MicroRNA miR-7-5p targets MARK2 to control metamorphosis in Galeruca daurica

The MARK2 gene, coding microtubule affinity-regulating kinase or serine/threonine protein kinase, is an important modulator in organism microtubule generation and cell polarity. However, its role in the metamorphosis of insects remains unknown. In this study, we found a conserved miRNA, miR-7-5p, which targets MARK2 to participate in the regulation of the larval-pupal metamorphosis in Galeruca daurica. The dual luciferase reporter assay showed that miR-7-5p interacted with the 3' UTR of MARK2 and repressed its expression. The expression profiling of miR-7-5p and MARK2 displayed an opposite trend during the larval-adult development process. In in-vivo experiments, overexpression of miR-7-5p by injecting miR-7-5p agomir in the final instar larvae down-regulated MARK2 and up-regulated main ecdysone signaling pathway genes including E74, E75, ECR, FTZ-F1 and HR3, which was similar to the results from knockdown of MARK2 by RNAi. In contrast, repression of miR-7-5p by injecting miR-7-5p antagomir obtained opposite effects. Notably, both overexpression and repression of miR-7-5p in the final instar larvae caused abnormal molting and high mortality during the larval-pupal transition, and high mortality during the pupal-adult transition. The 20-hydroxyecdysone (20E) injection experiment showed that 20E up-regulated miR-7-5p whereas down-regulated MARK2. This study reveals that the accurate regulation of miRNAs and their target genes is indispensable for insect metamorphosis.

Lfc subcellular localization and activity is controlled by αv-class integrin

Fibronectin (FN)-binding integrins control a variety of cellular responses through Rho GTPases. The FN-binding integrins, αvβ3 and α5β1, are known to induce different effects on cell morphology and motility. Here, we report that FN-bound αvβ3 integrin, but not FN-bound α5β1 integrin, triggers the dissociation of the RhoA GEF Lfc (also known as GEF-H1 and ARHGEF2 in humans) from microtubules (MTs), leading to the activation of RhoA, formation of stress fibres and maturation of focal adhesions (FAs). Conversely, loss of Lfc expression decreases RhoA activity, stress fibre formation and FA size, suggesting that Lfc is the major GEF downstream of FN-bound αvβ3 that controls RhoA activity. Mechanistically, FN-engaged αvβ3 integrin activates a kinase cascade involving MARK2 and MARK3, which in turn leads to phosphorylation of several phospho-sites on Lfc. In particular, S151 was identified as the main site involved in the regulation of Lfc localization and activity. Our findings indicate that activation of Lfc and RhoA is orchestrated in FN-adherent cells in an integrin-specific manner.

Bi-allelic CAMSAP1 variants cause a clinically recognizable neuronal migration disorder

Non-centrosomal microtubules are essential cytoskeletal filaments that are important for neurite formation, axonal transport, and neuronal migration. They require stabilization by microtubule minus-end-targeting proteins including the CAMSAP family of molecules. Using exome sequencing on samples from five unrelated families, we show that bi-allelic CAMSAP1 loss-of-function variants cause a clinically recognizable, syndromic neuronal migration disorder. The cardinal clinical features of the syndrome include a characteristic craniofacial appearance, primary microcephaly, severe neurodevelopmental delay, cortical visual impairment, and seizures. The neuroradiological phenotype comprises a highly recognizable combination of classic lissencephaly with a posterior more severe than anterior gradient similar to PAFAH1B1(LIS1)-related lissencephaly and severe hypoplasia or absence of the corpus callosum; dysplasia of the basal ganglia, hippocampus, and midbrain; and cerebellar hypodysplasia, similar to the tubulinopathies, a group of monogenic tubulin-associated disorders of cortical dysgenesis. Neural cell rosette lineages derived from affected individuals displayed findings consistent with these phenotypes, including abnormal morphology, decreased cell proliferation, and neuronal differentiation. Camsap1-null mice displayed increased perinatal mortality, and RNAScope studies identified high expression levels in the brain throughout neurogenesis and in facial structures, consistent with the mouse and human neurodevelopmental and craniofacial phenotypes. Together our findings confirm a fundamental role of CAMSAP1 in neuronal migration and brain development and define bi-allelic variants as a cause of a clinically distinct neurodevelopmental disorder in humans and mice.

A ZFP42/MARK2 regulatory network reduces the damage of retinal ganglion cells in glaucoma: a study based on GEO dataset and in vitro experiments

