Na/H Exchanger Regulatory Factors Control Parathyroid Hormone Receptor Signaling by Facilitating Differential Activation of Gα Protein Subunits

The Na/H exchanger regulatory factors, NHERF1 and NHERF2, are adapter proteins involved in targeting and assembly of protein complexes. The parathyroid hormone receptor (PTHR) interacts with both NHERF1 and NHERF2. The NHERF proteins toggle PTHR signaling from predominantly activation of adenylyl cyclase in the absence of NHERF to principally stimulation of phospholipase C when the NHERF proteins are expressed. We hypothesized that this signaling switch occurs at the level of the G protein. We measured G protein activation by [S-35]GTP gamma S binding and G alpha subtype-specific immunoprecipitation using three different cellular models of PTHR signaling. These studies revealed that PTHR interactions with NHERF1 enhance receptor-mediated stimulation of G alpha(q) but have no effect on stimulation of G alpha(i) or G alpha(s). In contrast, PTHR associations with NHERF2 enhance receptor-mediated stimulation of both G alpha(q) and G alpha(i) but decrease stimulation of G alpha(s). Consistent with these functional data, NHERF2 formed cellular complexes with both G alpha(q) and G alpha(i), whereas NHERF1 was found to interact only with G alpha(q). These findings demonstrate that NHERF interactions regulate PTHR signaling at the level of G proteins and that NHERF1 and NHERF2 exhibit isotype-specific effects on G protein activation.