Calcium-sensing receptors (CaSRs) regulate systemic Ca 2? ho-meostasis. Loss-of-function mutations cause familial benign hy-pocalciuric hypercalcemia (FHH) or neonatal severe hyperparathy-roidism (NSHPT). FHH/NSHPT mutations can reduce trafficking ofCaSRs to the plasma membrane. CaSR signaling is potentiated byagonist-driven anterograde CaSR trafficking, leading to a newsteadystatelevelofplasmamembraneCaSR,whichismaintained,with minimal functional desensitization, as long as extracellularCa 2? iselevated.ThisrequirementforCaSRsignalingtodriveCaSRtraffickingtotheplasmamembraneledustoreconsiderthemech-anism(s)contributingtodysregulatedtraffickingofFHH/NSHPTmu-tants. We simultaneously monitored dynamic changes in plasmamembrane levels of CaSR and intracellular Ca 2? , using a chimericCaSR construct, which allowed explicit tracking of plasma mem-brane levels of mutant or wild-type CaSRs in the presence of non-chimericpartners.Expressionofmutantsalonerevealedseverede-fects in plasma membrane targeting and Ca 2? signaling, whichwere substantially rescued by coexpression with wild-type CaSR.Biasing toward heterodimerization of wild-type and FHH/NSHPTmutants revealed that intracellular Ca 2? oscillations were insuffi-cient to rescue plasma membrane targeting. Coexpression of thenonfunctional mutant E297K with the truncation CaSR?868 ro-bustly rescued trafficking and Ca 2? signaling, whereas coexpres-sionofdistinctFHH/NSHPTmutantsrescuedneithertraffickingnorsignaling. Our study suggests that rescue of FHH/NSHPT mutantsrequires a steady state intracellular Ca 2? response when extracel-lular Ca 2? is elevated and argues that Ca 2? signaling by wild-typeCaSRs rescues FHH mutant trafficking to the plasma membrane.
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