Negative regulation of ligand-initiated Ca2+uptake by PKC-βII in differentiated HL60 cells

Abstract

In phagocytic cells, fMet-Leu-Phe triggers phosphoinositide remodeling, activation of protein kinase C (PKC), release of intracellular Ca2+ and uptake of extracellular Ca2+. Uptake of extracellular Ca2+ can be triggered by store-operated Ca2+channels (SOCC) and via a receptor-operated nonselective cation channel(s). In neutrophilic HL60 cells, the PKC activator phorbol myristate acetate (PMA) activates multiple PKC isotypes, PKC-α, PKC-β, and PKC-δ, and inhibits ligand-initiated mobilization of intracellular Ca2+ and uptake of extracellular Ca2+. Therefore PKC is a negative regulator at several points in Ca2+ mobilization. In contrast, selective depletion of PKC-β in HL60 cells by an antisense strategy enhanced fMet-Leu-Phe-initiated Ca2+ uptake but not mobilization of intracellular Ca2+. Thapsigargin-induced Ca2+ uptake through SOCC was not affected by PKC-βII depletion. Thus PKC-βII is a selective negative regulator of Ca2+ uptake but not release of intracellular Ca2+ stores. PKC-βII inhibits a receptor-operated cation or Ca2+ channel, thus inhibiting ligand-initiated Ca2+ uptake.