Caveolins and caveolae: molecular and functional relationships

Using evolutionary data to make sense of macromolecules with a "face-lifted" ConSurf

The ConSurf web-sever for the analysis of proteins, RNA, and DNA provides a quick and accurate estimate of the per-site evolutionary rate among homologues. The analysis reveals functionally important regions, such as catalytic and ligand-binding sites, which often evolve slowly. Since the last report in 2016, ConSurf has been improved in multiple ways. It now has a user-friendly interface that makes it easier to perform the analysis and to visualize the results. Evolutionary rates are calculated based on a set of homologous sequences, collected using hidden Markov model-based search tools, recently embedded in the pipeline. Using these, and following the removal of redundancy, ConSurf assembles a representative set of effective homologues for protein and nucleic acid queries to enable informative analysis of the evolutionary patterns. The analysis is particularly insightful when the evolutionary rates are mapped on the macromolecule structure. In this respect, the availability of AlphaFold model structures of essentially all UniProt proteins makes ConSurf particularly relevant to the research community. The UniProt ID of a query protein with an available AlphaFold model can now be used to start a calculation. Another important improvement is the Python re-implementation of the entire computational pipeline, making it easier to maintain. This Python pipeline is now available for download as a standalone version. We demonstrate some of ConSurf's key capabilities by the analysis of caveolin-1, the main protein of membrane invaginations called caveolae.

Epidermal growth factor regulates autophagy activity and endocytosis of yak cumulus cells in a concentration-dependent manner

Introduction

Autophagy and endocytosis are crucial biological activities in mammalian follicle development and oocyte maturation, which are easily affected by external environmental factors. Epidermal growth factor (EGF), as an important component of follicular fluid, regulates the growth and apoptosis of follicular cells. However, its regulatory mechanism of autophagy and endocytosis in mammals, especially in large domestic animals such as plateau yak, remains unclear. This study aimed to investigate the regulatory mechanism of EGF on autophagy and endocytosis in yak cumulus cells.

Methods

Yak cumulus cells were treated with different concentrations of EGF and appropriate concentrations of EGFR inhibitor gefitinib (10 μM). The dynamic expression levels of Atg5, Beclin1, LC3, Cav1 and Cav2 were detected by immunofluorescence staining, qRT-PCR and Western-blot.

Results

EGF inhibited autophagy in yak cumulus cells by down-regulating the expression of Atg5, Beclin1, and LC3. The level of autophagy varied with the concentration of ligands, and the inhibition was most significant at 100 ng/mL. Noteworthy, EGF can promote endocytosis by regulating the expression of Cav1 and Cav2, but the EGFR-mediated signaling pathway is not the main way to regulate the expression of these proteins.

Discussion

These results provide a reference for further exploring the effects of growth factors on livestock germ cells and the regulatory role of autophagy-endocytosis crosstalk mechanism in follicle development and oocyte maturation, to improve the fecundity of yaks.

Caveolin-1 regulates OMV-induced macrophage pro-inflammatory activation and multiple Toll-like receptors

Macrophages (MФ), the primary cell of the innate immune system, serves as the first line of defense. During bacterial infection, Gram-negative (G-) bacteria release nanosized outer membrane vesicles (OMVs), facilitating the crosstalk between the microbe and the host. The underlying mechanisms by which OMVs induced pro-inflammatory (M1) activation are still unknown. Our study shows that OMVs caused M1 activation via modulating various toll-like receptor (TLR) expressions as they contain LPS, LTA, bacterial DNAs, and flagellins. Also, we found that caveolin-1 (cav-1), a 21-kDa scaffolding protein of caveolae and lipid rafts, plays a significant role in OMV-induced pro-inflammatory response in regulating various TLR signaling pathways. Specifically, cav-1 deletion increased the expression of OMV-induced TLRs, pro-inflammatory cytokine secretions (TNF-α and IL-1β), and the reactive oxygen species (ROS) production in MФs. Further, we examined the interaction between Cav-1 and TLR4 by immunoprecipitation, colocalization, and computational models, providing future direction to explore the role of cav-1 in OMV-induced other TLR signaling. Altogether, Cav-1 is a key regulator in OMV-induced multiple TLRs response. This study promotes future research to develop drugs by targeting the specific motif of cav-1 or TLRs against bacterial infection and macrophage-mediated inflammation.

Isoliquiritigenin alleviates liver fibrosis through caveolin-1-mediated hepatic stellate cells ferroptosis in zebrafish and mice

BACKGROUND

Liver fibrosis is a major disease that threatens people's health around the world. However, there is a lack of effective treatment to completely reverse liver fibrosis. Liver transplantation is currently the only curative option for patients with advanced cirrhosis. Ferroptosis is a newly discovered type of cell death and plays an important role in the process of liver fibrosis, but the specific mechanism needs to be clarified.

HYPOTHESIS/PURPOSE

To explore the regulatory mechanism of isoliquiritigenin (ISL) in the process of liver fibrosis and the relationship between Cav-1 and ferroptosis.

METHODS

In this research, zebrafish, HSC-T6 cells, and mice were used as the research object. Different ROS probes to visually detect the content and distribution of ROS in live zebrafish and cells. Lentivirus and siRNA-mediated transfection techniques were used for the construction of Cav-1 overexpression and knockdown cell lines to verify the important role of Cav-1 in vitro.

RESULTS

Generally, we first elucidated that ISL relieved liver fibrosis by inducing hepatic stellate cells (HSCs) ferroptosis through repressing GPX4 expression and increasing the expression of TFR and DMT1, thus producing a large number of ROS, we also found that Cav-1 exerted its anti-hepatic fibrosis effect by promoting HSCs ferroptosis.

CONCLUSION

Our results have shown that Cav-1-mediated HSCs ferroptosis is necessary for ISL to play an anti-fibrotic effect in vitro and in vivo.

Annexins and Membrane Repair Dysfunctions in Muscular Dystrophies

Muscular dystrophies constitute a group of genetic disorders that cause weakness and progressive loss of skeletal muscle mass. Among them, Miyoshi muscular dystrophy 1 (MMD1), limb girdle muscular dystrophy type R2 (LGMDR2/2B), and LGMDR12 (2L) are characterized by mutation in gene encoding key membrane-repair protein, which leads to severe dysfunctions in sarcolemma repair. Cell membrane disruption is a physiological event induced by mechanical stress, such as muscle contraction and stretching. Like many eukaryotic cells, muscle fibers possess a protein machinery ensuring fast resealing of damaged plasma membrane. Members of the annexins A (ANXA) family belong to this protein machinery. ANXA are small soluble proteins, twelve in number in humans, which share the property of binding to membranes exposing negatively-charged phospholipids in the presence of calcium (Ca²⁺). Many ANXA have been reported to participate in membrane repair of varied cell types and species, including human skeletal muscle cells in which they may play a collective role in protection and repair of the sarcolemma. Here, we discuss the participation of ANXA in membrane repair of healthy skeletal muscle cells and how dysregulation of ANXA expression may impact the clinical severity of muscular dystrophies.

Presence of Titanium and Toxic Effects Observed in Rat Lungs, Kidneys, and Central Nervous System in vivo and in Cultured Astrocytes in vitro on Exposure by Titanium Dioxide Nanorods

Background

Non-spherical titanium dioxide (TiO₂) nanoparticles have been increasingly applied in various biomedical and technological fields. Their toxicological characterization is, however, less complete than that of roundish nanoparticles.

Materials and Methods

Anatase form TiO₂ nanorods, ca. 15x65 nm in size, were applied to cultured astrocytes in vitro and to the airways of young adult Wistar rats in vivo in 5, 10, and 8 mg/kg BW dose for altogether 28 days. Presence of nanorods and cellular damage was investigated in the astrocytes and in rat lungs and kidneys. Functional damage of the nervous system was studied by electrophysiological methods.

