Decreased expression of caveolin 1 in patients with systemic sclerosis: crucial role in the pathogenesis of tissue fibrosis.

OBJECTIVE: Recent studies have implicated caveolin 1 in the regulation of transforming growth factor beta (TGFbeta) downstream signaling. Given the crucial role of TGFbeta in the pathogenesis of systemic sclerosis (SSc), we sought to determine whether caveolin 1 is also involved in the pathogenesis of tissue fibrosis in SSc. We analyzed the expression of CAV1 in affected SSc tissues, studied the effects of lack of expression of CAV1 in vitro and in vivo, and analyzed the effects of restoration of caveolin 1 function on the fibrotic phenotype of SSc fibroblasts in vitro. METHODS: CAV1 expression in tissues was analyzed by immunofluorescence and confocal microscopy. The extent of tissue fibrosis in Cav1-knockout mice was assessed by histologic/histochemical analyses and quantified by hydroxyproline assays. Cav1-null and SSc fibroblast phenotypes and protein production were analyzed by real-time polymerase chain reaction, immunofluorescence, Western blot, and multiplexed enzyme-linked immunosorbent assay techniques. The effects of restoration of caveolin 1 function in SSc fibroblasts in vitro were also examined using a cell-permeable recombinant CAV1 peptide. RESULTS: CAV1 was markedly decreased in the affected lungs and skin of SSc patients. Cav1-knockout mice developed pulmonary and skin fibrosis. Down-regulation of caveolin 1 was maintained in cultured SSc fibroblasts, and restoration of caveolin 1 function in vitro normalized their phenotype and abrogated TGFbeta stimulation through inhibition of Smad3 activation. CONCLUSION: Caveolin 1 appears to participate in the pathogenesis of tissue fibrosis in SSc. Restoration of caveolin 1 function by treatment with a cell-permeable peptide corresponding to the CAV1 scaffolding domain may be a novel therapeutic approach in SSc

Caveolin-1, TGF-β receptor internalization, and the pathogenesis of systemic sclerosis

PURPOSE OF REVIEW: To review the scientific literature supporting the participation of caveolin-1 in the pathogenesis of tissue fibrosis and the notion that modulation of the caveolin-1 pathway may represent a novel treatment for systemic sclerosis and other fibrotic diseases. RECENT FINDINGS: Caveolin-1 plays an important role in the regulation of transforming growth factor-beta (TGF-beta) signaling owing to its participation in TGF-beta receptor internalization. TGF-beta receptor internalized through caveolin-1 lipid rafts undergoes rapid degradation, effectively decreasing TGF-beta signaling. Studies have shown that caveolin-1 knockdown in vitro markedly increased collagen gene expression in normal human lung fibroblasts. Caveolin-1 was reduced in affected systemic sclerosis lungs and skin and in idiopathic pulmonary fibrosis lung tissues and fibroblasts. Increasing caveolin-1 expression markedly improved bleomycin-induced pulmonary fibrosis. Restoration of caveolin bioavailability employing penetratin, a cell-permeable peptide carrier for a bioactive caveolin-1 fragment, abrogated TGF-beta activation of cultured human dermal fibroblasts. Systemic administration of penetratin-caveolin-1 peptide to mice with bleomycin-induced lung fibrosis reduced fibrosis. SUMMARY: Caveolin-1 plays an important role in the regulation of TGF-beta signaling and participates in the pathogenesis of systemic sclerosis and idiopathic pulmonary fibrosis. Restoration of caveolin function employing active caveolin-1 fragments coupled to cell-permeable carrier peptides may represent a novel approach for their treatment

Caveolin-1 recruitment to the trailing edge of motile cells results in focal adhesion disassembly and nascent interaction with actin stress fibers

