Caveolin-2 is a negative regulator of anti-proliferative function and signaling of transforming growth factor-β in endothelial cells

Sex-biased TGFβ signalling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare cardiovascular disorder leading to pulmonary hypertension and, often fatal, right heart failure. Sex differences in PAH are evident, which primarily presents with a female predominance and increased male severity. Disturbed signalling of the transforming growth factor-β (TGFβ) family and gene mutations in the bone morphogenetic protein receptor 2 (BMPR2) are risk factors for PAH development, but how sex-specific cues affect the TGFβ family signalling in PAH remains poorly understood. In this review, we aim to explore the sex bias in PAH by examining sex differences in the TGFβ signalling family through mechanistical and translational evidence. Sex hormones including oestrogens, progestogens, and androgens, can determine the expression of receptors (including BMPR2), ligands, and soluble antagonists within the TGFβ family in a tissue-specific manner. Furthermore, sex-related genetic processes, i.e. Y-chromosome expression and X-chromosome inactivation, can influence the TGFβ signalling family at multiple levels. Given the clinical and mechanistical similarities, we expect that the conclusions arising from this review may apply also to hereditary haemorrhagic telangiectasia (HHT), a rare vascular disorder affecting the TGFβ signalling family pathway. In summary, we anticipate that investigating the TGFβ signalling family in a sex-specific manner will contribute to further understand the underlying processes leading to PAH and likely HHT.

Extracellular Vesicles Mediate Communication between Endothelial and Vascular Smooth Muscle Cells

The recruitment of pericytes and vascular smooth muscle cells (SMCs) that enwrap endothelial cells (ECs) is a crucial process for vascular maturation and stabilization. Communication between these two cell types is crucial during vascular development and in maintaining vessel homeostasis. Extracellular vesicles (EVs) have emerged as a new communication tool involving the exchange of microRNAs between cells. In the present study, we searched for microRNAs that could be transferred via EVs from ECs to SMCs and vice versa. Thanks to a microRNA profiling experiment, we found that two microRNAs are more exported in each cell type in coculture experiments: while miR-539 is more secreted by ECs, miR-582 is more present in EVs from SMCs. Functional assays revealed that both microRNAs can modulate both cell-type phenotypes. We further identified miR-539 and miR-582 targets, in agreement with their respective cell functions. The results obtained in vivo in the neovascularization model suggest that miR-539 and miR-582 might cooperate to trigger the process of blood vessel coverage by smooth muscle cells in a mature plexus. Taken together, these results are the first to highlight the role of miR-539 and miR-582 in angiogenesis and communication between ECs and SMCs.

Noncoding RNAs Interactions in Hepatic Stellate Cells during Hepatic Fibrosis

Hepatic fibrosis is a reversible wound healing process following liver injury. Although this process is necessary for maintaining liver integrity, severe excessive extracellular matrix accumulation (ECM) could lead to permanent scar formation and destroy the liver structure. The activation of hepatic stellate cells (HSCs) is a key event in hepatic fibrosis. Previous studies show that most antifibrotic therapies focus on the apoptosis of HSCs and the prevention of HSC activation. Noncoding RNAs (ncRNAs) play a substantial role in HSC activation and are likely to be biomarkers or therapeutic targets for the treatment of hepatic fibrosis. This review summarizes and discusses the previously reported ncRNAs, including the microRNAs, long noncoding RNAs, and circular RNAs, highlighting their regulatory roles and interactions in the signaling pathways that regulate HSC activation in hepatic fibrosis.

Elevated postischemic tissue injury and leukocyte-endothelial adhesive interactions in mice with global deficiency in caveolin-2: role of PAI-1

