The absence of caveolin-1 increases proliferation and anchorage- independent growth by a Rac-dependent, Erk-independent mechanism

Identification and validation of a prognostic risk model based on caveolin family genes for breast cancer

Background: Breast cancer (BC) is the most vicious killer of women’s health and is accompanied by increased incidence and mortality rates worldwide. Many studies have demonstrated that caveolins (CAVs) were abnormally expressed in a variety of tumors and implicated in tumorigenesis and cancer progression. However, the role of CAVs in BC remains somewhat contentious.

Methods: We comprehensively explored the expression and prognostic value of CAVs (CAV1-3) in BC utilizing public databases (ONCOMINE, TIMER, UALCAN, and TCGA databases). Then we constructed a prognostic model based on the expression profiles. Also, a prognostic nomogram was built to predict the overall survival (OS). We further investigated the relationship between this signature and immune cell infiltration and the mutational landscape in BC. The R package “pRRophetic” was used to predict chemotherapeutic response in BC patients. Finally, we employed loss-of-function approaches to validate the role of CAVs in BC.

Results: We found that CAVs were significantly downregulated in various cancer types, especially in BC. Low CAV expression was closely related to the malignant clinicopathological characteristics and worse OS and relapse-free survival (RFS) in BC. Then we constructed a prognostic model based on the expression profiles of CAVs, which divided BC patients into two risk groups. The Kaplan–Meier analysis showed that patients in the high-risk group tend to have a poorer prognosis than those in the low-risk group. Multivariate analysis indicated that the risk score and stage were both independent prognostic factors for BC patients, suggesting a complementary value. The clinical profiles and risk module were used to construct a nomogram that could accurately predict the OS in BC. In addition, we found that patients in the low-risk group tend to have a relatively high immune status and a lower mutation event frequency compared to the high-risk group. Furthermore, this signature could predict the response to chemotherapy and immunotherapy. Finally, CAV depletion promoted the colony formation, migration, and invasion of BC cells.

Conclusion: CAVs may serve as novel biomarkers and independent prognostic factors for BC patients. Also, the constructed signature based on CAVs may predict immunotherapeutic responses and provide a novel nomogram for precise outcome prediction of BC.

Neuroblastoma signalling models unveil combination therapies targeting feedback-mediated resistance

Very high risk neuroblastoma is characterised by increased MAPK signalling, and targeting MAPK signalling is a promising therapeutic strategy. We used a deeply characterised panel of neuroblastoma cell lines and found that the sensitivity to MEK inhibitors varied drastically between these cell lines. By generating quantitative perturbation data and mathematical modelling, we determined potential resistance mechanisms. We found that negative feedbacks within MAPK signalling and via the IGF receptor mediate re-activation of MAPK signalling upon treatment in resistant cell lines. By using cell-line specific models, we predict that combinations of MEK inhibitors with RAF or IGFR inhibitors can overcome resistance, and tested these predictions experimentally. In addition, phospho-proteomic profiling confirmed the cell-specific feedback effects and synergy of MEK and IGFR targeted treatment. Our study shows that a quantitative understanding of signalling and feedback mechanisms facilitated by models can help to develop and optimise therapeutic strategies. Our findings should be considered for the planning of future clinical trials introducing MEKi in the treatment of neuroblastoma.

Folate Receptor Alpha Is Preferentially Expressed in the Carcinoma Component of Endometrial Carcinosarcomas: A Potential Target for Adjuvant Therapy

Carcinosarcomas (CSs) of the endometrium are biphasic malignancies, composed of high-grade carcinomatous and sarcomatous components. Surgical stage and pathologic characteristics are the most important prognostic findings, with a 5-yr survival of 15% to 30% in advance stage disease. Folate receptor alpha (FRA) overexpression has been observed in endometrial carcinomas and not yet studied in CSs. This study evaluates semiquantitative expression of FRA in both carcinomatous and sarcomatous components of CSs on whole tissue sections. Immunohistochemistry for FRA expression was performed and extent and intensity of staining were recorded for each case for both histologic components. A total of 46 cases were stained for FRA. The majority of these (40/46, 87%) showed FRA staining at variable intensity in the carcinomatous component, stronger in serous carcinomas and high-grade endometrioid, while only a small subset of tumors demonstrated weak staining in the sarcomatous component (2/46, 4.35%). CS is known to be associated with poor prognosis and adjuvant therapy is recommended even in low stage disease. Serous and high-grade endometrioid carcinomas are the most common carcinomatous components of CSs and are known to show consistently high FRA expression. Folate plays a role in tumor cell migration and loss of cellular adhesion, which are key steps in epithelial-mesenchymal transition, the process by which CS develops from carcinoma cells. Our study shows expression of FRA in the carcinomatous component of almost all CS cases (87%), further favoring FRA as a target for adjuvant treatment. While expression of FRA in the sarcomatous component was rarely observed, the carcinomatous component being associated with metastatic potential underscores the importance of anti-FRA therapy for systemic disease control.

Genetic Liability for Internalizing Versus Externalizing Behavior Manifests in the Developing and Adult Hippocampus: Insight From a Meta-analysis of Transcriptional Profiling Studies in a Selectively Bred Rat Model

BACKGROUND

For more than 16 years, we have selectively bred rats for either high or low levels of exploratory activity within a novel environment. These bred high-responder (bHR) and bred low-responder (bLR) rats model temperamental extremes, exhibiting large differences in internalizing and externalizing behaviors relevant to mood and substance use disorders.

METHODS

We characterized persistent differences in gene expression related to bHR/bLR phenotype across development and adulthood in the hippocampus, a region critical for emotional regulation, by meta-analyzing 8 transcriptional profiling datasets (microarray and RNA sequencing) spanning 43 generations of selective breeding (postnatal day 7: n = 22; postnatal day 14: n = 49; postnatal day 21: n = 21; adult: n = 46; all male). We cross-referenced expression differences with exome sequencing within our colony to pinpoint candidates likely to mediate the effect of selective breeding on behavioral phenotype. The results were compared with hippocampal profiling from other bred rat models.

RESULTS

Genetic and transcriptional profiling results converged to implicate multiple candidate genes, including two previously associated with metabolism and mood: Trhr and Ucp2. Results also highlighted bHR/bLR functional differences in the hippocampus, including a network essential for neurodevelopmental programming, proliferation, and differentiation, centering on Bmp4 and Mki67. Finally, we observed differential expression related to microglial activation, which is important for synaptic pruning, including 2 genes within implicated chromosomal regions: C1qa and Mfge8.

CONCLUSIONS

These candidate genes and functional pathways may direct bHR/bLR rats along divergent developmental trajectories and promote a widely different reactivity to the environment.

Tumor-stroma biomechanical crosstalk: a perspective on the role of caveolin-1 in tumor progression

Tumor stiffening is a hallmark of malignancy that actively drives tumor progression and aggressiveness. Recent research has shed light onto several molecular underpinnings of this biomechanical process, which has a reciprocal crosstalk between tumor cells, stromal fibroblasts, and extracellular matrix remodeling at its core. This dynamic communication shapes the tumor microenvironment; significantly determines disease features including therapeutic resistance, relapse, or metastasis; and potentially holds the key for novel antitumor strategies. Caveolae and their components emerge as integrators of different aspects of cell function, mechanotransduction, and ECM-cell interaction. Here, we review our current knowledge on the several pivotal roles of the essential caveolar component caveolin-1 in this multidirectional biomechanical crosstalk and highlight standing questions in the field.

