MELK is an oncogenic kinase essential for mitotic progression in basal-like breast cancer cells

MELK as a Mediator of Stemness and Metastasis in Aggressive Subtypes of Breast Cancer

Triple-negative breast cancer (TNBC) is the breast cancer subtype with the poorest prognosis and lacks actionable molecular targets for treatment. Maternal embryonic leucine zipper kinase (MELK) is highly expressed in TNBC and has been implicated in poor clinical outcomes, though its mechanistic role in the aggressive biology of TNBC is poorly understood. Here, we demonstrate a role of MELK in TNBC progression and metastasis. Analysis of publicly available datasets revealed that high MELK expression correlates with worse overall survival, recurrence-free survival, and distant metastasis-free survival, and MELK is co-expressed with metastasis-related genes. Functional studies demonstrated that MELK inhibition, using genomic or pharmacologic inhibition, reduces mammosphere formation, migration, and invasion in high-MELK-expressing TNBC cell lines. Conversely, MELK overexpression in low-MELK-expressing cell lines significantly increased invasive capacity in vitro and metastatic potential in vivo, as evidenced by enhanced metastasis to the liver and lungs in a chorioallantoic membrane assay. These findings highlight MELK as a key regulator of TNBC aggressiveness and support its potential as a therapeutic target to mitigate metastasis and improve patient outcomes.

Targeting MELK in tumor cells and tumor microenvironment: from function and mechanism to therapeutic application

Maternal embryonic leucine zipper kinase (MELK), a member of the adenosine monophosphate-activated protein kinase (AMPK) protein family, has been reported to be involved in the regulation of many cellular events. The aberrant expression of MELK is associated with tumorigenesis and malignant progression of various tumors. Moreover, MELK plays an essential role in the regulation of tumor microenvironment (TME), which affects the function of immune cells and the responsiveness to immunotherapy. Currently, small molecule inhibitors targeting MELK have been developed and evaluated in clinical trials. A comprehensive understanding of MELK may provide clues and confidence for subsequent basic research and scientific transformation. In this review, we provide a comprehensive overview of the structural features, molecular biological functions, and critical roles of MELK in tumors and TME, as well as the targeted agents under development for the treatment of tumors and discuss the perspective for MELK-targeted therapies for tumors.

Phytochemical-Based Drug Discovery for Breast Cancer: Combining Virtual Screening and Molecular Dynamics to Identify Novel Therapeutics

Maternal embryonic leucine zipper kinase (MELK), a pivotal signaling protein, plays a crucial role in various physiological processes, such as cell growth, survival, and differentiation. There is currently a growing interest in MELK as a promising therapeutic target for multiple cancers, including triple-negative breast cancer (TNBC). Exploring MELK as a target offers a prospective strategy to impede cancer progression and enhance the efficacy of conventional anticancer therapies. In this study, we employed a multistep docking procedure to evaluate the anticancer potential of phyto-compounds from the NPACT and PhytoHub databases targeting the MELK protein. A collection of 23 740 compounds underwent hierarchical multistep docking, accompanied by an analysis of binding interactions. The extensive analysis identified five compounds (PHUB000697, PHUB002010, NPACT00373, PHUB002005, and PHUB001739) as potent inhibitors of the MELK protein, exhibiting docking scores lower than -11 Kcal/mol, that is, -12.90, -12.00, -11.23, -11.19, and -11.09 Kcal/mol, respectively. PHUB000697 exhibited very crucial interactions with Gly20, Lys40, Cys89, and Glu93 (2.74 Å). To evaluate the stability of protein-ligand interactions in dynamic states, 100 ns molecular dynamics (MD) simulations were conducted using the entire trajectory, revealing a substantial binding affinity for all identified compounds toward the MELK protein. Consequently, these five compounds emerge as promising candidates for future drug development targeting the MELK protein in treating TNBC. However, experimental assessment is essential to understand the molecular interaction mechanisms better. We are aiming to report a few in vitro and in vivo studies on these compounds to validate the computational results.

CDKN3 as a key regulator of G2M phase in triple-negative breast cancer: Insights from multi-transcriptomic analysis

Triple-negative breast cancer (TNBC) remains a significant global health challenge, emphasizing the need for precise identification of patients with specific therapeutic targets and those at high risk of metastasis. This study aimed to identify novel therapeutic targets for personalized treatment of TNBC patients by elucidating their roles in cell cycle regulation. Using weighted gene co-expression network analysis (WGCNA), we identified 83 hub genes by integrating gene expression profiles with clinical pathological grades. A machine learning-based integrative approach further pinpointed 12 prognostic genes, among which CDKN3 exhibited the highest hazard ratio and the most adverse impact on overall survival (OS) in BC patients. Additionally, CDKN3 was identified as an independent prognostic factor for OS prediction. CDKN3 overexpression was confirmed in BC patients and validated at both mRNA and protein levels in BC cells. Knockdown of CDKN3 significantly inhibited the migration and proliferation of BC cells. Cell cycle pathway analysis revealed significant enrichment in G2M-associated pathways in BC patients, with multi-transcriptomic data indicating a close association between enhanced G2M cell cycle activity and CDKN3 upregulation in basal cancer subtypes. Pseudotime analysis further suggested CDKN3 upregulation during the G2M phase at the terminal trajectory of basal cancer subtypes, implying that CDKN3 may drive BC cell progression by promoting G2M cell cycle activity. Mechanistically, CDKN3 knockdown induced G2M cell cycle arrest in TNBC cells by downregulating CCNB2. In conclusion, CDKN3 knockdown effectively inhibits TNBC by arresting the G2M cell cycle, underscoring CDKN3 as a promising therapeutic target in TNBC treatment.

Spatiotemporal regulation of MELK during mitosis

Maternal Embryonic Leucine Zipper Kinase (MELK) has been studied intensively in recent years due to its overexpression in multiple cancers. However, the cell biology of MELK remains less characterized despite its well-documented association with mitosis. Here we report a distinctive pattern of human MELK that translocates from the cytoplasm to cell cortex within 3 min of anaphase onset. The cortex association lasts about 30 min till telophase. The spatiotemporal specific localization of MELK depends on the interaction between its Threonine-Proline (TP) rich domain and kinase associated 1 (KA1) domain, which is regulated by CDK1 kinase and PP4 protein phosphatase. KA1 domains are known to regulate kinase activities through various intramolecular interactions. Our results revealed a new role for KA1 domain to control subcellular localization of a protein kinase.

SUV39H1 Expression as a Guideline for Omitting Radiotherapy in Lymph Node-positive Triple-negative Breast Cancer Patients

BACKGROUND/AIM

The role of postoperative radiotherapy (RT) combined with chemotherapy (CT) for lymph node-positive (LN+) triple-negative breast cancer (TNBC) remains controversial. SUV39H1-mediated epigenetic regulation is associated with cancer cell migration, invasion, metastasis, and treatment resistance. This study aims to identify the role of SUV39H1 in TNBCs.

MATERIALS AND METHODS

Overall, 498 TNBCs with SUV39H1 RNA-seq profiles were retrieved from TCGA-BRCA and analyzed; the X-tile algorithm was used to stratify the population into low, intermediate, and high SUV39H1. Furthermore, we performed an in vitro clonogenic cell survival assay using the MDA-MB-231 cell line to assess the effects of SUV39H1 on cellular responses.

RESULTS

The results showed that SUV39H1 was significantly higher in TNBC than normal tissue and luminal subtype breast cancer. Notably, SUV39H1 is significantly expressed in the basal-like 1 (BL1) and immunomodulatory (IM) subgroups, compared to other subtypes. Compared to patients with a low or medium expression of SUV39H1, omitting RT only worsens disease-free survival (DFS) in those with high SUV39H1 expression. The experimental results showed SUV39H1 was suppressed by si-SUV39H1, and SUV39H1 knockdown in MDA-MB-231-IV2-1 cells enhanced the cellular toxicity of doxorubicin and paclitaxel.

CONCLUSION

Targeting SUV39H1 may provide a potential guiding indication of omitting RT to avoid over-treatment and chemosensitivity for TNBC.

