The protein encoded by this gene is a basic leucine zipper (bZIP) transcription factor that plays an important role in the regulation of lineage-specific hematopoiesis. The encoded nuclear protein represses ETS1-mediated transcription of erythroid-specific genes in myeloid cells. This gene contains no introns. [provided by RefSeq, Jul 2008]
MAFB is frequently overexpressed in Myeloma thought to be caused by translocations of IGH (14q32) with a number of different partner genes. MAFB itself is a translocation partner of IGH in a small proportion of Myeloma patients.
BACKGROUND: Multiple myeloma (MM) patients with t(14;20) have a poor prognosis and their outcome has not improved following the introduction of bortezomib (Bzb). The mechanism underlying the resistance to proteasome inhibitors (PIs) for this subset of patients is unknown. METHODS: IC50 of Bzb and carfilzomib (CFZ) in human myeloma cell lines (HMCLs) were established by MTT assay. Gene Expression profile (GEP) analysis was used to determine gene expression in primary myeloma cells. Immunoblotting analysis was performed for MAFb and caspase family proteins. Immunofluorescence staining was used to detect the location of MAFb protein in MM cells. Lentiviral infections were used to knock-down MAFb expression in two lines. Apoptosis detection by flow cytometry and western blot analysis was performed to determine the molecular mechanism MAFb confers resistance to proteasome inhibitors. RESULTS: We found high levels of MAFb protein in cell lines with t(14;20), in one line with t(6;20), in one with Igλ insertion into MAFb locus, and in primary plasma cells from MM patients with t(14;20). High MAFb protein levels correlated with higher IC50s of PIs in MM cells. Inhibition of GSK3β activity or treatment with Bzb or CFZ prevented MAFb protein degradation without affecting the corresponding mRNA level indicating a role for GSK3 and proteasome inhibitors in regulation of MAFb stability. Silencing MAFb restored sensitivity to Bzb and CFZ, and enhanced PIs-induced apoptosis and activation of caspase-3, - 8, - 9, PARP and lamin A/C suggesting that high expression of MAFb protein leads to insensitivity to proteasome inhibitors. CONCLUSION: These results highlight the role of post-translational modification of MAFb in maintaining its protein level, and identify a mechanism by which proteasome inhibitors induced stabilization of MAFb confers resistance to proteasome inhibitors, and provide a rationale for the development of targeted therapeutic strategies for this subset of patients.
Retinoids exert antitumor effects through the retinoic acid receptor α (RARα). In the present study, we sought to identify the factors involved in the RARα-mediated transcriptional regulation of the tumor suppressor gene and the tissue factor pathway inhibitor 2 (TFPI2) in hepatocellular carcinoma (HCC). All-
Lam CF, Yeung HT, Lam YM, Ng RK Reactive oxygen species activate differentiation gene transcription of acute myeloid leukemia cells via the JNK/c-JUN signaling pathway. Leuk Res. 2018; 68:112-119 [PubMed] Related Publications
Reactive oxygen species (ROS) and altered cellular redox status are associated with many malignancies. Acute myeloid leukemia (AML) cells are maintained at immature state by differentiation blockade, which involves deregulation of transcription factors in myeloid differentiation. AML cells can be induced to differentiate by phorbol-12-myristate-13-acetate (PMA), which possesses pro-oxidative activity. However, the signaling events mediated by ROS in the activation of transcriptional program during AML differentiation has not been fully elucidated. Here, we investigated AML cell differentiation by treatment with PMA and ROS scavenger N-acetyl-l-cysteine (NAC). We observed elevation of intracellular ROS level in the PMA-treated AML cells, which correlated with differentiated cell morphology and increased CD11b
Zhang S, Li X, Wang HY, Steven Zheng XF Beyond regulation of pol III: Role of MAF1 in growth, metabolism, aging and cancer. Biochim Biophys Acta Gene Regul Mech. 2018; 1861(4):338-343 [PubMed] Related Publications
MAF1 was discovered as a master repressor of Pol III-dependent transcription in response to diverse extracellular signals, including growth factor, nutrient and stress. It is regulated through posttranslational mechanisms such as phosphorylation. A prominent upstream regulator of MAF1 is the mechanistic target of rapamycin (mTOR) pathway. mTOR kinase directly phosphorylates MAF1, controlling its localization and transcriptional activity. In mammals, MAF1 has also been shown to regulate Pol I- and Pol II-dependent transcription. Interestingly, MAF1 modulates Pol II activity both as a repressor and activator, depending on specific target genes, to impact on cellular growth and metabolism. While MAF1 represses genes such as TATA-binding protein (TBP) and fatty acid synthase (FASN), it activates the expression of PTEN, a major tumor suppressor and an inhibitor of the mTOR signaling. Increasing evidence indicates that MAF1 plays an important role in different aspects of normal physiology, lifespan and oncogenesis. Here we will review the current knowledge on MAF1 in growth, metabolism, aging and cancer. This article is part of a Special Issue entitled: SI: Regulation of tRNA synthesis and modification in physiological conditions and disease edited by Dr. Boguta Magdalena.
