Glia Maturation Factor-γ Regulates Monocyte Migration through Modulation of β1-Integrin

Identification of GMFG as a novel biomarker in IgA nephropathy based on comprehensive bioinformatics analysis

Background

IgA nephropathy (IgAN) stands as the most prevalent form of glomerulonephritis and ranks among the leading causes of end-stage renal disease worldwide. Regrettably, we continue to grapple with the absence of dependable diagnostic markers and specific therapeutic agents for IgAN. Therefore, this study endeavors to explore novel biomarkers and potential therapeutic targets in IgAN, while also considering their relevance in the context of tumors.

Methods

We gathered IgAN datasets from the Gene Expression Omnibus (GEO) database. Subsequently, leveraging these datasets, we conducted an array of analyses, encompassing differential gene expression, weighted gene co-expression network analysis (WGCNA), machine learning, receiver operator characteristic (ROC) curve analysis, gene expression validation, clinical correlations, and immune infiltration. Finally, we carried out pan-cancer analysis based on hub gene.

Results

We obtained 1391 differentially expressed genes (DEGs) in GSE93798 and 783 DGEs in GSE14795, respectively. identifying 69 common genes for further investigation. Subsequently, GMFG was identified the hub gene based on machine learning. In the verification set and the training set, the GMFG was higher in the IgAN group than in the healthy group and all of the GMFG area under the curve (AUC) was more 0.8. In addition, GMFG has a close relationship with the prognosis of malignancies and a range of immune cells.

Conclusions

Our study suggests that GMFG could serve as a promising novel biomarker and potential therapeutic target for both IgAN and certain types of tumors.

The double-edged role of neutrophil heterogeneity in inflammatory diseases and cancers

Neutrophils are important immune cells act as the body's first line of defense against infection and respond to diverse inflammatory cues. Many studies have demonstrated that neutrophils display plasticity in inflammatory diseases and cancers. Clarifying the role of neutrophil heterogeneity in inflammatory diseases and cancers will contribute to the development of novel treatment strategies. In this review, we have presented a review on the development of the understanding on neutrophil heterogeneity from the traditional perspective and a high-resolution viewpoint. A growing body of evidence has confirmed the double-edged role of neutrophils in inflammatory diseases and tumors. This may be due to a lack of precise understanding of the role of specific neutrophil subsets in the disease. Thus, elucidating specific neutrophil subsets involved in diseases would benefit the development of precision medicine. Thusly, we have summarized the relevance and actions of neutrophil heterogeneity in inflammatory diseases and cancers comprehensively. Meanwhile, we also discussed the potential intervention strategy for neutrophils. This review is intended to deepen our understanding of neutrophil heterogeneity in inflammatory diseases and cancers, while hold promise for precise treatment of neutrophil-related diseases.

High Level of GMFG Correlated to Poor Clinical Outcome and Promoted Cell Migration and Invasion through EMT Pathway in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) has a very poor prognosis due to the disease's lack of established targeted treatment options. Glia maturation factor γ (GMFG), a novel ADF/cofilin superfamily protein, has been reported to be differentially expressed in tumors, but its expression level in TNBC remains unknown. The question of whether GMFG correlates with the TNBC prognosis is also unclear. In this study, data from the Cancer Genome Atlas (TCGA), Clinical Proteomic Tumor Analysis Consortium (CPTAC), Human Protein Atlas (HPA), and Genotype-Tissue Expression (GTEx) databases were used to analyze the expression of GMFG in pan-cancer and the correlation between clinical factors. Gene Set Cancer Analysis (GSCA) and Gene Set Enrichment Analysis (GSEA) were also used to analyze the functional differences between the different expression levels and predict the downstream pathways. GMFG expression in breast cancer tissues, and its related biological functions, were further analyzed by immunohistochemistry (IHC), immunoblotting, RNAi, and function assay; we found that TNBC has a high expression of GMFG, and this higher expression was correlated with a poorer prognosis in TCGA and collected specimens of the TNBC. GMFG was also related to TNBC patients' clinicopathological data, especially those with histological grade and axillary lymph node metastasis. In vitro, GMFG siRNA inhibited cell migration and invasion through the EMT pathway. The above data indicate that high expression of GMFG in TNBC is related to malignancy and that GMFG could be a biomarker for the detection of TNBC metastasis.