Targeting the oncogenic transcription factor FOXM1 to improve outcomes in all subtypes of breast cancer

FOXM1 (Forkhead box M1) is an oncogenic transcription factor that is greatly upregulated in breast cancer and many other cancers where it promotes tumorigenesis, and cancer growth and progression. It is expressed in all subtypes of breast cancer and is the factor most associated with risk of poor patient survival, especially so in triple negative breast cancer (TNBC). Thus, new approaches to inhibiting FOXM1 and its activities, and combination therapies utilizing FOXM1 inhibitors in conjunction with known cancer drugs that work together synergistically, could improve cancer treatment outcomes. Targeting FOXM1 might prove especially beneficial in TNBC where few targeted therapies currently exist, and also in suppressing recurrent advanced estrogen receptor (ER)-positive and HER2-positive breast cancers for which treatments with ER or HER2 targeted therapies that were effective initially are no longer beneficial. We present these perspectives and future directions in the context of what is known about FOXM1, its regulation, and its key roles in promoting cancer aggressiveness and metastasis, while being absent or very low in most normal non-regenerating adult tissues. We discuss new inhibitors of FOXM1 and highlight FOXM1 as an attractive target for controlling drug-resistant and difficult-to-suppress breast cancers, and how blocking FOXM1 might improve outcomes for patients with all subtypes of breast cancer.

Maternal Embryonic Leucine Zipper Kinase is Associated with Metastasis in Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) has high relapse and metastasis rates and a high proportion of cancer stem-like cells (CSC), which possess self-renewal and tumor initiation capacity. MELK (maternal embryonic leucine zipper kinase), a protein kinase of the Snf1/AMPK kinase family, is known to promote CSC maintenance and malignant transformation. However, the role of MELK in TNBC metastasis is unknown; we sought to address this in the current study. We found that MELK mRNA levels were higher in TNBC tumors [8.11 (3.79-10.95)] than in HR+HER2- tumors [6.54 (2.90-9.26)]; P < 0.001]. In univariate analysis, patients with breast cancer with high-MELK-expressing tumors had worse overall survival (P < 0.001) and distant metastasis-free survival (P < 0.01) than patients with low-MELK-expressing tumors. In a multicovariate Cox regression model, high MELK expression was associated with shorter overall survival after adjusting for other baseline risk factors. MELK knockdown using siRNA or MELK inhibition using the MELK inhibitor MELK-In-17 significantly reduced invasiveness, reversed epithelial-to-mesenchymal transition, and reduced CSC self-renewal and maintenance in TNBC cells. Nude mice injected with CRISPR MELK-knockout MDA-MB-231 cells exhibited suppression of lung metastasis and improved overall survival compared with mice injected with control cells (P < 0.05). Furthermore, MELK-In-17 suppressed 4T1 tumor growth in syngeneic BALB/c mice (P < 0.001). Our findings indicate that MELK supports metastasis by promoting epithelial-to-mesenchymal transition and the CSC phenotype in TNBC.

Significance

These findings indicate that MELK is a driver of aggressiveness and metastasis in TNBC.

Screening of potential hub genes and key pathways associated with breast cancer by bioinformatics tools

Breast cancer (BC) remains the leading cause of cancer-related death in women worldwide. The development of new targeted therapies that may improve patient survival remains an area of growing interest. This study aimed to identify new biomarkers involved in BC progression that could be used as potential targeted therapies. DEGs were selected from three gene expression profiles, GSE55715, GSE124646, and GSE87049, using the GEO2R tool and Venn diagram software. Gene Ontology and KEGG pathways were then performed using DAVID software. Next, the PPI network was constructed using STRING and visualized using Cytoscape software, and hub genes were extracted using the cytoHubba plug-in. Survival analysis was performed using the Kaplan-Meier Plotter, while the expression of hub genes in BC was verified using the GEPIA2 tool. Finally, transcription the factors of hub genes were determined using the NetworkAnalyst database, and the TIMER tool was employed to explore the infiltration levels of tumor immune cells with related genes. A total of 146 DEGs were identified in the three datasets, including 60 upregulated genes that were enriched in the cell cycle, and 86 downregulated genes that were mainly enriched in the TNF signaling pathway and pathways in cancer. Ten genes were identified: BUB1, CDK1, HMMR, MAD2L1, CEP55, AURKA, CCNB2, TPX2, MELK, and KIF20A. The overexpression of hub genes, except CDK1, was associated with poor survival in BC and was regulated by several transcription factors involved in DNA binding activity and transcription regulation. The infiltration levels of immune cells were positively correlated with hub genes, particularly macrophages and CD4+ T cells. This study identified new reliable molecular biomarkers that can serve as potential therapeutic targets for BC treatment.

Maternal embryonic leucine zipper kinase in tumor cell and tumor microenvironment: Emerging player and promising therapeutic opportunities

Maternal embryonic leucine zipper kinase (MELK) is a member of the AMPK (AMP-activated protein kinase) protein family, which is widely and highly expressed in multiple cancer types. Through direct and indirect interactions with other proteins, it mediates various cascades of signal transduction processes and plays an important role in regulating tumor cell survival, growth, invasion and migration and other biological functions. Interestingly, MELK also plays an important role in the regulation of the tumor microenvironment, which can not only predict the responsiveness of immunotherapy, but also affect the function of immune cells to regulate tumor progression. In addition, more and more small molecule inhibitors have been developed for the target of MELK, which exert important anti-tumor effects and have achieved excellent results in a number of clinical trials. In this review, we outline the structural features, molecular biological functions, potential regulatory mechanisms and important roles of MELK in tumors and tumor microenvironment, as well as substances targeting MELK. Although many molecular mechanisms of MELK in the process of tumor regulation are still unknown, it is worth affirming that MELK is a potential tumor molecular therapeutic target, and its unique superiority and important role provide clues and confidence for subsequent basic research and scientific transformation.

siRNA-Mediated MELK Knockdown Induces Accelerated Wound Healing with Increased Collagen Deposition

Skin wounds remain a significant problem for the healthcare system, affecting the clinical outcome, patients' quality of life, and financial costs. Reduced wound healing times would improve clinical, economic, and social aspects for both patients and the healthcare system. Skin wound healing has been studied for years, but effective therapy that leads to accelerated wound healing remains to be discovered. This study aimed to evaluate the potential of MELK silencing to accelerate wound healing. A vectorless, transient knockdown of the MELK gene using siRNA was performed in a murine skin wound model. The wound size, total collagen, type 3 collagen, vessel size, vessel number, cell proliferation, cell apoptosis, number of mast cells, and immune infiltration by CD45, CD11b, CD45, and CD8a cells were evaluated. We observed that treatment with MELK siRNA leads to significantly faster wound closing associated with increased collagen deposition.

Preclinical assessment of synergistic efficacy of MELK and CDK inhibitors in adrenocortical cancer

BACKGROUND

Adrenocortical cancer (ACC) is a rare and aggressive cancer with dismal 5-year survival due to a lack of effective treatments. We aimed to identify a new effective combination of drugs and investigated their synergistic efficacy in ACC preclinical models.

METHODS

A quantitative high-throughput drug screening of 4,991 compounds was performed on two ACC cell lines, SW13 and NCI-H295R, based on antiproliferative effect and caspase-3/7 activity. The top candidate drugs were pairwise combined to identify the most potent combinations. The synergistic efficacy of the selected inhibitors was tested on tumorigenic phenotypes, such as cell proliferation, migration, invasion, spheroid formation, and clonogenicity, with appropriate mechanistic validation by cell cycle and apoptotic assays and protein expression of the involved molecules. We tested the efficacy of the drug combination in mice with luciferase-tagged human ACC xenografts. To study the mRNA expression of target molecules in ACC and their clinical correlations, we analyzed the Gene Expression Omnibus and The Cancer Genome Atlas.

RESULTS

We chose the maternal embryonic leucine zipper kinase (MELK) inhibitor (OTS167) and cyclin-dependent kinase (CDK) inhibitor (RGB-286638) because of their potent synergy from the pairwise drug combination matrices derived from the top 30 single drugs. Multiple publicly available databases demonstrated overexpression of MELK, CDK1/2, and partnering cyclins mRNA in ACC, which were independently associated with mortality and other adverse clinical features. The drug combination demonstrated a synergistic antiproliferative effect on ACC cells. Compared to the single-agent treatment groups, the combination treatment increased G2/M arrest, caspase-dependent apoptosis, reduced cyclins A2, B1, B2, and E2 expression, and decreased cell migration and invasion with reduced vimentin. Moreover, the combination effectively decreased Foxhead Box M1, Axin2, glycogen synthase kinase 3-beta, and β-catenin. A reduction in p-stathmin from the combination treatment destabilized microtubule assembly by tubulin depolymerization. The drug combination treatment in mice with human ACC xenografts resulted in a significantly lower tumor burden than those treated with single-agents and vehicle control groups.

