCLs), 20 MGUS, 63 diagnostic myeloma, and 30 relapsed myeloma samples by methylation-specific PCR. In myeloma lines, miR-1258 methylation, verified by pyrosequencing, was detected in 62·5% HMCLs but not normal controls, and expression of miR-1258 correlated with that of ZNF385B. 5-Aza-2'-deoxycytidine resulted in promoter demethylation and ZNF385B/miR-1258 re-expression. Luciferase assay confirmed programmed cell death ligand-1 (PDL1) as a direct target of miR-1258. Over-expression of miR-1258 in completely methylated myeloma cells led to reduced cellular proliferation and enhanced apoptosis, hence a tumour suppressor role, in addition to repression of PDL1. In primary samples, miR-1258 methylation, with lower expression of miR-1258, was detected in 49·2% diagnostic myeloma, imparting an inferior PFS (P = 0·034) in addition to 50·0% relapsed myeloma but not MGUS. Therefore, miR-1258 is a tumour suppressor miRNA co-regulated with its host gene, and frequently hypermethylated in active myeloma instead of MGUS, hence acquired during myeloma progression. Methylation-mediated miR-1258 silencing led to overexpression of PDL1 and inferior PFS, implicating miR-1258 in the modulation of myeloma-specific cytotoxicity.

Promoter methylation induced epigenetic silencing of DAZAP2, a downstream effector of p38/MAPK pathway, in multiple myeloma cells

Multiple myeloma (MM) is hematological malignancy characterized by clonal proliferation of malignant plasma cells in the bone marrow environment. Previously, we identified DAZAP2 as a candidate cancer suppressor gene, the downregulation of which is regulated by its own promoter methylation status. In the current study, we analyzed the DAZAP2 promoter in MM cell lines KM3, MM.1S, OPM-2, and ARH77 by bisulfite genomic sequencing assay. We identified the binding site for transcription factor cyclic adenosine monophosphate response element binding (CREB) in the DAZAP2 promoter CpG2, and we found that hypermethylation of the CREB binding motif in the DAZAP2 promoter is responsible for the reduced DAZAP2 expression in MM cells. Later we checked the p38/MAPK signaling cascade, which is reported to regulate expression and function of CREB. Our results showed that the p38/MAPK signaling pathway drives the expression of DAZAP2 by phosphorylation of CREB, and hypermethylation of CREB binding motif in DAZAP2 promoter can inhibit binding of CREB to the latter, thus downregulating DAZAP2 expression. Moreover, treating the MM cells with 5-aza-2' deoxycytidine to demethylate DAZAP2 promoter restored the binding of CREB to its binding motif, and thus upregulated DAZAP2 expression. Our results not only identified DAZAP2 as a new downstream target of p38/MAPK/CREB signaling cascade, but we also clarified that the downregulation of DAZAP2 in MM cells is caused by hypermethylation of CREB binding motif in its own promoter region, which implies that demethylation of DAZAP2 promoter can be a novel therapeutic strategy for MM treatment.

Distinct promoter methylation profile reveals spatial epigenetic heterogeneity in 2 myeloma patients with multifocal extramedullary relapses

Spatial and subclonal genetic heterogeneity in multiple myeloma (MM) have been demonstrated by sequencing of plasma cells from multi-focal regions, but studies of spatial epigenetic heterogeneity are scanty. Herein, promoter methylation status of genes implicated in disease progression (CDKN2A and SHP1) and marrow escape (CDH1, CD56, and CXCR4) was studied in two patients with multi-focal extramedullary relapses. Patient 1 developed simultaneous chest wall and duodenal plasmacytoma at relapse. While SHP1 and CDKN2A were hypermethylated in both plasmacytomas, CDH1 hypermethylation was detected only in the chest wall. In patient 2, SHP1 methylation was found in the extradural plasmacytoma but not bone marrow (BM) at diagnosis, and the circulating PCs but not the BM at relapse. As the clonality, based on sequence of the complementarity-determining region 3 (CDR3) of the immunoglobulin gene, was conserved in plasma cells at diagnosis and relapse, differential methylation of CDH1 in patient 1 and SHP1 in patient 2 was an illustration of spatial epigenetic heterogeneity. Furthermore, subclonal epigenetic heterogeneity was identified by the presence of subclonal SHP1 promoter methylation within the chest wall plasmacytoma of patient 1. In summary, our data showed distinct promoter methylation profile of plasma cells from multiple regions. This is the first report of spatial epigenetic heterogeneity in MM.