Glia maturation factor-γ is required for initiation and maintenance of hematopoietic stem and progenitor cells

BACKGROUND

In vertebrates, hematopoietic stem and progenitor cells (HSPCs) emerge from hemogenic endothelium in the floor of the dorsal aorta and subsequently migrate to secondary niches where they expand and differentiate into committed lineages. Glia maturation factor γ (gmfg) is a key regulator of actin dynamics that was shown to be highly expressed in hematopoietic tissue. Our goal is to investigate the role and mechanism of gmfg in embryonic HSPC development.

METHODS

In-depth bioinformatics analysis of our published RNA-seq data identified gmfg as a cogent candidate gene implicated in HSPC development. Loss and gain-of-function strategies were applied to study the biological function of gmfg. Whole-mount in situ hybridization, confocal microscopy, flow cytometry, and western blotting were used to evaluate changes in the number of various hematopoietic cells and expression levels of cell proliferation, cell apoptosis and hematopoietic-related markers. RNA-seq was performed to screen signaling pathways responsible for gmfg deficiency-induced defects in HSPC initiation. The effect of gmfg on YAP sublocalization was assessed in vitro by utilizing HUVEC cell line.

RESULTS

We took advantage of zebrafish embryos to illustrate that loss of gmfg impaired HSPC initiation and maintenance. In gmfg-deficient embryos, the number of hemogenic endothelium and HSPCs was significantly reduced, with the accompanying decreased number of erythrocytes, myelocytes and lymphocytes. We found that blood flow modulates gmfg expression and gmfg overexpression could partially rescue the reduction of HSPCs in the absence of blood flow. Assays in zebrafish and HUVEC showed that gmfg deficiency suppressed the activity of YAP, a well-established blood flow mediator, by preventing its shuttling from cytoplasm to nucleus. During HSPC initiation, loss of gmfg resulted in Notch inactivation and the induction of Notch intracellular domain could partially restore the HSPC loss in gmfg-deficient embryos.

CONCLUSIONS

We conclude that gmfg mediates blood flow-induced HSPC maintenance via regulation of YAP, and contributes to HSPC initiation through the modulation of Notch signaling. Our findings reveal a brand-new aspect of gmfg function and highlight a novel mechanism for embryonic HSPC development.

Human Cytomegalovirus Manipulates Syntaxin 6 for Successful Trafficking and Subsequent Infection of Monocytes

Human cytomegalovirus (HCMV) exhibits a complex host-pathogen interaction with peripheral blood monocytes. We have identified a unique, cell-type specific retrograde-like intracellular trafficking pattern that HCMV utilizes to gain access to the monocyte nucleus and for productive infection. We show that infection of primary human monocytes, epithelial cells, and fibroblasts leads to an increase in the amount of the trafficking protein Syntaxin 6 (Stx6). However, only knockdown (KD) of Stx6 in monocytes inhibited viral trafficking to the trans-Golgi network (TGN), a requisite step for nuclear translocation in monocytes. Conversely, KD of Stx6 in epithelial cells and fibroblasts did not change the kinetics of nuclear translocation and productive infection. Stx6 predominantly functions at the level of the TGN where it facilitates retrograde transport, a trafficking pathway used by only a few cellular proteins and seldom by pathogens. We also newly identify that in monocytes, Stx6 exhibits an irregular vesicular localization rather than being concentrated at the TGN as seen in other cell-types. Lastly, we implicate that viral particles that associate with both Stx6 and EEA1 early in infection are the viral population that successfully traffics to the TGN at later time points and undergo nuclear translocation. Additionally, we show for the first time that HCMV enters the TGN, and that lack of Stx6 prevents viral trafficking to this organelle. We argue that we have identified an essential cell-type specific regulator that controls early steps in efficient productive infection of a cell-type required for viral persistence and disease. IMPORTANCE Human cytomegalovirus (HCMV) infection causes severe and often fatal disease in the immunocompromised. It is one of the leading infectious causes of birth defects and causes severe complications in transplant recipients. By uncovering the unique pathways used by the virus to infect key cells, such as monocytes, responsible for dissemination and persistence, we provide new potential targets for therapeutic intervention.

