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Estrogen directly and specifically downregulates NaPi-IIa through the activation of both estrogen receptor isoforms (ER? and ER?) in rat kidney proximal tubule.

ABSTRACT: We have previously demonstrated that estrogen (E2) downregulates phosphate transporter NaPi-IIa and causes phosphaturia and hypophosphatemia in ovariectomized rats. In the present study, we examined whether E2 directly targets NaPi-IIa in the proximal tubule (PT) and studied the respective roles of estrogen receptor isoforms (ER? and ER?) in the downregulation of NaPi-IIa using both in vivo and an in vitro expression systems. We found that estrogen specifically downregulates NaPi-IIa but not NaPi-IIc or Pit2 in the kidney cortex. Proximal tubules incubated in a "shake" suspension with E2 for 24 h exhibited a dose-dependent decrease in NaPi-IIa protein abundance. Results from OVX rats treated with specific agonists for either ER? [4,4',4?;-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol, PPT] or ER? [4,4',4?-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol, DPN] or both (PPT + DPN), indicated that only the latter caused a sharp downregulation of NaPi-IIa, along with significant phosphaturia and hypophosphatemia. Lastly, heterologous expression studies demonstrated that estrogen downregulated NaPi-IIa only in U20S cells expressing both ER? and ER?, but not in cells expressing either receptor alone. In conclusion, these studies demonstrate that rat PT cells express both ER? and ER? and that E2 induces phosphaturia by directly and specifically targeting NaPi-IIa in the PT cells. This effect is mediated via a mechanism involving coactivation of both ER? and ER?, which likely form a functional heterodimer complex in the rat kidney proximal tubule.

SUBMITTER: Burris D

PROVIDER: S-EPMC4360034 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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Estrogen directly and specifically downregulates NaPi-IIa through the activation of both estrogen receptor isoforms (ERα and ERβ) in rat kidney proximal tubule.

Burris Dara D Webster Rose R Sheriff Sulaiman S Faroqui Rashma R Levi Moshe M Hawse John R JR Amlal Hassane H

American journal of physiology. Renal physiology 20150121 6

We have previously demonstrated that estrogen (E2) downregulates phosphate transporter NaPi-IIa and causes phosphaturia and hypophosphatemia in ovariectomized rats. In the present study, we examined whether E2 directly targets NaPi-IIa in the proximal tubule (PT) and studied the respective roles of estrogen receptor isoforms (ERα and ERβ) in the downregulation of NaPi-IIa using both in vivo and an in vitro expression systems. We found that estrogen specifically downregulates NaPi-IIa but not NaP ...[more]

PMID: 25608964

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Project description:Transporters of the SLC34 family (NaPi-IIa,b,c) catalyze uptake of inorganic phosphate (Pi) in renal and intestinal epithelia. The transport cycle requires three Na(+) ions and one divalent Pi to bind before a conformational change enables translocation, intracellular release of the substrates, and reorientation of the empty carrier. The electrogenic interaction of the first Na(+) ion with NaPi-IIa/b at a postulated Na1 site is accompanied by charge displacement, and Na1 occupancy subsequently facilitates binding of a second Na(+) ion at Na2. The voltage dependence of cotransport and presteady-state charge displacements (in the absence of a complete transport cycle) are directly related to the molecular architecture of the Na1 site. The fact that Li(+) ions substitute for Na(+) at Na1, but not at the other sites (Na2 and Na3), provides an additional tool for investigating Na1 site-specific events. We recently proposed a three-dimensional model of human SLC34a1 (NaPi-IIa) including the binding sites Na2, Na3, and Pi based on the crystal structure of the dicarboxylate transporter VcINDY. Here, we propose nine residues in transmembrane helices (TM2, TM3, and TM5) that potentially contribute to Na1. To verify their roles experimentally, we made single alanine substitutions in the human NaPi-IIa isoform and investigated the kinetic properties of the mutants by voltage clamp and (32)P uptake. Substitutions at five positions in TM2 and one in TM5 resulted in relatively small changes in the substrate apparent affinities, yet at several of these positions, we observed significant hyperpolarizing shifts in the voltage dependence. Importantly, the ability of Li(+) ions to substitute for Na(+) ions was increased compared with the wild-type. Based on these findings, we adjusted the regions containing Na1 and Na3, resulting in a refined NaPi-IIa model in which five positions (T200, Q206, D209, N227, and S447) contribute directly to cation coordination at Na1.

Dataset Information

Estrogen directly and specifically downregulates NaPi-IIa through the activation of both estrogen receptor isoforms (ER? and ER?) in rat kidney proximal tubule.

Publications

Estrogen directly and specifically downregulates NaPi-IIa through the activation of both estrogen receptor isoforms (ERα and ERβ) in rat kidney proximal tubule.

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