The polycomb group protein BMI-1 inhibitor PTC-209 is a potent anti-myeloma agent alone or in combination with epigenetic inhibitors targeting EZH2 and the BET bromodomains

Multiple myeloma (MM) is a tumor of plasmablasts/plasma cells (PCs) characterized by the expansion of malignant PCs with complex genetic aberrations in the bone marrow (BM). Recent reports, by us and others, have highlighted the polycomb group (PcG) proteins as potential targets for therapy in MM. The PcG protein BMI-1 of the polycomb repressive complex 1 (PRC1) has been reported to be overexpressed and to possess oncogenic functions in MM. Herein, we report on the anti-myeloma effects of the BMI-1 inhibitor PTC-209 and demonstrate that PTC-209 is a potent anti-myeloma agent in vitro using MM cell lines and primary MM cells. We show that PTC-209 reduces the viability of MM cells via induction of apoptosis and reveal that the anti-MM actions of PTC-209 are mediated by on-target effects i.e. downregulation of BMI-1 protein and the associated repressive histone mark H2AK119ub, leaving other PRC1 subunits such as CBX-7 and the catalytic subunit RING1B unaffected. Importantly, we demonstrate that PTC-209 exhibits synergistic and additive anti-myeloma activity when combined with other epigenetic inhibitors targeting EZH2 and BET bromodomains. Collectively, these data qualify BMI-1 as a candidate for targeted therapy in MM alone or in combinations with epigenetic inhibitors directed to PRC2/EZH2 or BET bromodomains.

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.

Global methylation and promoter-specific methylation of the P16, SOCS-1, E-cadherin, P73 and SHP-1 genes and their expression in patients with multiple myeloma during active disease and remission

Tumor suppressor gene promoter CpG island methylation is a well-recognized mechanism in cancer pathogenesis, but its role in multiple myeloma (MM) is controversial. The present study investigated the methylation status and expression of P16, suppressor of cytokine signaling 1 (SOCS-1), P73, E-cadherin and Src homology region 2 domain-containing phosphatase 1 (SHP-1), as well as global methylation in patients with MM during active disease and remission. Bone marrow samples were obtained from 43 patients at the Multiple Myeloma Clinic, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán (Mexico City, Mexico) during active disease and remission. Methylation-specific polymerase chain reaction and ELISA were performed on bisulfite-treated or untreated DNA to determine promoter-specific or genomic methylation, respectively. Gene expression was measured using reverse-transcription polymerase chain reaction. The results indicated that SOCS-1 methylation occurred more frequently during active disease than remission [29 vs. 3.2% (P=0.021)] and was associated with more advanced forms of the disease [international staging system (ISS) 3, 16.67% vs. ISS 1, 8.3% (P=0.037)]. SHP-1 methylation during active disease was associated with a lower probability of survival at 39-month follow up (median), 52.5 vs. 87.5% (P=0.025). The percentage of methylation was associated with active disease at remission, but this was not significant. Global hypomethylation at remission was a negative predictor factor for overall survival (OS). The results indicated that methylated P16, SOCS-1 and SHP-1 were associated with clinical variables of poor prognosis in MM, likewise the persistence of global hypomethylation at remission. The negative impact on OS of global hypomethylation at remission must be confirmed in a larger sample. Future studies are necessary to investigate whether patients with global hypermethylation at remission should receive more aggressive treatments to improve their OS.

Methylation of miR124a-1, miR124a-2, and miR124a-3 in Hodgkin lymphoma

Deregulation of the microRNA miR124a by DNA methylation has been implicated in various malignancies, but no study reported its methylation status in Hodgkin lymphoma (HL). We evaluated the methylation of the three loci encoding for miR124a using methylation-specific PCR in 64 HL patients and 15 reactive lymph nodes obtained from patients with nonmalignant diseases. Results were correlated with clinicopathological parameters. Methylation rates of miR124a-1, miR124a-2, and miR124a-3 in HL were 17, 50, and 28%, respectively. None of the nontumoral samples showed aberrant hypermethylation in any of the miR tested. In HL cases, we found that miR124a-1 methylation correlates with high-risk International Prognostic Score (IPS) (score >3, p = 0.04) and that miR124a-2 methylation was more frequent in children (82.3%, p = 0.006) and men (63.9%, p = 0.01). Methylation of miR124a-3 was associated with advanced Ann-Arbor stages (p = 0.007). The survival analysis showed that methylation of at least one of the miR124a genes was associated with shortened event-free survival in univariate (p = 0.03) and multivariate (p = 0.02) analyses. These results suggest that miR124a methylation is associated with aggressive HL disease and may be an interesting factor for predicting treatment response.