Proteomic and Metabolomic Characterization of SARS-CoV-2-Infected Cynomolgus Macaque at Early Stage

Although tremendous effort has been exerted to elucidate the pathogenesis of severe COVID-19 cases, the detailed mechanism of moderate cases, which accounts for 90% of all patients, remains unclear yet, partly limited by lacking the biopsy tissues. Here, we established the COVID-19 infection model in cynomolgus macaques (CMs), monitored the clinical and pathological features, and analyzed underlying pathogenic mechanisms at early infection stage by performing proteomic and metabolomic profiling of lung tissues and sera samples from COVID-19 CMs models. Our data demonstrated that innate immune response, neutrophile and platelet activation were mainly dysregulated in COVID-19 CMs. The symptom of neutrophilia, lymphopenia and massive "cytokines storm", main features of severe COVID-19 patients, were greatly weakened in most of the challenged CMs, which are more semblable as moderate patients. Thus, COVID-19 model in CMs is rational to understand the pathogenesis of moderate COVID-19 and may be a candidate model to assess the safety and efficacy of therapeutics and vaccines against SARS-CoV-2 infection.

Expression and Prognostic Role of Glia Maturation Factor-γ in Gliomas

Background

Glia maturation factor-γ (GMFG) regulates actin cytoskeletal organization and promotes the invasion of cancer cells. However, its expression pattern and molecular function in gliomas have not been clearly defined.

Methods

In this study, public datasets comprising 2,518 gliomas samples were used to explore GMFG expression and its correlation with malignancy in gliomas. Immunohistochemistry (IHC) staining was performed to determine the expression of GMFG in gliomas using an in-house cohort that contained 120 gliomas samples. Gene ontology enrichment analysis was conducted using the DAVID tool. The correlation between GMFG expression and immune cell infiltration was evaluated using TIMER, Tumor Immune Single-Cell Hub (TISCH) database, and IHC staining assays. The Kaplan–Meier analysis was performed to determine the prognostic role of GMFG and its association with temozolomide (TMZ) response in gliomas.

Results

The GMFG expression was higher in gliomas compared with non-tumor brain tissues both in public datasets and in-house cohort. High expression of GMFG was significantly associated with WHO grade IV, IDH 1/2 wild-type, and mesenchymal (ME) subtypes. Bioinformatic prediction and IHC analysis revealed that GMFG expression obviously correlated with the macrophage marker CD163 in gliomas. Moreover, both lower grade glioma (LGG) and glioblastoma multiforme (GBM) patients with high GMFG expression had shorter overall survival than those with low GMFG expression. These results indicate that GMFG may be a therapeutic target for the treatment of such patients. Patients with low GMFG expression who received chemotherapy had a longer survival time than those with high GMFG expression. For patients who received ion radiotherapy (IR) only, the GMFG expression level had no effect on the overall survival neither in CGGA and TCGA datasets.

Conclusion

The GMFG is a novel prognostic biomarker for patients with both LGG and GBM. Increased GMFG expression is associated with tumor-associated macrophages (TAMs) infiltration and with a bad response to TMZ treatment.

RNF144A exerts tumor suppressor function in breast cancer through targeting YY1 for proteasomal degradation to downregulate GMFG expression

