Down-regulation by extracellular ATP of rat hepatocyte organic anion transport is mediated by serine phosphorylation of Oatp1

Joseph S. Glavy, Suet M. Wu, Pi Jun Wang, George A. Orr, Allan W. Wolkoff

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Abstract

Recent studies implicate a role in hepatocyte organic anion transport of a plasma membrane protein that has been termed oatp1 (organic anion transport protein 1). Little is known regarding mechanisms by which its transport activity is modulated in vivo. In previous studies (Campbell, C. G., Spray, D.C., and Wolkoff, A. W. (1993) J. Biol. Chem. 268, 15399-15404), we demonstrated that hepatocyte uptake of sulfobromophthalein was down-regulated by extracellular ATP. We have now found that extracellular ATP reduces the V(max) for transport of sulfobromophthalein by rat hepatocytes; K(m) remains unaltered. Reduced transport also results from incubation of hepatocytes with the phosphatase inhibitors okadaic acid and calyculin A. Immunoprecipitation of biotinylated cell surface proteins indicates that oatp1 remains on the cell surface after exposure of cells to ATP or phosphatase inhibitor, suggesting that loss of transport activity is not caused by transporter internalization. Exposure of 32P-loaded hepatocytes to extracellular ATP results in serine phosphorylation of oatp1 with the appearance of a single major tryptic phosphopeptide; oatp1 from control cells is not phosphorylated. This phosphopeptide comigrates with one of four phosphopeptides resulting from incubation of cells with okadaic acid. These studies indicate that the phosphorylation state of oatp1 must be an important consideration when assessing alterations of its functional expression in pathobiological states.

Original languageEnglish (US)
Pages (from-to)1479-1484
Number of pages6
JournalJournal of Biological Chemistry
Volume275
Issue number2
DOIs
StatePublished - Jan 14 2000

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Organic Anion Transport Protein 1
Phosphorylation
Serine
Anions
Rats
Hepatocytes
Down-Regulation
Adenosine Triphosphate
Phosphopeptides
Sulfobromophthalein
Okadaic Acid
Phosphoric Monoester Hydrolases
Membrane Proteins
Cell membranes
Immunoprecipitation
Blood Proteins
Cells
Cell Membrane

ASJC Scopus subject areas

  • Biochemistry

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Down-regulation by extracellular ATP of rat hepatocyte organic anion transport is mediated by serine phosphorylation of Oatp1. / Glavy, Joseph S.; Wu, Suet M.; Wang, Pi Jun; Orr, George A.; Wolkoff, Allan W.

In: Journal of Biological Chemistry, Vol. 275, No. 2, 14.01.2000, p. 1479-1484.

Research output: Contribution to journalArticle

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