Distribution Of Caveolin-1 Research Articles

Signaling proteins in raft-like microdomains are essential for Ca 2+ wave propagation in glial cells

The hypothesis that calcium signaling proteins segregate into lipid raft-like microdomains was tested in isolated membranes of rat oligodendrocyte progenitor (OP) cells and astrocytes using Triton X-100 solubilization and density gradient centrifugation. Western blot analysis of gradient fractions showed co-localization of caveolin-1 with proteins involved in the Ca 2+ signaling cascade. These included agonist receptors, P2Y 1, and M 1, TRPC1, IP 3R2, ryanodine receptor, as well as the G protein Gα q and Homer. Membranes isolated from agonist-stimulated astrocytes showed an enhanced recruitment of phospholipase C (PLCβ1), IP 3R2 and protein kinase C (PKC-α) into lipid raft fractions. IP 3R2, TRPC1 and Homer co-immunoprecipitated, suggesting protein–protein interactions. Disruption of rafts by cholesterol depletion using methyl-β-cyclodextrin (β-MCD) altered the distribution of caveolin-1 and GM1 to non-raft fractions with higher densities. β-MCD-induced disruption of rafts inhibited agonist-evoked Ca 2+ wave propagation in astrocytes and attenuated wave speeds. These results indicate that in glial cells, Ca 2+ signaling proteins might exist in organized membrane microdomains, and these complexes may include proteins from different cellular membrane systems. Such an organization is essential for Ca 2+ wave propagation.

Ultrahigh-resolution immunofluorescence microscopy using ultrathin cryosections: subcellular distribution of caveolin-1 and CD31 in human placental endothelial cells

We compared the z-axis resolutions achieved by immunofluorescence (IF) microscopic imaging of tissue sections of different thicknesses (ultrathin cryosections, optical sections of cryostat sections and conventional cryostat sections). We used these images to determine the distribution of caveolin-1alpha (CAV-1alpha) and CD31 in endothelial cells of full-term, human placenta. Anti-CAV-1alpha antibody was used to visualize caveolae, which are among the smallest organelles. By using ultrathin cryosections as substrates for IF microscopy, we were able to resolve discrete caveolae that were primarily present immediately beneath the endothelial cell surface. In contrast, neither conventional nor confocal images from cryostat sections were able to resolve individual caveolae, despite dramatic reductions in the confocal image degradation that arises from out-of-focus fluorescence signals. Anti-CD31 antibody labeled the endothelial cell surface exclusively. Quantitative analysis of ultrathin cryosections showed that about 2.5 times more CD31 was expressed on the luminal surface of cells than on the abluminal surface. Our results demonstrate that ultrathin cryosections can serve as excellent substrates for ultrahigh-resolution IF microscopy.

Deoxycholic Acid Induces Intracellular Signaling through Membrane Perturbations

Secondary bile acids have long been postulated to be tumor promoters in the colon; however, their mechanism of action remains unclear. In this study, we examined the actions of bile acids at the cell membrane and found that they can perturb membrane structure by alteration of membrane microdomains. Depletion of membrane cholesterol by treating with methyl-beta-cyclodextrin suppressed deoxycholic acid (DCA)-induced apoptosis, and staining for cholesterol with filipin showed that DCA caused a marked rearrangement of this lipid in the membrane. Likewise, DCA was found to affect membrane distribution of caveolin-1, a marker protein that is enriched in caveolae membrane microdomains. Additionally, fluorescence anisotropy revealed that DCA causes a decrease in membrane fluidity consistent with the increase in membrane cholesterol content observed after 4 h of DCA treatment of HCT116 cells. Significantly, by using radiolabeled bile acids, we found that bile acids are able to interact with and localize to microdomains differently depending on their physicochemical properties. DCA was also found to induce tyrosine phosphorylation and activate the receptor tyrosine kinase epidermal growth factor receptor in a ligand-independent manner. In contrast, ursodeoxycholic acid did not exhibit any of these effects even though it interacted significantly with the microdomains. Collectively, these data suggest that bile acid-induced signaling is initiated through alterations of the plasma membrane structure and the redistribution of cholesterol.

