Myristoylated alanine-rich C-kinase substrate (MARCKS) protein regulation of human neutrophil migration

Distinct functional neutrophil phenotypes in sepsis patients correlate with disease severity

Purpose

Sepsis is a clinical syndrome defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis is a highly heterogeneous syndrome with distinct phenotypes that impact immune function and response to infection. To develop targeted therapeutics, immunophenotyping is needed to identify distinct functional phenotypes of immune cells. In this study, we utilized our Organ-on-Chip assay to categorize sepsis patients into distinct phenotypes using patient data, neutrophil functional analysis, and proteomics.

Methods

Following informed consent, neutrophils and plasma were isolated from sepsis patients in the Temple University Hospital ICU (n=45) and healthy control donors (n=7). Human lung microvascular endothelial cells (HLMVEC) were cultured in the Organ-on-Chip and treated with buffer or cytomix ((TNF/IL-1β/IFNγ). Neutrophil adhesion and migration across HLMVEC in the Organ-on-Chip were used to categorize functional neutrophil phenotypes. Quantitative label-free global proteomics was performed on neutrophils to identify differentially expressed proteins. Plasma levels of sepsis biomarkers and neutrophil extracellular traps (NETs) were determined by ELISA.

Results

We identified three functional phenotypes in critically ill ICU sepsis patients based on ex vivo neutrophil adhesion and migration patterns. The phenotypes were classified as: Hyperimmune characterized by enhanced neutrophil adhesion and migration, Hypoimmune that was unresponsive to stimulation, and Hybrid with increased adhesion but blunted migration. These functional phenotypes were associated with distinct proteomic signatures and differentiated sepsis patients by important clinical parameters related to disease severity. The Hyperimmune group demonstrated higher oxygen requirements, increased mechanical ventilation, and longer ICU length of stay compared to the Hypoimmune and Hybrid groups. Patients with the Hyperimmune neutrophil phenotype had significantly increased circulating neutrophils and elevated plasma levels NETs.

Conclusion

Neutrophils and NETs play a critical role in vascular barrier dysfunction in sepsis and elevated NETs may be a key biomarker identifying the Hyperimmune group. Our results establish significant associations between specific neutrophil functional phenotypes and disease severity and identify important functional parameters in sepsis pathophysiology that may provide a new approach to classify sepsis patients for specific therapeutic interventions.

MARCKS Inhibition Alters Bovine Neutrophil Responses to Salmonella Typhimurium

Neutrophils are innate immune cells that respond quickly to sites of bacterial infection and play an essential role in host defense. Interestingly, some bacterial pathogens benefit from exuberant neutrophil inflammation. Salmonella is one such pathogen that can utilize the toxic mediators released by neutrophils to colonize the intestine and cause enterocolitis. Because neutrophils can aid gut colonization during Salmonella infection, neutrophils represent a potential host-directed therapeutic target. Myristoylated alanine-rich C-kinase substrate (MARCKS) is an actin-binding protein that plays an essential role in many neutrophil effector responses. We hypothesized that inhibition of MARCKS protein would alter bovine neutrophil responses to Salmonella Typhimurium (STm) ex vivo. We used a MARCKS inhibitor peptide to investigate the role of MARCKS in neutrophil responses to STm. This study demonstrates that MARCKS inhibition attenuated STm-induced neutrophil adhesion and chemotaxis. Interestingly, MARCKS inhibition also enhanced neutrophil phagocytosis and respiratory burst in response to STm. This is the first report describing the role of MARCKS protein in neutrophil antibacterial responses.

Myristoylated, alanine-rich C-kinase substrate (MARCKS) regulates toll-like receptor 4 signaling in macrophages

MARCKS (myristoylated alanine-rich C-kinase substrate) is a membrane-associated protein expressed in many cell types, including macrophages. MARCKS is functionally implicated in cell adhesion, phagocytosis, and inflammation. LPS (lipopolysaccharide) triggers inflammation via TLR4 (toll-like receptor 4).The presence of MARCKS and the formation of phospho-MARCKS in various cell types have been described, but the role(s) of MARCKS in regulating macrophage functions remain unclear. We investigated the role of MARCKS in inflammation. Confocal microscopy revealed that MARCKS and phospho-MARCKS increased localization to endosomes and the Golgi apparatus upon LPS stimulation.CRISPR-CAS9 mediated knockout of MARCKS in macrophages downregulated the production of TNF and IL6, suggesting a role for MARCKS in inflammatory responses. Our comprehensive proteomics analysis together with real-time metabolic assays comparing LPS-stimulation of WT and MARCKS knock-out macrophages provided insights into the involvement of MARCKS in specific biological processes including innate immune response, inflammatory response, cytokine production, and molecular functions such as extracellularly ATP-gated cation channel activity, electron transfer activity and oxidoreductase activity, uncovering specific proteins involved in regulating MARCKS activity upon LPS stimulation. MARCKS appears to be a key regulator of inflammation whose inhibition might be beneficial for therapeutic intervention in inflammatory diseases.

Myristoylated, Alanine-rich C-kinase Substrate (MARCKS) regulates Toll-like receptor 4 signaling in macrophages

MARCKS (Myristoylated Alanine-rich C-kinase Substrate) is a membrane protein expressed in many cell types, including macrophages. MARCKS is functionally implicated in cell adhesion, phagocytosis, and inflammation. LPS (lipopolysaccharide) triggers inflammation via TLR4 (Toll-like receptor 4). The presence of MARCKS and the formation of phospho-MARCKS in macrophages have been described, but the role(s) of MARCKS in regulating macrophage functions remain unclear. To investigate the role of MARCKS during inflammation, we activated macrophages using LPS with or without the addition of a PKC inhibitor. We found that PKC inhibition substantially decreased macrophage IL6 and TNF cytokine production. In addition, confocal microscopy revealed that MARCKS and phospho-MARCKS increased localization to endosomes and the Golgi apparatus upon LPS stimulation. CRISPR-CAS9 mediated knockout of MARCKS in macrophages downregulated TNF and IL6 production, suggesting a role for MARCKS in inflammatory responses. Our comprehensive proteomics analysis together with real-time metabolic assays comparing LPS-stimulation of WT and MARCKS knock-out macrophages provided insights into the involvement of MARCKS in specific biological processes and signaling pathways, uncovering specific proteins involved in regulating MARCKS activity upon LPS stimulation. MARCKS appears to be a key regulator of inflammation whose inhibition might be beneficial for therapeutic intervention in inflammatory related diseases.

Targeting Neutrophil β2-Integrins: A Review of Relevant Resources, Tools, and Methods

Neutrophils are important innate immune cells that respond during inflammation and infection. These migratory cells utilize β₂-integrin cell surface receptors to move out of the vasculature into inflamed tissues and to perform various anti-inflammatory responses. Although critical for fighting off infection, neutrophil responses can also become dysregulated and contribute to disease pathophysiology. In order to limit neutrophil-mediated damage, investigators have focused on β₂-integrins as potential therapeutic targets, but so far these strategies have failed in clinical trials. As the field continues to move forward, a better understanding of β₂-integrin function and signaling will aid the design of future therapeutics. Here, we provide a detailed review of resources, tools, experimental methods, and in vivo models that have been and will continue to be utilized to investigate the vitally important cell surface receptors, neutrophil β₂-integrins.

Patent landscape highlighting therapeutic implications of peptides targeting myristoylated alanine-rich protein kinase-C substrate (MARCKS)

INTRODUCTION

MARCKS protein, a protein kinase C (PKC) substrate, is known to be at the intersection of several intracellular signaling pathways and plays a pivotal role in cellular physiology. Unlike PKC inhibitors, MARCKS-targeting drug (BIO-11006) has shown early success in clinical trials involving lung diseases. Recent research investigations have identified two MARCKS-targeting peptides which possess multifaceted implications against asthma, cancer, inflammation, and lung diseases.

AREAS COVERED

This review article provides the patent landscape and recent developments on peptides targeting MARCKS for therapeutic purposes. Online free open-access databases were used to fetch out the patent information, and research articles were fetched using PubMed.

EXPERT OPINION

Research studies highlighting the intriguing role of MARCKS in human disease and physiology have dramatically increased in recent years. A similar increasing trend in the number of patents has also been observed related to the MARCKS-targeting peptides. Thus, there is a need to amalgamate and translate such a trend into therapeutic intervention. Our review article provides an overview of such recent advances, and we believe that our compilation will fetch the interest of researchers around the globe to develop MARCKS-targeting peptides in future for human diseases.

Increased MARCKS Activity in BRAF Inhibitor-Resistant Melanoma Cells Is Essential for Their Enhanced Metastatic Behavior Independent of Elevated WNT5A and IL-6 Signaling

Treatment of melanoma with a BRAF inhibitor (BRAFi) frequently initiates development of BRAFi resistance, leading to increased tumor progression and metastasis. Previously, we showed that combined inhibition of elevated WNT5A and IL-6 signaling reduced the invasion and migration of BRAFi-resistant (BRAFi-R) melanoma cells. However, the use of a combined approach per se and the need for high inhibitor concentrations to achieve this effect indicate a need for an alternative and single target. One such target could be myristoylated alanine-rich C-kinase substrate (MARCKS), a downstream target of WNT5A in BRAFi-sensitive melanoma cells. Our results revealed that MARCKS protein expression and activity are significantly elevated in PLX4032 and PLX4720 BRAFi-R A375 and HTB63 melanoma cells. Surprisingly, neither WNT5A nor IL-6 contributed to the increases in MARCKS expression and activity in BRAFi-R melanoma cells, unlike in BRAFi-sensitive melanoma cells. However, despite the above findings, our functional validation experiments revealed that MARCKS is essential for the increased metastatic behavior of BRAFi-R melanoma cells. Knockdown of MARCKS in BRAFi-R melanoma cells caused reductions in the F-actin content and the number of filopodia-like protrusions, explaining the impaired migration, invasion and metastasis of these cells observed in vitro and in an in vivo zebrafish model. In our search for an alternative explanation for the increased activity of MARCKS in BRAFi-R melanoma cells, we found elevated basal activities of PKCα, PKCε, PKCι, and RhoA. Interestingly, combined inhibition of basal PKC and RhoA effectively impaired MARCKS activity in BRAFi-R melanoma cells. Our results reveal that MARCKS is an attractive single antimetastatic target in BRAFi-R melanoma cells.