Ring finger protein 144A (RNF144A), a poorly characterized member of the RING-in-between-RING family of E3 ubiquitin ligases, is an emerging tumor suppressor, but its underlying mechanism remains largely elusive. To address this issue, we used Affymetrix GeneChip Human Transcriptome Array 2.0 to profile gene expression in MDA-MB-231 cells stably expressing empty vector pCDH and Flag-RNF144A, and found that 128 genes were differentially expressed between pCDH- and RNF144A-expressing cells with fold change over 1.5. We further demonstrated that RNF144A negatively regulated the protein and mRNA levels of glial maturation factor γ (GMFG). Mechanistical investigations revealed that transcription factor YY1 transcriptionally activated GMFG expression, and RNF144A interacted with YY1 and promoted its ubiquitination-dependent degradation, thus blocking YY1-induced GMFG expression. Functional rescue assays showed that ectopic expression of RNF144A suppressed the proliferative, migratory, and invasive potential of breast cancer cells, and the noted effects were partially restored by re-expression of GMFG in RNF144A-overexpressing breast cancer cells. Collectively, these findings reveal that RNF144A negatively regulates GMFG expression by targeting YY1 for proteasomal degradation, thus inhibiting the proliferation, migration, and invasion of breast cancer cells.

Glia Maturation Factor Beta as a Novel Biomarker and Therapeutic Target for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common types of cancer. The novel sensitive biomarkers and therapeutic targets are urgently needed for the early diagnosis of HCC and improvement of clinical outcomes. Glia maturation factor-β (GMFB) is a growth and differentiation factor for both glia and neurons and has been found to be tightly involved in inflammation and neurodegeneration conditions. In our study, the expression level of GMFB was significantly up-regulated in patients with HCC and positively co-expression with tumor node metastases (TNM) stage and histopathological grade of HCC. The high expression level of GMFB was remarkably associated with poor overall survival, which mainly occurred in males rather than females. Multivariate analysis revealed GMFB to be an independent prognostic factor for overall survival in patients with HCC. Results of Gene Ontology (GO) and KEGG pathways analysis showed that down-regulation of pathways related to protein translation and mitochondria function were enriched. Protein-protein interaction analysis revealed the central role of mitochondria protein in HCC. The downregulation of genes involved in glycolysis and gluconeogenesis was observed among the co-expression genes of GMFB. Knockdown of GMFB in Hep3B significantly inhibited proliferation, migration, and invasion of Hep3B cells, and also downregulated the expression levels of some of metal matrix proteinase (MMP), increased mtDNA copy number and loss of mitochondrial transmembrane potential. GMFB influences the malignancy rate of HCC possibly through regulation of the expression of MMPs, mtDNA function and glycolysis. We proposed that GMFB was a promising HCC diagnostic and prognostic biomarker and therapeutic target in HCC.

GMFG Has Potential to Be a Novel Prognostic Marker and Related to Immune Infiltrates in Breast Cancer

A growing amount of evidence has indicated immune genes perform a crucial position in the development and progression of breast cancer microenvironment. The purpose of our study was to identify immunogenic prognostic marker and explore potential regulatory mechanisms for breast cancer. We identified the genes related to ImmuneScore using ESTIMATE algorithm and WGCNA analysis, and we identified the differentially expressed gene (DEGs). Then, Glia maturation factor γ (GMFG) was determined as a predictive factor by intersecting immune-related genes with DEGs and survival analysis. We found the expression of GMFG was lower in breast cancer tissues compared with normal breast tissues, which was further verified by immunohistochemical (IHC). Moreover, the decreased expression of GMFG was significantly related to the poor prognosis. Besides, the expression of GMFG was related to the age, ER status, PR status, HER2 status and tumor size, which further suggested that the expression of GMFG was correlated with the subtype and the growth of tumor. The univariate and multivariate Cox regression analyses revealed that age, stage, the expression level of GMFG and radiotherapy were independent factors for predicting the prognosis of breast cancer patients. Subsequently, a prognostic model to predict the 3-year, 5-year and 10-year overall survival rate was developed based on the above four variables, and visualized as a nomogram. The values of area under the curve of the nomogram at 3-year, 5-year and 10-year were 0.897, 0.873 and 0.922, respectively, which was higher than stage in prognostic accuracy. In addition, we also found that GMFG expression level was correlated with sensitivity of some breast cancer chemotherapy drugs. Furthermore, the results of GSEA indicated immune-related pathways were mainly enriched in GMFG-high-expression group. CIBERSORT analysis for the proportion of tumor-infiltrating immune cells (TIICs) suggested that expression of GMFG was positively association with multiple kinds T-cell in BC. Among them, CD8+ T cells had the strongest correlation with GMFG expression, which revealed that GMFG might has an antitumor effect by increasing the infiltration of CD8+ T cells in breast cancer. Accordingly, GMFG has the potential to become a novel immune biomarker for the diagnosis and treatment of breast cancer.