Dynamic Regulation of Caveolin-1 Trafficking in the Germ Line and Embryo ofCaenorhabditis elegans

Caveolin is the major protein component required for the formation of caveolae on the plasma membrane. Here we show that trafficking of Caenorhabditis elegans caveolin-1 (CAV-1) is dynamically regulated during development of the germ line and embryo. In oocytes a CAV-1-green fluorescent protein (GFP) fusion protein is found on the plasma membrane and in large vesicles (CAV-1 bodies). After ovulation and fertilization the CAV-1 bodies fuse with the plasma membrane in a manner reminiscent of cortical granule exocytosis as described in other species. Fusion of CAV-1 bodies with the plasma membrane appears to be regulated by the advancing cell cycle, and not fertilization per se, because fusion can proceed in spe-9 fertilization mutants but is blocked by RNA interference-mediated knockdown of an anaphase-promoting complex component (EMB-27). After exocytosis, most CAV-1-GFP is rapidly endocytosed and degraded within one cell cycle. CAV-1 bodies in oocytes appear to be produced by the Golgi apparatus in an ARF-1-dependent, clathrin-independent, mechanism. Conversely endocytosis and degradation of CAV-1-GFP in embryos requires clathrin, dynamin, and RAB-5. Our results demonstrate that the distribution of CAV-1 is highly dynamic during development and provides new insights into the sorting mechanisms that regulate CAV-1 localization.

Regional myocardial ischemia-induced activation of MAPKs is associated with subcellular redistribution of caveolin and cholesterol

Ischemia-reperfusion activates ERK and p38 MAPK in cardiac membranes, but the role of caveolae in MAPK signaling during this stress has not been studied. The purpose of this study was to determine the effect of in vivo myocardial ischemia-reperfusion on the level and distribution of caveolin-1 and -3 and cholesterol as well as MAPK activation in caveolin-enriched fractions. Adult male rats were subjected to in vivo regional myocardial ischemia induced by 25 min of coronary artery occlusion and 10 min (n = 5) or 2 h (n = 4) of reperfusion. Another group of rats served as appropriate nonischemic time controls (n = 4). A discontinuous sucrose density gradient was used to isolate caveolae/lipid rafts from ischemic and nonischemic heart tissue. Caveolin-1 and -3, as well as cholesterol, were enriched in the light fractions. A redistribution of caveolin-3 and a reduction in caveolin-1 and cholesterol levels in the light fractions occurred after 10 min of reperfusion. The ERKs were activated in ischemic zone light and heavy fractions by 10 min of reperfusion. p44 ERK was activated after 2 h of reperfusion only in the light fractions, whereas p42 ERK phosphorylation was increased in the light and heavy fractions. Although no p38 MAPK activation occurred after 10 min of reperfusion, 2 h of reperfusion caused significant activation of p38 MAPK in nonischemic zone light and heavy fractions. These results show the importance of caveolar membrane/lipid rafts in MAPK signaling and suggest that subcellular compartmentation of p44/p42 ERKs and p38 MAPK may play distinct roles in the response to myocardial ischemia-reperfusion.

Cholesterol‐Induced Caveolin Targeting to Lipid Droplets in Adipocytes: A Role for Caveolar Endocytosis

We have investigated the targeting of caveolin to lipid bodies in adipocytes that express high levels of caveolins and contain well-developed lipid droplets. We observed that the lipid droplets isolated from adipocytes of caveolin-1 knock out mice contained dramatically reduced levels of cholesterol, indicating that caveolin is required for maintaining the cholesterol content of this organelle. Analysis of caveolin distribution by cell fractionation and fluorescent light microscopy in 3T3-L1 adipocytes indicated that addition of cholesterol rapidly stimulated translocation of caveolin to lipid droplets. The cholesterol-induced trafficking of caveolins to lipid droplets was shown to be dynamin- and protein kinase C (PKC)-dependent and modulated by src tyrosine kinase activation, suggesting a role for caveolar endocytosis in this novel trafficking pathway. Consistent with this, caveolae budding was stimulated by cholesterol addition. The present data identify lipid droplets as potential target organelles for caveolar endocytosis and demonstrate a role for caveolin-1 in the maintenance of free cholesterol levels in adipocyte lipid droplets.

