Phosphoinositide 3-kinase in nitric oxide synthesis in macrophage: critical dimerization of inducible nitric-oxide synthase.
Phosphoinositide 3-kinase (PI3K) has important functions in various biological systems, including immune response. Although the role of PI3K in signaling by antigen-specific receptors of the adaptive immune system has been extensively studied, less is known about the function of PI3K in innate immunity. In the present study, we demonstrate that macrophages deficient for PI3K (p85alpha regulatory subunit) are impaired in nitric oxide (NO) production upon lipopolysaccharide and interferon-gamma stimulation and thus vulnerable for intracellular bacterial infection such as Chlamydophila pneumoniae. Although expression of inducible nitric-oxide synthase (iNOS) is induced normally in PI3K-deficient macrophages, dimer formation of iNOS protein is significantly impaired. The amount of intracellular tetrahydrobiopterin, a critical stabilizing cofactor for iNOS dimerization, is decreased in the absence of PI3K. In addition, induction of GTP cyclohydrolase 1, a rate-limiting enzyme for biosynthesis of tetrahydrobiopterin, is greatly reduced. Our current results demonstrate a critical role of class IA type PI3K in the bactericidal activity of macrophages by regulating their NO production through GTP cyclohydrolase 1 induction.
Sakai
Kouhei
K
Department of Microbiology and Immunology, Yamaguchi University School of Medicine, 1-1-1 Minami-Kogushi, Ube-shi, Yamaguchi-Ken 755-8505, Japan.
Suzuki
Harumi
H
Oda
Hiroyo
H
Akaike
Takaaki
T
Azuma
Yoshinao
Y
Murakami
Tomoyuki
T
Sugi
Kazuro
K
Ito
Takehito
T
Ichinose
Hiroshi
H
Koyasu
Shigeo
S
Shirai
Mutsunori
M
D000818:Animals; D001708:Biopterins / Q000378:metabolism; D002478:Cells, Cultured; D023521:Chlamydophila Infections / Q000276:immunology / Q000378:metabolism; D016993:Chlamydophila pneumoniae / Q000254:growth & development; D019281:Dimerization; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D006136:GTP Cyclohydrolase / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000201:enzymology* / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009569:Nitric Oxide / Q000096:biosynthesis / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000737:chemistry* / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
D008070:Lipopolysaccharides; D001708:Biopterins; D009569:Nitric Oxide; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D019869:Phosphatidylinositol 3-Kinases; D006136:GTP Cyclohydrolase