Laulajainen M, Muranen T, Carpén O, Grönholm M
Department of Pathology, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland.
Oncogene. 2008 May 22;27(23):3233-43. doi: 10.1038/sj.onc.1210988. Epub 2007 Dec 10.
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.
编码默林（一种与膜突蛋白、埃兹蛋白、根蛋白类似的蛋白质）的神经纤维瘤病2型肿瘤抑制基因（NF2）发生突变会诱发神经系统肿瘤。默林定位于细胞膜，在那里它将肌动蛋白细胞骨架与膜蛋白相连。在许多细胞类型中，细胞增殖受默林调控，但默林的肿瘤抑制功能仍不清楚。有研究表明磷酸化作用可调节默林的活性。默林C端的丝氨酸518可被p21激活激酶（PAKs）和蛋白激酶A（PKA）磷酸化。在本研究中，我们在默林的N端鉴定出一个新的PKA磷酸化位点——丝氨酸10。我们发现丝氨酸10的非磷酸化形式（S10A）会影响细胞形态。对该位点的调控也会影响体内肌动蛋白细胞骨架的组织和动态变化，因为默林S10A会减少细胞内F-肌动蛋白的量，而默林S10D会使F-肌动蛋白丝稳定。通过伤口愈合试验和活细胞成像，我们证明丝氨酸10的去磷酸化会导致迁移缺陷，这可能是由于细胞形成片状伪足的能力改变所致。本研究表明默林在介导PKA诱导的肌动蛋白细胞骨架变化中发挥作用。