The protein caveolin-1 has been shown to positively affect angiogenesis and vascular remodeling in vivo via studies using knockout mice. In fact, defects in these two processes are among the major hallmarks of an otherwise benign caveolin-null phenotype. Current dogma on the function of caveolin-1 does not predict or account for these deficits. The overall objective of the following studies was to uncover the role of caveolin-1 in angiogenesis and vascular remodeling through study of the protein in cell-substratum remodeling during cell motility in vitro.;In the first study, caveolin-1 and its parent organelle, caveolae, conspicuously polarize to the rear of migrating human umbilical vein endothelial cells. Moreover, caveolin-1 localizated at the cell rear is mutually exclusive with focal adhesion staining and lamellipodial protrusion. Acute caveolin-1 knockdown by small, interfering RNA diminished the ability of endothelial cells to polarize and migrate toward a chemotactic stimulus.;In the second study, live cell imaging was used to study the dynamics between caveolin-1, focal adhesions, and the actin cytoskeleton. Caveolin-1 recruitment and transient association with focal adhesions at the trailing edge resulted in adhesion sliding and disassembly, concomitant with recoil of the trailing edge into the cell body proper. Moreover, association of caveolin-1 with actin stress fibers previously associated with adhesions in the collapsing trailing edge was observed. Mouse embryonic fibroblasts from caveolin-1 null mice demonstrated defects in trailing edge recoil compared to control cells with no decrease in cell contractility, suggesting a specific deficit in adhesion disassembly. Furthermore, caveolin-null cells displayed a decrease in overall chemokinetic motility and an increase in directional persistence, an indication that caveolin-1 contributes to movement plasticity via trailing edge focal adhesion disassembly.;In the final study, the interaction of polarized caveolin-1 with actin stress fibers at the cell rear was characterized. Caveolin-1 predictably associated with the cell perimeter depending on the direction of cell migration. Importantly, inhibition on non-muscle myosin by blebbistatin treatment abrogated initial polarization of caveolin-1, but did not affect caveolin-1 that had already polarized. Using live cell imaging in conjunction with photobleaching, actin-associated caveolin-1 was found to be extremely static upon polarization to the cell rear. In contrast, the initial polarization of caveolin-1 to retracting areas was highly dynamic. Furthermore, GM1 internalization at the cell rear was negligible, confirming that polarized caveolae are highly static. Forced disruption of the actin cytoskeleton by cytochalasin D treatment resulted in caveolin-1 depolarization and disaggregation into small puncta displaying frenetic, kiss-and-run movement. Furthermore, cytoskeletal remodeling in response to change in direction of a cell resulted in similar caveolin depolarization.;In summary, stress fibers associate with and exert traction on trailing edge focal adhesions during cell motility. This traction force is prerequisite for caveolin-1 recruitment. Arrival and transient association of caveolin-1 with focal adhesions results in adhesion disassembly and stable interaction of caveolin with actin stress fibers. Thus, a novel mechanism in cellular mechanotransduction can be described, whereby cells utilize caveolin-1 recruitment to relieve strain generated at the cell perimeter by the actin cytoskeleton during movement. This novel function of caveolin-1 may analogously occur in vivo, beyond the context of endothelial cell migration. The deficits in angiogenesis and vascular remodeling seen in caveolin-1 null mice might thus be explained by the role of caveolin-1 in cell-substratum remodeling in response to strain

Caveolin-1 expression is elevated in claudin-low mammary tumor cells

<p>Abstract</p> <p>Background</p> <p>Caveolin-1 is a scaffolding protein found in plasma membrane invaginations known as caveolae. Caveolin-1 can regulate a number of intracellular processes such as signal transduction, cholesterol metabolism and vesicular transport. With respect to breast cancer caveolin-1 has been observed in both tumor cells and stromal cells surrounding tumors however most of the recent research has focused on how the loss of caveolin-1 in the stromal cells surrounding the tumor alters the tumor microenvironment.</p> <p>Methods</p> <p>Caveolin-1 expression was evaluated in (1) mammary tumors induced by the transgenic overexpression of the type I insulin-like growth factor receptor (IGF-IR), (2) mammary tumors that became independent of IGF-IR signalling and acquired a claudin-low genotype, (3) two murine mammary epithelial tumor cell lines and (4) two murine mammary claudin-low tumor cell lines.</p> <p>Results</p> <p>We found that mammary tumors induced by IGF-IR overexpression expressed low levels of caveolin-1 while mammary tumors that became independent of IGF-IR signalling expressed considerably higher levels of caveolin-1. Interestingly, pockets of caveolin-1 positive cells could be observed in some of the IGF-IR-induced mammary tumors and these caveolin-1 positive cells were associated with tumor cells that expressed basal cytokeratins (cytokeratins 5 and 14). This caveolin-1 expression pattern was maintained in the murine mammary tumor cell lines in that the epithelial mammary tumor cell lines expressed little or no caveolin-1 while the claudin-low cell lines expressed caveolin-1.</p> <p>Conclusions</p> <p>Our model indicates that mammary tumor cells with epithelial characteristics lack caveolin-1 while mesenchymal tumor cells express caveolin-1 suggesting that caveolin-1 may serve as a marker of mammary tumor cells with mesenchymal characteristics such as claudin-low breast tumors.</p

Caveolin-1-Enhanced Motility and Focal Adhesion Turnover Require Tyrosine-14 but Not Accumulation to the Rear in Metastatic Cancer Cells

