Functions as an integral cofactor in cell pH regulation by controlling plasma membrane-type Na+/H+ exchange activity. Binds to and activates SLC9A1/NHE1 in a serum-independent manner, thus increasing pH and protecting cells from serum deprivation-induced death. Also plays a role in the regulation of cell proliferation and tumor growth by increasing the phosphatase activity of PPP3CA in a calcium-dependent manner. Activator of the calcineurin/NFAT signaling pathway. Involved in the cytoplasmic translocation of the transcription factor NFATC3 to the nucleus.Loftus B.J., Genomics 60:295-308(1999).Wang Y., J. Immunol. 169:1102-1109(2002).Pang T., J. Biol. Chem. 277:43771-43777(2002).