cAMP-mediated inhibition of the epithelial brush border Na+/H+ exchanger, NHE3, requires an associated regulatory protein

C. H.Chris Yun, Soohyuk Oh, Mirza Zizak, Deborah Steplock, Su Tsao, Chung Ming Tse, Edward J. Weinman, Mark Donowitz

Research output: Contribution to journalArticlepeer-review

Abstract

NHE3 is the Na+/H+ exchanger located on the intestinal and renal brush border membrane, where it functions in transepithelial Na+ absorption. The brush border Na+ absorptive process is acutely inhibited by activation of cAMP-dependent protein kinase, but the molecular mechanism of this inhibitory effect is poorly understood. We have identified two regulatory proteins, E3KARP and NHERF, that interact with NHE3 to enable cAMP to inhibit NHE3. The two regulatory proteins are structurally related, sharing ≃50% identity in amino acid sequences. It has been previously shown that when NHE3 is transfected into PS120 fibroblasts or Caco-2 cells, cAMP failed to inhibit NHE3 activity. Northern blot analysis showed that both PS120 and Caco-2 cells lacked the expression of both E3KARP and NHERF. In contrast, other cell lines in which cAMP inhibits NHE3, including OK, CHO, and LLC-PK1 cells, expressed NHERF-related regulatory proteins. To determine their functions in cAMP- dependent inhibition of NHE3, E3KARP and NHERF were transfected into PS120/NHE3 fibroblasts. Transfection in PS120/NHE3 fibroblasts with either NHERF or E3KARP reconstituted cAMP-induced inhibition of NHE3, resulting in 25-30% inhibition in these cells.

Original languageEnglish (US)
Pages (from-to)3010-3015
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume94
Issue number7
DOIs
StatePublished - Apr 1 1997

Keywords

  • Na absorption
  • pH regulation
  • signal transduction
  • sodium-hydrogen antiporter

ASJC Scopus subject areas

  • General

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