The deubiquitinase USP5 stabilizes c-Maf, a key transcription factor in multiple myeloma (MM), but the mechanisms and significance are unclear. In the present study, USP5 was found to interact with c-Maf and prevented it from degradation by decreasing its polyubiquitination level. Specifically, the 308th and 347th lysine residues in c-Maf were critical for USP5-mediated deubiquitination and stability. There are five key domains in the USP5 protein and subsequent studies revealed that the cryptic ZnF domain and the C-box domain interacted with c-Maf but the UBA1/UBA2 domain partly increased its stability. Notably, MafA and MafB are also members of the c-Maf family, however, USP5 failed to deubiquitinate MafA, suggesting its substrate specificity. In the functional studies, USP5 was found to promoted the transcriptional activity of c-Maf. Consistent with the high level of c-Maf protein in MM cells, USP5 was also highly expressed. When USP5 was knocked down, c-Maf underwent degradation. Interestingly, USP5 silence led to apoptosis of MM cells expressing c-Maf but not MM cells lacking c-Maf, indicating c-Maf is a key factor in USP5-mediated MM cell proliferation and survival. Consistent with this finding, WP1130, an inhibitor of several Dubs including USP5, suppressed the transcriptional activity of c-Maf and induced MM cell apoptosis. When c-Maf was overexpressed, WP1130-induced MM cell apoptosis was abolished. Taken together, these findings suggest that USP5 regulates c-Maf stability and MM cell survival. Targeting the USP5/c-Maf axis could be a potential strategy for MM treatment.
Goudot C, Coillard A, Villani AC, et al. Aryl Hydrocarbon Receptor Controls Monocyte Differentiation into Dendritic Cells versus Macrophages. Immunity. 2017; 47(3):582-596.e6 [PubMed] Related Publications
After entering tissues, monocytes differentiate into cells that share functional features with either macrophages or dendritic cells (DCs). How monocyte fate is directed toward monocyte-derived macrophages (mo-Macs) or monocyte-derived DCs (mo-DCs) and which transcription factors control these differentiation pathways remains unknown. Using an in vitro culture model yielding human mo-DCs and mo-Macs closely resembling those found in vivo in ascites, we show that IRF4 and MAFB were critical regulators of monocyte differentiation into mo-DCs and mo-Macs, respectively. Activation of the aryl hydrocarbon receptor (AHR) promoted mo-DC differentiation through the induction of BLIMP-1, while impairing differentiation into mo-Macs. AhR deficiency also impaired the in vivo differentiation of mouse mo-DCs. Finally, AHR activation correlated with mo-DC infiltration in leprosy lesions. These results establish that mo-DCs and mo-Macs are controlled by distinct transcription factors and show that AHR acts as a molecular switch for monocyte fate specification in response to micro-environmental factors.
The PIM kinase family (PIM1, 2 and 3) have a central role in integrating growth and survival signals, and are expressed in a wide range of solid and hematological malignancies. We now confirm that PIM2 is overexpressed in multiple myeloma (MM) patients, and within MM group it is overexpressed in the high-risk MF subset (activation of proto-oncogenes MAF/MAFB). This is consistent with our finding of PIM2's role in key signaling pathways (IL-6, CD28 activation) that confer chemotherapy resistance in MM cells. These studies have identified a novel PIM2-selective non-ATP competitive inhibitor (JP11646) that has a 4 to 760-fold greater suppression of MM proliferation and viability than ATP-competitive PIM inhibitors. This increased efficacy is due not only to the inhibition of PIM2 kinase activity, but also to a novel mechanism involving specific downregulation of PIM2 mRNA and protein expression not seen with the ATP competitive inhibitors. Treatment with JP11646 in xenogeneic myeloma murine models demonstrated significant reduction in tumor burden and increased median survival. Altogether our findings suggest the existence of previously unrecognized feedback loop(s) where PIM2 kinase activity regulates PIM2 gene expression in malignant cells, and that JP11646 represents a novel class of PIM2 inhibitors that interdicts this feedback.
Li Y, Min D, Wang K, et al. MicroRNA‑152 inhibits cell proliferation, migration and invasion by directly targeting MAFB in nasopharyngeal carcinoma. Mol Med Rep. 2017; 15(2):948-956 [PubMed] Related Publications
Aberrant expression of microRNAs (miRs) has been reported to be involved in nasopharyngeal carcinoma (NPC) carcinogenesis and development. The expression and functions of miR‑152 have previously been studied in several types of cancer. However, to the best of our knowledge, no previous studies have investigated the effects of miR‑152 on NPC. The present study aimed to explore the expression, functions and molecular mechanisms of miR‑152 in NPC. The expression levels of miR‑152 were detected in NPC tissues and cell lines using quantitative polymerase chain reaction (qPCR). Cell proliferation, migration and invasion were measured by MTT, cell migration and invasion assays, respectively. Dual‑luciferase reporter assay was used to determine whether V‑maf avian musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB) was a direct target gene of miR‑152. qPCR and western blotting were used to detect the mRNA and protein expression levels of MAFB. In addition, functional assays were performed to explore the effects of endogenous MAFB on NPC. The results of the present study demonstrated that miR‑152 was significantly downregulated in NPC tissues and cell lines. Furthermore, ectopic expression of miR‑152 suppressed cell proliferation, migration and invasion of NPC cells. Dual‑luciferase reporter assay demonstrated that MAFB was a direct target gene of miR‑152, and qPCR and western blotting indicated that miR‑152 negatively regulated MAFB expression at the mRNA and protein level. Knockdown of MAFB expression markedly suppressed NPC cell proliferation, migration and invasion. These findings suggested that miR‑152 may target MAFB to regulate NPC initiation and progression; therefore, it may be investigated as a target for the treatment of NPC.
