An Integrin-Linked Machinery of Cytoskeletal Regulation that Enables Experimental Tumor Initiation and Metastatic Colonization

• Abundance of filopodium-like protrusions (FLPs) depends on their persistence periods
• Integrin-actin linking proteins govern cofilin activity as well as FLP persistence
• FLPs critically support both metastatic outgrowth and experimental tumor formation
• Epithelial-mesenchymal transition (EMT) in carcinoma cells enhances FLP formation

SummaryRecently extravasated metastatic cancer cells use the Rif/mDia2 actin-nucleating/polymerizing machinery in order to extend integrin β1-containing, filopodium-like protrusions (FLPs), which enable them to interact productively with the surrounding extracellular matrix; this process governs the initial proliferation of these cancer cells. Here, we identify the signaling pathway governing FLP lifetime, which involves integrin-linked kinase (ILK) and β-parvin, two integrin:actin-bridging proteins that block cofilin-mediated actin-filament severing. Notably, the combined actions of Rif/mDia2 and ILK/β-parvin/cofilin pathways on FLPs are required not only for metastatic outgrowth but also for primary tumor formation following experimental implantation. This provides one mechanistic explanation for how the epithelial-mesenchymal transition (EMT) program imparts tumor-initiating powers to carcinoma cells, since it enhances FLP formation through the activation of ILK/β-parvin/cofilin pathway.

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