Cancer-associated fibroblasts (CAF) engage in tumor progression by promoting the ability of cancer cells to undergo epithelial-mesenchymal transition (EMT), and also by enhancing stem cells traits and metastatic dissemination. Here we show that the reciprocal interplay between CAFs and prostate cancer cells goes beyond the engagement of EMT to include mutual metabolic reprogramming. Gene expression analysis of CAFs cultured ex vivo or human prostate fibroblasts obtained from benign prostate hyperplasia revealed that CAFs undergo Warburg metabolism and mitochondrial oxidative stress. This metabolic reprogramming toward a Warburg phenotype occurred as a result of contact with prostate cancer cells. Intercellular contact activated the stromal fibroblasts, triggering increased expression of glucose transporter GLUT1, lactate production, and extrusion of lactate by de novo expressed monocarboxylate transporter-4 (MCT4). Conversely, prostate cancer cells, upon contact with CAFs, were reprogrammed toward aerobic metabolism, with a decrease in GLUT1 expression and an increase in lactate upload via the lactate transporter MCT1. Metabolic reprogramming of both stromal and cancer cells was under strict control of the hypoxia-inducible factor 1 (HIF1), which drove redox-and SIRT3-dependent stabilization of HIF1 in normoxic conditions. Prostate cancer cells gradually became independent of glucose consumption, while developing a dependence on lactate upload to drive anabolic pathways and thereby cell growth. In agreement, pharmacologic inhibition of MCT1-mediated lactate upload dramatically affected prostate cancer cell survival and tumor outgrowth. Hence, cancer cells allocate Warburg metabolism to their corrupted CAFs, exploiting their byproducts to grow in a low glucose environment, symbiotically adapting with stromal cells to glucose availability. Cancer Res; 72(19); 5130-40. Ó2012 AACR.

Limited information is available concerning the expression and role of microRNAs in prostate cancer. In this study, we investigated the involvement of miR-205 in prostate carcinogenesis. Significantly lower miR-205 expression levels were found in cancer than in normal prostate cell lines as well as in tumor compared with matched normal prostate tissues, with a particularly pronounced reduction in carcinomas from patients with local-regionally disseminated disease. Restoring the expression of miR-205 in prostate cancer cells resulted in cell rearrangements consistent with a mesenchymalto-epithelial transition, such as up-regulation of E-cadherin and reduction of cell locomotion and invasion, and in the down-regulation of several oncogenes known to be involved in disease progression (i.e., interleukin 6, caveolin-1, EZH2). Our evidence suggests that these events are driven by the concurrent repression of specific predicted miR-205 targets, namely N-chimaerin, ErbB3, E2F1, E2F5, ZEB2, and protein kinase CE. Strikingly, the latter seemed to play a direct role in regulating epithelial-to-mesenchymal transition. In fact, its down-regulation led to a cell phenotype largely reminiscent of that of cells ectopically expressing miR-205. Overall, we showed for the first time that miR-205 exerts a tumorsuppressive effect in human prostate by counteracting epithelial-to-mesenchymal transition and reducing cell migration/invasion, at least in part through the downregulation of protein kinase CE. [Cancer Res 2009;69(6):2287-95]

Prostate cancer cells release atypically large extracellular vesicles (EVs), termed large oncosomes, which may play a role in the tumor microenvironment by transporting bioactive molecules across tissue spaces and through the blood stream. In this study, we applied a novel method for selective isolation of large oncosomes applicable to human platelet-poor plasma, where the presence of caveolin-1-positive large oncosomes identified patients with metastatic disease. This procedure was also used to validate results of a miRNA array performed on heterogeneous populations of EVs isolated from tumorigenic RWPE-2 prostate cells and from isogenic non-tumorigenic RWPE-1 cells. The results showed that distinct classes of miRNAs are expressed at higher levels in EVs derived from the tumorigenic cells in comparison to their non-tumorigenic counterpart. Large oncosomes enhanced migration of cancer-associated fibroblasts (CAFs), an effect that was increased by miR-1227, a miRNA abundant in large oncosomes produced by RWPE-2 cells. Our findings suggest that large oncosomes in the circulation report metastatic disease in patients with prostate cancer, and that this class of EV harbors functional molecules that may play a role in conditioning the tumor microenvironment.

BackgroundAberrant expression of microRNAs, small non-coding RNA molecules that post-transcriptionally repress gene expression, seems to be causatively linked to the pathogenesis of cancer. In this context, miR-21 was found to be overexpressed in different human cancers (e.g. glioblastoma, breast cancer). In addition, it is thought to be endowed with oncogenic properties due to its ability to negatively modulate the expression of tumor-suppressor genes (e.g. PTEN) and to cause the reversion of malignant phenotype when knocked- down in several tumor models. On the basis of these findings, miR-21 has been proposed as a widely exploitable cancer-related target. However, scanty information is available concerning the relevance of miR-21 for prostate cancer. In the present study, we investigated the role of miR-21 and its potential as a therapeutic target in two prostate cancer cell lines, characterized by different miR-21 expression levels and PTEN gene status.ResultsWe provide evidence that miR-21 knockdown in prostate cancer cells is not sufficient per se i) to affect the proliferative and invasive potential or the chemo- and radiosensitivity profiles or ii) to modulate the expression of the tumor-suppressors PTEN and Pdcd4, which in other tumor types were found to be regulated by miR-21. We also show that miR-21 is not differently expressed in carcinomas and matched normal tissues obtained from 36 untreated prostate cancer patients subjected to radical prostatectomy.ConclusionsOverall, our data suggest that miR-21 is not a central player in the onset of prostate cancer and that its single hitting is not a valuable therapeutic strategy in the disease. This supports the notion that the oncogenic properties of miR-21 could be cell and tissue dependent and that the potential role of a given miRNA as a therapeutic target should be contextualized with respect to the disease.