MLK3 is a newly identified microRNA-520b target that regulates liver cancer cell migration

A primer for Fibroblast Growth Factor 16 (FGF16)

During the discovery of the Fibroblast Growth Factor superfamily, scientists were determined to uncover all the genes that encoded FGF proteins. In 1998, FGF16 was discovered with classical cloning techniques in human and rat heart samples. FGF16 loss- and gain-of-function experiments in several organisms demonstrated a conserved function in vertebrates, and as a component of the FGF9 subfamily of ligands (FGF-E/-9/-20), is functionally conserved and sufficient to rescue loss-of-function phenotypes in invertebrates, like C. elegans. FGF16 has a broad expression pattern, predominantly expressed in brown adipose tissue, heart, with low but detectable levels in the brain, olfactory bulb, inner ear, muscle, thymus, pancreas, spleen, stomach, small intestine, and gonads (testis and ovary). FGF16 is also expressed moderately in the late developing limb bud. Despite its expression levels, this ligand plays notable roles in autopod metacarpal development; loss of one allele causes congenital metacarpal 4-5 fusion and hand deformities in humans. The broad expression pattern of FGF16 in several tissues underscores its multifaceted roles in stem cell maintenance, proliferation, cell fate specification, and metabolism.

Molecular insights into the role of mixed lineage kinase 3 in cancer hallmarks

Mixed-lineage kinase 3 (MLK3) is a serine/threonine kinase of the MAPK Kinase kinase (MAP3K) family that plays critical roles in various biological processes, including cancer. Upon activation, MLK3 differentially activates downstream MAPKs, such as JNK, p38, and ERK. In addition, it regulates various non-canonical signaling pathways, such as β-catenin, AMPK, Pin1, and PAK1, to regulate cell proliferation, apoptosis, invasion, and metastasis. Recent studies have also uncovered other potentially diverse roles of MLK3 in malignancy, which include metabolic reprogramming, cancer-associated inflammation, and evasion of cancer-related immune surveillance. The role of MLK3 in cancer is complex and cancer-specific, and an understanding of its function at the molecular level aligned specifically with the cancer hallmarks will have profound therapeutic implications for diagnosing and treating MLK3-dependent cancers. This review summarizes the current knowledge about the effect of MLK3 on the hallmarks of cancer, providing insights into its potential as a promising anticancer drug target.

MLK3 promotes prooncogenic signaling in hepatocellular carcinoma via TGFβ pathway

Advanced hepatocellular carcinoma (HCC) is a lethal disease, with limited therapeutic options. Mixed Lineage Kinase 3 (MLK3) is a key regulator of liver diseases, although its role in HCC remains unclear. Analysis of TCGA databases suggested elevated MAP3K11 (MLK3 gene) expression, and TMA studies showed higher MLK3 activation in human HCCs. To understand MLK3's role in HCC, we utlized carcinogen-induced HCC model and compared between wild-type and MLK3 knockout (MLK3-/-) mice. Our studies showed that MLK3 kinase activity is upregulated in HCC, and MLK3 deficiency alleviates HCC progression. MLK3 deficiency reduced proliferation in vivo and MLK3 inhibition reduced proliferation and colony formation in vitro. To obtain further insight into the mechanism and identify newer targets mediating MLK3-induced HCCs, RNA-sequencing analysis was performed. These showed that MLK3 deficiency modulates various gene signatures, including EMT, and reduces TGFB1&2 expressions. HCC cells overexpressing MLK3 promoted EMT via autocrine TGFβ signaling. Moreover, MLK3 deficiency attenuated activated hepatic stellate cell (HSC) signature, which is increased in wild-type. Interestingly, MLK3 promotes HSC activation via paracrine TGFβ signaling. These findings reveal TGFβ playing a key role at different steps of HCC, downstream of MLK3, implying MLK3-TGFβ axis to be an ideal drug target for advanced HCC management.

miRGediNET: A comprehensive examination of common genes in miRNA-Target interactions and disease associations: Insights from a grouping-scoring-modeling approach

