Caveolin-1 deficiency (-/-) conveys premalignant alterations in mammary epithelia, with abnormal lumen formation, growth factor independence, and cell invasiveness

CRISPR-Cas9 based knockout of S100A8 in mammary epithelial cells enhances cell proliferation and triggers oncogenic transformation via the PI3K-Akt pathway: Insights from a deep proteomic analysis

S100A8 is a calcium-binding protein with multiple functions, including being a chemoattractant for phagocytes and playing a key role in the inflammatory response. Its expression has been shown to influence epithelial-mesenchymal transition (EMT) and metastasis in colorectal cancer. However, the role of S100A8 in cell proliferation and differentiation remains unknown. In this study, we used the CRISPR-Cas9 system to knock out S100A8 in healthy mammary epithelial cells and investigated the resulting changes in proteome profiling and signaling pathways. Our results showed that S100A8 knockout led to an increase in cell proliferation and migration, reduced cell-cell adhesion, and increased apoptosis compared to wildtype cells. Proteomics data indicated that S100A8 significantly affects cell cycle progression, cell proliferation, and cell survival through the PI3K-Akt pathway. Furthermore, our findings suggest that S100A8 function is associated with Pten expression, a negative regulator of the PI3K-Akt pathway. These results indicate that S100A8 dysregulation in healthy cells can lead to altered cellular physiology and higher proliferation, similar to cancerous growth. Therefore, maintaining S100A8 expression is critical for preserving healthy cell physiology. This study provides novel insights into the role of S100A8 in cell proliferation and differentiation and its potential relevance to cancer biology. SIGNIFICANCE: The study suggests that maintaining S100A8 expression is critical for preserving healthy cell physiology, and dysregulation of S100A8 in healthy cells can lead to altered cellular physiology and higher proliferation, similar to cancerous growth. Therefore, targeting the PI3K-Akt pathway or regulating Pten expression, a negative regulator of the PI3K-Akt pathway, may be potential strategies for cancer treatment by controlling S100A8 dysregulation. Additionally, S100A8 and S100A9 have been shown to promote metastasis of breast carcinoma by forming a metastatic milieu. However, the differential expression of S100A8 in tumors and its dual effects of antitumor and protumor make the relationship between S100A8 and tumors complicated. Currently, most research focuses on the function of S100A8 as a secretory protein in the microenvironment of tumors, and its function inside healthy cells without forming dimers remains unclear. Furthermore, the study provides insight into the role of S100A8 in cell proliferation and differentiation, which may have implications for other diseases beyond cancer. The functional role of S100A8 in normal mammary epithelial cells remains completely uncertain. Therefore, the objective of this study is to investigate the function of S100A8 on proliferation in mammary epithelial cells after its deletion and to elucidate the underlying proteins involved in downstream signaling. Our findings indicate that the deletion of S100A8 leads to excessive proliferation in normal mammary epithelial cells, reduces apoptosis, and affects cell-cell adhesion molecules required for cellular communication, resulting in a cancer-like phenotype.

Behind Brain Metastases Formation: Cellular and Molecular Alterations and Blood-Brain Barrier Disruption

Breast cancer (BC) brain metastases is a life-threatening condition to which accounts the poor understanding of BC cells' (BCCs) extravasation into the brain, precluding the development of preventive strategies. Thus, we aimed to unravel the players involved in the interaction between BCCs and blood-brain barrier (BBB) endothelial cells underlying BBB alterations and the transendothelial migration of malignant cells. We used brain microvascular endothelial cells (BMECs) as a BBB in vitro model, under conditions mimicking shear stress to improve in vivo-like BBB features. Mixed cultures were performed by the addition of fluorescently labelled BCCs to distinguish individual cell populations. BCC-BMEC interaction compromised BBB integrity, as revealed by junctional proteins (β-catenin and zonula occludens-1) disruption and caveolae (caveolin-1) increase, reflecting paracellular and transcellular hyperpermeability, respectively. Both BMECs and BCCs presented alterations in the expression pattern of connexin 43, suggesting the involvement of the gap junction protein. Myosin light chain kinase and phosphorylated myosin light chain were upregulated, revealing the involvement of the endothelial cytoskeleton in the extravasation process. β4-Integrin and focal adhesion kinase were colocalised in malignant cells, reflecting molecular interaction. Moreover, BCCs exhibited invadopodia, attesting migratory properties. Collectively, hub players involved in BC brain metastases formation were unveiled, disclosing possible therapeutic targets for metastases prevention.

Downregulation of caveolin-1 promotes murine breast cancer cell line progression by highly glycosylated CD147

Caveolin-1 (CAV-1) can extensively regulate lipid transportation, cell growth and cell death. In the present study, we revealed a novel function of CAV-1 in inhibiting glycosylation of other molecules in murine breast cancer cell line. After the silencing of CAV-1, we found that the mRNA and protein expressions of cluster of differentiation 147 (CD147) and its related molecules (MCT4, matrix metalloproteinase MMP2 and MMP9) increased in the breast cancer cells. Meanwhile, the migration and invasion of the breast cancer cells were significantly enhanced assessed by cell wound healing experiment and transwell assays. Further, the gelatin zymography and lactate assay in the cells also showed the strengthened enzyme activity of MMP9 and the increased extracellular lactate concentration, respectively, after the silencing of CAV-1. Notably, the glycosylation level of CD147 overtly increased after the inhibition of CAV-1 detected by Western Blot analysis, whereas upregulation of CAV-1 did the opposite. Therefore, the findings suggest that the downregulation of CAV-1 can promote breast cancer cell progression probably by highly glycosylated CD147.

Cells into tubes: Molecular and physical principles underlying lumen formation in tubular organs

Tubular networks, such as the vascular and respiratory systems, transport liquids and gases in multicellular organisms. The basic units of these organs are tubes formed by single or multiple cells enclosing a luminal cavity. The formation and maintenance of correctly sized and shaped lumina are fundamental steps in organogenesis and are essential for organismal homeostasis. Therefore, understanding how cells generate, shape and maintain lumina is crucial for understanding normal organogenesis as well as the basis of pathological conditions. Lumen formation involves polarized membrane trafficking, cytoskeletal dynamics, and the influence of intracellular as well as extracellular mechanical forces, such as cortical tension, luminal pressure or blood flow. Various tissue culture and in vivo model systems, ranging from MDCK cell spheroids to tubular organs in worms, flies, fish, and mice, have provided many insights into the molecular and cellular mechanisms underlying lumenogenesis and revealed key factors that regulate the size and shape of cellular tubes. Moreover, the development of new experimental and imaging approaches enabled quantitative analyses of intracellular dynamics and allowed to assess the roles of cellular and tissue mechanics during tubulogenesis. However, how intracellular processes are coordinated and regulated across scales of biological organization to generate properly sized and shaped tubes is only beginning to be understood. Here, we review recent insights into the molecular, cellular and physical mechanisms underlying lumen formation during organogenesis. We discuss how these mechanisms control lumen formation in various model systems, with a special focus on the morphogenesis of tubular organs in Drosophila.

Caveolin-1 enhances brain metastasis of non-small cell lung cancer, potentially in association with the epithelial-mesenchymal transition marker SNAIL

Background

Caveolin-1 (Cav-1) plays an important role in the development of various human cancers. We investigated the relationship between Cav-1 expression and non-small cell lung cancer (NSCLC) progression in the context of brain metastasis (BM).

Methods

Cav-1 expression was investigated in a series of 102 BM samples and 49 paired primary NSCLC samples, as well as 162 unpaired primary NSCLC samples with (63 cases) or without (99 cases) metastasis to distant organs. Human lung cancer cell lines were used for in vitro functional analysis.

Results

High Cav-1 expression in tumor cells was observed in 52% (38/73) of squamous cell carcinomas (SQCs) and 33% (45/138) of non-SQCs. In SQC, high Cav-1 expression was increased after BM in both paired and unpaired samples of lung primary tumors and BM (53% vs. 84% in paired samples, P = 0.034; 52% vs. 78% in unpaired samples, P = 0.020). Although the difference in median overall survival in patients NSCLC was not statistically significant, high Cav-1 expression in tumor cells (P = 0.005, hazard ratio 1.715, 95% confidence index 1.175–2.502) was independent prognostic factors of overall survival on multivariate Cox regression analyses, in addition to the presence of BM and non-SQC type. In vitro assays revealed that Cav-1 knockdown inhibited the invasion and migration of lung cancer cells. Genetic modulation of Cav-1 was consistently associated with SNAIL up- and down-regulation. These findings were supported by increased SNAIL and Cav-1 expression in BM samples of SQC.

