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

Estrogen receptors differentially modifies lamellipodial and focal adhesion dynamics in airway smooth muscle cell migration

Sex-steroid signaling, especially estrogen, has a paradoxical impact on regulating airway remodeling. In our previous studies, we demonstrated differential effects of 17β-estradiol (E2) towards estrogen receptors (ERs: α and β) in regulating airway smooth muscle (ASM) cell proliferation and extracellular matrix (ECM) production. However, the role of ERs and their signaling on ASM migration is still unexplored. In this study, we examined how ERα versus ERβ affects the mitogen (Platelet-derived growth factor, PDGF)-induced human ASM cell migration as well as the underlying mechanisms involved. We used Lionheart-FX automated microscopy and transwell assays to measure cell migration and found that activating specific ERs had differential effects on PDGF-induced ASM cell migration. Pharmacological activation of ERβ or shRNA mediated knockdown of ERα and specific activation of ERβ blunted PDGF-induced cell migration. Furthermore, specific ERβ activation showed inhibition of actin polymerization by reducing the F/G-actin ratio. Using Zeiss confocal microscopy coupled with three-dimensional algorithmic ZEN-image analysis showed an ERβ-mediated reduction in PDGF-induced expressions of neural Wiskott-Aldrich syndrome protein (N-WASP) and actin-related proteins-2/3 (Arp2/3) complex, thereby inhibiting actin-branching and lamellipodia. In addition, ERβ activation also reduces the clustering of actin-binding proteins (vinculin and paxillin) at the leading edge of ASM cells. However, cells treated with E2 or ERα agonists do not show significant changes in actin/lamellipodial dynamics. Overall, these findings unveil the significance of ERβ activation in regulating lamellipodial and focal adhesion dynamics to regulate ASM cell migration and could be a novel target to blunt airway remodeling.

The Role of c-Abl Tyrosine Kinase in Brain and Its Pathologies

Differentiated status, low regenerative capacity and complex signaling make neuronal tissues highly susceptible to translating an imbalance in cell homeostasis into cell death. The high rate of neurodegenerative diseases in the elderly population confirms this. The multiple and divergent signaling cascades downstream of the various stress triggers challenge researchers to identify the central components of the stress-induced signaling pathways that cause neurodegeneration. Because of their critical role in cell homeostasis, kinases have emerged as one of the key regulators. Among kinases, non-receptor tyrosine kinase (Abelson kinase) c-Abl appears to be involved in both the normal development of neural tissue and the development of neurodegenerative pathologies when abnormally expressed or activated. However, exactly how c-Abl mediates the progression of neurodegeneration remains largely unexplored. Here, we summarize recent findings on the involvement of c-Abl in normal and abnormal processes in nervous tissue, focusing on neurons, astrocytes and microglial cells, with particular reference to molecular events at the interface between stress signaling, DNA damage, and metabolic regulation. Because inhibition of c-Abl has neuroprotective effects and can prevent neuronal death, we believe that an integrated view of c-Abl signaling in neurodegeneration could lead to significantly improved treatment of the disease.

The intermediate filament protein nestin serves as a molecular hub for smooth muscle cytoskeletal signaling

BACKGROUND

The recruitment of the actin-regulatory proteins cortactin and profilin-1 (Pfn-1) to the membrane is important for the regulation of actin cytoskeletal reorganization and smooth muscle contraction. Polo-like kinase 1 (Plk1) and the type III intermediate filament protein vimentin are involved in smooth muscle contraction. Regulation of complex cytoskeletal signaling is not entirely elucidated. The aim of this study was to evaluate the role of nestin (a type VI intermediate filament protein) in cytoskeletal signaling in airway smooth muscle.

METHODS

Nestin expression in human airway smooth muscle (HASM) was knocked down by specific shRNA or siRNA. The effects of nestin knockdown (KD) on the recruitment of cortactin and Pfn-1, actin polymerization, myosin light chain (MLC) phosphorylation, and contraction were evaluated by cellular and physiological approaches. Moreover, we assessed the effects of non-phosphorylatable nestin mutant on these biological processes.

RESULTS

Nestin KD reduced the recruitment of cortactin and Pfn-1, actin polymerization, and HASM contraction without affecting MLC phosphorylation. Moreover, contractile stimulation enhanced nestin phosphorylation at Thr-315 and the interaction of nestin with Plk1. Nestin KD also diminished phosphorylation of Plk1 and vimentin. The expression of T315A nestin mutant (alanine substitution at Thr-315) reduced the recruitment of cortactin and Pfn-1, actin polymerization, and HASM contraction without affecting MLC phosphorylation. Furthermore, Plk1 KD diminished nestin phosphorylation at this residue.

CONCLUSIONS

Nestin is an essential macromolecule that regulates actin cytoskeletal signaling via Plk1 in smooth muscle. Plk1 and nestin form an activation loop during contractile stimulation.

