Regulation of human organic anion transporter 4 by progesterone and protein kinase C in human placental BeWo cells

Abstract

Human organic anion transporter 4 (hOAT4) belongs to a family of organic anion transporters that play critical roles in the body disposition of clinically important drugs, including anti-human immunodeficiency virus therapeutics, anti-tumor drugs, antibiotics, antihypertensives, and anti-inflammatories. hOAT4 is abundantly expressed in the placenta. In the current study, we examined the regulation of hOAT4 by pregnancy-specific hormones progesterone (P4) and 17␤-estradiol (E2) and by protein kinase C (PKC) in human placental BeWo cells. P4 induced a time-and concentration-dependent downregulation of hOAT4 transport activity, whereas E2 had no effect on hOAT4 function. The downregulation of hOAT4 activity by P4 mainly resulted from a decreased cell surface expression without a change in total cell expression of the transporter, kinetically revealed as a decreased Vmax without significant change in Km. Activation of PKC by phorbol 12,13-dibutyrate also resulted in an inhibition of hOAT4 activity through a decreased cell surface expression of the transporter. However, P4-induced downregulation of hOAT4 activity could not be prevented by treating hOAT4-expressing cells with the PKC inhibitor staurosporine. We concluded that both P4 and activation of PKC inhibited hOAT4 activity through redistribution of the transporter from cell surface to the intracellular compartments. However, P4 regulates hOAT4 activity by mechanisms independent of PKC pathway. acute regulation HUMAN ORGANIC ANION TRANSPORTER 4 (hOAT4) belongs to a family of organic anion transporters that play critical roles in the body disposition of clinically important drugs, including anti-human immunodeficiency virus therapeutics, anti-tumor drugs, antibiotics, antihypertensives, and anti-inflammatories (3,7,18,19,24). hOAT4 is abundantly expressed in the kidney and placenta (4). In the kidney, OAT4 functions as an organic anion/dicarboxylate exchanger at the apical membrane of the proximal tubule and is responsible for the reabsorption of organic anions driven by an outwardly directed dicarboxylate gradient (6). In the placenta, hOAT4 is localized to the basolateral membrane of syncytiotrophoblasts (20). It is believed that estrogen biosynthesis in the placenta uses dehydroepiandrosterone sulfate (DHEAS), a precursor produced in large amount by the fetal adrenals. Accumulation of excess DHEAS is associated with intrauterine growth retardation (17). DHEAS is an OAT4 substrate. Therefore, OAT4 may play an important role in efficient uptake of DHEAS by the placenta for the production of estrogens and for the protection of fetus from the cytotoxicity of DHEAS.Computer modeling has shown that hOAT4 contains multiple potential glycosylation sites in its first extracellular loop. The glycosylation process occurs in two major steps: the first step is the addition of oligosaccharides to the nascent protein, and the second step is the processing of added oligosaccharides during which the added oligosaccharides are modified and trimmed. Our group (27) previously sho...

Novel Mechanism of Impaired Function of Organic Anion-Transporting Polypeptide 1B3 in Human Hepatocytes: Post-Translational Regulation of OATP1B3 by Protein Kinase C Activation

“…PKC activation decreased surface levels of OAT1, OAT4, OATP2B1, and OATP1A2 without affecting total protein levels of these transport proteins after short-term treatment with a PKC activator for up to 1 hour (Zhou et al, 2007(Zhou et al, , 2011Zhang et al, 2008Zhang et al, , 2010Köck et al, 2010). Rapid downregulation of transport function by PKC activation is associated with increased phosphorylation of OATP2B1 (Köck et al, 2010), the brain glutamate/aspartate transporter GLAST-1 (Conradt and Stoffel, 1997), as well as dopamine (Huff et al, 1997) and serotonin transporters (Jayanthi et al, 2005).…”

“…The function of several human transport proteins is regulated by PKC activation. For example, PKC activation downregulates transport function of organic anion transporter (OAT) 1 (Zhang et al, 2008), OAT3 (Duan et al, 2010), and OAT4 (Zhou et al, 2007;Zhang et al, 2010); OATP2B1 (Köck et al, 2010) and OATP1A2 (Zhou et al, 2011); efflux transport protein P-glycoprotein (P-gp) (Miller et al, 1998); and multidrug resistance protein (MRP)2 (Kubitz et al, 2001). OATP1B3 has putative PKC phosphorylation sites as predicted by Scansite 3 (Obenauer et al, 2003).…”

Co-localization and interaction of human organic anion transporter 4 with caveolin-1 in primary cultured human placental trophoblasts

“…Even though the regulation mechanism of hOAT4 in the kidney has begun to be explored, its regulation mechanism in the placenta is largely unknown. Zhou and co-workers have shown that the function of hOAT4 was down regulated both by activation of PKC and by pregnancy-specific hormones progestetone in placental BeWo cells (Zhou et al, 2007). However, they have reported that progesterone-induced down regulated hOAT4 function is independent on PKC pathway.…”

Current Updates in the Genetic Polymorphisms of Human Organic Anion Transporters (OATs)

“…However, Kikuchi et al [35] discovered that promoter methylation could down regulate OAT function. At post-translational level, Protein Kinase C (PKC) regulated OAT functions through carrier mediated trafficking [37][38][39][40][41]. In addition, OAT activities could also be manipulated by phosphorylation at serine residue, or by epidermal growth factor [42][43][44][45].…”