Neutrophil Activated by the Famous and Potent PMA (Phorbol Myristate Acetate)

This review will briefly outline the major signaling pathways in PMA-activated neutrophils. PMA is widely used to understand neutrophil pathways and formation of NETs. PMA activates PKC; however, we highlight some isoforms that contribute to specific functions. PKC α, β and δ contribute to ROS production while PKC βII and PKC ζ are involved in cytoskeleton remodeling. Actin polymerization is important for the chemotaxis of neutrophils and its remodeling is connected to ROS balance. We suggest that, although ROS and production of NETs are usually observed together in PMA-activated neutrophils, there might be a regulatory mechanism balancing both. Interestingly, we suggest that serine proteases might determine the PAD4 action. PAD4 could be responsible for the activation of the NF-κB pathway that leads to IL-1β release, triggering the cleavage of gasdermin D by serine proteases such as elastase, leading to pore formation contributing to release of NETs. On the other hand, when serine proteases are inhibited, NETs are formed by citrullination through the PAD4 pathway. This review puts together results from the last 31 years of research on the effects of PMA on the neutrophil and proposes new insights on their interpretation.

MARCKS Is an Essential Regulator of Reactive Oxygen Species Production in the Monocytic Cell Type

Myristoylated alanine-rich C-kinase substrate (MARCKS) is a ubiquitous protein mediating versatile effects in a variety of cell types, including actin crosslinking, signal transduction, and intracellular transport processes. MARCKS’s functional role in monocyte/macrophages, however, has not yet been adequately addressed. Thus, the aim of this study was to further elucidate the impact of MARCKS on central cellular functions of monocytic cells. To address this topic, we generated monocytic THP-1 (Tohoku Hospital Pediatrics-1)-derived MARCKS wildtype and knockout (KO) cells using the CRISPR/Cas9 technique. Remarkably, in the absence of MARCKS, both total and intracellular reactive oxygen species (ROS) production were strongly suppressed but restored following transient MARCKS re-transfection. In contrast, proliferation, differentiation, cytokine expression, and phagocytosis remained unaltered. A complete inhibition of ROS production could also be achieved in THP-1-derived PKCβ KO cells or in PKC inhibitor Staurosporine-treated primary human monocytes. MARCKS deficiency also involved reduced basal Akt phosphorylation and delayed re-phosphorylation. Further analyses indicated that long-term TNF pre-incubation strongly enhances monocytic ROS production, which was completely blocked in MARCKS and PKCβ KO cells. Collectively, our study demonstrates that MARCKS is an essential molecule enabling ROS production by monocytic cells and suggests that MARCKS is part of a signal cascade involved in ROS formation.

Peptide Inhibitors of MARCKS Suppress Endotoxin Induced Uveitis in Rats

Purpose: To determine if inhibition of Myristoylated Alanine Rich C Kinase Substrate (MARCKS) protein, using novel MARCKS inhibitor peptides, will reduce the severity of endotoxin-induced uveitis (EIU) in rats. Methods: EIU was induced in Lewis rats using subcutaneous administration of lipopolysaccharide. In the first phase of the study, 3 different novel MARCKS inhibitor peptides that mimic the N-terminal region of MARCKS (BIO-11006, or lower molecular weight analogs BIO-91201 or BIO-91202; Biomarck Pharmaceuticals, Ltd., Newtown, PA) were administered intravitreally (IVT) at 50 and 100 μM. In the second phase, BIO-91201 was administered IVT at 10, 50, and 100 μM and topically at the 100 μM concentration. The efficacy of MARCKS inhibitor peptides was assessed by clinical examination using slit lamp biomicroscopy, optical coherence tomography (OCT) anterior chamber cell counts, histopathology, and aqueous humor cytokine analysis. Results: Clinical scores were significantly reduced 24 h following uveitis induction in the first phase of the study in the following treatment groups: BIO-11006 50 μM IVT and 100 μM IVT, BIO-91201 50 μM IVT, and BIO-91202 100 μM IVT (P < 0.05). OCT anterior chamber cell counts were significantly reduced in the first phase of the study in all treatment groups (P < 0.001). OCT anterior chamber cell counts and histopathology scores were significantly reduced in the second phase of the study in the BIO-91201 50 μM IVT group (P < 0.05). No effect was seen with topical administration. Conclusion: MARCKS inhibitor peptides were effective in reducing the severity of ocular inflammation and cellular influx in EIU.

δPKC-Mediated DRP1 Phosphorylation Impacts Macrophage Mitochondrial Function and Inflammatory Response to Endotoxin

BACKGROUND

Recent studies have demonstrated that alterations in mitochondrial dynamics can impact innate immune function. However, the upstream mechanisms that link mitochondrial dynamics to innate immune phenotypes have not been completely elucidated. This study asks if Protein Kinase C, subunit delta (δPKC)-mediated phosphorylation of dynamin-related protein 1 (Drp1), a key driver of mitochondrial fission, impacts macrophage pro-inflammatory response following bacterial-derived lipopolysaccharide (LPS) stimulation.

METHODS

Using RAW 264.7 cells, bone marrow-derived macrophages from C57BL/6J mice, as well as human monocyte-derived macrophages, we first characterized changes in δPKC-mediated phosphorylation of Drp1 following LPS stimulation. Next, using rationally designed peptides that inhibit δPKC activation (δV1-1) and δPKC-Drp1 interaction (ψDrp1), we determined whether δPKC-mediated phosphorylation of Drp1 impacts LPS-induced changes in mitochondrial morphology, mitochondrial function, and inflammatory response.

RESULTS

Our results demonstrated that δPKC-dependent Drp1 activation is associated with increased mitochondrial fission, impaired cellular respiration, and increased mitochondrial reactive oxygen species in LPS-treated macrophages. This is reversed using a rationally designed peptide that selectively inhibits δPKC phosphorylation of Drp1 (ψDrp1). Interestingly, limiting excessive mitochondrial fission using ψDrp1 reduced LPS-triggered pro-inflammatory response, including a decrease in NF-κB nuclear localization, decreased iNOS induction, and a reduction in pro-inflammatory cytokines (IL-1β, TNFα, IL-6).

CONCLUSION

These data suggest that inhibiting Drp1 phosphorylation by δPKC abates the excessive mitochondrial fragmentation and mitochondrial dysfunction that is seen following LPS treatment. Furthermore, these data suggest that limiting δPKC-dependent Drp1 activation decreases the pro-inflammatory response following LPS treatment. Altogether, δPKC-dependent Drp1 phosphorylation might be an upstream mechanistic link between alterations in mitochondrial dynamics and innate immune phenotypes, and may have therapeutic potential.

Polysialic Acid in the Immune System

Polysialic acid (polySia) is a highly regulated polymer of sialic acid (Sia) with such potent biophysical characteristics that when expressed drastically influences the interaction properties of cells. Although much of what is known of polySia in mammals has been elucidated from the study of its role in the central nervous system (CNS), polySia is also expressed in other tissues, including the immune system where it presents dynamic changes during differentiation, maturation, and activation of different types of immune cells of the innate and adaptive response, being involved in key regulatory mechanisms. At least six polySia protein carriers (CCR7, ESL-1, NCAM, NRP2, ST8Sia 2, and ST8Sia 4) are expressed in different types of immune cells, but there is still much to be explored in regard not only to the regulatory mechanisms that determine their expression and the structure of polySia chains but also to the identification of the cis- and trans- ligands of polySia that establish signaling networks. This review summarizes the current knowledge on polySia in the immune system, addressing its biosynthesis, its tools for identification and structural characterization, and its functional roles and therapeutic implications.

The myristoylated alanine-rich C-kinase substrates (MARCKS): A membrane-anchored mediator of the cell function

The myristoylated alanine-rich C-kinase substrate (MARCKS) and the MARCKS-related protein (MARCKSL1) are ubiquitous, highly conserved membrane-associated proteins involved in the structural modulation of the actin cytoskeleton, chemotaxis, motility, cell adhesion, phagocytosis, and exocytosis. MARCKS includes an N-terminal myristoylated domain for membrane binding, a highly conserved MARCKS Homology 2 (MH2) domain, and an effector domain (which is the phosphorylation site). MARCKS can sequester phosphatidylinositol-4, 5-diphosphate (PIP2) at lipid rafts in the plasma membrane of quiescent cells, an action reversed by protein kinase C (PKC), ultimately modulating the immune function. Being expressed mostly in innate immune cells, MARCKS promotes the inflammation-driven migration and adhesion of cells and the secretion of cytokines such as tumor necrosis factor (TNF). From a clinical point of view, MARCKS is overexpressed in patients with schizophrenia and bipolar disorders, while the brain level of MARCKS phosphorylation is associated with Alzheimer's disease. Furthermore, MARCKS is associated with the development and progression of numerous types of cancers. Data in autoimmune diseases are limited to rheumatoid arthritis models in which a connection between MARCKS and the JAK-STAT pathway is mediated by miRNAs. We provide a comprehensive overview of the structure of MARCKS, its molecular characteristics and functions from a biological and pathogenetic standpoint, and will discuss the clinical implications of this pathway.

