Journal
PLOS ONE
Volume 4, Issue 3, Pages -Publisher
PUBLIC LIBRARY SCIENCE
DOI: 10.1371/journal.pone.0004686
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Funding
- Instituto de Salud Carlos III [PI060239, PI060705, PI070908]
- Xunta de Galicia [PGIDIT05BTF20802PR, PGIDIT06PXIB918322PR, PGIDIT06PXIB918360PR]
- University of Santiago de Compostela [Pfizer Young Investigator Fellowship]
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The aim of the present study was to identify the signaling mechanisms to ghrelin-stimulated activation of the serine/threonine kinase Akt. In human embryonic kidney 293 (HEK293) cells transfected with GHS-R1a, ghrelin leads to the activation of Akt through the interplay of distinct signaling mechanisms: an early G(i/o) protein-dependent pathway and a late pathway mediated by beta-arrestins. The starting point is the G(i/o)-protein dependent PI3K activation that leads to the membrane recruitment of Akt, which is phosphorylated at Y by c-Src with the subsequent phosphorylation at A-loop (T308) and HM (S473) by PDK1 and mTORC2, respectively. Once the receptor is activated, a second signaling pathway is mediated by beta-arrestins 1 and 2, involving the recruitment of at least beta-arrestins, c-Src and Akt. This beta-arrestin-scaffolded complex leads to full activation of Akt through PDK1 and mTORC2, which are not associated to the complex. In agreement with these results, assays performed in 3T3-L1 preadipocyte cells indicate that b-arrestins and c-Src are implicated in the activation of Akt in response to ghrelin through the GHS-R1a. In summary this work reveals that c-Src is crucially involved in the ghrelin-mediated Akt activation. Furthermore, the results support the view that b-arrestins act as both scaffolding proteins and signal transducers on Akt activation.
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