Identification of the F1-ATPase at the Cell Surface of Colonic Epithelial Cells: ROLE IN MEDIATING CELL PROLIFERATION*

F1 domain of F₁F_o-ATPase was initially believed to be strictly expressed in the mitochondrial membrane. Interestingly, recent reports have shown that the F1 complex can serve as a cell surface receptor for apparently unrelated ligands. Here we show for the first time the presence of the F₁-ATPase at the cell surface of normal or cancerous colonic epithelial cells. Using surface plasmon resonance technology and mass spectrometry, we identified a peptide hormone product of the gastrin gene (glycine-extended gastrin (G-gly)) as a new ligand for the F₁-ATPase. By molecular modeling, we identified the motif in the peptide sequence (E(E/D)XY), that directly interacts with the F₁-ATPase and the amino acids in the F₁-ATPase that bind this motif. Replacement of the Glu-9 residue by an alanine in the E(E/D)XY motif resulted in a strong decrease of G-gly binding to the F₁-ATPase and the loss of its biological activity. In addition we demonstrated that F₁-ATPase mediates the growth effects of the peptide. Indeed, blocking F₁-ATPase activity decreases G-gly-induced cell growth. The mechanism likely involves ADP production by the membrane F₁-ATPase, which is induced by G-gly. These results suggest an important contribution of cell surface F₁-ATPase in the pro-proliferative action of this gastrointestinal peptide.