Loss Of Cav-1 Expression Research Articles

Caveolin-1 in tumor microenvironment: A review

Caveolins are a member of membrane-bound scaffolding proteins which could negatively regulate and compartmentalize signaling in caveloae. Loss of caveolin-1 (Cav-1) expression occurs in the pathogenesis of tumors, and loss of Cav-1 expression in cancer associated fibroblasts contributes to the activation of tumor microenvironment, thus advancing early recurrence and metastasis in prostate and breast cancer. Recent studies have indicated loss of stromal Cav-1 expression is a predictor of clinical outcome in cancers. Finally, we discuss the mechanism of loss of stromal Cav-1 facilitating the cancer progression, including extracellular matrix remodeling, fibrosis and origin of cancer associated fibroblasts. Key words: Caveolin-1; Tumor microenvironment; Cancer associated fibroblast

Caveolae-Mediated Endocytosis Is Critical for Albumin Cellular Uptake and Response to Albumin-Bound Chemotherapy.

Nab-paclitaxel, a nanoparticle conjugate of paclitaxel to human albumin, exhibits efficacy in pancreatic cancer, non-small cell lung cancer and breast cancer. However, there is a lack of predictive biomarkers to identify patients who might benefit most from its administration. This study addresses this gap in knowledge by identifying that caveolin-1 (Cav-1) is a candidate mechanism-based biomarker. Caveolae are small membrane invaginations important for transendothelial albumin uptake. Cav-1, the principal structural component of caveolae, is overexpressed in the cancers noted above that respond to nab-paclitaxel. Thus, we hypothesized that Cav-1 may be critical for albumin uptake in tumors and perhaps determine their response to this drug. Cav-1 protein levels correlated positively with nab-paclitaxel sensitivity. RNAi-mediated attenuation of Cav-1 expression reduced uptake of albumin and nab-paclitaxel in cancer cells and rendered them resistant to nab-paclitaxel-induced apoptosis. Conversely, Cav-1 overexpression enhanced sensitivity to nab-paclitaxel. Selection for cellular resistance to nab-paclitaxel in cell culture correlated with a loss of Cav-1 expression. In mouse xenograft models, cancer cells, where Cav-1 was attenuated, exhibited resistance to the antitumor effects of nab-paclitaxel therapy. Overall, our findings suggest Cav-1 as a predictive biomarker for the response to nab-paclitaxel and other albumin-based cancer therapeutic drugs. Cancer Res; 77(21); 5925-37. ©2017 AACR.

Abstract B8: Caveolae-mediated endocytosis is critical for tumor cell response to nab-paclitaxel