Results

The treated astrocytes showed loss of viability without detectable apoptosis. In rats, TiO₂ nanorods applied to the airways reached the blood and various organs including the lungs, kidneys, and the central nervous system. In lung and kidney samples, nanorods were observed within (partly damaged) phagolysosomes and attached to organelles, and apoptotic cell death was also detected. In cortical and peripheral electrophysiological activity, alterations corresponding to energy shortage (resulting possibly from mitochondrial damage) and astrocytic dysfunction were detected. Local titanium levels and relative weight of the investigated organs, apoptotic cell death in the lungs and kidneys, and changes in the central and peripheral nervous activity were mostly proportional to the applied doses, and viability loss of the cultured astrocytes was also dose-dependent, suggesting causal relationship of treatments and effects.

Conclusion

Based on localization of the visualized nanorods, on neuro-functional changes, and on literature data, the toxic mechanism involved mitochondrial damage, oxidative stress, and apoptotic cell death. These indicate potential human toxicity and occupational risk in case of exposure to rod-shaped TiO₂ nanoparticles.

Dysregulation of Signaling Pathways Due to Differentially Expressed Genes From the B-Cell Transcriptomes of Systemic Lupus Erythematosus Patients - A Bioinformatics Approach

Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disorder that is clinically complex and has increased production of autoantibodies. Via emerging technologies, researchers have identified genetic variants, expression profiling of genes, animal models, and epigenetic findings that have paved the way for a better understanding of the molecular and genetic mechanisms of SLE. Our current study aimed to illustrate the essential genes and molecular pathways that are potentially involved in the pathogenesis of SLE. This study incorporates the gene expression profiling data of the microarray dataset GSE30153 from the Gene Expression Omnibus (GEO) database, and differentially expressed genes (DEGs) between the B-cell transcriptomes of SLE patients and healthy controls were screened using the GEO2R web tool. The identified DEGs were subjected to STRING analysis and Cytoscape to explore the protein-protein interaction (PPI) networks between them. The MCODE (Molecular Complex Detection) plugin of Cytoscape was used to screen the cluster subnetworks that are highly interlinked between the DEGs. Subsequently, the clustered DEGs were subjected to functional annotation with ClueGO/CluePedia to identify the significant pathways that were enriched. For integrative analysis, we used GeneGo MetacoreTM, a Cortellis Solution software, to exhibit the Gene Ontology (GO) and enriched pathways between the datasets. Our study identified 4 upregulated and 13 downregulated genes. Analysis of GO and functional enrichment using ClueGO revealed the pathways that were statistically significant, including pathways involving T-cell costimulation, lymphocyte costimulation, negative regulation of vascular permeability, and B-cell receptor signaling. The DEGs were mainly enriched in metabolic networks such as the phosphatidylinositol-3,4,5-triphosphate pathway and the carnitine pathway. Additionally, potentially enriched pathways, such as the signaling pathways induced by oxidative stress and reactive oxygen species (ROS), chemotaxis and lysophosphatidic acid signaling induced via G protein-coupled receptors (GPCRs), and the androgen receptor activation pathway, were identified from the DEGs that were mainly associated with the immune system. Four genes (EGR1, CD38, CAV1, and AKT1) were identified to be strongly associated with SLE. Our integrative analysis using a multitude of bioinformatics tools might promote an understanding of the dysregulated pathways that are associated with SLE development and progression. The four DEGs in SLE patients might shed light on the pathogenesis of SLE and might serve as potential biomarkers in early diagnosis and as therapeutic targets for SLE.

GPMVs as a Tool to Study Caveolin-Interacting Partners

Caveolins, major components of small plasma membrane invaginations called caveolae, play a role in signaling, particularly in mechanosignaling. These proteins are known to interact with a variety of effector molecules, including G-protein-coupled receptors, Src family kinases, ion channels, endothelial nitric oxide synthase (eNOS), adenylyl cyclases, protein kinase A (PKA), and mitogen-activated PKs (MAPKs). There is, however, speculation on the relevance of these interactions and the mechanisms by which caveolins may control intracellular signaling. This chapter introduces a method of isolation of giant plasma membrane-derived vesicles (GPMVs), which possess full complexity of membrane they originate from, thus comprising an excellent platform to revisit some of the previously described interactions in a cleaner environment and possibly identifying new binding partners. It is also a powerful technique for studying membrane mechanics, as it was previously used to demonstrate the role of caveolae in mechanoprotection.

Immunofluorescence-Based Analysis of Caveolin-3 in the Diagnostic Management of Neuromuscular Diseases

Immunohistochemistry- and/or immunofluorescence-based analysis of muscular proteins represents a standard procedure in the diagnostic management of patients suffering from neuromuscular diseases such as "Caveolinopathies" which are caused by mutations in the CAV3 gene encoding for caveolin-3. Human caveolin-3 is a 151 amino acid sized transmembrane protein localized within caveolae, predominantly expressed in cardiac and skeletal muscle cells and involved in a diversity of cellular functions crucial for muscle cell homeostasis. Loss of caveolin-3 protein abundance is indicative for the presence of pathogenic mutations within the corresponding gene and thus for the diagnosis of "Caveolinopathies." Moreover, description of abnormal immunoreactivity findings for the caveolin-3 protein is increasing in the context of other neuromuscular diseases suggesting that profound knowledge of abnormal caveolin-3-expression and/or distribution findings can be decisive also for the diagnosis of other neurological diseases as well as for a better understanding of the biology of the protein. Here, we summarize the current knowledge about the caveolin-3, report on a protocol for immunofluorescence-based analysis of the protein in the diagnostic workup of neuromuscular patients-also considering problems encountered-and confirm as well as summarize already published abnormal histological findings in muscular pathologies beyond "Caveolinopathies."

Depletion of Caveolin-1 in Type 2 Diabetes Model Induces Alzheimer's Disease Pathology Precursors

Type 2 diabetes mellitus (T2DM) is a risk factor for the development of late-onset Alzheimer's disease (AD). However, the mechanism underlying the development of late-onset AD is largely unknown. Here we show that levels of the endothelial-enriched protein caveolin-1 (Cav-1) are reduced in the brains of T2DM patients compared with healthy aging, and inversely correlated with levels of β-amyloid (Aβ). Depletion of Cav-1 is recapitulated in the brains of db/db (Leprdb ) diabetic mice and corresponds with recognition memory deficits as well as the upregulation of amyloid precursor protein (APP), BACE-1, a trending increase in β-amyloid Aβ42/40 ratio and hyperphosphorylated tau (p-tau) species. Importantly, we show that restoration of Cav-1 levels in the brains of male db/db mice using adenovirus overexpressing Cav-1 (AAV-Cav-1) rescues learning and memory deficits and reduces pathology (i.e., APP, BACE-1 and p-tau levels). Knocking down Cav-1 using shRNA in HEK cells expressing the familial AD-linked APPswe mutant variant upregulates APP, APP carboxyl terminal fragments, and Aβ levels. In turn, rescue of Cav-1 levels restores APP metabolism. Together, these results suggest that Cav-1 regulates APP metabolism, and that depletion of Cav-1 in T2DM promotes the amyloidogenic processing of APP and hyperphosphorylation of tau. This may suggest that depletion of Cav-1 in T2DM underlies, at least in part, the development of AD and imply that restoration of Cav-1 may be a therapeutic target for diabetic-associated sporadic AD.SIGNIFICANCE STATEMENT More than 95% of the Alzheimer's patients have the sporadic late-onset form (LOAD). The cause for late-onset Alzheimer's disease is unknown. Patients with Type 2 diabetes mellitus have considerably higher incidence of cognitive decline and AD compared with the general population, suggesting a common mechanism. Here we show that the expression of caveolin-1 (Cav-1) is reduced in the brain in Type 2 diabetes mellitus. In turn, reduced Cav-1 levels induce AD-associated neuropathology and learning and memory deficits. Restoration of Cav-1 levels rescues these deficits. This study unravels signals underlying LOAD and suggests that restoration of Cav-1 may be an effective therapeutic target.

