Targeting of the Akt/PKB kinase to the actin skeleton

Exploring putative drug properties associated with TNF-alpha inhibition and identification of potential targets in cardiovascular disease using machine learning-assisted QSAR modeling and virtual reverse pharmacology approach

Cardiovascular disease is a chronic inflammatory disease with high mortality rates. TNF-alpha is pro-inflammatory and associated with the disease, but current medications have adverse effects. Therefore, efficient inhibitors are urgently needed as alternatives. This study represents a structural-activity relationship investigation of TNF-alpha, curated from the ChEMBL database. Exploratory data analysis was performed to visualize the physicochemical properties of different bioactivity groups. The extracted molecules were subjected to PubChem and SubStructure fingerprints, and a QSAR-based Random Forest (QSAR-RF) model was generated using the WEKA tool. The QSAR random Forest model was built based on the SubStructure fingerprint with a correlation coefficient of 0.992 and 0.716 as the respective tenfold cross-validation scores. The variance important plot (VIP) method was used to extract the important features for TNF-alpha inhibition. The Substructure-based QSAR-RF (SS-QSAR-RF) model was validated using molecules from PubChem and ZINC databases. The generated model also predicts the pIC50 value of the molecules selected from the docking study followed by molecular dynamic simulation with the time step of 100 ns. Through virtual reverse pharmacology, we determined the main drug targets from the top four hit compounds obtained via molecular docking study. Our analysis included an integrated bioinformatics approach to pinpoint crucial targets like EGRF, HSP900A1, STAT3, PSEN1, AKT1, and MDM2. Further, GO and KEGG pathways analysis identified relevant cardiovascular disease-related pathways for the hub gene involved. However, this study provides valuable insights, it is important to note that it lacks experimental application. Future research may benefit from conducting in-vitro and in-vivo studies.

Role of Akt/Protein Kinase B in Cancer Metastasis

Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer-related mortalities result from metastatic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms, i.e., cytoskeletal remodelling and epithelial to mesenchymal transition (EMT). Akt (also known as protein kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant activation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in metastatic cancers.

Repair of traumatic lesions to the plasmalemma of neurons and other cells: Commonalities, conflicts, and controversies

Neuroscientists and Cell Biologists have known for many decades that eukaryotic cells, including neurons, are surrounded by a plasmalemma/axolemma consisting of a phospholipid bilayer that regulates trans-membrane diffusion of ions (including calcium) and other substances. Cells often incur plasmalemmal damage via traumatic injury and various diseases. If the damaged plasmalemma is not rapidly repaired within minutes, activation of apoptotic pathways by calcium influx often results in cell death. We review publications reporting what is less-well known (and not yet covered in neuroscience or cell biology textbooks): that calcium influx at the lesion sites ranging from small nm-sized holes to complete axonal transection activates parallel biochemical pathways that induce vesicles/membrane-bound structures to migrate and interact to restore original barrier properties and eventual reestablishment of the plasmalemma. We assess the reliability of, and problems with, various measures (e.g., membrane voltage, input resistance, current flow, tracer dyes, confocal microscopy, transmission and scanning electron microscopy) used individually and in combination to assess plasmalemmal sealing in various cell types (e.g., invertebrate giant axons, oocytes, hippocampal and other mammalian neurons). We identify controversies such as plug versus patch hypotheses that attempt to account for currently available data on the subcellular mechanisms of plasmalemmal repair/sealing. We describe current research gaps and potential future developments, such as much more extensive correlations of biochemical/biophysical measures with sub-cellular micromorphology. We compare and contrast naturally occurring sealing with recently-discovered artificially-induced plasmalemmal sealing by polyethylene glycol (PEG) that bypasses all natural pathways for membrane repair. We assess other recent developments such as adaptive membrane responses in neighboring cells following injury to an adjacent cell. Finally, we speculate how a better understanding of the mechanisms involved in natural and artificial plasmalemmal sealing is needed to develop better clinical treatments for muscular dystrophies, stroke and other ischemic conditions, and various cancers.

SARS-CoV-2 replication in airway epithelia requires motile cilia and microvillar reprogramming

How SARS-CoV-2 penetrates the airway barrier of mucus and periciliary mucins to infect nasal epithelium remains unclear. Using primary nasal epithelial organoid cultures, we found that the virus attaches to motile cilia via the ACE2 receptor. SARS-CoV-2 traverses the mucus layer, using motile cilia as tracks to access the cell body. Depleting cilia blocks infection for SARS-CoV-2 and other respiratory viruses. SARS-CoV-2 progeny attach to airway microvilli 24 h post-infection and trigger formation of apically extended and highly branched microvilli that organize viral egress from the microvilli back into the mucus layer, supporting a model of virus dispersion throughout airway tissue via mucociliary transport. Phosphoproteomics and kinase inhibition reveal that microvillar remodeling is regulated by p21-activated kinases (PAK). Importantly, Omicron variants bind with higher affinity to motile cilia and show accelerated viral entry. Our work suggests that motile cilia, microvilli, and mucociliary-dependent mucus flow are critical for efficient virus replication in nasal epithelia.

Cardiovascular protection associated with cilostazol, colchicine and target of rapamycin inhibitors

ABSTRACT

An alteration in extracellular matrix production by vascular smooth muscle cells is a crucial event in the pathogenesis of vascular diseases such as aging-related, atherosclerosis and allograft vasculopathy. The human target of rapamycin (TOR) is involved in the synthesis of extracellular matrix by vascular smooth muscle cells. TOR inhibitors reduce arterial stiffness, blood pressure, and left ventricle hypertrophy and decrease cardiovascular risk in kidney graft recipients and patients with coronary artery disease and heart allograft vasculopathy. Other drugs that modulate extracellular matrix production such as cilostazol and colchicine have also demonstrated a beneficial cardiovascular effect. Clinical studies have consistently shown that cilostazol confers cardiovascular protection in peripheral vascular disease, coronary artery disease, and cerebrovascular disease. In patients with type 2 diabetes, cilostazol prevents the progression of subclinical coronary atherosclerosis. Colchicine reduces arterial stiffness in patients with Familial Mediterranean Fever and patients with coronary artery disease. Pathophysiological mechanisms underlying the cardioprotective effect of these drugs may be related to interactions between the cytoskeleton, TOR signaling and cyclic AMP synthesis that remain to be fully elucidated. Adult vascular smooth muscle cells exhibit a contractile phenotype and produce little extracellular matrix. Conditions that upregulate extracellular matrix synthesis induce a phenotypic switch toward a synthetic phenotype. TOR inhibition with rapamycin reduces extracellular matrix production by promoting the change to the contractile phenotype. Cilostazol increases the cytosolic level of cyclic AMP, which in turn leads to a reduction in extracellular matrix synthesis. Colchicine is a microtubule-destabilizing agent that may enhance the synthesis of cyclic AMP.

Down-regulation of kappa opioid receptor promotes ESCC proliferation, invasion and metastasis via the PDK1-AKT signaling pathway

BACKGROUND

As a class of the opioid receptors, the kappa opioid receptor (KOR) has been verified to be a potential biomarker and therapeutic target for human malignant tumors. However, a thorough understanding of whether KOR affects progression of esophageal squamous cell carcinoma (ESCC) is still lacking. This study focused on exploring the effect of knocking down KOR in ESCC and its underlying mechanism.

METHODS

Bioinformatics analysis was used to compare the different expression level of OPRK1 (KOR gene) in tumor and adjacent normal tissues, and predict the relationship between KOR expression and overall survival. RNA-sequence analysis was performed to detect the altered functions and mechanisms after down regulating KOR. The in vitro and in vivo assays were used to detect the effects of down-regulated KOR on cell proliferation, migration and invasion. Substrate gel zymography and 3D cell culture assays were used to find the effect of KOR knockdown on the degradation of extracellular matrix (ECM), and immunefluorescence was performed to detect the altered cytoskeleton. Western blotting and immunohistochemistry were used to explore the underlying mechanism pathway.

RESULTS

Bioinformatics analysis revealed that the expression of OPRK1 was lower in tumor tissue than that in adjacent normal tissues, and lowered expression of KOR was associated with poorer overall survival. The in vitro assays demonstrated that down-regulation of KOR enhanced ESCC proliferation, metastasis and invasion. Western blotting revealed that down-regulation of KOR could activate PDK1-AKT signaling pathway, which actively regulated the cancer progression. Down-regulation of KOR enhanced the formation of invadopodia, secretion of matrix metalloproteinase-2 (MMP2) and rearrangement of cytoskeleton, which were positively related with the invasion of ESCC. KOR knockdown enhanced the tumor invasion and elevated the AKT phosphorylation in nude mice. The AKT kinase inhibition could reverse the effect of down-regulation of KOR.

