Gene Summary

Gene:MELK; maternal embryonic leucine zipper kinase
Aliases: HPK38
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:maternal embryonic leucine zipper kinase
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
Show (16)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • p53 Protein
  • Biomarkers, Tumor
  • Cluster Analysis
  • Messenger RNA
  • Up-Regulation
  • Chromosome 9
  • Cancer Stem Cells
  • Cell Cycle Proteins
  • siRNA
  • Brain Stem Glioma, Childhood
  • Neoplastic Cell Transformation
  • Talin
  • Oligonucleotide Array Sequence Analysis
  • RNA Interference
  • Brain Tumours
  • Drug Resistance
  • Cancer Gene Expression Regulation
  • Peptides
  • Gene Regulatory Networks
  • Ultraviolet Rays
  • Transcriptome
  • Breast Cancer
  • Promoter Regions
  • Transcription
  • Gene Expression
  • Protein-Serine-Threonine Kinases
  • Spliceosomes
  • Signal Transduction
  • Gene Knockdown Techniques
  • Wnt1 Protein
  • Gene Expression Profiling
  • Ubiquitin-Conjugating Enzymes
  • Phosphorylation
  • Apoptosis
  • Xenograft Models
  • Stem Cells
  • Transfection
  • Neoplasm Grading
  • Brain Tumours
  • Cell Proliferation
  • Glioblastoma
Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: MELK (cancer-related)

Moiseeva NI, Susova OY, Mitrofanov AA, et al.
Connection between Proliferation Rate and Temozolomide Sensitivity of Primary Glioblastoma Cell Culture and Expression of YB-1 and LRP/MVP.
Biochemistry (Mosc). 2016; 81(6):628-35 [PubMed] Related Publications
Glioblastomas (GBL) are the most common and aggressive brain tumors. They are distinguished by high resistance to radiation and chemotherapy. To find novel approaches for GBL classification, we obtained 16 primary GBL cell cultures and tested them with real-time PCR for mRNA expression of several genes (YB-1, MGMT, MELK, MVP, MDR1, BCRP) involved in controlling cell proliferation and drug resistance. The primary GBL cultures differed in terms of proliferation rate, wherein a group of GBL cell cultures with low proliferation rate demonstrated higher resistance to temozolomide. We found that GBL primary cell cultures characterized by high proliferation rate and lower resistance to temozolomide expressed higher mRNA level of the YB-1 and MDR1 genes, whereas upregulated expression of MVP/LRP mRNA was a marker in the group of GBL with low proliferation rate and high resistance. A moderate correlation between expression of YB-1 and MELK as well as YB-1 and MDR1 was found. In the case of YB-1 and MGMT expression, no correlation was found. A significant negative correlation was revealed between mRNA expression of MVP/LRP and MELK, MDR1, and BCRP. No correlation in expression of YB-1 and MVP/LRP genes was observed. It seems that mRNA expression of YB-1 and MVP/LRP may serve as a marker for GBL cell cultures belonging to distinct groups, each of which is characterized by a unique pattern of gene activity.

Stavrovskaya AA, Shushanov SS, Rybalkina EY
Problems of Glioblastoma Multiforme Drug Resistance.
Biochemistry (Mosc). 2016; 81(2):91-100 [PubMed] Related Publications
Glioblastoma multiforme (GBL) is the most common and aggressive brain neoplasm. A standard therapeutic approach for GBL involves combination therapy consisting of surgery, radiotherapy, and chemotherapy. The latter is based on temozolomide (TMZ). However, even by applying such a radical treatment strategy, the mean patient survival time is only 14.6 months. Here we review the molecular mechanisms underlying the resistance of GBL cells to TMZ including genetic and epigenetic mechanisms. Present data regarding a role for genes and proteins MGMT, IDH1/2, YB-1, MELK, MVP/LRP, MDR1 (ABCB1), and genes encoding other ABC transporters as well as Akt3 kinase in developing resistance of GBL to TMZ are discussed. Some epigenetic regulators of resistance to TMZ such as microRNA and EZH2 are reviewed.

Kato T, Inoue H, Imoto S, et al.
Oncogenic roles of TOPK and MELK, and effective growth suppression by small molecular inhibitors in kidney cancer cells.
Oncotarget. 2016; 7(14):17652-64 [PubMed] Free Access to Full Article Related Publications
T-lymphokine-activated killer cell-originated protein kinase (TOPK) and maternal embryonic leucine zipper kinase (MELK) have been reported to play critical roles in cancer cell proliferation and maintenance of stemness. In this study, we investigated possible roles of TOPK and MELK in kidney cancer cells and found their growth promotive effect as well as some feedback mechanism between these two molecules. Interestingly, the blockade of either of these two kinases effectively caused downregulation of forkhead box protein M1 (FOXM1) activity which is known as an oncogenic transcriptional factor in various types of cancer cells. Small molecular compound inhibitors against TOPK (OTS514) and MELK (OTS167) effectively suppressed the kidney cancer cell growth, and the combination of these two compounds additively worked and showed the very strong growth suppressive effect on kidney cancer cells. Collectively, our results suggest that both TOPK and MELK are promising molecular targets for kidney cancer treatment and that dual blockade of OTS514 and OTS167 may bring additive anti-tumor effects with low risk of side effects.

