The Serine Protease Inhibitor Protease Nexin-1 Controls Mammary Cancer Metastasis through LRP-1–Mediated MMP-9 Expression

Abstract

Through their ability to degrade the extracellular matrix, proteases mediate cancer cell invasion and metastasis. Paradoxically, some serine protease inhibitors (serpins) are often overexpressed in human tumors. Using computational analysis, we found that the RNA level of protease nexin-1 (PN-1), a serpin that blocks numerous proteases activity, is significantly elevated in estrogen receptor-A-negative and in high-grade breast cancer. The in silico approach was complemented by mechanistic studies on two mammary cancer cell lines, the PN-1-negative 168FARN cells and the PN-1-positive 4T1 cells, both of which form primary mammary tumors, but only 4T1 tumors are able to metastasize to the lungs. We show that treatment of 168FARN cells with PN-1 stimulates extracellular signal-regulated kinase activation via low-density lipoprotein receptor-related protein-1 (LRP-1) binding, resulting in increased matrix metalloproteinase (MMP)-9 RNA, protein, and secreted activity. PN-1-silenced 4T1 cells express low MMP-9 levels. Moreover, injection of PN-1-silenced cells into mice did not affect 4T1 primary mammary tumor outgrowth; however, the tumors had impaired metastatic potential, which could be restored by reexpressing soluble MMP-9 in the PN-1-silenced 4T1 cells. Thus, using mammary tumor models, we describe a novel pathway whereby the serpin PN-1 by binding LRP-1 stimulates extracellular signal-regulated kinase signaling, MMP-9 expression, and metastatic spread of mammary tumors. Importantly, an analysis of 126 breast cancer patients revealed that those whose breast tumors had elevated PN-1 levels had a significantly higher probability to develop lung metastasis, but not metastasis to other sites, on relapse. These results suggest that PN-1 might become a prognostic marker in breast cancer.

Targeting the Cytoskeleton with Plant-Bioactive Compounds in Cancer Therapy

“…Cancer cell migration can convert between mesenchymal and amoeboid types. This later can occur, e.g., when cells are exposed to protease inhibitors [58] and thereby mesenchymal cancer cell invasion is repressed by speciic targeting of protease function. Inhibiting RhoA/ROCK signaling promotes the formation of multiple competing microilament-derived lamellipodia that suppress amoeboid migration of tumor cells [59].…”

Low Density Lipoprotein Receptor-related Protein 1 (LRP1) Forms a Signaling Complex with Platelet-derived Growth Factor Receptor-β in Endosomes and Regulates Activation of the MAPK Pathway

“…In addition to its effect on cell cycle regulation, recent studies have shown that ERK signaling initiated via LRP1 association with ligands has important consequences on the production of proteinases (47). Thus, the serpin protease nexin 1 (PN-1) in complex with target proteases binds LRP1 and activates ERK signaling, which in turn is required for induction of MMP-9 expression (47).…”

“…Thus, the serpin protease nexin 1 (PN-1) in complex with target proteases binds LRP1 and activates ERK signaling, which in turn is required for induction of MMP-9 expression (47).…”

Expression pattern of human SERPINE2 in a variety of human tumors

“…It also belongs to the nexin protease family according to its amino acid sequence, therefore also commonly called protease nexin-1 (PN-1) (4). SERPINE2 mainly presents in the extracellular matrix (ECM) and is secreted by many cell types, including endothelial cells, fibroblasts, macrophages, platelets, smooth muscle cells, chondrocytes, astrocytes and tumor cells (5)(6)(7)(8)(9). SERPINE2 binds to its specific target protein to form covalent complexes, which are endocytosed and degraded by cells (10).…”