CONCLUSION

KOR might act as a tumor suppressor in ESCC and down-regulation of KOR could enhance the ESCC tumor phenotype. Video Abstract.

The effects of glucagon and the target of rapamycin (TOR) on skeletal muscle protein synthesis and age-dependent sarcopenia in humans

BACKGROUND AND AIMS

Human target of rapamycin (TOR) is a kinase that stimulates protein synthesis in the skeletal muscle in response to amino acids and physical activity.

METHODS

A comprehensive literature search was conducted on the PubMed database from its inception up to May 2021 to retrieve information on the effects of TOR and glucagon on muscle function. Articles written in English regarding human subjects were included.

RESULTS

l-leucine activates TOR to initiate protein synthesis in the skeletal muscle. Glucagon has a crucial role suppressing skeletal muscle protein synthesis by increasing l-leucine oxidation and the irreversible loss of this amino acid. Glucagon-induced l-leucine oxidation suppresses TOR and attenuates the ability of skeletal muscle to synthesize proteins. Conditions associated with increased glucagon secretion typically feature reduced ability to synthesize proteins in the skeletal muscle that may evolve into sarcopenia. Animal protein ingestion, unlike vegetable protein, stimulates glucagon secretion. High intake of animal protein increases l-leucine oxidation and promotes the use of amino acids as fuel. Sarcopenia and arterial stiffness characteristically occur together in conditions featuring insulin resistance, such as aging. Insulin resistance mediates the relationship between aging and sarcopenia and arterial stiffness. The loss of skeletal muscle fibers that characterizes sarcopenia is followed by collagen and lipid accumulation. Likewise, insulin resistance is associated with arterial stiffness and intima-media thickening due to adaptive accretion of collagen and lipids in the arterial wall.

CONCLUSIONS

Human TOR participates in the pathogenesis of sarcopenia and arterial stiffness, although its effects remain to be fully elucidated.

MYO1F Regulates IgE and MRGPRX2-Dependent Mast Cell Exocytosis

The activation and degranulation of mast cells is critical in the pathogenesis of allergic inflammation and modulation of inflammation. Recently, we demonstrated that the unconventional long-tailed myosin, MYO1F, localizes with cortical F-actin and mediates adhesion and migration of mast cells. In this study, we show that knockdown of MYO1F by short hairpin RNA reduces human mast cell degranulation induced by both IgE crosslinking and by stimulation of the Mas-related G protein-coupled receptor X2 (MRGPRX2), which has been associated with allergic and pseudoallergic drug reactions, respectively. Defective degranulation was accompanied by a reduced reassembly of the cortical actin ring after activation but reversed by inhibition of actin polymerization. Our data show that MYO1F is required for full Cdc42 GTPase activation, a critical step in exocytosis. Furthermore, MYO1F knockdown resulted in less granule localization in the cell membrane and fewer fissioned mitochondria along with deficient mitochondria translocation to exocytic sites. Consistent with that, AKT and DRP1 phosphorylation are diminished in MYO1F knockdown cells. Altogether, our data point to MYO1F as an important regulator of mast cell degranulation by contributing to the dynamics of the cortical actin ring and the distribution of both the secretory granules and mitochondria.

Early pathological signs in young dysf-/- mice are improved by halofuginone

Dysferlinopathies are a non-lethal group of late-onset muscular dystrophies. Here, we evaluated the fusion ability of primary myoblasts from young dysf^-/- mice and the muscle histopathology prior to, and during early stages of disease onset. The ability of primary myoblasts of 5-week-old dysf^-/- mice to form large myotubes was delayed compared to their wild-type counterparts, as evaluated by scanning electron microscopy. However, their fusion activity, as reflected by the presence of actin filaments connecting several cells, was enhanced by the antifibrotic drug halofuginone. Early dystrophic signs were already apparent in 4-week-old dysf^-/- mice; their collagen level was double that in wild-type mice and continued to rise until 5 months of age. Continuous treatment with halofuginone from 4 weeks to 5 months of age reduced muscle fibrosis in a phosphorylated-Smad3 inhibition-related manner. Halofuginone also enhanced myofiber hypertrophy, reduced the percentage of centrally nucleated myofibers, and increased muscle performance. Together, the data suggest an inhibitory effect of halofuginone on the muscle histopathology at very early stages of dysferlinopathy, and enhancement of muscle performance. These results offer new opportunities for early pharmaceutical treatment in dysferlinopathies with favorable outcomes at later stages of life.

The dynamics and regulation of microfilament during spermatogenesis

Spermatogenesis is a highly complex physiological process which contains spermatogonia proliferation, spermatocyte meiosis and spermatid morphogenesis. In the past decade, actin binding proteins and signaling pathways which are critical for regulating the actin cytoskeleton in testis had been found. In this review, we summarized 5 actin-binding proteins that have been proven to play important roles in the seminiferous epithelium. Lack of them perturbs spermatids polarity and the transport of spermatids. The loss of Arp2/3 complex, Formin1, Eps8, Palladin and Plastin3 cause sperm release failure suggesting their irreplaceable role in spermatogenesis. Actin regulation relies on multiple signal pathways. The PI3K/Akt signaling pathway positively regulate the mTOR pathway to promote actin reorganization in seminiferous epithelium. Conversely, TSC1/TSC2 complex, the upstream of mTOR, is activated by the LKB1/AMPK pathway to inhibit cell proliferation, differentiation and migration. The increasing researches focus on the function of actin binding proteins (ABPs), however, their collaborative regulation of actin patterns and potential regulatory signaling networks remains unclear. We reviewed ABPs that play important roles in mammalian spermatogenesis and signal pathways involved in the regulation of microfilaments. We suggest that more relevant studies should be performed in the future.

Metabolic syndrome diminishes insulin-induced Akt activation and causes a redistribution of Akt-interacting proteins in cardiomyocytes

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors, with insulin resistance as a critical component for its development. Insulin signaling in the heart leads to Akt (also known as PKB) activation, a serine/threonine protein kinase, which regulates cardiac glucose metabolism and growth. Cardiac metabolic inflexibility, characterized by impaired insulin-induced glucose uptake and oxidation, has been reported as an early and consistent change in the heart of different models of MetS and diabetes; however, the evaluation of Akt activation has yielded variable results. Here we report in cardiomyocytes of MetS rats, diminished insulin-induced glucose uptake and Akt activation, evaluated by its impaired mobilization towards the plasma membrane and phosphorylation, and reflected in a re-distribution of its interacting proteins, assessed by label-free mass spectrometry (data are available via ProteomeXchange with identifier PXD013260). We report 45 proteins with diminished abundance in Akt complex of MetS cardiomyocytes, mainly represented by energy metabolism-related proteins, and also, 31 Akt-interacting proteins with increased abundance, which were mainly related to contraction, endoplasmic reticulum stress, and Akt negative regulation. These results emphasize the relevance of Akt in the regulation of energy metabolism in the heart and highlight Akt-interacting proteins that could be involved in the detrimental effects of MetS in the heart.

Metabolic Health, Insulin, and Breast Cancer: Why Oncologists Should Care About Insulin

Studies investigating the potential link between adult pre-menopausal obesity [as measured by body mass index (BMI)] and triple-negative breast cancer have been inconsistent. Recent studies show that BMI is not an exact measure of metabolic health; individuals can be obese (BMI > 30 kg/m²) and metabolically healthy or lean (BMI < 25 kg/m²) and metabolically unhealthy. Consequently, there is a need to better understand the molecular signaling pathways that might be activated in individuals that are metabolically unhealthy and how these signaling pathways may drive biologically aggressive breast cancer. One key driver of both type-2 diabetes and cancer is insulin. Insulin is a potent hormone that activates many pathways that drive aggressive breast cancer biology. Here, we review (1) the controversial relationship between obesity and breast cancer, (2) the impact of insulin on organs, subcellular components, and cancer processes, (3) the potential link between insulin-signaling and cancer, and (4) consider time points during breast cancer prevention and treatment where insulin-signaling could be better controlled, with the ultimate goal of improving overall health, optimizing breast cancer prevention, and improving breast cancer survival.