Membrane-bound estrogen receptor alpha initiated signaling is dynamin dependent in breast cancer cells

Background

Although membrane-associated estrogen receptors (mERs) have been known to play important role in steroid-induced signal transmission, we still know little about their function in the estrogen-induced proliferation of breast cancer cells.

Methods

In our current work we tried to separate membrane-initiated estrogen receptor signaling from the overall estrogenic effect in MCF-7 breast carcinoma cells. Re-analyzing expression data from multiple microarray experiments, we selected a set of key regulatory genes involved in proliferation regulation and estrogen signaling to monitor estrogen-induced transcription changes. We then compared these expression changes after 17β-estradiol and a membrane receptor selective estrogen–BSA treatment using quantitative real-time PCR. In order to follow receptor trafficking we used light and electron microscopy.

Results

Our quantitative real-time PCR results confirmed that the selective membrane receptor agonist, estrogen–BSA induces similarly pronounced expression changes regarding these genes as 17β-estradiol. Morphological study revealed that the membrane-bound form of classical estrogen receptor alpha is internalized after ligand binding via dynamin-dependent, caveola-mediated endocytosis. Inhibition of this internalization with dynamin inhibitor, dynasore practically abolished the regulatory effect of E2-BSA, suggesting that interaction and internalization with the scaffold protein is necessary for effective signaling.

Conclusions

The physiological role of plasma membrane estrogen receptor alpha is intensively studied, yet there are still several aspects of it to be resolved. The dynamin-dependent, ligand-mediated internalization of mERs seems to play an important role in estrogen signaling. Our results may serve as another example of how membrane initiated estrogen signaling and nuclear receptor initiated signaling overlap and form an intertwined system. 

Electronic supplementary material

The online version of this article (10.1186/s40001-018-0328-7) contains supplementary material, which is available to authorized users.

Quantitative proteomic Analysis Reveals up-regulation of caveolin-1 in FOXP3-overexpressed human gastric cancer cells

Forkhead box protein 3 (FOXP3) is implicated in tumor progression and prognosis in various types of tumor cells. We have recently reported that FOXP3 inhibited proliferation of gastric cancer (GC) cells through activating the apoptotic signaling pathway. In this study, we found that over-expression of FOXP3 inhibited GC cell migration, invasion and proliferation. Then, the label-free quantitative proteomic approach was employed to further investigating the down-stream proteins regulated by FOXP3, resulting in a total of 3,978 proteins quantified, including 186 significantly changed proteins. Caveolin-1 (CAV1), as a main constituent protein of caveolae, was one of those changed proteins up-regulated in FOXP3-overexpressed GC cells, moreover, it was assigned as one of the node proteins in the protein-protein interaction network and the key protein involved in focal adhesion pathway by bioinformatics analysis. Further biological experiments confirmed that FOXP3 directly bound to the promoter regions of CAV1 to positively regulate CAV1 transcription in GC cells. In summary, our study suggested that FOXP3 can be considered as a tumor suppressor in GC via positively regulating CAV1 through transcriptional activation, and this FOXP3-CAV1 transcriptional regulation axis may play an important role in inhibiting invasion and metastasis of GC cells. Data are available via ProteomeXchange under identifier PXD007725.

Roxithromycin suppresses airway remodeling and modulates the expression of caveolin-1 and phospho-p42/p44MAPK in asthmatic rats

Roxithromycin (RXM) expresses anti-asthmatic effects that are separate from its antibiotic activity, but its effects on airway remodeling are still unknown. Here, we evaluated the effects of RXM on airway remodeling and the expression of caveolin-1 and phospho-p42/p44mitogen-activated protein kinase (phospho-p42/p44MAPK) in chronic asthmatic rats. The chronic asthma was induced by ovalbumin/Al(OH)3 sensitization and ovalbumin challenge, RXM (30mg/kg) or dexamethasone (0.5mg/kg) was given before airway challenge initiation. We measured the thickness of bronchial wall and bronchial smooth muscle cell layer to indicate airway remodeling, and caveolin-1 and phospho-p42/p44MAPK expression in lung tissue and airway smooth muscle were detected by immunohistochemistry and western blot analysis, respectively. The results demonstrated that RXM treatment decreased the thickness of bronchial wall and bronchial smooth muscle cell layer, and also downregulated the phospho-p42/p44MAPK expression and upregulated the caveolin-1 expression. The above effects of RXM were similar to dexamethasone. Our results suggested that pretreatment with RXM could suppress airway remodeling and regulate the expression of caveolin-1 and phospho-p42/p44MAPK in chronic asthmatic rats.

Caveolin-1 in oral squamous cell carcinoma microenvironment: an overview

Caveolin-1 plays an important role in the pathogenesis of oncogenic cell transformation, tumorigenesis, and metastasis. Increased expression of caveolin-1 in an array of tumors has confirmed its value in prognosis. It has been established that oxidative stress is the main cause for loss of stromal caveolin-1 via autophagy in the tumor microenvironment. In this overview, we attempt to abridge the relationship between caveolin-1 and oral squamous cell carcinoma, taking all the established theories into consideration.

The interaction of enolase-1 with caveolae-associated proteins regulates its subcellular localization

Cell-surface-associated proteolysis plays a crucial role in embryonic development, monocyte/macrophage recruitment and tumour cell invasion. The glycolytic enzyme ENO-1 (enolase-1) is translocated from the cytoplasm to the cell surface, where it binds PLG (plasminogen) to enhance pericellular plasmin production and cell motility. In the present study, ENO-1 was found to localize to a specialized subset of lipid rafts called caveolae as demonstrated by fluorescence confocal microscopy and sucrose gradient ultracentrifugation. Co-immunoprecipitation studies revealed that ENO-1 interacts with Cav-1 (caveolin-1), but not with Cav-2, via the CSD (Cav-scaffolding domain). Moreover, an evolutionarily conserved CBM (Cav-binding motif) F296DQDDWGAW304 was identified within ENO-1. The point mutation W301A within the ENO-1 CBM was, however, not sufficient to disrupt ENO-1-Cav-1 interaction, whereas the mutations F296A and W304A markedly affected ENO-1 protein expression. Furthermore, ENO-1 was found associated with Annx2 (annexin 2), representing another caveolar protein, and this interaction was dependent on Cav-1 expression. Knockdown of Cav-1 and Annx2 markedly decreased cell surface expression of ENO-1. ENO-1 overexpression increased cell migration and invasion in a Cav-1-dependent manner. Thus the differential association of ENO-1 with caveolar proteins regulates ENO-1 subcellular localization and, consequently, ENO-1-dependent cell migration and invasion.

The expression of dual oxidase, thyroid peroxidase, and caveolin-1 differs according to the type of immune response (TH1/TH2) involved in thyroid autoimmune disorders

CONTEXT

Hashimoto's thyroiditis (HT) and Graves' disease (GD) are thyroid autoimmune disorders driven by Th1 and Th2 immune responses, respectively. Caveolin-1 (Cav-1), thyroid peroxidase (TPO), and dual oxidase (DUOX) are thought to be part of the thyroxisome, which is essential to maintain thyroid hormone synthesis, at the apical membrane.

OBJECTIVES

To analyze the thyroxisome in HT and GD thyroids, we investigated Cav-1, DUOX, and TPO expression as well as markers of oxidative stress (OS), cell proliferation, apoptosis, and antioxidant defenses. The effects of cytokines on Cav-1 expression were analyzed in vitro.

