Phosphatidylinositol-4-Kinase Ii Alpha Licenses Phagosomes For Tlr4 Signaling And Mhc-Ii Presentation In Dendritic Cells

Toll-like receptor (TLR) recruitment to phagosomes in dendritic cells (DCs) and downstream TLR signaling are essential to initiate antimicrobial immune responses. However, the mechanisms un-derlying TLR localization to phagosomes are poorly characterized. We show herein that phosphatidylinositol-4-kinase II alpha (PI4KII alpha) plays a key role in initiating phagosomal TLR4 responses in murine DCs by generating a phosphatidylinositol-4-phosphate (PtdIns4P) platform conducive to the binding of the TLR sorting adaptor TollIL1 receptor (TIR) domain-containing adaptor protein (TIRAP). PI4KII alpha is recruited to maturing lipopolysaccharide (LPS)-containing phagosomes in an adaptor protein-3 (AP-3)-dependent manner, and both PI4KII alpha and PtdIns4P are detected on phagosomal membrane tubules. Knockdown of PI4KII alpha-but not the related PI4KII beta- impairs TIRAP and TLR4 localization to phagosomes, reduces proinflammatory cytokine secretion, abolishes phagosomal tubule formation, and impairs major histocompatibility complex II (MHC-II) presentation. Phagosomal TLR responses in PI4KII alpha-deficient DCs are restored by reexpression of wild-type PI4KII alpha, but not of variants lacking kinase activity or AP-3 binding. Our data indicate that PI4KII alpha is an essential regulator of phagosomal TLR signaling in DCs by ensuring optimal TIRAP recruitment to phagosomes.