PGE(2), produced in the lung during
infection with microbes such as Klebsiella pneumoniae, inhibits alveolar macrophage (AM) antimicrobial functions by preventing H(2)O(2) production by
NADPH oxidase (NADPHox). Activation of the NADPHox complex is poorly understood in AMs, although in neutrophils it is known to be mediated by
kinases including PI3K/Akt,
protein kinase C (PKC) δ, p21-activated
protein kinase (PAK),
casein kinase 2 (CK2), and MAPKs. The
p40phox cytosolic subunit of NADPHox has been recently recognized to function as a
carrier protein for other subunits and a positive regulator of
oxidase activation, a role previously considered unique to another subunit, p47phox. The regulation of
p40phox remains poorly understood, and the effect of
PGE(2) on its activation is completely undefined. We addressed these issues in rat AMs activated with
IgG-opsonized K. pneumoniae. The kinetics of
kinase activation and the consequences of
kinase inhibition and silencing revealed a critical role for a PKCδ-PAK-class I PI3K/Akt1 cascade in the regulation of
p40phox activation upon bacterial challenge in AMs; PKCα, ERK, and CK2 were not involved.
PGE(2) inhibited the activation of
p40phox, and its effects were mediated by
protein kinase A type II, were independent of interactions with anchoring
proteins, and were directed at the distal class I PI3K/Akt1 activation step. Defining the
kinases that control AM
p40phox activation and that are the targets for inhibition by
PGE(2) provides new insights into immunoregulation in the infected lung.