Extracellular calumenin suppresses ERK1/2 signaling and cell migration by protecting fibulin-1 from MMP-13-mediated proteolysis.

Extracellular proteins are vital for cell activities, such as cell migration. Calumenin is highly conserved among eukaryotes, but its functions are largely unclear. Here, we identify extracellular calumenin as a suppressor of cell migration and tumor metastasis. Calumenin binds to and stabilizes fibulin-1, leading to inactivation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) signaling. We further identify the minimal functional domain of calumenin (amino acids 74-138 and 214-280). Depletion of calumenin induces fibulin-1- and phospho-ERK1/2 (pERK1/2)-dependent promotion of cell migration. Consistently, in hepatocellular and pancreatic carcinoma, both calumenin and fibulin-1 are downregulated. Furthermore, we show that matrix metalloproteinase-13 (MMP-13) proteolyzes fibulin-1 and that calumenin protects fibulin-1 from cleavage by MMP-13. Calumenin, together with fibulin-1, also interacts with fibronectin and depends on both syndecan-4 and α5β1-integrin to suppress ERK1/2 signaling and inhibit cell migration. Thus, extracellular calumenin regulates fibulin-1 to have crucial roles in ERK1/2 signaling and cell migration.