In vivo and in vitro interaction of calcineurin B homologous protein isoforms 1 and 2 with the Na + ‐ H + exchanger isoform 1 (796.10)

The Na + ‐H + exchanger isoform 1 (NHE1) is a key regulator of cell proliferation, migration and invasion in cells from a variety of solid tumors. The calcineurin B homologous proteins (CHP1 and CHP2) appear to be essential cofactors to support NHE1 function. CHP1 appears to be expressed ubiquitously in healthy tissue, while CHP2 is predominantly expressed in tumor cells. While both CHP isoforms are highly homologous and bind in nearly identical regions on NHE1, each has been identified to have a distinct impact on NHE1 function. In this study we investigate the ability of CHP1 and CHP2 to bind independently and competitively to NHE1. The impact of serum deprivation has been thought to drive CHP2‐NHE1 transport and the effect of low serum on CHP1/CHP2 interaction with NHE1 will be assessed. Using recombinant fusion CHP1, CHP2 and NHE1 proteins a reconstituted‐96 well plate based assay has been developed to quantitate the binding affinity of each CHP isoform for NHE1. We will also demonstrate the competition binding between CHP1 and CHP2 for NHE1 using this in vitro protein‐protein method.