Interfering with the ERC1-LL5β interaction disrupts plasma membrane-Associated platforms and affects tumor cell motility.

Cell migration requires a complex array of molecular events to promote protrusion at the front of motile cells. The scaffold protein LL5β interacts with the scaffold ERC1, and recruits it at plasma membrane–associated platforms that form at the front of migrating tumor cells. LL5 and ERC1 proteins support protrusion during migration as shown by the finding that depletion of either endogenous protein impairs tumor cell motility and invasion. In this study we have tested the hypothesis that interfering with the interaction between LL5β and ERC1 may be used to interfere with the function of the endogenous proteins to inhibit tumor cell migration. For this, we identified ERC1(270–370) and LL5β(381–510) as minimal fragments required for the direct interaction between the two proteins. The biochemical characteriza- tion demonstrated that the specific regions of the two proteins, including predicted intrinsi- cally disordered regions, are implicated in a reversible, high affinity direct heterotypic interaction. NMR spectroscopy further confirmed the disordered nature of the two fragments and also support the occurrence of interaction between them. We tested if the LL5β protein fragment interferes with the formation of the complex between the two full-length proteins. Coimmunoprecipitation experiments showed that LL5β(381–510) hampers the formation of the complex in cells. Moreover, expression of either fragment is able to specifically delocal- ize endogenous ERC1 from the edge of migrating MDA-MB-231 tumor cells. Coimmunopre- cipitation experiments show that the ERC1-binding fragment of LL5β interacts with endogenous ERC1 and interferes with the binding of endogenous ERC1 to full length LL5β. Expression of LL5β(381–510) affects tumor cell motility with a reduction in the density of invadopodia and inhibits transwell invasion. These results provide a proof of principle that interfering with heterotypic intermolecular interactions between components of plasma membrane–associated platforms forming at the front of tumor cells may represent a new approach to inhibit cell invasion.