Glaucoma is a common disorder in which the death of retinal ganglion cells (RGCs) results in a progressive loss of sight, even blindness. This study was performed to reveal the key molecular mechanism of RGC damage in glaucoma based on the Gene Expression Omnibus database. Glaucoma-related microarray datasets were identified, followed by collection of differentially expressed genes (DEGs) with the key genes discovered by weighted gene co-expression network analysis. Through LASSO regression analysis, candidate genes involved in the pathogenesis of glaucoma were identified with their accuracy evaluated by receiver operating characteristic curve analysis. The glaucoma-specific transcriptional regulatory network was constructed to determine the key transcription factor regulatory axis. Then, in vitro cell models were established using H₂O₂ for further verifying the regulatory role of identified ZFP42/MARK2 axis in RGC damage in glaucoma. Differential analysis of GSE27276, GSE45570, and GSE101727 microarray datasets yielded 165 DEGs, and 22 key genes were identified following. Then, 9 candidate genes involved in the pathogenesis of glaucoma was collected and the key ZFP42/MARK2 regulatory axis was found. In vitro cell experiments further confirmed that ZFP42 and MARK2 were down-regulated in RGCs treated with H₂O₂. In addition, overexpression of ZFP42 increased the expression of MARK2 to increase RGC cell viability, and reduce cell apoptosis and ROS levels, while silencing MARK2 could reverse the protective effect of ZFP42. We confirmed that ZFP42 reduced the damage of RGCs in glaucoma by up-regulating the expression of MARK2.

MARK2/4 promotes Warburg effect and cell growth in non-small cell lung carcinoma through the AMPKα1/mTOR/HIF-1α signaling pathway

MARKs kinase belongs to an AMPK-related family kinase plays a critical role in tumor progression, but its exact role and contribution of four different isoforms remain largely ambiguous. In this study, we used a clinical dataset compiled by The Cancer Genome Atlas (TCGA) and GEO revealed that MARK2 and MARK4 expressions were significantly upregulated in non-small cell lung cancer (NSCLC) compared with normal tissues. Furthermore, expressions of MARK2/4 were highly appeared in advanced stages and associated with the low survival rate of NSCLC patients. Functional assays demonstrated that MARK2/4 deletion or MARKs inhibition significantly suppressed aerobic glycolysis and cell growth in NSCLC cells. Mechanistically, MARK2/4 stimulates the mTOR/HIF-1α pathway and subsequently alleviates AMPK activity via physically associate with Raptor and AMPKα1, thereby facilitating aerobic glycolysis and cell growth in NSCLC cells. However, these effects were markedly reversed by MARKs inhibitor 39621, or MARK2/4 deletion, mTOR inhibitor rapamycin, or AMPK activator AICAR. Together, the data demonstrated that MARK2/4 exerts its oncogenic effects by facilitating metabolic reprogramming in NSCLC cells. Therefore, MARK2/4 might be a potential therapeutic target for lung cancer.

Identification of a reciprocal negative feedback loop between tau-modifying proteins MARK2 kinase and CBP acetyltransferase

The posttranslational regulation of the neuronal proteome is critical for brain homeostasis but becomes dysregulated in the aged or diseased brain, in which abnormal posttranslational modifications (PTMs) are frequently observed. While the full extent of modified substrates that comprise the "PTM-ome" are slowly emerging, how the upstream enzymes catalyzing these processes are regulated themselves is not well understood, particularly in the context of neurodegeneration. Here, we describe the reciprocal regulation of a kinase, the microtubule affinity-regulating kinase 2 (MARK2), and an acetyltransferase, CREB-binding protein (CBP), two enzymes known to extensively modify tau proteins in the progression of Alzheimer's disease. We found that MARK2 negatively regulates CBP and, conversely, CBP directly acetylates and inhibits MARK2 kinase activity. These findings highlight a reciprocal negative feedback loop between a kinase and an acetyltransferase, which has implications for how PTM interplay is coordinated on substrates including tau. Our study suggests that PTM profiles occur through the posttranslational control of the master PTM remodeling enzymes themselves.

MARK2 regulates directed cell migration through modulation of myosin II contractility and focal adhesion organization

Cancer cell migration during metastasis is mediated by a highly polarized cytoskeleton. MARK2 and its invertebrate homolog Par1B are kinases that regulate the microtubule cytoskeleton to mediate polarization of neurons in mammals and embryos in invertebrates. However, the role of MARK2 in cancer cell migration is unclear. Using osteosarcoma cells, we found that in addition to its known localizations on microtubules and the plasma membrane, MARK2 also associates with the actomyosin cytoskeleton and focal adhesions. Cells depleted of MARK proteins demonstrated that MARK2 promotes phosphorylation of both myosin II and the myosin phosphatase targeting subunit MYPT1 to synergistically drive myosin II contractility and stress fiber formation in cells. Studies with isolated proteins showed that MARK2 directly phosphorylates myosin II regulatory light chain, while its effects on MYPT1 phosphorylation are indirect. Using a mutant lacking the membrane-binding domain, we found that membrane association is required for focal adhesion targeting of MARK2, where it specifically enhances cell protrusion by promoting FAK phosphorylation and formation of focal adhesions oriented in the direction of migration to mediate directionally persistent cell motility. Together, our results define MARK2 as a master regulator of the actomyosin and microtubule cytoskeletal systems and focal adhesions to mediate directional cancer cell migration.