Srihari S, Kalimutho M, Lal S, et al.
Understanding the functional impact of copy number alterations in breast cancer using a network modeling approach.
Mol Biosyst. 2016; 12(3):963-72 [PubMed] Related Publications
UNLABELLED: Copy number alterations (CNAs) are thought to account for 85% of the variation in gene expression observed among breast tumours. The expression of cis-associated genes is impacted by CNAs occurring at proximal loci of these genes, whereas the expression of trans-associated genes is impacted by CNAs occurring at distal loci. While a majority of these CNA-driven genes responsible for breast tumourigenesis are cis-associated, trans-associated genes are thought to further abet the development of cancer and influence disease outcomes in patients. Here we present a network-based approach that integrates copy-number and expression profiles to identify putative cis- and trans-associated genes in breast cancer pathogenesis. We validate these cis- and trans-associated genes by employing them to subtype a large cohort of breast tumours obtained from the METABRIC consortium, and demonstrate that these genes accurately reconstruct the ten subtypes of breast cancer. We observe that individual breast cancer subtypes are driven by distinct sets of cis- and trans-associated genes. Among the cis-associated genes, we recover several known drivers of breast cancer (e.g. CCND1, ERRB2, MDM2 and ZNF703) and some novel putative drivers (e.g. BRF2 and SF3B3). siRNA-mediated knockdown of BRF2 across a panel of breast cancer cell lines showed significant reduction in cell viability for ER-/HER2+ (MDA-MB-453) cells, but not in normal (MCF10A) cells thereby indicating that BRF2 could be a viable therapeutic target for estrogen receptor-negative/HER2-enriched (ER-/HER2+) cancers. Among the trans-associated genes, we identify modules of immune response (CD2, CD19, CD38 and CD79B), mitotic/cell-cycle kinases (e.g. AURKB, MELK, PLK1 and TTK), and DNA-damage response genes (e.g. RFC4 and FEN1). siRNA-mediated knockdown of RFC4 significantly reduced cell proliferation in ER-negative normal breast and cancer lines, thereby indicating that RFC4 is essential for both normal and cancer cell survival but could be a useful biomarker for aggressive (ER-negative) breast tumours.
AVAILABILITY: under NetStrat.

Ajiro M, Jia R, Yang Y, et al.
A genome landscape of SRSF3-regulated splicing events and gene expression in human osteosarcoma U2OS cells.
Nucleic Acids Res. 2016; 44(4):1854-70 [PubMed] Free Access to Full Article Related Publications
Alternative RNA splicing is an essential process to yield proteomic diversity in eukaryotic cells, and aberrant splicing is often associated with numerous human diseases and cancers. We recently described serine/arginine-rich splicing factor 3 (SRSF3 or SRp20) being a proto-oncogene. However, the SRSF3-regulated splicing events responsible for its oncogenic activities remain largely unknown. By global profiling of the SRSF3-regulated splicing events in human osteosarcoma U2OS cells, we found that SRSF3 regulates the expression of 60 genes including ERRFI1, ANXA1 and TGFB2, and 182 splicing events in 164 genes, including EP300, PUS3, CLINT1, PKP4, KIF23, CHK1, SMC2, CKLF, MAP4, MBNL1, MELK, DDX5, PABPC1, MAP4K4, Sp1 and SRSF1, which are primarily associated with cell proliferation or cell cycle. Two SRSF3-binding motifs, CCAGC(G)C and A(G)CAGCA, are enriched to the alternative exons. An SRSF3-binding site in the EP300 exon 14 is essential for exon 14 inclusion. We found that the expression of SRSF1 and SRSF3 are mutually dependent and coexpressed in normal and tumor tissues/cells. SRSF3 also significantly regulates the expression of at least 20 miRNAs, including a subset of oncogenic or tumor suppressive miRNAs. These data indicate that SRSF3 affects a global change of gene expression to maintain cell homeostasis.

Mullapudi N, Ye B, Suzuki M, et al.
Genome Wide Methylome Alterations in Lung Cancer.
PLoS One. 2015; 10(12):e0143826 [PubMed] Free Access to Full Article Related Publications
Aberrant cytosine 5-methylation underlies many deregulated elements of cancer. Among paired non-small cell lung cancers (NSCLC), we sought to profile DNA 5-methyl-cytosine features which may underlie genome-wide deregulation. In one of the more dense interrogations of the methylome, we sampled 1.2 million CpG sites from twenty-four NSCLC tumor (T)-non-tumor (NT) pairs using a methylation-sensitive restriction enzyme- based HELP-microarray assay. We found 225,350 differentially methylated (DM) sites in adenocarcinomas versus adjacent non-tumor tissue that vary in frequency across genomic compartment, particularly notable in gene bodies (GB; p<2.2E-16). Further, when DM was coupled to differential transcriptome (DE) in the same samples, 37,056 differential loci in adenocarcinoma emerged. Approximately 90% of the DM-DE relationships were non-canonical; for example, promoter DM associated with DE in the same direction. Of the canonical changes noted, promoter (PR) DM loci with reciprocal changes in expression in adenocarcinomas included HBEGF, AGER, PTPRM, DPT, CST1, MELK; DM GB loci with concordant changes in expression included FOXM1, FERMT1, SLC7A5, and FAP genes. IPA analyses showed adenocarcinoma-specific promoter DMxDE overlay identified familiar lung cancer nodes [tP53, Akt] as well as less familiar nodes [HBEGF, NQO1, GRK5, VWF, HPGD, CDH5, CTNNAL1, PTPN13, DACH1, SMAD6, LAMA3, AR]. The unique findings from this study include the discovery of numerous candidate The unique findings from this study include the discovery of numerous candidate methylation sites in both PR and GB regions not previously identified in NSCLC, and many non-canonical relationships to gene expression. These DNA methylation features could potentially be developed as risk or diagnostic biomarkers, or as candidate targets for newer methylation locus-targeted preventive or therapeutic agents.

Ross-Adams H, Lamb AD, Dunning MJ, et al.
Integration of copy number and transcriptomics provides risk stratification in prostate cancer: A discovery and validation cohort study.
EBioMedicine. 2015; 2(9):1133-44 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Understanding the heterogeneous genotypes and phenotypes of prostate cancer is fundamental to improving the way we treat this disease. As yet, there are no validated descriptions of prostate cancer subgroups derived from integrated genomics linked with clinical outcome.
METHODS: In a study of 482 tumour, benign and germline samples from 259 men with primary prostate cancer, we used integrative analysis of copy number alterations (CNA) and array transcriptomics to identify genomic loci that affect expression levels of mRNA in an expression quantitative trait loci (eQTL) approach, to stratify patients into subgroups that we then associated with future clinical behaviour, and compared with either CNA or transcriptomics alone.
FINDINGS: We identified five separate patient subgroups with distinct genomic alterations and expression profiles based on 100 discriminating genes in our separate discovery and validation sets of 125 and 103 men. These subgroups were able to consistently predict biochemical relapse (p = 0.0017 and p = 0.016 respectively) and were further validated in a third cohort with long-term follow-up (p = 0.027). We show the relative contributions of gene expression and copy number data on phenotype, and demonstrate the improved power gained from integrative analyses. We confirm alterations in six genes previously associated with prostate cancer (MAP3K7, MELK, RCBTB2, ELAC2, TPD52, ZBTB4), and also identify 94 genes not previously linked to prostate cancer progression that would not have been detected using either transcript or copy number data alone. We confirm a number of previously published molecular changes associated with high risk disease, including MYC amplification, and NKX3-1, RB1 and PTEN deletions, as well as over-expression of PCA3 and AMACR, and loss of MSMB in tumour tissue. A subset of the 100 genes outperforms established clinical predictors of poor prognosis (PSA, Gleason score), as well as previously published gene signatures (p = 0.0001). We further show how our molecular profiles can be used for the early detection of aggressive cases in a clinical setting, and inform treatment decisions.
INTERPRETATION: For the first time in prostate cancer this study demonstrates the importance of integrated genomic analyses incorporating both benign and tumour tissue data in identifying molecular alterations leading to the generation of robust gene sets that are predictive of clinical outcome in independent patient cohorts.