Abstract INTRODUCTION: Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States and is typified by poor outcomes. Gemcitabine with nab-paclitaxel is a standard chemotherapy combination which recently demonstrated superiority compared to gemcitabine alone in a randomized trial. However, a predictive biomarker to select patients who may benefit from nab-paclitaxel is currently lacking. Nab-paclitaxel is a nanoparticle composed of paclitaxel bound to human albumin. Caveolin-1 (Cav-1) is a 22kD structural component of caveolae, 50-100 nM invaginations of the cell membrane. Cav-1 has been demonstrated to be an important component of albumin uptake in endothelial cells, and Cav-1 is overexpressed in pancreatic cancer. We hypothesize that Cav-1 expression may predict response to nab-paclitaxel therapy. METHODS: We compared Cav-1 expression to nab-paclitaxel sensitivity in a panel of pancreatic and non-small cell lung cancer cell lines. We stably knocked down Cav-1 expression in H23 and MIA-PaCa2 cells and performed cytotoxicity assays. In addition, we measured albumin and nab-paclitaxel uptake into tumor cells with immunoblotting, immunofluorescence and mass spectrometry. Sensitivity to the therapy was confirmed by quantifying apoptosis via flow cytometry and immunoblotting for activation of apoptotic pathway intermediates. Nab-paclitaxel resistant cell lines were created by selecting resistant cells over a period of time. Results were confirmed in vivo in a nude mouse model. RESULTS: Cav-1 expression in a panel of pancreatic cancer and non-small cell lung cancer (NSCLC) cell lines negatively correlated with their corresponding IC50 values for nab-paclitaxel, indicating a positive correlation with sensitivity to nab-paclitaxel. Cav-1 depletion resulted in reduced albumin uptake in tumor cells, reduced intracellular paclitaxel, and protection from nab-paclitaxel both in vitro and in vivo, while overexpression of Cav-1 enhanced sensitivity to nab-paclitaxel. Creation of nab-paclitaxel resistant cell lines demonstrated loss of Cav-1 expression in resistant cells. In support of our preclinical data, higher Cav-1 expression in the tumor microenvironment in patients with metastatic cancer treated with nab-paclitaxel also correlates with improved response and longer survival. CONCLUSIONS: Our data indicate that Cav-1 expression mediates entry of albumin and nab-paclitaxel, subsequent response to nab-paclitaxel, and that downregulation or re-expression of Cav-1 impairs or facilitates nab-paclitaxel uptake and response, respectively. This data supports further testing of Cav-1 as a potential predictive biomarker of response to nab-paclitaxel. Citation Format: Moumita Chatterjee, Marall Vedaie, Ryan Robb, Star Seum, Adriana Estrada-Bernal, Thirumoorthy Krishnan, Palanichamy Kamalakanan, Chen Lin, Arnab Chakravarti, Terence M. Williams. Caveolae-mediated endocytosis is critical for tumor cell response to nab-paclitaxel. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B8.

Caveolin-1 is a negative regulator of NADPH oxidase-derived reactive oxygen species

Changes in the expression and function of caveolin-1 (Cav-1) have been proposed as a pathogenic mechanism underlying many cardiovascular diseases. Cav-1 binds to and regulates the activity of numerous signaling proteins via interactions with its scaffolding domain. In endothelial cells, Cav-1 has been shown to reduce reactive oxygen species (ROS) production, but whether Cav-1 regulates the activity of NADPH oxidases (Noxes), a major source of cellular ROS, has not yet been shown. Herein, we show that Cav-1 is primarily expressed in the endothelium and adventitia of pulmonary arteries (PAs) and that Cav-1 expression is reduced in isolated PAs from multiple models of pulmonary artery hypertension (PH). Reduced Cav-1 expression correlates with increased ROS production in the adventitia of hypertensive PA. In vitro experiments revealed a significant ability of Cav-1 and its scaffolding domain to inhibit Nox1–5 activity and it was also found that Cav-1 binds to Nox5 and Nox2 but not Nox4. In addition to posttranslational actions, in primary cells, Cav-1 represses the mRNA and protein expression of Nox2 and Nox4 through inhibition of the NF-κB pathway. Last, in a mouse hypoxia model, the genetic ablation of Cav-1 increased the expression of Nox2 and Nox4 and exacerbated PH. Together, these results suggest that Cav-1 is a negative regulator of Nox function via two distinct mechanisms, acutely through direct binding and chronically through alteration of expression levels. Accordingly, the loss of Cav-1 expression in cardiovascular diseases such as PH may account for the increased Nox activity and greater production of ROS.

Hereditary ovarian cancer and two-compartment tumor metabolism

Mutations in the BRCA1 tumor suppressor gene are commonly found in hereditary ovarian cancers. Here, we used a co-culture approach to study the metabolic effects of BRCA1-null ovarian cancer cells on adjacent tumor-associated stromal fibroblasts. Our results directly show that BRCA1-null ovarian cancer cells produce large amounts of hydrogen peroxide, which can be abolished either by administration of simple antioxidants (N-acetyl-cysteine; NAC) or by replacement of the BRCA1 gene. Thus, the BRCA1 gene normally suppresses tumor growth by functioning as an antioxidant. Importantly, hydrogen peroxide produced by BRCA1-null ovarian cancer cells induces oxidative stress and catabolic processes in adjacent stromal fibroblasts, such as autophagy, mitophagy and glycolysis, via stromal NFκB activation. Catabolism in stromal fibroblasts was also accompanied by the upregulation of MCT4 and a loss of Cav-1 expression, which are established markers of a lethal tumor microenvironment. In summary, loss of the BRCA1 tumor suppressor gene induces hydrogen peroxide production, which then leads to metabolic reprogramming of the tumor stroma, driving stromal-epithelial metabolic coupling. Our results suggest that new cancer prevention trials with antioxidants are clearly warranted in patients that harbor hereditary/familial BRCA1 mutations.

