The Multidrug Resistance-Associated Protein 4 (MRP4) Appears as a Functional Carrier of Prostaglandins Regulated by Oxytocin in the Bovine Endometrium

Abstract

Prostaglandins (PG) are involved in several female reproductive processes, and their action is regulated at the levels of biosynthesis, catabolism, and signal transduction. Facilitated transport across cell membranes emerges as an additional checkpoint regulating PG action. We have already reported on the influx transporter solute carrier organic anion transporting polypeptide (SLCO2A1) [PG transporter (PGT)] in relation to PG action in the bovine endometrium. In the present study, we report on the functional expression and regulation of multidrug resistance-associated protein 4 (MRP4)/ATP-binding cassette carrier 4, an alternate PG transporter belonging to the ATP-binding cassette carrier (ABC) family. We have found that MRP4 protein was present throughout the estrous cycle and exhibited a pattern of expression similar to that of PGT with maximal expression during early-mid luteal phase in the bovine endometrium. Functional expression and regulation of MRP4 was studied in vitro using the newly developed bovine endometrial epithelial bEEL and stromal CSC cell lines. Oxytocin (OT) stimulated PGF2α production and MRP4 mRNA and protein in a time- and dose-dependent manner but had no effect on PGT. OT induced preferred accumulation of PG outside the cells and secretion toward the basolateral side of polarized bEEL cells grown on membrane inserts. MK-571 and indomethacin, two documented inhibitors of MRP4 activity, blocked preferred accumulation of PG, but interferon-τ and NS-398 had no effect on MRP4 expression or the direction of PG transport. Our results suggest that MRP4 is a functional PG carrier under the regulation of OT in the bovine endometrium.

Polarised bovine endometrial epithelial cells vectorially secrete prostaglandins and chemotactic factors under physiological and pathological conditions

“…This is in contrast to a previous report, where polarised bovine epithelial cells treated with OT had predominantly basolateral accumulation of PGF, but not PGE (Asselin et al 1996). However, porcine endometrial epithelial cells and the bovine endometrial epithelial cell line, bEEL, reportedly have predominantly basolateral release of both PGE and PGF (Bowen et al 1996, Lacroix-Pepin et al 2011. Prostaglandins are charged anions that diffuse poorly across cell membranes, thus require facilitated transport by the prostaglandin transporter (PGT) and multidrug resistance-associated protein 4 (MRP4; Schuster 1998, Banu et al 2003, Tithof et al 2007, Lacroix-Pepin et al 2011.…”

“…However, porcine endometrial epithelial cells and the bovine endometrial epithelial cell line, bEEL, reportedly have predominantly basolateral release of both PGE and PGF (Bowen et al 1996, Lacroix-Pepin et al 2011. Prostaglandins are charged anions that diffuse poorly across cell membranes, thus require facilitated transport by the prostaglandin transporter (PGT) and multidrug resistance-associated protein 4 (MRP4; Schuster 1998, Banu et al 2003, Tithof et al 2007, Lacroix-Pepin et al 2011. In the bovine reproductive tract, PGT is predominantly, but not exclusively, localised to the basolateral membrane of endometrial epithelial cells, whereas stromal cells have diffuse membrane expression of PGT (Banu et al 2003), and MRP4 appears to be specifically involved in the basolateral release of PGF and PGE by bEEL cells (Lacroix-Pepin et al 2011).…”

“…Prostaglandins are charged anions that diffuse poorly across cell membranes, thus require facilitated transport by the prostaglandin transporter (PGT) and multidrug resistance-associated protein 4 (MRP4; Schuster 1998, Banu et al 2003, Tithof et al 2007, Lacroix-Pepin et al 2011. In the bovine reproductive tract, PGT is predominantly, but not exclusively, localised to the basolateral membrane of endometrial epithelial cells, whereas stromal cells have diffuse membrane expression of PGT (Banu et al 2003), and MRP4 appears to be specifically involved in the basolateral release of PGF and PGE by bEEL cells (Lacroix-Pepin et al 2011). Basolateral release of prostaglandins may direct the prostaglandins towards the utero-ovarian plexus, which is necessary for efficient transport of prostaglandins from the uterus to the ovary in ruminants (Niswender et al 2000, Banu et al 2005.…”

The ABCC4 membrane transporter modulates platelet aggregation

“…One strategy to reduce platelet aggregation is to inhibit platelet phosphodiesterases (PDEs). 1 PDEs catalyze the hydrolysis of 39,59-cAMP to inactive 59-AMP by cleaving the PDE bond. This antithrombotic approach elevates the intracellular platelet cyclic AMP (cAMP) and impairs platelet aggregation.…”

Introducing, OncoTarget

“…It has been reported that upregulation/overexpression of MRP4 in colorectal cancer tissues and cell lines is correlated to high extracellular level of PGE 2 , suggesting its capacity in transporting PGE 2 [18]. Indeed, MRP4 has been reported to transport PGE 2 in the bovine endometrium [19] and that MRP4 knockout mice showed reduced litter size [20]. Given the importance of ENaC-regulated COX-2/PGE 2 signaling in embryo implantation and the PGE 2 -transporting capacity of MRP4, we hypothesized that MRP4 might be involved in mediating the ENaCdependent signaling required for embryo implantation.…”