The Actin-Disassembly Protein Glia Maturation Factor γ Enhances Actin Remodeling and B Cell Antigen Receptor Signaling at the Immune Synapse

Signaling by the B cell antigen receptor (BCR) initiates actin remodeling. The assembly of branched actin networks that are nucleated by the Arp2/3 complex exert outward force on the plasma membrane, allowing B cells to form membrane protrusions that can scan the surface of antigen-presenting cells (APCs). The resulting Arp2/3 complex-dependent actin retrograde flow promotes the centripetal movement and progressive coalescence of BCR microclusters, which amplifies BCR signaling. Glia maturation factor γ (GMFγ) is an actin disassembly-protein that releases Arp2/3 complex-nucleated actin filaments from actin networks. By doing so, GMFγ could either oppose the actions of the Arp2/3 complex or support Arp2/3 complex-nucleated actin polymerization by contributing to the recycling of actin monomers and Arp2/3 complexes. We now show that reducing the levels of GMFγ in human B cell lines via transfection with a specific siRNA impairs the ability of B cells to spread on antigen-coated surfaces, decreases the velocity of actin retrograde flow, diminishes the coalescence of BCR microclusters into a central cluster at the B cell-APC contact site, and decreases APC-induced BCR signaling. These effects of depleting GMFγ are similar to what occurs when the Arp2/3 complex is inhibited. This suggests that GMFγ cooperates with the Arp2/3 complex to support BCR-induced actin remodeling and amplify BCR signaling at the immune synapse.

Heme induces significant neutrophil adhesion in vitro via an NFκB and reactive oxygen species-dependent pathway

Intravascular hemolysis, a major manifestation of sickle cell disease (SCD) and other diseases, incurs the release of hemoglobin and heme from red blood cells, in turn triggering inflammatory processes. This study investigated the in vitro effects of heme, a major inflammatory DAMP, on the adhesive properties of isolated human neutrophils. Heme (20 and 50 µM) significantly increased the adhesion of neutrophils to fibronectin and to recombinant ICAM-1, under static conditions, even more efficiently than the potent pro-inflammatory cytokine, tumor necrosis factor-α (TNF); a microfluidic assay confirmed that heme stimulated neutrophil adhesion under conditions of shear stress. Heme-induced neutrophil adhesion was associated with the increased activities, but not expressions, of the Mac-1 and LFA-1 integrin subunits, CD11b and CD11a, on the cell surface. Notably, heme (50 µM) significantly induced NFκB translocation in neutrophils, and inhibition of NFκB activity with the BAY11-7082 molecule abolished heme-induced cell adhesion to fibronectin and significantly decreased CD11a activity. Flow cytometric analysis demonstrated major reactive oxygen species (ROS) generation in neutrophils following heme stimulation that could be inhibited by the antioxidant, α-tocopherol, and by BAY11-7082. Furthermore, co-incubation with α-tocopherol abrogated both heme-stimulated neutrophil adhesion and CD11a/CD11b activation. Thus, our data indicate that heme, at clinically relevant concentrations, is a potent activator of neutrophil adhesion, increasing the ligand affinity of the β2 integrins via a mechanism that may be partially mediated by an NFkB-dependent pathway and the generation of ROS. Given the fundamental role that the adhesion of neutrophils to the vascular wall plays in SCD vaso-occlusion and other vascular inflammatory processes, our findings provide further evidence that cell-free heme is a major therapeutic target in the hemolytic diseases.