Liu Y, Hu H, Zhang C, et al.
Co-expression of mitosis-regulating genes contributes to malignant progression and prognosis in oligodendrogliomas.
Oncotarget. 2015; 6(35):38257-69 [PubMed] Free Access to Full Article Related Publications
The clinical prognosis of patients with glioma is determined by tumor grades, but tumors of different subtypes with equal malignancy grade usually have different prognosis that is largely determined by genetic abnormalities. Oligodendrogliomas (ODs) are the second most common type of gliomas. In this study, integrative analyses found that distribution of TCGA transcriptomic subtypes was associated with grade progression in ODs. To identify critical gene(s) associated with tumor grades and TCGA subtypes, we analyzed 34 normal brain tissue (NBT), 146 WHO grade II and 130 grade III ODs by microarray and RNA sequencing, and identified a co-expression network of six genes (AURKA, NDC80, CENPK, KIAA0101, TIMELESS and MELK) that was associated with tumor grades and TCGA subtypes as well as Ki-67 expression. Validation of the six genes was performed by qPCR in additional 28 ODs. Importantly, these genes also were validated in four high-grade recurrent gliomas and the initial lower-grade gliomas resected from the same patients. Finally, the RNA data on two genes with the highest discrimination potential (AURKA and NDC80) and Ki-67 were validated on an independent cohort (5 NBTs and 86 ODs) by immunohistochemistry. Knockdown of AURKA and NDC80 by siRNAs suppressed Ki-67 expression and proliferation of gliomas cells. Survival analysis showed that high expression of the six genes corporately indicated a poor survival outcome. Correlation and protein interaction analysis provided further evidence for this co-expression network. These data suggest that the co-expression of the six mitosis-regulating genes was associated with malignant progression and prognosis in ODs.

Beke L, Kig C, Linders JT, et al.
MELK-T1, a small-molecule inhibitor of protein kinase MELK, decreases DNA-damage tolerance in proliferating cancer cells.
Biosci Rep. 2015; 35(6) [PubMed] Free Access to Full Article Related Publications
Maternal embryonic leucine zipper kinase (MELK), a serine/threonine protein kinase, has oncogenic properties and is overexpressed in many cancer cells. The oncogenic function of MELK is attributed to its capacity to disable critical cell-cycle checkpoints and reduce replication stress. Most functional studies have relied on the use of siRNA/shRNA-mediated gene silencing. In the present study, we have explored the biological function of MELK using MELK-T1, a novel and selective small-molecule inhibitor. Strikingly, MELK-T1 triggered a rapid and proteasome-dependent degradation of the MELK protein. Treatment of MCF-7 (Michigan Cancer Foundation-7) breast adenocarcinoma cells with MELK-T1 induced the accumulation of stalled replication forks and double-strand breaks that culminated in a replicative senescence phenotype. This phenotype correlated with a rapid and long-lasting ataxia telangiectasia-mutated (ATM) activation and phosphorylation of checkpoint kinase 2 (CHK2). Furthermore, MELK-T1 induced a strong phosphorylation of p53 (cellular tumour antigen p53), a prolonged up-regulation of p21 (cyclin-dependent kinase inhibitor 1) and a down-regulation of FOXM1 (Forkhead Box M1) target genes. Our data indicate that MELK is a key stimulator of proliferation by its ability to increase the threshold for DNA-damage tolerance (DDT). Thus, targeting MELK by the inhibition of both its catalytic activity and its protein stability might sensitize tumours to DNA-damaging agents or radiation therapy by lowering the DNA-damage threshold.

Almamun M, Levinson BT, van Swaay AC, et al.
Integrated methylome and transcriptome analysis reveals novel regulatory elements in pediatric acute lymphoblastic leukemia.
Epigenetics. 2015; 10(9):882-90 [PubMed] Free Access to Full Article Related Publications
Acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in children under the age of 15. In addition to genetic aberrations, epigenetic modifications such as DNA methylation are altered in cancer and impact gene expression. To identify epigenetic alterations in ALL, genome-wide methylation profiles were generated using the methylated CpG island recovery assay followed by next-generation sequencing. More than 25,000 differentially methylated regions (DMR) were observed in ALL patients with ∼ 90% present within intronic or intergenic regions. To determine the regulatory potential of the DMR, whole-transcriptome analysis was performed and integrated with methylation data. Aberrant promoter methylation was associated with the altered expression of genes involved in transcriptional regulation, apoptosis, and proliferation. Novel enhancer-like sequences were identified within intronic and intergenic DMR. Aberrant methylation in these regions was associated with the altered expression of neighboring genes involved in cell cycle processes, lymphocyte activation and apoptosis. These genes include potential epi-driver genes, such as SYNE1, PTPRS, PAWR, HDAC9, RGCC, MCOLN2, LYN, TRAF3, FLT1, and MELK, which may provide a selective advantage to leukemic cells. In addition, the differential expression of epigenetic modifier genes, pseudogenes, and non-coding RNAs was also observed accentuating the role of erroneous epigenetic gene regulation in ALL.