Derivation of stable embryonic stem cell-like, but transcriptionally heterogenous, induced pluripotent stem cells from non-permissive mouse strains

Genetic background is known to play a role in the ability to derive pluripotent, embryonic stem cells (ESC), a trait referred to as permissiveness. Previously we demonstrated that induced pluripotent stem cells (iPSC) can be readily derived from non-permissive mouse strains by addition of serum-based media supplemented with GSK3B and MEK inhibitors, termed 2iS media, 3 days into reprogramming. Here, we describe the derivation of second type of iPSC colony from non-permissive mouse strains that can be stably maintained independently of 2iS media. The resulting cells display transcriptional heterogeneity similar to that observed in ESC from permissive genetic backgrounds derived in conventional serum containing media supplemented with leukemia inhibitor factor. However, unlike previous studies that report exclusive subpopulations, we observe both exclusive and simultaneous expression of naive and primed cell surface markers. Herein, we explore shifts in pluripotency in the presence of 2iS and characterize heterogenous subpopulations to determine their pluripotent state and role in heterogenous iPSCs derived from the non-permissive NOD/ShiLtJ strain. We conclude that heterogeneity is a naturally occurring, necessary quality of stem cells that allows for the maintenance of pluripotency. This study further demonstrates the efficacy of the 2iS reprogramming technique. It is also the first study to derive stable ESC-like stem cells from the non-permissive NOD/ShiLtJ and WSB/EiJ strains, enabling easier and broader research possibilities into pluripotency for these and similar non-permissive mouse strains and species.

The mechano-sensitive response of β1 integrin promotes SRC-positive late endosome recycling and activation of Yes-associated protein

Yes-associated protein (YAP) signaling has emerged as a crucial pathway in several normal and pathological processes. Although the main upstream effectors that regulate its activity have been extensively studied, the role of the endosomal system has been far less characterized. Here, we identified the late endosomal/lysosomal adaptor MAPK and mTOR activator (LAMTOR) complex as an important regulator of YAP signaling in a preosteoblast cell line. We found that p18/LAMTOR1-mediated peripheral positioning of late endosomes allows delivery of SRC proto-oncogene, nonreceptor tyrosine kinase (SRC) to the plasma membrane and promotes activation of an SRC-dependent signaling cascade that controls YAP nuclear shuttling. Moreover, β1 integrin engagement and mechano-sensitive cues, such as external stiffness and related cell contractility, controlled LAMTOR targeting to the cell periphery and thereby late endosome recycling and had a major impact on YAP signaling. Our findings identify the late endosome recycling pathway as a key mechanism that controls YAP activity and explains YAP mechano-sensitivity.

Naegleria fowleri: differential genetic expression following treatment with Hesperidin conjugated with silver nanoparticles using RNA-Seq

Naegleria fowleri causes a deadly infection known as primary amoebic meningoencephalitis (PAM). To our knowledge, there are very few transcriptome studies conducted on these brain-eating amoebae, despite rise in the number of cases. Although the Naegleria genome has been sequenced, currently, it is not well annotated. Transcriptome level studies are needed to help understand the pathology and biology of this fatal parasitic infection. Recently, we showed that nanoparticles loaded with the flavonoid Hesperidin (HDN) are potential novel antimicrobial agents. N. fowleri trophozoites were treated with and without HDN-conjugated with silver nanoparticles (AgNPs) and silver only, and then, 50% minimum inhibitory concentration (MIC) was determined. The results revealed that the MIC of HDN-conjugated AgNPs was 12.5 microg/mL when treated for 3 h. As no reference genome exists for N. fowleri, de novo RNA transcriptome analysis using RNA-Seq and differential gene expression analysis was performed using the Trinity software. Analysis revealed that more than 2000 genes were differentially expressed in response to N. fowleri treatment with HDN-conjugated AgNPs. Some of the genes were linked to oxidative stress response, DNA repair, cell division, cell signalling and protein synthesis. The downregulated genes were linked with processes such as protein modification, synthesis of aromatic amino acids, when compared with untreated N. fowleri. Further transcriptome studies will lead to understanding of genetic mechanisms of the biology and pathogenesis and/or the identification of much needed drug candidates.

Caveolin-1 in oncogenic metabolic symbiosis

Metabolic phenotypes of cancer cells are heterogeneous and flexible as a tumor mass is a hurriedly evolving system capable of constant adaptation to oxygen and nutrient availability. The exact type of cancer metabolism arises from the combined effects of factors intrinsic to the cancer cells and factors proposed by the tumor microenvironment. As a result, a condition termed oncogenic metabolic symbiosis in which components of the tumor microenvironment (TME) promote tumor growth often occurs. Understanding how oncogenic metabolic symbiosis emerges and evolves is crucial for perceiving tumorigenesis. The process by which tumor cells reprogram their TME involves many mechanisms, including changes in intercellular communication, alterations in metabolic phenotypes of TME cells, and rearrangement of the extracellular matrix. It is possible that one molecule with a pleiotropic effect such as Caveolin-1 may affect many of these pathways. Here, we discuss the significance of Caveolin-1 in establishing metabolic symbiosis in TME.

The importance of caveolins and caveolae to dermatology: Lessons from the caves and beyond

Caveolae are flask-shaped invaginations of the cell membrane rich in cholesterol and sphingomyelin, with caveolin proteins acting as their primary structural components that allow compartmentalization and orchestration of various signalling molecules. In this review, we discuss how pleiotropic functions of caveolin-1 (Cav1) and its intricate roles in numerous cellular functions including lipid trafficking, signalling, cell migration and proliferation, as well as cellular senescence, infection and inflammation, are integral for normal development and functioning of skin and its appendages. We then examine how disruption of the homeostatic levels of Cav1 can lead to development of various cutaneous pathophysiologies including skin cancers, cutaneous fibroses, psoriasis, alopecia, age-related changes in skin and aberrant wound healing and propose how levels of Cav1 may have theragnostic value in skin physiology/pathophysiology.

Collective cancer invasion forms an integrin-dependent radioresistant niche

Cancer fatalities result from metastatic dissemination and therapy resistance, both processes that depend on signals from the tumor microenvironment. To identify how invasion and resistance programs cooperate, we used intravital microscopy of orthotopic sarcoma and melanoma xenografts. We demonstrate that these tumors invade collectively and that, specifically, cells within the invasion zone acquire increased resistance to radiotherapy, rapidly normalize DNA damage, and preferentially survive. Using a candidate-based approach to identify effectors of invasion-associated resistance, we targeted β1 and αVβ3/β5 integrins, essential extracellular matrix receptors in mesenchymal tumors, which mediate cancer progression and resistance. Combining radiotherapy with β1 or αV integrin monotargeting in invading tumors led to relapse and metastasis in 40-60% of the cohort, in line with recently failed clinical trials individually targeting integrins. However, when combined, anti-β1/αV integrin dual targeting achieved relapse-free radiosensitization and prevented metastatic escape. Collectively, invading cancer cells thus withstand radiotherapy and DNA damage by β1/αVβ3/β5 integrin cross-talk, but efficient radiosensitization can be achieved by multiple integrin targeting.

