Vitamin C inhibits diethylmaleate-induced L-cystine transport in human vascular smooth muscle cells

Adaptive increases in intracellular glutathione (GSH) in response to oxidative stress are mediated by induction of L-cystine uptake via the anionic amino acid transport system x(c)(-). The recently cloned transporter xCT forms a heteromultimeric complex with the heavy chain of 4F2 cell surface antigen (4F2hc/CD98). Depletion of GSH by the electrophile diethylmaleate (DEM) induces the activity and expression of xCT in peritoneal macrophages. We here examine the effects of vitamin C on induction of xCT by DEM in human umbilical artery smooth muscle cells. DEM caused time- (3-24 h) and concentration- (25-100 microM) dependent increases in L-cystine transport, with GSH depleted by 50% after 6 h and restored to basal values after 24 h. xCT mRNA levels increased after 4 h DEM treatment with negligible changes detected for 4F2hc mRNA. DEM caused a rapid (5-30 min) phosphorylation of p38(MAPK). Inhibition of p38(MAPK) by SB203580 (10 microM) enhanced DEM-induced increases in L-cystine transport and GSH, whereas inhibition of p42/p44(MAPK) (PD98059, 10 microM) had no effect. Pretreatment of cells with vitamin C (100 microM, 24 h) attenuated DEM-induced adaptive increases in L-cystine transport and GSH levels. Inhibition of p38(MAPK), but not p42/p44(MAPK), reduced the cytoprotective action of vitamin C. Our findings suggest that DEM induces activation of xCT via intracellular signaling pathways involving p38(MAPK), and that vitamin C, in addition to its antioxidant properties, may modulate this signaling pathway to protect smooth muscle cells from injury.