Ischemia/reperfusion (I/R)-induced rapid inflammation involving activation of leukocyte-endothelial adhesive interactions and leukocyte infiltration into tissues is a major contributor to postischemic tissue injury. However, the molecular mediators involved in this pathological process are not fully known. We have previously reported that caveolin-2 (Cav-2), a protein component of plasma membrane caveolae, regulated leukocyte infiltration in mouse lung carcinoma tumors. The goal of the current study was to examine if Cav-2 plays a role in I/R injury and associated acute leukocyte-mediated inflammation. Using a mouse small intestinal I/R model, we demonstrated that I/R downregulates Cav-2 protein levels in the small bowel. Further study using Cav-2-deficient mice revealed aggravated postischemic tissue injury determined by scoring of villi length in H&E-stained tissue sections, which correlated with increased numbers of MPO-positive tissue-infiltrating leukocytes determined by IHC staining. Intravital microscopic analysis of upstream events relative to leukocyte transmigration and tissue infiltration revealed that leukocyte-endothelial cell adhesive interactions in postcapillary venules, namely leukocyte rolling and adhesion were also enhanced in Cav-2-deficient mice. Mechanistically, Cav-2 deficiency increased plasminogen activator inhibitor-1 (PAI-1) protein levels in the intestinal tissue and a pharmacological inhibition of PAI-1 had overall greater inhibitory effect on both aggravated I/R tissue injury and enhanced leukocyte-endothelial interactions in postcapillary venules in Cav-2-deficient mice. In conclusion, our data suggest that Cav-2 protein alleviates tissue injury in response to I/R by dampening PAI-1 protein levels and thereby reducing leukocyte-endothelial adhesive interactions.NEW & NOTEWORTHY The role of caveolin-2 in regulating ischemia/reperfusion (I/R) tissue injury and the mechanisms underlying its effects are unknown. This study uses caveolin-2-deficient mouse and small intestinal I/R injury models to examine the role of caveolin-2 in the leukocyte-dependent reperfusion injury. We demonstrate for the first time that caveolin-2 plays a protective role from the I/R-induced leukocyte-dependent reperfusion injury by reducing PAI-1 protein levels in intestinal tissue and leukocyte-endothelial adhesive interactions in postcapillary venules.

The TGF-β1 Induces the Endothelial-to-Mesenchymal Transition via the UCA1/miR-455/ZEB1 Regulatory Axis in Human Umbilical Vein Endothelial Cells

Transforming growth factor-beta 1 (TGF-β1) plays important roles in the endothelial-to-mesenchymal transition (EndMT). Recently, long noncoding RNAs (lncRNAs) have been identified to be involved in the physiological and pathological processes of human diseases. However, the role of endothelial lncRNAs in the TGF-β1-mediated control of angiogenesis and its underlying mechanism remains largely unclear. In this study, we first demonstrated that TGF-β1 induced EndMT; promoted cell viability, proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs). Second, our study displayed that TGF-β1 upregulated the lncRNA UCA1 expression in HUVECs, knocked down UCA1 with small interfering RNAs, and inhibited the function of TGF-β1 in HUVECs. Third, our study showed that UCA1 was located in the cytoplasm and absorbed miR-455 in TGF-β1-treated HUVECs. Further, the miR-455 inhibitor restored the role of the inhibited UCA1 in HUVECs treated with TGF-β1. Fourth, our study revealed that miR-455 inhibited ZEB1 expression, and overexpression of ZEB1 restored the role of miR-455 in HUVECs treated with TGF-β1. Finally, our study revealed that UCA1 exerted its role via regulating the UCA1/miR-455/ZEB1 regulatory axis in HUVECs treated with TGF-β1. Collectively, our study identified the role of the UCA1/miR-455/ZEB1 pathway in HUVECs treated with TGF-β1 and indicated the potential therapeutic role of this regulatory axis in angiogenesis.

Lung Endothelial Transcytosis

Transcytosis of macromolecules through lung endothelial cells is the primary route of transport from the vascular compartment into the interstitial space. Endothelial transcytosis is mostly a caveolae-dependent process that combines receptor-mediated endocytosis, vesicle trafficking via actin-cytoskeletal remodeling, and SNARE protein directed vesicle fusion and exocytosis. Herein, we review the current literature on caveolae-mediated endocytosis, the role of actin cytoskeleton in caveolae stabilization at the plasma membrane, actin remodeling during vesicle trafficking, and exocytosis of caveolar vesicles. Next, we provide a concise summary of experimental methods employed to assess transcytosis. Finally, we review evidence that transcytosis contributes to the pathogenesis of acute lung injury. © 2020 American Physiological Society. Compr Physiol 10:491-508, 2020.

