Up-regulation of MELK by E2F1 promotes the proliferation in cervical cancer cells

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.

Up-regulation of NCAPG mediated by E2F1 facilitates the progression of osteosarcoma through the Wnt/β-catenin signaling pathway

Background

In recent years, there are few reports on non-SMC condensin I complex subunit G (NCAPG) in osteosarcoma. Our study aims to explore the biological role of NCAPG in osteosarcoma and its underlying molecular mechanism and to further clarify the reasons for the abnormal expression of NCAPG in osteosarcoma.

Methods

Here, we mined The Cancer Genome Atlas (TCGA) Program public database through bioinformatics methods, analyzed the differential expression of NCAPG in sarcoma tissue and normal tissue, and explored the relationship between NCAPG expression level and sarcoma tissue differentiation, including tumor recurrence, metastasis, and patient survival. Next, the transcription factors responsible for the abnormal expression of NCAPG in osteosarcoma tumors were predicted by multiple online website tools and verified via cellular experiments. Subsequently, loss of function and cell phenotype experiments were performed to confirm the effect of NCAPG on the malignant biological behavior of osteosarcoma cells. Mechanistically, by reviewing the literature, we found that NCAPG can affect the malignant progression of many solid tumors by regulating the Wnt/β-catenin signaling pathway. Therefore, we preliminarily investigated the potential effect of NCAPG on this pathway via western blot experiments in osteosarcoma.

Results

Increased expression of NCAPG was found in sarcoma compared to normal tissues, which was positively correlated with poor differentiation, metastasis, and poor prognosis. Combining the transcription factor prediction results, correlation analysis, and expression level in the TCGA public database with validation outcomes of in vitro cell assays, we found that E2F transcription factor 1 (E2F1) regulated the increased expression of NCAPG in osteosarcoma. The results of cell phenotype experiments showed that silencing NCAPG could inhibit the proliferation, migration, and invasion of osteosarcoma cells. The preliminary mechanistic investigation suggested that NCAPG may affect osteosarcoma progression through the Wnt/β-catenin pathway.

Conclusions

Our data reveal that E2F1 facilitates NCAPG expression in osteosarcoma by regulating the transcription of the NCAPG gene. Up-regulation of NCAPG promotes osteosarcoma progression via the Wnt/β-catenin signaling axis.

E2F1-EP300 co-activator complex potentiates immune escape in nasopharyngeal carcinoma through the mediation of MELK

BACKGROUND

Nasopharyngeal carcinoma (NPC) is characterized by a highly suppressive microenvironment that protects tumor cells against immune attack and facilitates tumor progression. MELK is upregulated in various tumors, whereas its function in the immune escape remains largely unknown. In this study, we investigated the role of MELK during immune escape in NPC.

METHODS

Differentially expressed genes were filtered using GEO datasets and PPI network analysis. NPC cell colony formation and motility were examined, and the impact of CD8⁺ T cells on NPC cells was evaluated. A xenograft model was constructed to detect the growth of tumor cells and the T-cell phenotype of tumor infiltration. ChIP-qPCR and dual-luciferase assays were used to verify the transcriptional regulation of MELK by EP300/E2F1.

FINDINGS

MELK was overexpressed in NPC, and sh-MELK suppressed the clonogenic ability, migration, and invasion of NPC cells and promoted the killing effects of CD8⁺ T cells. These in vitro findings were reproduced in vivo. EP300 synergized E2F1 to regulate the transcription of MELK in NPC cells. Loss of EP300 or E2F1 reverted the malignant phenotype of NPC cells and promoted the immune effect of CD8⁺ T cells. MELK further suppressed the immune effect of CD8⁺ T cells in the presence of sh-E2F1.

INTERPRETATION

EP300 coordinated with E2F1 to promote the transcription of MELK which promoted the growth of NPC cells and repressed the killing effect of CD8⁺ T cells. Blockage of MELK may be a potential way to suppress the immune escape of NPC cells.