Clinical and functional significance of loss of caveolin‐1 expression in breast cancer‐associated fibroblasts

Loss of caveolin-1 (Cav-1) expression in breast cancer-associated fibroblasts (CAFs) is predictive of poor prognosis in breast cancer, but its function has not been established. Our study tested the hypotheses that loss of Cav-1 expression in breast fibroblasts was associated with poor prognosis in breast cancer, through promotion of breast cancer cell invasion. Cav-1 stromal expression was immunohistochemically assessed in 358 breast cancers. Cav-1 expression in primary breast fibroblasts was analysed by western blot. Modified Boyden chamber assays determined fibroblast ability to promote invasion of breast cancer cells. The impact of siRNA silencing of Cav-1 in fibroblasts was evaluated using invasion assays and 3D co-culture assays. Loss of Cav-1 expression in breast stroma was significantly associated with decreased breast cancer-specific and disease-free survival (p = 0.01). Mean survival was 72 months (Cav-1(+) group) versus 29.5 months (Cav-1(-) group). This was confirmed in multivariate analysis. Cav-1 expression was significantly decreased in CAFs compared to normal fibroblasts (p = 0.01) and was associated with increased invasion-promoting capacity. Cav-1 siRNA-treated fibroblasts promoted significantly increased invasion of MDA-MB-468 and T47D breast cancer cells from 27% (control) to 67% (p = 0.006) and from 37% to 56%, respectively (p = 0.01). 3D co-cultures of MDA-MB-468 cells with myoepithelial cells led to the formation of organized cohesive structures when cultured with conditioned media from fibroblasts but resulted in a disorganized appearance in the presence of conditioned media from Cav-1 siRNA-treated fibroblasts, accompanied by loss of E-cadherin expression in tumour cells. Our data confirm that loss of stromal Cav-1 in breast cancer predicts poor outcome. At a functional level, Cav-1-deficient CAFs are capable of significantly increasing the invasive capacity of breast cancer cells.

Abstract 5013: CpG island shore methylation regulates caveolin-1 expression in breast cancer

Abstract Caveolin-1 (Cav1), a multifunctional membrane protein, regulates caveolae-dependent lipid trafficking, vesicular transport and signal transduction. Cav1 expression is decreased in breast carcinomas compared to normal tissue, and loss of Cav1 expression promotes mammary tumorigenesis. However, recent reports indicate that Cav1 is overexpressed in a subset of basal-like breast carcinomas and consider it as a basal marker. To investigate the mechanism that results in differential Cav1 expression in breast cancer, we performed genome-wide profiling of DNA methylation using affinity purification and subsequent next-generation sequencing of eluted DNA (MethylCap-seq) on 30 breast cancer cell lines. In breast cancer cell lines displaying low Cav1 expression (“Cav1-low;” n=15, mostly luminal subtype), Cav1 promoter CpG island (CGI) hypermethylation was observed in only four cell lines. In the remaining Cav1-low lines, dense methylation at “CGI shores” (methylation at regions outside of CGI) was seen, while Cav1 promoter CGI methylation was strikingly low or absent. In “Cav1-high” cell lines (n=15 of basal-like subtype), hypomethylation of both promoter CGI and CGI shores was observed. By integrating the methylome data with Cav1 mRNA expression profiles, we found a significant negative correlation between Cav1 CGI shore methylation and Cav1 gene expression. A similar DNA methylation pattern was observed in a panel of antiestrogen-sensitive and -resistant cell lines previously generated by our lab, with hypermethylation at CGI shores for a Cav1-low, tamoxifen-resistant line, and CGI shore hypomethylation in Cav1-high, fulvestrant-resistant lines (basal-like). Treatment of Cav1-low cells with the DNA methyltransferase inhibitor 5-aza-deoxycytidine resulted in demethylation of CGI shores and Cav1 re-expression, further confirming the regulation of Cav1 expression by CGI shore methylation. ChIP-seq results of Cav1-low cells indicated that the Cav1 CGI hypomethylation was due to H3K4me2 occupancy. SiRNA-mediated Cav1 knockdown resulted in a significant inhibition of cell growth and invasion, indicating an important role of Cav1 in supporting breast cancer cell progression. Furthermore, by using an on-line survival analysis tool (Kaplan Meier Plotter), we determined a significant negative correlation between Cav1 levels and overall survival for patients with ERα-negative breast tumors. The results of this study demonstrate that DNA methylation at Cav1 CGI shores is associated with tumor progression, displaying hypomethylation in normal breast epithelial cells, hypermethylation in luminal breast cancer cells, and hypomethylation in basal-like breast cancer cells. In addition, Cav1 CGI shore methylation may represent a novel prognostic factor for ERα-negative, fulvestrant-resistant breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5013. doi:1538-7445.AM2012-5013

