Ca2+-dependent inhibition of Na+/H+ exchanger 3 (NHE3) requires an NHE3-E3KARP-α-actinin-4 complex for oligomerization and endocytosis

Jae Ho Kim, Whaseon Lee-Kwon, Jong Bae Park, Sung Ho Ryu, C. H. Chris Yun, Mark Donowitz

Research output: Contribution to journalArticle

Abstract

Two PDZ domain-containing proteins, NHERF and E3KARP are necessary for cAMP-dependent inhibition of Na+/H+ exchanger 3 (NHE3). In this study, we demonstrate a specific role of E3KARP, which is not duplicated by NHERF, in Ca2+-dependent inhibition of NHE3 activity. NHE3 activity is inhibited by elevation of intracellular Ca2+ ([Ca2+]i) in PS120 fibroblasts stably expressing E3KARP but not those expressing NHERF. In addition, this Ca2+-dependent inhibition requires Ca2+-dependent association between α-actinin-4 and E3KARP. NHE3 is indirectly connected to α-actinin-4 in a protein complex through Ca2+-dependent interaction between α-actinin-4 and E3KARP, which occurs through the actin-binding domain plus spectrin repeat domain of α-actinin-4. Elevation of [Ca2+]i results in oligomerization and endocytosis of NHE3 as well as in inhibition of NHE3 activity. Over-expression of α-actinin-4 potentiates the inhibitory effect of ionomycin on NHE3 activity by accelerating the oligomerization and endocytosis of NHE3. In contrast, overexpression of the actin-binding domain plus spectrin repeat domain acts as a dominant-negative mutant and prevents the inhibitory effect of ionomycin on NHE3 activity as well as the oligomerization and internalization of NHE3. From these results, we propose that elevated Ca2+ inhibits NHE3 activity through oligomerization and endocytosis of NHE3, which occurs via formation of an NHE3-E3KARP-α-actinin-4 complex.

Original languageEnglish (US)
Pages (from-to)23714-23724
Number of pages11
JournalJournal of Biological Chemistry
Volume277
Issue number26
DOIs
StatePublished - Jun 28 2002

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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