However, many cancers have elevated expression or activity of proteins that facilitate increased pHi, including carbonic anhydrase 9 (Swietach et al., 2007), H+-ATPases (Martinez-Zaguilan et al., 1993; Sennoune et al., 2004; Hinton et al., 2009), the ubiquitously expressed Na+-H+ exchanger NHE1 (McLean et al., 2000; Miraglia et al., 2005; Chiang et al., 2008; Yang et al., 2011) and the monocarboxylate transporter family members MCT1 and MCT4 (Pinheiro et al., 2010; Halestrap, 2013). The gene discussed is SLC9A1; the disease is cancer.