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.

Abstract C22: Next-generation sequencing reveals CpG island shore methylation regulates caveolin-1 expression in breast cancer

Abstract Caveolin-1 (Cav1), a multifunctional membrane protein associated with cell surface caveolae, regulates caveolae-dependent lipid trafficking, vesicular transport and signal transduction. While reported to function as a tumor suppressor at early stages of cancer progression, a growing body of evidence indicates that Cav1 also performs a tumor-promoting role in various cancer types. Cav1 expression level is decreased in breast carcinomas compared to normal tissue, and loss of Cav1 expression promotes mammary tumorigenesis and is associated with the development of tamoxifen resistance. However, gene expression profiling of breast cancer cell lines revealed an inverse relationship between expression of Cav1 and estrogen receptor-alpha (ERα), and Cav1 overexpression was observed in a subset of basal-like breast carcinomas. To investigate the mechanism regulating Cav1 expression, we performed genome-wide profiling of DNA methylation using affinity purification and subsequent next-generation sequencing of eluted DNA (MethylCap-seq) on 30 breast cancer cell lines. In breast cancer cell lines displaying low Cav1 expression (“Cav1-low;” n=15 of primarily luminal subtype), Cav1 promoter CpG island (CGI) hypermethylation was observed in only four cell lines. In the remaining Cav1-low lines, dense methylation at “CGI shores” (methylation at regions outside of CGI) was seen, and Cav1 promoter CGI methylation was strikingly low or absent. In “Cav1-high” cell lines (n=15 of basal-like subtype), hypomethylation of both promoter CGI and CGI shores was observed. By integrating the methylome data with Cav1 mRNA expression profiles, we found a significant negative correlation between Cav1 CGI shore methylation and Cav1 gene expression. Treatment of Cav1-low cells with the DNA methyltransferase inhibitor 5-aza-deoxycytidine resulted in demethylation of CGI shores and Cav1 re-expression, further confirming the regulation of Cav1 expression by CGI shore methylation. MethylCap-seq results were validated by pyrosequencing, and we observed a similar phenomenon in a panel of antiestrogen-sensitive and -resistant cell lines previously generated by our lab, with hypermethylation at CGI shores for a Cav1-low, tamoxifen-resistant line, and CGI shore hypomethylation in Cav1-high, fulvestrant-resistant lines (basal-like). SiRNA-mediated Cav1 knockdown resulted in a significant cell growth inhibition, indicating an important role of Cav1 in supporting breast cancer cell proliferation. Furthermore, by using an on-line survival analysis tool (Kaplan Meier Plotter), we determined a significant positive correlation between Cav1 levels and poor overall survival for patients with ERα-negative breast tumors. The results of this study demonstrate that DNA methylation at Cav1 CGI shores is associated with tumor progression, displaying hypomethylation in normal breast epithelial cells, hypermethylation in luminal breast cancer cells, and hypomethylation in basal-like breast cancer cells. In addition, Cav1 CGI shore methylation may represent a novel prognostic factor for ERα-negative, fulvestrant-resistant breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C22.

