Histone H4K20 Demethylation by Two hHR23 Proteins

Area of Science:

• Epigenetics
• Molecular Biology
• Biochemistry

Background:

• Histone methylation regulates gene expression, and its removal is mediated by demethylases.
• While LSD1 and JmjC domain proteins are known histone demethylases, many enzymes for specific methylation states remain undiscovered.

Purpose of the Study:

• To identify novel histone demethylases.
• To characterize the enzymatic activity and function of newly identified demethylases.

Main Methods:

• Screening of a cDNA library of 2,500 nuclear proteins.
• In vitro and in vivo demethylation assays.
• