Procollagen C-proteinase enhancer-1 (PCPE-1) interacts with β₂-microglobulin (β2-m) and may help initiate β2-m amyloid fibril formation in connective tissues

Dialysis related amyloidosis (DRA) is a progressive and serious complication in patients under long-term hemodialysis and mainly leads to osteo-articular diseases. Although β₂-microglobulin (β2-m) is the major structural component of β2-m amyloid fibrils, the initiation of amyloid formation is not clearly understood. Here, we have identified procollagen C-proteinase enhancer-1 (PCPE-1) as a new interacting protein with β2-m by screening a human synovium cDNA library. The interaction of β2-m with full-length PCPE-1 was confirmed by immunoprecipitation, solid-phase binding and pull-down assays. By yeast two-hybrid analysis and pull-down assay, β2-m appeared to interact with PCPE-1 via the NTR (netrin-like) domain and not via the CUB (C1r/C1s, Uegf and BMP-1) domain region. In synovial tissues derived from hemodialysis patients with DRA, β2-m co-localized and formed a complex with PCPE-1. β2-m did not alter the basal activity of bone morphogenetic protein-1/procollagen C-proteinase (BMP-1/PCP) nor BMP-1/PCP activity enhanced by PCPE-1. PCPE-1 did not stimulate β2-m amyloid fibril formation from monomeric β2-m in vitro under acidic and neutral conditions as revealed by thioflavin T fluorescence spectroscopy and electron microscopy. Since PCPE-1 is abundantly expressed in connective tissues rich in type I collagen, it may be involved in the initial accumulation of β2-m in selected tissues such as tendon, synovium and bone. Furthermore, since such preferential deposition of β2-m may be linked to subsequent β2-m amyloid fibril formation, the disruption of the interaction between β2-m and PCPE-1 may prevent β2-m amyloid fibril formation and therefore PCPE-1 could be a new target for the treatment of DRA.