scholarly journals Down-regulation by Extracellular ATP of Rat Hepatocyte Organic Anion Transport Is Mediated by Serine Phosphorylation of Oatp1

2000 ◽  
Vol 275 (2) ◽  
pp. 1479-1484 ◽  
Author(s):  
Joseph S. Glavy ◽  
Suet M. Wu ◽  
Pi Jun Wang ◽  
George A. Orr ◽  
Allan W. Wolkoff
Keyword(s):  
Organic Anion ◽  
Anion Transport ◽  
Extracellular Atp ◽  
Serine Phosphorylation ◽  
Organic Anion Transport ◽  
Down Regulation ◽  
Rat Hepatocyte

Inhibition by extracellular ATP of organic anion transport in the perfused rat liver

2002 ◽  
Vol 454 (2-3) ◽  
pp. 225-234 ◽  
Author(s):  
Talma R.L Fernandes ◽  
Denise S de Oliveira ◽  
Fumie Suzuki-Kemmelmeier ◽  
Adelar Bracht
Keyword(s):  
Rat Liver ◽  
Organic Anion ◽  
Anion Transport ◽  
Extracellular Atp ◽  
Perfused Rat Liver ◽  
Organic Anion Transport

scholarly journals PDZK1 binding and serine phosphorylation regulate subcellular trafficking of organic anion transport protein 1a1

2011 ◽  
Vol 300 (3) ◽  
pp. G384-G393 ◽  
Author(s):  
Jo H. Choi ◽  
John W. Murray ◽  
Allan W. Wolkoff
Keyword(s):  
Cell Surface ◽  
Subcellular Distribution ◽  
Organic Anion ◽  
Surface Expression ◽  
Anion Transport ◽  
Transport Protein ◽  
Serine Phosphorylation ◽  
Cell Surface Expression ◽  
Organic Anion Transport ◽  
Huh7 Cells

Although perturbation of organic anion transport protein (oatp) cell surface expression can result in drug toxicity, little is known regarding mechanisms regulating its subcellular distribution. Many members of the oatp family, including oatp1a1, have a COOH-terminal PDZ consensus binding motif that interacts with PDZK1, while serines upstream of this site (S634 and S635) can be phosphorylated. Using oatp1a1 as a prototypical member of the oatp family, we prepared plasmids in which these serines were mutated to glutamic acid [E634E635 (oatp1a1EE), phosphomimetic] or alanine [A634A635 (oatp1a1AA), nonphosphorylatable]. Distribution of oatp1a1AA and oatp1a1EE was largely intracellular in transfected human embryonic kidney (HEK) 293T cells. Cotransfection with a plasmid encoding PDZK1 revealed that oatp1a1AA was now expressed largely on the cell surface, while oatp1a1EE remained intracellular. To quantify these changes, studies were performed in HuH7 cells stably transfected with these oatp1a1 plasmids. These cells endogenously express PDZK1. Surface biotinylation at 4°C followed by shift to 37°C showed that oatp1a1EE internalizes quickly compared with oatp1a1AA. To examine a physiological role for phosphorylation in oatp1a1 subcellular distribution, studies were performed in rat hepatocytes exposed to extracellular ATP, a condition that stimulates serine phosphorylation of oatp1a1 via activity of a purinergic receptor. Internalization of oatp1a1 under these conditions was rapid. Thus, although PDZK1 binding is required for optimal cell surface expression of oatp1a1, phosphorylation provides a mechanism for fast regulation of the distribution of oatp1a1 between the cell surface and intracellular vesicular pools. Identification of the proteins and motor molecules that mediate these trafficking events represents an important area for future study.

scholarly journals Characteristics of bile salt uptake into skate hepatocytes

1994 ◽  
Vol 299 (3) ◽  
pp. 665-670 ◽  
Author(s):  
G Fricker ◽  
V Dubost ◽  
K Finsterwald ◽  
J L Boyer
Keyword(s):  
Substrate Specificity ◽  
Bile Salt ◽  
Transport System ◽  
Bile Salts ◽  
Organic Anion ◽  
Anion Transport ◽  
Organic Anion Transport ◽  
Salt Uptake ◽  
Anion Transport System ◽  
Alpha 7

The substrate specificity for the transporter that mediates the hepatic uptake of organic anions in freshly isolated hepatocytes of the elasmobranch little skate (Raja erinacea) was determined for bile salts and bile alcohols. The Na(+)-independent transport system exhibits a substrate specificity, which is different from the specificity of Na(+)-dependent bile salt transport in mammals. Unconjugated and conjugated di- and tri-hydroxylated bile salts inhibit uptake of cholyltaurine and cholate competitively. Inhibition is significantly greater with unconjugated as opposed to glycine- or taurine-conjugated bile salts. However, the number of hydroxyl groups in the steroid moiety of the bile salts has only minor influences on the inhibition by the unconjugated bile salts. Since the transport system seems to represent an archaic organic-anion transport system, other anions, such as dicarboxylates, amino acids and sulphate, were also tested, but had no inhibitory effect on bile salt uptake. To clarify whether bile alcohols, the physiological solutes in skate bile, share this transport system, cholyltaurine transport was studied after addition of 5 beta-cholestane-3 beta,5 alpha,6 beta-triol, 5 alpha-cholestan-3 beta-ol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. These bile alcohols inhibit cholyltaurine uptake non-competitively. In contrast, uptake of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol, which is Na(+)-independent, is not inhibited by cholyltaurine. The findings further characterize a Na(+)-independent organic-anion transport system in skate liver cells, which is not shared by bile alcohols and has preference for unconjugated lipophilic bile salts.

scholarly journals Hepatocanalicular organic-anion transport is regulated by protein kinase C

1991 ◽  
Vol 278 (3) ◽  
pp. 637-641 ◽  
Author(s):  
H Roelofsen ◽  
R Ottenhoff ◽  
R P J Oude Elferink ◽  
P L M Jansen
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Organic Anion ◽  
Phosphodiesterase Inhibitor ◽  
Second Messenger ◽  
Anion Transport ◽  
Organic Anion Transport ◽  
Kinase C ◽  
Transport Assay ◽  
Messenger System

In order to investigate the regulation of canalicular organic-anion transport, we used a hepatocyte transport assay in which canalicular secretion of a model organic anion, dinitrophenyl-glutathione (GS-DNP), was measured in the presence of stimulators and inhibitors of the Ca2+/protein kinase C (PKC) second-messenger system and of the cyclic AMP (cAMP) second-messenger system. Vasopressin (24 nM) and the phorbol ester phorbol 12-myristate 13-acetate (1 microgram/ml), both stimulators of PKC, stimulated GS-DNP efflux by 65 +/- 36% and 55 +/- 28% respectively, whereas staurosporine (10 microM), an inhibitor of PKC, inhibited efflux by 53 +/- 13%. Glucagon and forskolin, both stimulators of the cAMP second-messenger system, as well as the cAMP analogue dibutyryl cAMP and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, did not significantly influence the GS-DNP efflux. It can be concluded that canalicular organic-anion transport in hepatocytes is either directly or indirectly regulated by PKC.

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