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Protein kinase A-mediated phosphorylation of the NF2 tumor suppressor protein merlin at serine 10 affects the actin cytoskeleton

Abstract

Mutations in the neurofibromatosis 2 tumor suppressor gene (NF2) encoding merlin (moesin–ezrin–radixin like-protein) induce tumors of the nervous system. Merlin localizes to the cell membrane where it links the actin cytoskeleton to membrane proteins. Cell proliferation is regulated by merlin in many cell types, but merlin's tumor suppressor function still remains unclear. Phosphorylation has been suggested to regulate merlin's activity. The C-terminal serine 518 is phosphorylated both by p21-activated kinases (PAKs) and protein kinase A (PKA). In this work, we identify a novel PKA phosphorylation site, serine 10, in the N terminus of merlin. We show that a non-phosphorylatable form of serine 10 (S10A) affects cellular morphology. Regulation of this site also influences actin cytoskeleton organization and dynamics in vivo, as merlin S10A reduces the amount of cellular F-actin and merlin S10D stabilizes F-actin filaments. By using a wound-healing assay and live cell imaging, we demonstrate that dephosphorylation of serine 10 leads to defects in migration, possibly through altered ability of the cells to form lamellipodia. This study suggests a role for merlin in mediating PKA-induced changes of the actin cytoskeleton.

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Acknowledgements

We thank Dr Giovannini for the Nf2−/− MEFs and Schwann cells and Dr Hanemann for the retroviral merlin construct. We also thank H Ahola and A Björg-Agustsdottir for their skillful technical assistance. This study was supported by the grants of Department of Defense W81XWH-05-1-0469, the Finnish Cancer Organizations, the Medical Research Fund of Turku University Central Hospital District, Helsinki Graduate School of Biotechnology and Molecular Biology, Biomedicum Helsinki Foundation, Medicinska Understödsföreningen Liv och Hälsa, Emil Aaltonen Foundation, Oskar Öflund Foundation and Svenska kulturfonden.

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Correspondence to M Laulajainen.

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Supplementary Information accompanies the paper on the Oncogene website (http://www.nature.com/onc).

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Laulajainen, M., Muranen, T., Carpén, O. et al. Protein kinase A-mediated phosphorylation of the NF2 tumor suppressor protein merlin at serine 10 affects the actin cytoskeleton. Oncogene 27, 3233–3243 (2008). https://doi.org/10.1038/sj.onc.1210988

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