Conclusions

Cav-1 plays an important role in the BM of NSCLC, especially in SQC. The mechanism may be linked to SNAIL regulation.

Electronic supplementary material

The online version of this article (10.1186/s12935-019-0892-0) contains supplementary material, which is available to authorized users.

Nanotherapeutics with suitable properties for advanced anticancer therapy based on HPMA copolymer-bound ritonavir via pH-sensitive spacers

Ritonavir (RIT) is a widely used antiviral drug that acts as an HIV protease inhibitor with emerging potential in anticancer therapies. RIT causes inhibition of P-glycoprotein, which plays an important role in multidrug resistance (MDR) in cancer cells when overexpressed. Moreover, RIT causes mitochondrial dysfunction, leading to decreased ATP production and reduction of caveolin I expression, which can affect cell migration and tumor progression. To increase its direct antitumor activity, decrease severe side effects induced by the use of free RIT and improve its pharmacokinetics, ritonavir 5-methyl-4-oxohexanoate (RTV) was synthesized and conjugated to a tumor-targeted polymer carrier based on a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer. Here we demonstrated that polymer-bound RTV enhanced the internalization of polymer-RTV conjugates, differing in RTV content from 4 to 15 wt%, in HeLa cancer cells compared with polymer without RTV. The most efficient influx and internalization properties were determined for the polymer conjugate bearing 11 wt% of RTV. This conjugate was internalized by cells using both caveolin- and clathrin-dependent endocytic pathways in contrast to the RTV-free polymer, which was preferentially internalized only by clathrin-mediated endocytosis. Moreover, we found the co-localization of the RTV-conjugate with mitochondria and a significant decrease of ATP production in treated cells. Thus, the impact on mitochondrial mechanism can influence the function of ATP-dependent P-glycoprotein and also the cell viability of MDR cancer cells. Overall, this study demonstrated that the polymer-RTV conjugate is a promising polymer-based nanotherapeutic, suitable for antitumor combination therapy with other anticancer drugs and a potential mitochondrial drug delivery system.

Pathway‑based detection of idiopathic pulmonary fibrosis at an early stage

Idiopathic pulmonary fibrosis (IPF) is the most common interstitial pneumonia and the most aggressive interstitial lung disease. Usually, IPF is confirmed by the histopathological pattern of typical interstitial pneumonia and requires an integrated multidisciplinary approach from pulmonologists, radiologists and pathologists. However, these diagnoses are performed at an advanced stage of IPF. At present, pathway‑based detection requires investigation, as it can be performed at an early stage of the disease. The aim of the present study was to find an effective method of diagnosing IPF at an early stage. Microarray data forE‑GEOD‑33566 were downloaded from the ArrayExpress database. Human pathways were downloaded from Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database. An individual pathway‑based method to diagnose IPF at an early stage was introduced. Pathway statistics were analyzed with an individualized pathway aberrance score. P‑values were obtained with different methods, including the Wilcoxon test, linear models for microarray data (Limma) test and attract methods, generating three pathway groups. Support vector machines (SVM) were used to identify the best group for diagnosing IPF at an early stage. There were 106 differential pathways in Wilcoxon‑based KEGG Pathway (n>5) group, 100 in the Limma‑based KEGG Pathway (n>5) group, and seven in the attract‑based KEGG Pathway (n>5) group. The pathway statistics of these differential pathways in three groups were analyzed with linear SVM. The results demonstrated that the Wilcoxon‑based KEGG Pathway (n>5) group performed best in diagnosing IPF.

Critical role of CAV1/caveolin-1 in cell stress responses in human breast cancer cells via modulation of lysosomal function and autophagy

CAV1 (caveolin 1, caveolae protein, 22kDa) is well known as a principal scaffolding protein of caveolae, a specialized plasma membrane structure. Relatively, the caveolae-independent function of CAV1 is less studied. Autophagy is a process known to involve various membrane structures, including autophagosomes, lysosomes, and autolysosomes for degradation of intracellular proteins and organelles. Currently, the function of CAV1 in autophagy remains largely elusive. In this study, we demonstrate for the first time that CAV1 deficiency promotes both basal and inducible autophagy. Interestingly, the promoting effect was found mainly in the late stage of autophagy via enhancing lysosomal function and autophagosome-lysosome fusion. Notably, the regulatory function of CAV1 in lysosome and autophagy was found to be caveolae-independent, and acts through lipid rafts. Furthermore, the elevated autophagy level induced by CAV1 deficiency serves as a cell survival mechanism under starvation. Importantly, downregulation of CAV1 and enhanced autophagy level were observed in human breast cancer cells and tissues. Taken together, our data reveal a novel function of CAV1 and lipid rafts in breast cancer development via modulation of lysosomal function and autophagy.

Significance of caveolin-1 and matrix metalloproteinase 14 gene expression in canine mammary tumours

Canine mammary tumours (CMTs) are the most common neoplasms affecting female dogs. There is an urgent need for molecular biomarkers that can detect early stages of the disease in order to improve accuracy of CMT diagnosis. The aim of this study was to examine whether caveolin-1 (Cav-1) and matrix metalloproteinase 14 (MMP14) are associated with CMT histological malignancy and invasion. Sixty-five benign and malignant CMT samples and six normal canine mammary glands were analysed using quantitative reverse transcription-polymerase chain reaction. Cav-1 and MMP14 genes were highly expressed in CMT tissues compared to normal tissues. Cav-1 especially was overexpressed in malignant and invasive CMT tissues. When a CMT cell line was cultured on fluorescent gelatin-coated coverslips, localisation of Cav-1 was observed at invadopodia-mediated degradation sites of the gelatin matrix. These findings suggest that Cav-1 may be involved in CMT invasion and that the markers may be useful for estimating CMT malignancy.

Value of caveolin-1 in cancer progression and prognosis: Emphasis on cancer-associated fibroblasts, human cancer cells and mechanism of caveolin-1 expression (Review)

Caveolin-1 (Cav-1) is found predominately in terminally differentiated cells, such as adipocytes, endothelia and smooth muscle cells, as well as type I pneumocytes. As a main structural component of caveolae, Cav-1 is important in modulating cellular signaling. In the present study, the expression and clinical role of Cav-1 were analyzed in tumor stromal and human cancer cells, respectively. The results of previous studies have shown that the downregulation of tumor stromal Cav-1 promotes tumor survival and predicts a poor tumor prognosis, predominantly concentrating on the mechanism of the metabolism of the cancer microenvironment (according to the autophagic tumor stroma model of cancer metabolism and the reverse Warburg effect). However, contradictory results concerning the expression, clinical roles and associated mechanisms of Cav-1 have been reported. An improved understanding of Cav-1 expression in tumor stromal and cancer cells will increase knowledge with regard to the clinical value of Cav-1 and its detailed mechanisms. This review summarizes the novel data concerning the clinical values and probable mechanisms of Cav-1 expression in tumor stromal (predominantly in cancer-associated fibroblasts) and cancer cells, respectively.

Mitochondrial alterations during carcinogenesis: a review of metabolic transformation and targets for anticancer treatments

Mitochondria play important roles in multiple cellular processes including energy metabolism, cell death, and aging. Regulated energy production and utilization are critical in maintaining energy homeostasis in normal cells and functional organs. However, mitochondria go through a series of morphological and functional alterations during carcinogenesis. The metabolic profile in transformed cells is altered to accommodate their fast proliferation, confer resistance to cell death, or facilitate metastasis. These transformations also provide targets for anticancer treatment at different levels. In this review, we discuss the major modifications in cell metabolism during carcinogenesis, including energy metabolism, apoptotic and autophagic cell death, adaptation of tumor microenvironment, and metastasis. We also summarize some of the main metabolic targets for treatments.

