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First published online 28 March 2006
doi: 10.1242/jcs.02889

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

¹ Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
² Department of Periodontology, Faculty of Dentistry, Khon Kaen University, Khon Kaen, 40002, Thailand
³ Department of Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA 02115, USA
⁴ Department of Immunology, University of Occupational and Environmental Health, Kitakyushu, 807, Japan
⁵ Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University School of Pharmacy, West Lafayette, IN 47907, USA
⁶ Center for Bone Biology, Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA

^* Author for correspondence (e-mail: auron{at}pitt.edu)

Accepted 9 January 2006

Interleukin 1 (IL-1) has been implicated in the reorganization of the actin cytoskeleton. An expression vector encoding a PKB/Akt pleckstrin-homology domain fused to a fluorescent protein was used to detect phosphoinositide 3-kinase (PI 3-kinase) products. It was observed that PI 3-kinase was activated either by treatment with IL-1 or by expression of either TRAF6, Src, MyD88 or dominant-positive PI 3-kinase, and resulted in the formation of long filopodia-like cellular protrusions that appeared to branch at membrane sites consisting of clusters of phosphoinositide. This depended upon a TRAF6 polyproline motif and Src catalytic activity, and was blocked by inhibitors of PI 3-kinase, Src and Ras. Using both conventional and split fluorescent protein probes fused to expressed TRAF6 and Src in living cells, the polyproline sequence of TRAF6 and the Src-homology 3 (SH3) domain of Src were shown to be required for interaction between these two proteins. Interaction occurred within the cytoplasm, and not at either the cell membrane or cytoplasmic sequestosomes. In addition, co-transfection of vectors expressing fluorescent-protein-fused TRAF6 and non-fluorescent MyD88, IRAK1 and IRAK2 revealed an inverse correlation between increased sequestosome formation and activation of both PI 3-kinase and NF-B. Although a key factor in TRAF6-dependent activation of PI 3-kinase, ectopic expression of Src was insufficient for NF-B activation and, in contrast to NF-B, was not inhibited by IRAK2.

Key words: Filopodia, BiFC/Split GFP, Sequestosome, Proteasome, IL-1/Toll receptor

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