Caveolin-2 deficiency induces a rapid anti-tumor immune response prior to regression of implanted murine lung carcinoma tumors

Immunosuppression is critical for tumor growth and metastasis as well as obstacle to effective immunotherapy. Here, we demonstrate that host deficiency in caveolin-2, a member of caveolin protein family, increases M1-polarized tumor-associated macrophage (TAM) and CD8 T cell infiltration into subcutaneously implanted murine lung carcinoma tumors. Importantly, increase in M1 TAM-specific markers and cytokines occurs prior to increased numbers of tumor-infiltrating CD8 T cells and tumor regression in caveolin-2 deficient mice, suggesting that an early increase in M1 TAMs is a novel mechanism, via which host deficiency in caveolin-2 inhibits tumor growth. Consistent with the latter, transfer and co-injection of caveolin-2 deficient bone marrow (origin of TAMs) suppresses tumor growth and increases numbers of M1-polarized TAMs in wild type mice. Collectively, our data suggest that lung cancer cells use caveolin-2 expressed in bone marrow-derived cell types including TAMs to promote tumor growth via suppressing the anti-tumor immune response and that caveolin-2 could be a potential target for cancer immunotherapy.

Caveolin-1 as a critical component in the pathogenesis of lung fibrosis of different etiology: Evidences and mechanisms

Caveolin is a structural protein of flask-shaped invaginations of the plasma membrane termed as caveolae and is widely expressed on the endothelial cells, smooth muscle cells and fibroblasts in the different parts of the body including the lung tissues. The expression of caveolin-1 in the lung tissues is important to prevent the fibrogenic actions of TGF-β1 in lung fibrosis of different etiology including idiopathic pulmonary fibrosis, systemic sclerosis-associated interstitial lung disease and allergen-induced airway remodeling. Caveolin-1-mediated internalization and degradation of TGF-β1 receptors may possibly account for the decreased actions of TGF-β1. Studies have shown that the deficiency of caveolin-1 is very important in inducing lung fibrosis and its upregulation is reported to prevent lung fibrosis. The biological actions of caveolin-1 involve signaling pathways including JNK signaling, IL-4, STAT-3, miR199a-5p, CXCR4⁺ and CXCL12. The present review discusses the key role of caveolin and associated signaling pathways in the pathogenesis of lung fibrosis of different etiology.

Caveolin-1 and Caveolin-2 Can Be Antagonistic Partners in Inflammation and Beyond

Caveolins, encoded by the CAV gene family, are the main protein components of caveolae. In most tissues, caveolin-1 (Cav-1) and caveolin-2 (Cav-2) are co-expressed, and Cav-2 targeting to caveolae depends on the formation of heterooligomers with Cav-1. Notwithstanding, Cav-2 has unpredictable activities, opposing Cav-1 in the regulation of some cellular processes. While the major roles of Cav-1 as a modulator of cell signaling in inflammatory processes and in immune responses have been extensively discussed elsewhere, the aim of this review is to focus on data revealing the distinct activity of Cav-1 and Cav-2, which suggest that these proteins act antagonistically to fine-tune a variety of cellular processes relevant to inflammation.

Expression-associated polymorphisms of CAV1-CAV2 affect intraocular pressure and high-tension glaucoma risk

PURPOSE

The human CAV1-CAV2 locus has been associated with susceptibility to primary open-angle glaucoma in four studies of Caucasian, Chinese, and Pakistani populations, although not in several other studies of non-Korean populations. In this study with Korean participants, the CAV1-CAV2 locus was investigated for associations with susceptibility to primary open-angle glaucoma accompanied by elevated intraocular pressure (IOP), namely, high-tension glaucoma (HTG), as well as with IOP elevation, which is a strong risk factor for glaucoma.

METHODS

Two single nucleotide polymorphisms (SNPs) were genotyped in 1,161 Korean participants including 229 patients with HTG and 932 healthy controls and statistically examined for association with HTG susceptibility and IOP. One SNP was rs4236601 G>A, which had been reported in the original study, and the other SNP was rs17588172 T>G, which was perfectly correlated (r2=1) with another reported SNP rs1052990. Expression quantitative trait loci (eQTL) analysis was performed using GENe Expression VARiation (Genevar) data.

RESULTS

Both SNPs were associated with HTG susceptibility, but the rs4236601 association disappeared when adjusted for the rs17588172 genotype and not vice versa. The minor allele G of rs17588172 was associated significantly with 1.5-fold increased susceptibility to HTG (p=0.0069) and marginally with IOP elevation (p=0.043) versus the major allele T. This minor allele was also associated with decreased CAV1 and CAV2 mRNA in skin and adipose according to the Genevar eQTL analysis.

CONCLUSIONS

The minor allele G of rs17588172 in the CAV1-CAV2 locus is associated with decreased expression of CAV1 and CAV2 in some tissues, marginally with IOP elevation, and consequently with increased susceptibility to HTG.