RESULTS

In HT, the decrease in Cav-1, DUOX, and TPO expression was marked in follicles having the morphological aspect of active follicles in normal glands and thus called active-like follicles. T4 was not detected in the colloid but in the cytoplasm as well as DUOX and TPO. These abnormalities were associated with increased OS and cell damage. In the hypofunctioning follicles of HT and normal thyroids, Cav-1, DUOX, and TPO were not expressed. In GD, they were expressed at the apical pole of thyrocytes, and T4 accumulated in the colloid of all follicles. Th1 cytokines IL-1α/interferonγ decreased Cav-1 expression in vitro, whereas the Th2 cytokine IL-4 had no effect.

CONCLUSION

Th1 cytokine-induced down-regulation of Cav-1 could be responsible for intracytoplasmic T4 synthesis and mislocalization of DUOX and TPO, suggesting an important role for Cav-1 in the preservation of thyroxisome integrity. The thyroxisome's disruption, leading to uncontrolled OS and cell apoptosis, is a key, event in HT pathogenesis.

Akt and RhoA activation in response to high glucose require caveolin-1 phosphorylation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic renal disease. Serine/threonine kinase PKC-β1 mediates glucose-induced Akt S473 phosphorylation, RhoA activation, and transforming growth factor (TGF)-β1 upregulation and finally leads to matrix upregulation in mesangial cells (MCs). It has been reported that glucose-induced PKC-β1 activation is dependent on caveolin-1 and the presence of intact caveolae in MCs; however, whether activated PKC-β1 regulates caveolin-1 expression and phosphorylation are unknown. Here, we showed that, although the caveolin-1 protein level had no significant change, the PKC-β-specific inhibitor LY-333531 blocked caveolin-1 Y14 phosphorylation in high glucose (HG)-treated MCs and in the renal cortex of diabetic rats. The Src-specific inhibitor SU-6656 prevented the HG-induced association between PKC-β1 and caveolin-1 and PKC-β1 membrane translocation, whereas PKC-β1 small interfering RNA failed to block Src activation, indicating that Src kinase is upstream of PKC-β1 activation. Although LY-333531 blocked PKC-β1 membrane translocation, it had no effect on the PKC-β1/caveolin-1 association, suggesting that PKC-β1 activation requires the interaction of caveolin-1 and PKC-β1. PKC-β1-mediated Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation in response to HG were prevented by SU-6656 and nonphosphorylatable mutant caveolin-1 Y14A. In conclusion, Src activation by HG mediates the PKC-β1/caveolin-1 association and PKC-β1 activation, which assists in caveolin-1 Y14 phosphorylation by Src kinase. The downstream effects, including Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation, require caveolin-1 Y14 phosphorylation. Caveolin-1 is thus an important mediator of the profibrogenic process in diabetic renal disease.

Vasopressin induces apical expression of caveolin in rat kidney collecting duct principal cells

Caveolin (Cav)1 is expressed in the basolateral membrane domain of renal collecting duct (CD) principal cells (PCs), where it is associated with caveolae. To reveal any potential involvement of Cav1 in vasopressin signaling, we used specific monoclonal and polyclonal antibodies to examine its localization in CD PCs of Brattleboro (BB) rats treated with vasopressin (DDAVP). Compared with controls, immunofluorescence revealed a time-dependent increase in Cav1 expression in the apical membrane domain of PCs, where it overlapped with aquaporin-2 (AQP2). After 24 h of DDAVP treatment, Cav1 was visible as an increased number of small apical spots. The staining gradually became more extensive, and, after 2 wk of DDAVP, it occupied the majority of the apical membrane domain of many PCs. Cav1 also assumed an apical localization in PCs of DDAVP-treated Sprague-Dawley and Long-Evans rats. Similarly, Cav2 appeared at the apical pole of PCs after DDAVP treatment of BB, Sprague-Dawley, and Long-Evans rats. Immunogold electron microscopy confirmed bipolar Cav1 membrane expression in DDAVP-treated BB rats, whereas caveolae were only detected on the basolateral membrane. Immunoblot analysis of BB rat whole kidney homogenates revealed no significant increase in Cav1 levels in DDAVP-treated rats, suggesting that DDAVP induces Cav1 relocalization or modifies its targeting. We conclude that Cav1 and Cav2 trafficking and membrane localization are dramatically altered by the action of DDAVP. Importantly, the absence of apical caveolae indicates that while Cavs may have an as yet undetermined role in vasopressin-regulated signaling processes, this is probably unrelated to AQP2 internalization by caveolae.

Ca2+ influx and tyrosine kinases trigger Bordetella adenylate cyclase toxin (ACT) endocytosis. Cell physiology and expression of the CD11b/CD18 integrin major determinants of the entry route

Humans infected with Bordetella pertussis, the whooping cough bacterium, show evidences of impaired host defenses. This pathogenic bacterium produces a unique adenylate cyclase toxin (ACT) which enters human phagocytes and catalyzes the unregulated formation of cAMP, hampering important bactericidal functions of these immune cells that eventually cause cell death by apoptosis and/or necrosis. Additionally, ACT permeabilizes cells through pore formation in the target cell membrane. Recently, we demonstrated that ACT is internalised into macrophages together with other membrane components, such as the integrin CD11b/CD18 (CR3), its receptor in these immune cells, and GM1. The goal of this study was to determine whether ACT uptake is restricted to receptor-bearing macrophages or on the contrary may also take place into cells devoid of receptor and gain more insights on the signalling involved. Here, we show that ACT is rapidly eliminated from the cell membrane of either CR3-positive as negative cells, though through different entry routes, which depends in part, on the target cell physiology and characteristics. ACT-induced Ca(2+) influx and activation of non-receptor Tyr kinases into the target cell appear to be common master denominators in the different endocytic strategies activated by this toxin. Very importantly, we show that, upon incubation with ACT, target cells are capable of repairing the cell membrane, which suggests the mounting of an anti-toxin cell repair-response, very likely involving the toxin elimination from the cell surface.

Effects of caveolin-1 and P-ERK1/2 on Ang II-induced glomerular mesangial cell proliferation

This study explored the effects of caveolin-1, p-ERK1/2 and transient receptor potential channel 6 (TRPC6) on angiotensin II (Ang II)-induced glomerular mesangial cell (GMC) proliferation, and investigated the role of Ang II on GMC proliferation. GMC cultures were divided into Control, Ang II (Ang II 10(-7 )mol/L), PD98059 (Ang II 10(-7 )mol/L + PD98059 5 × 10(-5 )mol/L) and MβCD groups (Ang II 10(-7 )mol/L + MβCD 10(-2 )mol/L). GMCs proliferation was measured by the methyl thiazolil tetracolium and trypan blue assays. The distribution of caveolin-1, p-ERK1/2 and TRPC6 was monitored by immunocytochemistry. Real time polymerase chain reaction (PCR) was used to assess mRNA expression of caveolin-1 and TRPC6. Western blot analysis was used to assess protein expression of caveolin-1, p-ERK1/2 and TRPC6. The results showed that Ang II promoted GMC proliferation. PD98059 and MβCD blocked Ang II-induced GMC proliferation, by 31.06% and 48.96%, respectively. In comparison with the control group, the expression of p-ERK1/2 and TRPC6 was significantly higher and caveolin-1 expression was significantly lower in the Ang II group. PD98059 markedly decreased p-ERK1/2 and TRPC6 expression and increased caveolin-1 expression. MβCD decreased the expression of p-ERK1/2 and TRPC6, but had no significant effect on caveolin-1 protein expression. These findings suggested that the intact caveolae structure was associated with Ang II-induced GMC proliferation, ERK1/2 activation and TRPC6 expression. And p-ERK1/2 acted as an upstream signal molecule for TRPC6. Moreover, p-ERK1/2 and caveolin-1 appeared to be inhibited reciprocally, thus regulated GMC proliferation by regulating TRPC6 expression.

