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A possible role of multidrug resistance-associated protein (MRP) in basic fibroblast growth factor secretion by
S Gupta1, S Aggarwal, S Nakamura
1Department of Medicine, University of California, Irvine 92697, USA. sgupta@uci.edu
Abstract:
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.
Insights
Multidrug resistance-associated protein (MRP) facilitates basic fibroblast growth factor (bFGF) secretion in AIDS-associated Kaposi
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Kaposi's sarcoma (KS) is a cytokine-mediated disorder.
- Basic fibroblast growth factor (bFGF) promotes AIDS-associated KS (AIDS-KS) cell growth.
- The secretion mechanism of bFGF, lacking a signal sequence, is unclear.
Purpose of the Study:
- To investigate the role of ATP-binding cassette transporters, P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP), in bFGF secretion from AIDS-KS cells.
- To determine if MRP is involved in bFGF transport.
Main Methods:
- Examined P-gp and MRP expression at mRNA and protein levels using RT-PCR and flow cytometry.
- Measured intracellular and secreted bFGF via ELISA.
- Assessed the effect of probenecid, an MRP inhibitor, on bFGF secretion and apoptosis.
Main Results:
- AIDS-KS cells expressed MRP but not P-gp at both mRNA and protein levels.
- Probenecid inhibited bFGF secretion in a dose-dependent manner, increasing intracellular bFGF.
- Probenecid induced apoptosis in AIDS-KS cells.
Conclusions:
- bFGF is secreted from AIDS-KS cells via a probenecid-sensitive transporter, likely MRP.
- Probenecid induces apoptosis by blocking bFGF secretion, suggesting MRP acts as a survival molecule in AIDS-KS.