Caveolae: an alternative membrane transport compartment

Long-term administration of Western diet induced metabolic syndrome in mice and causes cardiac microvascular dysfunction, cardiomyocyte mitochondrial damage, and cardiac remodeling involving caveolae and caveolin-1 expression

BACKGROUND

Long-term consumption of an excessive fat and sucrose diet (Western diet, WD) has been considered a risk factor for metabolic syndrome (MS) and cardiovascular disease. Caveolae and caveolin-1 (CAV-1) proteins are involved in lipid transport and metabolism. However, studies investigating CAV-1 expression, cardiac remodeling, and dysfunction caused by MS, are limited. This study aimed to investigate the correlation between the expression of CAV-1 and abnormal lipid accumulation in the endothelium and myocardium in WD-induced MS, and the occurrence of myocardial microvascular endothelial cell dysfunction, myocardial mitochondrial remodeling, and damage effects on cardiac remodeling and cardiac function.

METHODS

We employed a long-term (7 months) WD feeding mouse model to measure the effect of MS on caveolae/vesiculo-vacuolar organelle (VVO) formation, lipid deposition, and endothelial cell dysfunction in cardiac microvascular using a transmission electron microscopy (TEM) assay. CAV-1 and endothelial nitric oxide synthase (eNOS) expression and interaction were evaluated using real-time polymerase chain reaction, Western blot, and immunostaining. Cardiac mitochondrial shape transition and damage, mitochondria-associated endoplasmic reticulum membrane (MAM) disruption, cardiac function change, caspase-mediated apoptosis pathway activation, and cardiac remodeling were examined using TEM, echocardiography, immunohistochemistry, and Western blot assay.

RESULTS

Our study demonstrated that long-term WD feeding caused obesity and MS in mice. In mice, MS increased caveolae and VVO formation in the microvascular system and enhanced CAV-1 and lipid droplet binding affinity. In addition, MS caused a significant decrease in eNOS expression, vascular endothelial cadherin, and β-catenin interactions in cardiac microvascular endothelial cells, accompanied by impaired vascular integrity. MS-induced endothelial dysfunction caused massive lipid accumulation in the cardiomyocytes, leading to MAM disruption, mitochondrial shape transition, and damage. MS promoted brain natriuretic peptide expression and activated the caspase-dependent apoptosis pathway, leading to cardiac dysfunction in mice.

CONCLUSION

MS resulted in cardiac dysfunction, remodeling by regulating caveolae and CAV-1 expression, and endothelial dysfunction. Lipid accumulation and lipotoxicity caused MAM disruption and mitochondrial remodeling in cardiomyocytes, leading to cardiomyocyte apoptosis and cardiac dysfunction and remodeling.

Properties of rapamycin solid lipid nanoparticles for lymphatic access through the lungs & part I: the effect of size

Background: Lymphangioleiomyomatosis (LAM) is characterized by growth of smooth muscle-like cells in the lungs that spread to other organs via lymphatic vessels. Current oral rapamycin treatment is limited by low bioavailability of approximately 15%. Aim: The effect of inhaled rapamycin solid lipid nanoparticles (Rapa-SLNs) size on its penetration through the lymphatics. Method: Three Rapa-SLN formulations (200-1000 nm) were produced and assessed for particle characteristics and further for toxicity and performance in vitro. Results: Rapa-SLNs of 200 nm inhibited proliferation in TSC2-negative mouse embryonic fibroblast cells and penetrated the respiratory epithelium and lymphatic endothelium significantly faster compared with free rapamycin and larger Rapa-SLNs. Conclusion: Rapa-SLN approximately 200 nm allows efficient entry of rapamycin into the lymphatic system and is therefore a promising treatment for LAM patients.

Selective Liposomal Transport through Blood Brain Barrier Disruption in Ischemic Stroke Reveals Two Distinct Therapeutic Opportunities

The development of effective therapies for stroke continues to face repeated translational failures. Brain endothelial cells form paracellular and transcellular barriers to many blood-borne therapies, and the development of efficient delivery strategies is highly warranted. Here, in a mouse model of stroke, we show selective recruitment of clinically used liposomes into the ischemic brain that correlates with biphasic blood brain barrier (BBB) breakdown. Intravenous administration of liposomes into mice exposed to transient middle cerebral artery occlusion took place at early (0.5 and 4 h) and delayed (24 and 48 h) time points, covering different phases of BBB disruption after stroke. Using a combination of in vivo real-time imaging and histological analysis we show that selective liposomal brain accumulation coincides with biphasic enhancement in transcellular transport followed by a delayed impairment to the paracellular barrier. This process precedes neurological damage in the acute phase and maintains long-term liposomal colocalization within the neurovascular unit, which could have great potential for neuroprotection. Levels of liposomal uptake by glial cells are similarly selectively enhanced in the ischemic region late after experimental stroke (2-3 days), highlighting their potential for blocking delayed inflammatory responses or shifting the polarization of microglia/macrophages toward brain repair. These findings demonstrate the capability of liposomes to maximize selective translocation into the brain after stroke and identify two windows for therapeutic manipulation. This emphasizes the benefits of selective drug delivery for efficient tailoring of stroke treatments.

Targeting the Mitochondrial Potassium Channel Kv1.3 to Kill Cancer Cells: Drugs, Strategies, and New Perspectives

Cancer is the consequence of aberrations in cell growth or cell death. In this scenario, mitochondria and ion channels play a critical role in regard to cell proliferation, malignant angiogenesis, migration, and metastasis. In this review, we focus on Kv1.3 and specifically on mitoKv1.3, which showed an aberrant expression in cancer cells compared with healthy tissues and which is involved in the apoptotic pathway. In recent years, mitoKv1.3 has become an oncological target since its pharmacological modulation has been demonstrated to reduce tumor growth and progression both in vitro and in vivo using preclinical mouse models of different types of tumors.