New advances in urea transporter UT-A1 membrane trafficking

The vasopressin-regulated urea transporter UT-A1, expressed in kidney inner medullary collecting duct (IMCD) epithelial cells, plays a critical role in the urinary concentrating mechanisms. As a membrane protein, the function of UT-A1 transport activity relies on its presence in the plasma membrane. Therefore, UT-A1 successfully trafficking to the apical membrane of the polarized epithelial cells is crucial for the regulation of urea transport. This review summarizes the research progress of UT-A1 regulation over the past few years, specifically on the regulation of UT-A1 membrane trafficking by lipid rafts, N-linked glycosylation and a group of accessory proteins.

Role of caveolin-1 in fibrotic diseases

Fibrosis underlies the pathogenesis of numerous diseases and leads to severe damage of vital body organs and, frequently, to death. Better understanding of the mechanisms resulting in fibrosis is essential for developing appropriate treatment solutions and is therefore of upmost importance. Recent evidence suggests a significant antifibrotic potential of an integral membrane protein, caveolin-1. While caveolin-1 has been widely studied for its role in the regulation of cell signaling and endocytosis, its possible implication in fibrosis remains largely unclear. In this review we survey involvement of caveolin-1 in various cellular processes and highlight different aspects of its antifibrotic activity. We hypothesize that caveolin-1 conveys a homeostatic function in the process of fibrosis by (a) regulating TGF-β1 and its downstream signaling; (b) regulating critical cellular processes involved in tissue repair, such as migration, adhesion and cellular response to mechanical stress; and (c) antagonizing profibrotic processes, such as proliferation. Finally, we consider this homeostatic function of caveolin-1 as a possible novel approach in treatment of fibroproliferative diseases.

Cav1 suppresses tumor growth and metastasis in a murine model of cutaneous SCC through modulation of MAPK/AP-1 activation

Caveolin-1 (Cav1) is a scaffolding protein that serves to regulate the activity of several signaling molecules. Its loss has been implicated in the pathogenesis of several types of cancer, but its role in the development and progression of cutaneous squamous cell carcinoma (cSCC) remains largely unexplored. Herein, we use the keratinocyte cell line PAM212, a murine model of cSCC, to determine the function of Cav1 in skin tumor biology. We first show that Cav1 overexpression decreases cell and tumor growth, whereas Cav1 knockdown increases these attributes in PAM212 cells. In addition, Cav1 knockdown increases the invasive ability and incidence of spontaneous lymph node metastasis. Finally, we demonstrate that Cav1 knockdown increases extracellular signaling-related kinase 1/2 mitogen-activated protein kinase/activator protein-1 pathway activation. We attribute the growth and invasive advantage conferred by Cav1 knockdown to increased expression of activator protein-1 transcriptional targets, including cyclin D1 and keratin 18, which show inverse expression in PAM212 based on the expression level of Cav1. In summary, we demonstrate that loss of Cav1 affects several characteristics associated with aggressive human skin tumors and that this protein may be an important modulator of tumor growth and invasion in cSCC.

Caveolin-1 deficiency induces spontaneous endothelial-to-mesenchymal transition in murine pulmonary endothelial cells in vitro

It was previously demonstrated that transforming growth factor β (TGF-β) induces endothelial-to-mesenchymal transition (EndoMT) in murine lung endothelial cells (ECs) in vitro. Owing to the important role of caveolin-1 (CAV1) in TGF-β receptor internalization and TGF-β signaling, the participation of CAV1 in the induction of EndoMT in murine lung ECs was investigated. Pulmonary ECs were isolated from wild-type and Cav1 knockout mice using immunomagnetic methods with sequential anti-CD31 and anti-CD102 antibody selection followed by in vitro culture and treatment with TGF-β1. EndoMT was assessed by semiquantitative RT-PCR for Acta2, Col1a1, Snai1, and Snai2; by immunofluorescence for α-smooth muscle actin; and by Western blot analysis for α-smooth muscle actin, SNAIL1, SNAIL2, and the α2 chain of type I collagen. The same studies were performed in Cav1(-/-) pulmonary ECs after restoration of functional CAV1 domains using a cell-permeable CAV1 scaffolding domain peptide. Pulmonary ECs from Cav1 knockout mice displayed high levels of spontaneous Acta2, Col1A, Snai1, and Snai2 expression, which increased after TGF-β treatment. Spontaneous and TGF-β1-stimulated EndoMT were abrogated by the restoration of functional CAV1 domains using a cell-permeable peptide. The findings suggest that CAV1 regulation of EndoMT may play a role in the development of fibroproliferative vasculopathies.

Detection of caveolin-3/caveolin-1/P2X7R complexes in mice atrial cardiomyocytes in vivo and in vitro

Caveolae and caveolins, structural components of caveolae, are associated with specific ion channels in cardiac myocytes. We have previously shown that P2X purinoceptor 7 (P2X7R), a ligand-gated ion channel, is increased in atrial cardiomyocytes of caveolin-1 knockout mice; however, the specific biochemical relationship of P2X7R with caveolins in the heart is not clear. The aim of this work was to study the presence of the P2X7R in atrial cardiomyocytes and its biochemical relationship to caveolin-1 and caveolin-3. Caveolin isoforms and P2X7R were predominantly localized in buoyant membrane fractions (lipid rafts/caveolae) prepared from hearts using detergent-free sucrose gradient centrifugation. Caveolin-1 knockout mice showed normal distribution of caveolin-3 and P2X7R to buoyant membranes indicating the importance of caveolin-3 to formation of caveolae. Using clear native-PAGE, we showed that caveolin-1, -3 and P2X7R contribute to the same protein complex in the membranes of murine cardiomyocytes and in the immortal cardiomyocyte cell line HL-1. Western blot analysis revealed increased caveolin-1 and -3 proteins in tissue homogenates of P2X7R knockout mice. Finally, tissue homogenates of atrial tissues from caveolin-3 knockout mice showed elevated mRNA for P2X7R in atria. The colocalization of caveolins with P2X7R in a biochemical complex and compensated upregulation of P2X7R or caveolins in the absence of any component of the complex suggests P2X7R and caveolins may serve an important regulatory control point for disease pathology in the heart.

Caveolae and propofol effects on airway smooth muscle

BACKGROUND

The i.v. anaesthetic propofol produces bronchodilatation. Airway relaxation involves reduced intracellular Ca(2+) ([Ca(2+)](i)) in airway smooth muscle (ASM) and lipid rafts (caveolae), and constitutional caveolin proteins regulate [Ca(2+)](i). We postulated that propofol-induced bronchodilatation involves caveolar disruption.

METHODS

Caveolar fractions of human ASM cells were tested for propofol content. [Ca(2+)](i) responses of ASM cells loaded with fura-2 were performed in the presence of 10 µM histamine with and without clinically relevant concentrations of propofol (10 and 30 μM and intralipid control). Effects on sarcoplasmic reticulum (SR) Ca(2+) release were evaluated in zero extracellular Ca(2+) using the blockers Xestospongin C and ryanodine. Store-operated Ca(2+) entry (SOCE) after SR depletion was evaluated using established techniques. The role of caveolin-1 in the effect of propofol was tested using small interference RNA (siRNA) suppression. Changes in intracellular signalling cascades relevant to [Ca(2+)](i) and force regulation were also evaluated.

RESULTS

Propofol was present in ASM caveolar fractions in substantial concentrations. Exposure to 10 or 30 µM propofol form decreased [Ca(2+)](i) peak (but not plateau) responses to histamine by ~40%, an effect persistent in zero extracellular Ca(2+). Propofol effects were absent in caveolin-1 siRNA-transfected cells. Inhibition of ryanodine receptors prevented propofol effects on [Ca(2+)](i), while propofol blunted [Ca(2+)](i) responses to caffeine. Propofol reduced SOCE, an effect also prevented by caveolin-1 siRNA. Propofol effects were associated with decreased caveolin-1 expression and extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

These novel data suggest a role for caveolae (specifically caveolin-1) in propofol-induced bronchodilatation. Due to its lipid nature, propofol may transiently disrupt caveolar regulation, thus altering ASM [Ca(2+)](i).

