RGS2-Mediated Intracellular Ca²⁺ Level Plays a Key Role in the Intracellular Replication of Brucella abortus Within Phagocytes

Background. Brucella abortus can proliferate within professional and nonprofessional phagocytic host cells and thereby successfully bypass the bacteriocidal effects of phagocytes. However, the intracellular survival mechanism and factors of virulence are not fully understood. Methods. We have investigated the role of the regulator of G protein signaling 2 (RGS2), an intracellular calcium ([Ca²⁺] ¡ ) regulator of the host cell, in the intracellular survival of B. abortus within phagocytes. Results. B. abortus infection markedly induced RGS2 messenger RNA expression in early phase and increased the [Ca²⁻] ¡ level up to 24 hours postinfection within macrophages from wild-type mice. The [Ca²⁺] ¡ level, however, was not influenced by B. abortus infection within macrophages from RGS2-deficient mice. Furthermore, B. abortus survival was reduced within RGS2-deficient macrophages, and hence bacterial proliferation was inhibited in RGS2-deficient mice. Moreover, treatment with the Ca²⁺ chelator ethylenediaminetetraacetic acid (EDTA) or l, 2-bis-(2-amino-phenoxy) ethane-N, N, N˒,N˒-tetraacetic acid acetoxymethyl ester (BAPTA-AM) and the L-type Ca²⁺ channel-blocking agent nifedipine or genistein also showed a reduced intracellular replication of B. abortus within macrophages. Conclusion. These results indicate that B. abortus infection induces host RGS2 expression and that up-regulation of [Ca²⁺] ¡ levels is an essential factor for the intracellular survival of B. abortus within phagocytes.