A possible role of multidrug resistance-associated protein (MRP) in basic fibroblast growth factor secretion by AIDS-associated Kaposi's sarcoma cells: a survival molecule?
Kaposi's sarcoma (KS) is considered a disorder of cytokines. Basic fibroblast growth factor (bFGF) is produced by AIDS-associated KS (AIDS-KS) cells and supports their growth in an autocrine and paracrine manner. bFGF lacks a signal sequence; therefore, its mechanism of secretion is unclear. In this study, we investigate the role of two important members of ATP-binding cassette transport proteins, the P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP), in the secretion of bFGF from AIDS-KS cells. Expression of P-gp and MRP was examined at both the protein and the mRNA levels by flow cytometry and RT-PCR respectively. Intracellular and secreted bFGF was measured by ELISA. AIDS-KS cells expressed MRP at both the mRNA and the protein levels; however, no P-gp expression was detected at either the mRNA or the protein level. Probenecid, a putative inhibitor of MRP efflux function, in a concentration-dependent manner, inhibited bFGF secretion, with a concomitant increase in intracellular bFGF, demonstrating that probenecid blocks bFGF secretion without inhibiting its synthesis. In addition, probenecid induced apoptosis in AIDS-KS cells. AIDS-KS cells expressed fas, bcl-2, and bcl-xL genes but lacked fasL and bax gene expression. These data suggest that bFGF is secreted from AIDS-KS cells via a probencid-sensitive transporter, most likely in MRP. Furthermore, probenecid appears to induce apoptosis in AIDS-KS cells by depriving them of the growth promoting activity of bFGF. These data suggest that MRP may play a role as a survival molecule in AIDS-KS cells.
Department of Medicine, University of California, Irvine 92697, USA. sgupta@uci.edu
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Gupta
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Aggarwal
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Nakamura
D017088:AIDS-Related Opportunistic Infections; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D017209:Apoptosis / Q000235:genetics*; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D052138:Genes, Neoplasm; D006801:Humans; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D016133:Polymerase Chain Reaction; D011339:Probenecid / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D012514:Sarcoma, Kaposi / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology*; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D016222:Fibroblast Growth Factor 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011339:Probenecid; D012333:RNA, Messenger