The retinoblastoma tumor suppressor pathway modulates the invasiveness of ErbB2-positive breast cancer

The processes that control the progression of ductal carcinoma in situ (DCIS) to invasive breast cancer remain poorly understood. Epidermal growth factor receptor 2 (ErbB2) over expression is common in DCIS, as is disruption of the retinoblastoma tumor suppressor (RB) pathway. Here we examined the cooperative impact of ErbB2 and RB deregulation on facets of disease progression. Our studies demonstrate that RB deficiency altered the expression of key molecules needed for proper cellular organization and epithelial cell-cell adhesion as part of a program related to the epithelial to mesenchymal transition (EMT). An increase in the invasive potential of ErbB2 over expressing cells was observed upon RB depletion. Furthermore, stable knockdown of RB resulted in invasive lesions in orthotopic xenograft assays, compared to DCIS-like lesions developing from RB-proficient cells. Conversely, the invasive phenotype observed in ErbB2-positive cancer models was inhibited through CDK4/6 inhibition in an RB-dependent manner. Lastly, in a cohort of DCIS cases, we show that while elevated levels of ErbB2 are associated with increased risk of a subsequent DCIS recurrence, it is not associated with progression to invasive disease. In contrast, RB loss in ErbB2 positive DCIS cases was associated with increased risk for invasive breast cancer. Taken together, these data demonstrate a key role for the RB-pathway in invasion associated with breast tumor progression, and shed light on the key molecular events that promote the progression of DCIS to invasive disease.

Model cell membranes: Techniques to form complex biomimetic supported lipid bilayers via vesicle fusion

Vesicle fusion has long provided an easy and reliable method to form supported lipid bilayers (SLBs) from simple, zwitterionic vesicles on siliceous substrates. However, for complex compositions, such as vesicles with high cholesterol content and multiple lipid types, the energy barrier for the vesicle-to-bilayer transition is increased or the required vesicle-vesicle and vesicle-substrate interactions are insufficient for vesicle fusion. Thus, for vesicle compositions that more accurately mimic native membranes, vesicle fusion often fails to form SLBs. In this paper, we review three approaches to overcome these barriers to form complex, biomimetic SLBs via vesicle fusion: (i) optimization of experimental conditions (e.g., temperature, buffer ionic strength, osmotic stress, cation valency, and buffer pH), (ii) α-helical (AH) peptide-induced vesicle fusion, and (iii) bilayer edge-induced vesicle fusion. AH peptide-induced vesicle fusion can form complex SLBs on multiple substrate types without the use of additional equipment. Bilayer edge-induced vesicle fusion uses microfluidics to form SLBs from vesicles with complex composition, including vesicles derived from native cell membranes. Collectively, this review introduces vesicle fusion techniques that can be generalized for many biomimetic vesicle compositions and many substrate types, and thus will aid efforts to reliably create complex SLB platforms on a range of substrates.

FoxO3a (Forkhead Box O3a) deficiency protects Idiopathic Pulmonary Fibrosis (IPF) fibroblasts from type I polymerized collagen matrix-induced apoptosis via caveolin-1 (cav-1) and Fas

Idiopathic Pulmonary Fibrosis is a lethal fibrotic disease characterized by the unrelenting proliferation and persistence of fibroblasts in a type I collagen-rich matrix that result in an expanding reticular network of fibrotic tissue. However, the underlying mechanism responsible for the persistence of myofibroblasts in IPF remains unclear. During normal tissue repair, unwanted fibroblasts are eliminated during collagen-matrix contraction by a mechanism whereby high PTEN activity suppresses Akt. We have previously found that FoxO3a, a transcriptional activator of apoptosis-inducing proteins, is inactivated in IPF fibroblasts resulting from aberrantly high PI3K/Akt activity due to inappropriately low PTEN activity. Here we demonstrate that this low FoxO3a activity confers IPF fibroblasts with resistance to collagen-mediated apoptosis. We show that the mechanism by which low FoxO3a activity confers IPF fibroblasts with an apoptotic resistant phenotype involves suppression of Fas expression as a result of down regulation of cav-1 expression via a PTEN/Akt-dependent pathway. We demonstrate that PTEN over-expression or Akt inhibition increases FoxO3a expression in IPF fibroblasts, resulting in up-regulation of caveolin-1. We show that FoxO3a binds to the cav-1 promoter region and ectopic expression of FoxO3a transcriptionally increases cav-1 mRNA and protein expression. In turn, we show that overexpression of caveolin-1 increases Fas levels and caspase-3/7 activity and promotes IPF fibroblast apoptosis on polymerized type I collagen. We have found that the expression of caveolin-1, Fas and cleaved caspase-3 proteins in fibroblasts within the fibroblastic foci of IPF patient specimens is low. Our data indicate that the pathologically altered PTEN/Akt axis inactivates FoxO3a down-regulating cav-1 and Fas expression. This confers IPF fibroblasts with an apoptosis-resistant phenotype and may be responsible for IPF progression.

Divergent control of Cav-1 expression in non-cancerous Li-Fraumeni syndrome and human cancer cell lines

Li-Fraumeni syndrome (LFS) is primarily characterized by development of tumors exhibiting germ-line mutations in the p53 gene. Cell lines developed from patients of a LFS family have decreased p53 activity as evidenced by the absence of apoptosis upon etoposide treatment. To test our hypothesis that changes in gene expression beyond p53 per se are contributing to the development of tumors, we compared gene expression in non-cancerous skin fibroblasts of LFS-affected (p53 heterozygous) vs. non-affected (p53 wild-type homozygous) family members. Expression analysis showed that several genes were differentially regulated in the p53 homozygous and heterozygous cell lines. We were particularly intrigued by the decreased expression (~88%) of a putative tumor-suppressor protein, caveolin-1 (Cav-1), in the p53-mutant cells. Decreased expression of Cav-1 was also seen in both p53-knockout and p21-knockout HTC116 cells suggesting that p53 controls Cav-1 expression through p21 and leading to the speculation that p53, Cav-1 and p21 may be part of a positive auto-regulatory feedback loop. The direct relationship between p53 and Cav-1 was also tested with HeLa cells (containing inactive p53), which expressed a significantly lower Cav-1 protein. A panel of nonfunctional and p53-deficient colon and epithelial breast cancer cell lines showed undetectable expression of Cav-1 supporting the role of p53 in the control of Cav-1. However, in two aggressively metastasizing breast cancer cell lines, Cav-1 was strongly expressed suggesting a possible role in tumor metastasis. Thus, there is a divergent control of Cav-1 expression as evidenced in non-cancerous Li-Fraumeni syndrome and some aggressive human cancer cell lines.

Taurine attenuates lipopolysaccharide-induced disfunction in mouse mammary epithelial cells

The intent of this study was to evaluate the active defense reaction of mouse mammary epithelial cells and the cytoprotective and anti-inflammatory properties of taurine to lipopolysaccharide (LPS)-induced disfunction in mouse mammary epithelial cells. (1) Primary cultured mouse mammary epithelial cells were stimulated with LPS for 24 h (final concentration=0, 5, 10, 20 μg/mL). Western blotting demonstrated a significant decrease in the secretion of β-casein in the 20 μg/mL LPS treatment group (P<0.05), while nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), lactoferrin (LF) and N-acetyl-β-D-glucosaminidase (NAGase) were all significantly increased following LPS treatment (P<0.01). Furthermore, cell survival was significantly inhibited after treatment with 20 μg/mL LPS; however, neither 5 μg/mL nor 10 μg/mL LPS had any effect on cell survival. Therefore, a level of 10 μg/mL LPS was selected to test the protective effect of taurine on mouse mammary epithelial cells. (2) Primary cultured mouse mammary epithelial cells were treated with 0, 5, 15 or 45 mmol/L taurine for 3 h, followed by 10 μg/mL LPS for 24 h. Taurine significantly attenuated the LPS-induced increase in NAGase activity, NO concentrations and the level of TNF-α, IL-1β, IL-6 and LF. Taurine at 45 mmol/L markedly increased β-casein secretion in response to LPS-induced disfunction. This study demonstrated that the addition of taurine to a culture medium significantly inhibited the LPS-induced release of inflammatory factors and increased β-casein secretion from mammary epithelial cells, thereby providing a possible explanation for the protective effect proposed for taurine in the prevention of LPS-induced disfunction in mammary epithelial cells.