This study was designed to investigate the mode of action of trabectedin in myelomonocytic leukemia cells by applying systems biology approaches to mine gene expression profiling data and pharmacological assessment of the cellular effects. Significant enrichment was found in regulons of target genes inferred for specific transcription factors, among which MAFB was the most upregulated after treatment and was central in the transcriptional network likely to be relevant for the specific therapeutic effects of trabectedin against myelomonocytic cells. Using the Connectivity Map, similarity among transcriptional signatures elicited by treatment with different compounds was investigated, showing a high degree of similarity between transcriptional signatures of trabectedin and those of the topoisomerase I inhibitor, irinotecan, and an anti-dopaminergic antagonist, thioridazine. The study highlights the potential importance of systems biology approaches to generate new hypotheses that are experimentally testable to define the specificity of the mechanism of action of drugs.
The transcription factor, v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB), promotes tumorigenesis in some cancers. In this study, we found that MAFB levels were increased in clinical colorectal cancer (CRC) samples, and higher expression correlated with more advanced TNM stage. We identified MAFB amplifications in a majority of tumor types in an assessment of The Cancer Genome Atlas database. Altered MAFB levels due to gene amplification, deletion, mutation, or transcription upregulation occurred in 9% of CRC cases within the database. shRNA knockdown experiments demonstrated that MAFB deficiency blocked CRC cell proliferation by arresting the cell cycle at G0/G1 phase in vitro. We found that MAFB could be SUMOylated by SUMO1 at lysine 32, and this modification was critical for cell cycle regulation by MAFB in CRC cells. SUMOylated MAFB directly regulated cyclin-dependent kinase 6 transcription by binding to its promoter. MAFB knockdown CRC cell xenograft tumors in mice grew more slowly than controls, and wild-type MAFB-overexpressing tumors grew more quickly than tumors overexpressing MAFB mutated at lysine 32. These data suggest that SUMOylated MAFB promotes CRC tumorigenesis through cell cycle regulation. MAFB and its SUMOylation process may serve as novel therapeutic targets for CRC treatment.
Yu H, Jiang HL, Xu D, et al. Transcription Factor MafB Promotes Hepatocellular Carcinoma Cell Proliferation through Up-Regulation of Cyclin D1. Cell Physiol Biochem. 2016; 39(2):700-8 [PubMed] Related Publications
BACKGROUND/AIMS: MafB, a member of the Maf transcription factor family, plays a key role in the regulation of pancreatic alpha and beta cell differentiation. However, its function in the control of cancer cell proliferation remains unknown. METHODS: The mRNA and protein expression levels of MafB in hepatocellular carcinoma tissues and adjacent non-tumor normal specimens were determined by real-time RT-PCR and Western blot, respectively. Report assay was performed to determine whether the regulation of Cyclin D1 by MafB is at the transcriptional level. The binding of MafB to the Cyclin D1 promoter was determined by Chromatin Immunoprecipitation (ChIP) assays. To determine the potential oncogenic effects of MafB in vivo, HepG2 cells transfected with adenovirus containing empty vector or MafB were injected subcutaneously to the skin under the front legs of the nude mice. RESULTS: In the current study, we showed that MafB was markedly up-regulated in hepatocellular carcinoma (HCC) tissues and cells. Enforced overexpression of MafB enhanced, while its deficiency inhibited HCC cell proliferation. Mechanistically, Cyclin D1, an important regulator of cell cycle progression, was identified as a direct transcriptional target of MafB. Consistently, knockdown of Cyclin D1 largely attenuated the proliferative roles of MafB in HCC cells. Importantly, MafB overexpression significantly promoted cancer cell growth in mice. CONCLUSIONS: Collectively, our results identified a novel HCC regulatory pathway involving MafB and Cyclin D1, the dysfunction of which drives proliferative character in HCC.
Using a data set of 1217 patients with multiple myeloma enrolled in Total Therapies, we have examined the impact of novel therapies on molecular and risk subgroups and the clinical value of molecular classification. Bortezomib significantly improved the progression-free survival (PFS) and overall survival (OS) of the MMSET (MS) subgroup. Thalidomide and bortezomib positively impacted the PFS of low-risk (LoR) cases defined by the GEP70 signature, whereas high-risk (HiR) cases showed no significant changes in outcome. We show that molecular classification is important if response rates are to be used to predict outcomes. The t(11;14)-containing CD-1 and CD-2 subgroups showed clear differences in time to response and cumulative response rates but similar PFS and OS. Furthermore, complete remission was not significantly associated with the outcome of the MAF/MAFB (MF) subgroup or HiR cases. HiR cases were enriched in the MF, MS and proliferation subgroups, but the poor outcome of these groups was not linked to subgroup-specific characteristics such as MAF overexpression per se. It is especially important to define risk status if HiR cases are to be managed appropriately because of their aggressive clinical course, high rates of early relapse and the need to maintain therapeutic pressure on the clone.
