Protein disulfide isomerase (PDI) / NADPH oxidase interaction is a pathway bridging unfolded protein response (UPR) and oxidative stress in vascular smooth muscle cells (VSMC)

Abstract

We recently described close interaction between NADPH oxidase and endoplasmic reticulum-resident PDI in VSMC. We hypothesized that such pathway connects oxidative stress to UPR. UPR inducer tunicamycin (Tn) (2microg/ml) led to phosphorylation of translation initiator eIF2alfa at 2hs and overexpression of KDEL proteins at 12 hs, together with procaspase 12 cleavage. Cell loss occurred after 48h. Tn led to increased VSMC superoxide levels (HPLC/hydroethidine) at 4 hs and decreased GSH/GSSG ratio, indicating oxidative stress at levels to known oxidase agonist angiotensin-II (100nM). Superoxide dismutase activity decreased 50% at 14 hs. Also, UPR induction by a novel TAP-directed peptide bearing N-glycosylation sites strongly increased superoxide levels (200%) after 2 hs and GRP78 expression after 12hs. UPR disruption by overexpression of GADD34 gene promoting eIF2alfa dephosphorylation reduced Tn-mediated superoxide production, thus confirming that UPR triggers VSMC oxidative stress. Tn induced concentration and time-dependent increase in membrane NADPH oxidase activity, totally prevented by brefeldin A. Such role for protein traffic in oxidase activation was supported by PDI shift to membranes. VSMC membrane incubation with PDI inhibitors (Bacitracin and Ab-PDI) strongly decreased NADPH oxidase activity. Relevance of such interactions was evidenced in neointimal cells, which co-overexpressed NADPH oxidase, PDI and UPR markers. Thus, PDI/NADPH oxidase interaction couples UPR and oxidative stress. (FAPESP)