Novel functional interaction between Na+/H+ exchanger 1 and tyrosine phosphatase SHP-2

Besides being a intracellular pH (pHi) regulator, Na+/H+ exchanger (NHE) I has recently been postulated as a membrane scaffold that assembles protein complexes and coordinates various signaling pathways. The aim of the present study was to uncover NHE1 interactive partners and study their functional implications. NHE1 interactive partners were screened in the mouse brain with a signal transduction Antibody Array. Ten of 400 tested proteins appeared to be potentially associated with NHE1. These partners have been shown to be involved in either cell proliferative or apoptotic pathways. The interactions between NHE1 and Src homology 2 domain-containing protein tyrosine phosphatase (SHP-2), Bin1, and heat shock protein (HSP)70 were reciprocally confirmed by coimmunoprecipitation. Moreover, in vitro binding data have shown that NHE1COOH terminus interacts directly with SHP-2. The functional significance of the association between NHE1 and SHP-2 was further investigated by measuring pHi, cell proliferation, and cell death with the fluorescent dye BCECF, [H-3]thymidine incorporation, and medium lactate dehydrogenase activity, respectively. Our results revealed that cells with SHP-2 overexpression exhibited a higher steady-state pH(i) and a faster, NHE1-dependent pHi recovery rate from acid load in HEPES buffer. In addition, SHP-2 overexpression diminished the HOE-642-induced inhibition of cell proliferation and protected cells from hypoxic injury, especially in the presence of HOE-642. Together, our findings demonstrate that SHP-2 not only is physically associated with NHE1 but also modulates NHE1 functions such as pHi regulation, cell proliferation, and cell death under hypoxia.