BACKGROUND: Mounting evidence suggests that miRNAs have major functions in tumor pathogenesis, and this study aimed to identify the candidate miRNA and investigate its role in nasopharyngeal carcinoma (NPC). METHODS: MiRNA and mRNA expressions were screened by microarray assays. The cell proliferation, colony formation and migration ability were measured by MTT, soft agar and wound healing assays, respectively. The tumor growth suppression was evaluated by xenografting in nude mice. The plasma miR-223 levels in NPC patients were detected by TaqMan analysis. Real-time quantitative PCR and Western blotting were used to confirm miR-223 and MAFB expression levels. The targeting relationship between miR-223 and MAFB was verified using dual luciferase reporter assay. RESULTS: The miR-223 expression was decreased in CNE-1, CNE-2 cells as compared with NP69 cells, an immortalized human nasopharyngeal epithelial cell line, and its level also reduced in NPC patients' plasma as compared with healthy controls. Exogenous expression of miR-223 in CNE-2 cells could inhibit cell proliferation both in vitro and in vivo. Extrogenous miR-223 in CNE-2 cells would decrease the ability of colony formation and migration. MAFB, a transcription factor of Maf family members, was identified as a target gene of miR-223. We found that migration and invasion abilities were inhibited by MAFB silencing. CONCLUSIONS: MiR-223 negatively regulates the growth and migration of NPC cells via reducing MAFB expression, and this finding provides a novel insight into understanding miR-223 regulation mechanism in nasopharyngeal carcinoma tumorigenesis.
We have sequenced 463 presenting cases of myeloma entered into the UK Myeloma XI study using whole exome sequencing. Here we identify mutations induced as a consequence of misdirected AID in the partner oncogenes of IGH translocations, which are activating and associated with impaired clinical outcome. An APOBEC mutational signature is seen in 3.8% of cases and is linked to the translocation-mediated deregulation of MAF and MAFB, a known poor prognostic factor. Patients with this signature have an increased mutational load and a poor prognosis. Loss of MAF or MAFB expression results in decreased APOBEC3B and APOBEC4 expression, indicating a transcriptional control mechanism. Kataegis, a further mutational pattern associated with APOBEC deregulation, is seen at the sites of the MYC translocation. The APOBEC mutational signature seen in myeloma is, therefore, associated with poor prognosis primary and secondary translocations and the molecular mechanisms involved in generating them.
Yang L, Liu Y, Zhu L, Xiao M DNMT3A R882 mutation is associated with elevated expression of MAFB and M4/M5 immunophenotype of acute myeloid leukemia blasts. Leuk Lymphoma. 2015; 56(10):2914-22 [PubMed] Related Publications
Researchers have recognized that aberrant methylation is an important initiating event in the pathogenesis of hematological malignancies. DNMT3A is a DNA methyltransferase that plays a vital role in de novo methylation of DNA. Somatic mutation of DNMT3A, especially at the Arg882 (R882) site of the DNMT3A coding sequence, has been identified in pre-leukemic stem cell clones as one of the driver mutations of acute myeloid leukemia (AML). Statistical analysis has indicated that patients with AML with DNMT3A mutation tend to have the M4/M5 subtype of AML according to the French-American-British classification. In this study we aimed to investigate the association between the typical immunophenotype of leukemic blasts and mutation of DNMT3A R882. In addition, we further determined the relationship between DNMT3A R882 mutation and the expression of monocytic differentiation genes, and its clinical significance.
Türkmen S, Binder A, Gerlach A, et al. High prevalence of immunoglobulin light chain gene aberrations as revealed by FISH in multiple myeloma and MGUS. Genes Chromosomes Cancer. 2014; 53(8):650-6 [PubMed] Related Publications
Multiple myeloma (MM) is a malignant B-cell neoplasm characterized by an uncontrolled proliferation of aberrant plasma cells in the bone marrow. Chromosome aberrations in MM are complex and represent a hallmark of the disease, involving many chromosomes that are altered both numerically and structurally. Nearly half of the cases are nonhyperdiploid and show IGH translocations with the following partner genes: CCND1, FGFR3 and MMSET, MAF, MAFB, and CCND3. The remaining 50% are grouped into a hyperdiploid group that is characterized by multiple trisomies involving chromosomes 3, 5, 7, 9, 11, 15, 19, and 21. In this study, we analyzed the immunoglobulin light chain kappa (IGK, 2p12) and lambda (IGL, 22q11) loci in 150 cases, mostly with MM but in a few cases monoclonal gammopathy of undetermined significance (MGUS), without IGH translocations. We identified aberrations in 27% (= 40 patients) including rearrangements (12%), gains (12%), and deletions (4.6%). In 6 of 18 patients with IGK or/and IGL rearrangements, we detected a MYC rearrangement which suggests that MYC is the translocation partner in the majority of these cases.
