Summary
Multimerin 1 (MMRN1) is a large, soluble, polymeric, factor V binding protein and
member of the EMILIN protein family.In vivo, MMRN1 is found in platelets, megakaryocytes, endothelium and extracellular matrix
fibers, but not in plasma. To address the mechanism of MMRN1 binding to activated
platelets and endothelial cells, we investigated the identity of the major MMRN1 receptors
on these cells using wild-type and RGE-forms of recombinant MMRN1. Ligand capture,
cell adhesion, ELISA and flow cytometry analyses of platelet-MMRN1 binding, indicated
that MMRN1 binds to integrins αIIbβ3 and αvβ3. Endothelial cell binding to MMRN1 was
predominantly mediated by αvβ3 and did not require the MMRN1 RGD site or cellular
activation. Like many other αvβ3 ligands, MMRN1 had the ability to support adhesion
of additional cell types, including stimulated neutrophils. Expression studies, using
a cell line capable of endothelial-like MMRN1 processing, indicated that MMRN1 adhesion
to cellular receptors enhanced its extracellular matrix fiber assembly. These studies
implicate integrin-mediated binding in MMRN1 attachment to cells and indicate that
MMRN1 is a ligand for αIIbβ3 and αvβ3.
Keywords
Multimerin 1 - cell adhesion - integrin - platelet - endothelial cell