The Phosphatidylinositol 3-Kinase-Akt Pathway Limits Lipopolysaccharide Activation of Signaling Pathways and Expression of Inflammatory Mediators in Human Monocytic Cells

Guha, Mausumee; Mackman, Nigel

doi:10.1074/jbc.m203298200

Cited by 716 publications

(707 citation statements)

References 58 publications

Supporting

Mentioning

595

Contrasting

Unclassified

Order By: Relevance

“…3B). In agreement with previous data [4][5][6], the presence of wortmannin in LPSstimulated WT BMDMs completely blocked the phosphorylation of Akt and p70 S6k and further decreased IkBa levels; however, in Cot/tpl2 KO BMDMs the presence of wortmannin did not amplify the LPS-mediated decrease in IkBa expression (Fig. 3C).…”

supporting

confidence: 93%

“…Furthermore, the presence of wortmannin further decreases IkBa in LPS-stimulated WT macrophages, reaching the levels observed in stimulated Cot/tpl2 KO BMDMs. It should be noted that Cot/tpl2 deficiency also impairs IkBa recovery in mouse embryonic fibroblasts following TNF-a receptor activation [34].TLR-activated PI3K pathway also represses Erk1/2 phosphorylation [5]; these data suggest that activated Erk1/2 induces its own down-regulation via a negative feedback loop by controlling Akt phosphorylation. Nevertheless, and overall, these data indicate that the capacity of Cot/tpl2-MKK1-Erk1/2 to mediate the TLR-dependent activation of Akt and p70 S6k allows Cot/tpl2 to fine-control the activation state of other signalling pathways.…”

mentioning

confidence: 83%

See 1 more Smart Citation

Cot/tpl2 activity is required for TLR‐induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

et al. 2011

View full text Add to dashboard Cite

LPS stimulation activates IKK and different MAP kinase pathways, as well as the PI3K-AktmTOR-p70 S6k pathway, a negative regulator of these MyD88-dependent intracellular signals. Here, we show that Cot/tpl2, a MAP3K responsible for the activation of the MKK1-Erk1/2, controls P-Ser473 Akt and P-Thr389 p70 S6k phosphorylation in LPS-stimulated macrophages. Analysis of the intracellular signalling in Cot/tpl2 KO macrophages versus WT macrophages reveals lower IjBa recovery and higher phosphorylation of JNK and p38a after 1 h of LPS stimulation. Moreover, Cot/tpl2 deficiency increases LPS-induced NO synthase 2 (NOS2) expression in macrophages. Inhibition of the PI3K pathway abolishes the differences in IjBa and NOS2 expression between Cot/tpl2 KO and WT macrophages following LPS administration. Furthermore, in zymosan-and polyI:C-stimulated macrophages, Cot/tpl2 mediates P-Ser473 Akt phosphorylation, increases IjBa levels and decreases NOS2 expression. In conclusion, these data reveal a novel role for the Cot/tpl2 pathway in mediating TLR activation of the Akt-mTOR-p70 S6k pathway, allowing Cot/tpl2 to fine-control the activation state of other signalling pathways.Key words: Akt . Cot/tpl2 . Macrophage . NO synthase 2 . p70 S6k . TLR See accompanying Commentary by Martinez Supporting Information available online IntroductionStimulation of TLRs by the different PAMPs triggers macrophage activation, starting a specific functional program that culminates in the production of inflammatory mediators. With the exception of TLR3, TLRs use MyD88 as a central intracellular adaptor, thereby activating multiple downstream intracellular pathways including IKK. TLR3 and TLR4 recruit the TRIF adaptor, which also activates IKK, but specifically activating TBK1 and the transcription factor IRF3 (reviewed in [1,2]). Translocation of IRF3 to the nucleus is necessary, although not sufficient, to induce IFN-b expression [3]. Most TLRs also activate the PI3K-Akt-mTOR-p70 S6k pathway, which is considered to be a negative regulator of TLR activation in macrophages and myeloid dendritic cells. Inhibition of this PI3K-Akt-mTOR-p70 S6k pathway in TLR-activated cells augments NO synthase 2 (NOS2) expression [4][5][6][7][8].Adequate TLR4 stimulation induces the formation of a TLR receptor complex that recruits proteins such as MyD88 and p85 PI3 K [9]. PI3K subsequently activates the Akt-mTOR-p70 S6k pathway. Moreover, TLR-bound MyD88 recruits IRAK4 and IRAK1. The phosphorylation of IRAK1 by IRAK4 facilitates TRAF6 [1,10]). Activated IKK-b phosphorylates p105 NF-kB at multiple residues [11][12][13], which targets the rapid degradation of p105 NF-kB to p50 NF-kB [11][12][13][14]. In resting cells, Cot/tpl-2 forms a stable and inactive complex with p105 NF-kB and ABIN2 (A20-binding inhibitor of NF-kB2), among other proteins, protecting Cot/tpl-2 from degradation. The partial proteolysis of p105 NFkB to p50 NF-kB releases Cot/tpl-2 from the complex [15][16][17][18][19][20]. Dissociated and adequately phosphorylated Cot/tpl2 [21][22][23][24] fully...