Caveolin-1 is known to promote cell migration, and increased caveolin-1 expression is associated with tumor progression and metastasis. In fibroblasts, caveolin-1 polarization and phosphorylation of tyrosine-14 are essential to promote migration. However, the role of caveolin-1 in migration of metastatic cells remains poorly defined. Here, caveolin-1 participation in metastatic cell migration was evaluated by shRNA targeting of endogenous caveolin-1 in MDA-MB-231 human breast cancer cells and ectopic expression in B16-F10 mouse melanoma cells. Depletion of caveolin-1 in MDA-MB-231 cells reduced, while expression in B16-F10 cells promoted migration, polarization and focal adhesion turnover in a sequence of events that involved phosphorylation of tyrosine-14 and Rac-1 activation. In B16-F10 cells, expression of a non-phosphorylatable tyrosine-14 to phenylalanine mutant failed to recapitulate the effects observed with wild-type caveolin-1. Alternatively, treatment of MDA-MB-231 cells with the Src family kinase inhibitor PP2 reduced caveolin-1 phosphorylation on tyrosine-14 and cell migration. Surprisingly, unlike for fibroblasts, caveolin-1 polarization and re-localization to the trailing edge were not observed in migrating metastatic cells. Thus, expression and phosphorylation, but not polarization of caveolin-1 favor the highly mobile phenotype of metastatic cells

Impact of Caveolin-1 Expression on the Prognosis of Transitional Cell Carcinoma of the Upper Urinary Tract

This study aimed to investigate the relationship of caveolin-1 expression with prognosis in patients with transitional cell carcinoma of the upper urinary tract (TCC-UUT). Formalin-fixed, paraffin-embedded tissue sections of TCC-UUT from 98 patients, who had undergone radical nephroureterectomy, were stained immunohistochemically using antibodies against caveolin-1. The expression pattern of caveolin-1 was compared with the clinicopathological variables. The caveolin-1 expression was significantly correlated with T stage (p<0.001) and grade (p=0.036). The survival rate of patients with caveolin-1 positive tumors was significantly lower than that of patients with caveolin-1 negative tumors (p<0.0001). The univariate analyses identified T stage, grade, and caveolin-1 expression as significant prognostic factors for cancer-specific survival, whereas the multivariate analyses indicated that T stage and caveolin-1 expression were independent prognostic factors. These results show that the increased expression of caveolin-1 is associated with tumor progression and poor prognosis in TCC-UUT, suggesting that caveolin-1 may play an important role in the progression of TCC-UUT

Caveolin-1 and -2 in the Exocytic Pathway of MDCK Cells

Abstract. We have studied the biosynthesis and transport of the endogenous caveolins in MDCK cells. We show that in addition to homooligomers of caveolin-1, heterooligomeric complexes of caveolin-1 and -2 are formed in the ER. The oligomers become larger, increasingly detergent insoluble, and phosphorylated on caveolin-2 during transport to the cell surface. In the TGN caveolin-1/-2 heterooligomers are sorted into basolateral vesicles, whereas larger caveolin-1 homooligomers are targeted to the apical side. Caveolin-1 is present on both the apical and basolateral plasma membrane, whereas caveolin-2 is enriched on the basolateral surface where caveolae are present. This suggests that caveolin-1 and -2 heterooligomers are involved in caveolar biogenesis in the basolateral plasma membrane. Anti–caveolin-1 antibodies inhibit the apical delivery of influenza virus hemagglutinin without affecting basolateral transport of vesicular stomatitis virus G protein. Thus, we suggest that caveolin-1 homooligomers play a role in apical transport

Interaction of caveolin-1 with Ku70 inhibits Bax-mediated apoptosis

Caveolin-1, the structural protein component of caveolae, acts as a scaffolding protein that functionally regulates signaling molecules. We show that knockdown of caveolin-1 protein expression enhances chemotherapeutic drug-induced apoptosis and inhibits long-term survival of colon cancer cells. In vitro studies demonstrate that caveolin-1 is a novel Ku70-binding protein, as shown by the binding of the scaffolding domain of caveolin-1 (amino acids 82-101) to the caveolin-binding domain (CBD) of Ku70 (amino acids 471-478). Cell culture data show that caveolin-1 binds Ku70 after treatment with chemotherapeutic drugs. Mechanistically, we found that binding of caveolin-1 to Ku70 inhibits the chemotherapeutic drug-induced release of Bax from Ku70, activation of Bax, translocation of Bax to mitochondria and apoptosis. Potentiation of apoptosis by knockdown of caveolin-1 protein expression is greatly reduced in the absence of Bax expression. Finally, we found that overexpression of wild type Ku70, but not a mutant form of Ku70 that cannot bind to caveolin-1 (Ku70 Φ→A), limits the chemotherapeutic drug-induced Ku70/Bax dissociation and apoptosis. Thus, caveolin-1 acts as an anti-apoptotic protein in colon cancer cells by binding to Ku70 and inhibiting Bax-dependent cell death. © 2012 Zou et al