Sun L, Li J, Yan B
Gene expression profiling analysis of osteosarcoma cell lines.
Mol Med Rep. 2015; 12(3):4266-72 [PubMed] Free Access to Full Article Related Publications
Osteosarcoma (OS) is the most common type of primary bone malignancy and has a poor prognosis. To investigate the mechanisms of osteosarcoma, the present analyzed the GSE28424 microarray. GSE28424 was downloaded from the Gene Expression Omnibus, and included a collective of 19 OS cell lines and four normal bone cell lines, which were used as controls. Subsequently, the differentially expressed genes (DEGs) were screened using the Limma package in Bioconductor. Gene Ontology (GO) and pathway enrichment analysis of the DEGs was performed using the Database for Annotation, Visualization and Integrated Discovery, interactions between the proteins encoded by the DEGs were identified using STRING, and the protein‑protein interaction (PPI) network was visualized using Cytoscape. In addition, modular analysis of the PPI network was performed using the Clique Percolation Method (CPM) in CFinder. A total of 1,170 DEGs were screened, including 530 upreguated and 640 downregulated genes. The enriched functions included organelle fission, immune response and response to wounding. In addition, RPL8 was observed to be involved with the ribosomal pathway in module A of the PPI network of the DEGs. PLCG1, SYK and PLCG2 were also involved in the B‑cell receptor signaling pathway in module B and the Fc‑epsilon RI signaling pathway in module C. In addition, AURKA (degree=39), MAD2L1 (degree=38), CDCA8 (degree=38), BUB1 (degree=37) and MELK (degree=37) exhibited higher degrees of connectivity in module F. The results of the present study suggested that the RPL8, PLCG1, PLCG2, SYK, MAD2L1, AURKA, CDCA8, BUB1 and MELK genes may be involved in OS.

Liu R, Lv QL, Yu J, et al.
Correlating transcriptional networks with pathological complete response following neoadjuvant chemotherapy for breast cancer.
Breast Cancer Res Treat. 2015; 151(3):607-18 [PubMed] Related Publications
We aimed to investigate the association between gene co-expression modules and responses to neoadjuvant chemotherapy in breast cancer by using a systematic biological approach. The gene expression profiles and clinico-pathological data of 508 (discovery set) and 740 (validation set) patients with breast cancer who received neoadjuvant chemotherapy were analyzed. Weighted gene co-expression network analysis was performed and identified seven co-regulated gene modules. Each module and gene signature were evaluated with logistic regression models for pathological complete response (pCR). The association between modules and pCR in each intrinsic molecular subtype was also investigated. Two transcriptional modules were correlated with tumor grade, estrogen receptor status, progesterone receptor status, and chemotherapy response in breast cancer. One module that constitutes upregulated cell proliferation genes was associated with a high probability for pCR in the whole (odds ratio (OR) = 5.20 and 3.45 in the discovery and validation datasets, respectively), luminal B, and basal-like subtypes. The prognostic potentials of novel genes, such as MELK, and pCR-related genes, such as ESR1 and TOP2A, were identified. The upregulation of another gene co-expression module was associated with weak chemotherapy responses (OR = 0.19 and 0.33 in the discovery and validation datasets, respectively). The novel gene CA12 was identified as a potential prognostic indicator in this module. A systems biology network-based approach may facilitate the discovery of biomarkers for predicting chemotherapy responses in breast cancer and contribute in developing personalized medicines.

Liu W, Selçuk F, Rütgen BC, et al.
Evaluation of Stem Cell Marker Expression in Canine B-Cell Lymphoma Cell Lines, B-Cell Lymphoma-generated Spheres and Primary Samples.
Anticancer Res. 2015; 35(5):2805-16 [PubMed] Related Publications
BACKGROUND: Canine lymphoma has lately drawn focus as a model of human non-Hodgkin's lymphoma due to its spontaneous occurrence and similar biological behavior. Cells with stem cell-like characteristics are believed to play a key role in therapeutic failure. Thus, an initial characterization and the possibility of specific detection of such cells could bear significant value.
MATERIALS AND METHODS: Expression of 12 stem cell markers were analyzed in two canine B-cell lymphoma cell lines, their generated spheres, and in primary lymphoma samples by quantitative real-time polymerase chain reaction and partially by flow cytometry and immunocytochemistry.
RESULTS: Expression of maternal embryonic leucine zipper kinase (Melk) was significantly higher in CLBL-1, CLBL-1M and in primary B-cell lymphoma samples compared to non-neoplastic lymph nodes. Spheres displayed a higher expression of v-myc myelocytomatosis viral oncogene homolog (Myc) and lower expression of Cd44 compared to original cell lines and primary B-cell lymphoma samples.
CONCLUSION: The results suggest a potential interesting role of Melk in canine B-cell lymphoma. Furthermore, the up-regulation of Myc in serum-free-generated spheres offers interesting possibilities for functional assays characterizing the specific generated sub-population.

Liu R, Guo CX, Zhou HH
Network-based approach to identify prognostic biomarkers for estrogen receptor-positive breast cancer treatment with tamoxifen.
Cancer Biol Ther. 2015; 16(2):317-24 [PubMed] Free Access to Full Article Related Publications
This study aims to identify effective gene networks and prognostic biomarkers associated with estrogen receptor positive (ER+) breast cancer using human mRNA studies. Weighted gene coexpression network analysis was performed with a complex ER+ breast cancer transcriptome to investigate the function of networks and key genes in the prognosis of breast cancer. We found a significant correlation of an expression module with distant metastasis-free survival (HR = 2.25; 95% CI .21.03-4.88 in discovery set; HR = 1.78; 95% CI = 1.07-2.93 in validation set). This module contained genes enriched in the biological process of the M phase. From this module, we further identified and validated 5 hub genes (CDK1, DLGAP5, MELK, NUSAP1, and RRM2), the expression levels of which were strongly associated with poor survival. Highly expressed MELK indicated poor survival in luminal A and luminal B breast cancer molecular subtypes. This gene was also found to be associated with tamoxifen resistance. Results indicated that a network-based approach may facilitate the discovery of biomarkers for the prognosis of ER+ breast cancer and may also be used as a basis for establishing personalized therapies. Nevertheless, before the application of this approach in clinical settings, in vivo and in vitro experiments and multi-center randomized controlled clinical trials are still needed.

