Dynamin2, clathrin, and lipid rafts mediate endocytosis of the apical Na/K/2Cl cotransporter NKCC2 in thick ascending limbs

J Biol Chem. 2012 Nov 2;287(45):37824-34. doi: 10.1074/jbc.M112.386425. Epub 2012 Sep 12.

Abstract

Steady-state surface levels of the apical Na/K/2Cl cotransporter NKCC2 regulate NaCl reabsorption by epithelial cells of the renal thick ascending limb (THAL). We reported that constitutive endocytosis of NKCC2 controls NaCl absorption in native THALs; however, the pathways involved in NKCC2 endocytosis are unknown. We hypothesized that NKCC2 endocytosis at the apical surface depends on dynamin-2 and clathrin. Measurements of steady-state surface NKCC2 and the rate of NKCC2 endocytosis in freshly isolated rat THALs showed that inhibition of endogenous dynamin-2 with dynasore blunted NKCC2 endocytosis by 56 ± 11% and increased steady-state surface NKCC2 by 67 ± 27% (p < 0.05). Expression of the dominant negative Dyn2K44A in THALs slowed the rate of NKCC2 endocytosis by 38 ± 8% and increased steady-state surface NKCC2 by 37 ± 8%, without changing total NKCC2 expression. Inhibition of clathrin-mediated endocytosis with chlorpromazine blunted NKCC2 endocytosis by 54 ± 6%, while preventing clathrin from interacting with synaptojanin also blunted NKCC2 endocytosis by 52 ± 5%. Disruption of lipid rafts blunted NKCC2 endocytosis by 39 ± 4% and silencing caveolin-1 by 29 ± 4%. Simultaneous inhibition of clathrin- and lipid raft-mediated endocytosis completely blocked NKCC2 internalization. We concluded that dynamin-2, clathrin, and lipid rafts mediate NKCC2 endocytosis and maintain steady-state apical surface NKCC2 in native THALs. These are the first data identifying the endocytic pathway for apical NKCC2 endocytosis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Caveolin 1 / genetics
  • Caveolin 1 / metabolism
  • Chlorpromazine / pharmacology
  • Clathrin Heavy Chains / antagonists & inhibitors
  • Clathrin Heavy Chains / metabolism*
  • Dynamin II / antagonists & inhibitors
  • Dynamin II / genetics
  • Dynamin II / metabolism*
  • Endocytosis*
  • Hydrazones / pharmacology
  • Loop of Henle / drug effects
  • Loop of Henle / metabolism*
  • Male
  • Membrane Microdomains / metabolism*
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Mutation
  • RNA Interference
  • Rats
  • Rats, Sprague-Dawley
  • Signal Transduction / drug effects
  • Sodium-Potassium-Chloride Symporters / metabolism*
  • Solute Carrier Family 12, Member 1

Substances

  • Caveolin 1
  • Hydrazones
  • N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide
  • Slc12a1 protein, rat
  • Sodium-Potassium-Chloride Symporters
  • Solute Carrier Family 12, Member 1
  • Clathrin Heavy Chains
  • Dynamin II
  • Chlorpromazine