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 (PubMed:14661968). Homodimer; disulfide-linked (PubMed:14661968). Interacts with SLC9A1/NHE1; the interaction enables an optimal Na(+)/H(+) exchange activity (By similarity). Colocalizes with SLC9A1 at the cell membrane. Expressed in embryonic, newborn and adult testis, but not in prepubertal testis. Expressed in the embryonic testis during testis determination but is not expressed at any time in the embryonic ovary. In embryonic testis, expression is restricted to the testis cords and is seen in both Sertoli cells and germ cells. Expression is excluded from the myoid cells which surround the cords. Expressed in the embryonic adrenal after the initial stages of differentiation. Expressed at a lower level in the embryonic brain, heart and lung but not in liver or gut. May be expressed at a very low level in the embryonic kidney. In the embryonic brain, expressed in the nasal placode and in fibers extending from the olfactory epithelium to the primordial olfactory bulb. In adults, expressed in the heart, and weakly in the brain and kidney. Highly expressed in terminally differentiated megakaryocytes (at protein level). Not detected in fetal liver cells (at protein level). Expression is first detected in the male gonad at 11.5 dpc, peaks at 14.5 dpc, declines slightly by 15.5 dpc, and continues to at least 17.5 dpc. Binds calcium via its EF-hands. Calcium-binding mediates a conformational change. Can also bind magnesium. According PubMed:22285131, mice show a normal number of megakaryocytes and platelets. Belongs to the calcineurin regulatory subunit family. CHP subfamily. The region of SLC9A1/NHE1 that interacts with CHP3 is conflicting: In human, interaction with SLC9A1/NHE1 has been reported via residues 507-549, the juxtamembrane region of the cytoplasmic C-terminus. However, another publication has reported interaction with SLC9A1/NHE1 via residues 637-820, the region of the cytoplasmic C-terminus more distal to the membrane.