Endocytic deficiency induced by ITSN-1s knockdown alters the Smad2/3-Erk1/2 signaling balance downstream of Alk5

Recently, we demonstrated in cultured endothelial cells and in vivo that deficiency of an isoform of intersectin-1, ITSN-1s, impairs caveolae and clathrin-mediated endocytosis and functionally upregulates compensatory pathways and their morphological carriers (i.e. enlarged endocytic structures, membranous rings or tubules) that are normally underrepresented. We now show that these endocytic structures internalize the broadly expressed transforming growth factor β receptor I (TGFβ-RI or TGFBR1), also known as Alk5, leading to its ubiquitylation and degradation. Moreover, the apoptotic or activated vascular cells of the ITSN-1s-knockdown mice release Alk5-bearing microparticles to the systemic circulation. These interact with and transfer Alk5 to endocytosis-deficient endothelial cells, resulting in lung endothelial cell survival and phenotypic alteration towards proliferation through activation of Erk1 and Erk2 (also known as MAPK3 and MAPK1, respectively). We also show that non-productive assembly of the Alk5–Smad–SARA (Smad anchor for receptor activation, also known as ZFYVE9) signaling complex and preferential formation of the Alk5–mSos–Grb2 complex account for Erk1/2 activation downstream of Alk5 and proliferation of pulmonary endothelial cells. Taken together, our studies demonstrate a functional relationship between the intercellular transfer of Alk5 by microparticles and endothelial cell survival and proliferation, and define a novel molecular mechanism for TGFβ and Alk5-dependent Erk1/2^MAPK signaling that is significant for proliferative signaling and abnormal growth.

Systematic analysis of blood cell transcriptome in end-stage chronic respiratory diseases

Background

End-stage chronic respiratory diseases (CRD) have systemic consequences, such as weight loss and susceptibility to infection. However the mechanisms of such dysfunctions are as yet poorly explained. We hypothesized that the genes putatively involved in these mechanisms would emerge from a systematic analysis of blood mRNA profiles from pre-transplant patients with cystic fibrosis (CF), pulmonary hypertension (PAH), and chronic obstructive pulmonary disease (COPD).

Methods

Whole blood was first collected from 13 patients with PAH, 23 patients with CF, and 28 Healthy Controls (HC). Microarray results were validated by quantitative PCR on a second and independent group (7PAH, 9CF, and 11HC). Twelve pre-transplant COPD patients were added to validate the common signature shared by patients with CRD for all causes. To further clarify a role for hypoxia in the candidate gene dysregulation, peripheral blood mononuclear cells from HC were analysed for their mRNA profile under hypoxia.

Results

Unsupervised hierarchical clustering allowed the identification of 3 gene signatures related to CRD. One was common to CF and PAH, another specific to CF, and the final one was specific to PAH. With the common signature, we validated T-Cell Factor 7 (TCF-7) and Interleukin 7 Receptor (IL-7R), two genes related to T lymphocyte activation, as being under-expressed. We showed a strong impact of the hypoxia on modulation of TCF-7 and IL-7R expression in PBMCs from HC under hypoxia or PBMCs from CRD. In addition, we identified and validated genes upregulated in PAH or CF, including Lectin Galactoside-binding Soluble 3 and Toll Like Receptor 4, respectively.

Conclusions

Systematic analysis of blood cell transcriptome in CRD patients identified common and specific signatures relevant to the systemic pathologies. TCF-7 and IL-7R were downregulated whatever the cause of CRD and this could play a role in the higher susceptibility to infection of these patients.

Host deficiency in caveolin-2 inhibits lung carcinoma tumor growth by impairing tumor angiogenesis

