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Int J Biol Sci. 2014 Jul 4;10(7):771-6. doi: 10.7150/ijbs.9539. eCollection 2014.

Direct evidence for calcineurin binding to the exon-7 loop of the sodium-bicarbonate cotransporter NBCn1.

Author information

  • 11. Department of Medicine, The George Washington University, Washington, DC 20052 ; 2. Division of Renal Diseases and Hypertension, The George Washington Medical Faculty Associates, Washington, DC 20037.
  • 23. GE Healthcare, Piscataway, NJ 08554.
  • 34. Hospital of University of Pennsylvania, Philadelphia, PA 19104.
  • 42. Division of Renal Diseases and Hypertension, The George Washington Medical Faculty Associates, Washington, DC 20037.

Abstract

The NaHCO3 cotransporter NBCn1 plays a role in neutralizing intracellular acid loads at the basolateral membrane in cells of the medullary thick ascending limb (mTAL). Calcineurin inhibitors (Cn-Is) are known to both downregulate NBCn1 expression in the distal nephron and cause renal tubular acidosis (RTA), a risk factor for nephrocalcinosis and nephrolithiasis. In this report, we provide a new perspective on concurrent studies of NBCn1 in various tissues by using cell-free binding assays to investigate the interaction of NBCn1 with the calcineurin (Cn) isoform PPP3CA. Surface plasmon resonance (SPR) analyses show that the protein domain Exon 7 (translated from cassette II of NBCn1) binds Cn with an equilibrium dissociation constant (KD) of 30 +/- 15 nm. Linked-reaction tests suggest that the binding involves a conformational change. Nested PCR reactions were used to show that NBCn1-Exon 7 splice variants with alternative N-termini regions are expressed in the kidney, as well as other tissues. Additionally, we discuss NBCn1-Exon 7 implication in acid-base balance and calcium crystallization in the kidney.

KEYWORDS:

bicarbonate; calcineurin; renal physiology; surface plasmon resonance; transporters

PMID:
25076853
[PubMed - indexed for MEDLINE]
PMCID:
PMC4115197
Free PMC Article
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