Loss Of Stromal Cav-1 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

The different functions and clinical significances of caveolin-1 in human adenocarcinoma and squamous cell carcinoma.

Caveolin-1 (Cav-1), a major structural protein of caveolae, is an integral membrane protein which plays an important role in the progression of carcinoma. However, whether Cav-1 acts as a tumor promoter or a tumor suppressor still remains controversial. For example, the tumor-promoting function of Cav-1 has been found in renal cancer, prostate cancer, tongue squamous cell carcinoma (SCC), lung SCC and bladder SCC. In contrast, Cav-1 also plays an inhibitory role in esophagus adenocarcinoma, lung adenocarcinoma and cutaneous SCC. The role of Cav-1 is still controversial in thyroid cancer, hepatocellular carcinoma, gastric adenocarcinoma, colon adenocarcinoma, breast cancer, pancreas cancer, oral SCC, laryngeal SCC, head and neck SCC, esophageal SCC and cervical SCC. Besides, it has been reported that the loss of stromal Cav-1 might predict poor prognosis in breast cancer, gastric cancer, pancreas cancer, prostate cancer, oral SCC and esophageal SCC. However, the accumulation of stromal Cav-1 has been found to be promoted by the progression of tongue SCC. Taken together, Cav-1 seems playing a different role in different cancer subtypes even of the same organ, as well as acting differently in the same cancer subtype of different organs. Thus, we hereby explore the functions of Cav-1 in human adenocarcinoma and SCC from the perspective of clinical significances and pathogenesis. We envision that novel targets may come with the further investigation of Cav-1 in carcinogenesis.

Abstract A76: MicroRNA mediated negative regulation of caveolin 1 as a biological mechanism driving breast cancer disparities

Abstract Although rates of breast cancer incidence are lower in African American (AA) women, the mortality rates are significantly higher compared to non-Hispanic white (WNH) women. This shocking statistic illustrates the racial disparities in breast cancer, as AA women have a poorer prognosis compared to WNH women. While this may be due in part to socioeconomic and standard of care issues, increasing evidence suggests that the racial disparity exists independent of these issues and could also be attributed to poorly understood inherent genetic and molecular characteristics within racial specific tumors. Caveolin-1 (Cav1) is a scaffolding protein with a tumor suppressor role. Loss of Cav1 in the tumor stromal compartment has emerged as a novel biomarker for predicting poor clinical outcome in all of the most common subtypes of human breast cancer, including the more lethal triple negative subtype which is significantly more common in AA women. While the loss of stromal Cav1 is becoming well established as a marker of poor outcome in breast cancer, the mechanism of this loss is still unknown. We propose that differences in microRNA mediated stromal Cav1 loss between AA and WNH women is driving the racial disparity in breast cancer. MicroRNAs (miRNAs) are short, endogenous, non-coding RNA that function as negative regulators of gene expression. miR-510 is an oncogenic miRNA that has been shown to be elevated in breast tumors. Cav1 is a predicted target of miR-510 and therefore miR-510 mediated negative regulation may be a novel mechanism of Cav1 loss in the tumor stroma. Our research shows that Cav1 is directly targeted by miR-510 by luciferase reporter assay and that overexpression of miR-510 leads to downregulation of Cav1 protein expression, specifically in the stromal compartment. Tumor epithelium and stroma co-culture assays demonstrate that epithelial derived miR-510 may be transferred to neighboring stromal cells and negatively regulate Cav1 expression in the stromal compartment. This may be racially significant as our supporting studies also show that miR-510 levels are elevated and Cav1 levels are reduced in AA breast cancer patients compared to their white counterparts. Our results suggest that the difference in miR-510 mediated regulation of stromal Cav1 is driving racial disparity in breast cancer. Citation Format: Qi Jin Guo, Brooke King, Bobbie Blake, Amanda C. LaRue, Judith D. Salley, Marvella E. Ford, Ashley Evans-Knowell, Victoria J. Findlay. MicroRNA mediated negative regulation of caveolin 1 as a biological mechanism driving breast cancer disparities. [abstract]. In: Proceedings of the Seventh AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 9-12, 2014; San Antonio, TX. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2015;24(10 Suppl):Abstract nr A76.

Loss of stromal caveolin-1 expression: a novel tumor microenvironment biomarker that can predict poor clinical outcomes for pancreatic cancer.