Antibody-specific detection of caveolin-1 in subapical compartments of MDCK cells

Caveolin-1 is the major structural component of caveolae and is also found in the Golgi complex of many cell types. Occasionally, caveolin-1 has been observed in additional intracellular compartments, including recycling endosomes. Why caveolin-1 expression is detected at these sites only infrequently is not clear. In this study, we test the hypothesis that non-caveolar, non-Golgi pools of caveolin-1 display unique and/or fixation-dependent epitopes. We compared the ability of a panel of antibodies raised against various domains of caveolin-1 to detect distinct subcellular pools of the protein by immunofluorescence microscopy in Madin-Darby canine kidney (MDCK) cells, a cell line where the subcellular localization of caveolin-1 has been extensively characterized. We show that three antibodies directed to the N-terminus of caveolin-1 recognize a previously undetected pool of caveolin-1 in the subapical region of MDCK cells, a localization characteristic of endosomal recycling compartments. The antibodies vary in their ability to label caveolin-1 at the cell surface, and the epitopes detected by each are highly fixation dependent. Our findings suggest that no single caveolin antibody or staining condition is capable of detecting all the caveolin-1 in a cell simultaneously. Consequently, the subcellular distribution of caveolin-1 may be much broader than currently believed.

Expression and localization of caveolins during postnatal development in rat heart: implication of thyroid hormone

Caveolins modulate signaling pathways involved in cardiac development. Caveolin-1 exists in two isoforms: the beta-isoform derivates from an alternative translational start site that creates a protein truncated by 31 amino acids, mainly expressed in endothelial cells, whereas caveolin-3 is present in muscle cells. Our aim was to define caveolin distribution and expression during cardiac postnatal development using immunofluorescence and Western blotting. Caveolin-3 sarcolemmal labeling appeared as dotted lines from days 1 to 5 and as continuous lines after 14 days of age. Caveolin-3 expression, low at birth, increased (4-fold) to reach a maximum (P < 0.05) by day 5 and then decreased to stabilize in adults. Total caveolin-1 and its alpha-isoform were codistributed at birth in endothelial and smooth muscle cells; afterward, only the caveolin-1alpha labeling became limited to endothelium. Quantitative analysis indicated a similar temporal pattern of both total caveolin-1 and caveolin-1alpha expression, suggesting that caveolin-1alpha and -1beta are coregulated; the caveolin-1alpha levels increased fourfold by day 5 to reach a maximum by day 14 (P < 0.05). Tyrosine-14-caveolin-1 phosphorylation, low at birth, increased suddenly around day 14 (8-fold vs. day 1) and returning afterward to basal level. Because the T3/T4 level is maximal by day 14, caveolin-1 expression/phosphorylation profiles were analyzed in hypothyroid heart. The levels of caveolin-1alpha and consequently tyrosine-14-caveolin-1 phosphorylation, but not that of caveolin-3, decreased (50%) in hypothyroid 14-day-old rats. Our data demonstrate that, during postnatal cardiac growth, 1) caveolins are distinctly regulated, and 2) thyroid hormones are involved in caveolin-1alpha expression.