Caveolin-2 (Cav-2), a member of caveolin protein family, is largely different from better known caveolin-1 (Cav-1) and thus might play distinct functions. Here, we provide the first genetic evidence suggesting that host-expressed Cav-2 promotes subcutaneous tumor growth and tumor-induced neovascularization using two independent syngeneic mouse models. Host deficiency in Cav-2 resulted in defective and reduced growth of subcutaneously implanted Lewis lung carcinoma (LLC) and B16-F10 melanoma tumors, respectively. Consistent with the defective growth, LLC and B16-F10 melanoma tumors implanted into Cav-2 KO mice displayed reduced microvascular density (MVD) determined by IHC with anti-CD31 antibodies, suggesting impaired pathologic angiogenesis. Additional studies involving LLC tumors extracted from Cav-2 KO mice just 10 days after implantation determined reduced cell proliferation, massive necrotic cell death, and fibrosis. In contrast with day 10, only MVD but not cell proliferation and survival was reduced in the earliest palpable LLC tumors extracted 6 days after implantation into Cav-2 KO mice, suggesting that impaired angiogenesis is the causative factor. Mechanistically, impaired LLC tumor growth and angiogenesis in Cav-2 KO mice was associated with increased expression levels of antiangiogenic thrombospondin-1 and inhibited S1177 phosphorylation of endothelial nitric oxide synthase. Taken together, our data suggest that host deficiency in Cav-2 impairs tumor-induced angiogenesis, leading to compromised tumor cell survival/proliferation manifested by the defective tumor growth. In conclusion, host-expressed Cav-2 may promote tumor growth via supporting tumor-induced angiogenesis. Thus, Cav-2 expressed in tumor microenvironment may potentially become a novel target for cancer therapy.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

Intestinal Salmonella typhimurium infection leads to miR-29a induced caveolin 2 regulation

BACKGROUND

Salmonella are able to modulate host cell functions facilitating both uptake and resistance to cellular host defence mechanisms. While interactions between bacterial modulators and cellular proteins have been the main focus of Salmonella research, relatively little is known about mammalian gene regulation in response to Salmonella infection. A major class of mammalian gene modulators consists of microRNAs. For our study we examined interactions of microRNAs and regulated mRNAs in mammalian intestinal Salmonella infections using a piglet model.

METHODOLOGY/PRINCIPAL FINDINGS

After performing microRNA as well as mRNA specific microarray analysis of ileal samples from Salmonella infected as well as control piglets, we integrated expression analysis with target prediction identifying microRNAs that mainly regulate focal adhesion as well as actin cytoskeleton pathways. Particular attention was given to miR-29a, which was involved in most interactions including Caveolin 2. RT-qPCR experiments verified up-regulation of miR-29a after infection while its predicted target Caveolin 2 was significantly down-regulated as examined by transcript and protein detection. Reporter gene assays as well as RNAi experiments confirmed Caveolin 2 to be a miR-29a target. Knock-down of Caveolin 2 in intestinal epithelial cells resulted in retarded proliferation as well as increased bacterial uptake. In addition, our experiments showed that Caveolin 2 regulates the activation of the small Rho GTPase CDC42 but apparently not RAC1 in human intestinal cells.

CONCLUSIONS/SIGNIFICANCE

Our study outlines for the first time important regulation pathways in intestinal Salmonella infection pointing out that focal adhesion and organisation of actin cytoskeleton are regulated by microRNAs. Functional relevance is shown by miR-29a mediated Caveolin 2 regulation, modulating the activation state of CDC42. Further analysis of examined interactions may support the discovery of novel strategies impairing the uptake of intracellular pathogens.

N-terminal tyrosine phosphorylation of caveolin-2 negates anti-proliferative effect of transforming growth factor beta in endothelial cells

Here we show that tyrosine phosphorylation of caveolin-2 (Cav-2) negatively regulates the anti-proliferative function of transforming growth factor beta (TGF-beta) in endothelial cells. In contrast to wild-type-Cav-2, retroviral re-expression of Y19/27F-Cav-2 in Cav-2 knockout endothelial cells did not affect anti-proliferative effect of TGF-beta compared to empty vector. Conversely, although less effective than wild-type, re-expression of S23/36A-Cav-2 reduced the effect of TGF-beta compared to empty vector. This differential effect of tyrosine and serine phosphorylation mutants of Cav-2 correlated with TGF-beta-induced Smad3 phosphorylation and transcriptional activation of plasminogen activator inhibitor-1. Thus tyrosine-phosphorylated Cav-2 counteracts anti-proliferative effect of TGF-beta in endothelial cells.

