RP105 Engages Phosphatidylinositol 3-Kinase p110δ To Facilitate the Trafficking and Secretion of Cytokines in Macrophages during Mycobacterial Infection

Abstract

Cytokines are key regulators of adequate immune responses to infection with Mycobacterium tuberculosis. We demonstrate that the p110δ catalytic subunit of PI3K acts as a downstream effector of the TLR family member RP105 (CD180) in promoting mycobacteria-induced cytokine production by macrophages. Our data show that the significantly reduced release of TNF and IL-6 by RP105−/− macrophages during mycobacterial infection was not accompanied by diminished mRNA or protein expression. Mycobacteria induced comparable activation of NF-κB and p38 MAPK signaling in wild-type (WT) and RP105−/− macrophages. In contrast, mycobacteria-induced phosphorylation of Akt was abrogated in RP105−/− macrophages. The p110δ-specific inhibitor, Cal-101, and small interfering RNA–mediated knockdown of p110δ diminished mycobacteria-induced TNF secretion by WT but not RP105−/− macrophages. Such interference with p110δ activity led to reduced surface-expressed TNF in WT but not RP105−/− macrophages, while leaving TNF mRNA and protein expression unaffected. Activity of Bruton’s tyrosine kinase was required for RP105-mediated activation of Akt phosphorylation and TNF release by mycobacteria-infected macrophages. These data unveil a novel innate immune signaling axis that orchestrates key cytokine responses of macrophages and provide molecular insight into the functions of RP105 as an innate immune receptor for mycobacteria.

Identification of STOML2 as a putative novel asthma risk gene associated with IL6R

“…enhancers) or transcription factors. The top three genes most correlated with IL6R expression in this analysis were: FYN (negative correlation), which regulates mast cell function (41), B-cell development (42) and is phosphorylated upon IL-6 binding to IL-6R (43); CD180 (positive correlation), which belongs to the Toll-like receptor family and is involved in innate immune response to mycobacteria (44); and ATP8B2 (positive correlation), which is located in close proximity (53 kb) to IL6R , suggesting that both genes might share a nearby regulatory element. Our results demonstrate that the expression of these genes is to some extent coordinated with that of IL6R in LCLs, and is consistent with the previously suggested role for IL6R in Treg development (4), innate immunity (45) and inflammation (46).…”

The N-terminal peptide moiety of the Mycobacterium tuberculosis 19 kDa lipoprotein harbors RP105-agonistic properties

“…Pam 3 CSK 4 , Pam 2 CSK 4 , and ultrapure LPS from Escherichia coli strain 0111:B4 were obtained from InvivoGen (San Diego, CA, USA). M. tuberculosis 19 kDa lipoprotein was purified as described previously . Limulus amebocyte lysate assays (Lonza, Basel, Switzerland) demonstrated 4 ng endotoxin units per mg of the 19 kDa lipoprotein in all samples tested.…”

“…We previously identified RP105 as a positive regulator of proinflammatory cytokine responses in M. tuberculosis ‐ and M. bovis bacille Calmette Guerin (BCG)‐infected macrophages . Mice deficient in RP105 displayed elevated bacterial burden and pathology in the chronic phase of M. tuberculosis infection .…”

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“…63 It was also shown that RP105 deficient mice are more susceptible to TB and RP105 deficient macrophages produced significantly reduced amounts of inflammatory cytokines than their wild-type counterparts. 64 However, neither mRNA nor protein expression of inflammatory cytokines such as TNF were affected in RP105 deficient mutants macrophages. 64 Through their work the Blumenthal group have demonstrated the RP105-mediated macrophage activation to be distinct from classical Toll-like receptor (TLR) signaling where RP105 directs cytokine trafficking.…”

“…64 However, neither mRNA nor protein expression of inflammatory cytokines such as TNF were affected in RP105 deficient mutants macrophages. 64 Through their work the Blumenthal group have demonstrated the RP105-mediated macrophage activation to be distinct from classical Toll-like receptor (TLR) signaling where RP105 directs cytokine trafficking. 65,66 This novel innate immune signaling pathway involves RP105, BTK and the p110d subunit of phosphoinositide 3-kinase.…”