Tian E, Sawyer JR, Heuck CJ, et al. In multiple myeloma, 14q32 translocations are nonrandom chromosomal fusions driving high expression levels of the respective partner genes. Genes Chromosomes Cancer. 2014; 53(7):549-57 [PubMed] Free Access to Full ArticleRelated Publications
MicroRNA-199a (miRNA-199a) has been shown to have comprehensive functions and behave differently in different systems and diseases. It is encoded by two loci in the human genome, miR-199a-1 in chromosome 19 and miR-199a-2 in chromosome 1. Both loci give rise to the same miRNAs (miR-199a-5p and miR-199a-3p). The cause of the diverse action of the miRNA in different systems is not clear. However, it is likely due to different regulation of the two genomic loci and variable targets of the miRNA in different cells and tissues. Here we studied promoter methylation of miR-199a in testicular germ cell tumors (TGCTs) and glioblastomas (gliomas) and discovered that hypermethylation in TGCTs of both miR-199a-1 and -2 resulted in its reduced expression, while hypomethylation of miR-199a-2 but not -1 in gliomas may be related to its elevated expression. We also identified a common regulator, REST, which preferentially bound to the methylated promoters of both miR-199a-1 and miR-199a-2. The action of miR-199a is dependent on its downstream targets. We identified MAFB as a putative target of miRNA-199a-5p in TGCTs and confirmed that the tumor suppression activity of the microRNA is mediated by its target MAFB. By studying the mechanisms that control the expressions of miR-199a and its various downstream targets, we hope to use miR-199a as a model to understand the complexity of miRNA biology.
Tucci M, Stucci S, Savonarola A, et al. Immature dendritic cells in multiple myeloma are prone to osteoclast-like differentiation through interleukin-17A stimulation. Br J Haematol. 2013; 161(6):821-31 [PubMed] Related Publications
Interleukin 17A (IL17A), a cytokine involved in allergy, inflammation and osteoclastogenesis, was investigated in multiple myeloma (MM) to assess its role in the osteoclast (OC)-like activity of marrow immature dendritic cells (iDCs). Comparing nine MM patients with control subjects affected by monoclonal gammopathy of undetermined significance, we found high IL17A expression in the marrow plasma of MM patients in parallel with its deposits within the stromal matrix. Increased expression of the IL17A receptor (IL17RA) was also found in primary myeloma iDCs, which underwent OC-like transdifferentiation after IL17A stimulation. To assess the role of IL17A, we measured the activity of the IL17/IL17RA pathway in IL17A-transdifferentiated iDCs and the expression of functional OC genes by Western blotting and real-time polymerase chain reaction. These cells showed increased RNA transcription of genes enrolled in the maturation of OCs, while NFATC1 and FOS were induced by IL17A, independently of NFKB1 phosphorylation. Moreover, the concurrent phosphorylation of the Lip isoform of CEBPB and the down-regulation of MAFB supported the activation of IL17RA pathway in OC-like transdifferentiated iDCs that was apparently unrelated to TNFRSF11A signalling. These data emphasize the involvement of iDCs in MM hyperactive osteoclastogenesis and suggest that their bone resorption activity is also regulated, at least in vitro, by IL17RA.
Rio-Machin A, Ferreira BI, Henry T, et al. Downregulation of specific miRNAs in hyperdiploid multiple myeloma mimics the oncogenic effect of IgH translocations occurring in the non-hyperdiploid subtype. Leukemia. 2013; 27(4):925-31 [PubMed] Related Publications
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.
Vicente-Dueñas C, González-Herrero I, García Cenador MB, et al. Loss of p53 exacerbates multiple myeloma phenotype by facilitating the reprogramming of hematopoietic stem/progenitor cells to malignant plasma cells by MafB. Cell Cycle. 2012; 11(20):3896-900 [PubMed] Free Access to Full ArticleRelated Publications
Multiple myeloma (MM) is a serious, mostly incurable human cancer of malignant plasma cells. Chromosomal translocations affecting MAFB are present in a significant percentage of multiple myeloma patients. Genetically engineered Sca1-MafB mice, in which MafB expression is limited to hematopoietic stem/progenitor cells (HS/P-Cs), display the phenotypic features of MM. Contrary to many other types of cancer, it is not yet known if the p53 gene plays any essential role in the pathogenesis of this disease. Here, we show, taking advantage of the Sca1-MafB MM mouse model, that loss of p53 does not rescue the multiple myeloma disease, but instead accelerates its development and exacerbates the MM phenotype. Therefore, the efficiency of the MafB-induced MM reprogramming of normal HS/P-Cs to terminally differentiated malignant plasma cells is enhanced by p53 deficiency, in analogy to what happens in reprogramming to pluripotency. These results raise caution about interfering with p53 function when treating multiple myeloma.
