ACE2 (angiotensin converting enzyme 2) plays a critical role in the local tissue RAS (renin-angiotensin system) by hydrolysing the potent hypertensive and mitogenic peptide AngII (angiotensin II). Changes in the levels of ACE2 have been observed in a number of pathologies, including cardiovascular disease, but little is known of the mechanisms regulating its expression. In the present study, therefore, the potential role of miRNAs in the regulation of ACE2 expression in primary human cardiac myofibroblasts was examined. Putative miRNA-binding sites were identified in the 3'-UTR of the ACE2 transcript using online prediction algorithms. Two of these, miR-200b and miR-421, were selected for further analysis. A reporter system using the 3'-UTR of ACE2 fused to the coding region of firefly luciferase was used to determine the functionality of the identified binding sites in vitro. This identified miR-421, but not miR-200b, as a potential regulator of ACE2. The ability of miR-421, an miRNA implicated in the development of thrombosis, to down-regulate ACE2 expression was subsequently confirmed by Western blot analysis of both primary cardiac myofibroblasts and transformed cells transfected with a synthetic miR-421 precursor. Real-time PCR analysis of miR-421 revealed widespread expression in human tissues. miR-421 levels in cardiac myofibroblasts showed significant inter-patient variability, in keeping with the variability of ACE2 expression we have observed previously. In conclusion, the present study is the first to demonstrate that ACE2 may be subject to post-transcriptional regulation and reveals a novel potential therapeutic target, miR-421, which could be exploited to modulate ACE2 expression in disease.

Cross-talk between tumour and stromal cells can profoundly influence cancer cell invasion by increasing the availability of mitogenic peptides such as endothelin-1 (ET-1). Endothelin-1 is elevated in men with metastatic prostate cancer (PC), and can exert both an autocrine (epithelial) and a paracrine (stromal) influence on growth. Endothelin-1 is generated from its inactive precursor big-ET-1 by endothelin-converting enzyme 1 (ECE-1). We and others have demonstrated that ECE-1 expression is significantly elevated in tumours and surrounding stromal tissue. Our current data show siRNA-mediated knockdown of stromal ECE-1 reduces epithelial (PC-3) cell invasion in coculture. Interestingly, readdition of ET-1 only partially recovers this effect suggesting a novel role for ECE-1 independent of ET-1 activation. Parallel knockdown of ECE-1 in both stromal and epithelial compartments results in an additive decrease in cell invasion. We extrapolated this observation to the four recognised isoforms ECE-1a, ECE-1b, ECE-1c and ECE-1d. Only ECE-1a and ECE-1c were significant but with reciprocal effects on cell invasion. Transient ECE-1c overexpression increased PC-3 invasiveness through matrigel, whereas transient ECE-1a expression suppressed invasion. Furthermore, transient ECE-1a expression in stromal cells strongly counteracts the effect of transient ECE-1c expression in PC-3 cells. The ECE-1 isoforms may, therefore, be relevant targets for antiinvasive therapy in prostate and other cancers.

The zinc metalloprotease, endothelin-converting enzyme-1 (ECE-1), which converts the mitogenic peptide endothelin-1 (ET-1) from its biologically inactive precursor big-ET-1, is commonly upregulated in prostate cancer (PC) cells. Consequently, we have sought to suppress ECE-1 expression by using RNAi as a potentially novel therapeutic approach. Therefore, a synthetic 64-nt short-hairpin RNA (shRNA), designed to target the ECE-1 gene, was expressed in an Herpesvirus saimiri (HVS)-based delivery vector. ECE-1 expression in cells transduced with the vector was examined by real-time PCR and Western blotting. The effects of ECE-1 knockdown on PC cell migration and invasion were studied using a scratch assay and Matrigel invasion. These studies, in vitro and ex vivo, demonstrated that the HVS-shRNA viruses could infect and silence ECE-1 expression effectively in human PC cells. Furthermore, it was observed that ECE-1 knockdown in either stromal cells or epithelial cells could significantly reduce invasion of PC-3 cells in coculture by 33 and 31%, respectively. In addition, suppressed migration was also observed in HVS-ECE-1 shRNA-infected PC-3 cells compared to uninfected and HVS-GFP-infected control cell cultures. These findings highlight the potential tumor-suppressing effect of ECE-1 knockdown in cancer cells and novel strategies for future therapeutic developments in advanced PC.Prostate cancer (PC) is the most frequently diagnosed cancer and the second leading cause of cancer death in western males. 1 Although androgen withdrawal can initially give effective control of cancer progression, 2 subsequent transition to the more malignant and metastatic androgen-independent form, which is neuropeptide-driven, requires novel approaches to treatment. In particular, the upregulation of protein components involved in the endothelin-1 (ET-1) signaling axis plays a key role in progression of many types of cancer, including ovarian, colorectal, breast and PC. 3-6 Specifically, plasma levels of ET-1 are abnormally elevated in patients with advanced, androgen-independent PC 7 , and the potent ET receptor subtype A (ET A R) antagonist atrasentan (ABT-627) has been reported to suppress partially prostate tumor growth. 8 Hence, inhibition of ET formation or downstream signaling could provide a novel strategy to treat advanced PC.The final and rate-limiting step in the biosynthesis of ET-1 is catalyzed by endothelin-converting enzyme-1 (ECE-1), a 120-130 kDa integral membrane-associated glycoprotein, belonging to the M13 zinc-metalloprotease family, which also includes neprilysin (NEP), the major ET-1 degradative enzyme. 9 Four isoforms of ECE-1 (ECE-1a-1d) have been identified, which are transcribed from a single gene using alternative promoters. 10,11 They have a common catalytic domain but show distinct subcellular localization because of the differences in their N-terminal tails, with ECE-1a and ECE-1c predominantly being expressed at the plasma membrane, whereas ECE-1b and ECE-1d mainly occur in endosomal membranes. 10,12 Alth...

Plasma concentrations of the mitogenic peptide endothelin-1 (ET-1) are significantly elevated in men with metastatic prostate cancer (PC). ET-1 also contributes to the transition of hormonally regulated androgen-dependent PC to androgen-independent disease. ET-1 is generated from big-ET-1 by endothelin-converting enzyme (ECE-1). ECE-1 is present in PC cell lines and primary tissue and is elevated in primary malignant stromal cells compared with benign. siRNA or shRNA-mediated knockdown of endogenous ECE-1 in either the epithelial or stromal compartment significantly reduced PC cell (PC-3) invasion and migration. The re-addition of ET-1 only partially recovered the effect, suggesting ET-1-dependent and -independent functions for ECE-1 in pPC. The ET-1-independent effect of ECE-1 on PC invasion may be due to modulation of downstream signalling events. Addition of an ECE-1 specific inhibitor to PC-3 cells reduced phosphorylation of focal adhesion kinase (FAK), a signalling molecule known to play a role in PC. siRNA-mediated knockdown of ECE-1 resulted in a significant reduction in FAK phosphorylation. Accordingly, transient ECE-1 overexpression in PNT1-a cells increased FAK phosphorylation. In conclusion, ECE-1 influences PC cell invasion via both ET-1-mediated FAK phosphorylation and ET-1 independent mechanisms.