Tumour necrosis factor α-induced adipose-related protein (TIARP): co-localization with caveolin-1

We previously identified TIARP (TNF(alpha)-induced adipose-related protein, where TNF(alpha) stands for tumour necrosis factor alpha), a novel plasma-membrane protein that is induced during 3T3-L1 preadipocytes differentiation by TNF(alpha). Whereas the biological function of TIARP is currently unknown, its protein sequence is reminiscent of transporter protein and/or NAD(P)/NAD(P)H-dependent oxidoreductase activities. We hypothesized that TIARP could be associated with the 3T3-L1 adipocyte plasma-membrane caveolae domains that contain many proteins involved in cellular trafficking and signalling processes. Studies by confocal microscopy showed that TIARP and caveolin-1, a major protein of caveolae, co-localized as patches at the plasma membrane. Immunoblot analysis of cell extracts indicated that TIARP was completely detergent-extractible from membranes, whereas caveolin-1 was present as both detergent-extractible and -insoluble pools. Since TIARP is compartmentalized with caveolin-1 within caveolae domains, we suggest this protein to be part of a signalling complex in association with caveolin-1 and regulatory proteins.

Atherosclerosis, caveolae and caveolin-1

Atherosclerosis is a disease of the blood vessel characterized by the development of an arterial occlusion containing lipid and cellular deposits. Caveolae are 50-100 nm cell surface plasma membrane invaginations that are believed to play an important role in the regulation of cellular signaling and transport of molecules among others. These organelles are enriched in sphingolipids and cholesterol and are characterized by the presence of the protein caveolin-1. Caveolin-1 and caveolae are present in most of the cells involved in the development of atherosclerosis. The current literature suggests a rather complex role for caveolin-1 in this disease, with evidence of either pro- or anti-atherogenic functions depending on the cell type examined. In the present chapter, the various roles of caveolae and caveolin-1 in the development of atherosclerosis are examined.

High glucose-induced RhoA activation requires caveolae and PKCβ1-mediated ROS generation

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. We previously showed that RhoA activation by high glucose in mesangial cells (MC) leads to matrix upregulation (Peng F, Wu D, Gao B, Ingram AJ, Zhang B, Chorneyko K, McKenzie R, Krepinsky JC. Diabetes 57: 1683-1692, 2008). Here, we study the mechanism whereby RhoA is activated. In primary rat MC, RhoA activation required glucose entry and metabolism. Broad PKC inhibitors (PMA, bisindolylmaleimide, Gö6976), as well as specific PKCβ blockade with an inhibitor and small interfering RNA (siRNA), prevented RhoA activation by glucose. PKCβ inhibition also abrogated reactive oxygen species (ROS) generation by glucose. The ROS scavenger N-acetylcysteine (NAC) or NADPH oxidase inhibitors apocynin and DPI prevented glucose-induced RhoA activation. RhoA and some PKC isoforms localize to caveolae. Chemical disruption of these microdomains prevented RhoA and PKCβ1 activation by glucose. In caveolin-1 knockout cells, glucose did not induce RhoA and PKCβ1 activation; these responses were rescued by caveolin-1 reexpression. Furthermore, glucose-induced ROS generation was significantly attenuated by chemical disruption of caveolae and in knockout cells. Downstream of RhoA signaling, activator protein-1 (AP-1) activation was also inhibited by disrupting caveolae, was absent in caveolin-1 knockout MC and rescued by caveolin-1 reexpression. Finally, transforming growth factor (TGF)-β1 upregulation, mediated by AP-1, was prevented by RhoA signaling inhibition and by disruption or absence of caveolae. In conclusion, RhoA activation by glucose is dependent on PKCβ1-induced ROS generation, most likely through NADPH oxidase. The activation of PKCβ1 and its downstream effects, including upregulation of TGF-β1, requires caveolae. These microdomains are thus important mediators of the profibrogenic process associated with diabetic nephropathy.

Differential infectious entry of human influenza A/NWS/33 virus (H1N1) in mammalian kidney cells

In this report we focused our interest on the early events of the replication cycle of NWS/33 human influenza A (NWS) virus in MDCK (canine), LLC-MK2 (simian), and NSK (swine) kidney cells, with different susceptibility upon infection. We have previously demonstrated that actin organization induces restriction to viral replication during the early stages of NWS virus infection in simian kidney cells. To explore how cell endocytic mechanisms are hijacked by NWS virus and may modulate the outcome of viral infection, the effect of drugs affecting selectively the entry via clathrin-coated pits, caveolar/raft-dependent endocytosis and macropinocytosis was analyzed. Results point to critical differences in terms of internalization pathways exploited by NWS virus to enter the examined cell models. Moreover, we show that some ways of entry do not allow an effective virus internalization, depending on the cell type. Understanding how specific cell functions/components may regulate early phases of viral replication allows us to deepen our knowledge on influenza virus infection and provides new insights for anti-viral researches.

Mechanical strain-induced RhoA activation requires NADPH oxidase-mediated ROS generation in caveolae

Increased intraglomerular pressure leads to kidney fibrosis, and can be modeled by exposing glomerular mesangial cells (MC) to mechanical strain. We previously showed that RhoA mediates strain-induced matrix production. Here we investigate whether reactive oxygen species (ROS) are required for RhoA activation. Maximal RhoA activation (1 min) was inhibited by ROS scavenge or NADPH oxidase inhibition. Strain activated NADPH oxidase, with Rac1, p47(phox), and p67(phox) membrane translocation, and Rac1 activation, observed within 30 sec. Epidermal growth factor receptor (EGFR) inhibition blocked RhoA and Rac1 activation, p67(phox) membrane translocation, and ROS generation. However, EGFR activation was unaffected by ROS inhibitors, placing it upstream of ROS generation. We previously showed, using chemical disruption, that caveolae mediate strain-induced EGFR and RhoA activation. In MC from caveolin-1 knockout mice, which lack caveolae, RhoA and Rac1 activation, p67(phox) membrane translocation, and ROS generation were absent. These were rescued by caveolin-1 re-expression. ROS generation, Rac1 activation, and p67(phox) membrane translocation were also prevented by Src inhibition. They were absent in MC stably infected with caveolin-1 Y14A, a mutant resistant to Src phosphorylation. In MC, caveolae are thus important mediators of strain-induced ROS generation through NADPH oxidase, mediating a signaling cascade which results in RhoA activation.

Caveolae and caveolin-1 are implicated in 1alpha,25(OH)2-vitamin D3-dependent modulation of Src, MAPK cascades and VDR localization in skeletal muscle cells

We previously reported that 1alpha,25(OH)2D3 induces non-transcriptional rapid responses through activation of MAPKs in C2C12 skeletal muscle cells. However, there is little information on the molecular mechanism underlying the initiation of 1alpha,25(OH)2D3 signaling through this pathway. Plasma membrane components have been involved in some non-genomic effects. In this work, we investigated the role of caveolae and caveolin-1 (cav-1) in 1alpha,25(OH)2D3-stimulation of c-Src and MAPKs. When proliferating cells were pretreated with methyl beta cyclodextrin (MbetaCD), a caveolae disrupting agent, under conditions in which cell morphology is not affected and no signs of apoptosis are observed, 1alpha,25(OH)2D3-dependent activation of ERK1/2, p38 MAPK and c-Src was suppressed. Similar results were obtained by siRNA technology whereby silencing of cav-1 expression abolished activation of c-Src and MAPKs induced by the hormone. By confocal immunocytochemistry it was observed that cav-1 colocalizes with c-Src in the periplasma membrane zone at basal conditions. Hormone treatment disrupted the colocalization of these proteins and redistributed them into cytoplasm and nucleus. Co-immunoprecipitation assays corroborated these observations. Changes in VDR localization after 1alpha,25(OH)2D3 exposure were also investigated. Confocal microscopy images showed that the hormone induces VDR translocation to the plasma membrane, and this effect is abolished by MbetaCD. Altogether, these data suggest that caveolae is involved upstream in c-Src-MAPKs activation by 1alpha,25(OH)2D3 and that VDR and cav-1 participate in the rapid signaling elicited by the hormone.