Penehyclidine hydrochloride alleviates lipopolysaccharide‑induced acute lung injury in rats: Potential role of caveolin‑1 expression upregulation

The aim of the present study was to examine the protective effect of caveolin-1 (Cav-1) in the penehyclidine hydrochloride (PHC)-based inhibition of lipopolysaccharide (LPS)-induced acute lung injury (ALI) in vivo and in vitro, in addition to the potential underlying mechanisms. In vivo, an ALI rat model was established via intratracheal administration of LPS (5 mg/kg), and PHC (2 mg/kg) was administered 30 min following LPS treatment. In vitro, the Cav-1 gene was knocked down by small interfering (si)RNA in J774A.1 cells. Cells were incubated with LPS (1 µg/ml) for 2 h, and subsequently incubated with PHC (2 µg/ml) for an additional 2 h. Lung injury was assessed by lung histology and the ratio of polymorphonuclear leukocytes (PMNs) to total cells was assessed in bronchoalveolar lavage fluid (BALF), myeloperoxidase (MPO) activity, BALF protein content and lung wet/dry (W/D) ratio. The levels of pro-inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin (IL)-6 and IL-1β, in the sera of rats and cell culture supernatant were determined by ELISA. The protein expression levels of Cav-1, toll-like receptor 4 (TLR4), phosphorylated (p)-p38 mitogen activated protein kinases (p38 MAPKs) and nuclear factor kappa-light-chain-enhancer of activated B cells transcription factor p65 subunit (NF-κB p65) in lung tissues and J774A.1 cells were analyzed by western blot analysis. The results indicated that PHC effectively alleviated lung injury by decreasing neutrophil infiltration and protein concentration in BALF, and the lung W/D ratio and MPO activity and pro-inflammatory cytokine production induced by LPS. Furthermore, PHC significantly decreased the degrees of histopathological changes and pulmonary dysfunction. In vitro, treatment with PHC inhibited pro-inflammatory cytokine levels and MPO activity in LPS-stimulated J774A.1 cells. However, the results in the J774A.1 cells with Cav-1 gene knockdown were contrary. In addition, PHC decreased TLR4, p-p38 MAPKs and nuclear NF-κB p65 expression levels and upregulated the expression level of Cav-1, in vivo and in vitro. These data demonstrated that PHC exhibited a protective effect against LPS-induced ALI in rats and LPS-stimulated J774A.1 cells, which may be due to the inhibition of p38 MAPKs phosphorylation and TLR4/NF-κB signaling pathway by Cav-1 upregulation.

Ratiometric co-encapsulation and co-delivery of doxorubicin and paclitaxel by tumor-targeted lipodisks for combination therapy of breast cancer

Combination therapy is a promising treatment for certain advanced drug-resistant cancers. Although effective inhibition of various tumor cells was reported in vitro, combination treatment requires improvement in vivo due to uncontrolled ratiometric delivery. In this study, a tumor-targeting lipodisk nanoparticle formulation was developed for ratiometric loading and the transportation of two hydrophobic model drugs, doxorubicin (DOX) and paclitaxel (PTX), in one single platform. Furthermore, a slightly acidic pH-sensitive peptide (SAPSP) incorporated into lipodisks effectively enhanced the tumor-targeting and cell internalization. The obtained co-loaded lipodisks were approximately 30 nm with a pH-sensitive property. The ratiometric co-delivery of two drugs via lipodisks was confirmed in both the drug-resistant MCF-7/ADR cell line and its parental MCF-7 cell line in vitro, as well as in a tumor-bearing mouse model in vivo compared with a cocktail solution of free drugs. Co-loaded lipodisks exerted improved cytotoxicity to tumor cells in culture, particularly to drug-resistant tumor cells at synergistic drug ratios. In an in vivo xenograft mouse model, the anti-tumor ability of co-loaded lipodisks was evidenced by the remarkable inhibitory effect on tumor growth of either MCF-7 or MCF-7/ADR tumors, which may be attributed to the increased and ratiometric accumulation of both drugs in the tumor tissues. Therefore, tumor-specific lipodisks were crucial for the combination treatment of DOX and PTX to completely exert a synergistic anti-cancer effect. It is concluded that for co-loaded lipodisks, cytotoxicity data in vitro could be used to predict their inhibitory activity in vivo, potentially enhancing the clinical outcome of synergistic therapy.

Folic Acid-Conjugated Cellulose Nanocrystals Show High Folate-Receptor Binding Affinity and Uptake by KB and Breast Cancer Cells

The study evaluates cellulose nanocrystals (CNCs) as nanocarriers for targeted, intracellular delivery of molecular agents. CNCs were labeled with fluorescein-5'-isothiocyanate as an imaging agent and conjugated to folic acid (FA) as a targeting ligand. The CNC conjugates were characterized by UV-vis spectroscopy, ζ-potential analysis, dynamic light scattering, and atomic force microscopy. Cellular binding/uptake of the FA-conjugated CNCs by KB and MDA-MB-468 cells was quantified with cellular uptake assays. Internalization of the particles was confirmed by confocal microscopy. Uptake mechanisms were determined by inhibition studies with chlorpromazine and genistein. Binding affinity was qualitatively assessed with a free folate inhibition assay. Both KB and MDA-MB-468 cells exhibited significant and folate-receptor specific binding/uptake of FA-conjugated CNCs. Clathrin-mediated endocytosis was a significant uptake mechanism in both cell types, whereas caveolae-mediated endocytosis only played a significant role in MDA-MB-468 cells. Uptake inhibition of FA-conjugated CNCs by KB cells required high concentrations (>1 mM) of free FA. The observed FR-specific internalization of FA-conjugated CNCs by FR-positive cancer cells and tumors and their remarkable high affinity for the FR demonstrate the great potential of CNCs as novel nanocarriers for imaging agents and chemotherapeutics in the early detection and treatment of cancer.

Inhibition of transient receptor potential vanilloid 4 decreases the expressions of caveolin-1 and caveolin-2 after focal cerebral ischemia and reperfusion in rats

This study aimed to investigate the effects of transient receptor potential vanilloid 4 (TRPV4) inhibition on blood-brain barrier (BBB) integrity and the expressions of caveolae structural proteins caveolin-1 and caveolin-2 in rats with focal cerebral ischemia and reperfusion. BBB permeability was assessed by Evans blue extravasation. The mRNA and protein expressions of caveolin-1 and caveolin-2 were determined by RT-PCR, Western blot and immunohistochemistry assays. We found that BBB permeability significantly increased and reaches its peak at 72 h of reperfusion in cerebral ischemia-reperfusion rats and is able to be ameliorated by administration of HC-067047, an antagonist of TRPV4. Additionally, it shows a significant upregulation of caveolin-1 and caveolin-2 expression in cerebral microvessels of ischemic tissue. However, treatment with HC-067047 was shown to downregulate caveolin-1 and caveolin-2 expression during cerebral ischemia-reperfusion. This study demonstrates that inhibition of TRPV4 ameliorates BBB leakage induced by ischemia-reperfusion injury through the downregulation of caveolin-1 and caveolin-2.

Improved oral bioavailability of docetaxel by nanostructured lipid carriers: in vitro characteristics, in vivo evaluation and intestinal transport studies

The objective of the current study was to explore the potential of nanostructured lipid carriers (NLC) for oral delivery of docetaxel (DTX) and investigate the absorption mechanismin vivo.