MARCKS affects cell motility and response to BTK inhibitors in CLL

Bruton tyrosine kinase (BTK) inhibitors are highly active drugs for the treatment of chronic lymphocytic leukemia (CLL). To understand the response to BTK inhibitors on a molecular level, we performed (phospho)proteomic analyses under ibrutinib treatment. We identified 3466 proteins and 9184 phosphopeptides (representing 2854 proteins) in CLL cells exhibiting a physiological ratio of phosphorylated serines (pS), threonines (pT), and tyrosines (pY) (pS:pT:pY). Expression of 83 proteins differed between unmutated immunoglobulin heavy-chain variable region (IGHV) CLL (UM-CLL) and mutated IGHV CLL (M-CLL). Strikingly, UM-CLL cells showed higher basal phosphorylation levels than M-CLL samples. Effects of ibrutinib on protein phosphorylation levels were stronger in UM-CLL, especially on phosphorylated tyrosines. The differentially regulated phosphopeptides and proteins clustered in pathways regulating cell migration, motility, cytoskeleton composition, and survival. One protein, myristoylated alanine-rich C-kinase substrate (MARCKS), showed striking differences in expression and phosphorylation level in UM-CLL vs M-CLL. MARCKS sequesters phosphatidylinositol-4,5-bisphosphate, thereby affecting central signaling pathways and clustering of the B-cell receptor (BCR). Genetically induced loss of MARCKS significantly increased AKT signaling and migratory capacity. CD40L stimulation increased expression of MARCKS. BCR stimulation induced phosphorylation of MARCKS, which was reduced by BTK inhibitors. In line with our in vitro findings, low MARCKS expression is associated with significantly higher treatment-induced leukocytosis and more pronounced decrease of nodal disease in patients with CLL treated with acalabrutinib.

Pathophysiological roles of myristoylated alanine-rich C-kinase substrate (MARCKS) in hematological malignancies

The myristoylated alanine-rich C-kinase substrate (MARCKS) protein has been at the crossroads of multiple signaling pathways that govern several critical operations in normal and malignant cellular physiology. Functioning as a target of protein kinase C, MARCKS shuttles between the phosphorylated cytosolic form and the unphosphorylated plasma membrane-bound states whilst regulating several molecular partners including, but not limited to calmodulin, actin, phosphatidylinositol-4,5-bisphosphate, and phosphoinositide-3-kinase. As a result of these interactions, MARCKS directly or indirectly modulates a host of cellular functions, primarily including cytoskeletal reorganization, membrane trafficking, cell secretion, inflammatory response, cell migration, and mitosis. Recent evidence indicates that dysregulated expression of MARCKS is associated with the development and progression of hematological cancers. While it is understood that MARCKS impacts the overall carcinogenesis as well as plays a part in determining the disease outcome in blood cancers, we are still at an early stage of interpreting the pathophysiological roles of MARCKS in neoplastic disease. The situation is further complicated by contradictory reports regarding the role of phosphorylated versus an unphosphorylated form of MARCKS as an oncogene versus tumor suppressor in blood cancers. In this review, we will investigate the current body of knowledge and evolving concepts of the physical properties, molecular network, functional attributes, and the likely pathogenic roles of MARCKS in hematological malignancies. Key emphasis will also be laid upon understanding the novel mechanisms by which MARCKS determines the overall disease prognosis by playing a vital role in the induction of therapeutic resistance. Additionally, we will highlight the importance of MARCKS as a valuable therapeutic target in blood cancers and will discuss the potential of existing strategies available to tackle MARCKS-driven blood cancers.

MARCKS mediates vascular contractility through regulating interactions between voltage-gated Ca2+ channels and PIP2

Phosphatidylinositol 4,5-bisphosphate (PIP₂) acts as substrate and unmodified ligand for Gq-protein-coupled receptor signalling in vascular smooth muscle cells (VSMCs) that is central for initiating contractility. The present work investigated how PIP₂ might perform these two potentially conflicting roles by studying the effect of myristoylated alanine-rich C kinase substrate (MARCKS), a PIP₂-binding protein, on vascular contractility in rat and mouse mesenteric arteries. Using wire myography, MANS peptide (MANS), a MARCKS inhibitor, produced robust contractions with a pharmacological profile suggesting a predominantly role for L-type (CaV1.2) voltage-gated Ca²⁺ channels (VGCC). Knockdown of MARCKS using morpholino oligonucleotides reduced contractions induced by MANS and stimulation of α₁-adrenoceptors and thromboxane receptors with methoxamine (MO) and U46619 respectively. Immunocytochemistry and proximity ligation assays demonstrated that MARCKS and CaV1.2 proteins co-localise at the plasma membrane in unstimulated tissue, and that MANS and MO reduced these interactions and induced translocation of MARCKS from the plasma membrane to the cytosol. Dot-blots revealed greater PIP₂ binding to MARCKS than CaV1.2 in unstimulated tissue, with this binding profile reversed following stimulation by MANS and MO. MANS evoked an increase in peak amplitude and shifted the activation curve to more negative membrane potentials of whole-cell voltage-gated Ca²⁺ currents, which were prevented by depleting PIP₂ levels with wortmannin. This present study indicates for the first time that MARCKS is important regulating vascular contractility and suggests that disinhibition of MARCKS by MANS or vasoconstrictors may induce contraction through releasing PIP₂ into the local environment where it increases voltage-gated Ca²⁺ channel activity.

Interaction between Polysialic Acid and the MARCKS-ED Peptide at the Molecular Level

Polysialic acid (polySia) is a highly negatively charged linear homopolymer comprising α-2,8-linked sialic acids. It is abundant in the embryonic brain and modulates various functions such as differentiation and synaptic plasticity in the adult central nervous system by direct binding to its protein partners. One such example is the binding of polySia to myristoylated-alanine rich C-kinase substrate (MARCKS) to modulate neuritogenesis. To understand their interaction mechanism at the molecular level, we performed a binding assay which showed a direct binding of the MARCKS-ED peptide (KKKKKRFSFKKSFKLSGFSFKKNKK) with polySia in a concentration-dependent manner. Molecular dynamics simulations revealed that this binding is not exclusively dominated by electrostatics but can in part be attributed to the presence of near-regularly spaced Phe residues, that confer a compact 3D conformation based on pseudoglycine loop structures supported by Phe-Phe interactions. Our simulations, which are confirmed by circular dichroism measurements, also indicate that the peptide-polySia binding induces large-scale conformational rearrangement of polySia into coils at the binding site, whereas the peptide conformation is relatively unperturbed. As a consequence, we predict that each peptide can bind to a domain extending ∼14 polySia repeat units. Using the fluorescently tagged MARCKS-ED peptide on rat brainstem tissue sections, we demonstrate the ability of the peptide to detect polySia, similarly to polySia-specific antibody mAb735, especially in the spinal trigeminal nucleus and the dorsal vagal complex. This study provides information about the interaction between polySia and its CNS protein binding partner, MARCKS, and provides a fundamental platform for further studies to explore the prospect of the MARCKS-ED as an effective polySia-binding peptide for bioimaging and drug delivery applications.

MARCKS and Lung Disease

MARCKS (myristoylated alanine-rich C kinase substrate) is a prominent PKC substrate expressed in all eukaryotic cells. It is known to bind to and cross-link actin filaments, to serve as a bridge between Ca²⁺/calmodulin and PKC signaling, and to sequester the signaling molecule phosphatidylinositol 4,5-bisphosphate in the plasma membrane. Since the mid-1980s, this evolutionarily conserved and ubiquitously expressed protein has been associated with regulating cellular events that require dynamic actin reorganization, including cellular adhesion, migration, and exocytosis. More recently, translational studies have implicated MARCKS in the pathophysiology of a number of airway diseases, including chronic obstructive pulmonary disease, asthma, lung cancer, and acute lung injury/acute respiratory distress syndrome. This article summarizes the structure and cellular function of MARCKS (also including MARCKS family proteins and MARCKSL1 [MARCKS-like protein 1]). Evidence for MARCKS's role in several lung diseases is discussed, as are the technological innovations that took MARCKS-targeting strategies from theoretical to therapeutic. Descriptions and updates derived from ongoing clinical trials that are investigating inhalation of a MARCKS-targeting peptide as therapy for patients with chronic bronchitis, lung cancer, and ARDS are provided.

Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression

Targeting activated fibroblasts, including myofibroblast differentiation, has emerged as a key therapeutic strategy in patients with idiopathic pulmonary fibrosis (IPF). However, there is no available therapy capable of selectively eradicating myofibroblasts or limiting their genesis. Through an integrative analysis of the regulator genes that are responsible for the activation of IPF fibroblasts, we noticed the phosphatidylinositol 4,5-bisphosphate (PIP2)-binding protein, myristoylated alanine-rich C-kinase substrate (MARCKS), as a potential target molecule for IPF. Herein, we have employed a 25-mer novel peptide, MARCKS phosphorylation site domain sequence (MPS), to determine if MARCKS inhibition reduces pulmonary fibrosis through the inactivation of PI3K/protein kinase B (AKT) signaling in fibroblast cells. We first observed that higher levels of MARCKS phosphorylation and the myofibroblast marker α-smooth muscle actin (α-SMA) were notably overexpressed in all tested IPF lung tissues and fibroblast cells. Treatment with the MPS peptide suppressed levels of MARCKS phosphorylation in primary IPF fibroblasts. A kinetic assay confirmed that this peptide binds to phospholipids, particularly PIP2, with a dissociation constant of 17.64 nM. As expected, a decrease of phosphatidylinositol (3,4,5)-trisphosphate pools and AKT activity occurred in MPS-treated IPF fibroblast cells. MPS peptide was demonstrated to impair cell proliferation, invasion, and migration in multiple IPF fibroblast cells in vitro as well as to reduce pulmonary fibrosis in bleomycin-treated mice in vivo. Surprisingly, we found that MPS peptide decreases α-SMA expression and synergistically interacts with nintedanib treatment in IPF fibroblasts. Our data suggest MARCKS as a druggable target in pulmonary fibrosis and also provide a promising antifibrotic agent that may lead to effective IPF treatments.-Yang, D. C., Li, J.-M., Xu, J., Oldham, J., Phan, S. H., Last, J. A., Wu, R., Chen, C.-H. Tackling MARCKS-PIP3 circuit attenuates fibroblast activation and fibrosis progression.

Targeting the phosphorylation site of myristoylated alanine-rich C kinase substrate alleviates symptoms in a murine model of steroid-resistant asthma

BACKGROUND AND PURPOSE

Myristoylated alanine-rich C kinase substrate (MARCKS), a PKC substrate, facilitates mucus production and neutrophil migration. However, the effects of therapeutic procedures targeting the phosphorylation site of MARCKS on steroid-resistant asthma and the mechanisms underlying such effects have not yet been investigated. We designed a peptide that targets the MARCKS phosphorylation site (MPS peptide) and assessed its therapeutic potential against steroid-resistant asthma.

EXPERIMENTAL APPROACH

Mice were sensitized with ovalbumin (OVA), alum, and challenged with aerosolized OVA five times a week for 1 month. The mice were intratracheally administered MPS peptides three times a week, 1 hr before OVA challenge. Asthma symptoms and cell profiles in the bronchoalveolar lavage were assessed, and key proteins were analysed using Western blotting.

KEY RESULTS

Phosphorylated (p)-MARCKS was highly expressed in inflammatory and bronchial epithelial cells in OVA-immunized mice. MPS peptide reduced eosinophils, neutrophils, mucus production, collagen deposition, and airway hyper-responsiveness. Dexamethasone (Dexa) did not alleviate steroid-resistant asthma symptoms. MPS peptide caused a decrease in p-MARCKS, nitrotyrosine and the expression of oxidative stress enzymes, NADPH oxidase dual oxidase 1 and inducible NOS, in lung tissues. Compared to Dexa, MPS peptides inhibited C5a production and attenuated IL-17A and KC production in the airway more effectively, thus suppressing asthma symptoms.

CONCLUSIONS AND IMPLICATIONS

Our findings indicate that targeting MARCKS phosphorylation through MPS treatment may inhibit neutrophilic inflammation and relieve asthma symptoms, thereby highlighting its potential as a therapeutic agent for steroid-resistant asthma.

Proteomic profiling reveals key cancer progression modulators in shed microvesicles released from isogenic human primary and metastatic colorectal cancer cell lines

Extracellular vesicles comprise two main classes - exosomes and shed microvesicles (sMVs). Whilst much is known about exosome cargo content and functionality, sMVs are poorly understood. Here, we describe the large-scale purification of sMVs released from primary (SW480) and metastatic (SW620) human isogenic colorectal cancer (CRC) cell lines using a combination of differential ultracentrifugation and isopycnic iodixanol density centrifugation. The yield of SW480-sMVs and SW620-sMVs was 0.75 mg and 0.80 mg, respectively. Both SW480-/SW620-sMVs are heterogeneous in size (100-600 nm diameter) and exhibit identical buoyant densities (1.10 g/mL). In contrast to exosomes, sMVs are ALIX^-, TSG101^-, CD63^- and CD9^-. Quantitative mass spectrometry identified 1295 and 1300 proteins in SW480-sMVs and SW620-sMVs, respectively. Gene Ontology enrichment analysis identified 'cell adhesion' (CDH1, OCLN, CTN families), 'signalling pathway' (KRAS, NRAS, MAPK1, MAP2K1), and 'translation/RNA related' processes (EIF, RPL, HNRNP families) in both sMV types. Strikingly, SW480- and SW620-sMVs exhibit distinct protein signatures - SW480-sMVs being enriched in ITGA/B, ANXA1, CLDN7, CD44 and EGFR/NOTCH signalling networks, while SW620-sMVs are enriched in PRKCA, MACC1, FGFR4 and MTOR/MARCKS signalling networks. Both SW480- and SW620-sMVs are taken up by NIH3T3 fibroblasts resulting in similar cell invasion capability. This study provides, for the first time, molecular insights into sMVs and CRC biology.

Identification of DKK-1 as a novel mediator of statin effects in human endothelial cells

This study shows that DKK-1, a member of the Dickkopf family and a regulator of the Wnt pathways, represents a novel target of statins which, through the inhibition of HMG-CoA reductase and of non-steroidal isoprenoid intermediates, exert extra-beneficial effect in preventing atherosclerosis beyond their effect on the lipid profile. We found that atorvastatin downregulates DKK-1 protein (−88.3 ± 4.1%) and mRNA expression (−90 ± 4.2%) through the inhibition of Cdc42, Rho and Rac geranylgeranylated proteins. Further, a combined approach based on the integration of label-free quantitative mass spectrometry based-proteomics and gene silencing allowed us to demonstrate that DKK-1 itself mediates, at least in part, statin effects on human endothelial cells. Indeed, DKK-1 is responsible for the regulation of the 21% of the statin-modulated proteins, which include, among others, clusterin/apoJ, plasminogen activator inhibitor type 1 (PAI-1), myristoylated alanine-rich C-kinase substrate (MARCKS), and pentraxin 3 (PTX3). The Gene Ontology enrichment annotation revealed that DKK-1 is also a potential mediator of the extracellular matrix organization, platelet activation and response to wounding processes induced by statin. Finally, we found that plasma level of DKK-1 from cholesterol-fed rabbits treated with atorvastatin (2.5 mg/kg/day for 8 weeks) was lower (−42 ± 23%) than that of control animals. Thus, DKK-1 is not only a target of statin but it directly regulates the expression of molecules involved in a plethora of biological functions, thus expanding its role, which has been so far restricted mainly to cancer.

Quantitative gingival crevicular fluid proteome in type 2 diabetes mellitus and chronic periodontitis

OBJECTIVE

The aim of this study was to investigate the proteome of the gingival crevicular fluid comparing the relative abundance of proteins from type 2 diabetes mellitus (2DM) individuals and chronic periodontitis (CP) affected sites, subjects affected by both conditions and healthy individuals.

MATERIAL AND METHODS

Twenty individuals were equally allocated in four groups, 2DM with CP, 2DM periodontally healthy, CP without 2DM, and periodontally healthy without 2DM. The relative quantification of proteins was accessed with iTRAQ labeling and mass spectrometry.

RESULTS AND CONCLUSION

A total of 104 proteins showed significant differences in abundance in pairwise comparisons. Some presented different levels in all diseased groups as compared to control, either increasing (rap guanine nucleotide exchange factor, S100A8, S100A9, and immunoglobulins) or decreasing (actins, myristoylated alanine-rich C-kinase substrate, and glutathione S-transferase). Other differences were specific for a given condition: Titin, neutrophil elastase, and myeloperoxidase levels were higher in the DP group, cathelicidin antimicrobial peptide decreased in CP, and annexin decreased in DH. These differences in the proteome can provide clues for further studies that will validate the variation in their levels and their role in both diseases.

MARCKS regulates neuritogenesis and interacts with a CDC42 signaling network

Through the process of neuronal differentiation, newly born neurons change from simple, spherical cells to complex, sprawling cells with many highly branched processes. One of the first stages in this process is neurite initiation, wherein cytoskeletal modifications facilitate membrane protrusion and extension from the cell body. Hundreds of actin modulators and microtubule-binding proteins are known to be involved in this process, but relatively little is known about how upstream regulators bring these complex networks together at discrete locations to produce neurites. Here, we show that Myristoylated alanine-rich C kinase substrate (MARCKS) participates in this process. Marcks^−/− cortical neurons extend fewer neurites and have less complex neurite arborization patterns. We use an in vitro proteomics screen to identify MARCKS interactors in developing neurites and characterize an interaction between MARCKS and a CDC42-centered network. While the presence of MARCKS does not affect whole brain levels of activated or total CDC42, we propose that MARCKS is uniquely positioned to regulate CDC42 localization and interactions within specialized cellular compartments, such as nascent neurites.

MARCKS and MARCKS-like proteins in development and regeneration

BACKGROUND

The Myristoylated Alanine-Rich C-kinase Substrate (MARCKS) and MARCKS-like protein 1 (MARCKSL1) have a wide range of functions, ranging from roles in embryonic development to adult brain plasticity and the inflammatory response. Recently, both proteins have also been identified as important players in regeneration. Upon phosphorylation by protein kinase C (PKC) or calcium-dependent calmodulin-binding, MARCKS and MARCKSL1 translocate from the membrane into the cytosol, modulating cytoskeletal actin dynamics and vesicular trafficking and activating various signal transduction pathways. As a consequence, the two proteins are involved in the regulation of cell migration, secretion, proliferation and differentiation in many different tissues.