Targeting MELK improves PD-1 blockade efficiency in cervical cancer via enhancing antitumor immunity

The balance between T helper 1 (Th1) and T helper 2 (Th2) has a critical function in determining intratumoral immune response and anti-PD-1 immunotherapy. The level of maternal embryonic leucine zipper kinase (MELK) is reported to correlate with infiltration of immune cells in cancers, but the underlying molecular mechanism is not clarified. In the present study, we aimed to elucidate the potential function of MELK in cervical cancer. We found that MELK was upregulated and played an oncogenic role in cervical cancer. MELK overexpression shifted Th1/Th2 balance toward Th2 predisposition in mouse cervical tumors in vivo and naive T cells from human PBMCs in vitro, whereas MELK knockdown exhibited opposite effects. MELK overexpression activated NF-κB signaling and promoted IL-6 secretion by cervical cancer cells. Depletion of IL-6 by neutralization antibodies abrogated the influence of MELK on Th1/Th2 balance. In addition, MELK modulated the antitumor activity of cytotoxic CD8+ T cells in cervical tumors, but depletion of Th2 cells by IL-4 neutralization abrogated this effect. Finally, MELK overexpression conferred tolerance to PD-1 blockade in cervical tumors, whereas targeting MELK by OTSSP167 significantly enhanced PD-1 blockade efficiency. Our data elucidated a novel role of MELK in regulating Th1/Th2 balance and anti-PD-1 immunotherapy in cervical cancer.

MELK promotes HCC carcinogenesis through modulating cuproptosis-related gene DLAT-mediated mitochondrial function

Cuproptosis caused by copper overload is mediated by a novel regulatory mechanism that differs from previously documented mechanisms regulating cell death. Cells dependent on mitochondrial respiration showed increased sensitivity to a copper ionophore elesclomol that induced cuproptosis. Maternal embryonic leucine zipper kinase(MELK) promotes tumorigenesis and tumor progression through the PI3K/mTOR pathway, which exerts its effects partly by targeting the pyruvate dehydrogenase complex(PDHc) and reprogramming the morphology and function of mitochondria. However, the role of MELK in cuproptosis remains unclear. Here, we validated that elevated MELK expression enhanced the activity of PI3K/mTOR signaling and subsequently promoted Dihydrolipoamide S-Acetyltransferase (DLAT) expression and stabilized mitochondrial function. This regulatory effect helped to improve mitochondrial respiration, eliminate excessive intracellular reactive oxygen species (ROS), reduce intracellular oxidative stress/damage and the possibility of mitochondria-induced cell fate alternations, and ultimately promote the progression of HCC. Meanwhile, elesclomol reduced translocase of outer mitochondrial membrane 20(TOM 20) expression and increased DLAT oligomers. Moreover, the above changes of MELK to HCC were abolished by elesclomol. In conclusion, MELK enhanced the levels of the cuproptosis-related signature(CRS) gene DLAT (especially the proportion of DLAT monomer) by activating the PI3K/mTOR pathway, thereby promoting elesclomol drug resistance, altering mitochondrial function, and ultimately promoting HCC progression.

The Functional Role and Regulatory Mechanism of FTO m6A RNA Demethylase in Human Uterine Leiomyosarcoma

Uterine leiomyosarcoma (uLMS) is the most frequent subtype of uterine sarcoma that presents a poor prognosis and high rates of recurrence and metastasis. The origin and molecular mechanism underlying and driving its clinical and biological behavior remain largely unknown. Recently, we and others have revealed the role of microRNAs, DNA methylation, and histone modifications in contributing to the pathogenesis of uLMS. However, the connection between reversible m6A RNA methylation and uLMS pathogenesis remains unclear. In this study, we assessed the role and mechanism of FTO m6A RNA demethylase in the pathogenesis of uLMS. Immunohistochemistry analysis revealed that the levels of RNA demethylases FTO and ALKBH5 were aberrantly upregulated in uLMS tissues compared to adjacent myometrium with a significant change by histochemical scoring assessment (p < 0.01). Furthermore, the inhibition of FTO demethylase with its small, potent inhibitor (Dac51) significantly decreased the uLMS proliferation dose-dependently via cell cycle arrest. Notably, RNA-seq analysis revealed that the inhibition of FTO with Dac51 exhibited a significant decrease in cell-cycle-related genes, including several CDK members, and a significant increase in the expression of CDKN1A, which correlated with a Dac51-exerted inhibitory effect on cell proliferation. Moreover, Dac51 treatment allowed the rewiring of several critical pathways, including TNFα signaling, KRAS signaling, inflammation response, G2M checkpoint, and C-Myc signaling, among others, leading to the suppression of the uLMS phenotype. Moreover, transcription factor (TF) analyses suggested that epitranscriptional alterations by Dac51 may alter the cell cycle-related gene expression via TF-driven pathways and epigenetic networks in uLMS cells. This intersection of RNA methylation and other epigenetic controls and pathways provides a framework to better understand uterine diseases, particularly uLMS pathogenesis with a dysregulation of RNA methylation machinery. Therefore, targeting the vulnerable epitranscriptome may provide an additional regulatory layer for a promising and novel strategy for treating patients with this aggressive uterine cancer.