Caveolin-1 regulates P2X7 receptor signaling in osteoblasts

The synthesis of new bone in response to a novel applied mechanical load requires a complex series of cellular signaling events in osteoblasts and osteocytes. The activation of the purinergic receptor P2X(7)R is central to this mechanotransduction signaling cascade. Recently, P2X(7)R have been found to be associated with caveolae, a subset of lipid microdomains found in several cell types. Deletion of caveolin-1 (CAV1), the primary protein constituent of caveolae in osteoblasts, results in increased bone mass, leading us to hypothesize that the P2X(7)R is scaffolded to caveolae in osteoblasts. Thus, upon activation of the P2X(7)R, we postulate that caveolae are endocytosed, thereby modulating the downstream signal. Sucrose gradient fractionation of MC3T3-E1 preosteoblasts showed that CAV1 was translocated to the denser cytosolic fractions upon stimulation with ATP. Both ATP and the more specific P2X(7)R agonist 2'(3')-O-(4-benzoylbenzoyl)ATP (BzATP) induced endocytosis of CAV1, which was inhibited when MC3T3-E1 cells were pretreated with the specific P2X7R antagonist A-839977. The P2X7R cofractionated with CAV1, but, using superresolution structured illumination microscopy, we found only a subpopulation of P2X(7)R in these lipid microdomains on the membrane of MC3T3-E1 cells. Suppression of CAV1 enhanced the intracellular Ca(2+) response to BzATP, suggesting that caveolae regulate P2X(7)R signaling. This proposed mechanism is supported by increased mineralization in CAV1 knockdown MC3T3-E1 cells treated with BzATP. These data suggest that caveolae regulate P2X(7)R signaling upon activation by undergoing endocytosis and potentially carrying with it other signaling proteins, hence controlling the spatiotemporal signaling of P2X(7)R in osteoblasts.

Role of caveolin-1 in the biology of the blood-brain barrier

Caveolin-1 is the principal marker of caveolae in endothelial cells. It plays an important role in physiological and pathological conditions of the blood-brain barrier and serves as a mediator in drug delivery through the blood-brain barrier. Caveolin-1 is related to the diminished expression of tight junction-associated proteins and metabolic pinocytosis vesicles when the blood-brain barrier is destroyed by outside invaders or malignant stimulus. The permeability of the blood-brain barrier, regulated by types of drugs or physical irradiation, is connected with drug transportation with the participation of caveolin-1. Caveolin-1, which serves as a platform or medium for signal transduction, cooperates with several signal molecules by forming a complex. Silencing of caveolin-1 and disruption of caveolae can attenuate or remove pathological damage and even engender the opposite effects in the blood-brain barrier. This review considers the role of caveolin-1 in the blood-brain barrier that may have profound implications for central nervous system disease and drug delivery through the blood-brain barrier.

Network of telocytes in the temporomandibular joint disc of rats

The phenotypes of the temporomandibular joint (TMJ) disc cells range from fibroblasts to chondrocytes. There are relatively few reported studies using transmission electron microscopy (TEM) to determine the ultrastructural features of these cells. It was hypothesized that at least a subpopulation of TMJ stromal cells could be represented by the telocytes, cells with telopodes. In this regard a TEM study was performed on rat TMJ samples. Collagen-embedded networks were found built-up by cells with telopodes with subplasmalemmal caveolae, moderate content in matrix secretory organelles and well-represented intermediate filaments. Appositions of cell bodies were found. Prolongations of such cells were closely related to nerves and microvessels. Our study indicates that the TMJ disc attachment seems equipped with telocytes capable of stromal signaling. However, further studies are needed to assess whether the telocytes belong to a renewed cell population derived from circulating precursors.

[Recombinant human alpha-fetoprotein as a regulator of adipose tissue stromal cell activity]

Recombinant human alpha-fetoprotein (rhAFP) expressed in yeast system as a glycoprotein, was isolated and purified to 98% by multistep method. The testing of the rhAFP in the culture of adipose tissue stromal cells (hASC) has revealed its ability to enhance hASC proliferation and migration as well as vascular endothelial growth factor production, with no significant influence on cell invasion and matrix metalloproteinase-2 and -9 secretion. It has been also estimated that rhAFP is internalized in hASC via clathrin-dependent mechanism. A study in the murine experimental model of hindlimb ischemia has shown the capability of rhAFP to enhance blood flow recovery. These data suggest that rhAFP is a promising agent for enhancement of the hASC regenerative ability.

Co-transfection gene delivery of dendritic cells induced effective lymph node targeting and anti-tumor vaccination

PURPOSE

Successful genetically engineered Dendritic Cell (DC) can enhance DC's antigen presentation and lymph node migration. The present study aims to genetically engineer a DC using an efficient non-viral gene delivery vector to induce a highly efficient antigen presentation and lymph node targeting in vivo.

METHODS

Spermine-dextran (SD), a cationic polysaccharide vector, was used to prepare a gene delivery system for DC engineering. Transfection efficiency, nuclear trafficking, and safety of the SD/DNA complex were evaluated. A vaccine prepared by engineering DC with SD/gp100, a plasmid encoding melanoma-associated antigen, was injected subcutaneously into mice to evaluate the tumor suppression. The migration of the engineered DCs was also evaluated in vitro and in vivo.

RESULTS

SD/DNA complex has a better transfection behavior in vitro than commercially purchased reagents. The DC vaccine co-transfected with plasmid coding CCR7, a chemokine receptor essential for DC migration, and plasmid coding gp100 displayed superior tumor suppression than that with plasmid coding gp100 alone. Migration assay demonstrated that DC transfected with SD/CCR7 can promote DC migration capacity.

CONCLUSIONS

The study is the first to report the application of nonviral vector SD to co-transfect DC with gp100 and CCR7-coding plasmid to induce both the capacity of antigen presentation and lymph node targeting.

Lung endothelial cells strengthen, but brain endothelial cells weaken barrier properties of a human alveolar epithelium cell culture model

The blood-air barrier in the lung consists of the alveolar epithelium, the underlying capillary endothelium, their basement membranes and the interstitial space between the cell layers. Little is known about the interactions between the alveolar and the blood compartment. The aim of the present study was to gain first insights into the possible interplay between these two neighbored cell layers. We established an in vitro Transwell model of the alveolar epithelium based on human cell line H441 and investigated the influence of conditioned medium obtained from human lung endothelial cell line HPMEC-ST1.6R on the barrier properties of the H441 layers. As control for tissue specificity H441 layers were exposed to conditioned medium from human brain endothelial cell line hCMEC/D3. Addition of dexamethasone was necessary to obtain stable H441 cell layers. Moreover, dexamethasone increased expression of cell type I markers (caveolin-1, RAGE) and cell type II marker SP-B, whereas decreased the transepithelial electrical resistance (TEER) in a concentration dependent manner. Soluble factors obtained from the lung endothelial cell line increased the barrier significantly proven by TEER values and fluorescein permeability on the functional level and by the differential expression of tight junctional proteins on the molecular level. In contrast to this, soluble factors derived from brain endothelial cells weakened the barrier significantly. In conclusion, soluble factors from lung endothelial cells can strengthen the alveolar epithelium barrier in vitro, which suggests communication between endothelial and epithelial cells regulating the integrity of the blood-air barrier.

