OXIDATIVE STRESS LEADS TO A RAPID ALTERATION OF TRANSFERRIN RECEPTOR INTRAVESICULAR TRAFFICKING

Several studies have demonstrated that perturbations of intracellular oxidative balance play a key role in numerous physiological as well as pathological conditions leading to various morbidity states. In previ ous studies we have shown that the free radical inducer menadione rapi dly and specifically downmodulates the membrane transferrin in recepto r (TfR) by blocking receptor recycling. This modulation is due to rece ptor redistribution and not to receptor loss. Here we show that other oxidant; compounds, such as hydrogen peroxide, also induce a rapid dow nmodulation of membrane TfR and that pretreatment of cells with the an tioxidant, thiol supplier, N-acetylcysteine inhibits the downmodulatio n of these receptors elicited by either menadione or hydrogen peroxide . This observation suggests that intracellular thiol redox status may be a critical determinant of TfR downmodulation induced by oxidative s tress. Furthermore, immunocytochemical results show that, in menadione -treated cells, TfRs ape associated with the Golgi complex, where norm ally only 20% of total cellular TfRs is found and is mainly detected i nn the cytoplasm as scattered punctuations. Accordingly, menadione and hydrogen peroxide also elicited a downmodulation of low density lipop rotein receptor (LDLR) which mediates, like TfB, the transport of nutr ients to the cell and is endocytosed through clathrin-coated pits. Fin ally, experiments carried out using okadaic acid, an inhibitor of phos phatases, suggest that H2O2 and menadione downmodulate surface TfR via different biochemical pathways. Taken together these results suggest the existence of a potentially important protective mechanism through which iron uptake is prevented in oxidatively imbalanced cells. Iron u ptake can in fact ave rise to the formation of highly toxic hydroxyl r adicals reacting with hydrogen peroxide and leading to cytotoxicity. D ownmodulation of surface TfR may thus represent the physiological cont rol mechanism for reducing iron uptake in diverse pathological conditi ons including hypoxia-reperfusion injury, acquired immunodeficiency dr ome, and aging. (C) 1998 Academic Press.