Molecular regulation and clinical significance of caveolin-1 methylation in chronic lung diseases

Chronic lung diseases represent a largely global burden whose pathogenesis remains largely unknown. Research increasingly suggests that epigenetic modifications, especially DNA methylation, play a mechanistic role in chronic lung diseases. DNA methylation can affect gene expression and induce various diseases. Of the caveolae in plasma membrane of cell, caveolin-1 (Cav-1) is a crucial structural constituent involved in many important life activities. With the increasingly advanced progress of genome-wide methylation sequencing technologies, the important impact of Cav-1 DNA methylation has been discovered. The present review overviews the biological characters, functions, and structure of Cav-1; epigenetic modifications of Cav-1 in health and disease; expression and regulation of Cav-1 DNA methylation in the respiratory system and its significance; as well as clinical potential as disease-specific biomarker and targets for early diagnosis and therapy.

Systems-wide analysis unravels the new roles of CCM signal complex (CSC)

Cerebral cavernous malformations (CCMs) are characterized by abnormally dilated intracranial capillaries that result in increased susceptibility to stroke. Three genes have been identified as causes of CCMs; KRIT1 (CCM1), MGC4607 (CCM2) and PDCD10 (CCM3); one of them is disrupted in most CCM cases. It was demonstrated that both CCM1 and CCM3 bind to CCM2 to form a CCM signaling complex (CSC) to modulate angiogenesis. In this report, we deployed both RNA-seq and proteomic analysis of perturbed CSC after depletion of one of three CCM genes to generate interactomes for system-wide studies. Our results demonstrated a unique portrait detailing alterations in angiogenesis and vascular integrity. Interestingly, only in-direct overlapped alterations between RNA and protein levels were detected, supporting the existence of multiple layers of regulation in CSC cascades. Notably, this is the first report identifying that both β4 integrin and CAV1 signaling are downstream of CSC, conveying the angiogenic signaling. Our results provide a global view of signal transduction modulated by the CSC, identifies novel regulatory signaling networks and key cellular factors associated with CSC.

Caveolin-1 in skin aging - From innocent bystander to major contributor

Caveolin-1 (Cav-1) appears to be both a pathophysiological contributor and a target in different inflammatory and hyperproliferative skin conditions as well as in skin aging. Skin fibroblasts demonstrate an up-regulation of Cav-1 expression both in chronological and UV-induced aging, and such an up-regulation was observed both in vitro and in vivo. Typical alterations in aging skin involve a reduction of the dermis thickness, a significant expansion of the dermal white adipose tissue as well as modifications of the content and distribution of hyaluronan, impairment of autophagic flux, a reduction of collagen expression and an increase in tissue inflammation. All of these phenomena can be connected with changes in Cav-1 expression in the aging skin. Modified expression of Cav-1 can also significantly influence the mechanical properties of individual skin layers, thus changing the total mechanical stability of the layered composite skin/WAT, leading to typical structural modifications of the skin surface in the aging skin. Selective reduction of Cav-1 expression has the potential to exert anti-aging effects on the skin.

RNA-Binding Protein HuR Regulates Rac1 Nucleocytoplasmic Shuttling Through Nucleophosmin in the Intestinal Epithelium

BACKGROUND & AIMS

The mammalian intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is tightly regulated via well-controlled mechanisms. The RNA-binding protein HuR is essential for maintaining gut epithelial integrity, and targeted deletion of HuR in intestinal epithelial cells (IECs) disrupts mucosal regeneration and delays repair after injury. Here, we defined the role of HuR in regulating subcellular distribution of small guanosine triphosphatase Rac1 and investigated the implication of nucleophosmin (NPM) as a molecular chaperone in this process.

METHODS

Studies were conducted in intestinal epithelial tissue-specific HuR knockout (IE-HuR^-/-) mice and cultured IEC-6 cells, derived from rat small intestinal crypts. Functions of HuR and NPM in vitro were investigated via their gene silencing and overexpression.

RESULTS

The abundance of cytoplasmic Rac1 in the small intestinal mucosa increased significantly in IE-HuR^-/- mice, although HuR deletion did not alter total Rac1 levels. HuR silencing in cultured IECs also increased the cytoplasmic Rac1 levels, without an effect on whole-cell Rac1 content. In addition, HuR deficiency in the intestinal epithelium decreased the levels of NPM in IE-HuR^-/- mice and cultured IECs. NPM physically interacted with Rac1 and formed the NPM/Rac1 complex. NPM silencing decreased the NPM/Rac1 association and inhibited nuclear accumulation of Rac1, along with an increase in cytoplasmic abundances of Rac1. In contrast, ectopically expressed NPM enhanced Rac1 nuclear translocation and restored Rac1 subcellular localization to near normal in HuR-deficient cells.

CONCLUSIONS

These results indicate that HuR regulates Rac1 nucleocytoplasmic shuttling in the intestinal epithelium by altering NPM expression.

Role of the Endocytosis of Caveolae in Intracellular Signaling and Metabolism

Caveolae are 60-80 nm invaginated plasma membrane (PM) nanodomains, with a specific lipid and protein composition, which assist and regulate multiple processes in the plasma membrane-ranging from the organization of signalling complexes to the mechanical adaptation to changes in PM tension. However, since their initial descriptions, these structures have additionally been found tightly linked to internalization processes, mechanoadaptation, to the regulation of signalling events and of endosomal trafficking. Here, we review caveolae biology from this perspective, and its implications for cell physiology and disease.

BioID identifies proteins involved in the cell biology of caveolae

The mechanisms controlling the abundance and sub-cellular distribution of caveolae are not well described. A first step towards determining such mechanisms would be identification of relevant proteins that interact with known components of caveolae. Here, we applied proximity biotinylation (BioID) to identify a list of proteins that may interact with the caveolar protein cavin1. Screening of these candidates using siRNA to reduce their expression revealed that one of them, CSDE1, regulates the levels of mRNAs and protein expression for multiple components of caveolae. A second candidate, CD2AP, co-precipitated with cavin1. Caveolar proteins were observed in characteristic and previously un-described linear arrays adjacent to cell-cell junctions in both MDCK cells, and in HeLa cells overexpressing an active form of the small GTPase Rac1. CD2AP was required for the recruitment of caveolar proteins to these linear arrays. We conclude that BioID will be useful in identification of new proteins involved in the cell biology of caveolae, and that interaction between CD2AP and cavin1 may have an important role in regulating the sub-cellular distribution of caveolae.