MAIN BODY

Throughout vertebrate development, MARCKS and MARCKSL1 are widely expressed in tissues derived from all germ layers, with particularly strong expression in the nervous system. They have been implicated in the regulation of gastrulation, myogenesis, brain development, and other developmental processes. Mice carrying loss of function mutations in either Marcks or Marcksl1 genes die shortly after birth due to multiple deficiencies including detrimental neural tube closure defects. In adult vertebrates, MARCKS and MARCKL1 continue to be important for multiple regenerative processes including peripheral nerve, appendage, and tail regeneration, making them promising targets for regenerative medicine.

CONCLUSION

This review briefly summarizes the molecular interactions and cellular functions of MARCKS and MARCKSL1 proteins and outlines their vital roles in development and regeneration.

A PKC-MARCKS-PI3K regulatory module links Ca2+ and PIP3 signals at the leading edge of polarized macrophages

The leukocyte chemosensory pathway detects attractant gradients and directs cell migration to sites of inflammation, infection, tissue damage, and carcinogenesis. Previous studies have revealed that local Ca²⁺ and PIP₃ signals at the leading edge of polarized leukocytes play central roles in positive feedback loop essential to cell polarization and chemotaxis. These prior studies showed that stimulation of the leading edge Ca²⁺ signal can strongly activate PI3K, thereby triggering a larger PIP₃ signal, but did not elucidate the mechanistic link between Ca²⁺ and PIP₃ signaling. A hypothesis explaining this link emerged, postulating that Ca²⁺-activated PKC displaces the MARCKS protein from plasma membrane PIP₂, thereby releasing sequestered PIP₂ to serve as the target and substrate lipid of PI3K in PIP₃ production. In vitro single molecule studies of the reconstituted pathway on lipid bilayers demonstrated the feasibility of this PKC-MARCKS-PI3K regulatory module linking Ca²⁺ and PIP₃ signals in the reconstituted system. The present study tests the model predictions in live macrophages by quantifying the effects of: (a) two pathway activators—PDGF and ATP that stimulate chemoreceptors and Ca²⁺ influx, respectively; and (b) three pathway inhibitors—wortmannin, EGTA, and Go6976 that inhibit PI3K, Ca²⁺ influx, and PKC, respectively; on (c) four leading edge activity sensors—AKT-PH-mRFP, CKAR, MARCKSp-mRFP, and leading edge area that report on PIP₃ density, PKC activity, MARCKS membrane binding, and leading edge expansion/contraction, respectively. The results provide additional evidence that PKC and PI3K are both essential elements of the leading edge positive feedback loop, and strongly support the existence of a PKC-MARCKS-PI3K regulatory module linking the leading edge Ca²⁺ and PIP₃ signals. As predicted, activators stimulate leading edge PKC activity, displacement of MARCKS from the leading edge membrane and increased leading edge PIP₃ levels, while inhibitors trigger the opposite effects. Comparison of the findings for the ameboid chemotaxis of leukocytes with recently published findings for the mesenchymal chemotaxis of fibroblasts suggests that some features of the emerging leukocyte leading edge core pathway (PLC-DAG-Ca²⁺-PKC-MARCKS-PIP₂-PI3K-PIP₃) may well be shared by all chemotaxing eukaryotic cells, while other elements of the leukocyte pathway may be specialized features of these highly optimized, professional gradient-seeking cells. More broadly, the findings suggest a molecular mechanism for the strong links between phospho-MARCKS and many human cancers.

Myristoylated alanine-rich C kinase substrate (MARCKS): a multirole signaling protein in cancers

Emerging evidence implicates myristoylated alanine-rich C-kinase substrate (MARCKS), a major substrate of protein kinase C (PKC), in a critical role for cancer development and progression. MARCKS is tethered to the plasma membrane but can shuttle between the cytosol and plasma membrane via the myristoyl-electrostatic switch. Phosphorylation of MARCKS by PKC leads to its translocation from the plasma membrane to the cytosol where it functions in actin cytoskeletal remodeling, Ca²⁺ signaling through binding to calmodulin, and regulation of exocytic vesicle release in secretory cells such as neurons and airway goblet cells. Although the contribution of MARCKS to various cellular processes has been extensively studied, its roles in neoplastic disease have been conflicting. This review highlights the molecular and functional differences of MARCKS that exist between normal and tumor cells. We also discuss the recent advances in the potential roles of MARCKS in tumorigenesis, metastasis, and resistance to anti-cancer therapies, with a focus on addressing the inconsistent results regarding the function of MARCKS as a promoter or inhibitor of oncogenesis.

A Reaction-Diffusion Model Explains Amplification of the PLC/PKC Pathway in Fibroblast Chemotaxis

During the proliferative phase of cutaneous wound healing, dermal fibroblasts are recruited into the clotted wound by a concentration gradient of platelet-derived growth factor (PDGF), together with other spatial cues. Despite the importance of this chemotactic process, the mechanisms controlling the directed migration of slow-moving mesenchymal cells such as fibroblasts are not well understood. Here, we develop and analyze a reaction-diffusion model of phospholipase C/protein kinase C (PKC) signaling, which was recently identified as a requisite PDGF-gradient-sensing pathway, with the goal of identifying mechanisms that can amplify its sensitivity in the shallow external gradients typical of chemotaxis experiments. We show that phosphorylation of myristoylated alanine-rich C kinase substrate by membrane-localized PKC constitutes a positive feedback that is sufficient for local pathway amplification. The release of phosphorylated myristoylated alanine-rich C kinase substrate and its subsequent diffusion and dephosphorylation in the cytosol also serves to suppress the pathway in down-gradient regions of the cell. By itself, this mechanism only weakly amplifies signaling in a shallow PDGF gradient, but it synergizes with other feedback mechanisms to enhance amplification. This model offers a framework for a mechanistic understanding of phospholipase C/PKC signaling in chemotactic gradient sensing and can guide the design of experiments to assess the roles of putative feedback loops.

An Inhaled Inhibitor of Myristoylated Alanine-Rich C Kinase Substrate Reverses LPS-Induced Acute Lung Injury in Mice

Intratracheal instillation of bacterial LPS is a well-established model of acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). Because the myristoylated alanine-rich C kinase substrate (MARCKS) protein is involved in neutrophil migration and proinflammatory cytokine production, we examined whether an aerosolized peptide that inhibits MARCKS function could attenuate LPS-induced lung injury in mice. The peptide, BIO-11006, was delivered at 50 μM via inhalation either just before intratracheal instillation of 5 μg of LPS into Balb/C mice, or 4, 12, 24, or 36 hours after LPS instillation. Effects of BIO-11006 were evaluated via analysis of mouse disease-related behavior, lung histology, bronchoalveolar lavage fluid total protein, neutrophil counts and percentages, cytokine (KC [CXCl1, mouse IL-8 equivalent] and TNF-α) expression, and activation of NF-κB in lung tissue. Treatment with aerosolized BIO-11006 at 0, 4, 12, 24, and even 36 hours after LPS instillation reversed the disease process: mouse behavior returned to normal after two treatments 12 hours apart with the inhaled peptide after LPS injury, whereas control LPS-instilled animals treated with PBS only remained moribund. Histological appearance of inflammation, bronchoalveolar lavage fluid protein levels, leukocyte and neutrophil numbers, KC and TNF-α gene and protein expression, and NF-κB activation were all significantly attenuated by inhaled BIO-11006 at all time points. These results implicate MARCKS protein in the pathogenesis of ALI/ARDS and suggest that MARCKS-inhibitory peptide(s), delivered by inhalation, could represent a new and potent therapeutic treatment for ALI/ARDS, even if administered well after the disease process has begun.

MARCKS promotes invasion and is associated with biochemical recurrence in prostate cancer

BACKGROUND

Overtreatment of low-grade prostate cancer is a recognised problem for clinicians and patients. However, under-treatment runs the risk of missing the opportunity for cure in those who could benefit. Identification of new biomarkers of disease progression, including metastases, is required to better stratify and appropriately treat these patients. The ability to predict if prostate cancer will recur is an important clinical question that would impact treatment options for patients. Studies in other cancers have associated MARCKS with metastasis.

METHODS

Tissue microarrays of local prostatectomy samples from a cohort of biochemical recurrent and non-biochemical recurrent tumours were assayed for MARCKS protein expression. Prostate cancer cell lines were transfected with siRNA targeting MARCKS or a control and functional endpoints of migration, invasion, proliferation, viability and apoptosis were measured. Actin was visualised by fluorescent microscopy and evidence of a cadherin switch and activation of the AKT pathway were assayed.

RESULTS

MARCKS was upregulated in biochemical recurrent patients compared to non-biochemical recurrent. Knockdown of MARCKS reduced migration and invasion of prostate cancer cells, reduced MMP9 mRNA expression, as well as decreasing cell spreading and increased cell:cell adhesion in prostate cancer cell colonies. Knockdown of MARCKS had no effect on proliferation, viability or apoptosis of the prostate cancer cells.

CONCLUSIONS

In conclusion, MARCKS promotes migration and invasion and is associated with biochemical recurrence in localised prostate cancer tumours. The mechanisms by which this occurs have yet to be fully elucidated but lack of a cadherin switch indicates it is not via epithelial-to-mesenchymal transition. Actin rearrangement indicates that MARCKS promotes invasion through regulating the architecture of the cell.