Vicente-Dueñas C, Romero-Camarero I, González-Herrero I, et al. A novel molecular mechanism involved in multiple myeloma development revealed by targeting MafB to haematopoietic progenitors. EMBO J. 2012; 31(18):3704-17 [PubMed] Free Access to Full ArticleRelated Publications
Understanding the cellular origin of cancer can help to improve disease prevention and therapeutics. Human plasma cell neoplasias are thought to develop from either differentiated B cells or plasma cells. However, when the expression of Maf oncogenes (associated to human plasma cell neoplasias) is targeted to mouse B cells, the resulting animals fail to reproduce the human disease. Here, to explore early cellular changes that might take place in the development of plasma cell neoplasias, we engineered transgenic mice to express MafB in haematopoietic stem/progenitor cells (HS/PCs). Unexpectedly, we show that plasma cell neoplasias arise in the MafB-transgenic mice. Beyond their clinical resemblance to human disease, these neoplasias highly express genes that are known to be upregulated in human multiple myeloma. Moreover, gene expression profiling revealed that MafB-expressing HS/PCs were more similar to B cells and tumour plasma cells than to any other subset, including wild-type HS/PCs. Consistent with this, genome-scale DNA methylation profiling revealed that MafB imposes an epigenetic program in HS/PCs, and that this program is preserved in mature B cells of MafB-transgenic mice, demonstrating a novel molecular mechanism involved in tumour initiation. Our findings suggest that, mechanistically, the haematopoietic progenitor population can be the target for transformation in MafB-associated plasma cell neoplasias.
BACKGROUND: Multiple myeloma is a plasma-cell tumor with heterogeneity in molecular abnormalities and treatment response. DESIGN AND METHODS: We have assessed whether human myeloma cell lines have kept patients' heterogeneity using Affymetrix gene expression profiling of 40 human myeloma cell lines obtained with or without IL6 addition and could provide a signature for stratification of patient risk. RESULTS: Human myeloma cell lines, especially those derived in the presence of IL6, displayed a heterogeneity that overlaps that of the patients with multiple myeloma. Human myeloma cell lines segregated into 6 groups marked by overexpression of MAF, MMSET, CCND1, FRZB with or without overexpression of cancer testis antigens (CTA). Cell lines of CTA/MAF and MAF groups have a translocation involving C-MAF or MAFB, cell lines of groups CCND1-1 and CCND1-2like have a t(11;14) and cell lines of group MMSET have a t(4;14). The CTA/FRZB group comprises cell lines that had no or no recurrent 14q32 translocation. Expression of 248 genes accounted for human myeloma cell line molecular heterogeneity. Human myeloma cell line heterogeneity genes comprise genes with prognostic value for survival of patients making it possible to build a powerful prognostic score involving a total of 13 genes. CONCLUSIONS: Human myeloma cell lines derived in the presence of IL6 recapitulate the molecular diversity of multiple myeloma that made it possible to design, using human myeloma cell line heterogeneity genes, a high-risk signature for patients at diagnosis. We propose this classification to be used when addressing the physiopathology of multiple myeloma with human myeloma cell lines.
C/EBPs are a family of B-Zip transcription factors--TFs--involved in the regulation of differentiation in several tissues. The two most studied members--C/EBPα and C/EBPβ--play important roles in skin homeostasis and their ablation reveals cells with stem cells signatures. Much less is known about C/EBPδ which is highly expressed in the granular layer of interfollicular epidermis and is a direct target of p63, the master regular of multilayered epithelia. We identified C/EBPδ target genes in human primary keratinocytes by ChIP on chip and profiling of cells functionally inactivated with siRNA. Categorization suggests a role in differentiation and control of cell-cycle, particularly of G2/M genes. Among positively controlled targets are numerous genes involved in barrier function. Functional inactivation of C/EBPδ as well as overexpressions of two TF targets--MafB and SOX2--affect expression of markers of keratinocyte differentiation. We performed IHC on skin tumor tissue arrays: expression of C/EBPδ is lost in Basal Cell Carcinomas, but a majority of Squamous Cell Carcinomas showed elevated levels of the protein. Our data indicate that C/EBPδ plays a role in late stages of keratinocyte differentiation.