Isoflurane via TGF-beta1 release increases caveolae formation and organizes sphingosine kinase signaling in renal proximal tubules

We previously showed that the inhalational anesthetic isoflurane protects against renal proximal tubule necrosis via isoflurane-mediated stimulation and translocation of sphingosine kinase-1 (SK1) with subsequent synthesis of sphingosine-1-phosphate (S1P) in renal proximal tubule cells (Kim M, Kim M, Kim N, D'Agati VD, Emala CW Sr, Lee HT. Am J Physiol Renal Physiol 293: F1827-F1835, 2007). We also demonstrated that the anti-necrotic and anti-inflammatory effect of isoflurane is due in part to phosphatidylserine (PS) externalization and subsequent release of transforming growth factor-beta1 (TGF-beta1) (Lee HT, Kim M, Kim J, Kim N, Emala CW. Am J Nephrol 27: 416-424, 2007). In this study, we tested the hypothesis that isoflurane, via TGF-beta1 release, increases caveolae formation in the buoyant fraction of the cell membrane of human renal proximal tubule (HK-2) cells to organize SK1 and S1P signaling. To detect SK1 protein in the caveolae/caveolin fractions, we overexpressed human SK1 in HK-2 cells (SK1-HK-2). SK1-HK-2 cells exposed to isoflurane increased caveolae/caveolin formation in the buoyant membrane fractions which contained key signaling intermediates involved in isoflurane-mediated renal tubule protection, including S1P, SK1, ERK MAPK, and TGF-beta1 receptors. Furthermore, treating SK1-HK-2 cells with recombinant TGF-beta1 or PS liposome mixture increased caveolae formation, mimicking the effects of isoflurane. Conversely, TGF-beta1-neutralizing antibody blocked the increase in caveolae formation induced by isoflurane in SK1-HK-2 cells. The increase in SK1 activity in the caveolae-enriched fractions from isoflurane-treated nonlentivirus-infected HK-2 cells, while smaller in magnitude, was qualitatively similar to that found in the SK1-HK-2 cell line. Finally, isoflurane also increased caveolae formation in the kidneys of TGF-beta1 +/+ mice but not in TGF-beta1 +/- mice (mice with reduced levels of TGF-beta1). Our study demonstrates that isoflurane organizes several key cytoprotective signaling intermediates including TGF-beta1 receptors, SK1 and ERK, within the caveolae fraction of the plasma membrane. Our findings may help to unravel the cellular signaling pathways of volatile anesthetic-mediated renal protection and lead to new therapeutic applications of inhalational anesthetics during the perioperative period.

Changes in mammary caveolin-1 signaling pathways are associated with breast cancer risk in rats exposed to estradiol in utero or during prepuberty

Developmental stage of rat mammary gland at the time of estrogen exposure determines whether the exposure increases or reduces later breast cancer risk. For example, in utero exposure to 17β-estradiol (E2) increases, whereas prepubertal exposure to this hormone decreases susceptibility of developing carcinogen-induced mammary tumors. E2 mediates its actions by interacting with caveolin-1 (CAV1), a putative tumor suppressor gene in breast cancer. Mammary tissues from 2-month-old rats exposed to E2 in utero contained decreased levels of CAV1, whereas prepubertal E2 exposure increased the levels, when compared to vehicle controls. Low CAV1 expression was associated with increased cell proliferation and estrogen receptor α expression, and reduced apoptosis in the mammary glands of rats exposed to E2 in utero. In contrast, high CAV1 expression correlated with reduced cell proliferation and cyclin D1 and phospho-Akt levels, and increased apoptosis in the mammary glands of rats exposed to E2 during prepuberty. In support of the role of CAV1 as a negative regulator of a variety of pro-growth signaling proteins, we detected decreased levels of Src and ErbB2 in rats exposed to E2 during prepuberty. Thus, estrogen exposure during mammary gland development affects the expression and function of CAV1 in a manner consistent with observed changes in susceptibility to mammary tumorigenesis.

Effect of modification of the physicochemical properties of ICAM-1-derived peptides on internalization and intracellular distribution in the human leukemic cell line HL-60

The objective of this work is to test the hypothesis that increasing the hydrophilicity of DOX-peptide conjugates may modify their entry mechanisms into HL-60 cells from passive diffusion to receptor-mediated uptake. To test this hypothesis, the entry mechanisms and the intracellular disposition of DOX-cIBR7, DOX-PEGcIBR7, FITC-cIBR, and FITC-cIBR7 were evaluated in HL-60 cells. To increase the hydrophilicity of the peptide, the cIBR peptide (cyclo(1,12)Pen-PRGGSVLVTGC) was modified to cIBR7 peptide (cyclo(1,8)CPRGGSVC) by removing the hydrophobic residues at the C-terminus. DOX-cIBR7 conjugate, which has higher hydrophilicity than DOX-cIBR, was synthesized. Second, a hydrophilic linker (11-amino-3,6,9-trioxaundecanate linker) was incorporated between DOX and cIBR7 to generate DOX-PEGcIBR7 with higher hydrophilicity than DOX-cIBR7. As controls, FITC-cIBR and FITC-cIBR7 were used to check for any endocytic uptake process of the peptide. As previously found with DOX-cIBR, DOX-cIBR7, and DOX-PEGcIBR7, conjugates enter the cells via passive diffusion and not via the energy-dependent endocytic process. This result suggests that an increase in hydrophilicity does not influence the entry mechanism of the DOX-peptide conjugates. In contrast to the DOX-cIBR7 conjugate, the FITC-cIBR7 conjugate showed energy-dependent cellular entry into the cells and followed an endocytic pathway similar to that for dextran. Finally, the entry of DOX-cIBR7 and DOX-PEGcIBR into the cell cytosol was shown to be due to the properties of DOX and not to those of the peptide.

Varying the chain length in N4,N9-diacyl spermines: non-viral lipopolyamine vectors for efficient plasmid DNA formulation

The aims of this work are to study the effect of varying the chain length in synthesized N4,N9-diacyl spermines on DNA condensation and then to compare their transfection efficiencies in cell lines. The five novel N4,N9-diacyl lipopolyamines: N4,N9-[didecanoyl, dilauroyl, dimyristoyl, dimyristoleoyl, and dipalmitoyl]-1,12-diamino-4,9-diazadodecane were synthesized from the naturally occurring polyamine spermine. The abilities of these novel compounds to condense DNA and to form nanoparticles were studied using ethidium bromide fluorescence quenching and nanoparticle characterization techniques. Transfection efficiency was studied in FEK4 primary skin cells and in an immortalized cancer cell line (HtTA), and compared with a saturated (distearoyl) analogue and also with the non-liposomal transfection formulation Lipogen, N4,N9-dioleoyl-1,12-diamino-4,9-diazadodecane. By incorporating two aliphatic chains and changing their length in a stepwise manner, we show efficient circular plasmid DNA (pEGFP) formulation and transfection of primary skin and cancer cell lines. Two C14 chains (both saturated or both cis-monounsaturated) were efficient transfecting agents, even in the presence of serum, but they were too toxic. N4,N9-Dioleoyl spermine efficiently condenses pDNA and achieves the highest transfection levels with the highest cell viability among the studied lipopolyamines in cultured cells even in the presence of serum.

