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Molecular & Cellular Proteomics 6:114-124, 2007.
© 2007 by The American Society for Biochemistry and Molecular Biology, Inc.

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Research

Proteomics Exploration Reveals That Actin Is a Signaling Target of the Kinase Akt^*

Franck Vandermoere^,, Ikram El Yazidi-Belkoura, Yohann Demont, Christian Slomianny^¶, Johann Antol, Jérôme Lemoine^||,** and Hubert Hondermarck^,

From the ERI-8 INSERM (JE-2488), "Growth factor signaling in breast cancer. Functional proteomics" and ^¶ EMI-0228 INSERM and ^|| UMR-8576 CNRS, IFR-118, University of Sciences and Technologies Lille, 59655 Villeneuve d’Ascq, France

The serine/threonine kinase Akt is a key mediator of cell survival and cell growth that is activated by most growth factors, but its downstream signaling largely remains to be elucidated. To identify signaling partners of Akt, we analyzed proteins co-immunoprecipitated with Akt in MCF-7 breast cancer cells. Mass spectrometry analysis (MALDI-TOF and MS-MS) of SDS-PAGE-separated Akt co-immunoprecipitates allowed the identification of 10 proteins: -actinin, valosin-containing protein, inhibitor B kinase, mortalin, tubulin ß, cytokeratin 8, actin, 14-3-3, proliferating cell nuclear antigen, and heat shock protein HSP27. The identification of these putative Akt binding partners were validated with specific antibodies. Interestingly, the major protein band observed in Akt co-immunoprecipitates was found to be the cytoskeleton protein actin for which a 14-fold increase was observed in Akt-activated compared with non-activated conditions. The interaction between Akt and actin was further confirmed by reverse immunoprecipitation, and confocal microscopy demonstrated a co-localization specifically induced under growth factor stimulation. The use of wortmannin indicated a dependence on the phosphatidylinositol 3-kinase pathway. Using a phospho-Akt substrate antibody, the phosphorylation of actin on an Akt consensus site was detected upon growth factor stimulation, both in cellulo and in vitro, suggesting that actin is a substrate of Akt kinase activity. Interestingly, cortical remodeling of actin associated with cell migration was reversed by small interfering RNA directed against Akt, indicating the involvement of Akt in the dynamic reorganization of actin cytoskeleton germane to breast cancer cell migration. Together these data identify actin as a new functional target of Akt signaling.

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