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

Multisolitons-like patterns in a one-dimensional MARCKS protein cyclic model

In this paper, we study the nonlinear dynamics of the MARCKS protein between cytosol and cytoplasmic membrane through the modulational instability phenomenon. The reaction-diffusion generic model used here is firstly transformed into a cubic complex Ginzburg-Landau equation. Then, modulational instability (MI) is carried out in order to derive the MI criteria. We find the domains of some parameter space where nonlinear patterns are expected in the model. The analytical results on the MI growth rate predict that phosphorylation and binding rates affect MARCKS dynamics in opposite way: while the phosphorylation rate tends to support highly localized structures of MARCKS, the binding rate in turn tends to slow down such features. On the other hand, self-diffusion process always amplifies the MI phenomenon. These predictions are confirmed by numerical simulations. As a result, the cyclic transport of MARCKS protein from membrane to cytosol may be done by means of multisolitons-like patterns.

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.

PKCδ regulates the vascular biology in diabetic atherosclerosis

Diabetes mellitus, known for its complications, especially vascular complications, is becoming a globally serious social problem. Atherosclerosis has been recognized as a common vascular complication mechanism in diabetes. The diacylglycerol (DAG)-protein kinase C (PKC) pathway plays an important role in atherosclerosis. PKCs can be divided into three subgroups: conventional PKCs (cPKCs), novel PKCs (nPKCs), and atypical PKCs (aPKCs). The aim of this review is to provide a comprehensive overview of the role of the PKCδ pathway, an isoform of nPKC, in regulating the function of endothelial cells, vascular smooth muscle cells, and macrophages in diabetic atherosclerosis. In addition, potential therapeutic targets regarding the PKCδ pathway are summarized. Video Abstract.

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.

Phenotypic Variability in PRKCD: a Review of the Literature

PURPOSE

Protein kinase C δ (PKCδ) deficiency is a rare genetic disorder identified as a monogenic cause of systemic lupus erythematosus in 2013. Since the first cases were described, the phenotype has expanded to include children presenting with autoimmune lymphoproliferative syndrome-related syndromes and infection susceptibility similar to chronic granulomatous disease or combined immunodeficiency. We review the current published data regarding the pathophysiology, clinical presentation, investigation and management of PKCδ deficiency.

METHODS

Literature review was performed using MEDLINE.

RESULTS

Twenty cases have been described in the literature with significant heterogeneity.

CONCLUSION

The variation in clinical presentation delineates the broad and critical role of PKCδ in immune tolerance and effector functions against pathogens.

TFEB: a double-edged sword for tumor metastasis

Transcription factor EB, a member of the microphthalmia-associated transcription factor (MiTF/TFE) family, is a master regulator of autophagy, lysosome biogenesis, and TAMs. Metastasis is one of the main reasons for the failure of tumor therapy. Studies on the relationship between TFEB and tumor metastasis are contradictory. On the positive side, TFEB mainly affects tumor cell metastasis via five aspects, including autophagy, epithelial-mesenchymal transition (EMT), lysosomal biogenesis, lipid metabolism, and oncogenic signaling pathways; on the negative side, TFEB mainly affects tumor cell metastasis in two aspects, including tumor-associated macrophages (TAMs) and EMT. In this review, we described the detailed mechanism of TFEB-mediated regulation of metastasis. In addition, we also described the activation and inactivation of TFEB in several aspects, including the mTORC1 and Rag GTPase systems, ERK2, and AKT. However, the exact process by which TFEB regulates tumor metastasis remains unclear in some pathways, which requires further studies.

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.

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.

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.

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.

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.

