INDUCTION OF CYSTINE TRANSPORT VIA SYSTEM X(C)(-) AND MAINTENANCE OF INTRACELLULAR GLUTATHIONE LEVELS IN PANCREATIC ACINAR AND ISLET-CELL LINES

The relationship between L-cystine transport and intracellular glutath ione (GSH) levels was investigated in cultured pancreatic AR42J acinar and beta TC3 islet cells exposed to diethylmaleate, an electrophilic agent known to activate cellular antioxidant responses. Cystine transp ort was mediated predominantly by the Na+-independent anionic amino ac id transport system x(c)(-), with influx inhibited potently by glutama te and homocysteate but unaffected by cationic or neutral amino acids. Saturable cystine transport was 10-fold higher in AR42J (531 pmol (mg protein)(-1) min(-1)) than in beta TC3 (49 pmol (mg protein)(-1) min( -1)) cells, and GSH levels were higher in AR42J cells. Treatment with 9-mercaptoethanol increased GSH levels in beta TC3 cells from 7.5 to 3 6 nmol (mg protein)(-1), whilst the GSH content in AR42J cells (64 nmo l (mg protein)(-1)) was not altered significantly. Incubation of AR42J or beta TC3 cells with homocysteate (2.5 mM, 0-48 h), a competitive i nhibitor of cystine transport via system x(c)(-), reduced intracellula r GSH levels and resulted in a time-dependent (6-24 h) induction of sy stem x(c)(-) transport activity. Treatment of AR42J cells with diethyl maleate (100 mu M, 0-48 h) resulted in a time- (5-10 h) and protein sy nthesis-dependent induction of cystine transport, with intracellular G SH levels initially decreasing and then increasing 2-fold above contro l levels after 24 h. Diethylmaleate also depressed GSH levels in beta TC3 cells, but cystine transport was not elevated significantly. In bo th AR42J and beta TC3 cells, inhibition of gamma-glutamyl cysteine syn thetase by buthionine sulphoximine (100 mu M, 24 h) reduced GSH levels but had no effect on cystine transport. The present findings establis h that induction of system x(c)(-) leads to changes in GSH levels in p ancreatic AR42J acinar and beta TC3 islet cells, with changes in the i ntracellular redox state stimulating transporter expression Induction of activity of system x(c)(-), together with adaptive increases in GSH synthesis in response to oxidative stress, may contribute to cellular antioxidant defences in pancreatic disease. (C) 1998 Elsevier Science B.V. All rights reserved.