Caveolin-1 directly interacts with UT-A1 urea transporter: the role of caveolae/lipid rafts in UT-A1 regulation at the cell membrane

The cell plasma membrane contains specialized microdomains called lipid rafts which contain high amounts of sphingolipids and cholesterol. Lipid rafts are involved in a number of membrane protein functions. The urea transporter UT-A1, located in the kidney inner medullary collecting duct (IMCD), is important for urine concentrating ability. In this study, we investigated the possible role of lipid rafts in UT-A1 membrane regulation. Using sucrose gradient cell fractionation, we demonstrated that UT-A1 is concentrated in the caveolae-rich fraction both in stably expressing UT-A1 HEK293 cells and in freshly isolated kidney IMCD suspensions. In these gradients, UT-A1 at the cell plasma membrane is codistributed with caveolin-1, a major component of caveolae. The colocalization of UT-A1 in lipid rafts/caveolae was further confirmed in isolated caveolae from UT-A1-HEK293 cells. The direct association of UT-A1 and caveolin-1 was identified by immunoprecipitation and GST pull-down assay. Examination of internalized UT-A1 in pEGFP-UT-A1 transfected HEK293 cells fluorescent overlap with labeled cholera toxin subunit B, a marker of the caveolae-mediated endocytosis pathway. Disruption of lipid rafts by methyl-beta-cyclodextrin or knocking down caveolin-1 by small-interference RNA resulted in UT-A1 cell membrane accumulation. Functionally, overexpression of caveolin-1 in oocytes decreased UT-A1 urea transport activity and UT-A1 cell surface expression. Our results indicate that lipid rafts/caveolae participate in UT-A1 membrane regulation and this effect is mediated via a direct interaction of caveolin-1 with UT-A1.

Membrane shape as a reporter for applied forces

Recent advances have enabled 3-dimensional reconstructions of biological structures in vivo, ranging in size and complexity from single proteins to multicellular structures. In particular, tomography and confocal microscopy have been exploited to capture detailed 3-dimensional conformations of membranes in cellular processes ranging from viral budding and organelle maintenance to phagocytosis. Despite the wealth of membrane structures available, there is as yet no generic, quantitative method for their interpretation. We propose that by modeling these observed biomembrane shapes as fluid lipid bilayers in mechanical equilibrium, the externally applied forces as well as the pressure, tension, and spontaneous curvature can be computed directly from the shape alone. To illustrate the potential power of this technique, we apply an axial force with optical tweezers to vesicles and explicitly demonstrate that the applied force is equal to the force computed from the membrane conformation.

TGFbeta-induced RhoA activation and fibronectin production in mesangial cells require caveolae

Glomerular sclerosis of diverse etiologies is characterized by mesangial matrix accumulation, with transforming growth factor-beta (TGFbeta) an important pathogenic factor. The GTPase RhoA mediates TGFbeta-induced matrix accumulation in some settings. Here we study the role of the membrane microdomain caveolae in TGFbeta-induced RhoA activation and fibronectin upregulation in mesangial cells (MC). In primary rat MC, TGFbeta1 time dependently increased RhoA and downstream Rho kinase activation. Rho pathway inhibition blocked TGFbeta1-induced upregulation of fibronectin transcript and protein. TGFbeta1-induced RhoA activation was prevented by disrupting caveolae with cholesterol depletion and rescued by cholesterol repletion. Compared with wild types, RhoA/Rho kinase activation was absent in MC lacking caveolae. Reexpression of caveolin-1 (and caveolae) restored these responses. Phosphorylation of caveolin-1 on Y14, effected by Src kinases, has been implicated in signaling responses. Overexpression of nonphosphorylatable caveolin-1 Y14A prevented TGFbeta1-induced RhoA activation. TGFbeta1 also activated Src, and its inhibition blocked RhoA activation. Furthermore, TGFbeta1 led to association of RhoA and caveolin-1. This was prevented by Src or TGFbeta receptor I inhibition, and by caveolin-1 Y14A overexpression. Last, fibronectin upregulation by TGFbeta1 was blocked by Src inhibition, not seen in caveolin-1 knockout MC, and restored by caveolin-1 reexpression in the latter. TGFbeta1-induced collagen I accumulation also required caveolae. TGFbeta1-mediated Smad2/3 activation, however, did not require caveolae. We conclude that RhoA/Rho kinase mediates TGFbeta-induced fibronectin upregulation. This requires caveolae and caveolin-1 interaction with RhoA. Interference with caveolin/caveolae or RhoA signaling thus represents a potential target for the treatment of fibrotic renal disease.

Regulation of caveolar cardiac sodium current by a single Gsα histidine residue

Cardiac sodium channels (voltage-gated Na+ channel subunit 1.5) reside in both the plasmalemma and membrane invaginations called caveolae. Opening of the caveolar neck permits resident channels to become functional. In cardiac myocytes, caveolar opening can be stimulated by applying β-receptor agonists, which initiates an interaction between the stimulatory G protein subunit-α (Gsα) and caveolin-3. This study shows that, in adult rat ventricular myocytes, a functional Gsα-caveolin-3 interaction occurs, even in the absence of the caveolin-binding sequence motif of Gsα. Consistent with previous data, whole cell experiments conducted in the presence of intracellular PKA inhibitor stimulation with β-receptor agonists increased the sodium current ( INa) by 35.9 ± 8.6% ( P < 0.05), and this increase was mimicked by application of Gsα protein. Inclusion of anti-caveolin-3 antibody abolished this effect. These findings suggest that Gsα and caveolin-3 are components of a PKA-independent pathway that leads to the enhancement of INa. In this study, alanine scanning mutagenesis of Gsα (40THR42), in conjunction with voltage-clamp studies, demonstrated that the histidine residue at position 41 of Gsα (H41) is a critical residue for the functional increase of INa. Protein interaction assays suggest that GsαFL (full length) binds to caveolin-3, but the enhancement of INa is observed only in the presence of Gsα H41. We conclude that Gsα H41 is a critical residue in the regulation of the increase in INa in ventricular myocytes.

Pharmacology of airway smooth muscle proliferation

Airway smooth muscle thickening is a pathological feature that contributes significantly to airflow limitation and airway hyperresponsiveness in asthma. Ongoing research efforts aimed at identifying the mechanisms responsible for the increased airway smooth muscle mass have indicated that hyperplasia of airway smooth muscle, due in part to airway myocyte proliferation, is likely a major factor. Airway smooth muscle proliferation has been studied extensively in culture and in animal models of asthma, and these studies have revealed that a variety of receptors and mediators contributes to this response. This review aims to provide an overview of the receptors and mediators that control airway smooth muscle cell proliferation, with emphasis on the intracellular signalling mechanisms involved.

Caveolae and endothelial dysfunction: filling the caves in cardiovascular disease

Discovery in the early 1990s of caveolin-1, the structural protein responsible for maintaining the ohm shape of caveolae, greatly enhanced investigations to elucidate the role of these little caves in the plasma membrane. Perhaps one of the most important realizations concerning caveolae and caveolin is that these elements play an important functional role in the modulation of cell signal transduction pathways, including those involved in endothelial nitric oxide synthase (eNOS) function. Their role was confirmed by studies with caveolin-1 knockout mice which lack caveolae and display abnormal endothelial function responses. One limitation of these knockout models, however, is that absence of the caveolin protein not only results in the lack of caveolae as a structure but also in the lack of interaction/modulation of enzymes/molecules (e.g. eNOS) to which caveolin binds (whether in- or outside caveolae). In contrast to caveolin knockout models, recent experimental findings suggest that in certain cardiovascular diseases caveolin may dissociate from caveolae to the cytosol, hence decreasing the number of caveolae without a change in the total amount of caveolin. Therefore, as the importance of defining the role of caveolins both in caveolae and in cellular regions is being highlighted, it seems also important at the same time to further define the role of caveolae per se being present in the plasma membrane as a structural entity. The objective of this review is to make an explorative tour on the role of caveolae in vascular endothelial function based on existing literature together with some preliminary experimental findings. Evidence and arguments are put forward that alterations in endothelial caveolae do occur in cardiovascular disease and may contribute to the observed endothelial dysfunction in these conditions.