show abstract

supporting

confidence: 93%

mentioning

confidence: 83%

Cot/tpl2 activity is required for TLR‐induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

et al. 2011

View full text Add to dashboard Cite

show abstract

“…Seemingly at variance with this scenario of transcriptional regulation is that in RAW264.7 macrophages, LPS-induced downregulation of TLR4 mRNA has been attributed to an increase in TLR4 mRNA turnover (Roger et al, 2005). LPS is known to activate the PI3K/Akt pathway (Guha and Mackman, 2002) and this event may, through inactivation of MAPK p38 (Fukao and Koyasu, 2003), decrease mRNA stability at the 3 -UTR region of a variety of genes (Dean et al, 2004). In favor of this mechanism is our finding that inhibtion of the PI3K/Akt pathway enhances NF-B activation as well as the LPS-mediated downregulation of TLR4 and TLR5 mRNA and upregulation of TLR2 and MIP-2 mRNA (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…To further investigate the basis of the differential cross-regulation of the TLRs, we investigated the role of the phosphatidylinositol 3-kinase (PI3K/Akt) pathway implicated in the regulation of TLR signaling and cytokine production (Guha and Mackman, 2002;Martin et al, 2003). In mIC cl2 cells, specific inhibition of PI3K with wortmannin (Hazeki et al, 2006;Yano et al, 1993) caused an increase of NF-B luciferase activity in response to Pam 3 CSK 4 , LPS as well as flagellin (Fig.…”

Section: Contribution Of the Pi3k/akt Pathway To Tlr Cross-regulationmentioning

confidence: 99%

Ligand-induced differential cross-regulation of Toll-like receptors 2, 4 and 5 in intestinal epithelial cells

Aubel

Keestra

Krooshoop

et al. 2007

Molecular Immunology

View full text Add to dashboard Cite

Toll-like receptors (TLR) 2, TLR4 and TLR5 are primary mucosal sensors of microbial patterns. Dissection of the cross-talk between TLRs in intestinal cells has thus far been hampered by the lack of functional TLR2 and TLR4 in in vitro model systems. Here we report that the mouse intestinal epithelial cell line mIC cl2 expresses these TLRs and that receptor expression and function are regulated by environmental TLR stimuli. Our results show that stimulation of TLR5 by bacterial flagellin resulted in upregulated TLR2 and TLR4 mRNA and concomitant sensitization of the cells for subsequent TLR2 (Pam 3 CSK 4 ) and TLR4 (LPS) stimulation. Exposure to low amounts of either Pam 3 CSK 4 or LPS in turn downregulated TLR5 mRNA and attenuated subsequent flagellin-mediated NF-B activation, pointing to a negative feedback mechanism. Pam 3 CSK 4 and LPS also downregulated TLR4 mRNA but upregulated TLR2 mRNA and sensitized cells for subsequent TLR2 stimulation. Inhibition of the phosphatidylinositol-3-kinase/Akt pathway only affected LPS-mediated TLR cross-talk indicating that differential TLR cross-regulation was conferred via different mechanisms. Together, our results demonstrate that the expression and function of TLR in intestinal cells are highly dynamic and tightly regulated in response to encountered bacterial stimuli.