Regulation of a Coupled MARCKS-PI3K Lipid Kinase Circuit by Calmodulin: Single-Molecule Analysis of a Membrane-Bound Signaling Module

Amoeboid cells that employ chemotaxis to travel up an attractant gradient possess a signaling network assembled on the leading edge of the plasma membrane that senses the gradient and remodels the actin mesh and cell membrane to drive movement in the appropriate direction. In leukocytes such as macrophages and neutrophils, and perhaps in other amoeboid cells as well, the leading edge network includes a positive feedback loop in which the signaling of multiple pathway components is cooperatively coupled. Cytoplasmic Ca²⁺ is a recently recognized component of the feedback loop at the leading edge where it stimulates phosphoinositide-3-kinase (PI3K) and the production of its product signaling lipid phosphatidylinositol 3,4,5-trisphosphate (PIP₃). A previous study implicated Ca²⁺-activated protein kinase C (PKC) and the phosphatidylinositol 4,5-bisphosphate (PIP₂) binding protein MARCKS as two important players in this signaling, because PKC phosphorylation of MARCKS releases free PIP₂ that serves as the membrane binding target and substrate for PI3K. This study asks whether calmodulin (CaM), which is known to directly bind MARCKS, also stimulates PIP₃ production by releasing free PIP₂. Single-molecule fluorescence microscopy is used to quantify the surface density and enzyme activity of key protein components of the hypothesized Ca²⁺-CaM-MARCKS-PIP₂-PI3K-PIP₃ circuit. The findings show that CaM does stimulate PI3K lipid kinase activity by binding MARCKS and displacing it from PIP₂ headgroups, thereby releasing free PIP₂ that recruits active PI3K to the membrane and serves as the substrate for the generation of PIP₃. The resulting CaM-triggered activation of PI3K is complete in seconds and is much faster than PKC-triggered activation, which takes minutes. Overall, the available evidence implicates both PKC and CaM in the coupling of Ca²⁺ and PIP₃ signals and suggests these two different pathways have slow and fast activation kinetics, respectively.

Elevated MARCKS phosphorylation contributes to unresponsiveness of breast cancer to paclitaxel treatment

Accumulating evidence has suggested that myristoylated alanine-rich C-kinase substrate (MARCKS) is critical for regulating multiple pathophysiological processes. However, the molecular mechanism underlying increased phosphorylation of MARCKS at Ser159/163 (phospho-MARCKS) and its functional consequence in neoplastic disease remain to be established. Herein, we investigated how phospho-MARCKS is regulated in breast carcinoma, and its role in the context of chemotherapy. In a screen of patients with breast tumors, we find that the abundance of phospho-MARCKS, not MARCKS protein per se, increased in breast cancers and positively correlated with tumor grade and metastatic status. Among chemotherapeutic agents, mitotic inhibitors, including paclitaxel, vincristine or eribulin, notably promoted phospho-MARCKS accumulation in multiple breast cancer cells. We further show that phospho-MARCKS acted upstream of Src activation upon paclitaxel exposure. Reduction of phospho-MARCKS by knockdown of MARCKS or pharmacological agents increased paclitaxel sensitivity. Particularly, a known phospho-MARCKS inhibitor, MANS peptide, was demonstrated to increase paclitaxel efficacy and attenuate angiogenesis/metastasis of xenografted breast cancer cells by decreasing abundance of phospho-MARCKS and messages of inflammatory mediators. Our data suggest that unresponsiveness of breast cancer to paclitaxel treatment is, at least in part, mediated by phospho-MARCKS and also provide an alternative therapeutic strategy against breast cancer by improving taxanes sensitivity.

Involvement of myristoylated alanine-rich C kinase substrate phosphorylation and translocation in cholecystokinin-induced amylase release in rat pancreatic acini

Cholecystokinin (CCK) is a gastrointestinal hormone that induces exocytotic amylase release in pancreatic acinar cells. The activation of protein kinase C (PKC) is involved in the CCK-induced pancreatic amylase release. Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed substrate of PKC. MARCKS has been implicated in membrane trafficking in several cell types. The phosphorylation of MARCKS by PKC results in the translocation of MARCKS from the membrane to the cytosol. Here, we studied the involvement of MARCKS in the CCK-induced amylase release in rat pancreatic acini. Employing Western blotting, we detected MARCKS protein in the rat pancreatic acini. CCK induced MARCKS phosphorylation. A PKC-δ inhibitor, rottlerin, inhibited the CCK-induced MARCKS phosphorylation and amylase release. In the translocation assay, we also observed CCK-induced PKC-δ activation. An immunohistochemistry study showed that CCK induced MARCKS translocation from the membrane to the cytosol. When acini were lysed by a detergent, Triton X-100, CCK partially induced displacement of the MARCKS from the GM1a-rich detergent-resistant membrane fractions (DRMs) in which Syntaxin2 is distributed. A MARCKS-related peptide inhibited the CCK-induced amylase release. These findings suggest that MARCKS phosphorylation by PKC-δ and then MARCKS translocation from the GM1a-rich DRMs to the cytosol are involved in the CCK-induced amylase release in pancreatic acinar cells.

In Vitro Neutrophil Migration Requires Protein Kinase C-Delta (δ-PKC)-Mediated Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Phosphorylation

Dysregulated release of neutrophil reactive oxygen species and proteolytic enzymes contributes to both acute and chronic inflammatory diseases. Therefore, molecular regulators of these processes are potential targets for new anti-inflammatory therapies. We have shown previously that myristoylated alanine-rich C-kinase substrate (MARCKS), a well-known actin binding protein and protein kinase C (PKC) substrate, is a key regulator of neutrophil functions. In the current study, we investigate the role of PKC-mediated MARCKS phosphorylation in neutrophil migration and adhesion in vitro. We report that treatment of human neutrophils with the δ-PKC inhibitor rottlerin significantly attenuates f-Met-Leu-Phe (fMLF)-induced MARCKS phosphorylation (IC50=5.709 μM), adhesion (IC50=8.4 μM), and migration (IC50=6.7 μM), while α-, β-, and ζ-PKC inhibitors had no significant effect. We conclude that δ-PKC-mediated MARCKS phosphorylation is essential for human neutrophil migration and adhesion in vitro. These results implicate δ-PKC-mediated MARCKS phosphorylation as a key step in the inflammatory response of neutrophils.

Myristoylated Alanine-Rich Protein Kinase Substrate (MARCKS) Regulates Small GTPase Rac1 and Cdc42 Activity and Is a Critical Mediator of Vascular Smooth Muscle Cell Migration in Intimal Hyperplasia Formation

BACKGROUND

Transcription of the myristoylated alanine-rich C kinase substrate (MARCKS) is upregulated in animal models of intimal hyperplasia. MARCKS knockdown inhibits vascular smooth muscle cell (VSMC) migration in vitro; however, the mechanism is as yet unknown. We sought to elucidate the mechanism of MARCKS-mediated motility and determine whether MARCKS knockdown reduces intimal hyperplasia formation in vivo.

METHODS AND RESULTS

MARCKS knockdown blocked platelet-derived growth factor (PDGF)-induced translocation of cortactin to the cell cortex, impaired both lamellipodia and filopodia formation, and attenuated motility of human coronary artery smooth muscle cells (CASMCs). Activation of the small GTPases, Rac1 and Cdc42, was prevented by MARCKS knockdown. Phosphorylation of MARCKS resulted in a transient shift of MARCKS from the plasma membrane to the cytosol. MARCKS knockdown significantly decreased membrane-associated phosphatidylinositol 4,5-bisphosphate (PIP2) levels. Cotransfection with an intact, unphosphorylated MARCKS, which has a high binding affinity for PIP2, restored membrane-associated PIP2 levels and was indispensable for activation of Rac1 and Cdc42 and, ultimately, VSMC migration. Overexpression of MARCKS in differentiated VSMCs increased membrane PIP2 abundance, Rac1 and Cdc42 activity, and cell motility. MARCKS protein was upregulated early in the development of intimal hyperplasia in the murine carotid ligation model. Decreased MARKCS expression, but not total knockdown, attenuated intimal hyperplasia formation.

CONCLUSIONS

MARCKS upregulation increases VSMC motility by activation of Rac1 and Cdc42. These effects are mediated by MARCKS sequestering PIP2 at the plasma membrane. This study delineates a novel mechanism for MARCKS-mediated VSMC migration and supports the rational for MARCKS knockdown to prevent intimal hyperplasia.

Targeting myristoylated alanine-rich C kinase substrate phosphorylation site domain in lung cancer. Mechanisms and therapeutic implications

RATIONALE

Phosphorylation of myristoylated alanine-rich C kinase substrate (phospho-MARCKS) at the phosphorylation site domain (PSD) is crucial for mucus granule secretion and cell motility, but little is known concerning its function in lung cancer.

OBJECTIVES

We aimed to determine if MARCKS PSD activity can serve as a therapeutic target and to elucidate the molecular basis of this potential.

METHODS

The clinical relevance of phospho-MARCKS was first confirmed. Next, we used genetic approaches to verify the functionality and molecular mechanism of phospho-MARCKS. Finally, cancer cells were pharmacologically inhibited for MARCKS activity and subjected to functional bioassays.