CONCLUSIONS

Our preclinical study revealed a novel synergistic combination of OTS167 and RGB-286638 in ACC that effectively targets multiple molecules associated with ACC aggressiveness. A phase Ib/II clinical trial in patients with advanced ACC is therefore warranted.

MELK predicts poor prognosis and promotes metastasis in esophageal squamous cell carcinoma via activating the NF‑κB pathway

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide with a low 5-year survival rate due to the lack of effective therapeutic strategies. Accumulating evidence has indicated that maternal embryonic leucine zipper kinase (MELK) is highly expressed in several tumors and associated with tumor development. However, the biological effects of MELK in ESCC remain unknown. In the present study, cell phenotypical experiments and animal metastasis assays were performed to detect the influence of MELK knockdown in vitro and in vivo. The potential molecular mechanism of MELK-mediated ESCC metastasis was further investigated by western blotting and immunofluorescence staining. The results revealed that the expression of MELK in human ESCC tissues was higher than that in adjacent normal tissues and was positively associated with the poor prognosis of patients. Reducing MELK expression resulted in growth inhibition and suppression of the invasive ability of ESCC cells in vitro and in vivo. MELK inhibition induced alterations of epithelial-mesenchymal transition-associated proteins. Mechanistically, MELK interacted with IκB kinase (IKK) and promoted the phosphorylation of IKK, by which MELK regulated activation of the NF-κB pathway. Collectively, the present study revealed the function and mechanism of MELK in the cell metastasis of ESCC, which may be a potential therapeutic target for ESCC.

Subtype-specific expression of MELK is partly due to copy number alterations in breast cancer

Maternal embryonic leucine-zipper kinase (MELK) regulates cell cycle progression and is highly expressed in many cancers. The molecular mechanism of MELK dysregulation has not been determined in aggressive forms of breast cancer, such as triple negative breast cancer (TNBC). To evaluate molecular markers of MELK aberrations in aggressive breast cancer, we assessed MELK gene amplification and expression in breast tumors. MELK mRNA expression is highly up-regulated in basal-like breast cancer (BLBC), the major molecular subtype of TNBC, compared to luminal or other subtypes of breast tumors. MELK copy number (CN) gains are significantly associated with BLBC, whereas no significant association of CpG site methylation or histone modifications with breast cancer subtypes was observed. Accordingly, the CN gains appear to contribute to an increase in MELK expression, with a significant correlation between mRNA expression and CN in breast tumors and cell lines. Furthermore, immunohistochemistry (IHC) assays revealed that both nuclear and cytoplasmic staining scores of MELK were significantly higher in invasive ductal carcinoma (IDC) tumors compared to ductal carcinoma in situ (DCIS) and normal breast tissues. Our data showed that upregulation of MELK in BLBC may be in part driven by CN gains, rather than epigenetic modifications, indicating a potential for overexpression and CN gains of MELK to be developed as a diagnostic and prognostic marker to identify patients who have more aggressive breast cancer.

Celastrol with a Knockdown of miR-9-2, miR-17 and miR-19 Causes Cell Cycle Changes and Induces Apoptosis and Autophagy in Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is a cancer with extremely high aggressiveness, malignancy and mortality. Because of all of the poor prognosis features of GBM, new methods should be sought that will effectively cure it. We examined the efficacy of a combination of celastrol and a knockdown of the miR-9-2, miR-17 and miR-19 genes in the human glioblastoma U251MG cell line. U251MG cells were transfected with specific siRNA and exposed to celastrol. The effect of the knockdown of the miRs genes in combination with exposure to celastrol on the cell cycle (flow cytometry) and the expression of selected genes related to its regulation (RT-qPCR) and the regulation of apoptosis and autophagy was investigated. We found a significant reduction in cell viability and proliferation, an accumulation of the subG1-phase cells and a decreased population of cells in the S and G2/M phases, as well as the induction of apoptosis and autophagy. The observed changes were not identical in the case of the silencing of each of the tested miRNAs, which indicates a different mechanism of action of miR9-2, miR-17, miR-19 silencing on GBM cells in combination with celastrol. The multidirectional effects of the silencing of the genes encoding miR-9-2, miR-17 and miR-19 in combination with exposure to celastrol is possible. The studied strategy of silencing the miR overexpressed in GBM could be important in developing more effective treatments for glioblastoma. Additional studies are necessary in order to obtain a more detailed interpretation of the obtained results. The siRNA-induced miR-9-2, miR-17 and miR-19 mRNA knockdowns in combination with celastrol could offer a novel therapeutic strategy to more effectively control the growth of human GBM cells.

Targeting Apoptosis in Cancer

PURPOSE OF REVIEW

Apoptosis is a major mechanism of cancer cell death. Thus, evasion of apoptosis results in therapy resistance. Here, we review apoptosis modulators in cancer and their recent developments, including MDM2 inhibitors and kinase inhibitors that can induce effective apoptosis.

RECENT FINDINGS

Both extrinsic pathways (external stimuli through cell surface death receptor) and intrinsic pathways (mitochondrial-mediated regulation upon genotoxic stress) regulate the complex process of apoptosis through orchestration of various proteins such as members of the BCL-2 family. Dysregulation within these complex steps can result in evasion of apoptosis. However, via the combined evolution of medicinal chemistry and molecular biology, omics assays have led to innovative inducers of apoptosis and inhibitors of anti-apoptotic regulators. Many of these agents are now being tested in cancer patients in early-phase trials. We believe that despite a sluggish speed of development, apoptosis targeting holds promise as a relevant strategy in cancer therapeutics.

A Non-redundant Function of MNS5: A Class I α-1, 2 Mannosidase, in the Regulation of Endoplasmic Reticulum-Associated Degradation of Misfolded Glycoproteins

Endoplasmic Reticulum-Associated Degradation (ERAD) is one of the major processes in maintaining protein homeostasis. Class I α-mannosidases MNS4 and MNS5 are involved in the degradation of misfolded variants of the heavily glycosylated proteins, playing an important role for glycan-dependent ERAD in planta. MNS4 and MNS5 reportedly have functional redundancy, meaning that only the loss of both MNS4 and MNS5 shows phenotypes. However, MNS4 is a membrane-associated protein while MNS5 is a soluble protein, and both can localize to the endoplasmic reticulum (ER). Furthermore, MNS4 and MNS5 differentially demannosylate the glycoprotein substrates. Importantly, we found that their gene expression patterns are complemented rather than overlapped. This raises the question of whether they indeed work redundantly, warranting a further investigation. Here, we conducted an exhaustive genetic screen for a suppressor of the bri1-5, a brassinosteroid (BR) receptor mutant with its receptor downregulated by ERAD, and isolated sbi3, a suppressor of bri1-5 mutant named after sbi1 (suppressor of bri1). After genetic mapping together with whole-genome re-sequencing, we identified a point mutation G343E in AT1G27520 (MNS5) in sbi3. Genetic complementation experiments confirmed that sbi3 was a loss-of-function allele of MNS5. In addition, sbi3 suppressed the dwarf phenotype of bri1-235 in the proteasome-independent ERAD pathway and bri1-9 in the proteasome-dependent ERAD pathway. Importantly, sbi3 could only affect BRI1/bri1 with kinase activities such that it restored BR-sensitivities of bri1-5, bri1-9, and bri1-235 but not null bri1. Furthermore, sbi3 was less tolerant to tunicamycin and salt than the wild-type plants. Thus, our study uncovers a non-redundant function of MNS5 in the regulation of ERAD as well as plant growth and ER stress response, highlighting a need of the traditional forward genetic approach to complement the T-DNA or CRISPR-Cas9 systems on gene functional study.

