Extended interaction network of procollagen C-proteinase enhancer-1 in the extracellular matrix

PCPE-1 (procollagen C-proteinase enhancer-1) is an extracellular matrix glycoprotein that can stimulate procollagen processing by procollagen C-proteinases such as BMP-1 (bone morphogenetic protein 1). PCPE-1 interacts with several proteins in addition to procollagens and BMP-1, suggesting that it could be involved in biological processes other than collagen maturation. We thus searched for additional partners of PCPE-1 in the extracellular matrix, which could provide new insights into its biological roles. We identified 17 new partners of PCPE-1 by SPR (surface plasmon resonance) imaging. PCPE-1 forms a transient complex with the beta-amyloid peptide, whereas it forms high or very high affinity complexes with laminin-111 (K-D = 58.8 pM), collagen VI (K-D = 9.5 nM), TSP-1 (thrombospondin-1) (K-D1 = 19.9 pM, K-D2 = 14.5 nM), collagen IV (K-D = 49.4 nM) and endostatin, a fragment of collagen XVIII (K-D1 = 0.30 nM, K-D2 = 1.1 nM). Endostatin binds to the NTR (netrin-like) domain of PCPE-1 and decreases the degree of superstimulation of PCPE-1 enhancing activity by heparin. The analysis of the PCPE-1 interaction network based on Gene Ontology terms suggests that, besides its role in collagen deposition, PCPE-1 might be involved in tumour growth, neurodegenerative diseases and angiogenesis. In vitro assays have indeed shown that the CUB1CUB2 (where CUB is complement protein subcomponents C1r/C1s, urchin embryonic growth factor and BMP-1) fragment of PCPE-1 inhibits angiogenesis.