Abstract 1510: Transcriptional profiling of a lethal breast cancer tumor microenvironment

Abstract Breast cancer growth and progression are governed by complex and reciprocal interactions between tumor cells and surrounding stromal elements. We have previously shown that a loss of stromal Cav-1 expression is associated with an increased risk of early tumor recurrence, metastasis and decreased overall survival. To identify and characterize the signaling pathways activated in Cav-1 negative tumor stroma, we performed gene expression profiling using laser micro-dissected breast cancer associated stroma. Methods: Tumor stroma was laser capture micro-dissected using a Leica LCM system from 4 cases showing high stromal Cav-1 expression and 7 cases with loss of stromal Cav-1. Total RNA was amplified using the NuGEN™ WT-Ovation™ FFPE RNA Amplification System V2 and cDNA was hybridized to Affymetrix GeneChip® arrays. One-way ANOVA was setup to extract differentially expressed genes between Cav-1 positive and negative stromal samples. Results: We identified 238 genes that were up-regulated and 232 genes that were down-regulated in the stroma of tumors showing a loss of Cav-1 expression (p-value < = 0.01 and fold change > = 1.5) Gene set enrichment analysis revealed “stemness”, inflammation, DNA damage, oxidative stress, hypoxia, autophagy, and mitochondrial dysfunction in the tumor stroma of patients lacking stromal Cav-1. Conclusions: Our findings are consistent with the recently proposed “Autophagic Tumor Stroma Model of Cancer Metabolism”. In this model, cancer cells induce oxidative stress in adjacent stromal cells, which then forces these stromal cells to undergo autophagy. This, in turn, produces recycled nutrients to feed “hungry” cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1510. doi:10.1158/1538-7445.AM2011-1510

Transcriptional evidence for the "Reverse Warburg Effect" in human breast cancer tumor stroma and metastasis: Similarities with oxidative stress, inflammation, Alzheimer's disease, and "Neuron-Glia Metabolic Coupling"

Caveolin-1 (-/-) null stromal cells are a novel genetic model for cancer-associated fibroblasts and myofibroblasts. Here, we used an unbiased informatics analysis of transcriptional gene profiling to show that Cav-1 (-/-) bone-marrow derived stromal cells bear a striking resemblance to the activated tumor stroma of human breast cancers. More specifically, the transcriptional profiles of Cav-1 (-/-) stromal cells were most closely related to the primary tumor stroma of breast cancer patients that had undergone lymph-node (LN) metastasis. This is consistent with previous morphological data demonstrating that a loss of stromal Cav-1 protein (by immuno-histochemical staining in the fibroblast compartment) is significantly associated with increased LN-metastasis. We also provide evidence that the tumor stroma of human breast cancers shows a transcriptional shift towards oxidative stress, DNA damage/repair, inflammation, hypoxia, and aerobic glycolysis, consistent with the "Reverse Warburg Effect". Finally, the tumor stroma of "metastasis-prone" breast cancer patients was most closely related to the transcriptional profiles derived from the brains of patients with Alzheimer's disease. This suggests that certain fundamental biological processes are common to both an activated tumor stroma and neuro-degenerative stress. These processes may include oxidative stress, NO over-production (peroxynitrite formation), inflammation, hypoxia, and mitochondrial dysfunction, which are thought to occur in Alzheimer?s disease pathology. Thus, a loss of Cav-1 expression in cancer-associated myofibroblasts may be a protein biomarker for oxidative stress, aerobic glycolysis, and inflammation, driving the "Reverse Warburg Effect" in the tumor micro-environment and cancer cell metastasis.