Caveolin-1 and breast cancer: a new clinical perspective

The current chapter focuses on the role of Caveolin-1 (Cav-1) in cellular growth with an emphasis on its implication in breast cancer initiation, progression, clinical prognosis and as a potential therapeutic target. The role of Cav-1 as a tumor suppressor in breast cancer has emerged in the past few years, with dual functions on both cancer epithelium as well as the cancer stroma. Its multiple functions as a regulator of estrogen signaling and kinase activity and its newly found role as an important factor controlling the dynamic relationship between cancer epithelia and stroma position Cav-1 as a new therapeutic target for the treatment of breast cancer.

The two faces of Janus kinases and their respective STATs in mammary gland development and cancer

Since its discovery as “just another kinase” more than twenty years ago, the family of JAK tyrosine kinases and their respective Signal Transducers and Activators of Transcription (STATs) has been a center of attention in the areas of signal transduction, development, and cancer. The subsequent designation of JAKs as Janus kinases after the mythical two-faced Roman God of the doorways accurately portrays the analogous and sometimes contrasting molecular and biological characteristics of these tyrosine kinases. The two “faces” of JAKs are their structurally similar kinase and pseudo-kinase domains. As essential parts of various transmembrane receptor complexes, these tyrosine kinases function at cellular gateways and relay signals from growth factors to their respective intracellular targets. The multifaceted nature of JAKs becomes evident from their ability to activate specific STATs during distinct phases of normal mammary gland development. Studies in breast cancer cells and genetically engineered mouse models also show that JAK/STAT signaling possesses a "two-faced" role during breast cancer initiation and progression. This review will highlight recent findings about important biological functions of JAKs and STATs during normal mammogenesis, with particular emphasis on the Jak2/Stat5 pathway as well as Jak1/2/Stat3 signaling complexes. In addition, we will discuss how the importance of these signaling networks changes during carcinogenesis. With JAK inhibitors currently under development to treat myeloproliferative disorders, determining the essential functions of JAKs at particular stages of disease initiation and progression is of critical importance to predict the efficacy of these agents for targeted therapies against breast cancer.

Caveolin-1 and cancer metabolism in the tumor microenvironment: markers, models, and mechanisms

Caveolins are a family of membrane-bound scaffolding proteins that compartmentalize and negatively regulate signal transduction. Recent studies have implicated a loss of caveolin-1 (Cav-1) expression in the pathogenesis of human cancers. Loss of Cav-1 expression in cancer-associated fibroblasts results in an activated tumor microenvironment, thereby driving early tumor recurrence, metastasis, and poor clinical outcome in breast and prostate cancers. We describe various paracrine signaling mechanism(s) by which the loss of stromal Cav-1 promotes tumor progression, including fibrosis, extracellular matrix remodeling, and the metabolic/catabolic reprogramming of cancer-associated fibroblast, to fuel the growth of adjacent tumor cells. It appears that oxidative stress is the root cause of initiation of the loss of stromal Cav-1 via autophagy, which provides further impetus for the use of antioxidants in anticancer therapy. Finally, we discuss the functional role of Cav-1 in epithelial cancer cells.

Caveolin-1 promotes pancreatic cancer cell differentiation and restores membranous E-cadherin via suppression of the epithelial-mesenchymal transition

Pancreatic cancer is one of the deadliest cancers due to early rapid metastasis and chemoresistance. Recently, epithelial to mesenchymal transition (EMT) was shown to play a key role in the pathogenesis of pancreatic cancer. To understand the role of caveolin-1 (Cav-1) in EMT, we over-expressed Cav-1 in a pancreatic cancer cell line, Panc 10.05, that does not normally express Cav-1. Here, we show that Cav-1 expression in pancreatic cancer cells induces an epithelial phenotype and promotes cell-cell contact, with increased expression of plasma membrane bound E-cadherin and beta-catenin. Mechanistically, Cav-1 induces Snail downregulation and decreased activation of AKT, MAPK and TGF-beta-Smad signaling pathways. In vitro, Cav-1 expression reduces cell migration and invasion, and attenuates doxorubicin-chemoresistance of pancreatic cancer cells. Importantly, in vivo studies revealed that Cav-1 expression greatly suppresses tumor formation in a xenograft model. Most interestingly, Panc/Cav-1 tumors displayed organized nests of differentiated cells that were totally absent in control tumors. Confirming our in vitro results, these nests of differentiated cells showed reexpression of E-cadherin and beta-catenin at the cell membrane. Thus, we provide evidence that Cav-1 functions as a crucial modulator of EMT and cell differentiation in pancreatic cancer.

Signal transducer and activator of transcription 5 as a key signaling pathway in normal mammary gland developmental biology and breast cancer

STAT5 consists of two proteins, STAT5A/B, that impact mammary cell differentiation, proliferation, and survival. In normal development, STAT5 expression and activity are regulated by prolactin signaling with JAK2/ELF5, EGF signaling networks that include c-Src, and growth hormone, insulin growth factor, estrogen, and progesterone signaling pathways. In cancer, erythropoietin signaling can also regulate STAT5. Activation levels are influenced by AKT, caveolin, PIKE-A, Pak1, c-Myb, Brk, beta-integrin, dystroglycan, other STATs, and STAT pathway molecules JAK1, Shp2, and SOCS. TGF-β and PTPN9 can downregulate prolactin- and EGF-mediated STAT5 activation, respectively. IGF, AKT, RANKL, cyclin D1, BCL6, and HSP90A lie downstream of STAT5.

The role of caveolin-1 in human breast cancer

Caveolin-1 is the essential constituent protein of specialised plasma membrane invaginations called caveolae. The unique topology of caveolin-1 facilitates the role of caveolae as molecular hubs, integrating the activity of a multitude of signalling molecules. Despite improvements in our understanding of caveolin-1 interactions and the function of caveolae, the relationship between dysfunctional caveolin-1 and tumourigenesis remains contentious. Perhaps most intriguing has been the demonstration of both oncogenic and tumour suppressor function within particular tumour types, including breast cancer. In this review, the biological and clinical relevance of caveolin-1 in human breast cancer are considered. Evidence is systematically presented for the potential tumour suppressor and oncogenic functions of caveolin-1. Specific reference is made to interactions between caveolin-1 and signalling pathways in the clinical and biological subtypes of breast cancer. Areas of controversy are discussed and technical considerations are highlighted. Translational implications and potential for specific therapeutic manipulation of caveolin-1 are evaluated in the context of evidence from in vitro and in vivo studies.

Neuron-targeted caveolin-1 protein enhances signaling and promotes arborization of primary neurons

Decreased expression of prosurvival and progrowth-stimulatory pathways, in addition to an environment that inhibits neuronal growth, contribute to the limited regenerative capacity in the central nervous system following injury or neurodegeneration. Membrane/lipid rafts, plasmalemmal microdomains enriched in cholesterol, sphingolipids, and the protein caveolin (Cav) are essential for synaptic development/stabilization and neuronal signaling. Cav-1 concentrates glutamate and neurotrophin receptors and prosurvival kinases and regulates cAMP formation. Here, we show that primary neurons that express a synapsin-driven Cav-1 vector (SynCav1) have increased raft formation, neurotransmitter and neurotrophin receptor expression, NMDA- and BDNF-mediated prosurvival kinase activation, agonist-stimulated cAMP formation, and dendritic growth. Moreover, expression of SynCav1 in Cav-1 KO neurons restores NMDA- and BDNF-mediated signaling and enhances dendritic growth. The enhanced dendritic growth occurred even in the presence of inhibitory cytokines (TNFα, IL-1β) and myelin-associated glycoproteins (MAG, Nogo). Targeting of Cav-1 to neurons thus enhances prosurvival and progrowth signaling and may be a novel means to repair the injured and neurodegenerative brain.

Prognostic significance of tumor/stromal caveolin-1 expression in breast cancer patients

Caveolin-1 (Cav-1) has been extensively characterized in cancer biological research. However, the role of Cav-1 in the interaction between tumor and stromal cells remains unclear. In the present study, we examined Cav-1 expression in tumor cells and stromal cells in breast cancer tissue by immunohistochemical analysis and evaluated its prognostic value in a training cohort. Immunohistochemical analysis of Cav-1 expression was scored as (++), (+) or (-) according to the proportion of positively stained tumor cells (T) and stromal cells (S). Correlation analysis between tumor/stromal Cav-1 expression and clinicopathological parameters revealed that only T(++) Cav-1 status was positively associated with tumor size and histological nodal status (P = 0.019 and 0.021, respectively). Univariate analysis revealed that combined T(++)/S(-) status was significantly correlated with unfavorable prognostic outcomes (P < 0.001). Multivariate analysis demonstrated that this combined status is an independent prognostic factor for primary breast cancer (P = 0.002). Clinical outcomes in different subgroups of breast cancer patients were also strictly dependent on this combined status (P < 0.05). The prognostic value of T(++)/S(-) Cav-1 status was also validated in the testing cohort. Collectively, our data indicate that high Cav-1 expression in tumor cells and lack of this expression in stromal cells could help identify a particular subgroup of breast cancer patients with potentially poor survival. Further studies are required to understand the regulatory mechanism of Cav-1 in the tumor microenvironment.