MEASUREMENTS AND MAIN RESULTS

We demonstrated that higher phospho-MARCKS levels were correlated with shorter overall survival of lung cancer patients. Using shRNA silencing and ectopic expression of wild-type and PSD-mutated (S159/163A) MARCKS, we showed that elevated phospho-MARCKS promoted cancer growth and erlotinib resistance. Further studies demonstrated an interaction of phosphoinositide 3-kinase with MARCKS, but not with phospho-MARCKS. Interestingly, phospho-MARCKS acted in parallel with increased phosphatidylinositol (3,4,5)-triphosphate pools and AKT activation in cells. Through treatment with a 25-mer peptide targeting the MARCKS PSD motif (MPS peptide), we were able to suppress tumor growth and metastasis in vivo, and reduced levels of phospho-MARCKS, phosphatidylinositol (3,4,5)-triphosphate, and AKT activity. This peptide also enhanced the sensitivity of lung cancer cells to erlotinib treatment, especially those with sustained activation of phosphoinositide 3-kinase/AKT signaling.

CONCLUSIONS

These results suggest a key role for MARCKS PSD in cancer disease and provide a unique strategy for inhibiting the activity of MARCKS PSD as a treatment for lung cancer.

Myristoylated Alanine Rich C Kinase Substrate (MARCKS) is essential to β2-integrin dependent responses of equine neutrophils

Neutrophil infiltration is a prominent feature in a number of pathologic conditions affecting horses including recurrent airway obstruction, ischemia-reperfusion injury, and laminitis. Cell signaling components involved in neutrophil migration represent targets for novel anti-inflammatory therapies. In order to migrate into tissue, neutrophils must respond to chemoattractant signals in their external environment through activation of adhesion receptors (i.e. integrins) and reorganization of the actin cytoskeleton. Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS), a highly conserved actin-binding protein, has a well demonstrated role in cytoskeletal dependent cellular functions (i.e. adhesion, spreading, and migration), but the details of MARCKS involvement in these processes remain vague. We hypothesized that MARCKS serves as a link between the actin cytoskeleton and integrin function in neutrophils. Using a MARCKS-specific inhibitor peptide known as MANS on equine neutrophils in vitro, we demonstrate that inhibition of MARCKS function significantly attenuates β2-integrin-dependent neutrophil functions including migration, adhesion, and immune complex-mediated respiratory burst. The MANS peptide did not, however, inhibit the β2-integrin-independent PMA mediated respiratory burst. These results attest to the essential role of MARCKS function in regulating neutrophil responses, and strongly implicate MARCKS as a potential regulator of β2-integrins in neutrophils.

A peptide that inhibits function of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) reduces lung cancer metastasis

Myristoylated Alanine-Rich C Kinase Substrate (MARCKS), a substrate of protein kinase C, is a key regulatory molecule controlling mucus granule secretion by airway epithelial cells as well as directed migration of leukocytes, stem cells and fibroblasts. Phosphorylation of MARKCS may be involved in these responses. However, the functionality of MARCKS and its related phosphorylation in lung cancer malignancy have not been characterized. This study demonstrated elevated levels of MARCKS and phospho-MARCKS in highly invasive lung cancer cell lines and lung cancer specimens from non-small-cell lung cancer patients. siRNA knockdown of MARCKS expression in these highly invasive lung cancer cell lines reduced cell migration and suppressed PI3K (phosphatidylinositol 3'-kinase)/Akt phosphorylation and Slug level. Interestingly, treatment with a peptide identical to the MARCKS N-terminus sequence (the MANS peptide) impaired cell migration in vitro and also the metastatic potential of invasive lung cancer cells in vivo. Mechanistically, MANS peptide treatment resulted in a coordination of increase of E-cadherin expression, suppression of MARCKS phosphorylation and AKT/Slug signalling pathway but not the expression of total MARCKS. These results indicate a crucial role for MARCKS, specifically its phosphorylated form, in potentiating lung cancer cell migration/metastasis and suggest a potential use of MARCKS-related peptides in the treatment of lung cancer metastasis.

Fibroblast Migration Is Regulated by Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Protein

Myristoylated alanine-rich C-kinase substrate (MARCKS) is a ubiquitously expressed substrate of protein kinase C (PKC) that is involved in reorganization of the actin cytoskeleton. We hypothesized that MARCKS is involved in regulation of fibroblast migration and addressed this hypothesis by utilizing a unique reagent developed in this laboratory, the MANS peptide. The MANS peptide is a myristoylated cell permeable peptide corresponding to the first 24-amino acids of MARCKS that inhibits MARCKS function. Treatment of NIH-3T3 fibroblasts with the MANS peptide attenuated cell migration in scratch wounding assays, while a myristoylated, missense control peptide (RNS) had no effect. Neither MANS nor RNS peptide treatment altered NIH-3T3 cell proliferation within the parameters of the scratch assay. MANS peptide treatment also resulted in inhibited NIH-3T3 chemotaxis towards the chemoattractant platelet-derived growth factor-BB (PDGF-BB), with no effect observed with RNS treatment. Live cell imaging of PDGF-BB induced chemotaxis demonstrated that MANS peptide treatment resulted in weak chemotactic fidelity compared to RNS treated cells. MANS and RNS peptides did not affect PDGF-BB induced phosphorylation of MARCKS or phosphoinositide 3-kinase (PI3K) signaling, as measured by Akt phosphorylation. Further, no difference in cell migration was observed in NIH-3T3 fibroblasts that were transfected with MARCKS siRNAs with or without MANS peptide treatment. Genetic structure-function analysis revealed that MANS peptide-mediated attenuation of NIH-3T3 cell migration does not require the presence of the myristic acid moiety on the amino-terminus. Expression of either MANS or unmyristoylated MANS (UMANS) C-terminal EGFP fusion proteins resulted in similar levels of attenuated cell migration as observed with MANS peptide treatment. These data demonstrate that MARCKS regulates cell migration and suggests that MARCKS-mediated regulation of fibroblast migration involves the MARCKS amino-terminus. Further, this data demonstrates that MANS peptide treatment inhibits MARCKS function during fibroblast migration and that MANS mediated inhibition occurs independent of myristoylation.

Temporal induction of immunoregulatory processes coincides with age-dependent resistance to viral-induced type 1 diabetes

The dilute plasma cytokine milieu associated with type 1 diabetes (T1D), while difficult to measure directly, is sufficient to drive transcription in a bioassay that uses healthy leukocytes as reporters. Previously, we reported disease-associated, partially IL-1 dependent, transcriptional signatures in both T1D patients and the BioBreeding (BB) rat model. Here, we examine temporal signatures in congenic BBDR.lyp/lyp rats that develop spontaneous T1D, and BBDR rats where T1D progresses only after immunological perturbation in young animals. After weaning, the BBDR temporal signature showed early coincident induction of transcription related to innate inflammation as well as IL-10- and TGF-β-mediated regulation. BBDR plasma cytokine levels mirrored the signatures showing early inflammation, followed by induction of a regulated state that correlated with failure of virus to induce T1D in older rats. In contrast, the BBDR.lyp/lyp temporal signature exhibited asynchronous dynamics, with delayed induction of inflammatory transcription and later, weaker induction of regulatory transcription, consistent with their deficiency in regulatory T cells. Through longitudinal analyses of plasma-induced signatures in BB rats and a human T1D progressor, we have identified changes in immunoregulatory processes that attenuate a preexisting innate inflammatory state in BBDR rats, suggesting a mechanism underlying the decline in T1D susceptibility with age.

A myristoylated alanine-rich C kinase substrate-related peptide suppresses cytokine mRNA and protein expression in LPS-activated canine neutrophils

Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed protein kinase C substrate that has emerged as a potential therapeutic target for the amelioration of mucin secretion and inflammation in patients with chronic obstructive pulmonary disease. MARCKS also plays a key role in regulating the adhesion, migration, and degranulation of neutrophils. Moreover, given its biological role in epithelial and immune cells, we hypothesized that MARCKS may play an integral role in cytokine secretion by neutrophils. Because the amino terminus of MARCKS is highly conserved across vertebrate species, we successfully applied the well-characterized human MARCKS inhibitory peptide, myristoylated N-terminal sequence (MANS), to attenuate the function of MARCKS in isolated canine neutrophils. Pretreatment of canine neutrophils with MANS peptide significantly reduced both mRNA and protein expression in a broad range of LPS-induced cytokines, including IL-8, a chemokine (C-X-C motif) ligand-1 orthologue, and TNF-α, in comparison with untreated cells or those treated with a control peptide. This reduction in cytokine expression was observed even when neutrophils were treated with MANS 2 hours after LPS exposure. The observed reduction in cytokine secretion was not attributable to protein retention or cell death, but was associated with reduced cytokine transcript synthesis. These observations identify MARCKS protein as a promising therapeutic target in the treatment of inflammatory diseases or syndromes attributed to neutrophil influx and inflammatory cytokine production, such as sepsis, acute lung injury, and acute respiratory distress syndrome.

