TRANSPORT OF GLUTATHIONE CONJUGATES INTO SECRETORY VESICLES IS MEDIATED BY THE MULTIDRUG-RESISTANCE PROTEIN-1

Intracellular glutathione-conjugate transport was evaluated in the hum an small cell lung carcinoma cell line GLC(4) with low multidrug resis tance protein (MRP1) expression and its 300x doxorubicin-resistant, MR P1-over-expressing, GLC(4)-Adr subline. Transport of non-toxic concent rations of monochlorobimane and 5-chloro-methyl fluorescein diacetate was evaluated using fluorescence microscopy. After exposure to these c ompounds, fluorescence was observed especially in intracellular vesicl es in GLC(4)-Adr. Immunotransmission electron microscopy showed that M RP1 was present in the vesicle membranes and plasma membrane, while in side the vesicles the glutathione conjugate of 1-chloro-2,4-dinitroben zene could be detected. Experiments with brefeldin A, which induces ar rest in vesicle release from the Golgi complex, indicated that these v esicles may originate from the trans-Golgi network, In GLC(4)-Adr cell s, doxorubicin also was transported in vesicles, with an arrest in ves icle release from the Golgi complex. Our results indicate that MRP1 fu nctions as a glutathione-conjugate transporter not only at the plasma membrane but also in intracellular secretory vesicles. (C) 1998 Wiley- Liss, Inc.