Angiopoietin-2 drives lymphatic metastasis of pancreatic cancer

Lymphatic metastasis constitutes a critical route of disease dissemination, which limits the prognosis of patients with pancreatic ductal adenocarcinoma (PDAC). As lymphangiogenesis has been implicated in stimulation of lymphatic metastasis by vascular endothelial growth factor-C (VEGF-C) and VEGF-D, we studied the effect of the angioregulatory growth factor angiopoietin-2 (Ang-2) on PDAC progression. Ang-2 was found to be expressed in transformed cells of human PDAC specimens, with corresponding Tie-2 receptors present on blood and lymphatic endothelium. In vitro in PDAC cells, Ang-2 was subject to autocrine/paracrine TGF-β stimulation (2-fold induction, P=0.0106) acting on the -61- to +476-bp element of the human Ang-2 promoter. In turn, Ang-2 regulated the expression of genes involved in cell motility and tumor suppression. Orthotopic PDAC xenografts with forced expression of Ang-2, but not Ang-1, displayed increased blood and lymphatic vessel density, and an enhanced rate of lymphatic metastasis (6.7- to 9.1-fold, P<0.01), which was prevented by sequestration of Ang-2 via coexpression of soluble Tie-2. Notably, elevated circulating Ang-2 in patients with PDAC correlated with the extent of lymphatic metastasis. Furthermore, median survival was reduced from 28.4 to 7.7 mo in patients with circulating Ang-2 ≥ 75th percentile (P=0.0005). These findings indicate that Ang-2 participates in the control of lymphatic metastasis, constitutes a noninvasive prognostic biomarker, and may provide an accessible therapeutic target in PDAC.

Caveolin-1 is related to invasion, survival, and poor prognosis in hepatocellular cancer

Caveolin-1 is the principal components of caveolae membranes, implicated in oncogenesis and angiogenesis. Until now, its expression and functional significance in hepatocellular carcinoma (HCC) are still unclear. In the present study, we demonstrated that expression of caveolin-1 was markedly upregulated in HCC patients. In addition, increased caveolin-1 expression correlated positively with the histological differentiation, portal venous invasion, hepatic venous invasion, intrahepatic metastases, and recurrence, suggesting a role for caveolin-1 in the progression of HCC. HepG2 cell line was transfected with pcDNA3.1/caveolin-1 to observe the significance of the change in caveolin-1 expression. We showed that caveolin-1 overexpression could not only protect HepG2 cells from apoptosis but also enhance its migration and invasion by upregulating MMP-2, MMP-9, and VEGF expressions. Collectively, our clinical and in vitro data indicate that the status of caveolin-1 expression may be one of causative factors for the invasion and poor prognosis in HCC.

Pilot study on the effects of dietary conjugated linoleic acid on tumorigenesis and gene expression in PyMT transgenic mice

Conjugated linoleic acid (CLA) is a class of commercially available fatty acids that have been associated with anticancer properties in rodent models of chemical carcinogenesis. We conducted a pilot study to examine the antitumor effect of dietary CLA in a polyoma virus-middle T antigen (PyMT) mouse model of invasive breast cancer. Virgin 4-week-old PyMT mice were administered a mixed-isomer CLA diet (1% wt/wt) or control AIN-93G diet for 4 weeks (N = 6 and 5, respectively) and tumor burden was assessed at 8 weeks of age. Thoracic mammary glands were prepared as whole mounts with other glands being formalin fixed and paraffin embedded for histology and immunohistochemistry (IHC). Total RNA was prepared for microarray and real-time reverse transcription-polymerase chain reaction analysis. Western blots were performed for protein expression analysis. Tumor incidence was significantly increased in CLA-treated animals compared with controls (P = 0.009) and occurred with extensive lobular-alveolar expansion and loss of mammary adipose tissue. More than 100 genes were downregulated > or = 2-fold in the CLA-treated group compared with controls, including adipose-specific markers, as wells as cytoskeletal and adhesion-related genes. This was supported by dramatic decreases in the epithelial adherens E-cadherin and beta-catenin as demonstrated by IHC. Taken together, these results suggest that dietary CLA affects the mammary stromal environment, leading to tumor progression and cellular expansion in the PyMT mouse model. Further studies of the potential for cancer promotion are needed, especially because mixed-isomer CLA formulations are sold commercially as a nutritional supplement.

Induction of the apoptosis inhibitor ARC by Ras in human cancers

Inhibition of apoptosis is critical for carcinogenesis. ARC (apoptosis repressor with caspase recruitment domain) is an endogenous inhibitor of apoptosis that antagonizes both intrinsic and extrinsic apoptosis pathways. Although normally expressed in striated myocytes and neurons, ARC is markedly induced in a variety of primary human epithelial cancers and renders cancer cells resistant to killing. The mechanisms that mediate the induction of ARC in cancer are unknown. Herein we demonstrate that increases in ARC abundance are stimulated by Ras through effects on transcription and protein stability. Overexpression of activated N-Ras or H-Ras in normal cells is sufficient to increase ARC mRNA and protein levels. Similarly, transgenic expression of activated H-Ras induces ARC in both the normal mammary epithelium and resulting tumors of intact mice. Conversely, knockdown of endogenous N-Ras in breast and colon cancer cells significantly reduces ARC mRNA and protein levels. The promoter of the Nol3 locus, encoding ARC, is activated by N-Ras and H-Ras in a MEK/ERK-dependent manner. Ras also stabilizes ARC protein by suppressing its polyubiquitination and subsequent proteasomal degradation. In addition to the effects of Ras on ARC abundance, ARC mediates Ras-induced cell survival and cell cycle progression. Thus, Ras induces ARC in epithelial cancers, and ARC plays a role in the oncogenic actions of Ras.

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

OBJECTIVE

Recent studies have implicated caveolin 1 in the regulation of transforming growth factor beta (TGFbeta) downstream signaling. Given the crucial role of TGFbeta in the pathogenesis of systemic sclerosis (SSc), we sought to determine whether caveolin 1 is also involved in the pathogenesis of tissue fibrosis in SSc. We analyzed the expression of CAV1 in affected SSc tissues, studied the effects of lack of expression of CAV1 in vitro and in vivo, and analyzed the effects of restoration of caveolin 1 function on the fibrotic phenotype of SSc fibroblasts in vitro.

METHODS

CAV1 expression in tissues was analyzed by immunofluorescence and confocal microscopy. The extent of tissue fibrosis in Cav1-knockout mice was assessed by histologic/histochemical analyses and quantified by hydroxyproline assays. Cav1-null and SSc fibroblast phenotypes and protein production were analyzed by real-time polymerase chain reaction, immunofluorescence, Western blot, and multiplexed enzyme-linked immunosorbent assay techniques. The effects of restoration of caveolin 1 function in SSc fibroblasts in vitro were also examined using a cell-permeable recombinant CAV1 peptide.

RESULTS

CAV1 was markedly decreased in the affected lungs and skin of SSc patients. Cav1-knockout mice developed pulmonary and skin fibrosis. Down-regulation of caveolin 1 was maintained in cultured SSc fibroblasts, and restoration of caveolin 1 function in vitro normalized their phenotype and abrogated TGFbeta stimulation through inhibition of Smad3 activation.

CONCLUSION

Caveolin 1 appears to participate in the pathogenesis of tissue fibrosis in SSc. Restoration of caveolin 1 function by treatment with a cell-permeable peptide corresponding to the CAV1 scaffolding domain may be a novel therapeutic approach in SSc.