Calpain and MARCKS protein regulation of airway mucin secretion

Hypersecretion of mucin plays an important role in the pathophysiology of many inflammatory airway diseases, including asthma, chronic bronchitis, and cystic fibrosis. Myristoylated alanine-rich C-kinase substrate (MARCKS) protein has been shown to play an important role in regulation of airway mucin secretion, as peptides analogous to the amino (N)-terminus of MARCKS attenuate mucin secretion by airway epithelium in vitro and in vivo. Here, we investigated a potential role for the protease Calpain, a calcium-dependent cysteine protease that can cleave MARCKS, in the MARCKS-related secretory mechanism. We theorized that Calpain might cleave MARCKS near the N-terminus, thereby attenuating the ability of MARCKS to bind to membranes and/or creating a small N-terminal peptide that could act as a competitive intracellular inhibitor to remaining endogenous full-length MARCKS molecules. Primary normal human bronchial epithelial (NHBE) cells and the virally-transformed human bronchial epithelial HBE1 cell line were exposed to phorbol-12-myristate-13-acetate (PMA) to stimulate the Protein Kinase C (PKC) pathway, leading to enhanced mucin secretion, and Calpain activity within the cells was measured with a fluorescent cleavage assay. Calpain activity was increased by PMA, and pretreatment of the cells with Calpain inhibitors reduced both Calpain activity and mucin secretion in a concentration-dependent manner. Thus, as opposed to the original hypothesis, inactivating Calpain caused a decrease rather than an increase in secretion. HBE1 cells transfected with DNA constructs encoding a MARCKS-YFP fusion protein showed cleavage at a putative site near the N-terminus in response to PMA. Cleavage of MARCKS by Calpain may have an important role in regulation of the PKC/MARCKS pathway regulating airway mucin secretion.

DHEA-S inhibits human neutrophil and human airway smooth muscle migration

Airway diseases such as asthma, emphysema, and chronic bronchitis are, in part, characterized by reversible airflow obstruction and inflammation. In severe disease, marked decreases in lung function are associated with airway smooth muscle proliferation and airway neutrophilia. Inhaled glucocorticoids attenuate increased airflow obstruction and airway inflammation that occur, in part, due to increased smooth muscle migration and proliferation, as well as the airway neutrophilia. Glucocorticoids, however, have adverse side effects and, in some patients, are ineffective despite high doses. Recent research has explored the effects of non-traditional steroids on attenuation of inflammation associated with airway diseases. These non-traditional steroids have improved side effect profiles in comparison to glucocorticoid therapy. Our studies assessed effects of dehydroepiandrosterone-3-sulfate (DHEA-S) on migration of both human peripheral blood neutrophils (PMN) and human airway smooth muscle cells (HASM). DHEA-S dose-dependently inhibited chemotaxis of PMN and HASM while having no effect on the phosphorylation levels of Akt, ERK1/2, p38 MAPK or PKC, canonical positive regulators of cell migration. These studies demonstrate direct effects of DHEA-S on cell migration, thereby suggesting that DHEA-S may attenuate airway inflammation and cell migration.

Directed migration of mouse macrophages in vitro involves myristoylated alanine-rich C-kinase substrate (MARCKS) protein

A role for MARCKS protein in directed migration of macrophages toward a chemoattractant was investigated. A peptide identical to the N-terminus of MARCKS (the MANS peptide), shown previously to inhibit the function of MARCKS in various cell types, was used. We investigated whether this MARCKS-related peptide could affect migration of macrophages, using the mouse macrophage-like J774A.1 cell line and primary murine macrophages. Both of these cell types migrated in response to the chemoattractants macrophage/MCPs, MCP-1 (25-100 ng/ml) or C5a (5-20 ng/ml). Cells were preincubated (15 min) with MANS or a mis-sense control peptide (RNS), both at 50 μM, and effects on migration determined 3 h after addition of chemoattractants. The movement and interactions of MARCKS and actin also were followed visually via confocal microscopy using a fluorescently labeled antibody to MARCKS and fluorescently tagged phalloidin to identify actin. MANS, but not RNS, attenuated migration of J774A.1 cells and primary macrophages in response to MCP-1 or C5a, implicating MARCKS in the cellular mechanism of directed migration. Exposure of cells to MCP-1 resulted in rapid phosphorylation and translocation of MARCKS from plasma membrane to cytosol, whereas actin appeared to spread through the cell and into cell protrusions; there was visual and biochemical evidence of a transient interaction between MARCKS and actin during the process of migration. These results suggest that MARCKS is involved in directed migration of macrophages via a process involving its phosphorylation, cytoplasmic translocation, and interaction with actin.

Two myristoylated alanine-rich C-kinase substrate (MARCKS) paralogs are required for normal development in zebrafish

Myristoylated alanine-rich C-kinase substrate (MARCKS) is an actin binding protein substrate of protein kinase C (PKC) and critical for mouse and Xenopus development. Herein two MARCKS paralogs, marcksa and marcksb, are identified in zebrafish and the role of these genes in zebrafish development is evaluated. Morpholino-based targeting of either MARCKS protein resulted in increased mortality and a range of gross phenotypic abnormalities. Phenotypic abnormalities were classified as mild, moderate or severe, which is characterized by a slight curve of a full-length tail, a severe curve or twist of a full-length tail and a truncated tail, respectively. All three phenotypes displayed abnormal neural architecture. Histopathology of Marcks targeted embryos revealed abnormalities in retinal layering, gill formation and skeletal muscle morphology. These results demonstrate that Marcksa and Marcksb are required for normal zebrafish development and suggest that zebrafish are a suitable model to further study MARCKS function.

Opisthorchis viverrini-antigen induces expression of MARCKS during inflammation-associated cholangiocarcinogenesis

Myristoylated alanine rich C kinase substrate (MARCKS) has been implicated in PKC-mediated membrane-cytoskeleton alterations that underlie lipopolysaccharide (LPS)-induced macrophage responses. MARCKS is postulated to be involved in inflammation-associated CCA based on its overexpression in cholangiocarcinoma (CCA) and inflammatory cells. The aims of this study were to investigate localization patterns of MARCKS in hamster and human tissue during cholangiocarcinogenesis and to examine the involvement of MARCKS in inflammation. MARCKS protein expression was found prominently in inflammatory cells of Opisthorchis viverrini-treated as well as O. viverrini plus N-nitrosodimethylamine (NDMA)-treated hamsters from week 2 to week 3 of treatment. The positive signal decreased during week 4 to week 12, then increased again at week 26 when CCA developed. At the last time point the expression of MARCKS was observed in both cancer and inflammatory cells. MARCKS protein expression was also found in inflammatory cells, including macrophages in human CCA tissues. O. viverrini excretory/secretory products or worm antigen induced MARCKS mRNA and protein expression in a dose- and time-dependent manner in the human U937 macrophage cell line. The relative mRNA expression of MARCKS in white blood cells of O. viverrini-infected patients was significantly higher than in healthy subjects (P = 0.02). Thus, MARCKS is significantly expressed in macrophages and plays a role in inflammation-related CCA induced by O. viverrini.

Regulation of mucin secretion and inflammation in asthma: a role for MARCKS protein?

BACKGROUND

A major characteristic of asthmatic airways is an increase in mucin (the glycoprotein component of mucus) producing and secreting cells, which leads to increased mucin release that further clogs constricted airways and contributes markedly to airway obstruction and, in the most severe cases, to status asthmaticus. Asthmatic airways show both a hyperplasia and metaplasia of goblet cells, mucin-producing cells in the epithelium; hyperplasia refers to enhanced numbers of goblet cells in larger airways, while metaplasia refers to the appearance of these cells in smaller airways where they normally are not seen. With the number of mucin-producing and secreting cells increased, there is a coincident hypersecretion of mucin which characterizes asthma. On a cellular level, a major regulator of airway mucin secretion in both in vitro and in vivo studies has been shown to be MARCKS (myristoylated alanine-rich C kinase substrate) protein, a ubiquitous substrate of protein kinase C (PKC).

GENERAL SIGNIFICANCE

In this review, properties of MARCKS and how the protein may regulate mucin secretion at a cellular level will be discussed. In addition, the roles of MARCKS in airway inflammation related to both influx of inflammatory cells into the lung and release of granules containing inflammatory mediators by these cells will be explored. This article is part of a Special Issue entitled: Biochemistry of Asthma.

MARCKS-related peptide modulates in vivo the secretion of airway Muc5ac

In a mouse model of neutrophil elastase-induced bronchitis that exhibits goblet cell metaplasia and inflammation, we investigated the effects of intratracheal instillation of the MANS peptide, a peptide identical to the NH(2) terminus of the myristoylated alanine-rich C kinase substrate (MARCKS) on mucin protein airway secretion, inflammation, and airway reactivity. To induce mucus cell metaplasia in the airways, male BALB/c mice were treated repetitively with the serine protease, neutrophil elastase, on days 1, 4, and 7. On day 11, when goblet cell metaplasia was fully developed and profiles of proinflammatory cytokines were maximal, the animals were exposed to aerosolized methacholine after intratracheal instillation of MANS or a missense control peptide (RNS). MANS, but not RNS, attenuated the methacholine-stimulated secretion of the major respiratory mucin protein, Muc5ac (50% reduction). Concurrently, elastase-induced proinflammatory cytokines typically recovered in bronchoalveolar lavage (BAL), including KC, IL-1beta, IL-6, MCP-1, and TNFalpha, were reduced by the MANS peptide (mean levels decreased 50-60%). Secondary to the effects of MANS on mucin secretion and inflammation, mechanical lung function by forced oscillation technique was characterized with respect to airway reactivity in response to cumulative aerosol stimulation with serotonin. The MANS peptide was also found to effectively attenuate airway hyperresponsiveness to serotonin in this airway hypersecretory model. Collectively, these findings support the concept that even in airway epithelia remodeled with goblet cell metaplasia and in a state of mucin hypersecretion, exogenous attenuation of function of MARCKS protein via the MANS peptide decreases airway mucin secretion, inflammation, and hyperreactivity.