A synthetic lethal screen identifies HDAC4 as a potential target in MELK overexpressing cancers

Maternal embryonic leucine zipper kinase (MELK) is frequently overexpressed in cancer, but the role of MELK in cancer is still poorly understood. MELK was shown to have roles in many cancer-associated processes including tumor growth, chemotherapy resistance, and tumor recurrence. To determine whether the frequent overexpression of MELK can be exploited in therapy, we performed a high-throughput screen using a library of Saccharomyces cerevisiae mutants to identify genes whose functions become essential when MELK is overexpressed. We identified two such genes: LAG2 and HDA3. LAG2 encodes an inhibitor of the Skp, Cullin, F-box containing (SCF) ubiquitin-ligase complex, while HDA3 encodes a subunit of the HDA1 histone deacetylase complex. We find that one of these synthetic lethal interactions is conserved in mammalian cells, as inhibition of a human homolog of HDA3 (Histone Deacetylase 4, HDAC4) is synthetically toxic in MELK overexpression cells. Altogether, our work identified a novel potential drug target for tumors that overexpress MELK.

Molecular targets and therapeutics in chemoresistance of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a specific subtype of breast cancer (BC), which shows immunohistochemically negative expression of hormone receptor i.e., Estrogen receptor and Progesterone receptor along with the absence of Human Epidermal Growth Factor Receptor-2 (HER2/neu). In Indian scenario the prevalence of BC is 26.3%, whereas, in West Bengal the cases are of 18.4%. But the rate of TNBC has increased up to 31% and shows 27% of total BC. Conventional chemotherapy is effective only in the initial stages but with progression of the disease the effectivity gets reduced and shown almost no effect in later or advanced stages of TNBC. Thus, TNBC patients frequently develop resistance and metastasis, due to its peculiar triple-negative nature most of the hormonal therapies also fails. Development of chemoresistance may involve various factors, such as, TNBC heterogeneity, cancer stem cells (CSCs), signaling pathway deregulation, DNA repair mechanism, hypoxia, and other molecular factors. To overcome the challenges to treat TNBC various targets and molecules have been exploited including CSCs modulator, drug efflux transporters, hypoxic factors, apoptotic proteins, and regulatory signaling pathways. Moreover, to improve the targets and efficacy of treatments researchers are emphasizing on targeted therapy for TNBC. In this review, an effort has been made to focus on phenotypic and molecular variations in TNBC along with the role of conventional as well as newly identified pathways and strategies to overcome challenge of chemoresistance.

Functional genomics for breast cancer drug target discovery

Breast cancer is a heterogeneous disease that develops through a multistep process via the accumulation of genetic/epigenetic alterations in various cancer-related genes. Current treatment options for breast cancer patients include surgery, radiotherapy, and chemotherapy including conventional cytotoxic and molecular-targeted anticancer drugs for each intrinsic subtype, such as endocrine therapy and antihuman epidermal growth factor receptor 2 (HER2) therapy. However, these therapies often fail to prevent recurrence and metastasis due to resistance. Overall, understanding the molecular mechanisms of breast carcinogenesis and progression will help to establish therapeutic modalities to improve treatment. The recent development of comprehensive omics technologies has led to the discovery of driver genes, including oncogenes and tumor-suppressor genes, contributing to the development of molecular-targeted anticancer drugs. Here, we review the development of anticancer drugs targeting cancer-specific functional therapeutic targets, namely, MELK (maternal embryonic leucine zipper kinase), TOPK (T-lymphokine-activated killer cell-originated protein kinase), and BIG3 (brefeldin A-inhibited guanine nucleotide-exchange protein 3), as identified through comprehensive breast cancer transcriptomics.

Identification of Ten Mitosis Genes Associated with Tamoxifen Resistance in Breast Cancer

Background

Endocrine therapy is the backbone therapy in estrogen receptor α (ER)-positive breast cancer, and tamoxifen resistance is a great challenge for endocrine therapy. Tamoxifen-resistant and sensitive samples from the international public repository, the Gene Expression Omnibus (GEO) database, were used to identify therapeutic biomarkers associated with tamoxifen resistance.

Materials and Methods

In this study, integrated analysis was used to identify tamoxifen resistance-associated genes. Differentially expressed genes (DEGs) were identified. Gene ontology and pathway analysis were then analyzed. Weighted correlation network analysis (WGCNA) was performed to find modules correlated with tamoxifen resistance. Protein–protein interaction (PPI) network was used to find hub genes. Genes of prognostic significance were further validated in another GEO dataset and cohort from Shanghai Ruijin Hospital using RT-PCR.

Results

A total of 441 genes were down-regulated and 123 genes were up-regulated in tamoxifen-resistant samples. Those up-regulated genes were mostly enriched in the cell cycle pathway. Then, WGCNA was performed, and the brown module was correlated with tamoxifen resistance. An overlap of 81 genes was identified between differentially expressed genes (DEGs) and genes in the brown module. These genes were also enriched in the cell cycle. Twelve hub genes were identified using PPI network, which were involved in the mitosis phase of the cell cycle. Finally, 10 of these 12 genes were validated to be up-regulated in tamoxifen-resistant patients and were associated with poor prognosis in ER-positive patients.

Conclusion

Our study suggested mitosis-related genes are mainly involved in tamoxifen resistance, and high expression of these genes could predict poor prognosis of patients receiving tamoxifen. These genes may be potential targets to improve efficacy of endocrine therapy in breast cancer, and inhibitors targeted these genes could be used in endocrine-resistant patients.

MELK Inhibition Effectively Suppresses Growth of Glioblastoma and Cancer Stem-Like Cells by Blocking AKT and FOXM1 Pathways

Glioblastoma multiforme (GBM) is a devastating disease yet no effective drug treatment has been established to date. Glioblastoma stem-like cells (GSCs) are insensitive to treatment and may be one of the reasons for the relapse of GBM. Maternal embryonic leucine zipper kinase gene (MELK) plays an important role in the malignant proliferation and the maintenance of GSC stemness properties of GBM. However, the therapeutic effect of targeted inhibition of MELK on GBM remains unclear. This study analyzed the effect of a MELK oral inhibitor, OTSSP167, on GBM proliferation and the maintenance of GSC stemness. OTSSP167 significantly inhibited cell proliferation, colony formation, invasion, and migration of GBM. OTSSP167 treatment reduced the expression of cell cycle G2/M phase-related proteins, Cyclin B1 and Cdc2, while up-regulation the expression of p21 and subsequently induced cell cycle arrest at the G2/M phase. OTSSP167 effectively prolonged the survival of tumor-bearing mice and inhibited tumor cell growth in in vivo mouse models. It also reduced protein kinase B (AKT) phosphorylation levels by OTSSP167 treatment, thereby disrupting the proliferation and invasion of GBM cells. Furthermore, OTSSP167 inhibited the proliferation, neurosphere formation and self-renewal capacity of GSCs by reducing forkhead box M1 (FOXM1) phosphorylation and transcriptional activity. Interestingly, the inhibitory effect of OTSSP167 on the proliferation of GSCs was 4-fold more effective than GBM cells. In conclusion, MELK inhibition suppresses the growth of GBM and GSCs by double-blocking AKT and FOXM1 signals. Targeted inhibition of MELK may thus be potentially used as a novel treatment for GBM.

A novel carbon-11 radiolabeled maternal embryonic leucine zipper kinase inhibitor for PET imaging of triple-negative breast cancer

Maternal embryonic leucine zipper kinase (MELK) plays an important role in the regulation of tumor cell growth. It is abundant in triple-negative breast cancers (TNBC), making it a promising target for molecular imaging and therapy. Based on the structure of a potent MELK inhibitor (OTSSP167) with high affinity, we developed a novel carbon-11 radiolabeled molecular probe ¹¹C-methoxy-OTSSP167, and evaluated its application in positron emission tomography (PET) imaging of TNBC. ¹¹C-methoxy-OTSSP167 was successfully synthesized and was identical to its non-radiolabeled compound methoxy-OTSSP167 in high-pressure liquid chromatography (HPLC) chromatogram. The obtained tracer had 10 ± 2% radiolabeling yield with a total synthesis time of 40 min. The radiochemical purity of the tracer was more than 95%. The maximum uptake (9.97 ± 0.70%) of ¹¹C-methoxy-OTSSP167 in MELK-overexpressing MDA-MB-231 cells was at 60 min in vitro. On PET, MDA-MB-231 tumors were clearly visible at 30, 60, and 90 min after injection of ¹¹C-methoxy-OTSSP167, while no obvious radioactivity accumulation was found in the low-MELK MCF-7 tumors. In vivo biodistribution data were consistent with the findings of the PET images. However, the radioactive tracer showed high uptake in normal organs such as liver and intestine, which may limit the application of the tracer. In addition, a markedly different MELK expression level in MDA-MBA-231 and MCF-7 tumors was verified via IHC staining. In conclusion, ¹¹C-methoxy-OTSSP167 was successfully developed and exhibited elevated uptake in MELK overexpressed tumor, indicating its potential for noninvasively imaging of MELK overexpressed TNBC.