Bioinformatics and survival analysis of glia maturation factor-γ in pan-cancers

Background

Glia maturation factor-γ (GMFG) is reported to inhibit the actin nucleation through binding to the actin-related protein-2/3 complex (Arp2/3). Considering the main function of GMFG in actin remodeling, which is vital for immune response, angiogenesis, cell division and motility, GMFG is supposed to have important roles in tumor development, while up to now, only two studies described the role of GMFG in cancers. By investigating the clinical values of GMFG using The Cancer Genome Atlas (TCGA) data and the functional mechanisms of GMFG through analyses of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichments, this study was aimed to better understand the impact of GMFG in pan-cancers and to draw more attentions for the future research of GMFG.

Methods

RNA-seq and clinical data of cancer patients were collected from TCGA and analyzed by the Kaplan-Meier methods. GO and KEGG analyses were conducted using the online tools from the Database for Annotation, Visualization and Integrated Discovery (DAVID).

Results

Compared to the corresponding normal samples, GMFG was significantly upregulated in glioblastoma (GBM), kidney clear cell carcinoma (KIRC), lower grade glioma (LGG), acute myeloid leukemia (LAML), and pancreatic cancer (PAAD), testicular cancer (TGCT), but was downregulated in kidney chromophobe (KICH), lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) (P < 0.05 for all). High expression of GMFG predicted worse OS in GBM (HR = 1.5, P = 0.017), LGG (HR = 2.2, P < 0.001), LUSC (HR = 1.4, P = 0.022) and ocular melanomas (UVM) (HR = 7, P < 0.001), as well as worse DFS in LGG (HR = 1.8, P < 0.001) and prostate cancer (PRAD) (HR = 1.9, P = 0.004). In contrast, high expression of GMFG was associated with better OS in skin cutaneous melanoma (SKCM) (HR = 0.59, P < 0.001) and thymoma (THYM) (HR = 0.098, P = 0.031), as well as better DFS in bile duct cancer (CHOL) (HR = 0.2, P = 0.003). GMFG was mainly involved in the immune response, protein binding and cytokine-cytokine receptor interaction pathways, and was positively associated with multiple immunomodulators in most cancers.

Conclusion

Our study preliminarily identified that GMFG may cause different survivals for different cancers through modulating tumor progression, immune response status and tissue-specific tumor microenvironment (TME).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08163-2.

Glia maturation factor-γ regulates murine macrophage iron metabolism and M2 polarization through mitochondrial ROS

In macrophages, cellular iron metabolism status is tightly integrated with macrophage phenotype and associated with mitochondrial function. However, how molecular events regulate mitochondrial activity to integrate regulation of iron metabolism and macrophage phenotype remains unclear. Here, we explored the important role of the actin-regulatory protein glia maturation factor-γ (GMFG) in the regulation of cellular iron metabolism and macrophage phenotype. We found that GMFG was downregulated in murine macrophages by exposure to iron and hydrogen peroxide. GMFG knockdown altered the expression of iron metabolism proteins and increased iron levels in murine macrophages and concomitantly promoted their polarization toward an anti-inflammatory M2 phenotype. GMFG-knockdown macrophages exhibited moderately increased levels of mitochondrial reactive oxygen species (mtROS), which were accompanied by decreased expression of some mitochondrial respiration chain components, including the iron-sulfur cluster assembly scaffold protein ISCU as well as the antioxidant enzymes SOD1 and SOD2. Importantly, treatment of GMFG-knockdown macrophages with the antioxidant N-acetylcysteine reversed the altered expression of iron metabolism proteins and significantly inhibited the enhanced gene expression of M2 macrophage markers, suggesting that mtROS is mechanistically linked to cellular iron metabolism and macrophage phenotype. Finally, GMFG interacted with the mitochondrial membrane ATPase ATAD3A, suggesting that GMFG knockdown-induced mtROS production might be attributed to alteration of mitochondrial function in macrophages. Our findings suggest that GMFG is an important regulator in cellular iron metabolism and macrophage phenotype and could be a novel therapeutic target for modulating macrophage function in immune and metabolic disorders.