The chemopreventive isothiocyanate sulforaphane reduces anoikis resistance and anchorage-independent growth in non-small cell human lung cancer cells

The capacity of cancer cells to resist detachment-induced apoptosis, i.e. anoikis, as well as anchorage-independent growth are crucial prerequisites for tumor metastasis. Therefore, agents interfering these properties may provide novel anti-metastatic strategies. Sulforaphane (SFN), an isothiocyanate found in cruciferous vegetables, is known as a potent chemopreventive agent, but its effect on anoikis resistance has not been investigated. In this study, two non-small cell lung cancer (NSCLC) cell lines, A549 and CL1-5 cells, were treated with SFN under either suspension or adhesion conditions. SFN exhibited more potent cytotoxicity against suspending rather than adherent cancer cells. The selective cytotoxicity was due to the induction of anoikis, as evident by chromatin condensation, Annexin V binding, and activation of the mitochondrial apoptotic pathway. SFN also inhibited NSCLC cell to form spherical colonies, suggesting that anchorage-independent growth was prevented by SFN. Consistently, SFN treatment led to inactivation of FAK and Akt, down-regulation of β-catenin, and up-regulation of the cyclin-dependent kinase inhibitor p21. Because A549 cells with wild-type p53 are more sensitive to SFN than p53-mutant CL1-5 cells, p53 dependency of SFN responses were determined in p53-knockdown A549 cells. Knockdown of p53 attenuated the ability of SNF to inhibit anoikis resistance and sphere formation in A549 cancer cells, suggesting that the presence of p53 in NSCLC cancer cells is involved in the sensitivity to SFN. These results provide new insight into mechanisms underlying the chemopreventive ability of SFN and suggest a potential benefit of SFN to interfere with tumor metastasis.

Caveolae: Structure, Function, and Relationship to Disease

The plasma membrane of eukaryotic cells is not a simple sheet of lipids and proteins but is differentiated into subdomains with crucial functions. Caveolae, small pits in the plasma membrane, are the most abundant surface subdomains of many mammalian cells. The cellular functions of caveolae have long remained obscure, but a new molecular understanding of caveola formation has led to insights into their workings. Caveolae are formed by the coordinated action of a number of lipid-interacting proteins to produce a microdomain with a specific structure and lipid composition. Caveolae can bud from the plasma membrane to form an endocytic vesicle or can flatten into the membrane to help cells withstand mechanical stress. The role of caveolae as mechanoprotective and signal transduction elements is reviewed in the context of disease conditions associated with caveola dysfunction.

Chemotherapy induced PRL3 expression promotes cancer growth via plasma membrane remodeling and specific alterations of caveolae-associated signaling

BACKGROUND

The outcome of cancer therapy is greatly defined by the ability of a tumor cell to evade treatment and re-establish its bulk mass after medical interventions. Consequently, there is an urgent need for the characterization of molecules affecting tumor reoccurrence. The phosphatase of regenerating liver 3 (PRL3) protein was recently emerged among the targets that could affect such a phenomenon.

METHODS

The expression induction of PRL3 in melanoma cells treated with chemotherapeutic agents was assessed by western blotting. The effect of PRL3 expression on cancer growth was investigated both in vitro and in vivo. The association of PRL3 with the caveolae structures of the plasma membrane was analyzed by detergent free raft purification. The effect of PRL3 expression on the membrane organization was assayed by electron microscopy and by membrane biophysical measurements. Purification of the plasma membrane fraction and co-immunoprecipitation were used to evaluate the altered protein composition of the plasma membrane upon PRL3 expression.

RESULTS

Here, we identified PRL3 as a genotoxic stress-induced oncogene whose expression is significantly increased by the presence of classical antitumor therapeutics. Furthermore, we successfully connected the presence of this oncogene with increased tumor growth, which implies that tumor cells can utilize PRL3 effects as a survival strategy. We further demonstrated the molecular mechanism that is connected with the pro-growth action of PRL3, which is closely associated with its localization to the caveolae-type lipid raft compartment of the plasma membrane. In our study, PRL3 was associated with distinct changes in the plasma membrane structure and in the caveolar proteome, such as the dephosphorylation of integrin β1 at Thr788/Thr789 and the increased partitioning of Rac1 to the plasma membrane. These alterations at the plasma membrane were further associated with the elevation of cyclin D1 in the nucleus.

CONCLUSIONS

This study identifies PRL3 as an oncogene upregulated in cancer cells upon exposure to anticancer therapeutics. Furthermore, this work contributes to the existing knowledge on PRL3 function by characterizing its association with the caveolae-like domains of the plasma membrane and their resident proteins.

Caveolin-1 deficiency protects pancreatic β cells against palmitate-induced dysfunction and apoptosis

Lipotoxicity leads to insulin secretion deficiency, which is among the important causes for the onset of type 2 diabetes mellitus. Thus, the restoration of β-cell mass and preservation of its endocrine function are long-sought goals in diabetes research. Previous studies have suggested that the membrane protein caveolin-1 (Cav-1) is implicated in β-cell apoptosis and insulin secretion, however, the underlying mechanisms still remains unclear. Our objective is to explore whether Cav-1 depletion protects pancreatic β cells from lipotoxicity and what are the underlying mechanisms. In this study, we found that Cav-1 silencing significantly promoted β-cell proliferation, inhibited palmitate (PA)-induced pancreatic β-cell apoptosis and enhanced insulin production and secretion. These effects were associated with enhanced activities of Akt and ERK1/2, which in turn downregulated the expression of cell cycle inhibitors (FOXO1, GSK3β, P21, P27 and P53) and upregulated the expression of Cyclin D2 and Cyclin D3. Subsequent inhibition of PI3K/Akt and ERK/MAPK pathways abolished Cav-1 depletion induced β-cell mass protection. Furthermore, under PA induced endoplasmic reticulum (ER) stress, Cav-1 silencing significantly reduced eIF2α phosphorylation and the expression of ER stress-responsive markers BiP and CHOP, which are among the known sensitizers of lipotoxicity. Our findings suggest Cav-1 as potential target molecule in T2DM treatment via the preservation of lipotoxicity-induced β-cell mass reduction and the attenuation of insulin secretion dysfunction.

Emerging growth factor receptor antagonists for ovarian cancer treatment

INTRODUCTION

Epithelial Ovarian Cancer (EOC) is the most lethal gynecological malignancy. EOC outcomes remain unsatisfactory despite aggressive surgical approach, disease chemo-sensitivity and recent introduction of agents targeting angiogenesis and tumour genome instability. Advances in EOC research have allowed for a tailored treatment approach and accelerated development of novel treatments strategies from bench to bed side, anticipated to improve patient outcomes. Areas covered: Comprehensive review of growth factor receptor antagonists for EOC treatment currently in different stages of development was performed. English peer-reviewed articles and abstracts were searched in MEDLINE, PubMed, Embase and major conferences. We focused on agents that antagonize growth factors promoting sustained proliferative signaling, angiogenesis and evasion of immune destruction blocking the receptor or its stimulating factors. Expert opinion: Receptor signaling has been well characterized for most cancer generating pathways. Growth receptor antagonists are represented by both high receptor affinity monoclonal antibodies as well as tyrosine kinase inhibitors; both are especially effective when a related predictive biomarker of response is identified. Therefore, along with the promising development of novel receptor antagonists or modulators in EOC treatment, targeting essential growth pathways in the tumour and associated microenvironment, is fundamental for biomarker discovery and towards achieving significant improvements in response.