AKT/protein kinase B associates with β-actin in the nucleus of melanoma cells

The serine-threonine kinase AKT/PKB is a critical regulator of various essential cellular processes, and dysregulation of AKT has been implicated in many diseases, including cancer. Despite AKT action is known to function mainly in the cytoplasm, AKT has been reported to translocate to the nucleus. However, very little is known about the mechanism required for the nuclear import of AKT as well as its function in this cellular compartment. In the present study, we characterized the presence of endogenous nuclear AKT in human melanoma cells and addressed the possible role of AKT by exploring its potential association with key interaction nuclear partners. Confocal and Western blot analyses showed that both phosphorylated and non-phosphorylated forms of AKT are present in melanoma cells nuclei. Using mass spectrometry in combination with protein-crosslinking and co-immunoprecipitation, we identified a series of putative protein partners of nuclear AKT, including heterogeneous nuclear ribonucleoprotein (hnRNP), cytoskeleton proteins β-actin, γ-actin, β-actin-like 2 and vimentin. Confocal microscopy and biochemical analyses validated β-actin as a new nuclear AKT-interacting partner. Cofilin and active RNA Polymerase II, two proteins that have been described to interact and work in concert with nuclear actin in transcription regulation, were also found associated with nuclear AKT. Overall, the present study uncovered a yet unrecognized nuclear coupling of AKT and provides insights into the involvement of AKT in the interaction network of nuclear actin.

The Drosophila insulin pathway controls Profilin expression and dynamic actin-rich protrusions during collective cell migration

Understanding how different cell types acquire their motile behaviour is central to many normal and pathological processes. Drosophila border cells represent a powerful model for addressing this issue and to specifically decipher the mechanisms controlling collective cell migration. Here, we identify the Drosophila Insulin/Insulin-like growth factor signalling (IIS) pathway as a key regulator in controlling actin dynamics in border cells, independently of its function in growth control. Loss of IIS activity blocks the formation of actin-rich long cellular extensions that are important for the delamination and the migration of the invasive cluster. We show that IIS specifically activates the expression of the actin regulator chickadee, the Drosophila homolog of Profilin, which is essential for promoting the formation of actin extensions and migration through the egg chamber. In this process, the transcription factor FoxO acts as a repressor of chickadee expression. Altogether, these results show that local activation of IIS controls collective cell migration through regulation of actin homeostasis and protrusion dynamics.

The potassium channel KCNJ13 is essential for smooth muscle cytoskeletal organization during mouse tracheal tubulogenesis

Tubulogenesis is essential for the formation and function of internal organs. One such organ is the trachea, which allows gas exchange between the external environment and the lungs. However, the cellular and molecular mechanisms underlying tracheal tube development remain poorly understood. Here, we show that the potassium channel KCNJ13 is a critical modulator of tracheal tubulogenesis. We identify Kcnj13 in an ethylnitrosourea forward genetic screen for regulators of mouse respiratory organ development. Kcnj13 mutants exhibit a shorter trachea as well as defective smooth muscle (SM) cell alignment and polarity. KCNJ13 is essential to maintain ion homeostasis in tracheal SM cells, which is required for actin polymerization. This process appears to be mediated, at least in part, through activation of the actin regulator AKT, as pharmacological increase of AKT phosphorylation ameliorates the Kcnj13-mutant trachea phenotypes. These results provide insight into the role of ion homeostasis in cytoskeletal organization during tubulogenesis.

The role of heat shock proteins and co-chaperones in heart failure

The ongoing contractile and metabolic demands of the heart require a tight control over protein quality control, including the maintenance of protein folding, turnover and synthesis. In heart disease, increases in mechanical and oxidative stresses, post-translational modifications (e.g., phosphorylation), for example, decrease protein stability to favour misfolding in myocardial infarction, heart failure or ageing. These misfolded proteins are toxic to cardiomyocytes, directly contributing to the common accumulation found in human heart failure. One of the critical class of proteins involved in protecting the heart against these threats are molecular chaperones, including the heat shock protein70 (HSP70), HSP90 and co-chaperones CHIP (carboxy terminus of Hsp70-interacting protein, encoded by the Stub1 gene) and BAG-3 (BCL2-associated athanogene 3). Here, we review their emerging roles in the maintenance of cardiomyocytes in human and experimental models of heart failure, including their roles in facilitating the removal of misfolded and degraded proteins, inhibiting apoptosis and maintaining the structural integrity of the sarcomere and regulation of nuclear receptors. Furthermore, we discuss emerging evidence of increased expression of extracellular HSP70, HSP90 and BAG-3 in heart failure, with complementary independent roles from intracellular functions with important therapeutic and diagnostic considerations. While our understanding of these major HSPs in heart failure is incomplete, there is a clear potential role for therapeutic modulation of HSPs in heart failure with important contextual considerations to counteract the imbalance of protein damage and endogenous protein quality control systems.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Spaceflight Activates Protein Kinase C Alpha Signaling and Modifies the Developmental Stage of Human Neonatal Cardiovascular Progenitor Cells

Spaceflight impacts cardiovascular function in astronauts; however, its impact on cardiac development and the stem cells that form the basis for cardiac repair is unknown. Accordingly, further research is needed to uncover the potential relevance of such changes to human health. Using simulated microgravity (SMG) generated by two-dimensional clinorotation and culture aboard the International Space Station (ISS), we assessed the effects of mechanical unloading on human neonatal cardiovascular progenitor cell (CPC) developmental properties and signaling. Following 6-7 days of SMG and 12 days of ISS culture, we analyzed changes in gene expression. Both environments induced the expression of genes that are typically associated with an earlier state of cardiovascular development. To understand the mechanism by which such changes occurred, we assessed the expression of mechanosensitive small RhoGTPases in SMG-cultured CPCs and observed decreased levels of RHOA and CDC42. Given the effect of these molecules on intracellular calcium levels, we evaluated changes in noncanonical Wnt/calcium signaling. After 6-7 days under SMG, CPCs exhibited elevated levels of WNT5A and PRKCA. Similarly, ISS-cultured CPCs exhibited elevated levels of calcium handling and signaling genes, which corresponded to protein kinase C alpha (PKCα), a calcium-dependent protein kinase, activation after 30 days. Akt was activated, whereas phosphorylated extracellular signal-regulated kinase levels were unchanged. To explore the effect of calcium induction in neonatal CPCs, we activated PKCα using hWnt5a treatment on Earth. Subsequently, early cardiovascular developmental marker levels were elevated. Transcripts induced by SMG and hWnt5a-treatment are expressed within the sinoatrial node, which may represent embryonic myocardium maintained in its primitive state. Calcium signaling is sensitive to mechanical unloading and directs CPC developmental properties. Further research both in space and on Earth may help refine the use of CPCs in stem cell-based therapies and highlight the molecular events of development.

Vibrio vulnificus MARTX cytotoxin causes inactivation of phagocytosis-related signaling molecules in macrophages

Background

Vibrio vulnificus is a marine bacterial species that causes opportunistic infections manifested by serious skin lesions and fulminant septicemia in humans. We have previously shown that the multifunctional autoprocessing repeats in toxin (MARTX_Vv1) of a biotype 1 V. vulnificus strain promotes survival of this organism in the host by preventing it from engulfment by the phagocytes. The purpose of this study was to further explore how MARTX_Vv1 inhibits phagocytosis of this microorganism by the macrophage.

Methods

We compared between a wild-type V. vulnificus strain and its MARTX_Vv1-deficient mutant for a variety of phagocytosis-related responses, including morphological change and activation of signaling molecules, they induced in the macrophage. We also characterized a set of MARTX_Vv1 domain-deletion mutants to define the regions associated with antiphagocytosis activity.

Results

The RAW 264.7 cells and mouse peritoneal exudate macrophages underwent cell rounding accompanied by F-actin disorganization in the presence of MARTX_Vv1. In addition, phosphorylation of some F-actin rearrangement-associated signaling molecules, including Lyn, Fgr and Hck of the Src family kinases (SFKs), focal adhesion kinase (FAK), proline-rich tyrosine kinase 2 (Pyk2), phosphoinositide 3-kinase (PI3K) and Akt, but not p38, was decreased. By using specific inhibitors, we found that these kinases were all involved in the phagocytosis of MARTX_Vv1-deficient mutant in an order of SFKs-FAK/Pyk2-PI3K-Akt. Deletion of the effector domains in the central region of MARTX_Vv1 could lead to reduced cytotoxicity, depending on the region and size of deletion, but did not affect the antiphagocytosis activity and ability to cause rounding of macrophage. Reduced phosphorylation of Akt was closely associated with inhibition of phagocytosis by the wild-type strain and MARTX_Vv1 domain-deletion mutants, and expression of the constitutively active Akt, myr-Akt, enhanced the engulfment of these strains by macrophage.