Distribution of caveolin-1 and connexin43 in normal and injured alveolar epithelial R3/1 cells

Using the new alveolar epithelial type I-like cell line R3/1 derived from fetal rat lung, we studied the distribution of connexin43 and caveolin-1 under conditions of bleomycin-induced injury in vitro. We show that under normal as well as under conditions of injury, endogenous connexin43 does not directly interact with endogenous caveolin-1 as revealed by immunofluorescence, glutathione S-transferase/caveolin-1 "pull down" assay, and co-immunoprecipitation experiments. The assessment of Triton X-100 solubility revealed that caveolin-1 was abundant in detergent-resistant membrane fractions. This is consistent with the localization of caveolin-1 in the lipid rafts/caveolae. Similarly, phosphorylated connexin43 was preferably detected in the Triton-insoluble fraction. Using a sucrose gradient we demonstrated that the majority of phosphorylated connexin43 colocalizes with caveolin-1 in lipid rafts, whereas all other forms of connexin43 remain in the bulk of cellular membranes and cytosolic proteins. Triton solubility assessment of bleomycin-treated cells revealed no differences in the caveolin-1 and connexin43 distribution. A further interesting outcome of our study is the shift of caveolin-1 from the lipid raft/caveolae fractions to the non-caveolar fractions after bleomycin treatment indicating an intracellular retention of caveolin-1. This result suggests the possibility that the translocation of caveolin-1 could be an important event regulating the metabolism of alveolar epithelial lung cells after injury.

A PLCdelta1-binding protein, p122/RhoGAP, is localized in caveolin-enriched membrane domains and regulates caveolin internalization.

A GTPase activating protein (GAP), p122, has previously been cloned as a phospholipase C (PLC)delta1-interacting protein. p122 shows a specific GAP activity for Rho and enhances the enzyme activity of PLCdelta1. In this study, we examined the localization and functions of p122/RhoGAP, using enhanced green fluorescent protein (EGFP)-tagged proteins. EGFP-p122 was observed as punctate structures at the plasma membrane of BHK (fibroblastic) cells and MDCK (epithelial) cells. This patchy distribution depended on membrane cholesterol levels and the C-terminal region of p122 containing the GAP domain was responsible for it. Sucrose density gradient centrifugation and immunostaining of caveolin-1 revealed that p122 was localized in caveolin-enriched membrane domains mainly via its GAP domain. We demonstrated that transient expression of EGFP-p122 caused internalization of caveolin-1. Moreover, when the EGFP-tagged GAP domain was introduced in another fibroblastic cell line, NRK cells, punctate fluorescent structures were co-localized with caveolin-1. In this case, caveolin-1-positive structures were found in patches of F-actin, unlike those of untransfected cells that formed linear arrays along with actin stress fibres. These results suggest that p122 is localized in caveolae and plays an important role in caveolin distribution through reorganization of the actin cytoskeleton.

Distribution of caveolin-1 in bovine lens and redistribution in cultured bovine lens epithelial cells upon confluence

The distribution of caveolin-1 in the lens and lens epithelial cells was determined to assess possible roles in cholesterol trafficking, cell to cell communication and signal transduction. Bovine lenses and cultured bovine lens epithelial cells (BLEC) were divided into subcellular fractions and the distribution of proteins recognized by three different caveolin-1 antibodies determined. The immunolocalization of caveolin-1 in the lens epithelium and in subconfluent and confluent cultured BLEC was probed by fluorescence microscopy and laser scanning confocal microscopy. EGF induced phosphorylation of caveolin-1 was detected by Western blotting with an anti-phosphotyrosine antibody to immunoprecipitated caveolin-1 from BLEC and human cancer cells. Monomeric caveolin-1 of about 26 kDa was detected in the epithelial cell membrane of cultured BLEC and fresh epithelia and in the plasma membrane fraction of lens cortical fiber cells. Caveolin-1 of cultured BLEC redistributed from the cytoplasm to plasma membrane as the cells proceeded from subconfluent to confluent states. The apparent abundance of caveolin-1 in cortical fiber cell plasma membrane is consistent with possible roles in distribution of lens membrane cholesterol and membrane structure. The presence of caveolin-1 in the plasma membrane of epithelial cells at – but not before – confluency is consistent with a role of caveolin-1 in cell to cell communications. EGF stimulated phosphorylation of caveolin-1 in human A431 cells but not lens cells.

Caveolin-1 isoform reorganization studied by image correlation spectroscopy.