Kim SH, Joshi K, Ezhilarasan R, et al.
EZH2 protects glioma stem cells from radiation-induced cell death in a MELK/FOXM1-dependent manner.
Stem Cell Reports. 2015; 4(2):226-38 [PubMed] Free Access to Full Article Related Publications
Glioblastoma (GBM)-derived tumorigenic stem-like cells (GSCs) may play a key role in therapy resistance. Previously, we reported that the mitotic kinase MELK binds and phosphorylates the oncogenic transcription factor FOXM1 in GSCs. Here, we demonstrate that the catalytic subunit of Polycomb repressive complex 2, EZH2, is targeted by the MELK-FOXM1 complex, which in turn promotes resistance to radiation in GSCs. Clinically, EZH2 and MELK are coexpressed in GBM and significantly induced in postirradiation recurrent tumors whose expression is inversely correlated with patient prognosis. Through a gain-and loss-of-function study, we show that MELK or FOXM1 contributes to GSC radioresistance by regulation of EZH2. We further demonstrate that the MELK-EZH2 axis is evolutionarily conserved in Caenorhabditis elegans. Collectively, these data suggest that the MELK-FOXM1-EZH2 signaling axis is essential for GSC radioresistance and therefore raise the possibility that MELK-FOXM1-driven EZH2 signaling can serve as a therapeutic target in irradiation-resistant GBM tumors.

Alachkar H, Mutonga MB, Metzeler KH, et al.
Preclinical efficacy of maternal embryonic leucine-zipper kinase (MELK) inhibition in acute myeloid leukemia.
Oncotarget. 2014; 5(23):12371-82 [PubMed] Free Access to Full Article Related Publications
Maternal embryonic leucine-zipper kinase (MELK), which was reported to be frequently up-regulated in various types of solid cancer, plays critical roles in formation and maintenance of cancer stem cells. However, little is known about the relevance of this kinase in hematologic malignancies. Here we report characterization of possible roles of MELK in acute myeloid leukemia (AML). MELK is expressed in AML cell lines and AML blasts with higher levels in less differentiated cells. MELK is frequently upregulated in AML with complex karyotypes and is associated with worse clinical outcome. MELK knockdown resulted in growth inhibition and apoptosis of leukemic cells. Hence, we investigated the potent anti-leukemia activity of OTS167, a small molecule MELK kinase inhibitor, in AML, and found that the compound induced cell differentiation and apoptosis as well as decreased migration of AML cells. MELK expression was positively correlated with the expression of FOXM1 as well as its downstream target genes. Furthermore, MELK inhibition resulted in downregulation of FOXM1 activity and the expression of its downstream targets. Taken together, and given that OTS167 is undergoing a phase I clinical trial in solid cancer, our study warrants clinical evaluation of this compound as a novel targeted therapy for AML patients.

Nakano I
Transcription factors as master regulator for cancer stemness: remove milk from fox?
Expert Rev Anticancer Ther. 2014; 14(8):873-5 [PubMed] Related Publications
Some cancers display a cellular hierarchy of varying differentiation states, as if they phenocopy the normal organ development processes. Accumulating evidence suggests that the molecular signals that control carcinogenesis, at least partially, overlap with those involved in organogenesis. Cancer stem cells (CSCs) at the apex of cellular hierarchy are likely one, if not the only, critical therapeutic target in cancers. The proto-oncogene FOXM1 is a transcription factor (TF) defined as a master regulator for a broad array of genes required for CSCs and therefore FOXM1 is overexpressed in various cancers. In general, therapeutic development for TFs is a challenging task. Recently, on the other hand, novel insight has been brought by the discovery of a protein complex of FOXM1 with the mitotic kinase MELK in CSCs in brain cancers, as this protein complex appears to be cancer-specific. This editorial describes FOXM1 signaling in cancers and its potential therapeutic development.

Du T, Qu Y, Li J, et al.
Maternal embryonic leucine zipper kinase enhances gastric cancer progression via the FAK/Paxillin pathway.
Mol Cancer. 2014; 13:100 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Elevated MELK expression is featured in multiple tumors and correlated with tumorigenesis and tumor development. This study is aimed to investigate the mechanisms of MELK-mediated development of gastric cancer.
METHODS: MELK expression levels in human gastric cancer were determined by quantitative-PCR and immunohistochemistry. The effect of MELK on cell activity was explored by knockdown and overexpression experiments. Cell growth was measured using the CCK-8 assay. Apoptosis and cell cycle distributions were analyzed by flow cytometry. Migration and invasion were tested using a transwell migration assay. Cytoskeletal changes were analyzed by immunofluorescence. To explore the molecular mechanism and effect of MELK on migration and invasion, Western blotting was used to analyze the FAK/Paxillin pathway and pull down assays for the activity of small Rho GTPases. In vivo tumorigenicity and peritoneal metastasis experiments were performed by tumor cell engraftment into nude mice.
RESULTS: MELK mRNA and protein expression were both elevated in human gastric cancer, and this was associated with chemoresistance to 5-fluorouracil (5-FU). Knockdown of MELK significantly suppressed cell proliferation, migration and invasion of gastric cancer both in vitro and in vivo, decreased the percentages of cells in the G1/G0 phase and increased those in the G2/M and S phases. Moreover, knockdown of MELK decreased the amount of actin stress fibers and inhibited RhoA activity. Finally, knockdown of MELK decreased the phosphorylation of the FAK and paxillin, and prevented gastrin-stimulated FAK/paxillin phosphorylation. By contrast, MELK overexpression had the opposite effect.
CONCLUSIONS: MELK promotes cell migration and invasion via the FAK/Paxillin pathway, and plays an important role in the occurrence and development of gastric cancer. MELK may be a potential target for treatment against gastric cancer.