In the broad and complex field of biological data analysis, researchers frequently gather information from a single source or database. Despite being a widespread practice, this has disadvantages. Relying exclusively on a single source can limit our comprehension as it may omit various perspectives that could be obtained by combining multiple knowledge bases. Acknowledging this shortcoming, we report on miRGediNET, a novel approach combining information from three biological databases. Our investigation focuses on microRNAs (miRNAs), small non-coding RNA molecules that regulate gene expression post-transcriptionally. We delve deeply into the knowledge of these miRNA's interactions with genes and the possible effects these interactions may have on different diseases. The scientific community has long recognized a direct correlation between the progression of specific diseases and miRNAs, as well as the genes they target. By using miRGediNET, we go beyond simply acknowledging this relationship. Rather, we actively look for the critical genes that could act as links between the actions of miRNAs and the mechanisms underlying disease. Our methodology, which carefully identifies and investigates these important genes, is supported by a strategic framework that may open up new possibilities for comprehending diseases and creating treatments. We have developed a tool on the Knime platform as a concrete application of our research. This tool serves as both a validation of our study and an invitation to the larger community to interact with, investigate, and build upon our findings. miRGediNET is publicly accessible on GitHub at https://github.com/malikyousef/miRGediNET, providing a collaborative environment for additional research and innovation for enthusiasts and fellow researchers.

Hsa-miR-379 down-regulates Rac1/MLK3/JNK/AP-1/Collagen I cascade reaction by targeting connective tissue growth factor in human alveolar basal epithelial A549 cells

OBJECTIVE

This study was aimed to screen and identify miRNAs that could regulate human CTGF gene and downstream cascade reaction Rac1/MLK3/JNK/AP-1/Collagen I by bioinformatics and experimental means.

METHODS

TargetScan and Tarbase were used to predict miRNAs that may have regulatory effects on human CTGF gene. The dual-luciferase reporter gene assay was employed to verify the results obtained in bioinformatics. Human alveolar basal epithelial A549 cells were exposed to silica (SiO₂) culture medium for 24 h to establish an in vitro model of pulmonary fibrosis, and bleomycin (BLM) of 100 ng/mL was used as a positive control. The miRNA and mRNA expression levels were determined by RT-qPCR, and the protein levels were measured by western blot in hsa-miR-379-3p overexpression group or not.

RESULTS

A total of 9 differentially expressed miRNAs that might regulate the human CTGF gene were predicted. Hsa-miR-379-3p and hsa-miR-411-3p were selected for the subsequent experiments. The results of the dual-luciferase reporter assay showed that hsa-miR-379-3p could bind to CTGF, but hsa-miR-411-3p could not. Compared with the control group, SiO₂ exposure (25 and 50 μg/mL) could significantly reduce the expression level of hsa-miR-379-3p in A549 cells. SiO₂ exposure (50 μg/mL) could significantly increase the mRNA expression levels of CTGF, Collagen I, Rac1, MLK3, JNK, AP1, and VIM in A549 cells, while CDH1 level was significantly decreased. Compared with SiO₂ + NC group, the mRNA expression levels of CTGF, Collagen I, Rac1, MLK3, JNK, AP1, and VIM were significantly decreased, and CDH1 level was significantly higher when hsa-miR-379-3p was overexpressed. At the same time, overexpression of hsa-miR-379-3p improved the protein levels of CTGF, Collagen I, c-Jun and phospho-c-Jun, JNK1 and phospho-JNK1 significantly compared with SiO₂ + NC group.

CONCLUSION

Hsa-miR-379-3p was demonstrated for the first time that could directly target and down-regulate human CTGF gene, and further affect the expression levels of key genes and proteins in Rac1/MLK3/JNK/AP-1/Collagen I cascade reaction.

MLK3 Regulates Inflammatory Response via Activation of AP-1 Pathway in HEK293 and RAW264.7 Cells

Inflammation is a critically important barrier found in innate immunity. However, severe and sustained inflammatory conditions are regarded as causes of many different serious diseases, such as cancer, atherosclerosis, and diabetes. Although numerous studies have addressed how inflammatory responses proceed and what kinds of proteins and cells are involved, the exact mechanism and protein components regulating inflammatory reactions are not fully understood. In this paper, to determine the regulatory role of mixed lineage kinase 3 (MLK3), which functions as mitogen-activated protein kinase kinase kinase (MAP3K) in cancer cells in inflammatory response to macrophages, we employed an overexpression strategy with MLK3 in HEK293 cells and used its inhibitor URMC-099 in lipopolysaccharide (LPS)-treated RAW264.7 cells. It was found that overexpressed MLK3 increased the mRNA expression of inflammatory genes (COX-2, IL-6, and TNF-α) via the activation of AP-1, according to a luciferase assay carried out with AP-1-Luc. Overexpression of MLK3 also induced phosphorylation of MAPKK (MEK1/2, MKK3/6, and MKK4/7), MAPK (ERK, p38, and JNK), and AP-1 subunits (c-Jun, c-Fos, and FRA-1). Phosphorylation of MLK3 was also observed in RAW264.7 cells stimulated by LPS, Pam3CSK, and poly(I:C). Finally, inhibition of MLK3 by URMC-099 reduced the expression of COX-2 and CCL-12, phosphorylation of c-Jun, luciferase activity mediated by AP-1, and phosphorylation of MAPK in LPS-treated RAW264.7 cells. Taken together, our findings strongly suggest that MLK3 plays a central role in controlling AP-1-mediated inflammatory responses in macrophages and that this enzyme can serve as a target molecule for treating AP-1-mediated inflammatory diseases.

