Pro-cathepsin D interacts with the extracellular domain of the β chain of LRP1 and promotes LRP1-dependent fibroblast outgrowth

• DOI: 10.1242/jcs.070938
• Publication Date: 2010-09-09T00:19:46Z
• Authors: Mélanie Beaujouin; Christine Prébois; Danielle Derocq; Valérie Laurent-M...; Olivier Masson; Sophie Pattingre; Peter Coopman; Nadir Bettache; Jami Grossfield; Robert E. Holling...; Hongyu Zhang; Zemin Yao; Bradley T. Hyman; Peter van der Geer; Gary K. Smith; Emmanuelle Liaude...
• Keywords: 0301 basic medicine; LRP1; cathepsin D; [SDV.CAN]Life Sciences [q-bio]/Cancer; Breast Neoplasms; [SDV.BC]Life Sciences [q-bio]/Cellular Biology; Cell Growth Processes; Cathepsin D; Mice; 03 medical and health sciences; Membrane Microdomains; fibroblast outgrowth; Antigens, CD; Paracrine Communication; cancer; Animals; Humans; Protein Interaction Domains and Motifs; RNA, Small Interfering; Cell Line, Transformed; Enzyme Precursors; tumor micro-environment; Carcinoma; Fibroblasts; Coculture Techniques; 3. Good health; Female; Low Density Lipoprotein Receptor-Related Protein-1; Protein Binding

Interactions between cancer cells and fibroblasts are crucial in cancer progression. We have previously shown that the aspartic protease cathepsin D (cath-D), a marker of poor prognosis in breast cancer that is overexpressed and highly secreted by breast cancer cells, triggers mouse embryonic fibroblast outgrowth via a paracrine loop. Here, we show the requirement of secreted cath-D for human mammary fibroblast outgrowth using a three-dimensional co-culture assay with breast cancer cells that do or do not secrete pro-cath-D. Interestingly, proteolytically-inactive pro-cath-D remains mitogenic, indicating a mechanism involving protein-protein interaction. We identify the low-density lipoprotein (LDL) receptor-related protein-1, LRP1, as a novel binding partner for pro-cath-D in fibroblasts. Pro-cath-D binds to residues 349–394 of the β chain of LRP1, and is the first ligand of the extracellular domain of LRP1β to be identified. We show that pro-cath-D interacts with LRP1β in cellulo. Interaction occurs at the cell surface, and overexpressed LRP1β directs pro-cath-D to the lipid rafts. Our results reveal that the ability of secreted pro-cath-D to promote human mammary fibroblast outgrowth depends on LRP1 expression, suggesting that pro-cath-D–LRP1β interaction plays a functional role in the outgrowth of fibroblasts. Overall, our findings strongly suggest that pro-cath-D secreted by epithelial cancer cells promotes fibroblast outgrowth in a paracrine LRP1-dependent manner in the breast tumor microenvironment.