Low-frequency ultrasound irradiation increases blood-tumor barrier permeability by transcellular pathway in a rat glioma model

Low-frequency ultrasound (LFU) irradiation under certain acoustic intensity can increase blood-brain barrier permeability non-invasively and reversibly. The aim of this study was to find out the effect of LFU irradiation on blood-tumor barrier (BTB) permeability in rat C6 glioma model and the possible mechanism. In this research, Evans blue and H&E staining were used to evaluate the optimal parameter of LFU to open the BTB without damaging the normal brain tissue. Transmission electron microscopy was used to observe the changes of the number of pinocytotic vesicles in cerebral or glioma microvascular endothelial cells. The phosphorylation of tyrosine kinase Src, caveolin-1, and caveolin-2 was detected by western blot. The distribution and expressing levels of caveolae proteins, caveolin-1 and caveolin-2, were detected by immunohistochemical and immunofluorescent staining, RT-PCR, and western blot. Our research data showed that, in rat C6 glioma model, LFU irradiation at a frequency of 1 MHz, a power of 12 mW, and exposure time of 20 s induced the increase of BTB permeability temporally, which reached a peak at 1.5 h, then decreased and restored to normal level at 12 h after LFU irradiation. In the glioma microvascular endothelial cells of rat glioma model, LFU irradiation induced a significant increase of the pinocytotic vesicles' density. The phosphorylation of Src, caveolin-1, and caveolin-2 began to increase at 0.5 h and reached a maximum at 1 h. Immunohistochemical and immunofluorescent staining showed that caveolin-1 and caveolin-2 were co-localized in the glioma microvascular endothelial cells and glioma cells. The mRNA and protein expression levels of caveolin-1 and caveolin-2 were up-regulated, reached the peak value at 1.5 h, and re-normalized at 12 h after LFU irradiation. These results demonstrated that LFU irradiation increased BTB permeability by promoting transcellular transport in glioma microvascular endothelial cells. The phosphorylation of tyrosine kinase Src, caveolin-1, caveolin-2 and up-regulation of caveolin-1 and caveolin-2 were involved in LFU-induced caveolae-mediated endocytosis.

Non-degradative intracellular trafficking of highly compacted polymeric DNA nanoparticles

Highly compacted DNA nanoparticles (DNPs) composed of polyethylene glycol linked to a 30-mer of poly-l-lysine via a single cysteine residue (CK(30)PEG) have previously been shown to provide efficient gene delivery to the brain, eyes and lungs. In this study, we used a combination of flow cytometry, high-resolution live-cell confocal microscopy, and multiple particle tracking (MPT) to investigate the intracellular trafficking of highly compacted CK(30)PEG DNPs made using two different molecular weights of PEG, CK(30)PEG(10k) and CK(30)PEG(5k). We found that PEG MW did not have a major effect on particle morphology nor nanoparticle intracellular transport. CK(30)PEG(10k) and CK(30)PEG(5k) DNPs both entered human bronchial epithelial (BEAS-2B) cells via a caveolae-mediated pathway, bypassing degradative endolysosomal trafficking. Both nanoparticle formulations were found to rapidly accumulate in the perinuclear region of cells within 2h, 37±19% and 47±8% for CK(30)PEG(10k) and CK(30)PEG(5k), respectively. CK(30)PEG(10k) and CK(30)PEG(5k) DNPs moved within live cells at average velocities of 0.09±0.04μm/s and 0.11±0.04μm/s, respectively, in good agreement with reported values for caveolae. These findings show that highly compacted DNPs employ highly regulated trafficking mechanisms similar to biological pathogens to target specific intracellular compartments.

Nanoparticles electrostatically coated with folic acid for effective gene therapy

We developed a novel vector, electrostatically coated poly(ethylenimine) (PEI)/pDNA complexes with folic acid (FA). Without covalent binding, the FA molecules could coat the PEI/pDNA complexes, and stable anionic nanoparticles were formed at a charge ratio greater than 60. The addition of FA markedly decreased the cytotoxicity of the cationic PEI/pDNA complexes to the melanoma cell line, B16-F10 cells, which regularly expressed FA-specific receptor (FR). Furthermore, the anionic FA60/PEI/pDNA complexes showed high transgene efficiency via the FR-mediated pathway in B16-F10 cells. The FA60/PEI/pDNA complexes did not show agglutination with erythrocytes. After the intravenous injection of FA60/PEI/pDNA complexes into mice, a higher transgene efficiency than PEI/pDNA complexes was observed in the liver, kidney, spleen, and lung with FR. The gene expressions of FA60/PEI/pDNA complexes were significantly inhibited by preadministration of FA. Thus, the FA60/PEI/pDNA complexes were useful for effective gene therapy.

Caveolin-1: a critical regulator of lung injury

Caveolin-1 (cav-1), a 22-kDa transmembrane scaffolding protein, is the principal structural component of caveolae. Cav-1 regulates critical cell functions including proliferation, apoptosis, cell differentiation, and transcytosis via diverse signaling pathways. Abundant in almost every cell type in the lung, including type I epithelial cells, endothelial cells, smooth muscle cells, fibroblasts, macrophages, and neutrophils, cav-1 plays a crucial role in the pathogenesis of acute lung injury (ALI). ALI and its severe form, acute respiratory distress syndrome (ARDS), are responsible for significant morbidity and mortality in intensive care units, despite improvement in ventilation strategies. The pathogenesis of ARDS is still poorly understood, and therapeutic options remain limited. In this article, we summarize recent data regarding the regulation and function of cav-1 in lung biology and pathology, in particular as it relates to ALI. We further discuss the potential molecular and cellular mechanisms by which cav-1 expression contributes to ALI. Investigating the cellular functions of cav-1 may provide new insights for understanding the pathogenesis of ALI and provide novel targets for therapeutic interventions in the future.

Nanoscale imaging of epidermal growth factor receptor clustering: effects of inhibitors

The development of some solid tumors is associated with overexpression of the epidermal growth factor receptor (EGFR) and often correlates with poor prognosis. Near field scanning optical microscopy, a technique with subdiffraction-limited optical resolution, was used to examine the influence of two inhibitors (the chimeric 225 antibody and tyrosine phosphorylation inhibitor AG1478) on the nanoscale clustering of EGFR in HeLa cells. The EGFR is organized in small clusters, average diameter of 150 nm, on the plasma membrane for both control and EGF-treated cells. The numbers of receptors in individual clusters vary from as few as one or two proteins to greater than 100. Both inhibitors yield an increased cluster density and an increase in the fraction of clusters with smaller diameters and fewer receptors. Exposure to AG1478 also decreases the fraction of EGFR that colocalizes with both rafts and caveolae. EGF stimulation results in a significant loss of the full-length EGFR from the plasma membrane with the concomitant appearance of low molecular mass proteolytic products. By contrast, AG1478 reduces the level of EGFR degradation. Changes in receptor clustering provide one mechanism for regulating EGFR signaling and are relevant to the design of strategies for therapeutic interventions based on modulating EGFR signaling.