Improving target assessment in biomedical research: the GOT-IT recommendations

Academic research plays a key role in identifying new drug targets, including understanding target biology and links between targets and disease states. To lead to new drugs, however, research must progress from purely academic exploration to the initiation of efforts to identify and test a drug candidate in clinical trials, which are typically conducted by the biopharma industry. This transition can be facilitated by a timely focus on target assessment aspects such as target-related safety issues, druggability and assayability, as well as the potential for target modulation to achieve differentiation from established therapies. Here, we present recommendations from the GOT-IT working group, which have been designed to support academic scientists and funders of translational research in identifying and prioritizing target assessment activities and in defining a critical path to reach scientific goals as well as goals related to licensing, partnering with industry or initiating clinical development programmes. Based on sets of guiding questions for different areas of target assessment, the GOT-IT framework is intended to stimulate academic scientists' awareness of factors that make translational research more robust and efficient, and to facilitate academia-industry collaboration.

MELK/MPK38 in cancer: from mechanistic aspects to therapeutic strategies

Maternal embryonic leucine zipper kinase (MELK)/Murine protein serine-threonine kinase 38 (MPK38) is a member of the AMP-related serine-threonine kinase family, which has been reported to be involved in the regulation of many cellular events, including cell proliferation, apoptosis, and metabolism, partly by phosphorylation and regulation of several signaling molecules. The abnormal expression of MELK has been associated with tumorigenesis and malignant progression in various types of cancer. Currently, several small-molecule inhibitors of MELK are under investigation although only OTS167 has entered clinical trials. In this review, we elaborate on the relative contributions of MELK pathways in the physiological process, their oncogenic role in carcinogenesis, and targeted agents under development for the treatment of cancer.

PIG-1 MELK-dependent phosphorylation of nonmuscle myosin II promotes apoptosis through CES-1 Snail partitioning

The mechanism(s) through which mammalian kinase MELK promotes tumorigenesis is not understood. We find that the C. elegans orthologue of MELK, PIG-1, promotes apoptosis by partitioning an anti-apoptotic factor. The C. elegans NSM neuroblast divides to produce a larger cell that differentiates into a neuron and a smaller cell that dies. We find that in this context, PIG-1 MELK is required for partitioning of CES-1 Snail, a transcriptional repressor of the pro-apoptotic gene egl-1 BH3-only. pig-1 MELK is controlled by both a ces-1 Snail- and par-4 LKB1-dependent pathway, and may act through phosphorylation and cortical enrichment of nonmuscle myosin II prior to neuroblast division. We propose that pig-1 MELK-induced local contractility of the actomyosin network plays a conserved role in the acquisition of the apoptotic fate. Our work also uncovers an auto-regulatory loop through which ces-1 Snail controls its own activity through the formation of a gradient of CES-1 Snail protein.

Apoptosis is critical for the elimination of ‘unwanted’ cells. What distinguishes wanted from unwanted cells in developing animals is poorly understood. We report that in the C. elegans NSM neuroblast lineage, the level of CES-1, a Snail-family member and transcriptional repressor of the pro-apoptotic gene egl-1, contributes to this process. In addition, we demonstrate that C. elegans PIG-1, the orthologue of mammalian proto-oncoprotein MELK, plays a critical role in controlling CES-1^Snail levels. Specifically, during NSM neuroblast division, PIG-1^MELK controls partitioning of CES-1^Snail into one but not the other daughter cell thereby promoting the making of one wanted and one unwanted cell. Furthermore, we present evidence that PIG-1^MELK acts prior to NSM neuroblast division by locally activating the actomyosin network.

Identification of Metastasis-Associated Biomarkers in Synovial Sarcoma Using Bioinformatics Analysis

Synovial sarcoma (SS) is a highly aggressive soft tissue tumor with high risk of local recurrence and metastasis. However, the mechanisms underlying SS metastasis are still largely unclear. The purpose of this study is to screen metastasis-associated biomarkers in SS by integrated bioinformatics analysis. Two mRNA datasets (GSE40018 and GSE40021) were selected to analyze the differentially expressed genes (DEGs). Using the Database for Annotation, Visualization and Integrated Discovery (DAVID) and gene set enrichment analysis (GSEA), functional and pathway enrichment analyses were performed for DEGs. Then, the protein-protein interaction (PPI) network was constructed via the Search Tool for the Retrieval of Interacting Genes (STRING) database. The module analysis of the PPI network and hub genes validation were performed using Cytoscape software. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the hub genes were performed using WEB-based GEne SeT AnaLysis Toolkit (WebGestalt). The expression levels and survival analysis of hub genes were further assessed through Gene Expression Profiling Interactive Analysis (GEPIA) and the Kaplan-Meier plotter database. In total, 213 overlapping DEGs were identified, of which 109 were upregulated and 104 were downregulated. GO analysis revealed that the DEGs were predominantly involved in mitosis and cell division. KEGG pathways analysis demonstrated that most DEGs were significantly enriched in cell cycle pathway. GSEA revealed that the DEGs were mainly enriched in oocyte meiosis, cell cycle and DNA replication pathways. A key module was identified and 10 hub genes (CENPF, KIF11, KIF23, TTK, MKI67, TOP2A, CDC45, MELK, AURKB, and BUB1) were screened out. The expression and survival analysis disclosed that the 10 hub genes were upregulated in SS patients and could result in significantly reduced survival. Our study identified a series of metastasis-associated biomarkers involved in the progression of SS, and may provide novel therapeutic targets for SS metastasis.

Aurora A regulation by reversible cysteine oxidation reveals evolutionarily conserved redox control of Ser/Thr protein kinase activity

Reactive oxygen species (ROS) are physiological mediators of cellular signaling and play potentially damaging roles in human diseases. In this study, we found that the catalytic activity of the Ser/Thr kinase Aurora A was inhibited by the oxidation of a conserved cysteine residue (Cys290) that lies adjacent to Thr288, a critical phosphorylation site in the activation segment. Cys is present at the equivalent position in ~100 human Ser/Thr kinases, a residue that we found was important not only for the activity of human Aurora A but also for that of fission yeast MAPK-activated kinase (Srk1) and PKA (Pka1). Moreover, the presence of this conserved Cys predicted biochemical redox sensitivity among a cohort of human CAMK, AGC, and AGC-like kinases. Thus, we predict that redox modulation of the conserved Cys290 of Aurora A may be an underappreciated regulatory mechanism that is widespread in eukaryotic Ser/Thr kinases. Given the key biological roles of these enzymes, these findings have implications for understanding physiological and pathological responses to ROS and highlight the importance of protein kinase regulation through multivalent modification of the activation segment.

Maslinic Acid Enhances Docetaxel Response in Human Docetaxel-Resistant Triple Negative Breast Carcinoma MDA-MB-231 Cells via Regulating MELK-FoxM1-ABCB1 Signaling Cascade

Docetaxel (DOC) is the most important chemotherapeutic drug for the treatment of triple negative breast cancer (TNBC); however, acquired drug resistance upon the long-term treatment limits its therapeutic effect. Maslinic acid (MA), a natural triterpene from Olea europaea L., attracts increasing interest in recent years because of its promising anti-cancer activity, but the reversal effect of MA on drug resistance in cancer therapy is rarely explored. In this study, the combined effect of DOC and MA on human docetaxel-resistant triple negative breast carcinoma MDA-MB-231 (MDA-MB-231/DOC) cells was investigated. The enhanced effect of MA on DOC cytotoxicity and DOC accumulation was assessed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and HPLC (high performance liquid chromatography) analysis in MDA-MB-231/DOC cells. Western blot, co-immunoprecipitation assay, luciferase reporter assay, and chromatin immunoprecipitation (ChIP) assay were performed for exploring the underlying mechanisms. Our data indicated that the co-treatment of MA could dose-dependently enhance DOC sensitivity and cellular DOC accumulation in MDA-MB-231/DOC cells. Moreover, MELK-FoxM1-ABCB1 signaling cascade was confirmed to contribute to DOC resistance in MDA-MB-231/DOC cells. In such process, MA directly suppressed expressions and interaction of MELK and FoxM1 as well as the transcriptional activity of FoxM1, and thus reducing the expression of ABCB1. Overall, our study suggests that the combined use of DOC and MA may be helpful for overcoming DOC resistance in human TNBC therapy.