Oncogenic FLT3 internal tandem duplication activates E2F1 to regulate purine metabolism in acute myeloid leukaemia

Oncogene FLT3 internal tandem duplication (FLT3-ITD) mutation accounts for 30 % of acute myeloid leukaemia (AML) cases and induces transformation. Previously, we found that E2F transcription factor 1 (E2F1) was involved in AML cell differentiation. Here, we reported that E2F1 expression was aberrantly upregulated in AML patients, especially in AML patients carrying FLT3-ITD. E2F1 knockdown inhibited cell proliferation and increased cell sensitivity to chemotherapy in cultured FLT3-ITD-positive AML cells. E2F1-depleted FLT3-ITD⁺ AML cells lost their malignancy as shown by the reduced leukaemia burden and prolonged survival in NOD-Prkdc^scidIl2rg^em1/Smoc mice receiving xenografts. Additionally, FLT3-ITD-driven transformation of human CD34⁺ hematopoietic stem and progenitor cells was counteracted by E2F1 knockdown. Mechanistically, FLT3-ITD enhanced the expression and nuclear accumulation of E2F1 in AML cells. Further study using chromatin immunoprecipitation-sequencing and metabolomics analyses revealed that ectopic FLT3-ITD promoted the recruitment of E2F1 on genes encoding key enzymatic regulators of purine metabolism and thus supported AML cell proliferation. Together, this study demonstrates that E2F1-activated purine metabolism is a critical downstream process of FLT3-ITD in AML and a potential target for FLT3-ITD⁺ AML patients.

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.

AMPK-like proteins and their function in female reproduction and gynecologic cancer

Serine-threonine kinase (STK11), also known as liver kinase B1 (LKB1), is a regulator of cellular homeostasis through regulating the cellular ATP-to-ADP ratio. LKB1 is classified as a tumor suppressor and functions as the key activator of AMP-activated protein kinase (AMPK) and a family of serine-threonine kinases called AMPK-like proteins. These proteins include novel (nua) kinase family 1 (NUAK1 and 2), salt inducible kinase (SIK1), QIK (known as SIK2), QSK (known as SIK3 kinase), and maternal embryonic leuzine zipper kinase (MELK) on tightly controlled and specific residual sites. LKB1 also regulates brain selective kinases 1 and 2 (BRSK1 and 2), additional members of AMPK-like protein family, which functions are probably less studied. AMPK-like proteins play a role in variety of reproductive physiology functions such as follicular maturation, menopause, embryogenesis, oocyte maturation, and preimplantation development. In addition, dysfunctional activity of AMPK-like proteins contributes to apoptosis blockade in cancer cells and induction of the epithelial-mesenchymal transition required for metastasis. Dysregulation of these proteins occurs in ovarian, endometrial, and cervical cancers. AMPK-like proteins are still undergoing further classification and may represent novel targets for targeted gynecologic cancer therapies. In this chapter, we describe the AMPK-like family of proteins and their roles in reproductive physiology and gynecologic cancers.

E2F1 promotes cell cycle progression by stabilizing spindle fiber in colorectal cancer cells

BACKGROUND

E2F1 is a transcription factor that regulates cell cycle progression. It is highly expressed in most cancer cells and activates transcription of cell cycle-related kinases. Stathmin1 and transforming acidic coiled-coil-containing protein 3 (TACC3) are factors that enhance the stability of spindle fiber.