AimsCancer development and progression is not only associated with the tumor cell proliferation but also depends on the interaction between tumor cells and the stromal microenvironment. A new understanding of the role of the tumor microenvironment suggests that the loss of stromal caveolin-1 (Cav-1) as a key regulator may become a potential therapy target. This study aims to elucidate whether stromal Cav-1 expression in pancreatic cancer can be a strong prognosis biomarker.MethodsTissue samples from 45 pancreatic cancer patients were studied. Parenchyma and stroma were separated and purified using laser capture microdissection. Stromal Cav-1 expression was measured from pancreatic cancer, paraneoplastic, and normal tissue using immunohistochemistry. We analyzed the correlation of stromal Cav-1 expression with clinicopathologic features and prognostic indicators, such as tumor marker HER-2/neu gene.ResultsSpecimens from six patients (13.3%) showed high levels of stromal Cav-1 staining, those from eight patients (17.8%) showed a lower, intermediate level of staining, whereas those from 31 patients (68.9%) showed an absence of staining. Cav-1 expression in cancer-associated fibroblasts was lower than that in paracancer-associated and in normal fibroblasts. Stromal Cav-1 loss was associated with TNM stage (P = 0.018), lymph node metastasis (P = 0.014), distant metastasis (P = 0.027), and HER-2/neu amplification (P = 0.007). The relationships of age, sex, histological grade, and tumor size with stromal Cav-1 expression were not significant (P>0.05). A negative correlation was found between circulating tumor cells and stromal Cav-1 expression (P<0.05).ConclusionThe loss of stromal Cav-1 in pancreatic cancer was an independent prognostic indicator, thus suggesting that stromal Cav-1 may be an effective therapeutic target for patients with pancreatic cancer.

Metabolic reprogramming of cancer-associated fibroblasts by TGF-β drives tumor growth: Connecting TGF-β signaling with “Warburg-like” cancer metabolism and L-lactate production

We have previously shown that a loss of stromal Cav-1 is a biomarker of poor prognosis in breast cancers. Mechanistically, a loss of Cav-1 induces the metabolic reprogramming of stromal cells, with increased autophagy/mitophagy, mitochondrial dysfunction and aerobic glycolysis. As a consequence, Cav-1-low CAFs generate nutrients (such as L-lactate) and chemical building blocks that fuel mitochondrial metabolism and the anabolic growth of adjacent breast cancer cells. It is also known that a loss of Cav-1 is associated with hyperactive TGF-β signaling. However, it remains unknown whether hyperactivation of the TGF-β signaling pathway contributes to the metabolic reprogramming of Cav-1-low CAFs. To address these issues, we overexpressed TGF-β ligands and the TGF-β receptor I (TGFβ-RI) in stromal fibroblasts and breast cancer cells. Here, we show that the role of TGF-β in tumorigenesis is compartment-specific, and that TGF-β promotes tumorigenesis by shifting cancer-associated fibroblasts toward catabolic metabolism. Importantly, the tumor-promoting effects of TGF-β are independent of the cell type generating TGF-β. Thus, stromal-derived TGF-β activates signaling in stromal cells in an autocrine fashion, leading to fibroblast activation, as judged by increased expression of myofibroblast markers, and metabolic reprogramming, with a shift toward catabolic metabolism and oxidative stress. We also show that TGF-β-activated fibroblasts promote the mitochondrial activity of adjacent cancer cells, and in a xenograft model, enhancing the growth of breast cancer cells, independently of angiogenesis. Conversely, activation of the TGF-β pathway in cancer cells does not influence tumor growth, but cancer cell-derived-TGF-β ligands affect stromal cells in a paracrine fashion, leading to fibroblast activation and enhanced tumor growth. In conclusion, ligand-dependent or cell-autonomous activation of the TGF-β pathway in stromal cells induces their metabolic reprogramming, with increased oxidative stress, autophagy/mitophagy and glycolysis, and downregulation of Cav-1. These metabolic alterations can spread among neighboring fibroblasts and greatly sustain the growth of breast cancer cells. Our data provide novel insights into the role of the TGF-β pathway in breast tumorigenesis, and establish a clear causative link between the tumor-promoting effects of TGF-β signaling and the metabolic reprogramming of the tumor microenvironment.

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.

