NHE-RF, a Regulatory Cofactor for Na+-H+Exchange, Is a Common Interactor for Merlin and ERM (MERM) Proteins

doi:10.1074/jbc.273.3.1273

NHE-RF, a Regulatory Cofactor for Na⁺-H⁺Exchange, Is a Common Interactor for Merlin and ERM (MERM) Proteins*

From the Molecular Neurogenetics Unit, Massachusetts General Hospital, Charlestown, Massachusetts 02129 and the ^¶Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Abstract

We have identified the human homologue of a regulatory cofactor of Na⁺-H⁺ exchanger (NHE-RF) as a novel interactor for merlin, the neurofibromatosis 2 tumor suppressor protein. NHE-RF mediates protein kinase A regulation of Na⁺-H⁺ exchanger NHE3 to which it is thought to bind via one of its two PDZ domains. The carboxyl-terminal region of NHE-RF, downstream of the PDZ domains, interacts with the amino-terminal protein 4.1 domain-containing segment of merlin in yeast two-hybrid assays. This interaction also occurs in affinity binding assays with full-length NHE-RF expressed in COS-7 cells. NHE-RF binds to the related ERM proteins, moesin and radixin. We have localized human NHE-RF to actin-rich structures such as membrane ruffles, microvilli, and filopodia in HeLa and COS-7 cells, where it co-localizes with merlin and moesin. These findings suggest that hNHE-RF and its binding partners may participate in a larger complex (one component of which might be a Na⁺-H⁺exchanger) that could be crucial for the actin filament assembly activated by the ERM proteins and for the tumor suppressor function of merlin.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants NS24279 and NIDCD 03354 (to A. M.), the Deafness Foundation, and Neurofibromatosis Inc. (Massachusetts Chapter).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ The first two authors contributed equally to this work.
↵§ Supported in part by an young investigator award from the National Neurofibromatosis Foundation.
↵‖ To whom correspondence should be addressed: Molecular Neurogenetics Unit, Massachusetts General Hospital, Bldg. 149, 13th St., Charlestown, MA 02129. Tel.: 617-724-9733; Fax: 617-726-5736.
↵1 The abbreviations used are: NF2, neurofibromatosis 2; MERM, merlin, ezrin,radixin, moesin; NHE-RF, regulatory cofactor of Na⁺-H⁺ exchanger; NHE1–5, Na⁺-H⁺ exchanger isoforms; aa, amino acid(s); GST, glutathione S-transferase; HA, hemagglutinin; GFP, green fluorescent protein; PAGE, polyacrylamide gel electrophoresis.
- Received October 22, 1997.
The American Society for Biochemistry and Molecular Biology, Inc.