Dysregulation of cyclin D2 contributes to the pathogenesis of multiple myeloma, and can occur through translocations that activate MAF/MAFB or MMSET/FGFR3. However, cyclin D2 induction can also be seen in the absence of such translocations, such as in patients with hyperdiploid disease, through unknown mechanisms. In UniGene cluster data-mining and ECgene analysis, we found that zinc-finger with KRAB and SCAN domains 3 (ZKSCAN3), a novel transcription factor, is overrepresented in this malignancy, and three consensus ZKSCAN3 binding sites were found in the cyclin D2 promoter. Analysis of a panel of myeloma cell lines, primary patient samples and datasets from Oncomine and the Multiple Myeloma Genomics Portal (MMGP) revealed expression of ZKSCAN3 messenger RNA (mRNA) in a majority of samples. Studies of cell lines by western blotting, and of primary tissue microarrays by immunohistochemistry, showed ZKSCAN3 protein expression in a majority, and in a manner that paralleled messenger levels in cell lines. ZKSCAN3 overexpression was associated with increased gene copy number or genomic DNA gain/amplification in a subset based on analysis of data from the MMGP, and from fluorescence in situ hybridization studies of cell lines and primary samples. Overexpression of ZKSCAN3 induced cyclin D2 promoter activity in a MAF/MAFB-independent manner, and to an extent that was influenced by the number of consensus ZKSCAN3 binding sites. Moreover, ZKSCAN3 protein expression correlated with cyclin D2 levels in cell lines and primary samples, and its overexpression induced cyclin D2. Conversely, ZKSCAN3 suppression using small hairpin RNAs (shRNAs) reduced cyclin D2 levels, and, importantly, inhibited myeloma cell line proliferation. Finally, ZKSCAN3 was noted to specifically bind to oligonucleotides representing sequences from the cyclin D2 promoter, and to the endogenous promoter itself in myeloma cells. Taken together, the data support the conclusion that ZKSCAN3 induction represents a mechanism by which myeloma cells can induce cyclin D2 dysregulation, and contribute to disease pathogenesis.
Lutherborrow M, Bryant A, Jayaswal V, et al. Expression profiling of cytogenetically normal acute myeloid leukemia identifies microRNAs that target genes involved in monocytic differentiation. Am J Hematol. 2011; 86(1):2-11 [PubMed] Related Publications
MicroRNAs are short ribonucleic acids (RNAs) that play an important role in many aspects of cellular biology such as differentiation and apoptosis, due to their role in the regulation of gene expression. Using microRNA microarrays, we characterized the microRNA gene expression of 27 patients with acute myeloid leukemia (AML) with normal cytogenetics, focusing on the microRNAs differentially expressed between the M1 and M5 French-American-British (FAB) subtypes. An accurate delineation of these two AML entities was observed based on the expression of 12 microRNAs. We hypothesized that these microRNAs may potentially be involved in the differentiation block of M1 blasts and consequently monocytic differentiation. Using publically available mRNA data and microRNA target prediction software, we identified several key myeloid factors that may be targeted by our candidate microRNAs. The expression changes of the candidate microRNAs during monocytic differentiation of AML cell lines treated with Vitamin D and phorbol 12-myristate 13-acetate were examined. All six candidate microRNAs were significantly down-regulated over the time course by quantitative reverse transcriptase polymerase chain reaction suggesting a link between these microRNAs and monocytic differentiation. To further characterize these microRNAs, we confirmed by luciferase assays that these microRNA target several key myeloid factors such as MAFB, IRF8, and KLF4 identifying a possible mechanism for the control of differentiation by these microRNAs.
Kanai K, Reza HM, Kamitani A, et al. SUMOylation negatively regulates transcriptional and oncogenic activities of MafA. Genes Cells. 2010; 15(9):971-82 [PubMed] Related Publications
Dysregulated expression of Maf proteins (namely c-Maf, MafA and MafB) leads to multiple myeloma in humans and oncogenic transformation of chicken embryonic fibroblasts. Maf proteins are transcriptional activators of tissue-specific gene expression and regulators of cell differentiation. For example, MafA is a critical regulator of crystallin genes and the lens differentiation program in chickens. In mammals, MafA is essential for the development of mature insulin-producing beta-cells of pancreas. It has been shown that MafA protein stability is regulated by phosphorylations at multiple serine and threonine residues. Here, we report that Maf proteins are also post-translationally modified by small ubiquitin-like modifier (SUMO) proteins at a conserved lysine residue in the amino-terminal transactivator domain. A SUMOylation-deficient mutant of MafA (K32R) was more potent than wild-type MafA in transactivating luciferase reporter construct driven by alphaA-crystallin or insulin gene promoter. In ovo electroporation into developing chicken embryo showed that the K32R mutant induced ectopic delta-crystallin gene expression more efficiently than the wild-type MafA. We also demonstrated that the K32R mutant had enhanced ability to induce colony formation of a chicken fibroblast cell line DF-1. Therefore, SUMOylation is a functional post-translational modification of MafA that negatively regulates its transcriptional and transforming activities.
Nair B, van Rhee F, Shaughnessy JD, et al. Superior results of Total Therapy 3 (2003-33) in gene expression profiling-defined low-risk multiple myeloma confirmed in subsequent trial 2006-66 with VRD maintenance. Blood. 2010; 115(21):4168-73 [PubMed] Free Access to Full ArticleRelated Publications
The Total Therapy 3 trial 2003-33 enrolled 303 newly diagnosed multiple myeloma patients and was noted to provide superior clinical outcomes compared with predecessor trial Total Therapy 2, especially in gene expression profiling (GEP)-defined low-risk disease. We report here on the results of successor trial 2006-66 with 177 patients, using bortezomib, lenalidomide, and dexamethasone maintenance for 3 years versus bortezomib, thalidomide, and dexamethasone in year 1 and thalidomide/dexamethasone in years 2 and 3 in the 2003-33 protocol. Overall survival (OS) and event-free survival (EFS) plots were super-imposable for the 2 trials, as were onset of complete response and complete response duration (CRD), regardless of GEP risk. GEP-defined high-risk designation, pertinent to 17% of patients, imparted inferior OS, EFS, and CRD in both protocols and, on multivariate analysis, was the sole adverse feature affecting OS, EFS, and CRD. Mathematical modeling of CRD in low-risk myeloma predicted a 55% cure fraction (P < .001). Despite more rapid onset and higher rate of CR than in other molecular subgroups, CRD was inferior in CCND1 without CD20 myeloma, resembling outcomes in MAF/MAFB and proliferation entities. The robustness of the GEP risk model should be exploited in clinical trials aimed at improving the notoriously poor outcome in high-risk disease.