MARK2 potentiate aerobic glycolysis-mediated cell growth in breast cancer through regulating mTOR/HIF-1α and p53 pathways

The microtubule-affinity regulating kinases (MARKs) family plays a crucial role in regulating breast cancer development and progression. However, its precise function and the relevant molecular mechanism in breast cancer have not yet been elucidated. In this study, analysis of The Cancer Genome Atlas (TCGA) data revealed that MARK2 expression was markedly upregulated in breast cancer tissues, and high expression of MARK2 was correlated with poor survival. Functional assays showed that MARK2 deletion or inhibition suppressed aerobic glycolysis and cell growth as well as induced cell cycle arrest and apoptosis in breast cancer cells. Mechanistically, MARK2 stimulates mTOR-mediated hypoxia-inducible factor 1 alpha (HIF-1α) transcription activity and represses p53-transcription activity in breast cancer cells. TCGA data revealed that MARK2 expression was positively correlated with mTOR, Raptor, S6K1, glucose transporter 1, lactate dehydrogenase, HIF-1α, and 4E-BP1 expression, whereas negatively correlated with p53, p21, and Bax in breast cancer tissue. Conclusively, our study demonstrated that MARK2 promotes breast cancer aerobic glycolysis and cell proliferation, and inhibits apoptosis, in part, through regulating mTOR/HIF-1α and p53 signaling pathways. Overall, these findings point to the potential of targeting MARK2 for breast cancer treatment.

Long non-coding RNA ABHD11-AS1 facilitates the progression of cervical cancer by competitively binding to miR-330-5p and upregulating MARK2

Cervical cancer (CC) is among the most prevalent gynecological malignancies. Participation of long non-coding RNA (lncRNA) in modulating biological behaviors of CC cells has been confirmed. However, the function of lncRNA ABHD11 antisense RNA 1 (ABHD11-AS1) in CC is still unclear. RT-qPCR and Western blot were performed for measuring RNA and protein levels. Functional assays were done to evaluate ABHD11-AS1 influences on cell proliferation, apoptosis, invasion and migration. After the verification of ABHD11-AS1 distribution in CC cells, mechanism assays were conducted to study the interaction of relative RNAs. ABHD11-AS1 expression was abnormally high in CC cells. In vitro experiments showed ABHD11-AS1 downregulation restrained CC cell malignant phenotypes. In vivo experiments proved ABHD11-AS1 knockdown impeded tumor growth. Moreover, miR-330-5p was corroborated to bind with ABHD11-AS1 in CC cells and microtubule affinity regulating kinase 2 (MARK2) was confirmed to be targeted by miR-330-5p. MiR-330-5p inhibition or MARK2 overexpression could countervail the suppressive effect of ABHD11-AS1 knockdown on CC cell malignant behaviors. We found that ABHD11-AS1 facilitated CC tumorigenesis through competitively sequestering miR-330-5p to upregulate MARK2, indicating ABHD11-AS1 as a potential biomarker in CC.

LKB1-MARK2 signalling mediates lipopolysaccharide-induced production of cytokines in mouse macrophages

Lipopolysaccharide (LPS) is an endotoxin involved in a number of acute and chronic inflammatory syndromes. Although LPS-induced signalling has been extensively studied, there are still mysteries remaining to be revealed. In the current study, we used high-throughput phosphoproteomics to profile LPS-initiated signalling and aimed to find novel mediators. A total of 448 phosphoproteins with 765 phosphorylation sites were identified, and we further validated that the phosphorylation of MARK2 on T208 was important for the regulation on LPS-induced CXCL15 (human IL-8 homolog), IL-1β, IL-6 and TNF-α release, in which LKB1 had a significant contribution. In summary, induction of cytokines by LPS in mouse macrophage is regulated by LKB1-MARK2 signals. Our study provides new clues for further exploring the underlying mechanisms of LPS-induced diseases, and new therapeutic approaches concerning bacterial infection may be derived from these findings.

CAMSAP1 breaks the homeostatic microtubule network to instruct neuronal polarity

The establishment of axon/dendrite polarity is fundamental for neurons to integrate into functional circuits, and this process is critically dependent on microtubules (MTs). In the early stages of the establishment process, MTs in axons change dramatically with the morphological building of neurons; however, how the MT network changes are triggered is unclear. Here we show that CAMSAP1 plays a decisive role in the neuronal axon identification process by regulating the number of MTs. Neurons lacking CAMSAP1 form a multiple axon phenotype in vitro, while the multipolar-bipolar transition and radial migration are blocked in vivo. We demonstrate that the polarity regulator MARK2 kinase phosphorylates CAMSAP1 and affects its ability to bind to MTs, which in turn changes the protection of MT minus-ends and also triggers asymmetric distribution of MTs. Our results indicate that the polarized MT network in neurons is a decisive factor in establishing axon/dendritic polarity and is initially triggered by polarized signals.