Wang Y, Lee YM, Baitsch L, et al.
MELK is an oncogenic kinase essential for mitotic progression in basal-like breast cancer cells.
Elife. 2014; 3:e01763 [PubMed] Free Access to Full Article Related Publications
Despite marked advances in breast cancer therapy, basal-like breast cancer (BBC), an aggressive subtype of breast cancer usually lacking estrogen and progesterone receptors, remains difficult to treat. In this study, we report the identification of MELK as a novel oncogenic kinase from an in vivo tumorigenesis screen using a kinome-wide open reading frames (ORFs) library. Analysis of clinical data reveals a high level of MELK overexpression in BBC, a feature that is largely dependent on FoxM1, a master mitotic transcription factor that is also found to be highly overexpressed in BBC. Ablation of MELK selectively impairs proliferation of basal-like, but not luminal breast cancer cells both in vitro and in vivo. Mechanistically, depletion of MELK in BBC cells induces caspase-dependent cell death, preceded by defective mitosis. Finally, we find that Melk is not required for mouse development and physiology. Together, these data indicate that MELK is a normally non-essential kinase, but is critical for BBC and thus represents a promising selective therapeutic target for the most aggressive subtype of breast cancer.DOI:

Sarhadi VK, Lahti L, Scheinin I, et al.
Copy number alterations and neoplasia-specific mutations in MELK, PDCD1LG2, TLN1, and PAX5 at 9p in different neoplasias.
Genes Chromosomes Cancer. 2014; 53(7):579-88 [PubMed] Related Publications
Genetic alterations affecting 9p are commonly present in many cancer types and many cancer-related genes are located in this chromosomal region. We sequenced all of the genes located in a 32Mb region of 9p by targeted next generation sequencing (NGS) in 96 patients with different cancer types, including acute lymphoblastic leukemia, bone malignant fibrous histiocytoma/undifferentiated pleomorphic sarcoma, fibrosarcoma, Ewing's sarcoma, and lung carcinoma. Copy number alterations (CNA), and mutations were studied from the NGS data. We detected a deletion at the CDKN2A locus as being the most frequent genetic alteration in all cancer types. In addition to this locus, NGS also identified other small regions of copy number loss and gain. However, different cancer types did not reveal any statistically significant differences with regard to CNA frequency or type. Of the 191 genes within the target region, two novel recurrent mutations were found in the MELK and PDCD1LG2 genes. The most commonly mutated gene in sarcomas was TLN1 (8%) and PAX5 in ALL (9%). Mutations in PAX5, and RUSC2, were seen exclusively in ALL patients and those in KIAA1432, CA9, TLN1, and MELK only in sarcomas (MFH, FS, EFT). Thus using targeted NGS of the 9p region, in addition to commonly deleted CDKN2A locus, we were able to identify a number of small deletions and gains, as well as novel recurrent mutations in different cancer types. © 2014 Wiley Periodicals, Inc.

Warsow G, Struckmann S, Kerkhoff C, et al.
Differential network analysis applied to preoperative breast cancer chemotherapy response.
PLoS One. 2013; 8(12):e81784 [PubMed] Free Access to Full Article Related Publications
In silico approaches are increasingly considered to improve breast cancer treatment. One of these treatments, neoadjuvant TFAC chemotherapy, is used in cases where application of preoperative systemic therapy is indicated. Estimating response to treatment allows or improves clinical decision-making and this, in turn, may be based on a good understanding of the underlying molecular mechanisms. Ever increasing amounts of high throughput data become available for integration into functional networks. In this study, we applied our software tool ExprEssence to identify specific mechanisms relevant for TFAC therapy response, from a gene/protein interaction network. We contrasted the resulting active subnetwork to the subnetworks of two other such methods, OptDis and KeyPathwayMiner. We could show that the ExprEssence subnetwork is more related to the mechanistic functional principles of TFAC therapy than the subnetworks of the other two methods despite the simplicity of ExprEssence. We were able to validate our method by recovering known mechanisms and as an application example of our method, we identified a mechanism that may further explain the synergism between paclitaxel and doxorubicin in TFAC treatment: Paclitaxel may attenuate MELK gene expression, resulting in lower levels of its target MYBL2, already associated with doxorubicin synergism in hepatocellular carcinoma cell lines. We tested our hypothesis in three breast cancer cell lines, confirming it in part. In particular, the predicted effect on MYBL2 could be validated, and a synergistic effect of paclitaxel and doxorubicin could be demonstrated in the breast cancer cell lines SKBR3 and MCF-7.

Jiang P, Zhang D
Maternal embryonic leucine zipper kinase (MELK): a novel regulator in cell cycle control, embryonic development, and cancer.
Int J Mol Sci. 2013; 14(11):21551-60 [PubMed] Free Access to Full Article Related Publications
Maternal embryonic leucine zipper kinase (MELK) functions as a modulator of intracellular signaling and affects various cellular and biological processes, including cell cycle, cell proliferation, apoptosis, spliceosome assembly, gene expression, embryonic development, hematopoiesis, and oncogenesis. In these cellular processes, MELK functions by binding to numerous proteins. In general, the effects of multiple protein interactions with MELK are oncogenic in nature, and the overexpression of MELK in kinds of cancer provides some evidence that it may be involved in tumorigenic process. In this review, our current knowledge of MELK function and recent discoveries in MELK signaling pathway were discussed. The regulation of MELK in cancers and its potential as a therapeutic target were also described.

Joshi K, Banasavadi-Siddegowda Y, Mo X, et al.
MELK-dependent FOXM1 phosphorylation is essential for proliferation of glioma stem cells.
Stem Cells. 2013; 31(6):1051-63 [PubMed] Free Access to Full Article Related Publications
Glioblastoma multiforme (GBM) is a life-threatening brain tumor. Accumulating evidence suggests that eradication of glioma stem-like cells (GSCs) in GBM is essential to achieve cure. The transcription factor FOXM1 has recently gained attention as a master regulator of mitotic progression of cancer cells in various organs. Here, we demonstrate that FOXM1 forms a protein complex with the mitotic kinase MELK in GSCs, leading to phosphorylation and activation of FOXM1 in a MELK kinase-dependent manner. This MELK-dependent activation of FOXM1 results in a subsequent increase in mitotic regulatory genes in GSCs. MELK-driven FOXM1 activation is regulated by the binding and subsequent trans-phosphorylation of FOXM1 by another kinase PLK1. Using mouse neural progenitor cells (NPCs), we found that transgenic expression of FOXM1 enhances, while siRNA-mediated gene silencing diminishes neurosphere formation, suggesting that FOXM1 is required for NPC growth. During tumorigenesis, FOXM1 expression sequentially increases as cells progress from NPCs, to pretumorigenic progenitors and GSCs. The antibiotic Siomycin A disrupts MELK-mediated FOXM1 signaling with a greater sensitivity in GSC compared to neural stem cell. Treatment with the first-line chemotherapy agent for GBM, Temozolomide, paradoxically enriches for both FOXM1 (+) and MELK (+) cells in GBM cells, and addition of Siomycin A to Temozolomide treatment in mice harboring GSC-derived intracranial tumors enhances the effects of the latter. Collectively, our data indicate that FOXM1 signaling through its direct interaction with MELK regulates key mitotic genes in GSCs in a PLK1-dependent manner and thus, this protein complex is a potential therapeutic target for GBM.

