Multidrug resistance-associated protein 4 regulates cAMP-dependent signaling pathways and controls human and rat SMC proliferation

Abstract

The second messengers cAMP and cGMP can be degraded by specific members of the phosphodiesterase superfamily or by active efflux transporters, namely the multidrug resistance-associated proteins (MRPs) MRP4 and MRP5. To determine the role of MRP4 and MRP5 in cell signaling, we studied arterial SMCs, in which the effects of cyclic nucleotide levels on SMC proliferation have been well established. We found that MRP4, but not MRP5, was upregulated during proliferation of isolated human coronary artery SMCs and following injury of rat carotid arteries in vivo. MRP4 inhibition significantly increased intracellular cAMP and cGMP levels and was sufficient to block proliferation and to prevent neointimal growth in injured rat carotid arteries. The antiproliferative effect of MRP4 inhibition was related to PKA/CREB pathway activation. Here we provide what we believe to be the first evidence that MRP4 acts as an independent endogenous regulator of intracellular cyclic nucleotide levels and as a mediator of cAMP-dependent signal transduction to the nucleus. We also identify MRP4 inhibition as a potentially new way of preventing abnormal VSMC proliferation. Introduction cAMP and cGMP are second messengers that relay external signals to downstream effector proteins. The most common targets are cAMP-dependent PKA and cGMP-dependent PKG, which regulate a large number of processes by phosphorylating target proteins. In addition to PKA, recent evidence has highlighted a major role for guanine-nucleotide exchange factors for Rap proteins (namely EPAC1 and EPAC2) (1) in mediating cAMP signaling. cAMP and cGMP also act by binding certain ion channels (2). Signaling events triggered by extracellular stimuli arise from an ingenious system of regulation that involves the production and elimination of intracellular cyclic nucleotides. Classically, cyclic nucleotide elimination has been attributed to hydrolysis mediated by cyclic nucleotide phosphodiesterases (PDEs). PDEs constitute a large superfamily of enzymes encoded by several genes with tissue-specific expression of a large number of splice variants (3). In several models, including VSMCs, PDEs have been shown to regulate the amplitude and duration of intracellular cyclic nucleotide signaling (4, 5). For instance, sildenafil, a selective PDE5 inhibi-

Blockade of Multidrug Resistance-Associated Proteins Aggravates Acute Pancreatitis and Blunts Atrial Natriuretic Factor’s Beneficial Effect in Rats: Role of MRP4 (ABCC4)

“…MRP4 (ATP-binding cassette sub-family C member 4 [ABCC4]) is a member of the multidrug resistance proteins (MRPs) belonging to the C group of the ATP-binding cassette (ABC) protein superfamily, which functions as an energy-dependent, transmembrane efflux transporter. Compelling evidence supports that cAMP extrusion through MRP4 in several cell types provides a complementary mechanism to the phosphodiesterases (PDEs) as modulators of the intracellular concentration of the second messenger (6)(7)(8)(9)(10). In isolated pancreatic acini, we found that secretin-induced cAMP is extruded by ANF through NPR-C receptors coupled to the PLC/PKC pathway, thus restricting its intracellular accumulation.…”

Diabetes Induces Aberrant DNA Methylation in the Proximal Tubules of the Kidney

“…PT cells obtained from the diabetic and control mice showed a rather similar DNA methylation patterns, but the methylation pattern significantly differed among the eight genes with potentially functional roles (Table 1, Supplemental Figure 3). [16][17][18][19][20][21][22][23][24] Quantitative RT-PCR analysis demonstrated that the mRNA expressions of these genes in the PT cells were significantly different between the diabetic and control mice ( Table 1, Supplemental Figure 3). An inverse correlation between expression and methylation was seen at these loci except for Met.…”

Relax

“…7 Interestingly, a recent study describes that knockdown of MRP4 in smooth muscle cells increases cAMP and cGMP intracellular levels and blocks cell proliferation. 9 However, the functional relevance of MRP4 in smooth muscle relaxation has not been explored yet.…”