Conclusions

MARTX_Vv1 could inactivate the SFKs-FAK/Pyk2-PI3K-Akt signaling pathway in the macrophages. This might lead to impaired phagocytosis of the V. vulnificus-infected macrophage. The majority of the central region of MARTX_Vv1 is not associated with the antiphagocytosis activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-017-0368-2) contains supplementary material, which is available to authorized users.

Overexpression of Kinase-Dead mTOR Impairs Glucose Homeostasis by Regulating Insulin Secretion and Not β-Cell Mass

Regulation of glucose homeostasis by insulin depends on β-cell growth and function. Nutrients and growth factor stimuli converge on the conserved protein kinase mechanistic target of rapamycin (mTOR), existing in two complexes, mTORC1 and mTORC2. To understand the functional relevance of mTOR enzymatic activity in β-cell development and glucose homeostasis, we generated mice overexpressing either one or two copies of a kinase-dead mTOR mutant (KD-mTOR) transgene exclusively in β-cells. We examined glucose homeostasis and β-cell function of these mice fed a control chow or high-fat diet. Mice with two copies of the transgene [RIPCre;KD-mTOR (Homozygous)] develop glucose intolerance due to a defect in β-cell function without alterations in β-cell mass with control chow. Islets from RIPCre;KD-mTOR (Homozygous) mice showed reduced mTORC1 and mTORC2 signaling along with transcripts and protein levels of Pdx-1. Islets with reduced mTORC2 signaling in their β-cells (RIPCre;Rictor^fl/fl) also showed reduced Pdx-1. When challenged with a high-fat diet, mice carrying one copy of KD-mTOR mutant transgene developed glucose intolerance and β-cell insulin secretion defect but showed no changes in β-cell mass. These findings suggest that the mTOR-mediated signaling pathway is not essential to β-cell growth but is involved in regulating β-cell function in normal and diabetogenic conditions.

An improved Akt reporter reveals intra- and inter-cellular heterogeneity and oscillations in signal transduction

Akt is a key node in a range of signal transduction cascades and play a critical role in diseases such as cancer and diabetes. Fluorescently-tagged Akt reporters have been used to discern Akt localisation, yet it has not been clear how well these tools recapitulate the behaviour of endogenous Akt proteins. Here, we observed that fusion of eGFP to Akt2 impaired both its insulin-stimulated plasma membrane recruitment and its phosphorylation. Endogenous-like responses were restored by replacing eGFP with TagRFP-T. The improved response magnitude and sensitivity afforded by TagRFP-T-Akt2 over eGFP-Akt2 enabled monitoring of signalling outcomes in single cells at physiological doses of insulin with subcellular resolution and revealed two previously unreported features of Akt biology. In 3T3-L1 adipocytes, stimulation with insulin resulted in recruitment of Akt2 to the plasma membrane in a polarised fashion. Additionally, we observed oscillations in plasma membrane localised Akt2 in the presence of insulin with a consistent periodicity of 2 min. Our studies highlight the importance of fluorophore choice when generating reporter constructs and shed light on new Akt signalling responses that may encode complex signalling information.This article has an associated First Person interview with the first author of the paper.

An unpredicted aggregation-critical region of the actin-polymerizing protein TRIOBP-1/Tara, determined by elucidation of its domain structure

Aggregation of specific proteins in the brains of patients with chronic mental illness as a result of disruptions in proteostasis is an emerging theme in the study of schizophrenia in particular. Proteins including DISC1 (disrupted in schizophrenia 1) and dysbindin-1B are found in insoluble forms within brain homogenates from such patients. We recently identified TRIOBP-1 (Trio-binding protein 1, also known as Tara) to be another such protein through an epitope discovery and proteomics approach by comparing post-mortem brain material from schizophrenia patients and control individuals. We hypothesized that this was likely to occur as a result of a specific subcellular process and that it, therefore, should be possible to identify a region of the TRIOBP-1 protein that is essential for its aggregation to occur. Here, we probe the domain organization of TRIOBP-1, finding it to possess two distinct coiled-coil domains: the central and C-terminal domains. The central domain inhibits the depolymerization of F-actin and is also responsible for oligomerization of TRIOBP-1. Along with an N-terminal pleckstrin homology domain, the central domain affects neurite outgrowth. In neuroblastoma cells it was found that the aggregation propensity of TRIOBP-1 arises from its central domain, with a short "linker" region narrowed to within amino acids 324-348, between its first two coiled coils, as essential for the formation of TRIOBP-1 aggregates. TRIOBP-1 aggregation, therefore, appears to occur through one or more specific cellular mechanisms, which therefore have the potential to be of physiological relevance for the biological process underlying the development of chronic mental illness.

The critical role of Akt in cardiovascular function

Akt kinase, a member of AGC kinases, is important in many cellular functions including proliferation, migration, cell growth and metabolism. There are three known Akt isoforms which play critical and diverse roles in the cardiovascular system. Akt activity is regulated by its upstream regulatory pathways at transcriptional and post-translational levels. Beta-catenin/Tcf-4, GLI1 and Stat-3 are some of few known transcriptional regulators of AKT gene. Threonine 308 and serine 473 are the two critical phosphorylation sites of Akt1. Translocation of Akt to the cell membrane facilitates PDK1 phosphorylation of the threonine site. The serine site is phosphorylated by mTORC2. Ack1, Src, PTK6, TBK1, IKBKE and IKKε are some of the non-canonical pathways which affect the Akt activity. Protein-protein interactions of Akt to actin and Hsp90 increase the Akt activity while Akt binding to other proteins such as CTMP and TRB3 reduces the Akt activity. The action of Akt on its downstream targets determines its function in cardiovascular processes such as cell survival, growth, proliferation, angiogenesis, vasorelaxation, and cell metabolism. Akt promotes cell survival via caspase-9, YAP, Bcl-2, and Bcl-x activities. Inhibition of FoxO proteins by Akt also increases cell survival by transcriptional mechanisms. Akt stimulates cell growth and proliferation through mTORC1. Akt also increases VEGF secretion and mediates eNOS phosphorylation, vasorelaxation and angiogenesis. Akt can increase cellular metabolism through its downstream targets GSK3 and GLUT4. The alterations of Akt signaling play an important role in many cardiovascular pathological processes such as atherosclerosis, cardiac hypertrophy, and vascular remodeling. Several Akt inhibitors have been developed and tested as anti-tumor agents. They could be potential novel therapeutics for the cardiovascular diseases.

Ubl4A is required for insulin-induced Akt plasma membrane translocation through promotion of Arp2/3-dependent actin branching

The serine-threonine kinase Akt is a key regulator of cell proliferation and survival, glucose metabolism, cell mobility, and tumorigenesis. Activation of Akt by extracellular stimuli such as insulin centers on the interaction of Akt with PIP3 on the plasma membrane, where it is subsequently phosphorylated and activated by upstream protein kinases. However, it is not known how Akt is recruited to the plasma membrane upon stimulation. Here we report that ubiquitin-like protein 4A (Ubl4A) plays a crucial role in insulin-induced Akt plasma membrane translocation. Ubl4A knockout newborn mice have defective Akt-dependent glycogen synthesis and increased neonatal mortality. Loss of Ubl4A results in the impairment of insulin-induced Akt translocation to the plasma membrane and activation. Akt binds actin-filaments and colocalizes with actin-related protein 2 and 3 (Arp2/3) complex in the membrane ruffles and lamellipodia. Ubl4A directly interacts with Arp2/3 to accelerate actin branching and networking, allowing Akt to be in close proximity to the plasma membrane for activation upon insulin stimulation. Our finding reveals a new mechanism by which Akt is recruited to the plasma membrane for activation, thereby providing a missing link in Akt signaling.

