Sox2 is a key factor for maintaining embryonic stem cell (ESS) pluripotency, but little is known about its posttranslational regulation. Here we present evidence that the precise level of Sox2 proteins in ESCs is regulated by a balanced methylation and phosphorylation switch. Set7 monomethylates Sox2 at K119, which inhibits Sox2 transcriptional activity and induces Sox2 ubiquitination and degradation. The E3 ligase WWP2 specifically interacts with K119-methylated Sox2 through its HECT domain to promote Sox2 ubiquitination. In contrast, AKT1 phosphorylates Sox2 at T118 and stabilizes Sox2 by antagonizing K119me by Set7 and vice versa. In mouse ESCs, AKT1 activity toward Sox2 is greater than that of Set7, leading to Sox2 stabilization and ESC maintenance. In early development, increased Set7 expression correlates with Sox2 downregulation and appropriate differentiation. Our study highlights the importance of a Sox2 methylation-phosphorylation switch in determining ESC fate.

Lysine crotonylation on histones is a recently identified post-translational modification that has been demonstrated to associate with active promoters and to directly stimulate transcription. Given that crotonyl-CoA is essential for the acyl transfer reaction and it is a metabolic intermediate widely localized within the cell, we postulate that lysine crotonylation on nonhistone proteins could also widely exist. Using specific antibody enrichment followed by high-resolution mass spectrometry analysis, we identified hundreds of crotonylated proteins and lysine residues. Bioinformatics analysis reveals that crotonylated proteins are particularly enriched for nuclear proteins involved in RNA processing, nucleic acid metabolism, chromosome organization, and gene expression. Furthermore, we demonstrate that crotonylation regulates HDAC1 activity, expels HP1α from heterochromatin, and inhibits cell cycle progression through S-phase. Our data thus indicate that lysine crotonylation could occur in a large number of proteins and could have important regulatory roles in multiple nuclei-related cellular processes.

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Recent studies indicate that histones are subjected to various types of acylation including acetylation, propionylation and crotonylation. CBP and p300 have been shown to catalyze multiple types of acylation but are not conserved in evolution, raising the question as to the existence of other enzymes for histone acylation and the functional relationship between well-characterized acetylation and other types of acylation. In this study, we focus on enzymes catalyzing histone crotonylation and demonstrate that among the known histone acetyltransferases, MOF, in addition to CBP and p300, also possesses histone crotonyltransferase (HCT) activity and this activity is conserved in evolution. We provide evidence that CBP and p300 are the major HCTs in mammalian cells. Furthermore, we have generated novel CBP/p300 mutants with deficient histone acetyltransferase but competent HCT activity. These CBP/p300 mutants can substitute the endogenous CBP/p300 to enhance transcriptional activation in the cell, which correlates with enhanced promoter crotonylation and recruitment of DPF2, a selective reader for crotonylated histones. Taken together, we have identified MOF as an evolutionarily conserved HCT and provide first cellular evidence that CBP/p300 can facilitate transcriptional activation through histone acylation other than acetylation, thus supporting an emerging role for the non-acetylation type of histone acylation in transcription and possibly other chromatin-based processes.