Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St Louis, Missouri 63110, USA.
The low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional endocytic receptor involved in the metabolism of various extracellular ligands, including proteinases, that play critical roles in tumor invasion. Although several studies have shown an increased expression of LRP1 in cancer cells, its function in tumor development and progression remains largely unclear. Here, we reveal a novel mechanism by which LRP1 induces the expression of matrix metalloproteinase 2 (MMP2) and MMP9 and thereby promotes the migration and invasion of human glioblastoma U87 cells. Knockdown of LRP1 expression greatly decreased U87 cell migration and invasion, which was rescued by the forced expression of a functional LRP1 minireceptor. Inhibition of ligand binding to LRP1 by a specific antagonist, receptor-associated protein, also led to reduced cancer cell migration and invasion. Because MMPs play critical roles in cancer cell migration and invasion, we examined the expression of several MMPs and found that the expression of functional MMP2 and MMP9 was selectively decreased in LRP1 knockdown cells. More importantly, decreased cell migration and invasion of LRP1 knockdown cells were completely rescued by exogenous expression of MMP2 or MMP9, suggesting that these MMPs are likely downstream targets of LRP1-mediated signaling. We further show that the level of phosphorylated extracellular signal-regulated kinase (ERK) was significantly decreased in LRP1-silenced cells, suggesting that ERK is a potential mediator of LRP1-regulated MMP2 and MMP9 expression in U87 cells. Together, our data strongly suggest that LRP1 promotes glioblastoma cell migration and invasion by regulating the expression and function of MMP2 and MMP9 perhaps via an ERK-dependent signaling pathway.