Modulation of multidrug resistance protein (MRP1/ABCC1) expression: a novel physiological role for ouabain

Abstract

Besides being a (Na(+),K(+))-ATPase inhibitor, high doses of the hormone ouabain have also been reported to modulate both the expression and activity of proteins belonging to the ATP binding cassette family of transporters, such as ABCC7 (CFTR), ABCB1 (P-glycoprotein), and ABCC1 (MRP1). Although these proteins are present in the kidney, only ABCB1 has a putative physiological role in this organ, secreting endobiotics and xenobiotics. In the present work, we studied the relationship between ouabain and ABCC1 expression and function, aiming to establish a physiological role for ouabain. It was observed that prolonged (24 h) but not short (30 min) incubation with 1 nmol/L or higher ouabain concentrations decreased the expression of ABCC1 protein and induced its mRNA expression. This decrease was rapidly reversible, reaching control levels after incubation of cells in ouabain-free medium for 3 h, denoting a hormonal action. Moreover, concentrations equal or higher than 100 nmol/L ouabain also induced impairment of ABCC1 activity, increasing the accumulation of carboxyfluorescein diacetate, an ABCC1 fluorescent substrate. Because ouabain is now accepted as an endogenous hormone, our results suggest that ABCC1 is regulated by hormones related to body volume control, which may have implications for the treatment of hypertensive cancer patients. Moreover, providing ABCC1 is expressed in several other tissues, such as brain, testis, and the immune system, and is related to the transport of glutathione, it is possible that ouabain release may control a number of functions within these organs and tissues by modulating both the expression and the activity of ABCC1.

Diverse actions of ouabain and its aglycone ouabagenin in renal cells

“…The low expression of β subunit of Na-K-ATPase in Ma104 cells shown in the present work is in agreement with the low transepithelial resistance of this cell line in comparison to that of MDCK cells (Contreras et al 1995b). Why Ma104 cells possess altered α to β subunit ratio is not known at present, but the data obtained up to now suggest that the resistance of Ma104 cells to ouabain results from a multifactorial phenotype that relies on differential expression of Na-K-ATPase subunits, overexpression of proteins related to drug transport, specially ABCC1 (Valente et al 2007), and also the Fig. 6 Visualization of OUABDP binding to MDCK and Ma104 cells by fluorescence microscopy.…”

“…It is worthwhile to mention that ouabain also induces hormone-like responses in Ma104 cells, such as the inhibition of ABCC1 (or MRP1) expression in these cells in concentrations as low as 10 −9 M, where no inhibition of Na-K-ATPase can be detected (Valente et al 2007). Ouabain is a steroid hormone and the finding that its fluorescent analog OUABDP easily reaches the cytoplasm of this cell line raises the possibility that ouabain may conceivably reach the cytoplasm and trigger hormonal effects, probably binding to steroid receptors or, alternatively, to its own intracellular (yet unknown) receptor.…”

The A‐B‐C of small‐molecule ABC transport protein modulators: From inhibition to activation—a case study of multidrug resistance‐associated protein 1 (ABCC1)

“…Other natural compounds. One interesting report was made by Valente et al regarding the cardiac glycoside ouabain (Figure ), which induced MRP1 mRNA in MRP1‐overexpressing monkey embryonic kidney cells Ma104 by a factor of ~1.5‐2 between 10 pM and 10 µM . Strikingly, this increase in mRNA levels did not lead to increased protein levels.…”

ABCC1 Is Related to the Protection of the Distal Nephron against Hyperosmolality and High Sodium Environment: Possible Implications for Cancer Chemotherapy

“…Since the maintenance of intracellular GSH levels is closely associated with ABCC1 transport [34], [35] and given that MA104 and collecting duct cells express ABCC1 [14], [22], in the next experiments we tried to study a possible role of ABCC1 in the response of MA104 cells to NaCl and urea. However, when performing flow cytometry, we observed that NaCl lead to alterations in cell granularity (viewed by alterations in side scattering-SSC), with no changes in cell volume (viewed by alterations in forward scattering-FSC) as can be seen in Fig.…”

“…Cells were seeded onto 24 wells plates and the labeling assay was performed as described in a previous work from our group [22]. The polyclonal rabbit antibody A23 (Alexis Biochemicals, USA) and Alexa Fluor 488 (Invitrogen, USA) were used respectively as primary and fluorescent secondary antibodies.…”