SLC9A1 and cancer: The extrusion of H+ from cancer cells is positively regulated by several membrane-bound proton transporters, such as Na+/H+ exchanger 1 (NHE1), Na+/K+ ATPase pump, vacuolar H+-ATPase (V-ATPase), H+/Cl− symporter, monocarboxylate transporter (MCT), and carbonic anhydrase (CA) (10).