Role of Caveolin Proteins in Sepsis

Despite the progress in medical treatment sepsis remains one of the major causes of death in pediatric and elderly patients. Understanding signaling pathways associated with sepsis may be of key significance for designing more efficient therapeutic approaches which could alleviate sepsis outcome. Earlier studies suggested that cholesteroland sphingolipid-rich lipid rafts and their morphologically distinct subset, caveolaecan be utilized by certain bacterial pathogens to enter and invade host cells. Moreover, there is also evidence that the expression levels of the major caveolar coat proteincaveolin-1 can be regulated by the major component of the outer membrane of Gram-negative bacteria,lipopolysaccharide (LPS) in various cell types involved in sepsis. In particular recent studies using caveolin-1 knockout mice and cells have revealed that caveolin-1 is directly involved in regulating numerous signalingpathways and functions in various cell types of the immune system and other cell types involved in sepsis. Moreover, the most recent report implies that in addition to extensively studied caveolin-1, caveolin-2 is also important in regulating LPS-induced sepsis and might possibly play an opposite role to caveolin-1 in regulating certain pro-inflammatory signaling pathways. The purpose of this review is to discuss these new exciting discoveries relatedto the specific role of caveolin-1 and the less studiedcaveolin-2in regulating signaling and outcome associated with sepsis induced by LPS and pathogenic bacteria at molecular, cellular and systemic levels.

Caveolae, caveolins, cavins, and endothelial cell function: new insights

Caveolae are cholesterol and glycosphingolipid-rich flask-shaped invaginations of the plasma membrane which are particularly abundant in vascular endothelium and present in all other cell types of the cardiovascular system, including vascular smooth-muscle cells, macrophages, cardiac myocytes, and fibroblasts. Caveolins and the more recently discovered cavins are the major protein components of caveolae. When caveolae were discovered, their functional role was believed to be limited to transport across the endothelial cell barrier. Since then, however, a large body of evidence has accumulated, suggesting that these microdomains are very important in regulating many other important endothelial cell functions, mostly due to their ability to concentrate and compartmentalize various signaling molecules. Over the course of several years, multiple studies involving knockout mouse and small interfering RNA approaches have considerably enhanced our understanding of the role of caveolae and caveolin-1 in regulating many cardiovascular functions. New findings have been reported implicating other caveolar protein components in endothelial cell signaling and function, such as the understudied caveolin-2 and newly discovered cavin proteins. The aim of this review is to focus primarily on molecular and cellular aspects of the role of caveolae, caveolins, and cavins in endothelial cell signaling and function. In addition, where appropriate, the possible implications for the cardiovascular and pulmonary physiology and pathophysiology will be discussed.

Regulation of Cell Signaling and Function by Endothelial Caveolins: Implications in Disease

Caveolae are cholesterol- and glycosphingolipid-rich omega-shaped invaginations of the plasma membrane that are very abundant in vascular endothelial cells and present in most cell types. Caveolins are the major coat protein components of caveolae. Multiple studies using knockout mouse, small interfering RNA, and cell-permeable peptide delivery approaches have significantly enhanced our understanding of the role of endothelial caveolae and caveolin-1 in physiology and disease. Several postnatal pulmonary and cardiovascular pathologies have been reported in caveolin-1 knockout mice, many of which have been recently rescued by selective re-expression of caveolin-1 in endothelium of these mice. A large body of experimental evidence mostly using caveolin-1 knockout mice suggests that, depending on the disease model, endothelial caveolin-1 may play either a protective or a detrimental role. For instance, physiological or higher expression levels of caveolin-1 in endothelium might be beneficial in such diseases as pulmonary hypertension, cardiac hypertrophy, or ischemic injury. On the other hand, endothelial caveolin-1 might contribute to acute lung injury and inflammation, atherosclerosis or pathological angiogenesis associated with inflammatory bowel disease. Moreover, depending on the specific model, endothelial caveolin-1 may either promote or suppress tumor-induced angiogenesis. In addition to overwhelming evidence for the role of endothelial caveolin-1, more recent studies also suggest that endothelial caveolin-2 could possibly play a role in pulmonary disease. The purpose of this review is to focus on how caveolin-1 expressed in endothelial cells regulates endothelial cell signaling and function. The review places particular emphasis on relevance to disease, including but not limited to Pulmonary and cardiovascular disorders as well as cancer. In addition to caveolin-1, possible importance of the less-studied endothelial caveolin-2 in pulmonary diseases will be also discussed.

Novel insights into the role of caveolin-2 in cell- and tissue-specific signaling and function

Caveolin-2 is one of the major protein components of cholesterol- and glycosphingolipid-rich flask-shaped invaginations of plasma membrane caveolae. A new body of evidence suggests that caveolin-2 plays an important, and often more direct, role than caveolin-1 in regulating signaling and function in a cell- and tissue type-specific manner. The purpose of this paper is to primarily focus on discussing how these recent discoveries may help better understand the specific contribution of caveolin-2 to lipid raft- and caveolae-regulated cell/tissue-specific signaling and functions.