Mechanisms of the increase in the permeability of the blood-tumor barrier obtained by combining low-frequency ultrasound irradiation with small-dose bradykinin

The research was conducted to study the characteristics of the noninvasive, reversible, targeted opening of the blood-brain barrier (BBB) by use of low-frequency ultrasound (LFU) irradiation and the selective opening of the blood-tumor barrier (BTB) by intracarotid infusion of bradykinin (BK) in small-dose, with the objective of exploring maximum opening of the BTB by combining LFU irradiation with BK infusion. Thus, it provides new therapeutic strategies for targeted transport of macromolecular or granular drugs to the brain. By using the rat C6 glioma model it was shown that extravasation of Evans blue (EB) through the BTB was significantly increased by combining LFU irradiation (frequency = 1.0 MHz, power = 12 mW, duration = 20 s) with intracarotid small-dose BK infusion, compared with utilizing the two methods separately. By transmission electron microscopy (TEM) we observed that this combination significantly increased the number of pinocytotic vesicles of brain microvascular endothelial cells (BMECs) in the BTB. An even more significant increase was observed by using RT-PCR, western blot, immunohistochemistry, and immunofluorescence to detect mRNA and changes of expression of the caveolae structure proteins caveolin-1 and caveolin-2 of BMECs. In summary, this research concludes that LFU irradiation and small-dose BK together selectively enhance the permeability of the BTB and increase the number of pinocytic vesicles of BMECs to a maximum. Significant up-regulation of the level of expression of caveolae structure proteins caveolin-1 and caveolin-2 might be the molecular mechanism of the co-enhanced endocytotic transport by BMECs. Thus, this research provides new therapeutic strategies for targeted transport of macromolecular drugs and the design of drugs.

The role of caveolin-1 in pulmonary matrix remodeling and mechanical properties

Caveolin-1 (cav1) is a 22-kDa membrane protein essential to the formation of small invaginations in the plasma membrane, called caveolae. The cav1 gene is expressed primarily in adherent cells such as endothelial and smooth muscle cells and fibroblasts. Caveolae contain a variety of signaling receptors, and cav1 notably downregulates transforming growth factor (TGF)-beta signal transduction. In pulmonary pathologies such as interstitial fibrosis or emphysema, altered mechanical properties of the lungs are often associated with abnormal ECM deposition. In this study, we examined the physiological functions and the deposition of ECM in cav1(-/-) mice at various ages (1-12 mo). Cav1(-/-) mice lack caveolae and by 3 mo of age have significant reduced lung compliance and increased elastance and airway resistance. Pulmonary extravasation of fluid, as part of the cav1(-/-) mouse phenotype, probably contributed to the alteration of compliance, which was compounded by a progressive increase in deposition of collagen fibrils in airways and parenchyma. We also found that the increased elastance was caused by abundant elastic fiber deposition primarily around airways in cav1(-/-) mice at least 3 mo old. These observed changes in the ECM composition probably also contribute to the increased airway resistance. The higher deposition of collagen and elastic fibers was associated with increased tropoelastin and col1alpha2 and col3alpha1 gene expression in lung tissues, which correlated tightly with increased TGF-beta/Smad signal transduction. Our study illustrates that perturbation of cav1 function may contribute to several pulmonary pathologies as the result of the important role played by cav1, as part of the TGF-beta signaling pathway, in the regulation of the pulmonary ECM.

Subcellular compartment targeting of layered double hydroxide nanoparticles

Current investigations show that layered double hydroxide (LDH) nanoparticles have high potential as effective non-viral agents for cellular drug delivery due to their low cytotoxicity, good biocompatibility, high drug loading, control of particle size and shape, targeted delivery and drug release control. Two types of Mg(2)Al-LDH nanoparticles with fluorescein isothiocyanate (FITC) were controllably prepared. One is morphologically featured as typical hexagonal sheets (50-150 nm laterally wide and 10-20 nm thick), while the other as typical rods (30-60 nm wide and 100-200 nm long). These LDH(FTIC) nanoparticles are observed to immediately transfect into different mammalian cell lines. We found that internalized LDH(FITC) nanorods are quickly translocated into the nucleus while internalized LDH(FITC) nanosheets are retained in the cytoplasm. Inhibition experiments show that the cellular uptake is a clathrin-mediated time- and concentration-dependent endocytosis. Endosomal escape of LDH(FITC) nanoparticles is suggested to occur through the deacidification of LDH nanoparticles. Since quick nuclear targeting of LDH(FITC) nanorods requires an active process, and although the exact mechanism is yet to be fully understood, it probably involves an active transport via microtubule-mediated trafficking processes. Targeted addressing of two major subcellular compartments by simply controlling the particle morphology/size could find a number of applications in cellular biomedicine.

Caveolae structure and function

Studies on the structure and function of caveolae have revealed how this versatile subcellular organelle can influence numerous signalling pathways. This brief review will discuss a few of the key features of caveolae as it relates to signalling and disease processes.

Strategies to improve drug delivery across the blood-brain barrier

The blood-brain barrier (BBB), together with the blood-cerebrospinal-fluid barrier, protects and regulates the homeostasis of the brain. However, these barriers also limit the transport of small-molecule and, particularly, biopharmaceutical drugs such as proteins, genes and interference RNA to the brain, thereby limiting the treatment of many brain diseases. As a result, various drug delivery and targeting strategies are currently being developed to enhance the transport and distribution of drugs into the brain. In this review, we discuss briefly the biology and physiology of the BBB as the most important barrier for drug transport to the brain and, in more detail, the possibilities for delivering large-molecule drugs, particularly genes, by receptor-mediated nonviral drug delivery to the (human) brain. In addition, the systemic and intracellular pharmacokinetics of nonviral gene delivery, together with targeted brain imaging, are reviewed briefly.

