Calcium-sensing receptor-mediated ERK1/2 activation requires Gαi2 coupling and dynamin-independent receptor internalization

The calcium-sensing receptor (CaR) recently has been shown to activate MAP kinase (ERK1/2) in various cell types as well as in heterologous expression systems. In this study we show that the CaR agonist NPS R-467 (1 muM), which does not activate the CaR by itself, robustly activates ERK1/2 in the presence of a low concentration of Ca2+ (0.5 mM CaCl2) in human embryonic kidney (HEK) cells permanently expressing the human CaR (HEK-hCaR). Ca2+ (4 mM) also activates ERK1/2 but with differing kinetics. CaR-dependent ERK1/2 activation begins to desensitize to 4 mM Ca2+ after 10 min, whereas there is no desensitization to NPS R-467/CaCl2 as late as 4 h. Moreover, recovery from desensitization occurs as rapidly as 30 min with 4 mM CaCl2. Pretreatment of HEK-hCaR cells with concanavalin A (250 mug/ml) to block CaR internalization completely eliminated the NPS R-467/CaCl2-mediated ERK1/2 activation but did not block the 2-min time point of 4 mM Ca2+-mediated ERK1/2 activation. Neither dominant-negative dynamin (K44A) nor dominant-negative beta-arrestin inhibited ERK1/2 activation by either CaR agonist treatment, suggesting that CaR- elicited ERK1/2 signaling occurs via a dynamin-independent pathway. Pertussis toxin pretreatment partially attenuated the 4 mM Ca2+-ERK1/2 activation; this attenuated activity was completely restored by co-expression of the Galpha(i2)(C351I) but not Galpha(i1)(C351I) or Galpha(i3)(C351I) G proteins, PTX-insensitive G protein mutants. Taken together, these data suggest that both 4 mM Ca2+ and NPS R-467/CaCl2 activate ERK1/2 via distinguishable pathways in HEK-hCaR cells and may represent a nexus to differentially regulate differentiation versus proliferation via CaR activation.