Reciprocal regulation of the Cadherin-11/Stat3 axis by caveolin-1 in mouse fibroblasts and lung carcinoma cells

Caveolin-1 (Cav1) is an integral plasma membrane protein and a complex regulator of signal transduction. The Signal Transducer and Activator of Transcription-3 (Stat3) is activated by a number of receptor and non-receptor tyrosine kinases and is positively implicated in cancer. Despite extensive efforts, the relationship between Cav1 and Stat3 has been a matter of controversy. We previously demonstrated that engagement of E- or N-cadherin or cadherin-11 cell to cell adhesion molecules, as occurs with confluence of cultured cells, triggers a dramatic increase in the levels of tyr705 phosphorylated i.e. activated Stat3, by a mechanism requiring the cRac1 small GTPase. Since confluence was not taken into account in previous studies, we revisited the question of the relationship between Cav1 and Stat3-ptyr705 in non-transformed mouse fibroblasts and in human lung carcinoma cells, by examining their effect at different cell densities. Our results unequivocally demonstrate that Cav1 downregulates cadherin-11, by a mechanism which requires the Cav1 scaffolding domain. This cadherin-11 downregulation, in turn, leads to a reduction in cRac1 and Stat3 activity levels. Furthermore, in a feedback loop possibly through p53 upregulation, Stat3 downregulation increases Cav1 levels. Our data reveal the presence of a potent, negative regulatory loop between Cav1 and cadherin-11/Stat3, leading to Stat3 inhibition and apoptosis.

Caveolin-1 Inhibits Proliferation, Migration, and Invasion of Human Colorectal Cancer Cells by Suppressing Phosphorylation of Epidermal Growth Factor Receptor

Background

Although downregulation of caveolin-1 (Cav-1), which is a key constituent of membrane caveolae and a regulator of cellular processes, is associated with colorectal cancer (CRC), its involvement in the disease progression is largely unknown. This study aimed to explore the role of Cav-1 in CRC and the associated mechanisms.

Material/Methods

Fresh tissues from patients with CRC and human CRC SW480 cells were used to evaluate Cav-1 and Ki-67 expression using immunohistochemistry and Western blotting. The MTS and Transwell assays were performed to determine the effects of Cav-1 overexpression via pcDNA3.1/Cav-1 plasmid on cell proliferation and metastasis. The effect of Cav-1 on the epidermal growth factor receptor (EGFR) activation was evaluated by Western blotting. The correlation of Cav-1 expression with clinicopathological factors was statistically analyzed.

Results

Overexpression of Cav-1 significantly reduced proliferation, migration, and invasion of SW480 cancer cells in vitro. The EGF-induced phosphorylation of EGFR and activations of the RAF-MEK-ERK and PI3K-AKT pathways were adversely regulated by Cav-1 overexpression in vitro. In 76 cases of CRC patients with EGFR expression, a negative correlation was observed between the level of Cav-1 and tumor-node-metastasis stage, lymph node metastasis, and distant metastasis (All p<0.05). Finally, the expression level of Cav-1 was negatively correlated with that of Ki-67.

Conclusions

This report is the first to show that overexpression of Cav-1significantly inhibits the proliferation, migration, and invasion potential of SW480 cells, possibly through reducing EGF-induced EGFR activation. High Cav-1 expression level may be a predictor of positive outcomes in patients with colorectal cancer.

Targeting folate receptor alpha for cancer treatment

Promising targeted treatments and immunotherapy strategies in oncology and advancements in our understanding of molecular pathways that underpin cancer development have reignited interest in the tumor-associated antigen Folate Receptor alpha (FRα). FRα is a glycosylphosphatidylinositol (GPI)-anchored membrane protein. Its overexpression in tumors such as ovarian, breast and lung cancers, low and restricted distribution in normal tissues, alongside emerging insights into tumor-promoting functions and association of expression with patient prognosis, together render FRα an attractive therapeutic target. In this review, we summarize the role of FRα in cancer development, we consider FRα as a potential diagnostic and prognostic tool, and we discuss different targeted treatment approaches with a specific focus on monoclonal antibodies. Renewed attention to FRα may point to novel individualized treatment approaches to improve the clinical management of patient groups that do not adequately benefit from current conventional therapies.

Epigenetic Regulation of Caveolin-1 Gene Expression in Lung Fibroblasts

Fibrotic disorders are associated with tissue accumulation of fibroblasts. We recently showed that caveolin (Cav)-1 gene suppression by a profibrotic cytokine, transforming growth factor (TGF)-β1, contributes to fibroblast proliferation and apoptosis resistance. Cav-1 has been shown to be constitutively suppressed in idiopathic pulmonary fibrosis (IPF), but mechanisms for this suppression are incompletely understood. We hypothesized that epigenetic processes contribute to Cav-1 down-regulation in IPF lung fibroblasts, and after fibrogenic stimuli. Cav-1 expression levels, DNA methylation status, and histone modifications associated with the Cav-1 promoter were examined by PCR, Western blots, pyrosequencing, or chromatin immunoprecipitation assays in IPF lung fibroblasts, normal fibroblasts after TGF-β1 stimulation, or in murine lung fibroblasts after bleomycin injury. Methylation-specific PCR demonstrated methylated and unmethylated Cav-1 DNA copies in all groups. Despite significant changes in Cav-1 expression, no changes in DNA methylation were observed in CpG islands or CpG island shores of the Cav-1 promoter by pyrosequencing of lung fibroblasts from IPF lungs, in response to TGF-β1, or after bleomycin-induced murine lung injury, when compared with respective controls. In contrast, the association of Cav-1 promoter with the active histone modification mark, H3 lysine 4 trimethylation, correlated with Cav-1 down-regulation in activated/fibrotic lung fibroblasts. Our data indicate that Cav-1 gene silencing in lung fibroblasts is actively regulated by epigenetic mechanisms that involve histone modifications, in particular H3 lysine 4 trimethylation, whereas DNA methylation does not appear to be a primary mechanism. These findings support therapeutic strategies that target histone modifications to restore Cav-1 expression in fibroblasts participating in pathogenic tissue remodeling.

Cardiac Mechanoperception: A Life-Long Story from Early Beats to Aging and Failure

The life-long story of the heart starts concomitantly with primary differentiation events occurring in multipotent progenitors located in the so-called heart tube. This initially tubular structure starts a looping process, which leads to formation of the final four-chambered heart with a primary contribution of geometric and position-associated cell sensing. While this establishes the correct patterning of the final cardiac structure, it also provides feedbacks to fundamental cellular machineries controlling proliferation and differentiation, thus ensuring a coordinated restriction of cell growth and a myocyte terminal differentiation. Novel evidences provided by embryological and cell engineering studies have clarified the relevance of mechanics-supported position sensing for the correct recognition of cell fate inside developing embryos and multicellular aggregates. One of the main components of this pathway, the Hippo-dependent signal transduction machinery, is responsible for cell mechanics intracellular transduction with important consequences for gene transcription and cell growth control. Being the Hippo pathway also directly connected to stress responses and altered metabolism, it is tempting to speculate that permanent alterations of mechanosensing may account for modifying self-renewal control in tissue homeostasis. In the present contribution, we translate these concepts to the aging process and the failing of the human heart, two pathophysiologic conditions that are strongly affected by stress responses and altered metabolism.