Caveolae are small, flask shaped invaginations in the cell membrane. They are thought to play a crucial role in cell signaling, endocytosis and intracellular cholesterol transport. Caveolin-1, 2 and 3 are key proteins, which are important for the formation of the invaginations on the cell surface. Caveolin-1 exists in two isoforms: caveolin-1 alpha (a) and caveolin-1 beta (beta). Little is known about the difference between these two isoforms, and less in known about their role in cell signaling. Bone morphogenetic proteins IBMPs) are a subfamily of the TGF beta superfamily and their response is mediated by serine/threonine kinase receptors. Epidermal growth factor (EGF) is known to signal through tyrosine kinase receptors of the ErbB family. Here we report on the aggregation and association of caveolin-1 isoforms with these receptors and the effect of BMP and EGF activation on caveolin-1 distribution in A431 cells. Our data, obtained by application of a family of image correlation spectroscopy tools, indicate that BMP and EGF stimulation lead to a rearrangement of the caveolin-1 isoforms on the cell surface. BMP as well as EGF stimulation leads to a rearrangement of the caveolin-1 P isoform into domains enriched in the caveolin-1 alpha isoform. We further show that about 20-30% of the caveolin-1 present at the surface of the cells co-localize with the EGF and BMP receptors. Using a reporter gene assay sensitive to the activation of the BMP pathway, we show that overexpression of caveolin-1beta inhibits signaling. Our data suggest that the two isoforms of caveolin-1 play different roles on the cell surface and that caveolae are dynamic structures.

Cholesterol transporter caveolin-1 transits the lipid bilayer during intracellular cycling.

Caveolin-1, a major protein of cell surface invaginations called caveolae, is currently believed to cycle between the plasma membrane and intracellular compartments via the endocytotic pathway, at least for part of its itinerary. We studied the distribution of caveolin-1 in cell membranes, using ultrathin cryosections and freeze-fracture immunolabeling and found this protein not only in the cytoplasmic leaflet of the plasma membrane, but also in the exoplasmic leaflet of all intracellular membranes. This sidedness implies that caveolin-1 switches from one membrane leaflet to the other somewhere on its way through the cell and rules out the classic mechanism of endocytotic membrane budding and fusion for caveolin-1 intracellular trafficking. Underlying the sidedness of caveolin-1 may be a fundamental, hitherto unrecognized, mechanism by which proteins transit membranes.

Specific phospholipid oxidation products inhibit ligand activation of toll-like receptors 4 and 2.

We have previously shown that phospholipid oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) inhibit lipopolysaccharide (LPS)-induced E-selectin expression and neutrophil binding in human aortic endothelial cells (HAECs). The current studies identify specific phospholipids that inhibit chemokine induction by Toll-like receptor-4 (TLR4) and -2 (TLR2) ligands inECs and macrophages. Measurements of interleukin (IL)-8 and monocyte chemotactic protein-1 levels secreted from ox-PAPC- and LPS-cotreated ECs indicate that ox-PAPC inhibits activation of TLR4 by LPS. The effects of IL-1beta and tumor necrosis factor-alpha, which utilize the same intracellular signaling molecules, were not inhibited. Cell fractionation and immunofluorescence analyses demonstrate that LPS induces membrane translocation of the LPS receptor complex to a lipid raft/caveolar fraction in ECs. Ox-PAPC inhibits this translocation and alters caveolin-1 distribution. Supporting an important role for caveolae in LPS action, overexpression of caveolin-1 enhanced LPS-induced IL-8 synthesis. Ox-PAPC also inhibits the effect of TLR2 and TLR4 ligands in human macrophages. These studies report a novel mechanism that involves alterations to lipid raft/caveolar processing, by which specific phospholipid oxidation products inhibit activation by TLR4 and TLR2 ligands. These studies have broader implications for the role of ox-PAPC as a regulator of specific lipid raft/caveolar function.

Differential caveolin-1 polarization in endothelial cells during migration in two and three dimensions.