The role of epigenetics in the biology of multiple myeloma

Several recent studies have highlighted the biological complexity of multiple myeloma (MM) that arises as a result of several disrupted cancer pathways. Apart from the central role of genetic abnormalities, epigenetic aberrations have also been shown to be important players in the development of MM, and a lot of research during the past decades has focused on the ways DNA methylation, histone modifications and noncoding RNAs contribute to the pathobiology of MM. This has led to, apart from better understanding of the disease biology, the development of epigenetic drugs, such as histone deacetylase inhibitors that are already used in clinical trials in MM with promising results. This review will present the role of epigenetic abnormalities in MM and how these can affect specific pathways, and focus on the potential of novel 'epidrugs' as future treatment modalities for MM.

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.

DNA methylation of tumor suppressor miRNA genes: a lesson from the miR-34 family

miRNA is a small ncRNA of 22-25 nucleotides, which leads to mRNA degradation or translational inhibition of its target genes. miRNAs are involved in multiple cellular processes, including cellular differentiation, proliferation and apoptosis, and hence miRNA deregulation has been implicated in disease states, including cancer. On the other hand, DNA methylation leads to gene silencing, and serves as an alternative mechanism of gene inactivation. The aberrant DNA methylation of gene promoters has been shown to result in the inactivation of tumor suppressor genes, and therefore is also implicated in carcinogenesis. This article focuses on the role of miRNA methylation, in particular miR-34a, in cancer. The article begins with an overview of DNA methylation in normal and cancer cells and deregulation of miRNA expression by DNA methylation. These discussions are followed by a description of the gene structure of the miR-34 family of miRNA genes, the tumor suppressor role of miR-34a and the deregulation of miR-34a by DNA methylation in both epithelial and hematological cancers. Moreover, the methylation of miR-34b/c in cancer is also described. Finally, the potential role of miRNA methylation as a biomarker for diagnosis, prognosis (and hence the potential of developing a risk-stratified approach) and a therapeutic target is discussed.

Epigenetic silencing of MIR203 in multiple myeloma

Epigenetic inactivation of tumour suppressor microRNAs has been implicated in carcinogenesis. We studied the promoter methylation of MIR203 in eight normal marrow controls, eight multiple myeloma (MM) cell lines, 20 monoclonal gammopathy of undetermined significance (MGUS), 123 diagnostic MM and 19 relapsed MM samples by methylation-specific polymerase chain reaction. Promoter of MIR203 was unmethylated in normal controls but homozygously methylated in 25% MM cell lines. Treatment with 5-Aza-2'-deoxycytidine led to promoter demethylation and MIR203 re-expression. Cyclic AMP responsive element binding protein 1 (CREB1) mRNA was predicted as a MIR203 direct target. Luciferase activity was reduced in constructs carrying wild-type CREB1 3'UTR upon MIR203 expression but not in those carrying mutant CREB1 3'UTR. Moreover, restoration of MIR203 led to downregulation of CREB1 protein and inhibition of myeloma cell proliferation. In primary samples, MIR203 methylation occurred in 25·0% MGUS, 23·6% diagnostic MM, and 21·1% relapsed MM samples. In conclusion, MIR203 methylation is disease-specific with reversible gene silencing in MM. MIR203 is a tumour suppressor microRNA inhibiting cellular proliferation by targeting CREB1 mRNA in MM. Comparable occurrence of MIR203 methylation in MGUS and MM at diagnosis or relapse suggested that MIR203 methylation may be an early event in myelomagenesis instead of being acquired during disease progression.

