Cofactor-activated phosphorylation is required for inhibition of cortical neuron differentiation by Groucho/TLE1.
BACKGROUND: Transcriptional co-repressors of the Groucho/transducin-like Enhancer of split (Gro/TLE) family regulate the expression of a variety of genes and are involved in numerous developmental processes in both invertebrate and vertebrate species. More specifically, Gro/TLE1 participates in mechanisms that inhibit/delay the differentiation of cerebral cortex neural progenitor cells into neurons ... during mammalian forebrain development. The anti-neurogenic function of Gro/TLE1 depends on the formation of protein complexes with specific DNA-binding transcription factors that engage Gro/TLE1 through WRP(W/Y) sequences. Interaction with those transcription partners results in Gro/TLE1 recruitment to selected DNA sites and causes increased Gro/TLE1 phosphorylation. The physiological significance of the latter event, termed "cofactor-activated phosphorylation," had not been determined. Therefore, this study aimed at clarifying the role of cofactor-activated phosphorylation in the anti-neurogenic function of Gro/TLE1. METHODS AND PRINCIPAL FINDINGS: A combination of site-directed mutagenesis, mass spectrometry, biochemistry, primary cell culture, and immunocytochemical assays was utilized to characterize point mutations of Ser-286, a residue that is phosphorylated in vivo and is located within the serine/proline-rich (SP) domain of Gro/TLE1. Mutation of Ser-286 to alanine or glutamic acid does not perturb the interaction of Gro/TLE1 with DNA-binding partners, including the basic helix-loop-helix transcription factor Hes1, a prototypical anti-neurogenic WRP(W/Y) motif protein. Ser-286 mutations do not prevent the recruitment of Gro/TLE1 to DNA, but they impair cofactor-activated phosphorylation and weaken the interaction of Gro/TLE1 with chromatin. These effects are correlated with an impairment of the anti-neurogenic activity of Gro/TLE1. Similar results were obtained when mutations of Ser-289 and Ser-298, which are also located within the SP domain of Gro/TLE1, were analyzed. CONCLUSION: Based on the positive correlation between Gro/TLE1 cofactor-activated phosphorylation and ability to inhibit cortical neuron differentiation, we propose that hyperphosphorylation induced by cofactor binding plays a positive role in the regulation of Gro/TLE1 anti-neurogenic activity.
Mesh Terms:
Amino Acid Sequence, Animals, Cell Differentiation, Cell Line, Cerebral Cortex, Chromatin, Humans, Mice, Molecular Sequence Data, Neurogenesis, Neurons, Peptides, Phosphorylation, Point Mutation, Protein Structure, Tertiary, Repressor Proteins, Serine, Transcription Factors, Transfection
Amino Acid Sequence, Animals, Cell Differentiation, Cell Line, Cerebral Cortex, Chromatin, Humans, Mice, Molecular Sequence Data, Neurogenesis, Neurons, Peptides, Phosphorylation, Point Mutation, Protein Structure, Tertiary, Repressor Proteins, Serine, Transcription Factors, Transfection
PLoS ONE
Date: Dec. 04, 2009
PubMed ID: 19956621
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