Pro-Resolving FPR2 Agonists Regulate NADPH Oxidase-Dependent Phosphorylation of HSP27, OSR1, and MARCKS and Activation of the Respective Upstream Kinases

Background: Formyl peptide receptor 2 (FPR2) is involved in the pathogenesis of chronic inflammatory diseases, being activated either by pro-resolving or proinflammatory ligands. FPR2-associated signal transduction pathways result in phosphorylation of several proteins and in NADPH oxidase activation. We, herein, investigated molecular mechanisms underlying phosphorylation of heat shock protein 27 (HSP27), oxidative stress responsive kinase 1 (OSR1), and myristolated alanine-rich C-kinase substrate (MARCKS) elicited by the pro-resolving FPR2 agonists WKYMVm and annexin A1 (ANXA1). Methods: CaLu-6 cells or p22phox^Crispr/Cas9 double nickase CaLu-6 cells were incubated for 5 min with WKYMVm or ANXA1, in the presence or absence of NADPH oxidase inhibitors. Phosphorylation at specific serine residues of HSP27, OSR1, and MARCKS, as well as the respective upstream kinases activated by FPR2 stimulation was analysed. Results: Blockade of NADPH oxidase functions prevents WKYMVm- and ANXA1-induced HSP-27(Ser82), OSR1(Ser339) and MARCKS(Ser170) phosphorylation. Moreover, NADPH oxidase inhibitors prevent WKYMVm- and ANXA1-dependent activation of p38MAPK, PI3K and PKCδ, the kinases upstream to HSP-27, OSR1 and MARCKS, respectively. The same results were obtained in p22phox^Crispr/Cas9 cells. Conclusions: FPR2 shows an immunomodulatory role by regulating proinflammatory and anti-inflammatory activities and NADPH oxidase is a key regulator of inflammatory pathways. The activation of NADPH oxidase-dependent pro-resolving downstream signals suggests that FPR2 signalling and NADPH oxidase could represent novel targets for inflammation therapeutic intervention.

Triclosan-induced liver and brain injury in zebrafish (Danio rerio) via abnormal expression of miR-125 regulated by PKCα/Nrf2/p53 signaling pathways

Triclosan (TCS) is widely used in personal care products, and its chronic exposure leads to severely toxic effects in zebrafish (Danio rerio). PKCα, Nrf2 and p53 are three important signaling pathways concerned with cell development. Herein, we speculated on and verified a novel TCS regulatory pathway: (1) TCS acted on GPER (G-protein-coupled estrogen receptor) to activate MAPK/ERK pathway, further resulting in the expression changes of protein kinase C (PKC) family; (2) PKC participated in Nrf2 phosphorylation; (3) The expression of miR-125b was regulated by Nrf2; and (4) The expression changes of related genes in the PKCs-Nrf2-ARE pathway showed the specificity of zebrafish tissue and organ. TCS exposure led to down-regulation of the Nrf2 and phosphorylated Nrf2(Ser40) protein in diencephalon nucleus, stratum marginale and stratum centrale areas in adult zebrafish brain. The phosphorylated Nrf2(Ser40) was mainly expressed in PGz area, while it was not the case for Nrf2. Both Nrf2 and phosphorylated Nrf2 were activated by TCS exposure; however, the changing trend of PKCs was opposite to that of Nrf2 in the liver. Both DAPI staining and Merge images demonstrated that TCS induced oxidative phosphorylation, and phosphorylated Nrf2 is translocated into the nucleus as the transcription factor to regulate gene transcription in liver and brain. Nrf2 over-expression increased accumulation of lipid droplets in yolk, brain and liver, resulting from the upregulation of pri-miR-125b1, pri-miR-125b3, but not pri-miR-125b2. These findings reveal the upstream regulation mechanism of miR-125b for TCS-induced fat-metabolism disorder from the regulatory perspective of the pri-miR-125b promoter region.

MARCKSL1 promotes the proliferation, migration and invasion of lung adenocarcinoma cells