Våtsveen TK, Tian E, Kresse SH, et al. OH-2, a hyperdiploid myeloma cell line without an IGH translocation, has a complex translocation juxtaposing MYC near MAFB and the IGK locus. Leuk Res. 2009; 33(12):1670-7 [PubMed] Related Publications
Multiple myeloma can be classified into hyperdiploid (HRD) (with 48-74 chromosomes) and non-hyperdiploid tumors (usually with immunoglobulin heavy chain translocations). The OH-2 human myeloma cell line (HMCL) retains the same HRD genotype as the primary tumor, with extra copies of chromosomes 3, 7, 15, 19, and 21. Both OH-2 and primary cells have a complex secondary translocation in which the IGK 3' enhancer is inserted between MYC and MAFB, resulting in dysregulation of both oncogenes. OH-2 provides a unique example of an HMCL and the corresponding primary tumor that are shown to share the same HRD genotype.
Boersma-Vreugdenhil GR, Kuipers J, Van Stralen E, et al. The recurrent translocation t(14;20)(q32;q12) in multiple myeloma results in aberrant expression of MAFB: a molecular and genetic analysis of the chromosomal breakpoint. Br J Haematol. 2004; 126(3):355-63 [PubMed] Related Publications
Chromosomal translocations of the immunoglobulin heavy chain (IgH) gene region at 14q32 are regularly involved in B lymphoid malignancies; they may initiate transformation either by deregulation of existing (proto) oncogenes or creation of new hybrid genes with transforming properties. Previously, we reported a reciprocal novel translocation, t(14;20)(q32;q12), found in the myeloma cell line UM3. In this cell line, the t(14;20) is the only translocation involving the IgH locus. Using double colour immunofluorescence in situ hybridization, the t(14;20) was also found in the diagnostic bone marrow sample, excluding a possible in vitro artefact. We also have found this recurrent t(14;20) in four other cell lines and in additional patient material. We cloned the regions containing the breakpoints in the der(14) and der(20) chromosomes from UM3, and analysed ectopic mRNA expression of genes in the breakpoint regions of both derivative chromosomes. Ectopic gene expression was observed for the transcription factor MAFB in der(14). The breakpoint scatter in the five cell lines with a t(14;20)--all expressing MAFB--is comprised within a region of 0.8 Mb. Provisional data indicate that this t(14;20) is associated with an adverse prognosis. Aberrant expression of MAFB may be involved in the oncogenic transformation of myeloma cells that harbour the t(14;20).
Bergsagel PL, Kuehl WM Molecular pathogenesis and a consequent classification of multiple myeloma. J Clin Oncol. 2005; 23(26):6333-8 [PubMed] Related Publications
There appear to be two pathways involved in the pathogenesis of premalignant non-immunoglobulin M (IgM) monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM). Nearly half of tumors are nonhyperdiploid, and mostly have one of five recurrent IgH translocations: 16% 11q13 (CCN D1), 3% 6p21 (CCN D3), 5% 16q23 (MAF), 2% 20q12 (MAFB), and 15% 4p16 (FGFR3 and MMSET). The remaining hyperdiploid tumors have multiple trisomies involving chromosomes 3, 5, 7, 9, 11, 15, 19, and 21, and infrequently one of these five translocations. Although cyclin D1 is not expressed by healthy lymphoid cells, it is bi-allelically dysregulated in a majority of hyperdiploid tumors. Virtually all MM and MGUS tumors have dysregulated and/or increased expression of cyclin D1, D2, or D3, providing an apparent early, unifying event in pathogenesis. The patterns of translocations and cyclin D expression (TC) define a novel classification that includes eight groups: 11q; 6p; MAF; 4p; D1 (34%); D1+D2 (6%); D2 (17%); and none (2%). The hyperdiploid D1 group is virtually absent in extramedullary MM and MM cell lines, suggesting a particularly strong dependence on interaction with the bone marrow microenvironment. Despite shared progression events (RAS mutations, MYC dysregulation, p53 mutations, and additional disruption of the retinoblastoma pathway), the phenotypes of MGUS and MM tumors in the eight TC groups is determined mainly by early oncogenic events. Similar to acute lymphocytic leukemia, MM seems to include several diseases (groups) that have differences in early or initiating events, global gene expression patterns, bone marrow dependence, clinical features, prognosis, and response to therapy.