Phosphorylation Sites in Protein Kinases and Phosphatases Regulated by Formyl Peptide Receptor 2 Signaling

FPR1, FPR2, and FPR3 are members of Formyl Peptides Receptors (FPRs) family belonging to the GPCR superfamily. FPR2 is a low affinity receptor for formyl peptides and it is considered the most promiscuous member of this family. Intracellular signaling cascades triggered by FPRs include the activation of different protein kinases and phosphatase, as well as tyrosine kinase receptors transactivation. Protein kinases and phosphatases act coordinately and any impairment of their activation or regulation represents one of the most common causes of several human diseases. Several phospho-sites has been identified in protein kinases and phosphatases, whose role may be to expand the repertoire of molecular mechanisms of regulation or may be necessary for fine-tuning of switch properties. We previously performed a phospho-proteomic analysis in FPR2-stimulated cells that revealed, among other things, not yet identified phospho-sites on six protein kinases and one protein phosphatase. Herein, we discuss on the selective phosphorylation of Serine/Threonine-protein kinase N2, Serine/Threonine-protein kinase PRP4 homolog, Serine/Threonine-protein kinase MARK2, Serine/Threonine-protein kinase PAK4, Serine/Threonine-protein kinase 10, Dual specificity mitogen-activated protein kinase kinase 2, and Protein phosphatase 1 regulatory subunit 14A, triggered by FPR2 stimulation. We also describe the putative FPR2-dependent signaling cascades upstream to these specific phospho-sites.

MARK2 enhances cisplatin resistance via PI3K/AKT/NF-κB signaling pathway in osteosarcoma cells

Osteosarcoma is the most common primary bone malignancy found in children and young adults. Chemotherapy resistance, especially to cisplatin, presents a major clinical challenge in the treatment and prognosis of osteosarcoma. New biomarkers and mechanisms of cisplatin resistance in osteosarcoma are urgently needed due to poor survival outcomes and currently inadequate treatments. In this study, we investigate the role and potential mechanisms of microtubule-affinity regulating kinase2 (MARK2) during osteosarcoma cisplatin resistance. Gene Expression Omnibus dataset analyses indicated that high MARK2 expression was associated with poor prognosis and may positively correlate with chemoresistance. Moreover, we showed that MARK2 was significantly upregulated in osteosarcoma cells compared with normal cells. The overexpression and inhibition of MARK2 promoted and suppressed, respectively, cisplatin resistance in osteosarcoma cells in vitro and in vivo. Mechanistically, MARK2 overexpression enhanced P-glycoprotein expression and decreased cell apoptosis through PI3K/AKT/NF-κB signaling pathway activation, resulting in cisplatin resistance. Our results suggest that high MARK2 expression can enhance cisplatin resistance in osteosarcoma cells, supporting the potential of MARK2 as a new therapeutic target and biomarker for predicting cisplatin resistance in osteosarcoma.

The inhibition of MARK2 suppresses cisplatin resistance of osteosarcoma stem cells by regulating DNA damage and repair

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MARK2 plays an important role in the chemoresistance mechanism of osteosarcoma stem cells.

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Down-regulation of MARK2 in CD133+ MG-63 and MNNG/HOS cells inhibits the expression of DNA-PKcs by inhibiting the activity of the PI3K/Akt/mTOR pathway.

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New clues for the osteosarcoma chemotherapy strategy.

Objective

This study aims to explore the role of MARK2 in chemotherapeutic resistance and potential mechanism within cisplatin resistance models of CD133⁺ MG-63 and MNNG/HOS cells.

Methods

CD133⁻ and CD133⁺ MG-63 and MNNG/HOS cells were differentiated and obtained by MACS(Magnetic bead sorting). Cell activity was determined by CCK-8 assay. siRNA was employed to down regulate the Microtubule Affinity Regulated Kinase 2 (MARK2) expression. Immunofluorescence detection and RT-qPCR were used to measure the expressions of MARK2 and DNA-PKcs at both protein and mRNA levels. Western blot was applied to test the levels of MARK2, γH2AX (S139), DNA-PKcs, Phospho-PI3 Kinase p85 (Tyr458), Akt, phospho-Akt (T308) antibodies, mTOR, phospho-mTOR (Ser2448).

Results

Compared with CD133⁻ MG-63 cells, CD133⁺ MG-63 cells showed significantly strong cisplatin resistance, with high levels of MARK2, DNA-PKcs and potent DNA damage repair ability (p<0.05). Down regulation of MARK2 reduced the cisplatin resistance of CD133⁺ MG-63 cells, with deceasing expression of DNA-PKcs (p<0.05). PI3K/Akt/mTOR pathway was potentially activated in CD133⁺ MG-63 cells, and involved in the cisplatin resistance of MG-63 cells. The similar results were observed in CD133⁺ MNNG/HOS cells. The reduction of MARK2 retarded the activity of PI3K/Akt/mTOR pathway and further impeded the cisplatin resistance in CD133⁺ MG-63 and MNNG/HOS cell.

Conclusion

Our data suggested that MARK2 was related to cisplatin resistance in CD133⁺ MG-63 and MNNG/HOS cells. The decrease of MARK2 restricted the cisplatin resistance of CD133⁺ MG-63 and MNNG/HOS cells by down regulating the expression of DNA dependent protein kinase catalytic subunit (DNA-PKcs) and inhibiting activity of PI3K/Akt/mTOR signaling pathway, which provides new clues for the osteosarcoma chemotherapy strategy.