Primary porcine brain microvascular endothelial cells: biochemical and functional characterisation as a model for drug transport and targeting

The blood-brain barrier (BBB) remains a significant obstacle to the delivery of therapeutic agents into the central nervous system (CNS). Primary cell cultures of brain capillary endothelial cells represent the closest possible phenotype to the in vivo BBB cell providing a convenient model for the study of transport systems and events that mediate solute delivery to the CNS. In this investigation we have characterized an in vitro primary BBB model from porcine brain microvascular endothelial capillary (PBMVEC) cells after recovery from cryopreservation of upto 12 months and studied their modulation by astrocytes. Co-cultures of PBMVECs with astrocytes (C6 astroglioma) resulted in trans-endothelial electrical resistance of up to approximately 900Omega cm2 and marked discrimination between the para- and trans- cellular markers sucrose and propranolol. Micrographs of confluent monolayers of PBMVECs showed the presence of tight junction complexes and vesicles with the morphological characteristics of either caveolae or clathrin coated pits. Extensive RT-PCR evaluation highlighted the expression of tight junction transcripts, ABC transporters, leptin receptor and select nutrient transporters. Functional studies examined the kinetics of transport of glucose, large neutral amino acids and p-glycoprotein (P-gp). Our findings indicate primary PBMVECs retain many barrier characteristics and transport pathways of the in vivo BBB. Further, primary cells can be stored as frozen stocks which can be thawed and cultured without phenotypic drift many months after isolation. Frozen PBMVECs therefore serve as a robust and convenient in vitro cell culture tool for research programs involving CNS drug delivery and targeting and in studies addressing blood-brain barrier transport mechanisms.

Drug targeting to the brain

The central nervous system (CNS) is a sanctuary site and is protected by various barriers. These regulate brain homeostasis and the transport of endogenous and exogenous compounds by controlling their selective and specific uptake, efflux, and metabolism in the brain. Unfortunately, potential drugs for the treatment of most brain diseases are therefore often not able to cross these barriers. As a result, various drug delivery and targeting strategies are currently being developed to enhance the transport and distribution of drugs into the brain. Here we discuss briefly the biology and physiology of the blood-brain barrier (BBB) and the blood-cerebro-spinal-fluid barrier (BCSFB), and, in more detail, the possibilities for delivering large-molecular-weight drugs by local and global delivery and by viral and receptor-mediated nonviral drug delivery to the (human) brain.

Cellular delivery of small interfering RNA by a non-covalently attached cell-penetrating peptide: quantitative analysis of uptake and biological effect

Cell-penetrating peptides (CPPs) have evolved as promising new tools to deliver nucleic acids into cells. So far, the majority of these delivery systems require a covalent linkage between carrier and cargo. To exploit the higher flexibility of a non-covalent strategy, we focused on the characterisation of a novel carrier peptide termed MPGα, which spontaneously forms complexes with nucleic acids. Using a luciferase-targeted small interfering RNA (siRNA) as cargo, we optimised the conditions for MPGα-mediated transfection of mammalian cells. In this system, reporter gene activity could be inhibited up to 90% with an IC₅₀ value in the sub-nanomolar range. As a key issue, we addressed the cellular uptake mechanism of MPGα/siRNA complexes applying various approaches. First, transfection of HeLa cells with MPGα/siRNA complexes in the presence of several inhibitors of endocytosis showed a significant reduction of the RNA interference (RNAi) effect. Second, confocal laser microscopy revealed a punctual intracellular pattern rather than a diffuse distribution of fluorescently labelled RNA-cargo. These data provide strong evidence of an endocytotic pathway contributing significantly to the uptake of MPGα/siRNA complexes. Finally, we quantified the intracellular number of siRNA molecules after MPGα-mediated transfection. The amount of siRNA required to induce half maximal RNAi was 10 000 molecules per cell. Together, the combination of methods provided allows for a detailed side by side quantitative analysis of cargo internalisation and related biological effects. Thus, the overall efficiency of a given delivery technique as well as the mechanism of uptake can be assessed.

The blood-brain barrier transmigrating single domain antibody: mechanisms of transport and antigenic epitopes in human brain endothelial cells

Antibodies against receptors that undergo transcytosis across the blood-brain barrier (BBB) have been used as vectors to target drugs or therapeutic peptides into the brain. We have recently discovered a novel single domain antibody, FC5, which transmigrates across human cerebral endothelial cells in vitro and the BBB in vivo. The purpose of this study was to characterize mechanisms of FC5 endocytosis and transcytosis across the BBB and its putative receptor on human brain endothelial cells. The transport of FC5 across human brain endothelial cells was polarized, charge independent and temperature dependent, suggesting a receptor-mediated process. FC5 taken up by human brain endothelial cells co-localized with clathrin but not with caveolin-1 by immunochemistry and was detected in clathrin-enriched subcellular fractions by western blot. The transendothelial migration of FC5 was reduced by inhibitors of clathrin-mediated endocytosis, K+ depletion and chlorpromazine, but was insensitive to caveolae inhibitors, filipin, nystatin or methyl-beta-cyclodextrin. Following internalization, FC5 was targeted to early endosomes, bypassed late endosomes/lysosomes and remained intact after transcytosis. The transcytosis process was inhibited by agents that affect actin cytoskeleton or intracellular signaling through PI3-kinase. Pretreatment of human brain endothelial cells with wheatgerm agglutinin, sialic acid, alpha(2,3)-neuraminidase or Maackia amurensis agglutinin that recognizes alpha(2,3)-, but not with Sambucus nigra agglutinin that recognizes alpha(2,6) sialylgalactosyl residues, significantly reduced FC5 transcytosis. FC5 failed to recognize brain endothelial cells-derived lipids, suggesting that it binds luminal alpha(2,3)-sialoglycoprotein receptor which triggers clathrin-mediated endocytosis. This putative receptor may be a new target for developing brain-targeting drug delivery vectors.

Nuclear localizing anti-DNA antibodies enter cells via caveoli and modulate expression of caveolin and p53

After administration to normal mice, a subset of monoclonal (m) anti-DNA antibodies (Ab) derived from MRL-lpr/lpr mice was identified that enter cells, in vivo. In the kidneys, this was associated with glomerular hypercellularity and proteinuria. In cultured cells, the same mAb bound to myosin 1 on the cell surface, prior to internalization, nuclear localization and inhibition of apoptosis. The present study focuses on the mechanisms underlying the observed functional effects. Subcellular localization studies revealed that following internalization, a prototypic, nuclear localizing, m antibody (Ab; termed H7) co-localized with myosin 1, shortly after internalization, within caveolae, near the cell membrane. Cell fractionation studies confirmed the presence of both H7 and myosin within the caveolar fraction. Since variations in caveolin protein expression have been associated with apoptotic events in cancer cells, through p53 dependent and independent pathways, modulation of caveolin by intracellular H7 was evaluated. Cellular entry of the anti-DNA Ab resulted in an increase in caveolin protein expression. Furthermore, after exposure of cells to dexamethasone to induce apoptosis, the usual increase in p53 was inhibited in the presence of intracellular H7. Taken together, the results suggest that upregulation of caveolin and inhibition of p53 induction are involved in H7-induced, inhibition of apoptosis. Furthermore, they suggest that this inhibition contributes to the glomerular hypercellularity observed in normal mice with intranuclear H7. The results also raise the possibility that inhibition of apoptotic pathways during inflammation or/and autoimmunity could influence subsequent disease events. The novel mechanism of cellular perturbation is indirect and dependent on apoptotic stimuli, and it may account for the presence of intranuclear antibodies in inflammatory and normal tissues of individuals with lupus.