Signaling specificity in the Akt pathway in biology and disease

Akt/PKB is a key master regulator of a wide range of physiological functions including metabolism, proliferation, survival, growth, angiogenesis and migration and invasion. The Akt protein kinase family comprises three highly related isoforms encoded by different genes. The initial observation that the Akt isoforms share upstream activators as well as several downstream effectors, together with the high sequence homology suggested that their functions were mostly redundant. By contrast, an increasing body of evidence has recently uncovered the concept of Akt isoform signaling specificity, supported by distinct phenotypes displayed by animal strains genetically modified for each of the three genes, as well as by the identification of isoform-specific substrates and association with discrete subcellular locations. Given that Akt is regarded as a promising therapeutic target in a number of pathologies, it is essential to dissect the relative contributions of each isoform, as well as the degree of compensation in pathophysiological function. Here we summarize our view of how Akt selectivity is achieved in the context of subcellular localization, isoform-specific substrate phosphorylation and context-dependent functions in normal and pathophysiological settings.

Mechanisms of action of acetaldehyde in the up-regulation of the human α2(I) collagen gene in hepatic stellate cells: key roles of Ski, SMAD3, SMAD4, and SMAD7

Alcohol-induced liver fibrosis and eventually cirrhosis is a leading cause of death. Acetaldehyde, the first metabolite of ethanol, up-regulates expression of the human α2(I) collagen gene (COL1A2). Early acetaldehyde-mediated effects involve phosphorylation and nuclear translocation of SMAD3/4-containing complexes that bind to COL1A2 promoter to induce fibrogenesis. We used human and mouse hepatic stellate cells to elucidate the mechanisms whereby acetaldehyde up-regulates COL1A2 by modulating the role of Ski and the expression of SMADs 3, 4, and 7. Acetaldehyde induced up-regulation of COL1A2 by 3.5-fold, with concomitant increases in the mRNA (threefold) and protein (4.2- and 3.5-fold) levels of SMAD3 and SMAD4, respectively. It also caused a 60% decrease in SMAD7 expression. Ski, a member of the Ski/Sno oncogene family, is colocalized in the nucleus with SMAD4. Acetaldehyde induces translocation of Ski and SMAD4 to the cytoplasm, where Ski undergoes proteasomal degradation, as confirmed by the ability of the proteasomal inhibitor lactacystin to blunt up-regulation of acetaldehyde-dependent COL1A2, but not of the nonspecific fibronectin gene (FN1). We conclude that acetaldehyde up-regulates COL1A2 by enhancing expression of the transactivators SMAD3 and SMAD4 while inhibiting the repressor SMAD7, along with promoting Ski translocation from the nucleus to cytoplasm. We speculate that drugs that prevent proteasomal degradation of repressors targeting COL1A2 may have antifibrogenic properties.

mTORC2 regulates mechanically induced cytoskeletal reorganization and lineage selection in marrow-derived mesenchymal stem cells

The cell cytoskeleton interprets and responds to physical cues from the microenvironment. Applying mechanical force to mesenchymal stem cells induces formation of a stiffer cytoskeleton, which biases against adipogenic differentiation and toward osteoblastogenesis. mTORC2, the mTOR complex defined by its binding partner rictor, is implicated in resting cytoskeletal architecture and is activated by mechanical force. We asked if mTORC2 played a role in mechanical adaptation of the cytoskeleton. We found that during bi-axial strain-induced cytoskeletal restructuring, mTORC2 and Akt colocalize with newly assembled focal adhesions (FA). Disrupting the function of mTORC2, or that of its downstream substrate Akt, prevented mechanically induced F-actin stress fiber development. mTORC2 becomes associated with vinculin during strain, and knockdown of vinculin prevents mTORC2 activation. In contrast, mTORC2 is not recruited to the FA complex during its activation by insulin, nor does insulin alter cytoskeletal structure. Further, when rictor was knocked down, the ability of mesenchymal stem cells (MSC) to enter the osteoblastic lineage was reduced, and when cultured in adipogenic medium, rictor-deficient MSC showed accelerated adipogenesis. This indicated that cytoskeletal remodeling promotes osteogenesis over adipogenesis. In sum, our data show that mTORC2 is involved in stem cell responses to biophysical stimuli, regulating both signaling and cytoskeletal reorganization. As such, mechanical activation of mTORC2 signaling participates in mesenchymal stem cell lineage selection, preventing adipogenesis by preserving β-catenin and stimulating osteogenesis by generating a stiffer cytoskeleton.

Aging-induced proteostatic changes in the rat hippocampus identify ARP3, NEB2 and BRAG2 as a molecular circuitry for cognitive impairment

Disturbed proteostasis as a particular phenotype of the aging organism has been advanced in C. elegans experiments and is also conceived to underlie neurodegenerative diseases in humans. Here, we investigated whether particular changes in non-disease related proteostasis can be identified in the aged mammalian brain, and whether a particular signature of aberrant proteostasis is related to behavioral performance of learning and memory. Young (adult, n = 30) and aged (2 years, n = 50) Wistar rats were tested in the Morris Water Maze (MWM) to distinguish superior and inferior performers. For both young and old rats, the best and worst performers in the MWM were selected and the insoluble proteome, termed aggregome, was purified from the hippocampus as evidence for aberrant proteostasis. Quantitative proteomics (iTRAQ) was performed. The aged inferior performers were considered as a model for spontaneous, age-associated cognitive impairment. Whereas variability of the insoluble proteome increased with age, absolute changes in the levels of insoluble proteins were small compared to the findings in the whole C. elegans insoluble proteome. However, we identified proteins with aberrant proteostasis in aging. For the cognitively impaired rats, we identified a changed molecular circuitry of proteins selectively involved in F-actin remodeling, synapse building and long-term depression: actin related protein 3 (ARP3), neurabin II (NEB2) and IQ motif and SEC7 domain-containing protein 1 (BRAG2). We demonstrate that aberrant proteostasis is a specific phenotype of brain aging in mammals. We identify a distinct molecular circuitry where changes in proteostasis are characteristic for poor learning and memory performance in the wild type, aged rat. Our findings 1. establish the search for aberrant proteostasis as a successful strategy to identify neuronal dysfunction in deficient cognitive behavior, 2. reveal a previously unknown functional network of proteins (ARP3, NEB2, BRAG2) involved in age-associated cognitive dysfunction.

Rac1 pathway mediates stretch response in pulmonary alveolar epithelial cells

Alveolar epithelial cells (AECs) maintain the pulmonary blood-gas barrier integrity with gasketlike intercellular tight junctions (TJ) that are anchored internally to the actin cytoskeleton. We have previously shown that AEC monolayers stretched cyclically and equibiaxially undergo rapid magnitude- and frequency-dependent actin cytoskeletal remodeling to form perijunctional actin rings (PJARs). In this work, we show that even 10 min of stretch induced increases in the phosphorylation of Akt and LIM kinase (LIMK) and decreases in cofilin phosphorylation, suggesting that the Rac1/Akt pathway is involved in these stretch-mediated changes. We confirmed that Rac1 inhibitors wortmannin or EHT-1864 decrease stretch-stimulated Akt and LIMK phosphorylation and that Rac1 agonists PIP3 or PDGF increase phosphorylation of these proteins in unstretched cells. We also confirmed that Rac1 pathway inhibition during stretch modulated stretch-induced changes in occludin content and monolayer permeability, actin remodeling and PJAR formation, and cell death. As further validation, overexpression of Rac GTPase-activating protein β2-chimerin also preserved monolayer barrier properties in stretched monolayers. In summary, our data suggest that constitutive activity of Rac1, which is necessary for stretch-induced activation of the Rac1 downstream proteins, mediates stretch-induced increases in permeability and PJAR formation.

The protein kinase Akt/PKB regulates both prelamin A degradation and Lmna gene expression

The serine/threonine kinase Akt/PKB is a major signaling hub integrating metabolic, survival, growth, and cell cycle regulatory signals. The definition of the phospho-motif cipher driving phosphorylation by Akt led to the identification of hundreds of putative substrates, and it is therefore pivotal to identify those whose phosphorylation by Akt is of consequence to biological processes. The Lmna gene products lamin A/C and the lamin A precursor prelamin A are type V intermediate filament proteins forming a filamentous meshwork, the lamina, underneath the inner nuclear membrane, for nuclear envelope structures organization and interphase chromatin anchoring. In our previous work, we reported that A-type lamins are phosphorylated by Akt at S301 and S404 in physiological conditions and are therefore bona fide substrates of Akt. We report here that Akt phosphorylation at S404 targets the precursor prelamin A for degradation. We further demonstrate that Akt also regulates Lmna transcription. Our study unveils a previously unknown function of Akt in the control of prelamin A stability and expression. Moreover, given the large number of diseases related to prelamin A, our findings represent a further important step bridging basic A-type lamin physiology to therapeutic approaches for lamin A-linked disorders.