Memantine Improves Cognitive Function and Alters Hippocampal and Cortical Proteome in Triple Transgenic Mouse Model of Alzheimer's Disease

Memantine is a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist clinically approved for moderate-to-severe Alzheimer's disease (AD) to improve cognitive functions. There is no report about the proteomic alterations induced by memantine in AD mouse model yet. In this study, we investigated the protein profiles in the hippocampus and the cerebral cortex of AD-related transgenic mouse model (3×Tg-AD) treated with memantine. Mice (8-month) were treated with memantine (5 mg/kg/bid) for 4 months followed by behavioral and molecular evaluation. Using step-down passive avoidance (SDA) test, novel object recognition (NOR) test and Morris water maze (MWM) test, it was observed that memantine significantly improved learning and memory retention in 3xTg-AD mice. By using quantitative proteomic analysis, 3301 and 3140 proteins in the hippocampus and the cerebral cortex respectively were identified to be associated with AD abnormalities. In the hippocampus, memantine significantly altered the expression levels of 233 proteins, among which PCNT, ATAXIN2, TNIK, and NOL3 were up-regulated, and FLNA, MARK 2 and BRAF were down-regulated. In the cerebral cortex, memantine significantly altered the expression levels of 342 proteins, among which PCNT, PMPCB, CRK, and MBP were up-regulated, and DNM2, BRAF, TAGLN 2 and FRY1 were down-regulated. Further analysis with bioinformatics showed that memantine modulated biological pathways associated with cytoskeleton and ErbB signaling in the hippocampus, and modulated biological pathways associated with axon guidance, ribosome, cytoskeleton, calcium and MAPK signaling in the cerebral cortex. Our data indicate that memantine induces higher levels of proteomic alterations in the cerebral cortex than in the hippocampus, suggesting memantine affects various brain regions in different manners. Our study provides a novel view on the complexity of protein responses induced by memantine in the brain of AD.

Genetic Overlap Between Alzheimer's Disease and Bipolar Disorder Implicates the MARK2 and VAC14 Genes

Background: Alzheimer's disease (AD) and bipolar disorder (BIP) are complex traits influenced by numerous common genetic variants, most of which remain to be detected. Clinical and epidemiological evidence suggest that AD and BIP are related. However, it is not established if this relation is of genetic origin. Here, we applied statistical methods based on the conditional false discovery rate (FDR) framework to detect genetic overlap between AD and BIP and utilized this overlap to increase the power to identify common genetic variants associated with either or both traits. Methods: We obtained genome wide association studies data from the International Genomics of Alzheimer's Project part 1 (17,008 AD cases and 37,154 controls) and the Psychiatric Genetic Consortium Bipolar Disorder Working Group (20,352 BIP cases and 31,358 controls). We used conditional QQ-plots to assess overlap in common genetic variants between AD and BIP. We exploited the genetic overlap to re-rank test-statistics for AD and BIP and improve detection of genetic variants using the conditional FDR framework. Results: Conditional QQ-plots demonstrated a polygenic overlap between AD and BIP. Using conditional FDR, we identified one novel genomic locus associated with AD, and nine novel loci associated with BIP. Further, we identified two novel loci jointly associated with AD and BIP implicating the MARK2 gene (lead SNP rs10792421, conjunctional FDR = 0.030, same direction of effect) and the VAC14 gene (lead SNP rs11649476, conjunctional FDR = 0.022, opposite direction of effect). Conclusion: We found polygenic overlap between AD and BIP and identified novel loci for each trait and two jointly associated loci. Further studies should examine if the shared loci implicating the MARK2 and VAC14 genes could explain parts of the shared and distinct features of AD and BIP.

Loss of Par1b/MARK2 primes microglia during brain development and enhances their sensitivity to injury

Background

Microglia, the resident immune cells of the brain, exhibit various morphologies that correlate with their functions under physiological and pathological conditions. In conditions such as aging and stress, microglia priming occurs, which leads to altered morphology and lower threshold for activation upon further insult. However, the molecular mechanisms that lead to microglia priming are unclear.

Methods

To understand the role of Par1b/MARK2 in microglia, we first expressed shRNA targeting luciferase or Par1b/MARK2 in primary microglial cells and imaged the cells using fluorescent microscopy to analyze for morphological changes. A phagocytosis assay was then used to assess functional changes. We then moved in vivo and used a Par1b/MARK2 knockout mouse model to assess for changes in microglia density, morphology, and phagocytosis using immunohistochemistry, confocal imaging, and 3D image reconstruction. Next, we used two-photon in vivo imaging in live Par1b/MARK2 deficient mice to examine microglia dynamics. In addition, a controlled-cortical impact injury was performed on wild-type and Par1b/MARK2-deficient mice and microglial response was determined by confocal imaging. Finally, to help rule out non-cell autonomous effects, we analyzed apoptosis by confocal imaging, cytokine levels by multiplex ELISA, and blood-brain barrier permeability using Evans Blue assay.

