IRIP, a New Ischemia/Reperfusion-Inducible Protein That Participates in the Regulation of Transporter Activity

Abstract

We report the identification and characterization of a new ischemia/reperfusion-inducible protein (IRIP), which belongs to the SUA5/YrdC/YciO protein family. IRIP cDNA was isolated in a differential display analysis of an ischemia/reperfusion-treated kidney RNA sample. Mouse IRIP mRNA was expressed in all tissues tested, the highest level being in the testis, secretory, and endocrine organs. Besides ischemia/reperfusion, endotoxemia also activated the expression of IRIP in the liver, lung, and spleen. The transporter regulator RS1 was identified as an IRIP-interacting protein in yeast two-hybrid screening. The interaction between IRIP and RS1 was further confirmed in coimmunoprecipitation assays. A possible role of IRIP in regulating transporter activity was subsequently investigated. IRIP overexpression inhibited endogenous 1-methyl-4-phenylpyridinium (MPP ؉ ) uptake activity in HeLa cells. The activities of exogenous organic cation transporters (OCT2 and OCT3), organic anion transporter (OAT1), and monoamine transporters were also inhibited by IRIP. Conversely, inhibition of IRIP expression by small interfering RNA or antisense RNA increased MPP ؉ uptake. We measured transport kinetics of OCT2-mediated uptake and demonstrated that IRIP overexpression significantly decreased V max but did not affect K m . On the basis of these results, we propose that IRIP regulates the activity of a variety of transporters under normal and pathological conditions.

The Sua5 Protein Is Essential for Normal Translational Regulation in Yeast

“…1A). The SUA5 homolog in higher eukaryotes is known as IRIP (ischemia and reperfusion inducible protein) (10,29). The ectopic expression of mouse IRIP from the yeast TEF1 promoter also partially suppressed the slow-growth defect of the sua5⌬ strain, although the rescue was weaker than that observed with yrdC (Fig.…”

Role of the Transporter Regulator Protein (RS1) in the Modulation of Concentrative Nucleoside Transporters (CNTs) in Epithelia

“…In fact, IRIP (which apparently is also ubiquitous in mammals) similarly down-regulates, when overexpressed, OCT2 activity. This inhibitory effect was also shown for related proteins belonging to the SLC22 gene family, such as OCT3 and organic anion transporter 1, and for unrelated transporters such as the dopamine, norepinephrine, and serotonin transporters (Jiang et al, 2005). IRIP was shown to modulate expression levels at the plasma membrane for the multidrug resistance transporter protein P-glycoprotein, thus modulating doxorubicin-induced cytotoxicity in HeLa cells (Prokopenko and Mirochnitchenko, 2009).…”

“…Whether RS1 similarly modulates drug efflux remains to be established. However, the effects of RS1 and IRIP on OCT2 function were not additive, and the inhibition of OCT2 by RS1 was prevented by coexpression of a dominant-negative mutant of IRIP (Jiang et al, 2005), which suggests a common regulatory pathway for the two proteins. It is particularly interesting that IRIP is up-regulated during ischemia, a process in which extracellular adenosine is known to accumulate (Eltzschig et al, 2009).…”

“…This was mimicked by the fungal metabolite brefeldin, which is known to promote the release of various coat proteins from the Golgi apparatus. RS1 has been identified as a protein partner of the protein IRIP (Jiang et al, 2005). In fact, IRIP (which apparently is also ubiquitous in mammals) similarly down-regulates, when overexpressed, OCT2 activity.…”

Tripeptides of RS1 (RSC1A1) Inhibit a Monosaccharide-dependent Exocytotic Pathway of Na+-d-Glucose Cotransporter SGLT1 with High Affinity

“…This posttranscriptional down-regulation of SGLT1 by RS1 was increased by PKC and modulated by intracellular methyl-␣-D-glucopyranoside (AMG) (21). Interestingly RS1 was found to be associated with a 28-kDa protein called the IRIP protein that is up-regulated in kidneys after ischemia and reperfusion (31). The physiological and potential biomedical importance of RS1 was demonstrated by targeted disruption of the Rsc1A1 gene in mice (26).…”