Store-operated Ca2+ Entry (SOCE) Plays a Role in the Polarization of Neutrophil-like HL-60 Cells by Regulating the Activation of Akt, Src, and Rho Family GTPases

Abstract

Neutrophil polarization is a basic activity involved in the innate immune response, and it may be initiated by extracellular Ca²⁺ entry, a process primarily mediated through store-operated Ca²⁺ entry (SOCE). Yet, the mechanisms by which SOCE participates in cell polarization remain unclear. We hypothesized that Akt- and Src-dependent pathways, traditionally linked to neutrophil polarization, may interact with SOCE in this event. In this study, SKF96365 and 2-APB, inhibitors of SOCE as proved by their inhibition on Mn²⁺ influx, were observed to inhibit the formyl-methionyl-leucyl-phenylalanine (fMLP)–induced influx of Ca²⁺, the activation of Akt, Src, Rac1, Rac2, and Cdc42, and the polarization of differentiated HL-60 (dHL-60) cells. Downregulation of stromal interaction molecule 1 (STIM1), a Ca²⁺ sensor identified to induce SOCE, by siRNA led to decreases in the following indexes: Ca²⁺ entry, activation of Akt, Src, Rac2 (rather than Rac1) and Cdc42, and fMLP-induced polarization. This study suggests that SOCE might be the predominant form of Ca²⁺ entry involved in the regulation of cell polarization, and it may act through the Akt/Src/Rac pathways, as modeled in dHL-60 cells. It also suggests that STIM1 is a key modulator of cell polarization, potentially serving as a target for the designation of anti-immune deficiency therapies.