Results

Here, we show that loss of the cell polarity protein Par1b/MARK2 facilitates the activation of primary microglia in culture. We next found that microglia in Par1b/MARK2 deficient mice show increased density and a hypertrophic morphology. These morphological changes are accompanied with alterations in microglia functional responses including increased phagocytosis of neuronal particles early in development and decreased surveillance of the brain parenchyma, all reminiscent of a primed phenotype. Consistent with this, we found that microglia in Par1b/MARK2 deficient mice have a significantly lower threshold for activation upon injury.

Conclusions

Together, our studies show that loss of Par1b/MARK2 switches microglia from a surveillant to a primed state during development, resulting in an increased neuroinflammatory response to insults.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1390-3) contains supplementary material, which is available to authorized users.

Inhibition of polarity-regulating kinase PAR1b contributes to Helicobacter pylori inflicted DNA Double Strand Breaks in gastric cells

The serine/threonine kinase Par1 is a core component of the machinery that sets up polarity in the embryo and regulates cell fate decisions but its role in the homeostasis of adult tissues is poorly understood. Inhibition of Par1 by the bacterium Helicobacter pylori (H. pylori) represents the only established pathology that affects Par1 function in an adult epithelium. Thus, during chronic H. pylori infection of the gastric mucosa Par1 is one of the targets of the non-obligate H.pylori cytotoxic protein and oncogene CagA, which stimulates inflammation and triggers morphological changes, both believed to contribute to the gastric cancer risk imposed by H. pylori infection. Based on Par1's role in cell polarity, it has been speculated that Par1 inhibition affects epithelial polarity. Here we report the unexpected finding that CagA-mediated Par1-inhibition promotes the generation of DNA Double Strand Breaks in primary gastric epithelial cells, which likely contributes to the reported accumulation of mutations in chronically infected mucosal cells. Abbreviations: AGS: human gastric adenocarcinoma cell line; CM: CagA Multimerization (and Par1 binding) domain; H. pylori: Helicobacter pylori; DSB: Double Strand Break; HGECs: human (primary) gastric epithelial cells; IB: immunoblot; IF: immunofluorescence; MOI: Multiplicity of Infection; ROS: reactive oxygen species; Par1: Partitioning Defective 1 kinase; WT: wild type.

Localized Phosphorylation of a Kinesin-1 Adaptor by a Capsid-Associated Kinase Regulates HIV-1 Motility and Uncoating. Cell Rep. 2017;20:2792-2799. [PMID: 28930676 DOI: 10.1016/j.celrep.2017.08.076]

Although microtubule motors mediate intracellular virus transport, the underlying interactions and control mechanisms remain poorly defined. This is particularly true for HIV-1 cores, which undergo complex, interconnected processes of cytosolic transport, reverse transcription, and uncoating of the capsid shell. Although kinesins have been implicated in regulating these events, curiously, there are no direct kinesin-core interactions. We recently showed that the capsid-associated kinesin-1 adaptor protein, fasciculation and elongation protein zeta-1 (FEZ1), regulates HIV-1 trafficking. Here, we show that FEZ1 and kinesin-1 heavy, but not light, chains regulate not only HIV-1 transport but also uncoating. This required FEZ1 phosphorylation, which controls its interaction with kinesin-1. HIV-1 did not stimulate widespread FEZ1 phosphorylation but, instead, bound microtubule (MT) affinity-regulating kinase 2 (MARK2) to stimulate FEZ1 phosphorylation on viral cores. Our findings reveal that HIV-1 binds a regulatory kinase to locally control kinesin-1 adaptor function on viral cores, thereby regulating both particle motility and uncoating.

Rab11-FIP1 phosphorylation by MARK2 regulates polarity in MDCK cells

MARK2/Par1b/EMK1, a serine/threonine kinase, is required for correct apical/basolateral membrane polarization in epithelial cells. However, the specific substrates mediating MARK2 action are less well understood. We have now found that MARK2 phosphorylates Rab11-FIP1B/C at serine 234 in a consensus site similar to that previously identified in Rab11-FIP2. In MDCK cells undergoing repolarization after a calcium switch, antibodies specific for pS234-Rab11-FIP1 or pS227-Rab11-FIP2 demonstrate that the spatial and temporal activation of Rab11-FIP1 phosphorylation is distinct from that for Rab11-FIP2. Phosphorylation of Rab11-FIP1 persists through calcium switch and remains high after polarity has been reestablished whereas FIP2 phosphorylation is highest early in reestablishment of polarity but significantly reduced once polarity has been re-established. MARK2 colocalized with FIP1B/C/D and p(S234)-FIP1 in vivo. Overexpression of GFP-Rab11-FIP1C wildtype or non-phosphorylatable GFP-Rab11-FIP1C(S234A) induced two significant phenotypes following calcium switch. Overexpression of FIP1C wildtype and FIP1C(S234A) caused a psuedo-stratification of cells in early time points following calcium switch. At later time points most prominently observed in cells expressing FIP1C(S234A) a significant lateral lumen phenotype was observed, where F-actin-rich lateral lumens appeared demarcated by a ring of ZO1 and also containing ezrin, syntaxin 3 and podocalyxin. In contrast, p120 and E-Cadherin were excluded from the new apical surface at the lateral lumens and now localized to the new lateral surface oriented toward the media. GFP-FIP1C(S234A) localized to membranes deep to the lateral lumens, and immunostaining demonstrated the reorientation of the centrosome and the Golgi apparatus toward the lateral lumen. These results suggest that both Rab11-FIP1B/C and Rab11-FIP2 serve as critical substrates mediating aspects of MARK2 regulation of epithelial polarity.