Correlation of caveolin-1 expression with microlymphatic vessel density in colorectal adenocarcinoma tissues and its correlation with prognosis

AbstractObjectiveTo study the expression of caveolin-1 in colorectal adenocarcinoma tissues and its correlation with microlymphatic vessel density (LMVD), and to investigate the clinical pathological prognostic significance of caveolin-1 and LMVD in patients with colorectal cancer.MethodsThe expression of caveolin-1 and LMVD in 45 specimens of normal colorectal tissues, and 90 specimens of colorectal adenocarcinoma tissues were detected by immunohistochemistry technique. The correlation between their expression and the clinicopathologic features was analyzed. Multivariable Cox regression was used to analyze the association between the laboratory indices and overall survival time.ResultsThe positive rates of caveolin-1 in colorectal adenocarcinoma tissues were significantly higher than those in normal colorectal tissues (P < 0.01). LMVD in colorectal adenocarcinoma tissues were significantly higher than those in normal colorectal tissues (P < 0.01). Mean LMVD in group with caveolin-1 positive was significantly higher than in that with caveolin-1 negative. The median survival time was 26.7 months. Cox regression analysis showed that the caveolin-1 expression, invation depth, lymph node metastasis, TNM stage, liver metastasis and LMVD were independent risk factors of overall survival time of patients with colorectal carcinoma.ConclusionsCaveolin-1 may contribute to the lymphangiogenesis in the tumor. During the occurrence and development of colorectal adenocarcinoma, there is a close relationship between the expression of caveolin-1 and lymphatic microvessel of tumor. Caveolin-1 expression and microlymphatic vessel density are significant prognostic value of colorectal carcinoma

Analysis of peroxynitrite-mediated post-translational modifications of caveolin-1

Caveolin-1 is an important protein in caveolae, which plays a role in cholesterol transport, signal transduction, and transcytosis and tumor suppression. Caveolin-1 is found in endothelial cells, smooth muscle cells and adipocytes. The main focus of this study is to investigate the peroxynitrite-mediated in vitro post-translational modifications (PTMs) of caveolin-1. Bovine brain was used to isolate caveolin-1 as an initial step for isolation method development. Density gradient centrifugation was used to isolate caveolin-1 from bovine brain. From the isolate, caveolin-1α, caveolin-1β isomers and caveolin dimer were identified by western blotting with anti-caveolin monoclonal antibody. Glutathione S-transferase (GST)-caveolin fusion protein was used to isolate caveolin-1 and used for in vitro experiments in this study. During normal and pathological conditions, endothelial cells are subjected to locally generated reactive oxygen species such as peroxynitrite. Peroxynitrite is capable of modifying amino acids such as tyrosine, cysteine, tryptophan and methionine. Peroxynitrite mediated tyrosine nitration of caveolin-1 was detected by SDS-PAGE followed by western blotting with anti-nitrotyrosine monoclonal antibody. The approach used to identify potentially modified peptide sequences of caveolin-1 was ESI-MS/MS. Fluorometry was used to detect formation of dityrosine. Caveolin-1 was treated with different concentrations of peroxynitrite in caveolin- under the physiological conditions and found that caveolin-1 form dimer and oligomer under the physiological conditions. The stability of caveolin-1 dimer and oligomer suggests that the coupling mechanism could most likely be occurred via a covalent bond. Western blotting with anti-nitrotyrosine monoclonal antibody revealed the formation of nitrotyrosine upon the exposure to peroxynitrite. In this study, we report the nitration of specific tyrosine residues of caveolin-1 for the first time. ESI-MS/MS analysis revealed that peroxynitrite can selectively nitrate Tyr6 and Tyr14 located in the tryptic peptide YVDSEGHLYTVPIR under physiological conditions. Caveolin-1 can form dityrosine upon exposure to peroxynitrite as shown by fluorometry. Oxidative and nitrative modifications due to the reaction of peroxynitrite with caveolin-1 may lead to several pathological conditions. Our study can provide authentic standards of modified proteins, which will be used to determine post-translational modifications of caveolin-1 in vivo