show abstract

“…5 Exploiting AKT pathway to inhibit host cell apoptosis has also been documented during infection with Salmonella, Anaplasma, Toxoplasma and Trypanosome. 6,7 Host immune activation essential to eliminate intracellular pathogens is also negatively modulated by AKT 8 and constitutively active AKT was shown to increase the LPSinduced production of anti-inflammatory cytokine IL-10 (ref 9) and to down-regulate p65 and GSK-3β (ref 10). Two major proteins which contribute in diversifying AKT signaling are β-catenin and FOXO-1.…”

mentioning

confidence: 99%

Leishmania donovani inhibits macrophage apoptosis and pro-inflammatory response through AKT-mediated regulation of β-catenin and FOXO-1

et al. 2016

View full text Add to dashboard Cite

In order to establish infection, intra-macrophage parasite Leishmania donovani needs to inhibit host defense parameters like inflammatory cytokine production and apoptosis. In the present study, we demonstrate that the parasite achieves both by exploiting a single host regulator AKT for modulating its downstream transcription factors, β-catenin and FOXO-1. L. donovaniinfected RAW264.7 and bone marrow-derived macrophages (BMDM) treated with AKT inhibitor or dominant negative AKT constructs showed decreased anti-inflammatory cytokine production and increased host cell apoptosis resulting in reduced parasite survival. Infection-induced activated AKT triggered phosphorylation-mediated deactivation of its downstream target, GSK-3β. Inactivated GSK-3β, in turn, could no longer sequester cytosolic β-catenin, an anti-apoptotic transcriptional regulator, as evidenced from its nuclear translocation during infection. Constitutively active GSK-3β-transfected L. donovani-infected cells mimicked the effects of AKT inhibition and siRNA-mediated silencing of β-catenin led to disruption of mitochondrial potential along with increased caspase-3 activity and IL-12 production leading to decreased parasite survival. In addition to activating antiapoptotic β-catenin, phospho-AKT inhibits activation of FOXO-1, a pro-apoptotic transcriptional regulator. Nuclear retention of FOXO-1, inhibited during infection, was reversed when infected cells were transfected with dominant negative AKT constructs. Overexpression of FOXO-1 in infected macrophages not only documented increased apoptosis but promoted enhanced TLR4 expression and NF-κB activity along with an increase in IL-1β and decrease in IL-10 secretion. In vivo administration of AKT inhibitor significantly decreased liver and spleen parasite burden and switched cytokine balance in favor of host. In contrast, GSK-3β inhibitor did not result in any significant change in infectivity parameters. Collectively our findings revealed that L. donovani triggered AKT activation to regulate GSK-3β/β-catenin/FOXO-1 axis, thus ensuring inhibition of both host cell apoptosis and immune response essential for its intra-macrophage survival.

show abstract

The Phosphatidylinositol 3-Kinase-Akt Pathway Limits Lipopolysaccharide Activation of Signaling Pathways and Expression of Inflammatory Mediators in Human Monocytic Cells

Cited by 716 publications

References 58 publications

Cot/tpl2 activity is required for TLR‐induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

Cot/tpl2 activity is required for TLR‐induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

Ligand-induced differential cross-regulation of Toll-like receptors 2, 4 and 5 in intestinal epithelial cells

Leishmania donovani inhibits macrophage apoptosis and pro-inflammatory response through AKT-mediated regulation of β-catenin and FOXO-1

Contact Info

Product

Resources

About