PTPN12 controls PTEN and the AKT signalling to FAK and HER2 in migrating ovarian cancer cells

Several tyrosine phosphatases control cell motility; understanding their signaling helps to decipher cancer mechanisms. Previously, we found that the negative regulation of migration exerted by PTPN12 in ovarian cancer SKOV-3 cells involves direct FAK Y397 targeting, in HER2-dependent way. In this study, we describe that PTPN12 silencing depresses also PTEN RNA and protein. This, in turn, contributes to regulate FAK, through the activation of the PI3K/AKT pathway, resulting in GSK3 inactivation and decreased FAK phosphorylation at the inhibitory and GSK3 target S722. Altogether, in SKOV-3 cells, both PTPN12 and PTEN signaling merge on FAK which is negatively regulated through Y397 dephosphorylation (directly by PTPN12) and S722 phosphorylation (through PTEN/AKT/GSK3). Although HER2 activity sustains SKOV-3 cell motility, the HER2 inhibitor Ag825 impairs migration only in PTPN12 silenced cells, suggesting the ability of PTPN12 to affect HER2. This hypothesis is supported by the finding that, in migrating cells, Ag825 decreases HER2 phosphorylation at Y1248, Y1221/2, and Y877 (i.e., inactivates HER2) only after PTPN12 silencing. Conversely, cell exposure to the PI3K inhibitor LY294002 increases HER2 phosphorylation, suggesting the involvement of PI3K/AKT in HER2 regulation. Altogether, the results reveal a new PTEN mechanism in the control cell migration and suggest a complex cross-talk between PTPN12 and HER2.

Protein kinase B/AKT isoform 2 drives migration of human mesenchymal stem cells

This study was designed to investigate the migratory behavior of adult human mesenchymal stem cells (MSC) and the underlying mechanism. Cell migration was assessed by transwell, wound healing and time-lapse in vivo motility assays. Pharmacological inhibitors were used to determine the potential mechanism responsible for cell migration and invasion. The tests that were implemented revealed that MSC were fairly migratory. Protein kinase B (AKT) was strongly activated at the basal level. Through our analyses we demonstrated that pharmacological inactivation of AKT2 but not AKT1 significantly decreased cell migration and invasion. Although preliminary, collectively our results indicate that AKT2 activation plays a critical role in enabling MSC migration.

Afamin secreted from nonresorbing osteoclasts acts as a chemokine for preosteoblasts via the Akt-signaling pathway

Although it is well known that osteoclastic bone resorption is followed by osteoblastic bone formation, questions remain as to when coupling factors are produced during bone resorption and which stages of bone formation are affected by these factors. To clarify these mechanisms, we established an in vitro system to investigate the coupling phenomenon. We obtained conditioned media (CM) from osteoclasts in the early and late stages of differentiation and from bone resorption stages. The collected CM was used to treat primary mouse calvarial osteoblasts and preosteoblastic MC3T3-E1 cells and to evaluate its influence on the migration, viability, proliferation, and differentiation of osteoblasts. We found that CM from osteoclasts in the early stage of differentiation predominantly stimulated the migration of osteoblastic lineages. By further performing fractional analyses of the CM with liquid chromatography-tandem mass spectrometry, we identified afamin, which has binding activity with vitamin E, as a possible coupling factor. The CM collected from afamin siRNA-transfected osteoclasts significantly suppressed preosteoblast migration. Afamin activated Akt in preosteoblasts, and pretreatment with Akt inhibitor significantly blocked afamin-stimulated preosteoblast migration. In conclusion, these results indicate that osteoclasts themselves play a central role in the coupling of bone resorption and formation by stimulating preosteoblast migration. In addition, we identified afamin as one of osteoclast-derived chemokines that affect preosteoblasts through the activation of the Akt-signaling pathway.

Metastasis-associated protein 1/histone deacetylase 4-nucleosome remodeling and deacetylase complex regulates phosphatase and tensin homolog gene expression and function

Metastasis-associated protein 1 (MTA1) is widely overexpressed in human cancers and is associated with malignant phenotypic changes contributing to morbidity in the associated diseases. Here we discovered for the first time that MTA1, a master chromatin modifier, transcriptionally represses the expression of phosphatase and tensin homolog (PTEN), a tumor suppressor gene, by recruiting class II histone deacetylase 4 (HDAC4) along with the transcription factor Yin-Yang 1 (YY1) onto the PTEN promoter. We also found evidence of an inverse correlation between the expression levels of MTA1 and PTEN in physiologically relevant breast cancer microarray datasets. We found that MTA1 up-regulation leads to a decreased expression of PTEN protein and stimulation of PI3K as well as phosphorylation of its signaling targets. Accordingly, selective down-regulation of MTA1 in breast cancer cells increases PTEN expression and inhibits stimulation of the PI3K/AKT signaling. Collectively, these findings provide a mechanistic role for MTA1 in transcriptional repression of PTEN, leading to modulation of the resulting signaling pathways.

Phosphoinositides in chemotaxis

Phosphatidylinositol lipids generated through the action of phosphinositide 3-kinase (PI3K) are key mediators of a wide array of biological responses. In particular, their role in the regulation of cell migration has been extensively studied and extends to amoeboid as well as mesenchymal migration. Through the emergence of fluorescent probes that target PI3K products as well as the use of specific inhibitors and knockout technologies, the spatio-temporal distribution of PI3K products in chemotaxing cells has been shown to represent a key anterior polarity signal that targets downstream effectors to actin polymerization. In addition, through intricate cross-talk networks PI3K products have been shown to regulate signals that control posterior effectors. Yet, in more complex environments or in conditions where chemoattractant gradients are steep, a variety of cell types can still chemotax in the absence of PI3K signals. Indeed, parallel signal transduction pathways have been shown to coordinately regulate cell polarity and directed movement. In this chapter, we will review the current role PI3K products play in the regulation of directed cell migration in various cell types, highlight the importance of mathematical modeling in the study of chemotaxis, and end with a brief overview of other signaling cascades known to also regulate chemotaxis.

PTEN inhibition improves wound healing in lung epithelia through changes in cellular mechanics that enhance migration

The phosphoinositide-3 kinase/Akt pathway is a vital survival axis in lung epithelia. We previously reported that inhibition of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a major suppressor of this pathway, results in enhanced wound repair following injury. However, the precise cellular and biomechanical mechanisms responsible for increased wound repair during PTEN inhibition are not yet well established. Using primary human lung epithelia and a related lung epithelial cell line, we first determined whether changes in migration or proliferation account for wound closure. Strikingly, we observed that cell migration accounts for the majority of wound recovery following PTEN inhibition in conjunction with activation of the Akt and ERK signaling pathways. We then used fluorescence and atomic force microscopy to investigate how PTEN inhibition alters the cytoskeletal and mechanical properties of the epithelial cell. PTEN inhibition did not significantly alter cytoskeletal structure but did result in large spatial variations in cell stiffness and in particular a decrease in cell stiffness near the wound edge. Biomechanical changes, as well as migration rates, were mediated by both the Akt and ERK pathways. Our results indicate that PTEN inhibition rapidly alters biochemical signaling events that in turn provoke alterations in biomechanical properties that enhance cell migration. Specifically, the reduced stiffness of PTEN-inhibited cells promotes larger deformations, resulting in a more migratory phenotype. We therefore conclude that increased wound closure consequent to PTEN inhibition occurs through enhancement of cell migration that is due to specific changes in the biomechanical properties of the cell.

