Abstract
Depletion of liprin-α1, ERC1 or LL5 scaffolds inhibits extracellular matrix degradation by invasive cells. These proteins co-accumulate near invadosomes in NIH-Src cells, identifying a novel invadosome–associated compartment distinct from the core and adhesion ring of invadosomes. Depletion of either protein perturbs the organization of invadosomes without influencing the recruitment of MT1-MMP metalloprotease. Liprin-α1 is not required for de novo formation of invadosomes after their disassembly by microtubules and Src inhibitors, while its depletion inhibits invadosome motility, thus affecting matrix degradation. Fluorescence recovery after photobleaching shows that the invadosome–associated compartment is dynamic, while correlative light immunoelectron microscopy identifies bona fide membrane–free invadosome–associated regions enriched in liprin-α1, which is virtually excluded from the invadosome core. The results indicate that liprin-α1, LL5 and ERC1 define a novel dynamic membrane-less compartment that regulates matrix degradation by affecting invadosome motility.
Highlights
Different types of invasive cells including cancer cells, form specialized actin–rich membrane protrusions called invadopodia or podosomes, generally defined as invadosomes
MDA-MB-231 cells form functional invadopodia to degrade the extracellular matrix (ECM) during invasion. 88% of MDA-MB-231 cells plated on Oregon–green gelatin showed ECM degradation, and silencing of either liprin-α1, ERC1 or LL5 protein in these cells (Supplementary Figure 1A; 77–93% protein decrease) strongly inhibited ECM degradation (Fig. 1A–D)
While knockdown of either protein reduced the percentage of ECM degrading cells, only liprin-α1 silencing slightly decreased the percentage of cells with invadopodia compared to controls (Supplementary Figure 1C)
Summary
Different types of invasive cells including cancer cells, form specialized actin–rich membrane protrusions called invadopodia or podosomes, generally defined as invadosomes. Time-lapse imaging has shown that during cell migration liprin-α1, ERC1 and LL5 define new highly polarized and dynamic cytoplasmic structures uniquely localized near the protruding cell edge[11]. Based on these findings we have proposed that these proteins assemble into plasma membrane-associated platforms, large membrane-less assemblies that promote protrusion at the cell front[15]. We show that liprin-α1, ERC1 and LL5 promote the maturation and function of invadosomes, and that the three proteins colocalize near invadosomes, where they identify a novel dynamic, membrane–less invadosome–associated compartment
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