Neuroprotection of sevoflurane against ischemia/reperfusion-induced brain injury through inhibiting GluN2A/GluN2B-PSD-95-MLK3 module

To investigate the role of GluN2A and GluN2B in neuroprotective effect of sevoflurane preconditioning against cerebral ischemia-reperfusion injury (CIRI). Rats were randomly divided into five groups as follows: control, ischemia-reperfusion (I/R) 6 h, sevoflurane preconditioning (SP), SP + amantadine, SP + NMDA. Immunoblot and immunoprecipitation were used to detect the tyrosine phosphorylation of GluN2A/GluN2B, the interaction of GluN2A/GluN2B-PSD-95-MLK3 and the expression of phosphorylation of MLK3, MKK7 and JNK3. Cresyl violet staining was employed to analyse neuronal injury in rat hippocampal CA1 subfields. Sevoflurane preconditioning inhibits the tyrosine phosphorylation of GluN2A/GluN2B, the interaction of GluN2A/GluN2B-PSD-95-MLK3 and the phosphorylation of MLK3, MKK7 and JNK3 in rat hippocampus. An N-methyl-D-aspartate receptor (NMDAR) antagonist amantadine reversed the MLK3-MKK7- JNK3 signal events. Such reversion was also realized by NMDA (60 and 80 nmol) and low doses of NMDA (0-40 nmol) could not change the inhibitory effect of sevoflurane preconditioning on MLK3-MKK7-JNK3 signal events. Finally, Cresyl violet staining also confirmed that low dose of NMDA reduced neuronal loss in rat hippocampal CA1 subfields. Sevoflurane preconditioning provides neuroprotection against CIRI by inhibiting NMDAR over-activation.

FGF16 regulated by miR-520b enhances the cell proliferation of lung cancer

FGF16 is implicated in the progression of some specific types of cancers, such as embryonic carcinoma, ovarian cancer, and liver cancer. Yet, the function of FGF16 in the development of lung cancer remains largely unexplored. In this study, we present the novel function of FGF16 and the regulation of miR-520b on FGF16 in lung cancer progression. In clinical lung cancer tissues, FGF16 is overexpressed and its high level is negatively associated with the low level of miR-520b. Furthermore, both the transcription and translation levels of FGF16 are restrained by miR-520b in lung cancer cells. For the regulatory mechanism investigation, miR-520b is able to directly bind to the 3′-untranslated region (3′UTR) of FGF16 mRNA, leading to its mRNA cleavage in the cells. Functionally, miR-520b reduces the growth of lung cancer and its inhibitor anti-miR520b is able to promote the growth through competing endogenous miR-520b. Moreover, FGF16 silence using RNA interference is capable of doing great damage to anti-miR-520b-accelerated growth of lung cancer. Thus, our finding indicates that FGF16 is a new target gene of miR-520b in lung cancer. For lung cancer, FGF16 may serve as a novel biomarker and miR-520b/FGF16 may be useful in clinical treatment.

The regulatory function of mixed lineage kinase 3 in tumor and host immunity

Protein kinases are the second most sought-after G-protein coupled receptors as drug targets because of their overexpression, mutations, and dysregulated catalytic activities in various pathological conditions. Till 2019, 48 protein kinase inhibitors have received FDA approval for the treatment of multiple illnesses, of which the majority of them are indicated for different malignancies. One of the attractive sub-group of protein kinases that has attracted attention for drug development is the family members of MAPKs that are recognized to play significant roles in different cancers. Several inhibitors have been developed against various MAPK members; however, none of them as monotherapy has shown sustainable efficacy. One of the MAPK members, called Mixed Lineage Kinase 3 (MLK3), has attracted considerable attention due to its role in inflammation and neurodegenerative diseases; however, its role in cancer is an emerging area that needs more investigation. Recent advances have shown that MLK3 plays a role in cancer cell survival, migration, drug resistance, cell death, and tumor immunity. This review describes how MLK3 regulates different MAPK pathways, cancer cell growth and survival, apoptosis, and host's immunity. We also discuss how MLK3 inhibitors can potentially be used along with immunotherapy for different malignancies.