Using the “reverse Warburg effect” to identify high-risk breast cancer patients

We have recently proposed a new model of cancer metabolism to explain the role of aerobic glycolysis and L-lactate production in fueling tumor growth and metastasis. In this model, cancer cells secrete hydrogen peroxide (H2O2), initiating oxidative stress and aerobic glycolysis in the tumor stroma. This, in turn, drives L-lactate secretion from cancer-associated fibroblasts. Secreted L-lactate then fuels oxidative mitochondrial metabolism (OXPHOS) in epithelial cancer cells, by acting as a paracrine onco-metabolite. We have previously termed this type of two-compartment tumor metabolism the “Reverse Warburg Effect,” as aerobic glycolysis takes place in stromal fibroblasts, rather than epithelial cancer cells. Here, we used MCT4 immuno-staining of human breast cancer tissue microarrays (TMAs; > 180 triple-negative patients) to directly assess the prognostic value of the “Reverse Warburg Effect.” MCT4 expression is a functional marker of hypoxia, oxidative stress, aerobic glycolysis, and L-lactate efflux. Remarkably, high stromal MCT4 levels (score = 2) were specifically associated with decreased overall survival (< 18% survival at 10 y post-diagnosis). In contrast, patients with absent stromal MCT4 expression (score = 0), had 10-y survival rates of ~97% (p-value < 10−32). High stromal levels of MCT4 were strictly correlated with a loss of stromal Cav-1 (p-value < 10−14), a known marker of early tumor recurrence and metastasis. In fact, the combined use of stromal Cav-1 and stromal MCT4 allowed us to more precisely identify high-risk triple-negative breast cancer patients, consistent with the goal of individualized risk-assessment and personalized cancer treatment. However, epithelial MCT4 staining had no prognostic value, indicating that the “conventional” Warburg effect does not predict clinical outcome. Thus, the “Reverse Warburg Effect” or “parasitic” energy-transfer is a key determinant of poor overall patient survival. As MCT4 is a druggable-target, MCT4 inhibitors should be developed for the treatment of aggressive breast cancers, and possibly other types of human cancers. Similarly, we discuss how stromal MCT4 could be used as a biomarker for identifying high-risk cancer patients that could likely benefit from treatment with FDA-approved drugs or existing MCT-inhibitors (such as, AR-C155858, AR-C117977, and AZD-3965).

Cytokine production and inflammation drive autophagy in the tumor microenvironment

Recently, we proposed a new paradigm for understanding the role of the tumor microenvironment in breast cancer onset and progression. In this model, cancer cells induce oxidative stress in adjacent fibroblasts. This, in turn, results in the onset of stromal autophagy, which produces recycled nutrients to “feed” anabolic cancer cells. However, it remains unknown how autophagy in the tumor microenvironment relates to inflammation, another key driver of tumorigenesis. To address this issue, here we employed a well-characterized co-culture system in which cancer cells induce autophagy in adjacent fibroblasts via oxidative stress and NFκB-activation. We show, using this co-culture system, that the same experimental conditions that result in an autophagic microenvironment, also drive in the production of numerous inflammatory mediators (including IL-6, IL-8, IL-10, MIP1a, IFNg, RANTES (CCL5) and GMCSF). Furthermore, we demonstrate that most of these inflammatory mediators are individually sufficient to directly induce the onset of autophagy in fibroblasts. To further validate the in vivo relevance of these findings, we assessed the inflammatory status of Cav-1 (-/-) null mammary fat pads, which are a model of a bonafide autophagic microenvironment. Notably, we show that Cav-1 (-/-) mammary fat pads undergo infiltration with numerous inflammatory cell types, including lymphocytes, T-cells, macrophages and mast cells. Taken together, our results suggest that cytokine production and inflammation are key drivers of autophagy in the tumor microenvironment. These results may explain why a loss of stromal Cav-1 is a powerful predictor of poor clinical outcome in breast cancer patients, as it is a marker of both (1) autophagy and (2) inflammation in the tumor microenvironment. Lastly, hypoxia in fibroblasts was not sufficient to induce the full-blown inflammatory response that we observed during the co-culture of fibroblasts with cancer cells, indicating that key reciprocal interactions between cancer cells and fibroblasts may be required.

