Rab8a interacts directly with PI3Kγ to modulate TLR4-driven PI3K and mTOR signalling

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Toll-like receptor 4 (TLR4) activation by lipopolysaccharide (LPS) initiates innate immune responses.
• Regulation of TLR4-induced cytokine release is crucial for preventing excessive inflammation and disease.
• Emerging mechanisms for controlling TLR-induced immune responses are actively being investigated.

Purpose of the Study:

• To identify novel regulatory mechanisms of TLR4-induced cytokine production.
• To investigate the role of small GTPase Rab8a and phosphatidylinositol 3-kinase gamma (PI3Kγ) in TLR4 signaling.
• To elucidate how these molecules influence inflammatory responses and cytokine profiles.

Main Methods:

• Localization of TLR4 complexes in LPS-induced dorsal ruffles on macrophage surfaces.
• Analysis of Rab8a enrichment in these ruffles and its interaction with PI3Kγ.
• Assessment of Rab8a and PI3Kγ's impact on Akt and mammalian target of rapamycin (mTOR) signaling pathways.
• Evaluation of the effects on TLR4 endocytosis and cytokine profile biasing.

Main Results:

• TLR4 complexes were found in LPS-induced dorsal ruffles.
• Rab8a was enriched in these ruffles and recruited PI3Kγ via its Ras-binding domain.
• Rab8a and PI3Kγ regulate Akt signaling downstream of surface TLR4.
• These molecules do not affect TLR4 endocytosis but do regulate mTOR signaling.
• Rab8a and PI3Kγ bias the cytokine profile to constrain inflammation.

Conclusions:

• Rab8a and PI3Kγ are key regulators of TLR4 signaling at the macrophage surface.
• Their interaction influences Akt and mTOR pathways, impacting cytokine production.
• This mechanism provides a novel way to control innate immune inflammatory responses.