Lipopolysaccharide Increases the Expression of Multidrug Resistance-Associated Protein 1 (ABCC1) in Macrophages

Content Provider	Semantic Scholar
Author	Silverstein, Peter S. Audus, Kenneth L. Qureshi, Nilofer Kumar, Anil
Copyright Year	2014
Abstract	Multidrug resistance-associated protein 1 (MRP-1) is a ubiquitously expressed member of the ATP-binding cassette transporter family. MRP-1 is one of the primary transporters of glutathione and glutathione conjugates. This protein also transports antiretroviral therapeutics, such as HIV-1 protease inhibitors (PI). We hypothesized that inflammatory mediators that activate macrophages would modify the expression and activity of MRP-1 in macrophages. Real time PCR assays western blots and calcein efflux assays were used to show that exposure of macrophage cell line RAW 264.7 to LPS increased expression of MRP-1 at the level of mRNA and protein, as well as at the level of functional activity. Treatment of macrophages with LPS resulted in 2-fold increases of MRP-1 expression or functional activity. LPS-mediated increases in calcein efflux were repressed by the MRP-specific inhibitor MK-571. These results suggest that the effectiveness of HIV-1 PI therapy may be compromised by the presence of opportunistic infections. ATP-binding cassette (ABC) transporters are a large and diverse family of proteins in which translocation of both endogenous and xenobiotic compounds is coupled to the hydrolysis of ATP. These transporters function in drug absorption, distribution and excretion. MRP-1, which is the best characterized transporter in the ABCC family, transports organic anions. MRP-1 is expressed fairly ubiquitously, including tissues such as peripheral blood mononuclear cells, kidney, brain microvascular endothelial cells and testis (Leslie et al., 2005). It has been demonstrated that MRP-1 transports glutathione (GSH), glutathione conjugates and glutathione disulfide (GSSG) (Leier et al., 1996). Glutathione is not only a substrate of MRP-1, but it is also capable of modulating transport of other compounds by MRP-1 (Leslie et al., 2005). The interactions between GSH and MRP-1 are functionally complex, and at present, not completely understood. Address for correspondence: Peter S. Silverstein, Ph.D., Division of Pharmacology and Toxicology, School of Pharmacy, University of Missouri-Kansas City, Kansas City, MO 64108; Ph. (816) 235-1792; Fax: (816) 235-1776; Silversteinp@umkc.edu. NIH Public Access Author Manuscript J Neuroimmune Pharmacol. Author manuscript; available in PMC 2014 June 10. Published in final edited form as: J Neuroimmune Pharmacol. 2010 December ; 5(4): 516–520. doi:10.1007/s11481-009-9180-4. N IH -P A A uhor M anscript N IH -P A A uhor M anscript N IH -P A A uhor M anscript Due to its role in transport of GSH/GSSG, MRP-1 activity is a major determinant of intracellular redox status. Several independent investigations have demonstrated that MRP-1 expression is elevated in response to inducers that include oxidative stress. Both βglutamylcysteine synthetase, the rate limiting enzyme in GSH synthesis, and MRP-1show increased expression levels in response to prooxidants such as tertbutylhydroquinone (tBHQ) (Yamane et al., 1998). It is of particular note that exposure to the prooxidants increased the generation of reactive oxygen intermediates (ROI). Primary cultures of rat astrocytes have also been shown to express increased levels of MRP-1 in response to exposure to the HIV-1 viral envelope protein gp120. Exposure of these cells to gp120 induced ROI, as well as increased expression of MRP-1at the levels of mRNA, protein and functional expression (Ronaldson and Bendayan, 2008). HIV-1 Tat protein has also been demonstrated to induce MRP-1 expression in mouse brain microvascular endothelial cells (Hayashi et al., 2006). Previous studies have demonstrated the presence of functional MRP-1 in macrophages and microglial cells (Cao et al., 1992; Dallas et al., 2004). Due to the pivotal role of macrophages in various infectious diseases, our laboratory has sought to determine the effects of lipopolysaccharide (LPS) on MRP-1 expression in terms of mRNA and protein levels, as well as in terms of functional activity. Our working hypothesis is that LPS will significantly alter the expression and function of MRP-1 in a mouse macrophage cell line. Our results demonstrate that exposure to LPS increases MRP-1 expression in macrophages at the levels of mRNA, protein and functional expression.
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