Li Y, Tang H, Sun Z, et al.
Network-based approach identified cell cycle genes as predictor of overall survival in lung adenocarcinoma patients.
Lung Cancer. 2013; 80(1):91-8 [PubMed] Free Access to Full Article Related Publications
Lung adenocarcinoma is the most common type of primary lung cancer. The purpose of this study was to delineate gene expression patterns for survival prediction in lung adenocarcinoma. Gene expression profiles of 82 (discovery set) and 442 (validation set 1) lung adenocarcinoma tumor tissues were analyzed using a systems biology-based network approach. We also examined the expression profiles of 78 adjacent normal lung tissues from 82 patients. We found a significant correlation of an expression module with overall survival (adjusted hazard ratio or HR=1.71; 95% CI=1.06-2.74 in discovery set; adjusted HR=1.26; 95% CI=1.08-1.49 in validation set 1). This expression module contained genes enriched in the biological process of the cell cycle. Interestingly, the cell cycle gene module and overall survival association were also significant in normal lung tissues (adjusted HR=1.91; 95% CI, 1.32-2.75). From these survival-related modules, we further defined three hub genes (UBE2C, TPX2, and MELK) whose expression-based risk indices were more strongly associated with poor 5-year survival (HR=3.85, 95% CI=1.34-11.05 in discovery set; HR=1.72, 95% CI=1.21-2.46 in validation set 1; and HR=3.35, 95% CI=1.08-10.04 in normal lung set). The 3-gene prognostic result was further validated using 92 adenocarcinoma tumor samples (validation set 2); patients with a high-risk gene signature have a 1.52-fold increased risk (95% CI, 1.02-2.24) of death than patients with a low-risk gene signature. These results suggest that a network-based approach may facilitate discovery of key genes that are closely linked to survival in patients with lung adenocarcinoma.

Gu C, Banasavadi-Siddegowda YK, Joshi K, et al.
Tumor-specific activation of the C-JUN/MELK pathway regulates glioma stem cell growth in a p53-dependent manner.
Stem Cells. 2013; 31(5):870-81 [PubMed] Free Access to Full Article Related Publications
Accumulated evidence suggests that glioma stem cells (GSCs) may contribute to therapy resistance in high-grade glioma (HGG). Although recent studies have shown that the serine/threonine kinase maternal embryonic leucine-zipper kinase (MELK) is abundantly expressed in various cancers, the function and mechanism of MELK remain elusive. Here, we demonstrate that MELK depletion by shRNA diminishes the growth of GSC-derived mouse intracranial tumors in vivo, induces glial fibrillary acidic protein (+) glial differentiation of GSCs leading to decreased malignancy of the resulting tumors, and prolongs survival periods of tumor-bearing mice. Tissue microarray analysis with 91 HGG tumors demonstrates that the proportion of MELK (+) cells is a statistically significant indicator of postsurgical survival periods. Mechanistically, MELK is regulated by the c-Jun NH(2)-terminal kinase (JNK) signaling and forms a complex with the oncoprotein c-JUN in GSCs but not in normal progenitors. MELK silencing induces p53 expression, whereas p53 inhibition induces MELK expression, indicating that MELK and p53 expression are mutually exclusive. Additionally, MELK silencing-mediated GSC apoptosis is partially rescued by both pharmacological p53 inhibition and p53 gene silencing, indicating that MELK action in GSCs is p53 dependent. Furthermore, irradiation of GSCs markedly elevates MELK mRNA and protein expression both in vitro and in vivo. Clinically, recurrent HGG tumors following the failure of radiation and chemotherapy exhibit a statistically significant elevation of MELK protein compared with untreated newly diagnosed HGG tumors. Together, our data indicate that GSCs, but not normal cells, depend on JNK-driven MELK/c-JUN signaling to regulate their survival, maintain GSCs in an immature state, and facilitate tumor radioresistance in a p53-dependent manner.

Komatsu M, Yoshimaru T, Matsuo T, et al.
Molecular features of triple negative breast cancer cells by genome-wide gene expression profiling analysis.
Int J Oncol. 2013; 42(2):478-506 [PubMed] Related Publications
Triple negative breast cancer (TNBC) has a poor outcome due to the lack of beneficial therapeutic targets. To clarify the molecular mechanisms involved in the carcinogenesis of TNBC and to identify target molecules for novel anticancer drugs, we analyzed the gene expression profiles of 30 TNBCs as well as 13 normal epithelial ductal cells that were purified by laser-microbeam microdissection. We identified 301 and 321 transcripts that were significantly upregulated and downregulated in TNBC, respectively. In particular, gene expression profile analyses of normal human vital organs allowed us to identify 104 cancer-specific genes, including those involved in breast carcinogenesis such as NEK2, PBK and MELK. Moreover, gene annotation enrichment analysis revealed prominent gene subsets involved in the cell cycle, especially mitosis. Therefore, we focused on cell cycle regulators, asp (abnormal spindle) homolog, microcephaly-associated (Drosophila) (ASPM) and centromere protein K (CENPK) as novel therapeutic targets for TNBC. Small-interfering RNA-mediated knockdown of their expression significantly attenuated TNBC cell viability due to G1 and G2/M cell cycle arrest. Our data will provide a better understanding of the carcinogenesis of TNBC and could contribute to the development of molecular targets as a treatment for TNBC patients.