Endothelial cell (EC) migration is a critical event during multiple physiological and pathological processes. ECs move in the plane of the endothelium to heal superficially injured blood vessels but migrate in three dimensions during angiogenesis. We herein investigate differences in these modes of movement focusing on caveolae and their defining protein caveolin-1. Using a novel approach for morphological analysis of transmigrating cells, we show that ECs exhibit a polarized distribution of caveolin-1 when traversing a filter pore. Strikingly, in these cells caveolin-1 seems to be released from caveolar structures in the cell rear and to relocalize at the cell front in a cytoplasmic form. In contrast, during planar movement caveolin-1 is concentrated at the rear of ECs, colocalizing with caveolae. The phosphorylatable Tyr14 residue of caveolin-1 is required for polarization of the protein during transmigration but does not alter polarization during planar movement. Palmitoylation of caveolin-1 is not essential for redistribution of the protein during either mode of movement. Thus, ECs migrating in three dimensions uniquely exhibit dissociation of caveolin-1 from caveolae and phosphorylation-dependent relocalization to the cell front.

Correlative Microscopy of Ultrathin Cryosections is a Powerful Tool for Placental Research

In this report, we describe procedures for correlative fluorescence and electron microscopy in immunocytochemical studies on the human placenta. Ultrathin cryosections of placenta were used for detection of the distribution of antigens by immunofluorescence and subsequently by immunoelectron microscopy of the same ultrathin cryosection. This methodology has certain advantages over conventional immunohistochemistry and immunoelectron microscopy. The advantages are, most notably, that the same exact structures are examined by both imaging modalities. In addition, since the tissue is physically sectioned (50–100nm thickness), greater resolution for fluorescence can be obtained in the z-dimension than can be obtained by optical sectioning in confocal microscopy. This last point is of particular importance for discriminating between structures closely stacked in the z-dimension. In this report, we have determined the distribution of caveolin-1 in ultrathin cryosections of terminal villi of the human term placenta. We demonstrate that the use of ultrathin cryosections is a powerful approach for immunofluorescence and correlative microscopy for the in situ localization of antigens.

Distribution and localization of caveolin-1 in sinusoidal cells in rat liver.

Caveolin, the principal structural protein in caveolae, is involved in signal transduction. The aim of the present study was to clarify the distribution and ultrastructural localization of caveolin-1 in hepatic sinusoidal endothelial cells (SECs) and hepatic stellate cell (HSCs) by confocal microscopy and the electron immunogold method. Liver tissue sections were prepared from male Wistar rats. SECs and HSCs were isolated from rat livers by collagenase infusion. For immunohistochemistry, liver sections were reacted with anticaveolin-1 antibody. The localization and distribution of caveolin-1 were identified by confocal immunofluorescence. The ultrastructural localization of caveolin-1 on SECs and HSCs was identified by electron microscopy using the immunogold method. Immunohistochemical studies using liver tissues localized caveolin-1 in sinusoidal lining cells, bile canaliculi, portal vein, and hepatic artery. By confocal microscopy, caveolin-1 was mainly demonstrated at the Golgi complex in SECs and HSCs. Under an electron microscope, immunogold particles indicating the presence of caveolin-1 were demonstrated on the plasma membrane of sinusoidal endothelial fenestrae (SEF) and vesicles in SECs. Under an electron microscope, immunogold particles indicating the presence of caveolin-1 were demonstrated on the plasma membrane of caveolae and vesicles in HSCs. We concluded that caveolin-1 is localized from SEFs to the Golgi complex in SECs and from caveolae to the Golgi complex in HSCs.

Caveolin-1 and -3 dissociations from caveolae to cytosol in the heart during aging and after myocardial infarction in rat.

