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Kidney Int. 2005 Aug;68(2):632-41.

Expression of the polycystin-1 C-terminal cytoplasmic tail increases Cl channel activity in Xenopus oocytes.

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1
Molecular and Vascular Medicine Unit and Renal Division, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.

Abstract

Expression of the polycystin-1 C-terminal cytoplasmic tail increases Cl(-) channel activity in Xenopus oocytes.

BACKGROUND:

Cyst expansion in autosomal-dominant polycystic kidney disease (ADPKD) is characterized by active Cl(-) secretion in excess of solute reabsorption. However, the connections between elevated epithelial Cl(-) secretion and loss-of-function or dysregulation of either ADPKD gene polycystin-1 (PC1) or polycystin-2 (PC2) remain little understood.

METHODS:

Cl(-) transport in Xenopus oocytes expressing the CD16.7-PKD1 (115-226) fusion protein containing the final 112 amino acid (aa) of the PC1 C-terminal cytoplasmic tail, or in oocytes expressing related PC1 fusion protein mutants, was studied by isotopic flux, two-electrode voltage clamp, and outside-out patch clamp recording.

RESULTS:

Expression in oocytes of CD16.7-PKD1 (115-226) increased rates of both influx and efflux of (36)Cl(-), whereas CD16.7-PKD1 (1-92) containing the initial 92 aa of the PC1 C-terminal cytoplasmic tail was inactive. The increased Cl(-) transport resembled CD16.7-PKD1 (115-226)-stimulated cation current in its sensitivity to ADPKD-associated missense mutations, to mutations in phosphorylation sites, and to mutations within or encroaching upon the PC1 coiled-coil domain, as well as in its partial suppression by coexpressed PC2. The NS3623- and 4, 4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS)-sensitive (36)Cl(-) flux was not blocked by injected ethyleneglycol tetraacetate (EGTA) or by the cation channel inhibitor SKF96365, and was stimulated by the cation channel inhibitor La(3+), suggesting that CD16.7-PKD1 (115-226)-associated cation conductance was not required for (36)CI(-) flux activation. Outside-out patches from oocytes expressing CD16.7-PKD1 (115-226) also exhibited increased NS3623-sensitive Cl(-) current.

CONCLUSION:

These data show that CD16.7-PKD1 (115-226) activates Cl(-) channels in the Xenopus oocyte plasma membrane in parallel with, but not secondary to, activation of Ca(2+)-permeable cation channels.

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