Direct Evidence for Calcineurin Binding to the Exon-7 Loop of the Sodium-Bicarbonate Cotransporter NBCn1

作者：Gill Harindarpal S^*; Roush Eric D; Dutcher Lauren; Patel Samir

来源：International Journal of Biological Sciences, 2014, 10(7): 771-776.

DOI：10.7150/ijbs.9539

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

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.

• 出版日期2014