Caveolins, the structural proteins of caveolae, modulate numerous signaling pathways including Nitric Oxide (NO) production. Among the caveolin family, caveolin-1 and -3 are mainly expressed in endothelial and muscle cells, respectively. In this study, we investigate whether (i) changes in caveolin abundance and/or distribution occur during cardiac aging and failure in rat, and (ii) the process could influence NO synthase (NOS) activity. Using immunohistolabelling and Western blot approaches, expression and distribution of caveolins were analysed in adult (Ad), senescent (S-Sh) and myocardial infarction-induced failing (S-MI) hearts. NOS3/caveolin-1 interactions were evaluated by immunoprecipitation assays. At the microscope level, caveolin-1 distribution in the endothelial cells was unchanged between the groups. Conversely the typical distribution of caveolin-3 in myocyte sarcolemma was dramatically altered in S-MI rats, resulting in a heterogeneous pattern throughout the septum. Total abundance of caveolin-1 and -3 remained stable whatever the group. In the fractions free of caveolae (Triton X-100 soluble), the levels of caveolin-1 alpha and -3 increased with aging (+20%, and +104%, P<0.05 versus Ad, respectively) and were further enhanced in S-MI (+25%, +30%, P<0.05, P<0.001 versus S-Sh respectively). In these fractions, NOS3/caveolin-1 alpha complexes increased as well. In addition, NOS activity was negatively correlated to caveolin-1 level in the cytosolic fractions. We demonstrate that dissociation of caveolin from caveolae is associated with aging and heart failure, the process being related to the decreased NOS activity.

Downregulation and altered spatial pattern of caveolin-1 in chronic plaque psoriasis.

Caveolin-1 is a key structural and functional protein for plasmalemmal invaginations termed caveolae. Caveolin-1 is known to modulate multiple signal-transducing pathways involved in cell differentiation and proliferation. Psoriasis is viewed as a multifactorial pathology characterized by keratinocyte hyperproliferation and abnormal cell maturation. We hypothesized that loss of caveolin-1 within epidermal keratinocytes may contribute to the development and/or progression of the psoriatic phenotype. To examine the expression and spatial distribution of caveolin-1 in skin biopsies from normal subjects and in patients with psoriasis. Using immunohistochemical methods caveolin-1 protein expression was assayed in two independent patient groups. Firstly, a retrospective analysis was conducted on archival skin samples obtained from nine normal subjects and from involved tissue of 12 patients with psoriasis. Following this, a prospectively designed study was conducted in 10 further patients with active psoriasis and involving caveolin-1 staining of biopsy tissue from the uninvolved, advancing edge and lesional skin tissue from within the same subject. In normal skin or uninvolved skin from psoriasis patients intense caveolin-1 staining was present throughout full-thickness epidermis. In 20 of the 22 patient cases (combined retrospective and prospective samples) caveolin-1 protein was significantly reduced and consistently showed very weak or absent staining within the hyperproliferative basal cell layers of the psoriatic plaque (P < 0.002 for retrospective archival study and P < 0.01 for prospectively designed study). Comparisons between caveolin-1 staining in uninvolved tissue and at the advancing edge of a migrating plaque were more equivocal (P > 0.05). The findings of this study are consistent with a downregulation of caveolin-1 that may serve as an aetiological factor in the development and/or progression of psoriasis. Further mechanistic investigations are required with the potential that caveolin-1 protein may be a novel target for therapy of psoriasis.

Shear stress induces caveolin-1 translocation in cultured endothelial cells.

Considering that vascular endothelial caveolae could be flow sensors converting mechanical stimuli into chemical signals transmitted into the cell, this work studied, in vitro, the change of caveolin-1 expression and distribution of cultured endothelial cells exposed to laminar flows. Experimental results showed that, in control cells, caveolin-1 were primarily localized on the cell surface, and presented some local concentrations. In cells exposed to laminar flows, caveolin-1 distribution showed a time-dependent variation. After 24 h of shear (1.0 Pa), the expression of caveolin-1 increased and a local caveolin-1 concentration was found, in most cells, at the upstream side of the cell body where the hydrostatic pressure and the spatial gradient of shear stress were at a maximum. As a comparison, tumor necrosis factor-a induced a decrease of caveolin-1 in the cells.