Targeted delivery across the blood–brain barrier

The safest and most effective way of targeting drugs to the entire brain is via delivery systems directed at endogenous receptor-mediated uptake mechanisms present at the cerebral capillaries. Such systems have been shown to be effective in animal models including primates, but no clinical trials have been performed so far. This review focuses on the well-characterised transferrin and insulin receptor-targeted systems, as well as on the more recently described systems that use the low-density lipoprotein-related protein 1 receptor, the low-density lipoprotein-related protein 2 receptor (also known as megalin and glycoprotein 330) or the diphtheria toxin receptor (which is the membrane-bound precursor of heparin-binding epidermal growth factor-like growth factor). The possibilities and limitations of these systems are compared and their future for human application is discussed.

Actin microfilaments et al.--the many components, effectors and regulators of epithelial cell endocytosis

The aim of this review is to introduce the advances made over the past several years regarding the participation of actin and actin-associated proteins in clathrin-mediated endocytosis in simple cell models, and then to consider the evidence for the involvement of these effectors in apical clathrin-mediated endocytosis in epithelial cells. Basic mechanisms of clathrin-mediated endocytosis are initially addressed, followed by a detailed description of the actin cytoskeleton: its organization, function and, most importantly, the essential role played by proteins and signaling pathways responsible for the regulation of actin filament dynamics. Our focus then shifts to the GTPase, dynamin and its pivotal role as a bridge between various components of the clathrin endocytic machinery and the actin cytoskeleton. Mechanisms and effectors of dynamin-dependent endocytosis are then described, with a particular emphasis on novel proteins, which link dynamin to actin filaments. We consider additional effectors proposed to interact with actin to facilitate clathrin-mediated endocytosis in a dynamin-independent manner. The multiple roles which actin filaments are thought to play in endocytosis are addressed followed by a more detailed characterization of actin filament participation specifically in apical endocytosis. We conclude by discussing how these concepts may be integrated to improve drug internalization at the apical plasma membrane of epithelial cells.

Evaluation of the immortalised mouse brain capillary endothelial cell line, b.End3, as an in vitro blood–brain barrier model for drug uptake and transport studies

Well-characterised cell lines represent important tools for the study of endogenous solute or xenobiotic transport. A brain microvascular cell line, b.End3, isolated from mice transformed with the Polyoma virus middle T-antigen is available commercially. Here we report the characterisation of some features of b.End3 of relevance to its use in blood-brain barrier transport investigations. The b.End3 cells displayed a distinctive spindle-like squamous morphology in culture. Clathrin coated pits and numerous uncoated intracellular vesicles were evident within the cells, as was the expression of the vesicle-associated proteins, clathrin, caveolin-1, flotillin and dynamin II. In the presence of C6 astroglial co-culture b.End3 monolayers achieved a maximal transendothelial electrical resistance of 130 Omega cm2, but lacked real discrimination with respect to the permeation of transcellular and paracellular probes, e.g. permeability coefficients (x 10(-6) cm s(-1)) for propranolol of approximately 23 vs. 16 for sucrose. RT-PCR analysis confirmed the presence within the b.End3 cells of mRNA transcripts for the following transporters: GLUT-1; MCT 1 and 2; OAT1; Oatp1; mdr 1a and 1b; MRP 1 and 5; beta-alanine, system L and system y+L amino acid carriers; the nucleoside transporters cNT1 and 2, eNT1 and 2, and the tight junctional elements, ZO-1, JAM, occludin, claudin-1 and -5. The b.End3 cells actively accumulated D-glucose in a sodium-independent manner with characteristics consistant with that of GLUT-1. Functionality for P-glycoprotein efflux was evident as assessed by a rhodamine-123 accumulation and retention assay. The system L LAT1/4F2hc amino acid transporter was examined through uptake of L-leucine and L-phenylalanine and provided Km and Vmax values of approximately 16 microM and 350-480 pmol/mg protein/10 min, respectively; the affinity of transport for these substrates being weaker, approximately threefold, when the b.End3 cells were grown in the presence of C6 astroglial factors. Although the b.End3 cells appear unsuitable for transendothelial permeability assessments they display characteristics that would allow their worthwhile use in studies addressing blood-brain barrier transport mechanisms.

16HBE14o- human bronchial epithelial cell layers express P-glycoprotein, lung resistance-related protein, and caveolin-1

PURPOSE

To study the expression of P-glycoprotein (P-gp), lung resistance-related protein (LRP), and caveolin-1 (cav-1) in the human bronchial epithelial cell line 16HBE14o-.

METHODS

The presence of P-gp, LRP, and cav-1 in 16HBE14o- cell layers was evaluated using immunocytochemical staining and visualization with confocal laser scanning microscopy (CLSM). Functionality of P-gp was determined by bidirectional transport of rhodamine-123 with and without a P-gp inhibitor, verapamil. Caveolae were visualized using transmission electron microscopy (TEM). Flux of fluorescein-Na was also studied as a paracellular transport marker.

RESULTS

Immunocytochemical staining showed expression of P-gp localized at the apical membrane of 16HBE14o- cell layers. The flux of rhodamine 123 across cell layers exhibited a greater Papp value for the secretory (i.e., basolateral-to-apical) direction. This asymmetry disappeared in the presence of verapamil. CLSM provided evidence for the expression of LRP and cav-1. TEM further showed typically shaped caveolae at the apical and basolateral membranes.

CONCLUSION

Cell layers of 16HBE14o- express drug transport systems that are also present in the human bronchus in vivo, indicating that the 16HBE14o- cell line may be a suitable candidate for an in vitro model for mechanistic studies of drug transport processes involved in the smaller airways.