Signal transducer and activator of transcription (STAT)-5A and STAT5B differentially regulate human mammary carcinoma cell behavior

Increased activation of signal transducer and activator of transcription (STAT)-5 has been reported in various malignancies including mammary carcinoma. However, it is only recently that potentially distinct roles of STAT5A and STAT5B in neoplasia have begun to emerge. Herein we systematically delineate the functions of STAT5A and STAT5B in human mammary carcinoma cell lines MCF-7 and T47D. Forced expression of constitutively active (CA) STAT5A enhanced both survival and anchorage-independent growth of human mammary carcinoma cells but concordantly suppressed cell motility as revealed in colony scattering, cell migration, and invasion assays. In contrast, forced expression of CA STAT5B exhibited lower potency than CA STAT5A in enhancing survival and anchorage-independent growth of mammary carcinoma cells and exerted no effects on cell motility. Differential expression of genes that regulate cellular survival and motility was concomitantly observed on forced expression of CA STAT5A or CA STAT5B. Small interfering RNA-mediated depletion of STAT5A significantly impaired anchorage-independent growth of human mammary carcinoma cells, whereas a smaller reduction was observed upon small interfering RNA-mediated depletion of STAT5B. Depletion of endogenous STAT5A also significantly enhanced cell motility, whereas depletion of endogenous STAT5B exhibited no effect. Xenograft studies provided data concordant with the in vitro effects of the two STAT5 isoforms. We therefore demonstrate that STAT5A and STAT5B differentially regulate behavior of human mammary carcinoma cells.

Genetic ablation of caveolin-1 drives estrogen-hypersensitivity and the development of DCIS-like mammary lesions

Caveolin-1 (Cav-1) loss-of-function mutations are exclusively associated with estrogen receptor-positive (ER(+)) human breast cancers. To dissect the role of Cav-1 loss-of-function in the pathogenesis of human breast cancers, we used Cav-1(-/-) null mice as a model system. First, we demonstrated that Cav-1(-/-) mammary epithelia overexpress two well-established ER co-activator genes, CAPER and Foxa1, in addition to ER-alpha. Thus, the functional loss of Cav-1 may be sufficient to confer estrogen-hypersensitivity in the mammary gland. To test this hypothesis directly, we subjected Cav-1(-/-) mice to ovariectomy and estrogen supplementation. As predicted, Cav-1(-/-) mammary glands were hyper-responsive to estrogen and developed dysplastic mammary lesions with adjacent stromal angiogenesis that resemble human ductal carcinoma in situ. Based on an extensive biomarker analysis, these Cav-1(-/-) mammary lesions contain cells that are hyperproliferative and stain positively with nucleolar (B23/nucleophosmin) and stem/progenitor cell markers (SPRR1A and beta-catenin). Genome-wide transcriptional profiling identified many estrogen-related genes that were over-expressed in Cav-1(-/-) mammary glands, including CAPER--an ER co-activator gene and putative stem/progenitor cell marker. Analysis of human breast cancer samples revealed that CAPER is overexpressed and undergoes a cytoplasmic-to-nuclear shift during the transition from pre-malignancy to ductal carcinoma in situ. Thus, Cav-1(-/-) null mice are a new preclinical model for studying the molecular paradigm of estrogen hypersensitivity and the development of estrogen-dependent ductal carcinoma in situ lesions.

Nuclear factor-kappaB enhances ErbB2-induced mammary tumorigenesis and neoangiogenesis in vivo

The (HER2/Neu) ErbB2 oncogene is commonly overexpressed in human breast cancer and is sufficient for mammary tumorigenesis in transgenic mice. Nuclear factor (NF)-kappaB activity is increased in both human and murine breast tumors. The immune response to mammary tumorigenesis may regulate tumor progression. The role of endogenous mammary epithelial cell NF-kappaB had not previously been determined in immune-competent animals. Furthermore, the role of the NF-kappaB components, p50 and p65, in tumor growth was not known. Herein, the expression of a stabilized form of the NF-kappaB-inhibiting IkappaBalpha protein (IkappaBalphaSR) in breast tumor cell lines that express oncogenic ErbB2 inhibited DNA synthesis and growth in both two- and three-dimensional cultures. Either NF-kappaB inhibition or selective silencing of p50 or p65 led to a loss of contact-independent tumor growth in vitro. IkappaBalphaSR reversed the features of the oncogene-induced phenotype under three-dimensional growth conditions. The NF-kappaB blockade inhibited ErbB2-induced mammary tumor growth in both immune-competent and immune-deficient mice. These findings were associated with both reduced tumor microvascular density and a reduction in the amount of vascular endothelial growth factor. The expression of IkappaBalphaSR in breast cancer tumors inhibited angiogenesis. Thus, mammary epithelial cell NF-kappaB activity enhances ErbB2-mediated mammary tumorigenesis in vivo by promoting both growth and survival signaling via the promotion of tumor vasculogenesis.

Mechanisms of endocytosis

Endocytic mechanisms control the lipid and protein composition of the plasma membrane, thereby regulating how cells interact with their environments. Here, we review what is known about mammalian endocytic mechanisms, with focus on the cellular proteins that control these events. We discuss the well-studied clathrin-mediated endocytic mechanisms and dissect endocytic pathways that proceed independently of clathrin. These clathrin-independent pathways include the CLIC/GEEC endocytic pathway, arf6-dependent endocytosis, flotillin-dependent endocytosis, macropinocytosis, circular doral ruffles, phagocytosis, and trans-endocytosis. We also critically review the role of caveolae and caveolin1 in endocytosis. We highlight the roles of lipids, membrane curvature-modulating proteins, small G proteins, actin, and dynamin in endocytic pathways. We discuss the functional relevance of distinct endocytic pathways and emphasize the importance of studying these pathways to understand human disease processes.

Caveolin-1-/- null mammary stromal fibroblasts share characteristics with human breast cancer-associated fibroblasts

Recently, we reported that human breast cancer-associated fibroblasts show functional inactivation of the retinoblastoma (RB) tumor suppressor and down-regulation of caveolin-1 (Cav-1) protein expression. However, it remains unknown whether loss of Cav-1 is sufficient to confer functional RB inactivation in mammary fibroblasts. To establish a direct cause-and-effect relationship, mammary stromal fibroblasts (MSFs) were prepared from Cav-1(-/-) null mice and subjected to phenotypic analysis. Here, we provide evidence that Cav-1(-/-) MSFs share many characteristics with human cancer-associated fibroblasts. The Cav-1(-/-) MSF transcriptome significantly overlaps with human cancer-associated fibroblasts; both show a nearly identical profile of RB/E2F-regulated genes that are up-regulated, which is consistent with RB inactivation. This Cav-1(-/-) MSF gene signature is predictive of poor clinical outcome in breast cancer patients treated with tamoxifen. Consistent with these findings, Cav-1(-/-) MSFs show RB hyperphosphorylation and the up-regulation of estrogen receptor co-activator genes. We also evaluated the paracrine effects of "conditioned media" prepared from Cav-1(-/-) MSFs on wild-type mammary epithelia. Our results indicate that Cav-1(-/-) MSF "conditioned media" is sufficient to induce an epithelial-mesenchymal transition, indicative of an invasive phenotype. Proteomic analysis of this "conditioned media" reveals increased levels of proliferative/angiogenic growth factors. Consistent with these findings, Cav-1(-/-) MSFs are able to undergo endothelial-like transdifferentiation. Thus, these results have important implications for understanding the role of cancer-associated fibroblasts and RB inactivation in promoting tumor angiogenesis.

Cell biology of the movement of breast cancer cells: intracellular signalling and the actin cytoskeleton

Cell motility is a critical step in cancer invasion and metastasis that must be unravelled to gain an appropriate understanding of the behaviour of cancer cells. A broad spectrum of motility mechanisms that facilitate invasion of extramammary tissues and metastasis exists in breast cancer cells (e.g. reorganization of the actin cytoskeleton, regulation of focal adhesion, changes in response to a different microenvironment, epithelial mesenchymal transition, and control of membrane proteins through endocytosis). These cellular responses are tightly regulated by intracellular signalling pathways evoked by humoral factors that include growth factors, chemokines, and cytokines. Learning more about the cellular and molecular basis of these different motility programmes will aid in the development of treatments for breast cancer invasion and metastasis. This review of recent literature focuses on aspects of cell biology related to motility and metastasis, and suggests some directions for future breast cancer research.