Caveolin-1 regulates cancer cell metabolism via scavenging Nrf2 and suppressing MnSOD-driven glycolysis

Aerobic glycolysis is an indispensable component of aggressive cancer cell metabolism. It also distinguishes cancer cells from most healthy cell types in the body. Particularly for this reason, targeting the metabolism to improve treatment outcomes has long been perceived as a potentially valuable strategy. In practice, however, our limited knowledge of why and how metabolic reprogramming occurs has prevented progress towards therapeutic interventions that exploit the metabolic peculiarities of tumors. We recently described that in breast cancer, MnSOD upregulation is both necessary and sufficient to activate glycolysis. Here, we focused on determining the molecular mechanisms of MnSOD upregulation. We found that Caveolin-1 (Cav-1) is a central component of this mechanism due to its suppressive effects of NF-E2-related factor 2 (Nrf2), a transcription factor upstream of MnSOD. In transformed MCF10A(Er/Src) cells, Cav-1 loss preceded the activation of Nrf2 and its induction of MnSOD expression. Consistently, with previous observations, MnSOD expression secondary to Nrf2 activation led to an increase in the glycolytic rate dependent on mtH2O2 production and the activation of AMPK. Moreover, rescue of Cav-1 expression in a breast cancer cell line (MCF7) suppressed Nrf2 and reduced MnSOD expression. Experimental data were reinforced by epidemiologic nested case-control studies showing that Cav-1 and MnSOD are inversely expressed in cases of invasive ductal carcinoma, with low Cav-1 and high MnSOD expression being associated with lower 5-year survival rates and molecular subtypes with poorest prognosis.

Therapeutic targets and new directions for antibodies developed for ovarian cancer

Antibody therapeutics against different target antigens are widely used in the treatment of different malignancies including ovarian carcinomas, but this disease still requires more effective agents. Improved understanding of the biological features, signaling pathways, and immunological escape mechanisms involved in ovarian cancer has emerged in the past few years. These advances, including an appreciation of the cross-talk between cancer cells and the patient's immune system, have led to the identification of new targets. In turn, potential antibody treatments with various mechanisms of action, including immune activation or toxin-delivery, that are directed at these targets have been developed. Here, we identify established as well as novel targets for antibodies in ovarian cancer, and discuss how they may provide fresh opportunities to identify interventions with enhanced therapeutic potential.

Caveolin-1 regulates corneal wound healing by modulating Kir4.1 activity

The expression of caveolin-1 (Cav1) in corneal epithelium is associated with regeneration potency. We used Cav1(-/-) mice to study the role of Cav1 in modulating corneal wound healing. Western blot and whole cell patch clamp were employed to study the effect of Cav1 deletion on Kir4.1 current density in corneas. We found that Ba(2+)-sensitive K(+) currents in primary cultured murine corneal epithelial cells (pMCE) from Cav1(-/-) were dramatically reduced (602 pA) compared with those from wild type (WT; 1,300 pA). As a consequence, membrane potential was elevated in pMCE from Cav1(-/-) compared with that from WT (-43 ± 7.5 vs. -58 ± 4.0 mV, respectively). Western blot showed that either inhibition of Cav1 expression or Ba(2+) incubation stimulated phosphorylation of the EGFR. The transwell migration assay showed that Cav1 genetic inactivation accelerated cell migration. The regrowth efficiency of human corneal epithelial cells (HCE) transfected with siRNA-Cav1 or negative control was evaluated by scrape injury assay. With the presence of mitomycin C (10 μg/ml) to avoid the influence of cell proliferation, Cav1 inhibition with siRNA significantly increased migration compared with control siRNA in HCE. This promoting effect by siRNA-Cav1 could not be further enhanced by cotransfection with siRNA-Kcnj10. By using corneal debridement, we found that wound healing was significantly accelerated in Cav1(-/-) compared with WT mice (70 ± 10 vs. 36 ± 3%, P < 0.01). Our findings imply that the mechanism by which Cav-1 knockout promotes corneal regrowth is, at least partially, due to the inhibition of Kir4.1 which stimulates EGFR signaling.

Role of the folate receptor in ovarian cancer treatment: evidence, mechanism, and clinical implications

Folate can be transported into the cell by the reduced folate carrier (RFC), the proton-coupled folate transporter (PCFT), or the folate receptor (FR), of which various isoforms exist. While the RFC and PCFT are expressed by many normal cells, the FR is present only in a small proportion of normal tissues. In these tissues, the FR expression level is often low and restricted to the apical surface of polarized epithelial cells. In contrast, FR is expressed on the blood-accessible basal and lateral membranes of many types of epithelial cancer. Considering that FR is expressed in few nonmalignant cell types on luminal membranes generally not accessible for molecules transported in the blood, FR is considered a promising antitumor target. As FR expression seems associated with tumor progression and prognosis, anticancer therapies targeting FR are currently being developed, such as farletuzumab (Morphotek, Exton, PA, USA), IMGN853 (ImmunoGen, Waltham, MA, USA), vintafolide, and EC1456 (both Endocyte Inc., West Lafayette, IN, USA). FR expression could be used as a response-predictive biomarker for these treatments. The ability to identify patients and treat them with an effective therapy based on the known expression of the tumor marker would, indeed, be the next step in predictive medicine for these patients. This review summarizes the role of FR in ovarian cancer and the value of FR as a prognostic biomarker for ovarian cancer and a response-predictive biomarker for folate-targeted therapeutics.

Mitotic Membrane Turnover Coordinates Differential Induction of the Heart Progenitor Lineage

In response to microenvironmental cues, embryonic cells form adhesive signaling compartments that influence survival and patterning. Dividing cells detach from the surrounding matrix and initiate extensive membrane remodeling, but the in vivo impact of mitosis on adhesion-dependent signaling remains poorly characterized. We investigate in vivo signaling dynamics using the invertebrate chordate, Ciona intestinalis. In Ciona, matrix adhesion polarizes fibroblast growth factor (FGF)-dependent heart progenitor induction. Here, we show that adhesion inhibits mitotic FGF receptor internalization, leading to receptor enrichment along adherent membranes. Targeted disruption of matrix adhesion promotes uniform FGF receptor internalization and degradation while enhanced adhesion suppresses degradation. Chimeric analysis indicates that integrin β chain-specific impacts on induction are dictated by distinct internalization motifs. We also found that matrix adhesion impacts receptor enrichment through Caveolin-rich membrane domains. These results redefine the relationship between cell division and adhesive signaling, revealing how mitotic membrane turnover orchestrates adhesion-dependent signal polarization.