Caveolin expression during chondrogenesis in the avian limb

Caveolin is the principal component and critical structural and functional element of caveolae, omega-shaped plasmalemmal invaginations, which have been implicated in a wide range of cellular processes in several different tissues. In the present study, we have investigated both the spatial and temporal expression of caveolin proteins during chondrogenesis in the avian tibiotarsus at days 10-20 of embryonic development. By using semiquantitative Western blotting, we found that caveolin-1 was clearly expressed in developing avian cartilage. The positive expression of caveolin-1 in cartilage showed an upward trend of accumulation temporally, with the highest levels of expression at 20 days of development. By using immunocytochemistry, we detected all three caveolin proteins in the cells of the outer fibrous articular surface, although caveolin-1 demonstrated the strongest and most consistent reactivity. In all cases, however, immunoreactivity appeared to be concentrated in cells facing the articular cavity. In the epiphyseal cartilage, immunocytochemistry revealed that caveolin-1 was present in the majority of chondrocytes within all layers of the cartilage and at all stages examined. A discrete, intense band of caveolin-1 immunoreactivity was apparent within the layer of flattened cells immediately underlying the proliferating rounded chondrocytes and suggests that caveolin-1 might be involved in regulating the progression of cells through these gradually maturing cell layers. In contrast to the results for caveolin-1, in the case of caveolin-2 and -3, chondrocytes were devoid of immunoreactivity in all regions of the epiphyseal cartilage. Overall, this study demonstrates that caveolin-1, -2, and -3 are expressed during chondrogenesis in the developing avian limb, although the patterns of expression are restricted both spatially and temporally throughout the differentiating cell layers of the cartilage. The results suggest that caveolin proteins might play a differentiation-dependent role during avian chondrogenesis.

Targeting caveolae for vesicular drug transport

Caveolae are morphologically evident as omega-shaped invaginations of the plasma membrane with a diameter of 50-100 nm. They may also exist in a variety of other forms including flattened domains indistinguishable from the plasma membrane itself. At least in some cell types caveolae undertake transport functions including that of the endocytic and transcytotic movement of macromolecules, and indeed microbes and microbial toxins. Opportunities exist for basic and applied investigators working within the pharmaceutical sciences to exploit caveolae membrane interactions with the aim to develop of novel cellular or transcellular drug delivery strategies. This overview article will provide: pertinent information on the biology of the caveolae membrane system; review the various caveolae isolation methods; highlight some of the literature evidence showing that caveolae are functional with regard to macromolecule transport; discuss the role that caveolae could fulfill in the pulmonary absorption of therapeutic proteins from alveolar airspace to capillary blood following inhalational drug delivery, and finally review some very recent work showing proof-of-principle that caveolae domains can be targeted in a tissue-specific manner with highly selective ligands.

Inhibition of kinin breakdown prolongs retention and action of bradykinin in a myocardial B2 receptor compartment

1. The high efficacy of ACE inhibitors to potentiate the actions of kinins might be explained by a hypothetical compartment in which B(2)-receptors are colocalized with kinin degrading enzymes. To demonstrate the functional consequence of such a compartment we compared the myocardial uptake and the persistence of action of bradykinin under the influence of kininase inhibitors. 2. Bradykinin-induced vasodilation and uptake of tritiated bradykinin were studied in perfused rat hearts during inhibition of ACE and aminopeptidase P. B(2)-receptors were localized by immuno-gold labelling and electron-microscopy. 3. The EC(50) of bradykinin-induced vasodilation (5.1+/-0.8 nM) was shifted to 14 fold lower concentrations during inhibition of both kininases. The maximum persistence of vasodilation after termination of bradykinin application (half-life 112+/-20 s) was increased by kininase inhibitors to 398+/-130 s. This prolongation was reversed when B(2)-receptors were blocked simultaneously with the termination of bradykinin infusion. 4. Tritiated bradykinin (perfused for 1 min) was partially (1.7+/-0.24%) retained by the myocardium and consecutively released with a half-life of 70+/-9 s. Kinin uptake was increased during kininase inhibition (7.7+/-2.6%), and was normalized by HOE 140 (2.0+/-0.34%), or when a tritiated B(2)-receptor antagonist (NPC 17731) was used as label. 5. B(2)-receptors were localized in plasmalemmal and cytosolic vesicles of capillary endothelium. 6. Bradykinin is locally incorporated and can associate with B(2)-receptors repeatedly when kinin breakdown is inhibited. This is the kinetic and functional consequence of a colocalization of kininases and B(2)-receptors in a compartment constituted by endothelial membrane vesicles.

A specific binding protein/receptor for 1alpha,25-dihydroxyvitamin D(3) is present in an intestinal caveolae membrane fraction

The steroid hormone 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] produces biological responses by interaction with both a well-characterized nuclear receptor (VDR(nuc)) to regulate gene transcription and with an as-yet uncharacterized membrane-associated protein/receptor (VDR(mem)) to generate a variety of rapid, non-genotropic responses. We report for the first time that [3H]1alpha,25(OH)(2)D(3) binds with high affinity to a chick duodenal caveolae-enriched membrane fraction (CMF) isolated without the use of detergents. Caveolae are plasma membrane invaginations implicated in signal transduction and molecular transport processes. Using the CMF fraction as a possible source of VDR(mem), we found that the in vitro binding of [3H]1alpha,25(OH)(2)D(3) was ligand dependent and saturable; the K(D) and B(max) were 1.3+/-0.6nM and 29+/-11fmol 1,25(OH)(2)D(3)/mg protein (n=17), respectively. Immunoblot analysis of the CMF confirms the presence of caveolin-1, a marker protein for membranes with caveolae. Therefore, chick CMF may represent a good source for isolation and characterization of the putative VDR(mem) for 1alpha,25(OH)(2)D(3).

Non-genomic steroid receptors in the bovine ovary

Over the last few years, rapid and physiologically important non-genomic actions of all classes of steroid hormones have been described in many cell types. A putative non-genomic membrane progesterone receptor (NGPR) was the first, and so far the only, non-genomic steroid receptor cloned. Two homologous NGPR proteins have been identified in the human, and a similar protein in the bovine and rat. Various detection methods have been used to identify putative NGPRs in a range of tissues: however, different methods often yield quite different molecular weights, and probably detect distinct moieties. We describe some properties of the specific cell-surface membrane binding sites for [3H]-progesterone in enriched cell membrane preparations of bovine luteal and follicular cells. Similar binding sites were also detected in cell-membranes of some (but not all) bovine tissues. Western blots of detergent extracts of bovine luteal membranes identified a protein (85kDa) that reacted with an antiserum to the N-terminal peptide of porcine NGPR. Activity was low in native non-denatured extracts, but increased dramatically in a dose-dependent manner following pretreatment with the cholesterol-complexing agent, digitonin. This protein was co-precipitated by antisera to caveolin. In contrast, a specific monoclonal antibody to the ligand binding domain of the genomic progesterone receptor (Mab C262) detected two proteins (M(r), 55 and 60kDa) in luteal membrane detergent extracts. Immunostaining of these proteins by Mab C262 was abolished by digitonin concentration-dependent manner in non-denatured extracts. However, both proteins were unaffected by digitonin in fully denatured detergent extracts, suggesting that digitonin induced a conformational change in the native protein that prevented binding of Mab C262 to its epitope. Our data suggest the presence of a complex of two or more distinct membrane-associated progesterone-binding proteins in bovine luteal membranes. Moreover, their conformations are specifically affected by removal of bound cholesterol.