TRAF6 activation of PI 3-kinase-dependent cytoskeletal changes is cooperative with Ras and is mediated by an...

Area of Science:

• Cell Biology
• Molecular Biology
• Signal Transduction

Background:

• Interleukin-1 (IL-1) is known to influence the actin cytoskeleton.
• Phosphoinositide 3-kinase (PI 3-kinase) plays a critical role in cellular signaling pathways.

Purpose of the Study:

• To investigate the role of IL-1 in actin cytoskeleton reorganization.
• To elucidate the mechanism of PI 3-kinase activation by IL-1 and associated proteins.
• To identify the molecular interactions required for IL-1-induced cellular responses.

Main Methods:

• Utilized expression vectors encoding fluorescent protein-fused proteins to detect PI 3-kinase products.
• Employed conventional and split fluorescent protein probes in living cells to study protein interactions.
• Assessed protein interactions, PI 3-kinase activation, and NF-kappaB activation under various conditions.

Main Results:

• IL-1 treatment or expression of TRAF6, Src, MyD88, or dominant-positive PI 3-kinase activated PI 3-kinase, leading to filopodia formation.
• TRAF6 polyproline motif and Src catalytic activity were essential for IL-1-induced responses, blocked by PI 3-kinase, Src, and Ras inhibitors.
• TRAF6 and Src interaction, mediated by TRAF6 polyproline and Src SH3 domains, occurred in the cytoplasm and was required for PI 3-kinase activation.

Conclusions:

• The interaction between TRAF6 and Src is critical for IL-1-induced PI 3-kinase activation and subsequent cell morphology changes.
• Sequestosome formation is inversely correlated with PI 3-kinase and NF-kappaB activation.
• Src activation is necessary but not sufficient for NF-kappaB activation and is not inhibited by IRAK2, suggesting distinct signaling roles.