METHODS

The E2F1-mediated transcription of transforming acidic coiled-coil-containing protein 3 (TACC3) and stathmin1 was examined using the Cancer Genome Atlas (TCGA) analysis, quantitative polymerase chain reaction (qPCR), immunoblotting, chromatin immunoprecipitation (ChIP), and luciferase reporter. Protein-protein interaction was studied using co-IP. The spindle structure was shown by immunofluorescence. Phenotype experiments were performed through MTS assay, flow cytometry, and tumor xenografts. Clinical colorectal cancer (CRC) specimens were analyzed based on immunohistochemistry.

RESULTS

The present study showed that E2F1 expression correlates positively with the expression levels of stathmin1 and TACC3 in colorectal cancer (CRC) tissues, and that E2F1 transactivates stathmin1 and TACC3 in CRC cells. Furthermore, protein kinase A (PKA)-mediated phosphorylation of stathmin1 at Ser16 is essential to the phosphorylation of TACC3 at Ser558, facilitating the assembly of TACC3/clathrin/α-tubulin complexes during spindle formation. Overexpression of Ser16-mutated stathmin1, as well as knockdown of stathmin1 or TACC3, lead to ectopic spindle poles including disorganized and multipolar spindles. Overexpression of wild-type but not Ser16-mutated stathmin1 promotes cell proliferation in vitro and tumor growth in vivo. Consistently, a high level of E2F1, stathmin1, or TACC3 not only associates with tumor size, lymph node metastasis, TNM stage, and distant metastasis, but predicts poor survival in CRC patients.

CONCLUSIONS

E2F1 drives the cell cycle of CRC by promoting spindle assembly, in which E2F1-induced stathmin1 and TACC3 enhance the stability of spindle fiber.

Identification of Novel Tumor Microenvironment Regulating Factor That Facilitates Tumor Immune Infiltration in Cervical Cancer

Cervical cancer is one of the most common gynecologic malignancies and one of the leading causes of cancer-related deaths in women worldwide. There are more than 30 categories of human papillomavirus infections in the genital tract. The recently discovered immune checkpoint suppression is a potential approach to improve clinical outcomes in these patients by altering immune cell function. However, many questions remain unanswered in terms of this method. For example, the proportion of responders is limited and the exact mechanism of action is uncertain. The tumor microenvironment (TME) has long been regarded as having nonnegligible influence on effectiveness of immunotherapy. The programmed cell death protein 1 (PD-1) pathway has received much attention due to its involvement in activating T-cell immune checkpoint responses. Since tumor cells may evade immune detection and become highly resistant to conventional treatments, anti-PD-1/PD-L1 antibodies are preferred as a kind of cancer treatment and many have just been licensed. To provide a theoretical basis for the development of new therapies, investigating the effect of tumor microenvironment on the prognosis of cervical cancer is necessary. In this work, immunological scores obtained from the ESTIMATE algorithm were used to differentiate between patients with high and low immune cell infiltration. We identified 11 immunologically significant differentially expressed genes (DEGs). For example, CXCR3 was found to be an important factor in CD8⁺ T cell recruitment and tumor immunological infiltration in cervical cancer. These results may lead to novel directions of understanding complex interactions between cancer cells and the tumor microenvironment, as well as new treatment options for cervical cancer.

Computational exploration of maternal embryonic leucine zipper kinase (MELK) as a cancer drug target

Maternal embryonic leucine zipper kinase (MELK) is of vital importance due to its significant role in cancer development and its association with poor prognosis in different cancers. Here, we employed several computer aided drug design approaches to shortlist potential binding molecules of MELK. For virtual screening, asinex oncology library (containing 6334 drugs) and comprehensive marine natural products database (containing approximately 32,000 drugs) were used. The study identified two drug molecules: Top-2 and Top-3 as high affinity binding MELK molecules compared to the control co-crystalized Top-1 inhibitor. Both the shortlisted compounds and the control showed high stable binding free energy and high GOLD score. The compounds and control also reported stable dynamics with root mean square deviations (RMSD) value ∼ 2 Å in 500 ns. Similarly, the MELK active site residues were observed in good stability with the compounds. Further, it was noticed the compounds/control formed multiple hydrogen bonds with the MELK active pocket residues which is the main reason of high intermolecular stability. Atomic level binding free energies determined van der Waals and electrostatic energies to play vital role in stable complex formation. From drug likeness and pharmacokinetics perspective, the compounds are ideal molecules for further investigation. Overall, the results are promising and might be tested in in vivo and in vitro studies against MELK.

