Dendritic cells require multidrug resistance protein 1 (ABCC1) transporter activity for differentiation.

Dendritic cells (DC) express the ATP-binding cassette (ABC) transporters P-glycoprotein (ABCB1) and multidrug resistance protein 1 (MRP1; ABCC1). Functionally, both these transporters have been described to be required for efficient DC and T cell migration. In this study, we report that MRP1 activity is also crucial for differentiation of DC. Inhibition of MRP1, but not P-glycoprotein, transporter activity with specific antagonists during in vitro DC differentiation interfered with early DC development. Impaired interstitial and Langerhans DC differentiation was characterized by 1) morphological changes, reflected by dropped side scatter levels in flow cytometric analysis and 2) phenotypic changes illustrated by maintained expression of the monocytic marker CD14, lower expression levels of CD40, CD86, HLA-DR, and a significant decrease in the amount of cells expressing CD1a, CD1c, and Langerin. Defective DC differentiation also resulted in their reduced ability to stimulate allogeneic T cells. We identified the endogenous CD1 ligands sulfatide and monosialoganglioside GM1 as MRP1 substrates, but exogenous addition of these substrates could not restore the defects caused by blocking MRP1 activity during DC differentiation. Although leukotriene C(4) was reported to restore migration of murine Mrp1-deficient DC, the effects of MRP1 inhibition on DC differentiation appeared to be independent of the leukotriene pathway. Though MRP1 transporter activity is important for DC differentiation, the relevant MRP1 substrate, which is required for DC differentiation, remains to be identified. Altogether, MRP1 seems to fulfill an important physiological role in DC development and DC functions.

Multidrug-resistant tumor cells remain sensitive to a recombinant interleukin-4-Pseudomonas exotoxin, except when overexpressing the multidrug resistance protein MRP1.

Tumor cells may become resistant to conventional anticancer drugs through the occurrence of transmembrane transporter proteins such as P-glycoprotein (ABCB1), breast cancer resistance protein (ABCG2), or members of the multidrug resistance-associated protein family (MRP1-MRP5; ABCC1-ABCC5). In this report, we studied whether tumor cells that are cytostatic drug resistant because of overexpression of one of the above mentioned proteins are sensitive to a new anticancer agent, interleukin-4 toxin (IL-4 toxin). IL-4 toxin is a fusion protein composed of circularly permuted IL-4 and a truncated form of Pseudomonas exotoxin (PE) [IL-4(38-37)-PE38KDEL]. Ninety-six-h cytotoxicity assays and 10-day clonogenic assays showed that drug-selected multidrug resistant (MDR) tumor cells that overexpress P-glycoprotein or breast cancer resistance proteins are still sensitive to IL-4 toxin. Also, tumor cells transfected with cDNA for MRP2-5 showed no resistance, or marginal resistance, only to the toxin as compared with the parent cells. In contrast, MRP1-overexpressing cells, both drug selected and MRP1 transfected, are clearly resistant to IL-4 toxin with resistance factors of 4.3 to 8.4. MRP1-overexpressing cells were not resistant to PE itself. IL-4 toxin resistance in MRP1-overexpressing cells could be reversed by the MRP1 inhibitors probenecid or MK571 and were not affected by glutathione depletion by DL-buthionine-S,R-sulfoximine. In a transport assay using plasma membrane vesicles prepared from MRP1-overexpressing cells, IL-4 toxin and IL-4, but not PE, inhibited the translocation of the known MRP1 substrate 17beta-estradiol 17-(beta-D-glucuronide) (E(2)17betaG). These data suggest that MRP1-overexpressing cells are resistant to IL-4 toxin because of extrusion of this agent by MRP1. Still, the results of this study demonstrate that IL-4 toxin effectively kills most MDR tumor cells and, therefore, represents a promising anticancer drug.

Up-regulation of drug resistance-related vaults during dendritic cell development.

P-glycoprotein (Pgp) and vaults are associated with multidrug resistance in tumor cells, but their physiological functions are not yet clear. Pgp, the prototypical transmembrane transporter molecule, may also facilitate the migration of skin dendritic cells (DC). Vaults--ribonucleoprotein cell organelles, frequently overexpressed in Pgp-negative drug-resistant tumor cells--have also been associated with intracellular transport processes. Given the pivotal role of DC in dealing with exposure to potentially harmful substances, the present study was set out to examine the expression of Pgp and vaults during differentiation and maturation of DC. DC were obtained from different sources, including blood-derived monocytes, CD34(+) mononuclear cells, and chronic myeloid leukemia cells. Whereas flow cytometric and immunocytochemical analyses showed slightly augmented levels of Pgp, up-regulation of vault expression during DC culturing was strong, readily confirmed by Western blotting, and independent of the source of DC. In further exploring the functional significance of vault expression, it was found that supplementing DC cultures with polyclonal or mAbs against the major vault protein led to lower viabilities of LPS- or TNF-alpha-matured monocytes-DC. Moreover, expression of critical differentiation, maturation, and costimulatory molecules, including CD1a and CD83, was reduced and their capacity to induce Ag-specific T cell proliferative and IFN-gamma release responses was impaired. These data point to a role for vaults in both DC survival and functioning as APC.