Kuner R, Fälth M, Pressinotti NC, et al.
The maternal embryonic leucine zipper kinase (MELK) is upregulated in high-grade prostate cancer.
J Mol Med (Berl). 2013; 91(2):237-48 [PubMed] Related Publications
Loss of cell cycle control is a prerequisite for cancer onset and progression. In prostate cancer, increased activity of cell cycle genes has been associated with prognostic parameters such as biochemical relapse and survival. The identification of novel oncogenic and druggable targets in patient subgroups with poor prognosis may help to develop targeted therapy approaches. We analyzed prostate cancer and corresponding benign tissues (n = 98) using microarrays. The comparison of high- and low-grade tumors (Gleason score ≥ 4 + 3 vs. ≤ 3 + 4) revealed 144 differentially expressed genes (p < 0.05). Out of these, 15 genes were involved in the cell cycle process. The gene maternal embryonic leucine zipper kinase (MELK) was identified to be highly correlated with cell cycle genes like UBE2C, TOP2A, CCNB2, and AURKB. Increased MELK gene expression in high-risk prostate cancer was validated by qPCR in an independent patient cohort (p < 0.005, n = 79). Immunohistochemistry analysis using a tissue microarray (n = 94) revealed increased MELK protein expression in prostate cancer tissues of high Gleason scores. RNAi-based inhibition of MELK in PC3 and LNCaP cells suggested putative function in chromatin modification, embryonic development and cell migration. The concerted inhibition of MELK and other cell cycle targets by the antibiotic siomycin A strongly impaired cell viability of prostate cancer cells, and may point to a novel therapy approach for a subset of high-risk prostate cancer patients.

Visnyei K, Onodera H, Damoiseaux R, et al.
A molecular screening approach to identify and characterize inhibitors of glioblastoma stem cells.
Mol Cancer Ther. 2011; 10(10):1818-28 [PubMed] Free Access to Full Article Related Publications
Glioblastoma (GBM) is among the most lethal of all cancers. GBM consist of a heterogeneous population of tumor cells among which a tumor-initiating and treatment-resistant subpopulation, here termed GBM stem cells, have been identified as primary therapeutic targets. Here, we describe a high-throughput small molecule screening approach that enables the identification and characterization of chemical compounds that are effective against GBM stem cells. The paradigm uses a tissue culture model to enrich for GBM stem cells derived from human GBM resections and combines a phenotype-based screen with gene target-specific screens for compound identification. We used 31,624 small molecules from 7 chemical libraries that we characterized and ranked based on their effect on a panel of GBM stem cell-enriched cultures and their effect on the expression of a module of genes whose expression negatively correlates with clinical outcome: MELK, ASPM, TOP2A, and FOXM1b. Of the 11 compounds meeting criteria for exerting differential effects across cell types used, 4 compounds showed selectivity by inhibiting multiple GBM stem cells-enriched cultures compared with nonenriched cultures: emetine, n-arachidonoyl dopamine, n-oleoyldopamine (OLDA), and n-palmitoyl dopamine. ChemBridge compounds #5560509 and #5256360 inhibited the expression of the 4 mitotic module genes. OLDA, emetine, and compounds #5560509 and #5256360 were chosen for more detailed study and inhibited GBM stem cells in self-renewal assays in vitro and in a xenograft model in vivo. These studies show that our screening strategy provides potential candidates and a blueprint for lead compound identification in larger scale screens or screens involving other cancer types.

Choi S, Ku JL
Resistance of colorectal cancer cells to radiation and 5-FU is associated with MELK expression.
Biochem Biophys Res Commun. 2011; 412(2):207-13 [PubMed] Related Publications
It was reported that the local recurrence would be caused by cancer stem cells acquiring chemo- and radio-resistance. Recently, one of the potential therapeutic targets for colorectal and other cancers has been identified, which is maternal embryonic leucine zipper kinase (MELK). MELK is known as an embryonic and neural stem cell marker, and associated with the cell survival, cell proliferation, and apoptosis. In this study, SNU-503, which is a rectal cancer cell line, was treated with radiation or 5-fluorouracil (5-FU), and elevation of the MELK expression level was observed. Furthermore, the cell line was pre-treated with small interfering RNA (siRNA) against MELK mRNA before treatment of radiation or 5-FU and its effects on cell cycle and proliferation were observed. We demonstrated that knockdown of MELK reduced the proliferation of cells with radiation or 5-FU treatment. In addition, MELK suppression caused changes in cell cycle. In conclusion, MELK could be associated with increased resistance of colorectal cancer cells against radiation and 5-FU.

Al-Mayhani MT, Grenfell R, Narita M, et al.
NG2 expression in glioblastoma identifies an actively proliferating population with an aggressive molecular signature.
Neuro Oncol. 2011; 13(8):830-45 [PubMed] Free Access to Full Article Related Publications
Glioblastoma multiforme (GBM) is the most common type of primary brain tumor and a highly malignant and heterogeneous cancer. Current conventional therapies fail to eradicate or curb GBM cell growth. Hence, exploring the cellular and molecular basis of GBM cell growth is vital to develop novel therapeutic approaches. Neuroglia (NG)-2 is a transmembrane proteoglycan expressed by NG2+ progenitors and is strongly linked to cell proliferation in the normal brain. By using NG2 as a biomarker we identify a GBM cell population (GBM NG2+ cells) with robust proliferative, clonogenic, and tumorigenic capacity. We show that a significant proportion (mean 83%) of cells proliferating in the tumor mass express NG2 and that over 50% of GBM NG2+ cells are proliferating. Compared with the GBM NG2- cells from the same tumor, the GBM of NG2+ cells overexpress genes associated with aggressive tumorigenicity, including overexpression of Mitosis and Cell Cycling Module genes (e.g., MELK, CDC, MCM, E2F), which have been previously shown to correlate with poor survival in GBM. We also show that the coexpression pattern of NG2 with other glial progenitor markers in GBM does not recapitulate that described in the normal brain. The expression of NG2 by such an aggressive and actively cycling GBM population combined with its location on the cell surface identifies this cell population as a potential therapeutic target in a subset of patients with GBM.

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