Cross-talk between MECP2 post-translational modifications and MECP2 function upon glucocorticoid stress hormone stimulation

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MECP2 (methyl CpG binding protein 2) is a central epigenetic regulator, it controls chromatin structure and transcriptional state at a genome-wide level by binding to methylated DNA and recruiting histone modifying enzymes. MECP2 plays an essential role for the proper functioning of the central nervous system and mutations in the MECP2 gene are linked to severe neurological disorders in humans (such as Rett syndrome, the second most common human mental retardation disorder in females). Importantly, post-translational MECP2 modifications have been identified as a critical level of regulation of this protein. Notably, MECP2 phosphorylation has been linked to neuronal activity and stress. In a proteomic screen for MECP2 interacting proteins we have found that MECP2 interacts with and is poly(ADP-ribosyl)ated by PARP-1. We showed that this modification modulates MECP2 ability to bind to and condense chromatin. In a separate screen for MECP2 modifications we found, amongst other modifications, that MECP2 is arginine methylated in brain tissue. It is highly conceivable that the type of posttranslational modification and the genomic localization of differently modified MECP2 proteins are ways to fine tune and diversify MECP2 function in neuronal cells across the genome. However, very little is known about the effects of specific MECP2 modifications. In this project, we will investigate, in a systematic way, MECP2 post-translational modifications that occur upon stimulation with glucocorticoid stress hormones and study their role in regulating chromatin structure and gene activity in hippocampal cells. Building upon our preliminary results, we will focus on poly(ADP-ribosyl)ation and arginine methylation and relate these with phosphorylation. Our specific aims are to: i) characterize MECP2 post-translational modifications (PTMs) and their change upon stress hormone treatment; ii) analyze whether and how PTMs affect MECP2 protein interactions; iii) test the functional relevance of these modifications for MECP2 chromatin binding, chromatin structure and transcriptional regulation; iv) analyze how PTMs are affected by or affect the function of MECP2 proteins produced by disease mutant MECP2 genes. This work should significantly contribute to the elucidation of the role of MECP2 under physiological and pathophysiological conditions and provide important clues as to the etiology of MECP2-related neurological disorders. As post-translational modifications are very suited to pharmacological inhibition, it should also outline new therapeutic approaches.