Enigmatic MELK: The controversy surrounding its complex role in cancer

The Ser/Thr protein kinase MELK (maternal embryonic leucine zipper kinase) has been considered an attractive therapeutic target for managing cancer since 2005. Studies using expression analysis have indicated that MELK expression is higher in numerous cancer cells and tissues than in their normal, nonneoplastic counterparts. Further, RNAi-mediated MELK depletion impairs proliferation of multiple cancers, including triple-negative breast cancer (TNBC), and these growth defects can be rescued with exogenous WT MELK, but not kinase-dead MELK complementation. Pharmacological MELK inhibition with OTS167 (alternatively called OTSSP167) and NVS-MELK8a, among other small molecules, also impairs cancer cell growth. These collective results led to MELK being classified as essential for cancer proliferation. More recently, in 2017, the proliferation of TNBC and other cancer cell lines was reported to be unaffected by genetic CRISPR/Cas9-mediated MELK deletion, calling into question the essentiality of this kinase in cancer. To date, the requirement of MELK in cancer remains controversial, and mechanisms underlying the disparate growth effects observed with RNAi, pharmacological inhibition, and CRISPR remain unclear. Our objective with this review is to highlight the evidence on both sides of this controversy, to provide commentary on the purported requirement of MELK in cancer, and to emphasize the need for continued elucidation of the functions of MELK.

Cloning, tissue distribution, expression pattern, and function of porcine maternal embryonic leucine zipper kinase

Background

Maternal embryonic leucine zipper kinase (MELK) is an atypical member of the snf1/AMPK family of serine-threonine kinases, involved in diverse physiological and pathological processes, including cell proliferation, apoptosis, embryogenesis, cancer treatment resistance, and RNA processing. MELK is highly expressed in human cancers and is associated with more aggressive forms of astrocytoma, glioblastoma, breast cancer, and melanoma to date, no information about porcine MELK (pMELK) has been reported.

Methods

In this study, the pMELK coding sequence was cloned from swine spleen and characterized. We also quantitatively determined the expression of MELK in 11 tissues isolated from a piglet and determined its subcellular localization when expressed in swine umbilical vein endothelial cells (SUVEC) as a fusion protein. Moreover, we report the functional characterization of pMELK protein concerning its role in apoptosis.

Results

Sequencing analysis showed that full-length of pMELK is 2,072 bp with 17 exons, encoding 655 amino acids, including an S-TKc conserved domain. Comparison of pMELK with ten other mammalian species of their orthologous sequences showed >91% homology and an evolutionary distance <0.05, demonstrating that MELK is highly conserved in evolution. Relative quantification of MELK expression in 11 tissue samples isolated from 30-day-old piglets showed MELK expression in all tested organs and the highest expression in the superficial inguinal lymph node. Constructed a plasmid named pEGFP-MELK, and the fusion protein GFP-MELK was successfully expressed in SUVECs. Fluorescence microscopy revealed the subcellular distribution of the fusion protein GFP-MELK was limited to the cytoplasm. About function, Flow cytometry analysis showed that overexpression of GFP-pMELK in SUVEC cells enhances staurosporine (STS)—induced apoptosis, but not significantly different. The pMELK protein also was found to interact with porcine BCL-G and transient transfection of the recombinant plasmid pCMV-HA-pMELK into SUVEC cells stably expressing GFP-pBCL-G protein inhibited pBCL-G -induced apoptosis significantly.

Conclusions

The present study provided useful information on pMELK basic details and function in apoptosis offer a potential new molecular model for disease interventions and disease related to human MELK and BCL-G.

Mass spectrometry-based selectivity profiling identifies a highly selective inhibitor of the kinase MELK that delays mitotic entry in cancer cells

The maternal embryonic leucine zipper kinase (MELK) has been implicated in the regulation of cancer cell proliferation. RNAi-mediated MELK depletion impairs growth and causes G2/M arrest in numerous cancers, but the mechanisms underlying these effects are poorly understood. Furthermore, the MELK inhibitor OTSSP167 has recently been shown to have poor selectivity for MELK, complicating the use of this inhibitor as a tool compound to investigate MELK function. Here, using a cell-based proteomics technique called multiplexed kinase inhibitor beads/mass spectrometry (MIB/MS), we profiled the selectivity of two additional MELK inhibitors, NVS-MELK8a (8a) and HTH-01-091. Our results revealed that 8a is a highly selective MELK inhibitor, which we further used for functional studies. Resazurin and crystal violet assays indicated that 8a decreases triple-negative breast cancer cell viability, and immunoblotting revealed that impaired growth is due to perturbation of cell cycle progression rather than induction of apoptosis. Using double-thymidine synchronization and immunoblotting, we observed that MELK inhibition delays mitotic entry, which was associated with delayed activation of Aurora A, Aurora B, and cyclin-dependent kinase 1 (CDK1). Following this delay, cells entered and completed mitosis. Using live-cell microscopy of cells harboring fluorescent proliferating cell nuclear antigen, we confirmed that 8a significantly and dose-dependently lengthens G2 phase. Collectively, our results provide a rationale for using 8a as a tool compound for functional studies of MELK and indicate that MELK inhibition delays mitotic entry, likely via transient G2/M checkpoint activation.

Maternal Embryonic Leucine Zipper Kinase Promotes Tumor Growth and Metastasis via Stimulating FOXM1 Signaling in Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is a common gastrointestinal malignancy and is one of the most important cause of cancer related mortalities in the world. However, there is no clinically effective targeted therapeutic drugs for ESCC due to lack of valuable molecular therapeutic targets. In the present study, we investigated the biological function and molecular mechanisms of maternal embryonic leucine zipper kinase (MELK) in ESCC. The expression of MELK mRNA and protein was determined in cell lines and clinical samples of ESCC. MTT, focus formation and soft agar assays were carried out to measure cell proliferation and colony formation. Wound healing and transwell assays were used to assess the capacity of tumor cell migration and invasion. Nude mice models of subcutaneous tumor growth and lung metastasis were performed to examine the function of MELK in tumorigenecity and metastasis of ESCC cells. High expression of MELK was observed in ESCC cell line and human samples, especially in the metastatic tumor tissues. Moreover, overexpression of MELK promoted cell proliferation, colony formation, migration and invasion, and increased the expression and enzyme activity of MMP-2 and MMP-9 in ESCC cells. More importantly, enhanced expression of MELK greatly accelerated tumor growth and lung metastasis of ESCC cells in vivo. In contrast, knockdown of MELK by lentiviral shRNA resulted in an opposite effect both in vitro and in animal models. Mechanistically, MELK facilitated the phosphorylation of FOXM1, leading to activation of its downstream targets (PLK1, Cyclin B1, and Aurora B), and thereby promoted tumorigenesis and metastasis of ESCC cells. In conclusion, MELK enhances tumorigenesis, migration, invasion and metastasis of ESCC cells via activation of FOXM1 signaling pathway, suggesting MELK is a potential therapeutic target for ESCC patients, even those in an advanced stage.

MELK promotes Endometrial carcinoma progression via activating mTOR signaling pathway

Background

Endometrial carcinoma (EC) is one of the most common gynecological malignancies among women. Maternal embryonic leucine Zipper Kinase (MELK) is upregulated in a variety of human tumors, where it contributes to malignant phenotype and correlates with a poor prognosis. However, the biological function of MELK in EC progression remains largely unknown.

Methods

We explored the MELK expression in EC using TCGA and GEO databases and verified it using clinical samples by IHC methods. CCK-8 assay, colony formation assay, cell cycle assay, wound healing assay and subcutaneous xenograft mouse model were generated to estimate the functions of MELK and its inhibitor OTSSP167. qRT-PCR, western blotting, co-immunoprecipitation, chromatin immunoprecipitation and luciferase reporter assay were performed to uncover the underlying mechanism concerning MELK during the progression of EC.

