Perturbations of stromal -epithelial interactions in the developing tumour can contribute to cancer invasion and metastasis. The structurally related metallopeptidases endothelin-converting enzyme (ECE) and neutral endopeptidase (NEP) contribute sequentially to the synthesis and inactivation of ET-1, a mitogenic peptide that has been shown to affect tumour behaviour. This study has investigated the interaction between metastatic tumour epithelial cells, which lack NEP, and stromal cells, which we have shown to express ECE-1 (stromal -epithelial interactions), using Matrigel invasion chambers. The epithelial cell lines utilised in this study include androgen-sensitive LNCaP, androgen-independent PC-3, Du145 and recently established PNT-1a, PNT2-C2 and P4E6 prostate cell lines. Specific inhibition of endogenous ECE-1 activity in stromal cells reduced PC-3 and Du145 invasion by 70 and 50%, respectively. Addition of recombinant NEP to inactivate endogenous mitogenic peptides resulted in 50 and 20% reductions in invasion in PC-3 and Du145 cells, respectively. Neutral endopeptidase effects were reversed in the presence of thiorphan, a specific NEP inhibitor. Supplementation of defined media with bradykinin and ET-1 significantly increased PC-3 invasion by 40 and 50%, respectively. Du145 cell invasion increased by approximately 100% on adding ET-1. These studies implicate the metallopeptidases NEP and ECE-1 as mediators of prostate cancer invasion via a stromal/epithelial interaction.

The present study focused on the endothelin axis in human oral squamous cell carcinoma (SCC) cells. We investigated the expression and distribution of endothelin-1 (ET-1), its receptors (endothelin-A receptor (ET A R) and endothelin-B receptor (ET B R)) and isoforms of its specific converting enzyme 1b, 1c) and the report on their relative influences on cell proliferation. We also investigated the effect of an ECE-specific inhibitor (ECE-i) and siRNA targeting of the ECE-1 gene on SCC cell proliferation. We observed the expression of ET-1, ET A R, ET B R and all endothelin-converting enzyme-1 (ECE-1) isoforms in oral SCC cells, but only the expression of ET-1, ET B R and ECE-1 was increased when compared to normal human epidermal keratinocytes. ET-1 alone stimulated proliferation of oral SCC cells. Antagonists of either ET A R or ET B R inhibited ET-1-mediated proliferation. Decreased ECE-1 expression after ECE siRNA treatment reduced SCC cell proliferation. Antiproliferative effects were also observed by inhibiting ECE activity with ECE-i. In conclusion, the present study demonstrates that modulation of the endothelin system in oral SCC cells might provide a novel therapeutic protocol for oral cancer. ' 2005 Wiley-Liss, Inc.

Small interfering RNAs (siRNAs) have been widely exploited for nucleotide-sequence-specific posttranscriptional gene silencing, as a tool to investigate gene function in eukaryotes, and they hold promise as potential therapeutic agents. Conventionally designed siRNAs are 21-mers with symmetric 2-nt 3' overhangs that mimic intermediates (microRNAs or miRNAs) of the natural processing of longer dsRNA (double-stranded RNA). siRNAs are sequences with full complementarity to their target mRNA and can be generated by either chemical synthesis or processing of shRNAs (short hairpin RNAs) transcribed from DNA vectors. To minimize off-target effects, any homology to nontarget mRNA can be verified using the expressed sequence tag (EST) database for the relevant organism. Here, we provide a practical guide and an overview to the design and selection of effective and specific siRNAs.

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