SNED1 fibrillar assembly in the extracellular matrix requires fibronectin and collagen I.

The extracellular matrix (ECM) is a meshwork of proteins that orchestrates a broad range of cellular phenotypes, including proliferation, adhesion, migration and differentiation. SNED1 is a newly characterized ECM glycoprotein that promotes cell adhesion and is essential for embryonic development. Its upregulation is also associated with breast cancer metastasis and poor prognosis for breast cancer patients. We have recently shown that SNED1 assembles into fibrillar structures, but the mechanisms guiding its incorporation into the ECM scaffold remained unknown. Here, combining biochemical assays and confocal immunofluorescence imaging, we found that SNED1 assembly in the ECM occurs early in the process of ECM building and is concomitant and overlaps with the deposition of fibronectin and collagen I, two major ECM proteins. By knocking down fibronectin or destabilizing collagen I fibers, we further demonstrate that SNED1 requires the presence of these proteins for its assembly. Finally, using biolayer interferometry, we identify collagen I as the first direct binding partner of SNED1. Altogether, our results lay the foundation for future studies aimed at determining the mechanisms by which SNED1 fibers contribute to SNED1 pathophysiological functions.