Nestin Modulates Airway Smooth Muscle Cell Migration by Affecting Spatial Rearrangement of Vimentin Network and Focal Adhesion Assembly

Airway smooth muscle cell migration plays a role in the progression of airway remodeling, a hallmark of allergic asthma. However, the mechanisms that regulate cell migration are not yet entirely understood. Nestin is a class VI intermediate filament protein that is involved in the proliferation/regeneration of neurons, cancer cells, and skeletal muscle. Its role in cell migration is not fully understood. Here, nestin knockdown (KD) inhibited the migration of human airway smooth muscle cells. Using confocal microscopy and the Imaris software, we found that nestin KD attenuated focal adhesion sizes during cell spreading. Moreover, polo-like kinase 1 (Plk1) and vimentin phosphorylation at Ser-56 have been previously shown to affect focal adhesion assembly. Here, nestin KD reduced Plk1 phosphorylation at Thr-210 (an indication of Plk1 activation), vimentin phosphorylation at Ser-56, the contacts of vimentin filaments to paxillin, and the morphology of focal adhesions. Moreover, the expression of vimentin phosphorylation-mimic mutant S56D (aspartic acid substitution at Ser-56) rescued the migration, vimentin reorganization, and focal adhesion size of nestin KD cells. Together, our results suggest that nestin promotes smooth muscle cell migration. Mechanistically, nestin regulates Plk1 phosphorylation, which mediates vimenitn phosphorylation, the connection of vimentin filaments with paxillin, and focal adhesion assembly.

Smooth Muscle Myosin Localizes at the Leading Edge and Regulates the Redistribution of Actin-regulatory Proteins during Migration

Airway smooth muscle cell migration plays an essential role in airway development, repair, and remodeling. Smooth muscle myosin II has been traditionally thought to localize in the cytoplasm solely and regulates cell migration by affecting stress fiber formation and focal adhesion assembly. In this study, we unexpectedly found that 20-kDa myosin light chain (MLC20) and myosin-11 (MYH11), important components of smooth muscle myosin, were present at the edge of lamellipodia. The knockdown of MLC20 or MYH11 attenuated the recruitment of c-Abl, cortactinProfilin-1 (Pfn-1), and Abi1 to the cell edge. Moreover, myosin light chain kinase (MLCK) colocalized with integrin β1 at the tip of protrusion. The inhibition of MLCK attenuated the recruitment of c-Abl, cortactin, Pfn-1, and Abi1 to the cell edge. Furthermore, MLCK localization at the leading edge was reduced by integrin β1 knockdown. Taken together, our results demonstrate that smooth muscle myosin localizes at the leading edge and orchestrates the recruitment of actin-regulatory proteins to the tip of lamellipodia. Mechanistically, integrin β1 recruits MLCK to the leading edge, which catalyzes MLC20 phosphorylation. Activated myosin regulates the recruitment of actin-regulatory proteins to the leading edge, and promotes lamellipodial formation and migration.

Acetylation of Abelson interactor 1 at K416 regulates actin cytoskeleton and smooth muscle contraction

Actin cytoskeletal reorganization plays an important role in regulating smooth muscle contraction, which is essential for the modulation of various physiological functions including airway tone. The adapter protein Abi1 (Abelson interactor 1) participates in the control of smooth muscle contraction. The mechanisms by which Abi1 coordinates smooth muscle function are not fully understood. Here, we found that contractile stimulation elicited Abi1 acetylation in human airway smooth muscle (HASM) cells. Mutagenesis analysis identified lysine‐416 (K416) as a major acetylation site. Replacement of K416 with Q (glutamine) enhanced the interaction of Abi1 with neuronal Wiskott‐Aldrich syndrome protein (N‐WASP), an important actin‐regulatory protein. Moreover, the expression of K416Q Abi1 promoted actin polymerization and smooth muscle contraction without affecting myosin light chain phosphorylation at Ser‐19 and vimentin phosphorylation at Ser‐56. Furthermore, p300 is a lysine acetyltransferase that catalyzes acetylation of histone and non‐histone proteins in various cell types. Here, we discovered that a portion of p300 was localized in the cytoplasm of HASM cells. Knockdown of p300 reduced the agonist‐induced Abi1 acetylation in HASM cells and in mouse airway smooth muscle tissues. Smooth muscle conditional knockout of p300 inhibited actin polymerization and the contraction of airway smooth muscle tissues without affecting myosin light chain phosphorylation and vimentin phosphorylation. Together, our results suggest that contractile stimulation induces Abi1 acetylation via p300 in smooth muscle. Acetylation at K416 promotes the coupling of Abi1 with N‐WASP, which facilitates actin polymerization and smooth muscle contraction. This is a novel acetylation‐dependent regulation of the actin cytoskeleton in smooth muscle.