Thymosin-β4 (Tβ4) blunts PDGF-dependent phosphorylation and binding of AKT to actin in hepatic stellate cells

Hepatic stellate cell transdifferentiation is a key event in the fibrogenic cascade. Therefore, attempts to prevent and/or revert the myofibroblastic phenotype could result in novel therapeutic approaches to treat liver cirrhosis. The expression of platelet-derived growth factor (PDGF)-β receptor and the proliferative response to platelet-derived growth factor-ββ (PDGF-ββ) are hallmarks of the transdifferentiation of hepatic stellate cells (HSC). In this communication, we investigated whether thymosin-β4 (Tβ4), a chemokine expressed by HSC could prevent PDGF-BB-mediated proliferation and migration of cultured HSC. Using early passages of human HSC, we showed that Tβ4 inhibited cell proliferation and migration and prevented the expression of PDGF-β receptor (PDGF-βr), α-smooth muscle actin and α1(I) collagen mRNAs. Tβ4 also inhibited the reappearance of PDGF-βr after its PDGF-BB-dependent degradation. These PDGF-dependent events were associated with the inhibition of AKT phosphorylation at both T308 and S473 amino acid residues. The lack of AKT phosphorylation was not due to the inhibition of PDGF-βr phosphorylation, the activation of phosphoinositide 3-kinase (PI3K), pyruvate dehydrogenase kinase isozyme 1 (PDK1), and mammalian target of rapamycin (mTOR). We found that PDGF-BB induced AKT binding to actin, and that Tβ4 prevented this effect. Tβ4 also prevented the activation of freshly isolated HSC cultured in the presence of Dulbecco's modified Eagle's medium or Dulbecco's minimal essential medium containing 10% fetal bovine serum. In conclusion, overall, our findings suggest that Tβ4 by sequestering actin prevents binding of AKT, thus inhibiting its phosphorylation. Therefore, Tβ4 has the potential to be an antifibrogenic agent.

Silencer of death domains (SODD) inhibits skeletal muscle and kidney enriched inositol 5-phosphatase (SKIP) and regulates phosphoinositide 3-kinase (PI3K)/Akt signaling to the actin cytoskeleton

Phosphoinositide 3-kinase (PI3K) regulates cell polarity and migration by generating phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P(3)) at the leading edge of migrating cells. The serine-threonine protein kinase Akt binds to PI(3,4,5)P(3), resulting in its activation. Active Akt promotes spatially regulated actin cytoskeletal remodeling and thereby directed cell migration. The inositol polyphosphate 5-phosphatases (5-ptases) degrade PI(3,4,5)P(3) to form PI(3,4)P(2), which leads to diminished Akt activation. Several 5-ptases, including SKIP and SHIP2, inhibit actin cytoskeletal reorganization by opposing PI3K/Akt signaling. In this current study, we identify a molecular co-chaperone termed silencer of death domains (SODD/BAG4) that forms a complex with several 5-ptase family members, including SKIP, SHIP1, and SHIP2. The interaction between SODD and SKIP exerts an inhibitory effect on SKIP PI(3,4,5)P(3) 5-ptase catalytic activity and consequently enhances the recruitment of PI(3,4,5)P(3)-effectors to the plasma membrane. In contrast, SODD(-/-) mouse embryonic fibroblasts exhibit reduced Akt-Ser(473) and -Thr(308) phosphorylation following EGF stimulation, associated with increased SKIP PI(3,4,5)P(3)-5-ptase activity. SODD(-/-) mouse embryonic fibroblasts exhibit decreased EGF-stimulated F-actin stress fibers, lamellipodia, and focal adhesion complexity, a phenotype that is rescued by the expression of constitutively active Akt1. Furthermore, reduced cell migration was observed in SODD(-/-) macrophages, which express the three 5-ptases shown to interact with SODD (SKIP, SHIP1, and SHIP2). Therefore, this study identifies SODD as a novel regulator of PI3K/Akt signaling to the actin cytoskeleton.

The Pathobiology of Neisseria gonorrhoeae Lower Female Genital Tract Infection

Infection and disease associated with Neisseria gonorrhoeae, the gonococcus, continue to be a global health problem. Asymptomatic and subclinical gonococcal infections occur at a high frequency in females; thus, the true incidence of N. gonorrhoeae infections are presumed to be severely underestimated. Inherent to this asymptomatic/subclinical diseased state is the continued prevalence of this organism within the general population, as well as the medical, economic, and social burden equated with the observed chronic, disease sequelae. As infections of the lower female genital tract (i.e., the uterine cervix) commonly result in subclinical disease, it follows that the pathobiology of cervical gonorrhea would differ from that observed for other sites of infection. In this regard, the potential responses to infection that are generated by the female reproductive tract mucosa are unique in that they are governed, in part, by cyclic fluctuations in steroid hormone levels. The lower female genital tract has the further distinction of being able to functionally discriminate between resident commensal microbiota and transient pathogens. The expression of functionally active complement receptor 3 by the lower, but not the upper, female genital tract mucosa; together with data indicating that gonococcal adherence to and invasion of primary cervical epithelial cells and tissue are predominately aided by this surface-expressed host molecule; provide one explanation for asymptomatic/subclinical gonococcal cervicitis. However, co-evolution of the gonococcus with its sole human host has endowed this organism with variable survival strategies that not only aid these bacteria in successfully evasion of immune detection and function but also enhance cervical colonization and cellular invasion. To this end, we herein summarize current knowledge pertaining to the pathobiology of gonococcal infection of the human cervix.

LIM kinase mediates estrogen action on the actin depolymerization factor Cofilin

The ovarian hormone estrogen increases the axospinous synapse density in the hippocampal CA1 region of young female rats but fails to do so in aged rats. This estrogen-mediated alteration of spine synapse structures suggests the coincident requirement for the structural reorganization of the underlying actin cytoskeleton network. Actin reorganization is known to require the deactivation of Cofilin, an actin depolymerization factor. Cofilin is deactivated by LIM kinase (LIMK), and LIMK activity is modulated by the phosphorylation of specific residues. We have previously demonstrated that estrogen is able to increase phosphorylated LIMK (pLIMK) immunoreactivity (IR) in the hippocampus in vivo and that this estrogen-stimulated pLIMK-IR is decreased in the aged brain. Because Cofilin phosphorylation allows for actin filament elongation and spine synapse growth, we sought to determine if estrogen acts through Cofilin and if such estrogen action requires the observed LIMK activity. Using both hippocampal neurons and the NG108-15 neuroblastoma cell line, we demonstrate here that estrogen stimulates the phosphorylation of Cofilin in vitro. Furthermore, this estrogen action on Cofilin requires LIMK. Lastly, while initiating the phosphorylation of LIMK and Cofilin, estrogen can also stimulate the formation of filopodial extensions, an early step in the formation of nascent spines, demonstrating that estrogen can alter the actin-dependent neuronal morphology. This linkage of estrogen communication to Cofilin via LIMK provides the functionality to the age-sensitive pLIMK-IR that we have observed in vivo.

Cell invasion of Yersinia pseudotuberculosis by invasin and YadA requires protein kinase C, phospholipase C-gamma1 and Akt kinase

The outer membrane proteins YadA and invasin of Yersinia pseudotuberculosis promote invasion into mammalian cells through beta(1)-integrins and trigger the production of interleukin (IL)-8. FAK, c-Src and the PI3 kinase were previously found to be important for both YadA- and invasin-promoted uptake. Here, we demonstrate that two different downstream effectors of PI3 kinase, Akt and phospholipase Cgamma1 are required for efficient cell invasion. Inhibition of Akt or phospholipase C-gamma (PLC-gamma)1 by pharmaceutical agents as well as reduced expression of the isoforms Akt1 and Akt2, and of PLC-gamma1 by RNA interference decreased entry of YadA- and Inv-expressing bacteria significantly. In addition, we report that the conventional protein kinases C (PKC)alpha and -beta, positioned downstream of PLC-gamma1, are activated upon Inv- or YadA-promoted cell entry. They colocalize with intracellular bacteria and their depletion by siRNA treatment also resulted in a strong reduction of cell entry. In contrast, neither Akt nor PLC-gamma1, and the PKCs are essential for YadA- and Inv-mediated IL-8 synthesis and release. We conclude that YadA and invasin of Y. pseudotuberculosis both trigger similar signal transduction pathways during integrin-mediated phagocytosis into epithelial cells, which lead to the activation of Akt, PLC-gamma1, PKCalpha and -beta downstream of PI3 kinase, separate from the MAPK-dependent pathway that triggers IL-8 production.

Compartmentalization and regulation of insulin signaling to GLUT4 by the cytoskeleton

One of the early events in the development of Type 2 diabetes appears to be an inhibition of insulin-mediated GLUT4 redistribution to the cell surface in tissues that express GLUT4. Understanding this process, and how it begins to breakdown in the development of insulin resistance is quite important as we face treatment and prevention of metabolic diseases. Over the past few years, and increasing number of laboratories have produced compelling data to demonstrate a role for both the actin and microtubule networks in the regulation of insulin-mediated GLUT4 redistribution to the cell surface. In this review, we explore this process from insulin-signal transduction to fusion of GLUT4 membrane vesicles, focusing on studies that have implicated a role for the cytoskeleton. We see from this body of work that both the actin network and the microtubule cytoskeleton play roles as targets of insulin action and effectors of insulin signaling leading to changes in GLUT4 redistribution to the cell surface and insulin-mediated glucose uptake.

