Caveolae-mediated endocytosis of extracellular QSOX1b modulates the migration of fibroblasts.

Quiescin/sulfhydryl oxidase (QSOX1) is a secreted flavoprotein that modulates cellular proliferation, migration and adhesion, roles attributed to its ability to organize the extracellular matrix. We previously showed that exogenously added QSOX1b induces smooth muscle cells migration in a process that depends on its enzymatic activity and that is mediated by hydrogen peroxide derived from Nox1, a catalytic subunit of NAD(P)H oxidases. Here, we report that exogenous QSOX1b also stimulates the migration of L929 fibroblasts and that this effect is regulated by its endocytosis. The use of endocytosis inhibitors and caveolin 1-knockdown demonstrated that this endocytic pathway is caveola-mediated. QSOX1b colocalized with Nox1 in intracellular vesicles, as detected by confocal fluorescence, suggesting that extracellular QSOX1b is endocytosed with the transmembrane Nox1. These results reveal that endosomal QSOX1b is a novel intracellular redox regulator of cell migration.

Quiescin/sulfhydryl oxidase 1b (QSOX1b) induces migration and proliferation of vascular smooth muscle cells by distinct redox pathways.

Quiescent and contractile VSMC can switch to proliferative and migratory phenotype in response to growth factors and cytokines, an effect underscored by Nox family NADPH oxidases, particularly Nox1. We previously showed that quiescin/sulfhydryl oxidase 1 (QSOX1) has a role in neointima formation in balloon-injured rat carotid. Here, we investigated the intracellular redox mechanisms underlying these effects in primary VSMC. Our results show that exogenous incubation with wild type QSOX1b (wt QSOX), or with secreted QSOX1, but not with the inactive C452S QSOX 1b (C452S QSOX) or secreted inactive C455S QSOX1, induces VSMC migration and chemotaxis. PEG-catalase (PEG-CAT) prevented, while PEG-superoxide dismutase (PEG-SOD) increased migration induced by wt QSOX. Moreover, wt QSOX-induced migration was abrogated in NOX1-null VSMC. In contrast, both wt QSOX and C452S QSOX, and both secreted QSOX1 and C455S QSOX1, induce cell proliferation. Such effect was unaltered by PEG-CAT, while being inhibited by PEG-SOD. However, QSOX1-induced proliferation was not significantly affected in NOX1-null VSMC, compared with WT VSMC. These results indicate that hydrogen peroxide and superoxide mediate, respectively, migration and proliferation. However, Nox1 was required only for QSOX1-induced migration. In parallel, QSOX1-induced proliferation was independent of its redox activity, although mediated by intracellular superoxide.

The flavo-oxidase QSOX1 supports vascular smooth muscle cell migration and proliferation: Evidence for a role in neointima growth.

Quiescin sulfhydryl oxidase 1 (QSOX1) is a flavoenzyme largely present in the extracellular milieu whose physiological functions and substrates are not known. QSOX1 has been implicated in the regulation of tumor cell survival, proliferation and migration, in addition to extracellular matrix (ECM) remodeling. However, data regarding other pathophysiological conditions are still lacking. Arterial injury by balloon catheter is an established model of post-angioplasty restenosis. This technique induces neointima formation due to migration and proliferation of vascular smooth muscle cells (VSMC), followed by ECM synthesis and remodeling. Here, we show that QSOX1 knockdown inhibited VSMC migration and proliferation in vitro. In contrast, QSOX1 overexpression stimulated these processes. While migration could be induced by the incubation of cells with the active recombinant QSOX1, proliferation was induced by addition of the active and also of an inactive mutant QSOX1 protein. The proliferation induced by both recombinants was independent of intracellular hydrogen peroxide and dependent of the MEK/ERK pathway. To recapitulate in vivo VSMC pathophysiology, balloon-induced arterial injury was performed. The expression of QSOX1 in the neointimal layer of balloon-injured rat carotids was high and peaked at 14 days post-injury. In vivo QSOX1 knockdown led to a significant decrease in PCNA expression at day 14 post-injury and a decreased intima/media area ratio at day 21 post-injury, compared with scrambled siRNA transfection. In summary, our findings demonstrate that QSOX1 induces VSMC migration and proliferation in vitro and contributes to neointima thickening in balloon-injured rat carotids.