The calmodulin antagonist W-7 inhibits the epithelial Na+/H+ exchanger via modulating membrane surface potential

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Transport

Background:

• The sodium-hydrogen exchanger 3 (NHE3) plays a crucial role in regulating cellular pH and ion homeostasis.
• NHE3 activity is known to be modulated by alterations in the plasma membrane's surface charge.
• Cationic regions within the cytosolic C-terminus of NHE3 are implicated in its interaction with the negatively charged inner leaflet of the plasma membrane.

Purpose of the Study:

• To investigate the mechanism by which calmodulin antagonists, specifically W-7, inhibit NHE3 activity.
• To determine if W-7 affects the plasma membrane surface potential and its interaction with cationic or hydrophobic peptides.
• To elucidate the role of anionic phospholipids in the interaction between NHE3 and the plasma membrane, and how W-7 influences this interaction.

Main Methods:

• Utilized fluorescent protein-conjugated membrane probes to assess peptide binding to the plasma membrane.
• Investigated the interaction of cationic and hydrophobic peptides with the plasma membrane in the presence and absence of W-7.
• Examined the interaction between cationic regions of NHE3 and anionic phospholipids in reconstituted liposomes and in cell culture plasma membranes.

Main Results:

• W-7 prevented the binding of cationic, but not hydrophobic, peptides to the plasma membrane, indicating an effect on surface charge.
• W-7 inhibited the interaction between cationic segments of NHE3 and anionic phospholipids in both reconstituted liposomes and cell culture models.
• The inhibitory concentration of W-7 on NHE3 activity correlated with its effect on these molecular interactions.

Conclusions:

• W-7 inhibits NHE3 activity, at least in part, by altering the association of cationic segments in the NHE3 C-terminus with anionic phospholipids in the plasma membrane.
• The findings suggest that membrane surface charge and specific phospholipid interactions are critical regulatory mechanisms for NHE3 function.
• This study provides a molecular basis for the inhibitory action of W-7 on NHE3, linking it to disruptions in membrane-associated protein-lipid interactions.