Findings

MELK was significantly elevated in patients with EC, and high expression of MELK was associated with serous EC, high histological grade, advanced clinical stage and reduced overall survival and disease-free survival. MELK knockdown decreased the ability of cell proliferation and migration in vitro and subcutaneous tumorigenesis in vivo. In addition, high expression of MELK could be regulated by transcription factor E2F1. Moreover, we found that MELK had a direct interaction with MLST8 and then activated mTORC1 and mTORC2 signaling pathway for EC progression. Furthermore, OTSSP167, an effective inhibitor, could inhibit cell proliferation driven by MELK in vivo and vitro assays.

Interpretation

We have explored the crucial role of the E2F1/MELK/mTORC1/2 axis in the progression of EC, which could be served as potential therapeutic targets for treatment of EC.

Funding

This research was supported by National Natural Science Foundation of China (No:81672565), the Natural Science Foundation of Shanghai (Grant NO:17ZR1421400 to Dr. Zhihong Ai) and the fundamental research funds for central universities (No: 22120180595).

Mutant P53 induces MELK expression by release of wild-type P53-dependent suppression of FOXM1

Triple-negative breast cancer (TNBC) is the most aggressive form of breast cancer, and is associated with a poor prognosis due to frequent distant metastasis and lack of effective targeted therapies. Previously, we identified maternal embryonic leucine zipper kinase (MELK) to be highly expressed in TNBCs as compared with ER-positive breast cancers. Here we determined the molecular mechanism by which MELK is overexpressed in TNBCs. Analysis of publicly available data sets revealed that MELK mRNA is elevated in p53-mutant breast cancers. Consistent with this observation, MELK protein levels are higher in p53-mutant vs. p53 wild-type breast cancer cells. Furthermore, inactivation of wild-type p53, by loss or mutation of the p53 gene, increases MELK expression, whereas overexpression of wild-type p53 in p53-null cells reduces MELK promoter activity and MELK expression. We further analyzed MELK expression in breast cancer data sets and compared that with known wild-type p53 target genes. This analysis revealed that MELK expression strongly correlates with genes known to be suppressed by wild-type p53. Promoter deletion studies identified a p53-responsive region within the MELK promoter that did not map to the p53 consensus response elements, but to a region containing a FOXM1-binding site. Consistent with this result, knockdown of FOXM1 reduced MELK expression in p53-mutant TNBC cells and expression of wild-type p53 reduced FOXM1 expression. ChIP assays demonstrated that expression of wild-type p53 reduces binding of E2F1 (a critical transcription factor controlling FOXM1 expression) to the FOXM1 promoter, thereby, reducing FOXM1 expression. These results show that wild-type p53 suppresses FOXM1 expression, and thus MELK expression, through indirect mechanisms. Overall, these studies demonstrate that wild-type p53 represses MELK expression by inhibiting E2F1A-dependent transcription of FOXM1 and that mutation-driven loss of wild-type p53, which frequently occurs in TNBCs, induces MELK expression by suppressing FOXM1 expression and activity in p53-mutant breast cancers.

Inhibition of MELK produces potential anti-tumour effects in bladder cancer by inducing G1/S cell cycle arrest via the ATM/CHK2/p53 pathway

We aimed to investigate the biological function of MELK and the therapeutic potential of OTSSP167 in human bladder cancer (BCa). First, we observed overexpression of MELK in BCa cell lines and tissues and found that it was associated with higher tumour stage and tumour grade, which was consistent with transcriptome analysis. High expression of MELK was significantly correlated with poor prognosis in BCa patients, and MELK was found to have a role in the cell cycle, the G1/S transition in mitosis, and DNA repair and replication. Furthermore, BCa cells presented significantly decreased proliferation capacity following silencing of MELK or treatment with OTSSP167 in vitro and in vivo. Functionally, reduction in MELK or treatment of cells with OTSSP167 could induce cell cycle arrest and could suppress migration. In addition, these treatments could activate phosphorylation of ATM and CHK2, which would be accompanied by down‐regulated MDMX, cyclin D1, CDK2 and E2F1; however, p53 and p21 would be activated. Opposite results were observed when MELK expression was induced. Overall, MELK was found to be a novel oncogene in BCa that induces cell cycle arrest via the ATM/CHK2/p53 pathway. OTSSP167 displays potent anti‐tumour activities, which may provide a new molecule‐based strategy for BCa treatment.

Alterations of the interactome of Bcl-2 proteins in breast cancer at the transcriptional, mutational and structural level

Apoptosis is an essential defensive mechanism against tumorigenesis. Proteins of the B-cell lymphoma-2 (Bcl-2) family regulate programmed cell death by the mitochondrial apoptosis pathway. In response to intracellular stress, the apoptotic balance is governed by interactions of three distinct subgroups of proteins; the activator/sensitizer BH3 (Bcl-2 homology 3)-only proteins, the pro-survival, and the pro-apoptotic executioner proteins. Changes in expression levels, stability, and functional impairment of pro-survival proteins can lead to an imbalance in tissue homeostasis. Their overexpression or hyperactivation can result in oncogenic effects. Pro-survival Bcl-2 family members carry out their function by binding the BH3 short linear motif of pro-apoptotic proteins in a modular way, creating a complex network of protein-protein interactions. Their dysfunction enables cancer cells to evade cell death. The critical role of Bcl-2 proteins in homeostasis and tumorigenesis, coupled with mounting insight in their structural properties, make them therapeutic targets of interest. A better understanding of gene expression, mutational profile, and molecular mechanisms of pro-survival Bcl-2 proteins in different cancer types, could help to clarify their role in cancer development and may guide advancement in drug discovery. Here, we shed light on the pro-survival Bcl-2 proteins in breast cancer using different bioinformatic approaches, linking -omics with structural data. We analyzed the changes in the expression of the Bcl-2 proteins and their BH3-containing interactors in breast cancer samples. We then studied, at the structural level, a selection of interactions, accounting for effects induced by mutations found in the breast cancer samples. We find two complexes between the up-regulated Bcl2A1 and two down-regulated BH3-only candidates (i.e., Hrk and Nr4a1) as targets associated with reduced apoptosis in breast cancer samples for future experimental validation. Furthermore, we predict L99R, M75R as damaging mutations altering protein stability, and Y120C as a possible allosteric mutation from an exposed surface to the BH3-binding site.

Integrated Analysis To Identify Molecular Biomarkers Of High-Grade Serous Ovarian Cancer

Purpose

Ovarian cancer is the leading cause of gynecologic cancer-related death worldwide. Early diagnosis of ovarian cancer can significantly improve patient prognosis. Hence, there is an urgent need to identify key diagnostic and prognostic biomarkers specific for ovarian cancer. Because high-grade serous ovarian cancer (HGSOC) is the most common type of ovarian cancer and accounts for the majority of deaths, we identified potential biomarkers for the early diagnosis and prognosis of HGSOC.

Methods

Six datasets (GSE14001, GSE18520, GSE26712, GSE27651, GSE40595, and GSE54388) were downloaded from the Gene Expression Omnibus database for analysis. Differentially expressed genes (DEGs) between HGSOC and normal ovarian surface epithelium samples were screened via integrated analysis. Hub genes were identified by analyzing protein-protein interaction (PPI) network data. The online Kaplan-Meier plotter was utilized to evaluate the prognostic roles of these hub genes. The expression of these hub genes was confirmed with Oncomine datasets and validated by quantitative real-time PCR and Western blotting.

Results

A total of 103 DEGs in patients with HGSOC-28 upregulated genes and 75 downregulated genes-were successfully screened. Enrichment analyses revealed that the upregulated genes were enriched in cell division and cell proliferation and that the downregulated genes mainly participated in the Wnt signaling pathway and various metabolic processes. Ten hub genes were associated with HGSOC pathogenesis. Seven overexpressed hub genes were partitioned into module 1 of the PPI network, which was enriched in the cell cycle and DNA replication pathways. Survival analysis revealed that MELK, CEP55 and KDR expression levels were significantly correlated with the overall survival of HGSOC patients (P < 0.05). The RNA and protein expression levels of these hub genes were validated experimentally.

Conclusion

Based on an integrated analysis, we propose the further investigation of MELK, CEP55 and KDR as promising diagnostic and prognostic biomarkers of HGSOC.