Targeting Airway Smooth Muscle Hypertrophy in Asthma: An Approach Whose Time Has Come

Airway smooth muscle (ASM) cell dysfunction is an important component of several obstructive pulmonary diseases, particularly asthma. External stimuli such as allergens, dust, air pollutants, and change in environmental temperatures provoke ASM cell hypertrophy, proliferation, and migration without adequate mechanistic controls. ASM cells can switch between quiescent, migratory, and proliferative phenotypes in response to extracellular matrix proteins, growth factors, and other soluble mediators. While some aspects of airway hypertrophy and remodeling could have beneficial effects, in many cases these contribute to a clinical phenotype of difficult to control asthma. In this review, we discuss the factors responsible for ASM hypertrophy and proliferation in asthma, focusing on cytokines, growth factors, and ion transporters, and discuss existing and potential approaches that specifically target ASM hypertrophy to reduce the ASM mass and improve asthma symptoms. The goal of this review is to highlight strategies that appear ready for translational investigations to improve asthma therapy.

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.

Actin regulators in cancer progression and metastases: From structure and function to cytoskeletal dynamics

The cytoskeleton is a central factor contributing to various hallmarks of cancer. In recent years, there has been increasing evidence demonstrating the involvement of actin regulatory proteins in malignancy, and their dysregulation was shown to predict poor clinical prognosis. Although enhanced cytoskeletal activity is often associated with cancer progression, the expression of several inducers of actin polymerization is remarkably reduced in certain malignancies, and it is not completely clear how these changes promote tumorigenesis and metastases. The complexities involved in cytoskeletal induction of cancer progression therefore pose considerable difficulties for therapeutic intervention; it is not always clear which cytoskeletal regulator should be targeted in order to impede cancer progression, and whether this targeting may inadvertently enhance alternative invasive pathways which can aggravate tumor growth. The entire constellation of cytoskeletal machineries in eukaryotic cells are numerous and complex; the system is comprised of and regulated by hundreds of proteins, which could not be covered in a single review. Therefore, we will focus here on the actin cytoskeleton, which encompasses the biological machinery behind most of the key cellular functions altered in cancer, with specific emphasis on actin nucleating factors and nucleation-promoting factors. Finally, we discuss current therapeutic strategies for cancer which aim to target the cytoskeleton.

Distinctive roles of Abi1 in regulating actin-associated proteins during human smooth muscle cell migration

Smooth muscle cell migration is essential for many diverse biological processes such as pulmonary/cardiovascular development and homeostasis. Abi1 (Abelson interactor 1) is an adapter protein that has been implicated in nonmuscle cell migration. However, the role and mechanism of Abi1 in smooth muscle migration are largely unknown. Here, Abi1 knockdown by shRNA reduced human airway smooth muscle cell migration, which was restored by Abi1 rescue. Abi1 localized at the tip of lamellipodia and its protrusion coordinated with F-actin at the leading cell edge of live cells. In addition, we identified profilin-1 (Pfn-1), a G-actin transporter, as a new partner for Abi1. Abi1 knockdown reduced the recruitment of Pfn-1 to the leading cell edge. Moreover, Abi1 knockdown reduced the localization of the actin-regulatory proteins c-Abl (Abelson tyrosine kinase) and N-WASP (neuronal Wiskott–Aldrich Syndrome Protein) at the cell edge without affecting other migration-related proteins including pVASP (phosphorylated vasodilator stimulated phosphoprotein), cortactin and vinculin. Furthermore, we found that c-Abl and integrin β1 regulated the positioning of Abi1 at the leading edge. Taken together, the results suggest that Abi1 regulates cell migration by affecting Pfn-1 and N-WASP, but not pVASP, cortactin and focal adhesions. Integrin β1 and c-Abl are important for the recruitment of Abi1 to the leading edge.

Bnip3 regulates airway smooth muscle cell focal adhesion and proliferation

Increased airway smooth muscle (ASM) mass is a key contributor to airway narrowing and airway hyperresponsiveness in asthma. Besides conventional pathways and regulators of ASM proliferation, recent studies suggest that changes in mitochondrial morphology and function play a role in airway remodeling in asthma. In this study, we aimed at determining the role of mitochondrial Bcl-2 adenovirus E1B 19 kDa-interacting protein, Bnip3, in the regulation of ASM proliferation. Bnip3 is a member of the Bcl-2 family of proteins critical for mitochondrial health, mitophagy, and cell survival/death. We found that Bnip3 expression is upregulated in ASM cells from asthmatic donors compared with that in ASM cells from healthy donors and transient downregulation of Bnip3 expression in primary human ASM cells using an siRNA approach decreased cell adhesion, migration, and proliferation. Furthermore, Bnip3 downregulation altered the structure (electron density) and function (cellular ATP levels, membrane potential, and reacitve oxygen species generation) of mitochondria and decreased expression of cytoskeleton proteins vinculin, paxillin, and actinin. These findings suggest that Bnip3 via regulation of mitochondria functions and expression of adhesion proteins regulates ASM adhesion, migration, and proliferation. This study reveals a novel role for Bnip3 in ASM functions and establishes Bnip3 as a potential target in mitigating ASM remodeling in asthma.