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 &amp;lt; = 0.01 and fold change &amp;gt; = 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

Metabolic and Transcriptional Profiling of a Lethal Tumor Micro‐Environment

Loss of stromal Cav-1 in the fibroblast compartment is associated with early tumor recurrence, and lymph-node metastasis, resulting in poor clinical outcome in breast cancer patients. Here, we have used Cav-1 (−/−) mice as a pre-clinical model for this “lethal tumor micro-environment.” Metabolic profiling of Cav-1 (−/−) mammary fat pads revealed the upregulation of nearly 100 metabolites, indicative of a major catabolic phenotype. Our results are consistent with induction of oxidative stress, mitochondrial dysfunction, and autophagy/mitophagy. The two most prominent metabolites that emerged from this analysis were ADMA (asymmetric dimethyl arginine) and BHB (beta-hydroxybutyrate), which are markers of oxidative stress and mitochondrial dysfunction. Transcriptional profiling of Cav-1 (−/−) stromal cells and human tumor stroma from breast cancer patients directly supported an association with oxidative stress, mitochondrial dysfunction, and autophagy/mitophagy, as well as ADMA and ketone production. MircoRNA profiling of Cav-1 (−/−) stromal cells revealed the upregulation of two key cancer-related miR's, miR-31 and miR-34c. Consistent with our metabolic findings, these miR's are associated with oxidative stress and hypoxia. Thus, we have identified candidate biomarkers that could be used to identify high-risk cancer patients.

Loss of stromal caveolin-1 expression predicts poor clinical outcome in triple negative and basal-like breast cancers

Here, we investigated the possible predictive value of stromal caveolin-1 (Cav-1) as a candidate biomarker for clinical outcome in triple negative (TN) breast cancer patients. A cohort of 85 TN breast cancer patients was available, with the necessary annotation and nearly 12 years of follow-up data. Our primary outcome of interest in this study was overall survival. Interestingly, TN patients with high-levels of stromal Cav-1, had a good clinical outcome, with >50% of the patients remaining alive during the follow-up period. In contrast, the median survival for TN patients with moderate stromal Cav-1 staining was 33.5 months. Similarly, the median survival for TN patients with absent stromal Cav-1 staining was 25.7 months. A comparison of 5-year survival rates yields a similar pattern. TN patients with high stromal Cav-1 had a good 5-year survival rate, with 75.5% of the patients remaining alive. In contrast, TN patients with moderate or absent stromal Cav-1 levels had progressively worse 5-year survival rates, with 40% and 9.4% of the patients remaining alive. In contrast, in a parallel analysis, the levels of tumor epithelial Cav-1 had no prognostic significance. As such, the prognostic value of Cav-1 immunostaining in TN breast cancer patients is compartment-specific, and selective for an absence of Cav-1 staining in the stromal fibroblast compartment. A recursive-partitioning algorithm was used to assess which factors are most predictive of overall survival in TN breast cancer patients. In this analysis, we included tumor size, histologic grade, whether the patient received surgery, radiotherapy or chemotherapy, CK5/6, EGFR, p53 and Ki67 status, as well as the stromal Cav-1 score. This analysis indicated that stromal Cav-1 expression was the most important prognostic factor for overall survival in TN breast cancer. Virtually identical results were obtained with CK5/6 (+) and/or EGFR (+) TN breast cancer cases, demonstrating that a loss of stromal Cav-1 is also a strong prognostic factor for basal-like breast cancers. Our current findings may have important implications for the close monitoring and treatment stratification of TN and basal-like breast cancer patients.

Glycolytic cancer associated fibroblasts promote breast cancer tumor growth, without a measurable increase in angiogenesis: Evidence for stromal-epithelial metabolic coupling

Previously, we proposed a new model for understanding the Warburg effect in tumorigenesis and metastasis. In this model, the stromal fibroblasts would undergo aerobic glycolysis (a.k.a., the Warburg effect)—producing and secreting increased pyruvate/lactate that could then be used by adjacent epithelial cancer cells as “fuel” for the mitochondrial TCA cycle, oxidative phosphorylation, and ATP production. To test this model more directly, here we used a matched set of metabolically well-characterized immortalized fibroblasts that differ in a single gene. CL3 fibroblasts show a shift towards oxidative metabolism, and have an increased mitochondrial mass. In contrast, CL4 fibroblasts show a shift towards aerobic glycolysis, and have a reduced mitochondrial mass. We validated these differences in CL3 and CL4 fibroblasts by performing an unbiased proteomics analysis, showing the functional upregulation of 4 glycolytic enzymes, namely ENO1, ALDOA, LDHA and TPI1, in CL4 fibroblasts. Many of the proteins that were upregulated in CL4 fibroblasts, as seen by unbiased proteomics, were also transcriptionally upregulated in the stroma of human breast cancers, especially in the patients that were prone to metastasis. Importantly, when CL4 fibroblasts were co-injected with human breast cancer cells (MDA-MB-231) in a xenograft model, tumor growth was dramatically enhanced. CL4 fibroblasts induced a >4-fold increase in tumor mass, and a near 8-fold increase in tumor volume, without any measurable increases in tumor angiogenesis. In parallel, CL3 and CL4 fibroblasts both failed to form tumors when they were injected alone, without epithelial cancer cells. Mechanistically, under co-culture conditions, CL4 glycolytic fibroblasts increased mitochondrial activity in adjacent breast cancer cells (relative to CL3 cells), consistent with the “Reverse Warburg Effect”. Notably, Western blot analysis of CL4 fibroblasts revealed a significant reduction in caveolin-1 (Cav-1) protein levels. In human breast cancer patients, a loss of stromal Cav-1 is associated with an increased risk of early tumor recurrence, metastasis, tamoxifen-resistance, and poor clinical outcome. Thus, loss of stromal Cav-1 may be an effective marker for predicting the “Reverse Warburg Effect” in the stroma of human breast cancer patients. As such, CL4 fibroblasts are a new attractive model for mimicking the “glycolytic phenotype” of cancer-associated fibroblasts. Nutrients derived from glycolytic cancer associated fibroblasts could provide an escape mechanism to confer drug-resistance during anti-angiogenic therapy, by effectively reducing the dependence of cancer cells on a vascular blood supply.