Comprehensive Analyses of MELK-Associated ceRNA Networks Reveal a Potential Biomarker for Predicting Poor Prognosis and Immunotherapy Efficacy in Hepatocellular Carcinoma

Background: Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world with high morbidity and mortality. Identifying specific molecular markers that can predict HCC prognosis is extremely important. MELK has been reported to play key roles in several types of human cancers and predict poor prognosis. This study was aimed to explore the impact of MELK on HCC.

Methods: A pan-cancer analysis of MELK was conducted by The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) data. The prognosis of MELK in various cancers was analyzed in GEPIA. Then, a ceRNA network of MELK was constructed based on the comprehensive consideration of the expression analysis, the correlation analysis, and the survival analysis by R software. The correlation of MELK and immune cell infiltration was analyzed by TIMER and CIBERSORT. Then, the overall survival of differentially expressed immune cells was conducted. The correlation of MELK and immune checkpoints expression was analyzed by GEPIA.

Results: MELK was overexpressed in 14 types of human cancers, and its expression was significantly higher than that in both unmatched and paired normal samples in HCC. Higher MELK expression was correlated with poorer survival and advanced clinical stage, topography (T) stage, and histological grade. The univariate and multivariate Cox regression analyses showed that MELK was an independent risk factor for poor prognosis in HCC. Then, we constructed a ceRNA network consisting of MELK, miR-101-3p, and two lncRNAs (SNHG1 and SNHG6) after evaluating the expression and impact on prognosis in HCC of these RNAs. TIMER and CIBERSORT databases indicated that MELK was correlated with various immune cells including B cells, CD8+ T cells, CD4+ T cells, macrophage, neutrophil, and dendritic cells in HCC. Of them, B cells, CD4+ T cells, macrophage, and neutrophil were related to the prognosis of HCC. In addition, MELK was significantly positively correlated with the immune checkpoint genes.

Conclusions: MELK may be a novel potential biomarker for predicting prognosis and immunotherapy efficacy in patients with HCC. Our study may provide new molecular and therapeutic strategies for the treatment of HCC patients.

Identification of differentially expressed miRNAs derived from serum exosomes associated with gastric cancer by microarray analysis

AIMS

To explore the differentially expressed microRNAs (DEMs) in serum exosomes between gastric cancer (GC) patients and healthy people to provide new targets for GC diagnosis and treatment.

METHODS

DEMs in serum exosomes were screened by microarray analysis and verified by RT-qPCR. The target genes of DEMs were predicted using Targetscan and miRTarBase databases and then overlapped with the DEGs of STAD in TCGA database to obtain the common target genes. Biological function and pathway enrichment were analyzed using enrichr database, and a PPI network was constructed using STRING database. The potential target genes of DEMs were identified using the MCODE and cytoHubba plug-ins of Cytoscape software. Survival analysis were conducted using KMP and TCGA databases. The DEMs -target genes-pathways network was established using Cytoscape software. A Cox proportional hazards regression model formed by optimal target genes was used to access the reliability of this prediction process.

RESULTS

Three serum exosomal microRNAs (exo-miRNAs, has-miR-1273 g-3p, has-miR-4793-3p, has-miR-619-5p) were identified to be highly expressed in GC patients and performed excellent diagnostic ability. A total of 179 common target genes related to GC were predicted. They were mainly involved in 79 GO functional annotations and 6 KEGG pathways. The prognostic model formed by eight optimal target genes (TIMELESS, DNA2, MELK, CHAF1B, DBF4, PAICS, CHEK1 and NCAPG2), which were low-risk genes of GC, also performed perfect prognostic ability.

CONCLUSIONS

Serum exosomal has-miR-1273 g-3p, has-miR-4793-3p and has-miR-619-5p can be used as new diagnostic biomarkers for GC. Among them, serum exosomal hsa-miR-1273 g-3p / hsa-miR-4793-3p targets MELK and hsa-miR-619-5p targets NCAPG2 were identified as novel mechanisms involved in the development of GC. It provides new targets for the diagnosis and treatment of GC by exo-miRNAs.