Lung cancer is the most common cancer in males and females and ~40% of lung cancer cases are adenocarcinomas. Previous studies have demonstrated that myristoylated alanine rich protein kinase C substrate (MARCKS) is upregulated in several types of cancer and is associated with poor prognosis in patients with breast cancer. However, its expression level and role in lung adenocarcinoma remain unknown. Therefore, the aim of the present study was to investigate the expression level and biological functions of MARCKS like 1 (MARCKSL1), a member of the MARCKS family, in lung adenocarcinoma. The expression level of MARCKSL1 was examined in human lung adenocarcinoma tissues and cell lines. MARCKSL1-specific small interfering RNAs effectively suppressed its expression level and significantly inhibited the proliferation, migration and invasion of lung adenocarcinoma cells. Additionally, the role of MARCKSLI in the regulation of metastasis was examined. Silencing MARCKSL1 decreased the expression of the epithelial-mesenchymal transition (EMT)-associated proteins E-cadherin, N-cadherin, vimentin and snail family transcriptional repressor 2, and decreased the phosphorylation level of AKT. The results obtained in the current study suggested that MARCKSL1 promoted the progression of lung adenocarcinoma by regulating EMT. MARCKSLI may have prognostic value and serve as a novel therapeutic target in lung adenocarcinoma.

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.

Pulmonary fibroblasts-secreted CXCL10 polarizes alveolar macrophages under pro-inflammatory stimuli

BACKGROUND

During acute lung injury, lung fibroblasts produce chemokines that assist the activation and migration of resident macrophages. The interactions between pulmonary fibroblasts and alveolar macrophages demonstrate the early event in the recruitment of immune cells, and the production of chemokines appear to be central mediators of the initiation and progression of inflammatory responses. In this study, the aim was to investigate the signaling pathway leading to CXCL10 secretion and the effects of CXCL10 released by activated fibroblasts on regulating macrophage polarization in a pro-inflammatory microenvironment.

METHODS

The expression of chemokines CCL2, CCL5, CXCL10, and CXCL12, and the phosphorylation of signaling molecules STAT3, FAK, GSK3αβ and PKCδ were investigated by real time-PCR, ELISA, or Western blot on TNFα- or IL-1β-activated MRC-5 pulmonary fibroblasts. By collecting conditioned medium from TNFα-activated fibroblasts, the expression of iNOS and arginase I on MH-S alveolar macrophages were examined by real-time PCR. Surface markers CD86 and CD206 expressions on alveolar macrophages were also evaluated by flow cytometry.

RESULTS

We found that CXCL10 production was significantly elevated on MRC-5 fibroblasts under TNFα- or IL-1β treatment. In addition, we revealed that TNFα and IL-1β initiated phosphorylation of STAT3, FAK, GSK3αβ and PKCδ signaling cascade, leading to the elevation of CXCL10 expression. Moreover, conditioned medium collected from TNFα-activated MRC-5 fibroblasts increased iNOS and CD86 expressions and decreased arginase I and CD206 expressions on MH-S alveolar macrophages, and neutralization of CXCL10 abolished these observed phenomena.

CONCLUSION

These results suggest that CXCL10 is crucial in activated fibroblasts-promoted M1 phenotype polarization of alveolar macrophages. In this regard, targeting fibroblasts-released CXCL10 may be promising as anti-inflammatory therapy against acute lung injury.

PKCα promotes insulin secretion via TRPC1 phosphorylation in INS-1E cells

Protein kinase C (PKC) is a class of phospholipid-dependent serine/threonine kinases that contribute to cell survival, migration, and invasion. Previous studies demonstrated that PKC participates in insulin secretion. However, the role of PKC in glucose-stimulated insulin secretion (GSIS) remains unclear. Herein, we demonstrated that PKC is an important mediator of insulin secretion and revealed a close relationship between PKC activation and insulin secretion in INS-1E cells. Meanwhile, the presence of PKCα was found to induce TRPC1 phosphorylation in INS-1E cells. TRPC1 phosphorylation levels increased by activating PKCα activity. Inhibition of PKCα activity reduced TRPC1 phosphorylation. Finally, we showed that TRPC1 could reverse the decrease in intracellular Ca²⁺ levels and reduced insulin secretion induced by treatment with PKCα inhibitor under high glucose conditions. In conclusion, our findings indicated that TRPC1 and PKCα are involved in promoting insulin secretion and that PKCα promotes insulin secretion via TRPC1 phosphorylation in INS-1E cells.

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.

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.