Protein Scaffolds Control Localized Protein Kinase Cζ Activity

Atypical protein kinase C (aPKC) isozymes modulate insulin signaling and cell polarity, but how their activity is controlled in cells is not well understood. These enzymes are constitutively phosphorylated, insensitive to second messengers, and have relatively low activity. Here we show that protein scaffolds not only localize but also differentially control the catalytic activity of the aPKC PKCζ, thus promoting activity toward localized substrates and restricting activity toward global substrates. Using cellular substrate readouts and scaffolded activity reporters in live cell imaging, we show that PKCζ has highly localized and differentially controlled activity on the scaffolds p62 and Par6. Both scaffolds tether aPKC in an active conformation as assessed through pharmacological inhibition of basal activity, monitored using a genetically encoded reporter for PKC activity. However, binding to Par6 is of higher affinity and is more effective in locking PKCζ in an active conformation. FRET-based translocation assays reveal that insulin promotes the association of both p62 and aPKC with the insulin-regulated scaffold IRS-1. Using the aPKC substrate MARK2 as another readout for activity, we show that overexpression of IRS-1 reduces the phosphorylation of MARK2 and enhances its plasma membrane localization, indicating sequestration of aPKC by IRS-1 away from MARK2. These results are consistent with scaffolds serving as allosteric activators of aPKCs, tethering them in an active conformation near specific substrates. Thus, signaling of these intrinsically low activity kinases is kept at a minimum in the absence of scaffolding interactions, which position the enzymes for stoichiometric phosphorylation of substrates co-localized on the same protein scaffold.

Gene expression analysis of microtubule affinity-regulating kinase 2 in non-small cell lung cancer

Lung cancer is the leading cause of cancer death worldwide, and has a five-year survival rate of 18% [1]. MARK2 is a serine/threonine-protein kinase, and is a key component in the phosphorylation of microtubule-associated proteins [2], [3]. A recent study published by Hubaux et al. found that microtubule affinity-regulating kinase 2 (MARK2) showed highly frequent DNA and RNA level disruption in lung cancer cell lines and independent non-small cell lung cancer (NSCLC) cohorts [4]. These alterations result in the acquisition of oncogenic properties in cell lines, such as increased viability and anchorage-independent growth. Furthermore, a microarray-based transcriptome analysis of three short hairpin RNA (shRNA)-mediated MARK2 knockdown lung adenocarcinoma cell lines (GEO#: GSE57966) revealed an association between MARK2 gene expression and cell cycle activation and DNA damage response. Here, we present a detailed description of transcriptome analysis to support the described role of MARK2 in promoting a malignant phenotype.

Microtubule affinity-regulating kinase 2 is associated with DNA damage response and cisplatin resistance in non-small cell lung cancer

Microtubule affinity-regulating kinases (MARKs) are involved in several cellular functions but few studies have correlated MARK kinase expression with cancer, and none have explored their role in lung cancer. In this study, we identified MARK2 as frequently disrupted by DNA hypomethylation and copy gain, resulting in concordant overexpression in independent lung tumor cohorts and we demonstrate a role for MARK2 in lung tumor biology. Manipulation of MARK2 in lung cell lines revealed its involvement in cell viability and anchorage-independent growth. Analyses of both manipulated cell lines and clinical tumor specimens identified a potential role for MARK2 in cell cycle activation and DNA repair. Associations between MARK2 and the E2F, Myc/Max and NF-κB pathways were identified by luciferase assays and in-depth assessment of the NF-κB pathway suggests a negative association between MARK2 expression and NF-κB due to activation of non-canonical NF-κB signaling. Finally, we show that high MARK2 expression levels correlate with resistance to cisplatin, a standard first line chemotherapy for lung cancer. Collectively, our work supports a role for MARK2 in promoting malignant phenotypes of lung cancer and potentially modulating response to the DNA damaging chemotherapeutic, cisplatin.

Protein kinase A rescues microtubule affinity-regulating kinase 2-induced microtubule instability and neurite disruption by phosphorylating serine 409

Microtubule affinity-regulating kinase 2 (MARK2)/PAR-1b and protein kinase A (PKA) are both involved in the regulation of microtubule stability and neurite outgrowth, but whether a direct cross-talk exists between them remains unclear. Here, we found the disruption of microtubule and neurite outgrowth induced by MARK2 overexpression was blocked by active PKA. The interaction between PKA and MARK2 was confirmed by coimmunoprecipitation and immunocytochemistry both in vitro and in vivo. PKA was found to inhibit MARK2 kinase activity by phosphorylating a novel site, serine 409. PKA could not reverse the microtubule disruption effect induced by a serine 409 to alanine (Ala) mutant of MARK2 (MARK2 S409A). In contrast, mutation of MARK2 serine 409 to glutamic acid (Glu) (MARK2 S409E) did not affect microtubule stability and neurite outgrowth. We propose that PKA functions as an upstream inhibitor of MARK2 in regulating microtubule stability and neurite outgrowth by directly interacting and phosphorylating MARK2.