Phosphorylation of GMFγ by c-Abl Coordinates Lamellipodial and Focal Adhesion Dynamics to Regulate Airway Smooth Muscle Cell Migration

Airway smooth muscle cells require coordinated protrusion and focal adhesion dynamics to migrate properly. However, the signaling cascades that connect these two processes remain incompletely understood. Glia maturation factor (GMF)-γ has been implicated in inducing actin debranching and inhibiting nucleation. In this study, we discovered that GMFγ phosphorylation at Y104 regulates human airway smooth muscle cell migration. Using high-resolution microscopy coupled with three-dimensional object-based quantitative image analysis software, Imaris 9.2.0, phosphomimetic mutant, Y104D-GMFγ, was enriched at nascent adhesions along the leading edge where it recruited activated neural Wiskott-Aldrich syndrome protein (N-WASP; pY256) to promote actin-branch formation, which enhanced lamellipodial dynamics and limited the growth of focal adhesions. Unexpectedly, we found that nonphosphorylated mutant, Y104F-GMFγ, was enriched in growing adhesions where it promoted a linear branch organization and focal adhesion clustering, and recruited zyxin to increase maturation, thus inhibiting lamellipodial dynamics and cell migration. The localization of GMFγ between the leading edge and focal adhesions was dependent upon myosin activity. Furthermore, c-Abl tyrosine kinase regulated the GMFγ phosphorylation-dependent processes. Together, these results unveil the importance of GMFγ phosphorylation in coordinating lamellipodial and focal adhesion dynamics to regulate cell migration.

Cellular and pathophysiological consequences of Arp2/3 complex inhibition: role of inhibitory proteins and pharmacological compounds

The actin-related protein complex 2/3 (Arp2/3) generates branched actin networks important for many cellular processes such as motility, vesicular trafficking, cytokinesis, and intercellular junction formation and stabilization. Activation of Arp2/3 requires interaction with actin nucleation-promoting factors (NPFs). Regulation of Arp2/3 activity is achieved by endogenous inhibitory proteins through direct binding to Arp2/3 and competition with NPFs or by binding to Arp2/3-induced actin filaments and disassembly of branched actin networks. Arp2/3 inhibition has recently garnered more attention as it has been associated with attenuation of cancer progression, neurotoxic effects during drug abuse, and pathogen invasion of host cells. In this review, we summarize current knowledge on expression, inhibitory mechanisms and function of endogenous proteins able to inhibit Arp2/3 such as coronins, GMFs, PICK1, gadkin, and arpin. Moreover, we discuss cellular consequences of pharmacological Arp2/3 inhibition.

Synergy in Disruption of Mitochondrial Dynamics by Aβ (1-42) and Glia Maturation Factor (GMF) in SH-SY5Y Cells Is Mediated Through Alterations in Fission and Fusion Proteins

The pathological form of amyloid beta (Aβ) peptide is shown to be toxic to the mitochondria and implicates this organelle in the progression and pathogenesis of Alzheimer's disease (AD). Mitochondria are dynamic structures constantly undergoing fission and fusion, and altering their shape and size while traveling through neurons. Mitochondrial fission (Drp1, Fis1) and fusion (OPA1, Mfn1, and Mfn2) proteins are balanced in healthy neuronal cells. Glia maturation factor (GMF), a neuroinflammatory protein isolated and cloned in our laboratory plays an important role in the pathogenesis of AD. We hypothesized that GMF, a brain-localized inflammatory protein, promotes oxidative stress-mediated disruption of mitochondrial dynamics by alterations in mitochondrial fission and fusion proteins which eventually leads to apoptosis in the Aβ (1-42)-treated human neuroblastoma (SH-SY5Y) cells. The SH-SY5Y cells were incubated with GMF and Aβ (1-42) peptide, and mitochondrial fission and fusion proteins were analyzed by immunofluorescence, western blotting, and co-immunoprecipitation. We report that SH-SY5Y cells incubated with GMF and Aβ (1-42) promote mitochondrial fragmentation, by potentiating oxidative stress, mitophagy and shifts in the Bax/Bcl2 expression and release of cytochrome-c, and eventual apoptosis. In the present study, we show that GMF and Aβ treatments significantly upregulate fission proteins and downregulate fusion proteins. The study shows that extracellular GMF is an important inflammatory mediator that mediates mitochondrial dynamics by altering the balance in fission and fusion proteins and amplifies similar effects promoted by Aβ. Upregulated GMF in the presence of Aβ could be an additional risk factor for AD, and their synergistic actions need to be explored as a potential therapeutic target to suppress the progression of AD.

