Endoproteolytic processing of integrin pro-α subunits involves the redundant function of furin and proprotein convertase (PC) 5A, but not paired basic amino acid converting enzyme (PACE) 4, PC5B or PC7

Abstract

Several integrin alpha subunits undergo post-translational endoproteolytic processing at pairs of basic amino acids that is mediated by the proprotein convertase furin. Here we ask whether other convertase family members can participate in these processing events. We therefore examined the endoproteolysis rate of the integrin subunits pro-alpha5, alpha6 and alphav by recombinant furin, proprotein convertase (PC)5A, paired basic amino acid converting enzyme (PACE)4, PC1, PC2 and PC7 in vitro and/or ex vivo after overexpression in LoVo cells that were deficient in furin activity. We found that 60-fold more PC1 than furin was needed to produce 50% cleavage of pro-alpha subunit substrates in vitro; the defective pro-alpha chain endoproteolysis in LoVo cells was not rescued by overexpression of PC1 or PC2. No endoproteolysis occurred with PC7 either in vitro or ex vivo, although similar primary sequences of the cleavage site are found in integrins and in proteins efficiently processed by PC7, which suggests that a particular conformation of the cleavage site is required for optimal convertase-substrate interactions. In vitro, 50% cleavage of pro-alpha subunits was obtained with one-third of the amount of PC5A and PACE4 than of furin. In LoVo cells, PC5A remained more active than furin, PACE4 activity was quite low, and PC5B, which differs from PC5A by a C-terminal extension containing a transmembrane domain, was very inefficient in processing integrin alpha-subunit precursors. In conclusion, these results indicate that integrin alpha-subunit endoproteolytic processing involves the redundant function of furin and PC5A and to a smaller extent PACE4, but not of PC1, PC2, PC5B or PC7.

The Proprotein Convertase PC5A and a Metalloprotease Are Involved in the Proteolytic Processing of the Neural Adhesion Molecule L1

“…Furin is relatively inefficient in processing L1 to yield a 140-kDa fragment, and other proprotein proteases do not cleave L1. A similar result was obtained for the processing of integrin pro-␣-subunits: PC5A is more active than furin, whereas PC1, PC2, PACE4, PC7, and PC5B are inactive (38). In addition, although furin and other proprotein convertases do not efficiently process members of the transforming growth factor-␤ superfamily, PC5A appears to be responsible for the in vivo processing of these proteins (49).…”

“…Coexpression of wild-type L1 with furin, PC1, PC2, PACE4, or PC7 showed no increase in the amount of the 140-kDa fragment (data not shown), confirming that PC5A is the most efficient L1-cleaving proprotein convertase. This difference in cleavage efficiency is not due to different expression levels of each proprotein convertase, as shown previously in other studies (38,41,42). In contrast to the expression of wild-type L1, no 140-kDa fragment was found in the cell pellet (Fig.…”

“…HEK293 cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum. For expression of the different proprotein convertases (37), HEK293 cells were infected with pMJ601 constructs carrying the cDNA inserts coding for mouse PC1, PC2, and PC5A; for rat PC7; and for human PACE4 and furin (38). After infection of cells with 1 plaque-forming units/cell for 2 h in 5 ml of phosphatebuffered saline and 0.01% bovine serum albumin, cells were maintained for 48 h in Dulbecco's modified Eagle's medium supplemented with 10% fetal calf serum.…”

Proprotein convertase furin/PCSK3 and atherosclerosis: New insights and potential therapeutic targets

“…The in vitro study showed that furin is present in THP-1-derived macrophages, and cell-surface expression of integrin a v b 3 is enhanced during the maturation of monocytes to macrophages. Moreover, furin was identified as the major a v convertases [67]. Microscopy studies have shown the co-localization of integrins a v b 3 and its ligand vitronectin in the atherosclerotic intima [68].…”

Inhibition of Proprotein Convertases Enhances Cell Migration and Metastases Development of Human Colon Carcinoma Cells in a Rat Model

“…Some integrin ␣ chains undergo a post-translational cleavage in their extracellular domain by furin and PC5A, two proprotein convertases (PCs) of the subtilisin/kexin family. 8,9 The role of this cleavage in integrin function remains unclear. Arguably, this post-translational processing of the ␣ chain is not required for ligand binding, 10 -12 but is essential for the signaling function of ␣6␤1 and ␣v␤5 integrins.…”