Registered report: Biomechanical remodeling of the microenvironment by stromal caveolin-1 favors tumor invasion and metastasis

The Reproducibility Project: Cancer Biology seeks to address growing concerns about reproducibility in scientific research by conducting replicating selected results from a number of high-profile papers in the field of cancer biology. The papers, which were published between 2010 and 2012 were selected on the basis of citations and Altimetric scores (Errington et al., 2014). This Registered report describes the proposed replication plan of key experiments from ‘Biomechanical remodeling of the microenvironment by stromal caveolin-1 favors tumor invasion and metastasis’ by Goetz and colleagues, published in Cell in 2011 (Goetz et al., 2011). The key experiments being replicated are those reported in Figures 7C (a-d), Supplemental Figure S2A, and Supplemental Figure S7C (a-c) (Goetz et al., 2011). In these experiments, which are a subset of all the experiments reported in the original publication, Goetz and colleagues show in a subcutaneous xenograft model that stromal caveolin-1 remodels the intratumoral microenvironment, which is correlated with increased metastasis formation. The Reproducibility Project: Cancer Biology is a collaboration between the Center for Open Science and Science Exchange and the results of the replications will be published in eLife.

DOI:http://dx.doi.org/10.7554/eLife.04796.001

Rac1 nucleocytoplasmic shuttling drives nuclear shape changes and tumor invasion

Nuclear membrane microdomains are proposed to act as platforms for regulation of nuclear function, but little is known about the mechanisms controlling their formation. Organization of the plasma membrane is regulated by actin polymerization, and the existence of an actin pool in the nucleus suggests that a similar mechanism might operate here. We show that nuclear membrane organization and morphology are regulated by the nuclear level of active Rac1 through actin polymerization-dependent mechanisms. Rac1 nuclear export is mediated by two internal nuclear export signals and through its interaction with nucleophosmin-1 (B23), which acts as a Rac1 chaperone inside the nucleus. Rac1 nuclear accumulation alters the balance between cytosolic Rac1 and Rho, increasing RhoA signaling in the cytoplasm and promoting a highly invasive phenotype. Nuclear Rac1 shuttling is a finely tuned mechanism for controlling nuclear shape and organization and cell invasiveness.

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

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

Clathrin-independent pathways of endocytosis

There are many pathways of endocytosis at the cell surface that apparently operate at the same time. With the advent of new molecular genetic and imaging tools, an understanding of the different ways by which a cell may endocytose cargo is increasing by leaps and bounds. In this review we explore pathways of endocytosis that occur in the absence of clathrin. These are referred to as clathrin-independent endocytosis (CIE). Here we primarily focus on those pathways that function at the small scale in which some have distinct coats (caveolae) and others function in the absence of specific coated intermediates. We follow the trafficking itineraries of the material endocytosed by these pathways and finally discuss the functional roles that these pathways play in cell and tissue physiology. It is likely that these pathways will play key roles in the regulation of plasma membrane area and tension and also control the availability of membrane during cell migration.

Spatial and temporal control of Rho GTPase functions

Rho family GTPases control almost every aspect of cell physiology and, since their discovery, a wealth of knowledge has accumulated about their biochemical regulation and function. However, each Rho GTPase distributes between multiple cellular compartments, even within the same cell, where they are controlled by multiple regulators and signal to multiple effectors. Thus, major questions about spatial and temporal aspects of regulation remain unanswered. In particular, what are the nano-scale dynamics for their activation, membrane targeting, diffusion, effector activation and GTPase inactivation? How do these mechanisms differ in the different cellular compartments where Rho GTPases function? Addressing these complex aspects of Rho GTPase biology will significantly advance our understanding of the spatial and temporal control of cellular functions.

Expression and activity of Rac1 is negatively affected in the dehydroepiandrosterone induced polycystic ovary of mouse

Background

Polycystic ovarian syndrome (PCOS) is characterized by the presence of multiple follicular cysts, giving rise to infertility due to anovulation. This syndrome affects about 10% of women, worldwide. The exact molecular mechanism leading to PCOS remains obscure. RhoGTPase has been associated with oogenesis, but its role in PCOS remains unexplored. Therefore, we attempted to elucidate the Vav-Rac1 signaling in PCOS mice model.

Methods

We generated a PCOS mice model by injecting dehydroepiandrosterone (DHEA) for a period of 20 days. The expression levels of Rac1, pRac1, Vav, pVav and Caveolin1 were analyzed by employing immuno-blotting and densitometry. The association between Vav and Rac1 proteins were studied by immuno-precipitation. Furthermore, we analyzed the activity of Rac1 and levels of inhibin B and 17β-estradiol in ovary using biochemical assays.

Results

The presence of multiple follicular cysts in ovary were confirmed by histology. The activity of Rac1 (GTP bound state) was significantly reduced in the PCOS ovary. Similarly, the expression levels of Rac1 and its phosphorylated form (pRac1) were decreased in PCOS in comparison to the sham ovary. The expression level and activity (phosphorylated form) of guanine nucleotide exchanger of Rac1, Vav, was moderately down-regulated. We observed comparatively increased expressions of Caveolin1, 17β-estradiol, and inhibin B in the polycystic ovary.

Conclusion

We conclude that hyperandrogenization (PCOS) by DHEA diminishes ovarian Rac1 and Vav expression and activity along with an increase in expression of Caveolin1. This is accompanied by an increase in the intra-ovarian level of '17 β-estradiol and inhibin B.

Caveolin 1 knockdown inhibits the proliferation, migration and invasion of human breast cancer BT474 cells

Previous studies have demonstrated that caveolin 1 acts as a tumor suppressor in breast cancer, however, few studies have demonstrated that caveolin 1 also serves as a tumor promoter in breast cancer. In the present study, caveolin 1 small interfering RNA was used to knock down caveolin 1 expression in order to investigate the association between caveolin 1 and the proliferation and metastatic abilities of human breast cancer BT474 cells. The results revealed that cell proliferation, migration and invasion were attenuated by caveolin 1 knockdown in BT474 cells. Furthermore, caveolin 1 knockdown in BT474 cells arrested cells in the G0/G1 phase and decreased the number of cells in the S phase. In addition, caveolin 1 knockdown decreased the activation of the extracellular signal-regulated kinase 1/2 pathway and inhibited the expression of cell cycle-associated proteins (cyclin D1, c-Fos and β-catenin), whilst the expression of E-cadherin was increased. Furthermore, the protein expression of matrix metalloproteinase-2, -9 and -1 was also inhibited by caveolin 1 knockdown. In combination, these results demonstrated that caveolin 1 knockdown had a tumor suppressing effect on BT474 cells.

Role of caveolin-1 in fibrotic diseases

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

Caveolin-1 as a promoter of tumour spreading: when, how, where and why

Caveolae are non-clathrin invaginations of the plasma membrane in most cell types; they are involved in signalling functions and molecule trafficking, thus modulating several biological functions, including cell growth, apoptosis and angiogenesis. The major structural protein in caveolae is caveolin-1, which is known to act as a key regulator in cancer onset and progression through its role as a tumour suppressor. Caveolin-1 can also promote cell proliferation, survival and metastasis as well as chemo- and radioresistance. Here, we discuss recent findings and novel concepts that support a role for caveolin-1 in cancer development and its distant spreading. We also address the potential application of caveolin-1 in tumour therapy and diagnosis.