Glia Maturation Factor Dependent Inhibition of Mitochondrial PGC-1α Triggers Oxidative Stress-Mediated Apoptosis in N27 Rat Dopaminergic Neuronal Cells

Parkinson's disease (PD) is a progressive neurodegenerative disease affecting over five million individuals worldwide. The exact molecular events underlying PD pathogenesis are still not clearly known. Glia maturation factor (GMF), a neuroinflammatory protein in the brain plays an important role in the pathogenesis of PD. Mitochondrial dysfunctions and oxidative stress trigger apoptosis leading to dopaminergic neuronal degeneration in PD. Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α or PPARGC-α) acts as a transcriptional co-regulator of mitochondrial biogenesis and energy metabolism by controlling oxidative phosphorylation, antioxidant activity, and autophagy. In this study, we found that incubation of immortalized rat dopaminergic (N27) neurons with GMF influences the expression of peroxisome PGC-1α and increases oxidative stress, mitochondrial dysfunction, and apoptotic cell death. We show that incubation with GMF reduces the expression of PGC-1α with concomitant decreases in the mitochondrial complexes. Besides, there is increased oxidative stress and depolarization of mitochondrial membrane potential (MMP) in these cells. Further, GMF reduces tyrosine hydroxylase (TH) expression and shifts Bax/Bcl-2 expression resulting in release of cytochrome-c and increased activations of effector caspase expressions. Transmission electron microscopy analyses revealed alteration in the mitochondrial architecture. Our results show that GMF acts as an important upstream regulator of PGC-1α in promoting dopaminergic neuronal death through its effect on oxidative stress-mediated apoptosis. Our current data suggest that GMF is a critical risk factor for PD and suggest that it could be explored as a potential therapeutic target to inhibit PD progression.

GMF as an Actin Network Remodeling Factor

Glia maturation factor (GMF) has recently been established as a regulator of the actin cytoskeleton with a unique role in remodeling actin network architecture. Conserved from yeast to mammals, GMF is one of five members of the ADF-H family of actin regulatory proteins, which includes ADF/cofilin, Abp1/Drebrin, Twinfilin, and Coactosin. GMF does not bind actin, but instead binds the Arp2/3 complex with high affinity. Through this association, GMF catalyzes the debranching of actin filament networks and inhibits actin nucleation by Arp2/3 complex. Here, we discuss GMF's emerging role in controlling actin filament spatial organization and dynamics underlying cell motility, endocytosis, and other biological processes. Further, we attempt to reconcile these functions with its earlier characterization as a cell differentiation factor.

Contractile Skeletal Muscle Cells Cultured with a Conducting Soft Wire for Effective, Selective Stimulation

Contractile skeletal muscle cells were cultured so as to wrap around an electrode wire to enable their selective stimulation even when they were co-cultured with other electrically-excitable cells. Since the electrode wire was composed of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and polyurethane (PU), which is soft and highly capacitive (~10 mF cm-2), non-faradaic electrical stimulation with charge/discharge currents could be applied to the surrounding cells without causing significant damage even for longer periods (more than a week). The advantage of this new culture system was demonstrated in the study of chemotactic interaction of monocytes and skeletal muscle cells via myokines.

Function and regulation of the Arp2/3 complex during cell migration in diverse environments

As the first de novo actin nucleator discovered, the Arp2/3 complex has been a central player in models of protrusive force production via the dynamic actin network. Here, we review recent studies on the functional role of the Arp2/3 complex in the migration of diverse cell types in different migratory environments. These findings have revealed an unexpected level of plasticity, both in how cells rely on the Arp2/3 complex for migration and other physiological functions and in the intricate modulation of the Arp2/3 complex by other actin regulators and upstream signaling cascades.