Identification of Potential Crucial Genes and Key Pathways in Breast Cancer Using Bioinformatic Analysis

Background: The molecular mechanism of tumorigenesis remains to be fully understood in breast cancer. It is urgently required to identify genes that are associated with breast cancer development and prognosis and to elucidate the underlying molecular mechanisms. In the present study, we aimed to identify potential pathogenic and prognostic differentially expressed genes (DEGs) in breast adenocarcinoma through bioinformatic analysis of public datasets.

Methods: Four datasets (GSE21422, GSE29431, GSE42568, and GSE61304) from Gene Expression Omnibus (GEO) and the Cancer Genome Atlas (TCGA) dataset were used for the bioinformatic analysis. DEGs were identified using LIMMA Package of R. The GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses were conducted through FunRich. The protein-protein interaction (PPI) network of the DEGs was established through STRING (Search Tool for the Retrieval of Interacting Genes database) website, visualized by Cytoscape and further analyzed by Molecular Complex Detection (MCODE). UALCAN and Kaplan–Meier (KM) plotter were employed to analyze the expression levels and prognostic values of hub genes. The expression levels of the hub genes were also validated in clinical samples from breast cancer patients. In addition, the gene-drug interaction network was constructed using Comparative Toxicogenomics Database (CTD).

Results: In total, 203 up-regulated and 118 down-regulated DEGs were identified. Mitotic cell cycle and epithelial-to-mesenchymal transition pathway were the major enriched pathways for the up-regulated and down-regulated genes, respectively. The PPI network was constructed with 314 nodes and 1,810 interactions, and two significant modules are selected. The most significant enriched pathway in module 1 was the mitotic cell cycle. Moreover, six hub genes were selected and validated in clinical sample for further analysis owing to the high degree of connectivity, including CDK1, CCNA2, TOP2A, CCNB1, KIF11, and MELK, and they were all correlated to worse overall survival (OS) in breast cancer.

Conclusion: These results revealed that mitotic cell cycle and epithelial-to-mesenchymal transition pathway could be potential pathways accounting for the progression in breast cancer, and CDK1, CCNA2, TOP2A, CCNB1, KIF11, and MELK may be potential crucial genes. Further, it could be utilized as new biomarkers for prognosis and potential new targets for drug synthesis of breast cancer.

Identification and characterization of cancer vulnerabilities via targeted protein degradation

Target(ed) protein degradation (TPD) is a novel paradigm in drug discovery and a promising therapeutic strategy. TPD is based on small-molecules that catalyze the degradation of proteins by re-directing the ubiquitination activity of ubiquitin E3 ligases. Its unique molecular pharmacology enables robust, selective and fast elimination of proteins in cellular assays and in vivo. In addition to possible clinical applications, TPD is also emerging as an attractive alternative to traditional pharmacologic or genetic perturbation strategies. Directly acting degraders, as well as chemical-genetics derivatives offer unique opportunities in the pre-clinical identification, characterization and mechanistic validation of therapeutic targets.

MicroRNA-494-dependent WDHDI inhibition suppresses epithelial-mesenchymal transition, tumor growth and metastasis in cholangiocarcinoma

BACKGROUND

Cholangiocarcinoma (CCA) represents a devastating malignancy characterized by high mortality, and notoriously problematic to diagnose. Recently, microRNAs (miRs) have been intensively investigated due to their potential usefulness from a tumor treatment perspective.

AIMS

The current study was aimed to investigate whether miR-494 influences epithelial-mesenchymal transition (EMT), tumor growth and metastasis of CCA.

METHODS

The regulatory miRNAs of WDHD1 in CCA expression chip were predicted, followed by determination of the miR-494 and WDHD1 expression in normal cholangiocyte tissues and CCA tissues. The related protein levels were determined. CCA cell migration, invasion, viability, and cell cycle distribution and the dosage-dependent effect of miR-494 on CCA cell growth were subsequently detected. Finally, tumorigenicity and lymph node metastasis (LNM) were measured.

RESULTS

Initially, miR-194 affected the CCA development via negatively regulating WDHD1 and miR-494 which were downregulated while WDHD1 was upregulated in CCA. In addition, miR-494 overexpression elevated E-cadherin expression while decreased expressions of WDHD1, N-cadherin, Vimentin, Snail, Twist and MMP-9. Finally, overexpressed miR-494 was observed to suppress EMT, cell viability, migration, invasion, arrest cell cycle progression, tumor formation, and LNM while accelerating cell apoptosis in vivo.

CONCLUSION

This study indicated that miR-494 overexpression suppresses EMT, tumor formation and LNM while promoting CCA cell apoptosis through inhibiting WDHD1 in CCA.

Maternal Embryonic Leucine Zipper Kinase (MELK), a Potential Therapeutic Target for Neuroblastoma

Maternal embryonic leucine zipper kinase (MELK) activates pathways that mediate aggressive tumor growth and therapy resistance in many types of adult cancers. Pharmacologic and genomic inhibition of MELK impairs tumor growth and increases sensitivity to radiation and chemotherapy. On the basis of these promising preclinical studies, early-phase adult clinical trials testing the MELK inhibitor OTS167 are ongoing. To investigate whether MELK is also a therapeutic target in neuroblastoma, we analyzed MELK expression in primary tumors and cell lines, and examined the effects of OTS167 on neuroblastoma growth. In primary tumors, high levels of MELK were associated with advanced stage disease and inferior survival. Higher levels of MELK were also detected in tumorigenic versus nontumorigenic neuroblastoma cell lines, and cells with higher levels of MELK expression were more sensitive to OTS167 than low-MELK expressing cells. OTS167 suppressed the growth of neuroblastoma xenografts, and in a preclinical model of minimal residual disease, survival was prolonged with MELK inhibition. OTS167 treatment downregulated MELK and its target enhancer of zeste homolog 2 (EZH2), a component of the polycomb repressive complex 2 (PRC2) that is known to modulate the DNA damage response. We also show that OTS167 reduced the formation of collapsed replication forks induced by camptothecin or radiation. Taken together, our results indicate that MELK indirectly mediates efficient processing of replication-associated DNA lesions in neuroblastoma, and that OTS167 sensitizes cells to DNA-damaging agents by abrogating this process. Further studies evaluating the activity of combination treatment regimens with OTS167 in neuroblastoma are warranted.

The kinases PIG-1 and PAR-1 act in redundant pathways to regulate asymmetric division in the EMS blastomere of C. elegans

The PAR-1 kinase of C. elegans is localized to the posterior of the one-cell embryo and its mutations affect asymmetric spindle placement and partitioning of cytoplasmic components in the first cell cycle. However, par-1 mutations do not cause failure to restrict the anterior PAR polarity complex to the same extent as mutations in the posteriorly localized PAR-2 protein. Further, it has been difficult to examine the role of PAR-1 in subsequent divisions due to the early defects in par-1 mutant embryos. Here we show that the PIG-1 kinase acts redundantly with PAR-1 to restrict the anterior PAR-3 protein for normal polarity in the one-cell embryo. By using a temperature sensitive allele of par-1, which exhibits enhanced lethality when combined with a pig-1 mutation, we have further explored roles for these genes in subsequent divisions. We find that both PIG-1 and PAR-1 regulate spindle orientation in the EMS blastomere of the four-cell stage embryo to ensure that it undergoes an asymmetric division. In this cell, PIG-1 and PAR-1 act in parallel pathways for spindle positioning, PIG-1 in the MES-1/SRC-1 pathway and PAR-1 in the Wnt pathway.

A Conditional Dependency on MELK for the Proliferation of Triple-Negative Breast Cancer Cells

The role of maternal and embryonic leucine zipper kinase (MELK) in cancer cell proliferation has been contentious, with recent studies arriving at disparate conclusions. We investigated the in vitro dependency of cancer cells on MELK under a range of assay conditions. Abrogation of MELK expression has little effect under common culture conditions, in which cells are seeded at high densities and reach confluence in 3-5 days. However, MELK dependency becomes clearly apparent in clonogenic growth assays using either RNAi or CRISPR technologies to modulate MELK expression. This dependency is in sharp contrast to that of essential genes, such as those encoding classic mitotic kinases, but is similar to that of other oncogenes including MYC and KRAS. Our study provides an example demonstrating some of the challenges encountered in cancer target validation, and reveals how subtle, but important, technical variations can ultimately lead to divergent outcomes and conclusions.