Caveolae as plasma membrane sensors, protectors and organizers

Caveolae are submicroscopic, plasma membrane pits that are abundant in many mammalian cell types. The past few years have seen a quantum leap in our understanding of the formation, dynamics and functions of these enigmatic structures. Caveolae have now emerged as vital plasma membrane sensors that can respond to plasma membrane stresses and remodel the extracellular environment. Caveolae at the plasma membrane can be removed by endocytosis to regulate their surface density or can be disassembled and their structural components degraded. Coat proteins, called cavins, work together with caveolins to regulate the formation of caveolae but also have the potential to dynamically transmit signals that originate in caveolae to various cellular destinations. The importance of caveolae as protective elements in the plasma membrane, and as membrane organizers and sensors, is highlighted by links between caveolae dysfunction and human diseases, including muscular dystrophies and cancer.

Microarray analysis of gene expression in vestibular schwannomas reveals SPP1/MET signaling pathway and androgen receptor deregulation

Vestibular schwannomas are benign neoplasms that arise from the vestibular nerve. The hallmark of these tumors is the biallelic inactivation of neurofibromin 2 (NF2). Transcriptomic alterations, such as the neuregulin 1 (NRG1)/ErbB2 pathway, have been described in schwannomas. In this study, we performed a whole transcriptome analysis in 31 vestibular schwannomas and 9 control nerves in the Affymetrix Gene 1.0 ST platform, validated by quantitative real-time PCR (qRT-PCR) using TaqMan Low Density arrays. We performed a mutational analysis of NF2 by PCR/denaturing high-performance liquid chromatography (dHPLC) and multiplex ligation-dependent probe amplification (MLPA), as well as a microsatellite marker analysis of the loss of heterozygosity (LOH) of chromosome 22q. The microarray analysis demonstrated that 1,516 genes were deregulated and 48 of the genes were validated by qRT-PCR. At least 2 genetic hits (allelic loss and/or gene mutation) in NF2 were found in 16 tumors, seven cases showed 1 hit and 8 tumors showed no NF2 alteration. MET and associated genes, such as integrin, alpha 4 (ITGA4)/B6, PLEXNB3/SEMA5 and caveolin-1 (CAV1) showed a clear deregulation in vestibular schwannomas. In addition, androgen receptor (AR) downregulation may denote a hormonal effect or cause in this tumor. Furthermore, the osteopontin gene (SPP1), which is involved in merlin protein degradation, was upregulated, which suggests that this mechanism may also exert a pivotal role in schwannoma merlin depletion. Finally, no major differences were observed among tumors of different size, histological type or NF2 status, which suggests that, at the mRNA level, all schwannomas, regardless of their molecular and clinical characteristics, may share common features that can be used in their treatment.

Restoration of caveolin-1 expression suppresses growth, membrane-type-4 metalloproteinase expression and metastasis-associated activities in colon cancer cells

Caveolin-1 (cav-1) and flotillin-1 are two major structural proteins associated with lipid rafts in mammalian cells. The membrane-type matrix metalloproteinases (MT-MMPs) are expressed at the cell surface, hydrolyze extracellular matrix, and play an important role in cancer cell migration and metastasis. Expression of cav-1, flotillin-1, and MT4-MMP in lysates and lipid rafts of LS174T and HM-7 colon cancer cells was determined. The impact of restoration of cav-1 expression on proliferation, adhesion, motility in vitro, and growth of implanted tumors in vivo was characterized. Cav-1 is not expressed in lipid rafts of the highly metastatic colon cancer cell line (HM-7), but expressed in cytosolic fractions of the parental lower metastatic cell line (LS174T). In contrast, MT4-MMP was expressed in lipid rafts of HM-7 cells but not in LS174T cells. Overexpression of cav-1 in HM-7 cells down-regulate proliferation, viability, wound closure, adhesion to laminin, invasion, and development of filopodial and lamellipodial structures in a dose-dependent manner. Cav-1 positive HM-7 clones ceased to express MT4-MMP in their lipid rafts. Comparative proteomic analyses of lipid rafts from cav-1 positive and cav-1 negative cells demonstrated de novo expression of flotillin-1 only on the cells expressing cav-1. Xenografting control cells devoid of cav-1 in nude mice induced development of bigger tumors expressing higher levels of proliferating cell nuclear antigen as compared to mice injected with cells expressing the highest cav-1 levels. We conclude that cav-1 orchestrates and reorganize several proteins in lipid rafts, activities directly associated with reduced tumorigenic and metastatic ability of colon cancer cells.

Caveolin-1: role in cell signaling

Caveolins (Cavs) are integrated plasma membrane proteins that are complex signaling regulators with numerous partners and whose activity is highly dependent on cellular context. Cavs are both positive and negative regulators of cell signaling in and/or out of caveolae, invaginated lipid raft domains whose formation is caveolin expression dependent. Caveolins and rafts have been implicated in membrane compartmentalization; proteins and lipids accumulate in these membrane microdomains where they transmit fast, amplified and specific signaling cascades. The concept of plasma membrane organization within functional rafts is still in exploration and sometimes questioned. In this chapter, we discuss the opposing functions of caveolin in cell signaling regulation focusing on the role of caveolin both as a promoter and inhibitor of different signaling pathways and on the impact of membrane domain localization on caveolin functionality in cell proliferation, survival, apoptosis and migration.

Caveolar domain organization and trafficking is regulated by Abl kinases and mDia1

The biology of caveolin-1 (Cav1)/caveolae is intimately linked to actin dynamics and adhesion receptors. Caveolar domains are organized in hierarchical levels of complexity from curved or flattened caveolae to large, higher-order caveolar rosettes. We report that stress fibers controlled by Abl kinases and mDia1 determine the level of caveolar domain organization, which conditions the subsequent inward trafficking of caveolar domains induced upon loss of cell adhesion from the extracellular matrix. Abl-deficient cells have fewer stress fibers, a smaller pool of stress-fiber co-aligned Cav1 and increased clustering of Cav1/caveolae at the cell surface. Defective caveolar linkage to stress fibers prevents the formation of big caveolar rosettes upon loss of cell adhesion, correlating with a lack of inward trafficking. Live imaging of stress fibers and Cav1 showed that the actin-linked Cav1 pool loses its spatial organization in the absence of actin polymerization and is dragged and clustered by depolymerizing filaments. We identified mDia1 as the actin polymerization regulator downstream of Abl kinases that controls the stress-fiber-linked Cav1 pool. mDia1 knockdown results in Cav1/caveolae clustering and defective inward trafficking upon loss of cell adhesion. By contrast, cell elongation imposed by the excess of stress fibers induced by active mDia1 flattens caveolae. Furthermore, active mDia1 rescues the actin co-aligned Cav1 pool and Cav1 inward trafficking upon loss of adhesion in Abl-deficient cells. Thus, caveolar domain organization and trafficking are tightly coupled to adhesive and stress fiber regulatory pathways.