Caveolin-1 expression in human breast lobular cancer progression

Caveolin-1 is the principal structural protein of caveolae, and caveolin-1 gene plays a role as a tumour suppressor gene in human mammary cancer-derived cells. However, limited data are available concerning caveolin-1 expression in human breast cancer tissue. We evaluated caveolin-1 expression in normal lobular epithelial cells and in the whole human lobular neoplasia spectrum disease, with the aim to examine differences of caveolin-1 expression in human lobular neoplasia progression. We selected 147 cases of pure lobular lesions, ie lobular intraepithelial neoplasia and invasive lobular carcinoma, from 112 patients. Presence of caveolin-1 was evaluated by immunohistochemistry. Among 81 lobular intraepithelial neoplasia lesions studied, 43% were associated with invasive lobular carcinoma, with positive correlation between lobular intraepithelial neoplasia grade and presence of invasive component (P=0.01). In total, 64% of lobular lesions were positive for caveolin-1 (81% lobular intraepithelial neoplasia and 42% invasive lobular carcinoma), and a significant difference in terms of caveolin-1 expression was present between lobular intraepithelial neoplasia and invasive lobular carcinoma (P=0.0001). Variations in caveolin-1 expression were evident among the different lobular intraepithelial neoplasia grades (91% grade 1, 68% grade 2, 35% grade 3); the difference was significant comparing lobular intraepithelial neoplasia grade 3 vs 1 (P=0.0001) and grade 3 vs 2 (P=0.007) but not grade 1 vs 2. Furthermore, significant differences were found between lobular intraepithelial neoplasia grades 1 and 2 vs invasive lobular carcinoma (P=0.0001), but not between lobular intraepithelial neoplasia grade 3 and invasive lobular carcinoma (P=0.196). In conclusion, variations of caveolin-1 expression may have an important role in the progression of human breast lobular cancer; in addition, they confirm the powerful clinical impact of the lobular intraepithelial neoplasia classification for lobular intraepithelial neoplasia, supporting the direct origin of invasive lobular carcinoma from clonal expansion of the lobular intraepithelial neoplasia lesions cells.

Caveolin proteins and estrogen signaling in the brain

Best described outside the nervous system, caveolins are structural proteins that form caveolae, functional microdomains at the plasma membrane that cluster related signaling molecules. Caveolin-associated proteins include G protein-coupled receptors and G proteins, receptor tyrosine kinases, as well as protein kinases, ion channels and various other signaling enzymes. Not surprisingly, a wide array of biological disorders are thought to be rooted in caveolin dysfunction. In addition, caveolins traffic and cluster estrogen receptors to caveolae. Interactions between the estrogen receptors ERalpha and ERbeta with caveolins appear critical in many non-neuronal cell types, e.g., disruption of normal function may underlie many forms of breast cancer. Recent findings suggest caveolins may also play an essential role in membrane estrogen receptor function in the nervous system. Not only are they expressed in neurons and glia, but different caveolin isoforms also appear necessary to generate distinct functional signaling complexes. With membrane estrogen receptors responsible for the efficient activation of a multitude of intracellular signaling pathways, which in turn influence a wide variety of nervous system functions, caveolin proteins are poised to act as the central coordinators of these processes.

Caveolin-3 regulates myostatin signaling. Mini-review

Caveolins, components of the uncoated invaginations of plasma membrane, regulate signal transduction and vesicular trafflicking. Loss of caveolin-3, resulting from dominant negative mutations of caveolin-3 causes autosomal dominant limb-girdle muscular dystrophy (LGMD) 1C and autosomal dominant rippling muscle disease (AD-RMD). Myostatin, a member of the muscle-specific transforming growth factor (TGF)-beta superfamily, negatively regulates skeletal muscle volume. Herein we review caveolin-3 suppressing of activation of type I myostatin receptor, thereby inhibiting subsequent intracellular signaling. In addition, a mouse model of LGMD1C has shown atrophic myopathy with enhanced myostatin signaling. Myostatin inhibition ameliorates muscular phenotype in the model mouse, accompanied by normalized myostatin signaling. Enhanced myostatin signaling by caveolin-3 mutation in human may contribute to the pathogenesis of LGMD1C. Therefore, myostatin inhibition therapy may be a promising treatment for patients with LGMD1C. More recent studies concerning regulation of TGF-beta superfamily signaling by caveolins have provided new insights into the pathogenesis of several human diseases.

Signal transducer and activator of transcription 5A/B in prostate and breast cancers

Protein kinase signaling pathways, such as Janus kinase 2-Signal transducer and activator of transcription 5A/B (JAK2-STAT5A/B), are of significant interest in the search for new therapeutic strategies in both breast and prostate cancers. In prostate cancer, the components of the JAK2-STAT5A/B signaling pathway provide molecular targets for small-molecule inhibition of survival and growth signals of the cells. At the same time, new evidence suggests that the STAT5A/B signaling pathway is involved in the transition of organ-confined prostate cancer to hormone-refractory disease. This implies that the active JAK2-STAT5A/B signaling pathway potentially provides the means for pharmacological intervention of clinical prostate cancer progression. In addition, active STAT5A/B may serve as a prognostic marker for identification of those primary prostate cancers that are likely to progress to aggressive disease. In breast cancer, the role of STAT5A/B is more complex. STAT5A/B may have a dual role in the regulation of malignant mammary epithelium. Data accumulated from mouse models of breast cancer suggest that in early stages of breast cancer STAT5A/B may promote malignant transformation and enhance growth of the tumor. This is in contrast to established breast cancer, where STAT5A/B may mediate the critical cues for maintaining the differentiation of mammary epithelium. In addition, present data suggest that activation of STAT5A/B in breast cancer predicts favorable clinical outcome. The dual nature of STAT5A/B action in breast cancer makes the therapeutic use of STAT5 A/B more complex.

Caveats of caveolin-1 in cancer progression

Caveolin-1, an essential scaffold protein of caveolae and cellular transport processes, lately gained recognition as a stage- and tissue-specific tumor modulator in vivo. Patient studies and rodent models corroborated its janus-faced role as a tumor suppressor in non-neoplastic tissue, its down-regulation (loss of function) upon transformation and its re-expression (regain of function) in advanced-stage metastatic and multidrug resistant tumors. This review is focussed on the role of caveolin-1 in metastasis and angiogenesis and its clinical implications as a prognostic marker in cancer progression.

Do the cholesterol-lowering properties of statins affect cancer risk?

The potential of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors ('statins') to reduce the incidence and/or progression of certain malignancies remains uncertain. Some investigators have concluded that statins have no effects on malignancies of any kind. However, results of several epidemiologic studies, including four recent prospective cohort studies, suggest that long-term statin therapy inhibits the progression of prostate cancer. We argue that the principal mechanism of any anticancer effects from statin use arises from prolonged lowering of circulating cholesterol. Evidence suggests that prostate cancer might be particularly sensitive to this intervention. Our hypothesis provides a perspective from which mechanistic studies of cholesterol-lowering drugs and cancer, in addition to prospective trials in patients, might be designed.

1,1-Bis(3'-indolyl)-1-(p-biphenyl)methane inhibits basal-like breast cancer growth in athymic nude mice

Introduction

1,1-Bis (3'-indolyl)-1-(p-biphenyl) methane (CDIM9) has been identified as a new peroxisome proliferator-activated receptor (PPAR)-γ agonist that exhibits both receptor dependent and independent antitumor activities. CDIM9 has not previously been studied with respect to its effects against basal-like breast cancer. Our goal in the present study was to investigate the anti-basal-like breast tumor activity of CDIM9 in vitro and in vivo.

Methods

The effects of CDIM9 on cell protein and DNA syntheses were determined in basal-like breast cancer MDA-MB231 and BT549 cells in vitro. Maximum tolerated dose and dose-limited toxicity were determined in BalB/c mice, and antitumor growth activities were assessed in MDA-MB231 basal-like breast tumor xenografts in athymic nude mice.