The reverse Warburg effect: Aerobic glycolysis in cancer associated fibroblasts and the tumor stroma

Here, we propose a new model for understanding the Warburg effect in tumor metabolism. Our hypothesis is that epithelial cancer cells induce the Warburg effect (aerobic glycolysis) in neighboring stromal fibroblasts. These cancer-associated fibroblasts, then undergo myo-fibroblastic differentiation, and secrete lactate and pyruvate (energy metabolites resulting from aerobic glycolysis). Epithelial cancer cells could then take up these energy-rich metabolites and use them in the mitochondrial TCA cycle, thereby promoting efficient energy production (ATP generation via oxidative phosphorylation), resulting in a higher proliferative capacity. In this alternative model of tumorigenesis, the epithelial cancer cells instruct the normal stroma to transform into a wound-healing stroma, providing the necessary energy-rich micro-environment for facilitating tumor growth and angiogenesis. In essence, the fibroblastic tumor stroma would directly feed the epithelial cancer cells, in a type of host-parasite relationship. We have termed this new idea the "Reverse Warburg Effect." In this scenario, the epithelial tumor cells "corrupt" the normal stroma, turning it into a factory for the production of energy-rich metabolites. This alternative model is still consistent with Warburg's original observation that tumors show a metabolic shift towards aerobic glycolysis. In support of this idea, unbiased proteomic analysis and transcriptional profiling of a new model of cancer-associated fibroblasts (caveolin-1 (Cav-1) deficient stromal cells), shows the up-regulation of both i) myo-fibroblast markers and ii) glycolytic enzymes, under normoxic conditions. We validated the expression of these proteins in the fibroblastic stroma of human breast cancer tissues that lack stromal Cav-1. Importantly, a loss of stromal Cav-1 in human breast cancers is associated with tumor recurrence, metastasis, and poor clinical outcome. Thus, an absence of stromal Cav-1 may be a biomarker for the "Reverse Warburg Effect", explaining its powerful predictive value.

An absence of stromal caveolin-1 is associated with advanced prostate cancer, metastatic disease spread and epithelial Akt activation

Here, we examined the status of stromal Cav-1 expression in patients with benign prostatic hypertrophy (BPH), primary prostate cancers (PCa), and prostate-cancer metastases (Mets). Interestingly, an absence of stromal Cav-1 directly correlated with prostate cancer disease progression. For example, virtually all BPH samples showed abundant stromal Cav-1 immunostaining. In contrast, in a subset of patients with primary prostate cancer, the stromal levels of Cav-1 were significantly decreased, and this correlated with a high Gleason score, indicative of a worse prognosis and poor clinical outcome. Remarkably, all metastatic tumors (either from lymph node or bone) were completely negative for stromal Cav-1 staining. Thus, stromal Cav-1 expression may be considered as a new biomarker of prostate cancer disease progression and metastasis. Mechanistically, stromal Cav-1 levels were inversely correlated with the epithelial expression levels of Cav-1 and epithelial phospho-Akt. Thus, loss of stromal Cav-1 is predictive of elevated levels of epithelial Cav-1 and epithelial Akt-activation. This provides important new clinical evidence for paracrine signaling between prostate cancer epithelial cells and the tumor stromal micro-environment, especially related to disease progression and metastasis.