Phosphorylation of methyl-CpG binding protein 2 (MeCP2) regulates the intracellular localization during neuronal cell differentiation.

Methyl-CpG binding protein 2 (MeCP2) is a transcriptional repressor which recognizes methylated CpG dinucleotides. Mutations in the MeCP2 gene is known to cause human autistic disease Rett syndrome, but its molecular mechanisms remain to be elucidated. Since MeCP2 is a DNA-binding protein, it has been believed that MeCP2 functions only in the nucleus. We herein show that MeCP2 is localized in the cytosol as well as in the nucleus of neuronal cells. Through the use of immunofluorescence and Western blot analyses, MeCP2 was found to be localized both in the nucleus and cytosol of rat PC-12 and mouse Neuro2a cells before neuronal differentiation, and it was translocated into the nucleus during differentiation. In primary cultured neurons from mouse cortex, MeCP2 was expressed in whole cell bodies on the first day of culture while after 7 days of culture, MeCP2 was localized mainly in the nucleus. Furthermore, MeCP2 was re-localized in the nucleus and cytosol after 14 days of culture. To study the molecular mechanisms of translocation, we analyzed the post-translational modification of MeCP2. The cytosolic MeCP2 was Ser/Thr-phosphorylated, while the nuclear MeCP2 was not. Both the cytosolic and nuclear MeCP2 were SUMOylated, which has been reported to be a nuclear transport signal. Our data suggests that the nuclear translocation of neuronal MeCP2 was induced during differentiation and/or maturation, and that Ser/Thr-phosphorylation regulates its translocation.