MATER protein as substrate of PKCepsilon in human cumulus cells

High activity of the phosphoinositide 3-kinase/Akt pathway in cumulus cells plays an important role in FSH regulation of cell function and Protein Kinase C epsilon (PKCepsilon) collaborates with these signalling pathways to regulate cell proliferation. Relevant roles in follicular development are played by Maternal Antigen That Embryos Require (MATER) that is a cumulus cell- and oocyte-specific protein dependent on the maternal genome. We recently demonstrated that human MATER localizes at specific domains of oocytes and, for the first time, also in cumulus cells. MATER contains a carboxy-terminal leucine-rich repeat domain involved in protein-protein interactions regulating different cellular functions. Here we investigated the functional role of MATER. Thus, we performed coimmunoprecipitation experiments using HEK293T cells expressing human MATER; a similar approach was then followed in human cumulus/follicular cells. In MATER(+)HEK293T cells, we observed that this protein acts as a phosphorylation substrate of PKCepsilon. Western blot experiments indicate that, unlike oocytes, human cumulus cells express PKCepsilon. Immunoprecipitation and confocal analysis suggest for the first time that MATER protein interacts with this protein kinase in cumulus cells under physiological conditions. Since PKCepsilon is known to collaborate with antiapoptotic signalling pathways, this suggests a novel mechanism for the function of MATER in follicular maturation.

Laminin acts via focal adhesion kinase/phosphatidylinositol-3' kinase/protein kinase B to down-regulate beta1-adrenergic receptor signalling in cat atrial myocytes

We previously reported that short-term (2 h) plating of cat atrial myocytes on the extracellular matrix protein, laminin (LMN) decreases adenylate cyclase activity and beta(1)-adrenergic receptor (beta(1)-AR) stimulation of L-type Ca(2+) current (I(Ca,L)). The present study sought to determine whether LMN-mediated down-regulation of beta(1) signalling is due to down-regulation of adenylate cyclase and to gain insight into the signalling mechanisms responsible. beta(1)-AR stimulation was achieved by 0.01 microm isoproterenol (isoprenaline) plus 0.1 microm ICI 118551, a selective beta(2)-AR antagonist. Atrial myocytes were plated for at least 2 h on uncoated cover-slips (-LMN) or cover-slips coated with LMN (+LMN). As previously reported, beta(1)-AR stimulation of I(Ca,L) was significantly smaller in +LMN compared to -LMN atrial myocytes. In -LMN myocytes, 10 microm LY294002 (LY), a specific inhibitor of PI-(3)K, had no effect on beta(1)-AR stimulation of I(Ca,L). In +LMN myocytes, however, LY significantly increased beta(1)-AR stimulation of I(Ca,L). Western blots revealed that compared with -LMN myocytes, +LMN myocytes showed a significant increase in Akt phosphorylation at Ser-473, which was prevented by LY. In another approach, +LMN myocytes were infected (multiplicity of infection (MOI), 100; 24 h) with replication-defective adenoviruses (Adv) expressing dominant-negative inhibitors of focal adhesion kinase (FAK) (Adv-FRNK or Adv-Y397F-FAK) or Akt (Adv-dnAkt). Compared with control cells infected with Adv-beta-galactosidase, cells infected with Adv-FRNK, Adv-Y397F-FAK or Adv-dnAkt each exhibited a significantly greater beta(1)-AR stimulation of I(Ca,L). In -LMN myocytes LY had no effect on forskolin (FSK)-stimulated I(Ca,L). However, in +LMN myocytes LY significantly increased FSK-stimulated I(Ca,L). Similar results were obtained in +LMN atrial myocytes infected with Adv-FRNK. We conclude that LMN binding to beta(1)-integrin receptors acts via FAK/PI-(3)K/Akt to inhibit adenylate cyclase activity and thereby down-regulates beta(1)-AR-mediated stimulation of I(Ca,L). These findings provide new insight into the cellular mechanisms by which the extracellular matrix can modulate atrial beta-AR signalling.

Lamin A Ser404 is a nuclear target of Akt phosphorylation in C2C12 cells

Akt/PKB is a central activator of multiple signaling pathways coupled with a large number of stimuli. Although both localization and activity of Akt in the nuclear compartment are well-documented, most Akt substrates identified so far are located in the cytoplasm, while nuclear substrates have remained elusive. A proteomic-based search for nuclear substrates of Akt was undertaken, exploiting 2D-electrophoresis/MS in combination with an anti-Akt phosphosubstrate antibody. This analysis indicated lamin A/C as a putative substrate of Akt in C2C12 cells. In vitro phosphorylation of endogenous lamin A/C by recombinant Akt further validated this result. Moreover, by phosphopeptide analysis and point mutation, we established that lamin A/C is phosphorylated by Akt at Ser404, in an evolutionary conserved Akt motif. To delve deeper into this, we raised an antibody against the lamin A Ser404 phosphopeptide which allowed us to determine that phosphorylation of lamin A Ser404 is triggered by the well-known Akt activator insulin, and is therefore to be regarded as a physiological response. Remarkably, expression of S404A lamin A in primary cells from healthy tissue caused the nuclear abnormalities that are a hallmark of Emery-Dreifuss muscular dystrophy (EDMD) cells. Indeed, it is known that mutations at several sites in lamin A/C cause autosomal dominant EDMD. Very importantly, we show here that Akt failed to phosphorylate lamin A/C in primary cells from an EDMD-2 patient with lamin A/C mutated in the Akt consensus motif. Together, our data demonstrate that lamin A/C is a novel signaling target of Akt, and implicate Akt phosphorylation of lamin A/C in the correct function of the nuclear lamina.

HMG-CoA reductase inhibition induces IL-1beta release through Rac1/PI3K/PKB-dependent caspase-1 activation

Mevalonate kinase deficiency (MKD) is an autoinflammatory disorder characterized by recurring fever episodes and results from disturbed isoprenoid biosynthesis. Lipopolysaccharide-stimulated peripheral blood mononuclear cells from MKD patients secrete high levels of interleukin-1beta (IL-1beta) because of the presence of hyperactive caspase-1, and this has been proposed to be the primary cause of recurring inflammation. Here we show that inhibition of HMG-CoA reductase by simvastatin treatment, mimicking MKD, results in increased IL-1beta secretion in a Rac1/PI3K-dependent manner. Simvastatin treatment was found to activate protein kinase B (PKB)/c-akt, a primary effector of PI3K, and ectopic expression of constitutively active PKB was sufficient to induce IL-1beta release. The small GTPase Rac1 was activated by simvastatin, and this was required for both PKB activation and IL-1beta secretion. IL-1beta release is mediated by caspase-1, and simvastatin treatment resulted in increased caspase-1 activity in a Rac1/PI3K-dependent manner. These data suggest that, in MKD, dysregulated isoprenoid biosynthesis activates Rac1/PI3K/PKB, resulting in caspase-1 activation with increased IL-1beta release. Importantly, inhibition of Rac1 in peripheral blood mononuclear cells isolated from MKD patients resulted in a dramatic reduction in IL-1beta release. These data suggest that pharmacologic inhibition of Rac1 could provide a novel therapeutic strategy for treatment of MKD.

The regulation of cell motility and chemotaxis by phospholipid signaling

Phosphoinositide 3-kinase (PI3K), PTEN and localized phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] play key roles in chemotaxis, regulating cell motility by controlling the actin cytoskeleton in Dictyostelium and mammalian cells. PtdIns(3,4,5)P3, produced by PI3K, acts via diverse downstream signaling components, including the GTPase Rac, Arf-GTPases and the kinase Akt (PKB). It has become increasingly apparent, however, that chemotaxis results from an interplay between the PI3K-PTEN pathway and other parallel pathways in Dictyostelium and mammalian cells. In Dictyostelium, the phospholipase PLA2 acts in concert with PI3K to regulate chemotaxis, whereas phospholipase C (PLC) plays a supporting role in modulating PI3K activity. In adenocarcinoma cells, PLC and the actin regulator cofilin seem to provide the direction-sensing machinery, whereas PI3K might regulate motility.