Epigenetic inactivation of the miR-124-1 in haematological malignancies

miR-124-1 is a tumour suppressor microRNA (miR). Epigenetic deregulation of miRs is implicated in carcinogenesis. Promoter DNA methylation and histone modification of miR-124-1 was studied in 5 normal marrow controls, 4 lymphoma, 8 multiple myeloma (MM) cell lines, 230 diagnostic primary samples of acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), MM, and non-Hodgkin's lymphoma (NHL), and 53 MM samples at stable disease or relapse. Promoter of miR-124-1 was unmethylated in normal controls but homozygously methylated in 4 of 4 lymphoma and 4 of 8 myeloma cell lines. Treatment of 5-Aza-2′-deoxycytidine led to miR-124-1 demethylation and re-expression of mature miR-124, which also associated with emergence of euchromatic trimethyl H3K4 and consequent downregulation of CDK6 in myeloma cells harboring homozygous miR-124-1 methylation. In primary samples at diagnosis, miR-124-1 methylation was absent in CML but detected in 2% each of MM at diagnosis and relapse/progression, 5% ALL, 15% AML, 14% CLL and 58.1% of NHL (p<0.001). Amongst lymphoid malignancies, miR-124-1 was preferentially methylated in NHL than MM, CLL or ALL. In primary lymphoma samples, miR-124-1 was preferentially hypermethylated in B- or NK/T-cell lymphomas and associated with reduced miR-124 expression. In conclusion, miR-124-1 was hypermethylated in a tumour-specific manner, with a heterochromatic histone configuration. Hypomethylation led to partial restoration of euchromatic histone code and miR re-expression. Infrequent miR-124-1 methylation detected in diagnostic and relapse MM samples showed an unimportant role in MM pathogenesis, despite frequent methylation found in cell lines. Amongst haematological cancers, miR-124-1 was more frequently hypermethylated in NHL, and hence warrants further study.

DNA methylation analysis determines the high frequency of genic hypomethylation and low frequency of hypermethylation events in plasma cell tumors

Multiple myeloma (MM) is a plasma cell malignancy of the bone marrow, which evolves from a premalignant stage called monoclonal gammopathy of undetermined significance (MGUS). In some patients, an intermediate stage referred to as smoldering multiple myeloma (SMM) is clinically recognized, with the full-bore malignancy termed MM. We conducted a study to assess differential CpG methylation at 1,500 genic loci during MM progression and profiled CD138(+) plasma cells from MGUS, SMM, and MM specimens; human myeloma cell lines; and normal plasma cell (NPC) samples. We showed that the number of differentially methylated loci (DML) increased with tumor grade, and the vast majority were due to hypomethylation. Hierarchical clustering analysis revealed samples that coclustered tightly with NPC. These cases, referred to as "normal-like," contained significantly fewer DML when compared with their non-normal-like counterparts and displayed overall methylation levels resembling NPC. This study represents one of the first methylome interrogation studies in MM and points toward global hypomethylation at genic CpG loci as an important and early mechanism driving myelomagenesis. Determining the set of critical genes and pathways based on the myeloma methylome is expected to lead to an improved understanding of biological mechanisms involved in myelomagenesis.

Concurrent p16 methylation pattern as an adverse prognostic factor in multiple myeloma: a methylation-specific polymerase chain reaction study using two different primer sets

Disruption of cell cycle control genes, including p16, is known to contribute to the cancerogenesis of multiple myeloma (MM). We investigated the methylation status of p16 and its association with common cytogenetic changes, clinicolaboratory findings, and survival in MM. Methylation-specific polymerase chain reaction was performed in 99 newly diagnosed MM patients using two different sets of primers (p16M1 and p16M2). Four patterns of p16 promoter methylation were observed: (1) concurrent methylation of p16M1 and p16M2 (P1P2), 27.3%; (2) methylation of p16M1 alone (P1N2), 7.1%; (3) methylation of p16M2 alone (N1P2), 26.3%; and (4) no methylation (N1N2), 39.4%. Patients with p16P1P1 showed shorter survivals than those with the other methylation patterns (P1N2, N1P2, or N1N2; median survival, 12 vs. 43 months; P < 0.001), regardless of the treatment protocol. In a multivariate analysis, p16P1P2 was an independent prognostic factor of adverse outcome in MM. According to International Staging System (ISS), the study population could be divided into 21.2% (20/94) for stage I, 22.3% (21/94) for stage II, and 56.4% (53/94) for stage III (P = 0.003). ISS can divide patients into prognostic groups. Of note, in patients older than 60 years, ISS was not reflective of disease stage (P = 0.114). If p16P1P2 sets up as stage 4 of ISS, modified ISS could be a more reliable staging system irrespective of age in Korean MM patients (P = 0.003 and P = 0.004 in patients younger than 60 years and in patients older than 60 years, respectively). Our study suggests the potential use of p16 methylation status in predicting the outcome of MM patients and the applicability of demethylating agents in MM.

