Many tumor cells are characterized by an increased net acid production. Metastatic melanoma cells extrude the excess protons mainly through the Na⁺/H⁺ exchanger NHE1. One key step in metastasis is cell migration which requires the assembly and disassembly of integrin-mediated cell-matrix contacts (focal adhesions). NHE1 has been associated with focal adhesions. The present study investigates whether NHE1 plays different roles at adhesion sites in the initial adhesion process on the one hand and in forward locomotion on the other hand.

In order to determine the subcellular distribution of NHE1, immunolocalization was performed on melanoma cells (MV3), transfected with DsRed2-paxillin. Furthermore, TIRF microscopy-based measurements of the submembranous cytosolic and the pericellular pH were performed in Hepes buffer and, closer to the in vivo situation, in bicarbonate buffer.

In cells, just adhered but still roundish, NHE1 concentrated at the cell margin, where it was situated nearby but not right at the adhesion sites. In migrating cells, NHE1 accumulated right at focal adhesions of the cell front. Here, NHE1 generated local pH nanodomains, characterized by a cytosolic alkalinization and an acidification at the cell surface, regardless of whether Hepes- or bicarbonate-buffered solutions were used.

Given that integrin avidity is proton-sensitive, we suggest that NHE1 controls adhesion dynamics in migrating melanoma cells by stabilizing focal adhesions at the cell front. The initial adhesion process, however, seems to happen independently from NHE1.