Functions as an integral cofactor in cell pH regulation by controlling plasma membrane-type Na(+)/H(+) exchange activity. Promotes the maturation, transport, cell surface stability and exchange activity of SLC9A1/NHE1 at the plasma membrane. Promotes the induction of hematopoietic stem cell differentiation toward megakaryocytic lineage. Essential for the coupling of ERK cascade activation with the expression of ETS family genes in megakaryocytic differentiation. Also involved in granulocytic differentiation in a ERK-dependent manner. Inhibits the phosphatase activity of calcineurin. Monomer (By similarity). Homodimer; disulfide-linked (By similarity). Interacts with SLC9A1/NHE1; the interaction enables an optimal Na(+)/H(+) exchange activity (PubMed:11696366, PubMed:18321853, PubMed:30287853, PubMed:12809501). Colocalizes with SLC9A1 at the plasma membrane. Expressed in mature megakaryocytes and polymorphonuclear granulocytes (at protein level). Abundantly expressed in heart. Also expressed at a lower level in adult testis and salivary gland, and in the placenta. Strongly up-regulated in K562 cells treated by PMA to promote megakaryocytic differentiation, but not when treated by DMSO to promote granulocytic differentiation or by hemin to promote erythroid differentiation (at protein level). Up-regulated during granulocytic differentiation in a ERK-dependent manner (is mediated by activation of ERK) (at protein level). Up-regulated during the differentiation and maturation of primary megakaryocytes. Down-regulated during monocytic-macrophage differentiation in a ERK-dependent manner. Binds calcium via its EF-hands. Calcium-binding mediates a conformational change. Can also bind magnesium (By similarity). Belongs to the calcineurin regulatory subunit family. CHP subfamily. Although PubMed:12809501 reports that TESC results in a decrease in transporter activity of human SLC9A1, studies with rat SLC9A1 show that TESC-binding results in the maturation and accumulation of SLC9A1 at the cell surface. The interacting region of SLC9A1/NHE1 with CHP3 is conflicting: Interaction with SLC9A1/NHE1 has been reported via residues 503-545, the juxtamembrane region of the cytoplasmic C-terminus (PubMed:11696366, PubMed:18321853, PubMed:30287853). However, another publication has reported interaction with SLC9A1/NHE1 via residues 633-815, the region of the cytoplasmic C-terminus more distal to the membrane (PubMed:12809501). Extended N-terminus. Extended N-terminus.