Effects of T208E activating mutation on MARK2 protein structure and dynamics: Modeling and simulation

Microtubule Affinity-Regulating Kinase 2 (MARK2) protein has a substantial role in regulation of vital cellular processes like induction of polarity, regulation of cell junctions, cytoskeleton structure and cell differentiation. The abnormal function of this protein has been associated with a number of pathological conditions like Alzheimer disease, autism, several carcinomas and development of virulent effects of Helicobacter pyloriββαβββ.

Emerging modes of PINK1 signaling: another task for MARK2

PTEN-induced kinase 1 (PINK1) acts at multiple levels to promote mitochondrial health, including regulatory influence on ATP-synthesis, protein quality control, apoptosis, mitochondrial transport, and destiny. PINK1 mutations are linked to Parkinson disease (PD) and mostly result in loss of kinase activity. But the molecular events responsible for neuronal death as well as the physiological targets and regulators of PINK1 are still a matter of debate. This review highlights the recent progress evolving the cellular functions of the cytosolic pool of PINK1 in mitochondrial trafficking and neuronal differentiation. Regulation of PINK1 signaling occurs by mitochondrial processing to truncated forms of PINK1, differentially targeted to several subcellular compartments. The first identified activating kinase of PINK1 is MAP/microtubule affinity regulating kinase 2 (MARK2), which phosphorylates T313, a frequent mutation site linked to PD. Kinases of the MARK2 family perform diverse functions in neuronal polarity, transport, migration, and neurodegeneration such as Alzheimer disease (AD). This new protein kinase signaling axis might provide a link between neurodegenerative processes in AD and PD diseases and opens novel possibilities in targeting pathological signaling processes.

Phosphorylation of the E3 ubiquitin ligase RNF41 by the kinase Par-1b is required for epithelial cell polarity

The establishment and maintenance of cell polarity is an essential property governing organismal homeostasis, and loss of polarity is a common feature of cancer cells. The ability of epithelial cells to establish apical-basal polarity depends on intracellular signals generated from polarity proteins, such as the Par-1 family of proteins, as well as extracellular signals generated through cell contacts with the extracellular matrix (ECM). The Par-1 family has a well-established role in regulating cell-cell contacts in the form of tight junctions by phosphorylating Par-3. In addition, Par-1 has been shown to impact on cell-ECM interactions by regulating laminin receptor localization and laminin deposition on the basal surface of epithelial cells. Laminins are major structural and signaling components of basement membrane (BM), a sheet of specialized ECM underlying epithelia. In this study, we identify RNF41, an E3 ubiquitin ligase, as a novel Par-1b (also known as MARK2) effector in the cell-ECM pathway. Par-1b binds to and phosphorylates RNF41 on serine 254. Phosphorylation of RNF41 by Par-1b is required for epithelial cells to localize laminin-111 receptors to their basolateral surfaces and to properly anchor to laminin-111. In addition, phosphorylation of RNF41 is required for epithelial cells to establish apical-basal polarity. Our data suggests that phosphorylation of RNF41 by Par-1b regulates basolateral membrane targeting of laminin-111 receptors, thereby facilitating cell anchorage to laminin-111 and ultimately forming the cell-ECM contacts required for epithelial cells to establish apical-basal cell polarity.

Novel small-molecule AMPK activator orally exerts beneficial effects on diabetic db/db mice

AMP-activated protein kinase (AMPK), which is a pivotal guardian of whole-body energy metabolism, has become an attractive therapeutic target for metabolic syndrome. Previously, using a homogeneous scintillation proximity assay, we identified the small-molecule AMPK activator C24 from an optimization based on the original allosteric activator PT1. In this paper, the AMPK activation mechanism of C24 and its potential beneficial effects on glucose and lipid metabolism on db/db mice were investigated. C24 allosterically stimulated inactive AMPK α subunit truncations and activated AMPK heterotrimers by antagonizing autoinhibition. In primary hepatocytes, C24 increased the phosphorylation of AMPK downstream target acetyl-CoA carboxylase dose-dependently without changing intracellular AMP/ATP ratio, indicating its allosteric activation in cells. Through activating AMPK, C24 decreased glucose output by down-regulating mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) in primary hepatocytes. C24 also decreased the triglyceride and cholesterol contents in HepG2 cells. Due to its improved bioavailability, chronic oral treatment with multiple doses of C24 significantly reduced blood glucose and lipid levels in plasma, and improved the glucose tolerance of diabetic db/db mice. The hepatic transcriptional levels of PEPCK and G6Pase were reduced. These results demonstrate that this orally effective activator of AMPK represents a novel approach to the treatment of metabolic syndrome.