ナトリウム依存性リン酸トランスポーターIIa型（NaPi-IIa）の副甲状腺ホルモン（PTH）による調節機構

Parathyroid hormone （PTH） is the most potent and important regulator of the type II a sodium-dependent phosphate transporter （NaPi-IIa）, which plays a key role in renal phosphate reabsorption and maintaining inorganic phosphate homeostasis. PTH inhibits the NaPi-IIa activity by stimulation of translocation from the apical plasma membrane to the intracellular organelle. In this paper, we investigated the mechanism of the translo-cation of NaPi-IIa from the apical plasma membrane by cell fractionation analysis using OK-N２ cells that stably express human NaPi-IIa established from opossum kidney cells （OK-P cells）. NaPi-IIa was mostly localized in the caveolae-like membrane domains of the plasma membrane in OK-N２ cells We also clarified that PTH activated both PKA and PKC, and these kinases markedly increased the phosphorylation of their ８０kDa and ２５０kDa substrates on the caveolae-like membrane domains ; we identified ezrin as a candidate protein for the ８０kDa substrate. We conclude that caveolae-like membrane domains play an important role in the targeting, translocation, and signal compartmentalization for the translocational regulation of NaPi-IIa in renal proximal tubular cells.

四国医学雑誌 : http://www.tokushima-u.ac.jp/med/research/shikoku_acta_medica.html