HIF and HOIL-1L-mediated PKCζ degradation stabilizes plasma membrane Na,K-ATPase to protect against hypoxia-induced lung injury

Organisms have evolved adaptive mechanisms in response to stress for cellular survival. During acute hypoxic stress, cells down-regulate energy-consuming enzymes such as Na,K-ATPase. Within minutes of alveolar epithelial cell (AEC) exposure to hypoxia, protein kinase C zeta (PKCζ) phosphorylates the α₁-Na,K-ATPase subunit and triggers it for endocytosis, independently of the hypoxia-inducible factor (HIF). However, the Na,K-ATPase activity is essential for cell homeostasis. HIF induces the heme-oxidized IRP2 ubiquitin ligase 1L (HOIL-1L), which leads to PKCζ degradation. Here we report a mechanism of prosurvival adaptation of AECs to prolonged hypoxia where PKCζ degradation allows plasma membrane Na,K-ATPase stabilization at ∼50% of normoxic levels, preventing its excessive down-regulation and cell death. Mice lacking HOIL-1L in lung epithelial cells (Cre^SPC/HOIL-1L^fl/fl ) were sensitized to hypoxia because they express higher levels of PKCζ and, consequently, lower plasma membrane Na,K-ATPase levels, which increased cell death and worsened lung injury. In AECs, expression of an α₁-Na,K-ATPase construct bearing an S18A (α₁-S18A) mutation, which precludes PKCζ phosphorylation, stabilized the Na,K-ATPase at the plasma membrane and prevented hypoxia-induced cell death even in the absence of HOIL-1L. Adenoviral overexpression of the α₁-S18A mutant Na,K-ATPase in vivo rescued the enhanced sensitivity of Cre^SPC/HOIL-1L^fl/fl mice to hypoxic lung injury. These data suggest that stabilization of Na,K-ATPase during severe hypoxia is a HIF-dependent process involving PKCζ degradation. Accordingly, we provide evidence of an important adaptive mechanism to severe hypoxia, whereby halting the exaggerated down-regulation of plasma membrane Na,K-ATPase prevents cell death and lung injury.

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.

FGFs: crucial factors that regulate tumour initiation and progression

Fibroblast growth factors (FGFs) are crucial signalling molecules involved in normal cell growth, differentiation and proliferation. Over the past few decades, a large body of research has illustrated effects of individual FGFs on tumour initiation and progression. Tumour development is commonly accompanied with generation of new blood and lymph vessels, which support enhanced cell proliferation. Moreover, acquisition of tumour cells of the epithelial-mesenchymal transition (EMT) phenotype, enhances tumour cell migration and invasion potentials, crucial steps in tumour metastasis. This review summarizes recent findings concerning roles of FGFs in angiogenesis, lymphangiogenesis and EMT.

Early-life serotonin dysregulation affects the migration and positioning of cortical interneuron subtypes

Early-life deficiency of the serotonin transporter (SERT) gives rise to a wide range of psychiatric-relevant phenotypes; however, the molecular and cellular targets of serotonin dyregulation during neural circuit formation remain to be identified. Interestingly, migrating cortical interneurons (INs) derived from the caudal ganglionic eminence (CGE) have been shown to be more responsive to serotonin-mediated signalling compared with INs derived from the medial ganglionic eminence (MGE). Here we investigated the impact of early-life SERT deficiency on the migration and positioning of CGE-derived cortical INs in SERT-ko mice and in mice exposed to the SERT inhibitor fluoxetine during the late embryonic period. Using confocal time-lapse imaging and microarray-based expression analysis we found that genetic and pharmacological SERT deficiency significantly increased the migratory speed of CGE-derived INs and affected transcriptional programmes regulating neuronal migration. Postnatal studies revealed that SERT deficiency altered the cortical laminar distribution of subtypes of CGE-derived INs but not MGE-derived INs. More specifically, we found that the distribution of vasointestinal peptide (VIP)-expressing INs in layer 2/3 was abnormal in both genetic and pharmacological SERT-deficiency models. Collectively, these data indicate that early-life SERT deficiency has an impact on the migration and molecular programmes of CGE-derived INs, thus leading to specific alterations in the positioning of VIP-expressing INs. These data add to the growing evidence that early-life serotonin dysregulation affects cortical microcircuit formation and contributes to the emergence of psychiatric-relevant phenotypes.