SCF^FBXO22 Regulates Histone H3 Lysine 9 and 36 Methylation Levels by Targeting Histone Demethylase KDM4A for Ubiquitin-Mediated Proteasomal Degradation

Abstract

Reversible methylation of lysine residues has emerged as a central mechanism for epigenetic regulation and is a component of the "histone code," which engenders histones with gene regulatory information. KDM4A is a histone demethylase that targets tri-and dimethylation marks on histone H3 lysines 9 and 36. While the abundance of KDM4A oscillates in the cell cycle, little is known how this enzyme is regulated to achieve targeted effects on specific histone residues in chromatin. Here, we report that a previously unstudied SCF FBXO22 ubiquitin ligase complex controls the activity of KDM4A by targeting it for proteasomal turnover. FBXO22 functions as a receptor for KDM4A by recognizing its catalytic JmjN/JmjC domains via its intracellular signal transduction (FIST) domain. Modulation of FBXO22 levels by RNA interference or overexpression leads to increased or decreased levels of KDM4A, respectively. Changes in KDM4A abundance correlate with alterations in histone H3 lysine 9 and 36 methylation levels, and transcription of a KDM4A target gene, ASCL2. Taken together, these results demonstrate that SCF FBXO22 regulates changes in histone H3 marks and cognate transcriptional control pathways by controlling KDM4A levels, and they suggest a potential role for FBXO22 in development, differentiation, and disease through spatial and temporal control of KDM4A activity.Histones undergo many posttranslational modifications, including acetylation, methylation, phosphorylation, and ubiquitylation (8,17,41). These modifications are governed by enzymes that can add or remove these marks, and they are interpreted by proteins containing specific recognition modules whose action on chromatin alters the transcriptional properties or fate of the cell. Histone methylation typically occurs on lysine and arginine residues, and the extent (mono-, di-, or trimethylation) and position of methylation on histones are associated with often opposing biological outcomes (52). Histone methylation is a posttranslational modification regulated by two classes of proteins, histone methyltransferases and histone demethylases, which can add or remove the mark, respectively, often in a spatially and temporally regulated manner. As a result of its role in key cellular processes, misregulation of histone methylation is associated with human diseases, including cancer (33). Despite clear biological roles for histone methyltransferases and demethylases, to date little is known about how these enzymes are regulated, especially at the posttranslational level.

FBXO22 Protein Is Required for Optimal Synthesis of the N-Methyl-d-Aspartate (NMDA) Receptor Coagonist d-Serine

“…3A, Hom). As expected, the levels of the SCF FBXO22a substrate KDM4A increased in the purified nucleus and membrane fraction, confirming the role of hFBXO22a in regulating KDM4A levels (33).…”

“…Harper and co-workers (33) reported that the SCF hFBXO22a complex ubiquitinates and regulates the steady-state levels of KDM4A, which demethylates histone H3 lysine 9 and 36 . We wondered whether hFBXO22a is also required for ubiquitination and degradation of SR by the ubiquitin-proteasomal system.…”

“…1A). FBXO22a controls the degradation of KDM4A, a histone demethylase (33), and seems to be involved in the inflammatory response during Salmonella infection (45). In its C-terminal region, FBXO22a has an F-box intracellular transduction C-terminal domain (FIST C), presumably involved in amino acid sensing and signal transduction (46).…”

“…Scale bar ϭ 50 m. The panels are representative of at least three different experiments. *, p Ͻ 0.05; **, p Ͻ 0.01. and, ultimately, the levels of histone 3 methylation and transcription of KDM4A target genes (33). The interaction of FBXO22a with KDM4A is mediated via its FIST domain, whereas the F-Box motif is required for binding to SKP1 at the SCF complex (33).…”

“…*, p Ͻ 0.05; **, p Ͻ 0.01. and, ultimately, the levels of histone 3 methylation and transcription of KDM4A target genes (33). The interaction of FBXO22a with KDM4A is mediated via its FIST domain, whereas the F-Box motif is required for binding to SKP1 at the SCF complex (33). Conversely, we found that SR still interacts with an FBXO22 mutant that lacks both FIST and the F-Box motif (hFBXO22b ⌬20 -67), indicating that both of these domains are not required for the SR-FBXO22 interaction.…”