Results

CDIM9 exhibited selective cell cytotoxicity and anti-proliferation effects on basal-like breast cancer lines. In MDA-MB231 cell, CDIM9 induced caveolin-1 and p27 expression, which was significantly downregulated by co-treatment with the PPAR-γ antagonist GW9662. Nonsteroidal anti-inflammatory drug-activated gene-1 and activating transcription factor-3 were upregulated by CDIM9 through a PPAR-γ independent pathway. CDIM9 (40 mg/kg daily, intraperitoneally, for 35 days) inhibited the growth of subcutaneous MDA-MB231 tumor xenografts by 87%, and produced a corresponding decrease in proliferation index. Nearly half of the treated mice (46%) had complete durable remissions, confirmed by histology. The growth of an established tumor was inhibited by CDIM9 treatment (64 mg/kg daily, intraperitoneally, for 10 days), with a mean tumor growth inhibition of 67% as compared with controls. CDIM9 induced increases in tumor caveolin-1 and p27 in vivo, which may contribute to its antitumor activity in basal-like breast cancer.

Conclusion

CDIM9 showed potent antiproliferative effects on basal-like breast cancer cell in tissue culture and dramatic growth inhibition in animal models at safe doses. These findings justify further development of this drug for treatment of basal-like breast cancer.

Jak2/Stat5 signaling in mammogenesis, breast cancer initiation and progression

During normal mammary gland development, the tyrosine kinase Jak2 and its main substrate, the signal transducer and activator of transcription-5 (Stat5), are critical for the growth and differentiation of alveolar progenitors as well as the survival of secretory mammary epithelial cells. Genetic studies in mouse models support a role for the Stat5 transcription factor as a proto-oncogene in mammary tumor initiation. On the other hand, the analysis of nuclear Stat5 in human breast malignancies suggests a role of the Jak2/Stat5 pathway in the restriction of the metastatic potential of neoplastic mammary epithelial cells. Following an overview on the function of the Jak2/Stat5 pathway during normal mammary gland development, this review discusses recently published observations on human breast cancers as well as experimental evidence from genetically engineered mice that propose a dual role of Jak2/Stat5 signaling in breast cancer initiation and progression. Future studies to further test the concept of contrasting effects of Jak2/Stat5 pathway on breast cancer initiation and metastatic progression are proposed.

Smad Signaling in the Rat Model of Monocrotaline Pulmonary Hypertension

Mutations in the bone morphogenetic protein receptor type II (BMPrII) gene have been implicated in the development of familial pulmonary artery hypertension (PAH). The function of BMP signal transduction within the pulmonary vasculature and the role BMPrII mutations have in the development of PAH are incompletely understood. We used the monocrotaline (MCT) model of PAH to examine alterations in Smad signal transduction pathways in vivo. Lungs harvested from Sprague-Dawley rats treated with a single 60-mg/kg intraperitoneal (IP) injection of MCT were compared to saline-treated controls 2 weeks following treatment. Smad 4 was localized by immunohistochemistry to endothelial nuclei of the intra-acinar vessels undergoing remodeling. Smad 4, common to both BMP and transforming growth factor β (TGFβ) signaling, and BMP-specific Smad 1 were significantly decreased in western blot from whole lungs of treated animals, while no change was found for TGFβ-specific Smad 2. MCT-treated rats also had increased expression of phosphorylated Smad 1 (P-Smad 1) but not phosphorylated Smad 2 (P-Smad 2). There was a decrease in the expression of the full BMPrII protein but not its short form variant in MCT-treated rat lungs. The type I receptor Alk1 had increased expression. Collectively, our data indicate that vascular remodeling in the MCT model is associated with alterations in BMP receptors and persistent endothelial Smad 1 signaling.

Regulation of Cripto-1 signaling and biological activity by caveolin-1 in mammary epithelial cells

Human and mouse Cripto-1 (CR-1/Cr-1) proteins play an important role in mammary gland development and tumorigenesis. In this study, we examined the relationship between Cripto-1 and caveolin-1 (Cav-1), a membrane protein that acts as a tumor suppressor in the mammary gland. Cripto-1 was found to interact with Cav-1 in COS7 cells and mammary epithelial cells. Using EpH4 mouse mammary epithelial cells expressing Cr-1 (EpH4 Cr-1) or Cr-1 and Cav-1 (EpH4 Cr-1/Cav-1), we demonstrate that Cav-1 expression markedly reduced the ability of Cr-1 to enhance migration, invasion, and formation of branching structures in EpH4 Cr-1/Cav-1 cells as compared to EpH4 Cr-1 cells. Furthermore, coexpression of Cav-1 together with Cr-1 in EpH4 Cr-1/Cav-1 cells inhibited Cr-1-mediated activation of c-src and mitogen-activated protein kinase signaling pathways. Conversely, primary mammary epithelial cells isolated from Cav-1 null(-/-)/mouse mammary tumor virus-CR-1 transgenic animals showed enhanced motility and activation of mitogen-activated protein kinase and c-src as compared to Cav-1(+/-)/CR-1 mammary cells. Finally, mammary tumors derived from mouse mammary tumor virus-CR-1 mice showed a dramatic reduction of Cav-1 expression as compared to mammary tissue from normal FVB/N mice, suggesting that in vivo Cav-1 is down-regulated during the process of CR-1-mediated mammary tumorigenesis.

MUC1 oncoprotein activates the IkappaB kinase beta complex and constitutive NF-kappaB signalling

Nuclear factor-kappaB (NF-kappaB) is constitutively activated in diverse human malignancies by mechanisms that are not understood. The MUC1 oncoprotein is aberrantly overexpressed by most human carcinomas and, similarly to NF-kappaB, blocks apoptosis and induces transformation. This study demonstrates that overexpression of MUC1 in human carcinoma cells is associated with constitutive activation of NF-kappaB p65. We show that MUC1 interacts with the high-molecular-weight IkappaB kinase (IKK) complex in vivo and that the MUC1 cytoplasmic domain binds directly to IKKbeta and IKKgamma. Interaction of MUC1 with both IKKbeta and IKKgamma is necessary for IKKbeta activation, resulting in phosphorylation and degradation of IkappaBalpha. Studies in non-malignant epithelial cells show that MUC1 is recruited to the TNF-R1 complex and interacts with IKKbeta-IKKgamma in response to TNFalpha stimulation. TNFalpha-induced recruitment of MUC1 is dependent on TRADD and TRAF2, but not the death-domain kinase RIP1. In addition, MUC1-mediated activation of IKKbeta is dependent on TAK1 and TAB2. These findings indicate that MUC1 is important for physiological activation of IKKbeta and that overexpression of MUC1, as found in human cancers, confers sustained induction of the IKKbeta-NF-kappaB p65 pathway.

E-cadherin is required for caveolin-1-mediated down-regulation of the inhibitor of apoptosis protein survivin via reduced beta-catenin-Tcf/Lef-dependent transcription

Caveolin-1 reportedly acts as a tumor suppressor and promotes events associated with tumor progression, including metastasis. The molecular mechanisms underlying such radical differences in function are not understood. Recently, we showed that caveolin-1 inhibits expression of the inhibitor of apoptosis protein survivin via a transcriptional mechanism involving the beta-catenin-Tcf/Lef pathway. Surprisingly, while caveolin-1 expression decreased survivin mRNA and protein levels in HT29(ATCC) human colon cancer cells, this was not the case in metastatic HT29(US) cells. Survivin down-regulation was paralleled by coimmunoprecipitation and colocalization of caveolin-1 with beta-catenin in HT29(ATCC) but not HT29(US) cells. Unlike HT29(ATCC) cells, HT29(US) cells expressed small amounts of E-cadherin that accumulated in intracellular patches rather than at the cell surface. Re-expression of E-cadherin in HT29(US) cells restored the ability of caveolin-1 to down-regulate beta-catenin-Tcf/Lef-dependent transcription and survivin expression, as seen in HT29(ATCC) cells. In addition, coimmunoprecipitation and colocalization between caveolin-1 and beta-catenin increased upon E-cadherin expression in HT29(US) cells. In human embryonic kidney HEK293T and HT29(US) cells, caveolin-1 and E-cadherin cooperated in suppressing beta-catenin-Tcf/Lef-dependent transcription as well as survivin expression. Finally, mouse melanoma B16-F10 cells, another metastatic cell model with low endogenous caveolin-1 and E-cadherin levels, were characterized. In these cells, caveolin-1-mediated down-regulation of survivin in the presence of E-cadherin coincided with increased apoptosis. Thus, the absence of E-cadherin severely compromises the ability of caveolin-1 to develop activities potentially relevant to its role as a tumor suppressor.