Epigenetic inactivation of the miR-34a in hematological malignancies

miR-34a is a transcriptional target of p53 and implicated in carcinogenesis. We studied the role of miR-34a methylation in a panel of hematological malignancies including acute leukemia [acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL)], chronic leukemia [chronic lymphocytic leukemia (CLL) and chronic myeloid leukemia (CML)], multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL). The methylation status of miR-34a promoter was studied in 12 cell lines and 188 diagnostic samples by methylation-specific polymerase chain reaction. miR-34a promoter was unmethylated in normal controls but methylated in 75% lymphoma and 37% myeloma cell lines. Hypomethylating treatment led to re-expression of pri-miR-34a transcript in lymphoma cells with homozygous miR-34a methylation. In primary samples at diagnosis, miR-34a methylation was detected in 4% CLL, 5.5% MM samples and 18.8% of NHL at diagnosis but none of ALL, AML and CML (P = 0.011). In MM patients with paired samples, miR-34a methylation status remained unchanged at progression. Amongst lymphoid malignancies, miR-34a was preferentially methylated in NHL (P = 0.018), in particular natural killer (NK)/T-cell lymphoma. In conclusion, amongst hematological malignancies, miR-34a methylation is preferentially hypermethylated in NHL, in particular NK/T-cell lymphoma, in a tumor-specific manner, therefore the role of miR-34a in lymphomagenesis warrants further study.

Gene hypermethylation in multiple myeloma: lessons from a cancer pathway approach

Multiple myeloma (MM) is an incurable plasma cell neoplasm. Pathogenesis involves upregulation of D-type cyclins and activation of oncogenes, but little is known about the role of tumor suppressor genes. Gene hypermethylation is an alternative mechanism of tumor suppressor gene inactivation. Various approaches have been used to elucidate the role of gene hypermethylation in MM, including a candidate gene approach, microarray approach for genes upregulated by hypomethylating agents, and a cancer pathway approach, which enables a comprehensive picture of the involvement of multiple tumor suppressor genes in MM. Based on the cancer pathway approach, the following data on the involvement of cell cycle control, intrinsic tumor suppressor, and cell signaling were derived. First, among the INK4 and CIP/KIP families of cyclin-dependent kinase inhibitors, only CDKN2B and CDKN2A are frequently hypermethylated. Second, methylation of SHP1 and soluble Wnt inhibitors is associated with constitutive activation of JAK/STAT and Wnt signaling. Importantly, downregulation of the signaling pathways can be restored by demethylation and re-expression of SHP1 and soluble Wnt inhibitors, which is potentially important therapeutically. Third, of the tumor suppressor genes involved in the DAPK/P14/HDM2/P53/Apaf-1 pathway, only DAPK is frequently methylated, which appeared to be an adverse prognostic factor to survival. Lastly, apart from being implicated in the progression from monoclonal gammopathy of unknown significance to MM, aberrant gene promoter methylation might also account for late disease progression in MM. Future studies are needed to delineate the biologic consequence of gene hypermethylation, the prognostic effect of gene methylation, and the possibility of hypomethylation therapy.

Epigenetic dysregulation of Wnt signaling pathway in multiple myeloma

Wnt signaling has recently been implicated in carcinogenesis. We studied the activity of Wnt signaling and the methylation status of WIF1, DKK3, APC, SFRP1, SFRP2, SFRP4 and SFRP5 by methylation-specific PCR in myeloma cell lines and primary myeloma samples. Of the four cell lines, Wnt signaling was constitutively activated in LP1 and WL2, correlating with hypermethylation and hence silencing. Moreover, 5-aza-2'-deoxycytidine treatment of these two cell lines showed progressive demethylation of methylated Wnt inhibitors, re-expression of transcripts and downregulation of Wnt signaling. In both LP1 and WL2 cells, multiple Wnts and Fzs were simultaneously expressed. Treatment of WL2, in which SFRP1 was completely methylated, with recombinant secreted Frizzled-related protein 1 (SFRP1) induced downregulation of Wnt signaling and inhibition of proliferation. In primary myeloma samples, 42% patients had methylation of at least one of these seven genes, of which 61.9% had > or = 2 genes methylated. In conclusion, Wnt signaling is constitutively activated in myeloma, associated with methylation silencing of one or multiple soluble Wnt antagonists. An autocrine loop regulating Wnt signaling was demonstrated in the myeloma plasma cells, in which cellular proliferation was efficiently inhibited by recombinant SFRP1. Methylation study of a panel of genes, regulating a cellular pathway instead of isolated genes, is important.