Furin: a mammalian subtilisin/Kex2p-like endoprotease involved in processing of a wide variety of precursor proteins

Abstract

Limited endoproteolysis of inactive precursor proteins at sites marked by paired or multiple basic amino acids is a widespread process by which biologically active peptides and proteins are produced within the secretory pathway in eukaryotic cells. The identification of a novel family of endoproteases homologous with bacterial subtilisins and yeast Kex2p has accelerated progress in understanding the complex mechanisms underlying the production of the bioactive materials. Seven distinct proprotein convertases of this family (furin, PC2, PC1/PC3, PC4, PACE4, PC5/PC6, LPC/PC7/PC8/SPC7) have been identified in mammalian species, some having isoforms generated via alternative splicing. The family has been shown to be responsible for conversion of precursors of peptide hormones, neuropeptides, and many other proteins into their biologically active forms. Furin, the first proprotein convertase to be identified, has been most extensively studied. It has been shown to be expressed in all tissues and cell lines examined and to be mainly localized in the trans-Golgi network, although some proportion of the furin molecules cycle between this compartment and the cell surface. This endoprotease is capable of cleaving precursors of a wide variety of proteins, including growth factors, serum proteins, including proteases of the blood-clotting and complement systems, matrix metalloproteinases, receptors, viral-envelope glycoproteins and bacterial exotoxins, typically at sites marked by the consensus Arg-Xaa-(Lys/Arg)-Arg sequence. The present review covers the structure and function of mammalian subtilisin/Kex2p-like proprotein convertases, focusing on furin (EC 3.4.21.85).

Xenopus Lefty requires proprotein cleavage but not N‐linked glycosylation to inhibit nodal signaling

“…Calcium-dependent serine endoproteases of the subtilisin-like proprotein convertase family (SPCs) recognize the consensus R-X-X-R motif found in many intercellular signaling molecule proproteins, including Nodal and Lefty (Nakayama, 1997;Molloy et al, 1999). SPCs, of which there are seven distinct mammalian family members, have been shown to localize to the intracellular secretory network as well as having been detected as associated with the extracellular matrix.…”

“…SPCs, of which there are seven distinct mammalian family members, have been shown to localize to the intracellular secretory network as well as having been detected as associated with the extracellular matrix. SPCs may, therefore, work in both a cellautonomous and non-cell-autonomous manner (Nakayama, 1997;Molloy et al, 1999). SPC-mediated cleavage releases the active ligand during the maturation of TGF␤ proteins (Kingsley, 1994;Nakayama, 1997;Cui et al, 1998;Constam and Robertson, 1999;Molloy et al, 1999;Ulloa et al, 2001;Beck et al, 2002;Sakuma et al, 2002;Ben-Haim et al, 2006).…”

“…SPCs may, therefore, work in both a cellautonomous and non-cell-autonomous manner (Nakayama, 1997;Molloy et al, 1999). SPC-mediated cleavage releases the active ligand during the maturation of TGF␤ proteins (Kingsley, 1994;Nakayama, 1997;Cui et al, 1998;Constam and Robertson, 1999;Molloy et al, 1999;Ulloa et al, 2001;Beck et al, 2002;Sakuma et al, 2002;Ben-Haim et al, 2006). Although mammalian Lefty molecules have been shown to undergo proteolytic cleavage by SPC1, SPC4, and SPC6 in several transfected cell lines, the endogenous SPC enzyme(s) that is involved in proteolytic processing of Lefty in vivo is currently not known (Ulloa et al, 2001;Beck et al, 2002;Sakuma et al, 2002).…”

Replicating retroviral vectors mediating continuous production and secretion of therapeutic gene products from cancer cells

“…The results presented here extend these observations by demonstrating that RCR vectors created by strategical selection of a furin site from randomized libraries can be stable over Z12 cycles of infection. Since furin is a cellular protease involved in the processing of various secretory proteins in most eukarytic Protein delivery by replicating retrovirus C Finger et al cells, 22,[34][35][36] it is conceivable that a variety of peptides including the ones tested here fused to the Env protein via an RLRRGSR cleavage site (L36-scFv, 7A5-scFv, GM-CSF) can be efficiently cleaved off from chimeric Env protein without inhibiting viral infection, as assessed here in a variety of cell types (Figs 2-4). Hence, RCR vector replication in susceptible cells is accompanied by a tremendous amplification of gene distribution in target cells and delivery of secretory bioactive proteins.…”

“…21 During production of the Env protein in infected cells, the EGF molecule is cleaved off during transport to the cell surface, whereby the cleaved EGF-domain is most likely directed into the secretory pathway. Given the fact that furin is a highly conserved, Golgi-anchored processing enzyme that is present in most eukaryotic cells, 22 any protein domain linked to the MLV Env protein via a furin-cleavable linker peptide would likely be produced in and secreted from infected cells. By adapting this system, reliable MLV-based RCR vectors suitable for delivering secretory therapeutic proteins inside a variety of tumors could possibly be generated.…”