Meprin was first discovered in proximal epithelial cells of mouse kidney in 1981 by Beynon et al. (24). In addition, two other groups discovered the same metalloprotease in the early 1980s: Sterchi et al., in 1982, described the enzyme PABA peptide hydrolase (PPH) in microvillar membranes of human small www.selleckchem.com/products/Vorinostat-saha.html intestinal epithelial cells (25), and Kenny et al., in 1987, found the endopeptidase-2 in the microvillar membrane of proximal epithelial cells of rat kidney (26). This metalloprotease is now known as ��meprin.�� There are two evolutionary related isoforms: Meprin�� and meprin��. Both are synthesized as type I transmembrane proteins in the endoplasmic reticulum (27, 28). The membrane anchor of meprin�� is removed intracellularly leading to the secretion of this isoform from cells, whereas meprin�� remains an integral protein of the plasma membrane (29).

However, meprin�� may be retained at the plasma membrane via covalent interaction with the transmembrane meprin�� (30�C32). Meprin�� is expressed in epithelial cells of the healthy colon mucosa where it is secreted apically into the colon lumen (33). In colorectal cancer, meprin�� is released in a non-polarized fashion, leading to its accumulation in the tumor stroma (34, 35). This aberrant secretion of meprin�� into the tumor stroma exposes matrix components and other stromal elements to an increased proteolytic potential (35). Once secreted, meprin�� is activated in vitro and in the gut lumen by the removal of the pro-peptide through trypsin (28). An alternative activation mechanism has been suggested in colorectal cancer.

In colon carcinoma cells (Caco-2), basolaterally secreted meprin�� is activated by plasmin, which in turn, is activated by the fibroblast-derived urokinase-type plasminogen activator (36). Meprin�� has been demonstrated to have pro-migratory and pro-angiogenic effects in colorectal cancer, and thus may be involved in the transition from benign growth (adenomas) to malignant primary tumors (37, 38). We investigated the molecular mechanisms by which meprin�� may influence tumor progression. For the first time we demonstrate that meprin�� is able to shed EGF from the plasma membrane, resulting in the transactivation of EGFR signaling pathway and enhancement of Caco-2 cell proliferation and migration. We also confirm the shedding of TGF�� by meprin��.

EXPERIMENTAL PROCEDURES Antibodies and Recombinant Protein Antibodies specific for total EGFR (monoclonal rabbit antibody) and phospho-EGFR Y1068 (monoclonal rabbit antibody) were purchased Cilengitide from Epitomics (Burlingame, CA); antibodies specific for total ERK1/2 (monoclonal mouse antibody) and phospho-ERK1/2 (polyclonal rabbit antibody) were from Santa Cruz Biotechnology (Heidelberg, Germany). Horseradish peroxidase-linked anti-rabbit and anti-mouse secondary antibodies were obtained from Dako Cytomation (Denmark).