Caveolin-1-deficient aortic smooth muscle cells show cell autonomous abnormalities in proliferation, migration, and endothelin-based signal transduction

We previously showed that ablation of caveolin-1 (Cav-1) gene expression in mice promotes neointimal hyperplasia in vivo, a phenomenon normally characterized by smooth muscle cell (SMC) migration and proliferation. Whether these defects are cell autonomous, i.e., due to loss of Cav-1 within SMCs or loss of Cav-1 expression in other adjacent cell types in vivo, remains unknown. Cav-1 has been shown to associate with receptors for many vasoactive factors on the SMC surface. Therefore, Cav-1 might be an important regulator of SMC proliferation, migration, and signal transduction. To mechanistically dissect the role of Cav-1 in SMC signaling, we isolated SMCs from the aortas (AoSMCs) of Cav-1-deficient (Cav-1(-/-)) mice and characterized these cells with respect to their proliferation, migration, and Ca(2+) response to an important vasoactive factor, endothelin-1 (ET-1). 5-Bromo-2'-deoxyuridine incorporation and a wound-healing assay showed an increase in proliferation and migration rates in Cav-1(-/-) compared with wild-type (Cav-1(+/+)) AoSMCs. Cav-1(-/-) AoSMCs demonstrated upregulation of phosphorylated ERK1/2, cyclin D1, and proliferating cell nuclear antigen and reduced expression of the cyclin-dependent kinase inhibitor p27(Kip1). The Ca(2+) response was examined in the presence of ET-1 and assessed by confocal microscopy with the Ca(2+)-sensitive fluorescent probe fluo 3. When treated with ET-1, Cav-1(-/-) AoSMCs exhibited a faster and larger increase in free intracellular Ca(2+) than Cav-1(+/+) cells. The ET-1-induced response in Cav-1(-/-) cells was mediated by the ET(B) receptor, as shown using the ET(B) receptor antagonist BQ-788 and the ET(A) receptor antagonist BQ-123. In Cav-1(-/-) cells, ET(A) receptor expression was reduced and ET(B) receptor expression was upregulated. Therefore, Cav-1 ablation increased the ET-1-induced Ca(2+) response in SMCs by altering the type and expression level of the ET receptor (i.e., receptor isoform switching). These data suggest a novel regulatory role for Cav-1 in SMCs with respect to their proliferation, migration, and Ca(2+)-mediated signaling.

Caveolin-1 Deficiency (−/−) Conveys Premalignant Alterations in Mammary Epithelia, with Abnormal Lumen Formation, Growth Factor Independence, and Cell Invasiveness

During breast cancer development, the luminal space of the mammary acinar unit fills with proliferating epithelial cells that exhibit growth factor-independence, cell attachment defects, and a more invasive fibroblastic phenotype. Here, we used primary cultures of mammary epithelial cells derived from genetically engineered mice to identify caveolin-1 (Cav-1) as a critical factor for maintaining the normal architecture of the mammary acinar unit. Isolated cultures of normal mammary epithelial cells retained the capacity to generate mammary acini within extracellular matrix. However, those from Cav-1 (-/-) mice exhibited defects in three-dimensional acinar architecture, including disrupted lumen formation and epidermal growth factor-independent growth due to hyperactivation of the p42/44 mitogen-activated protein kinase cascade. In addition, Cav-1-null mammary epithelial cells deprived of exogenous extracellular matrix underwent a spontaneous epithelial-mesenchymal transition, with reorganization of the actin cytoskeleton, and E-cadherin redistribution. Mechanistically, these phenotypic changes appear to be caused by increases in matrix metalloproteinase-2/9 secretion and transforming growth factor-beta/Smad-2 hyperactivation. Finally, loss of Cav-1 potentiated the ability of growth factors (hepatocyte growth factor and basic fibroblast growth factor) to induce mammary acini branching, indicative of a more invasive fibroblastic phenotype. Thus, a Cav-1 deficiency profoundly affects mammary epithelia by modulating the activation state of important signaling cascades. Primary cultures of Cav-1-deficient mammary epithelia will provide a valuable new model to study the spatial/temporal progression of mammary cell transformation.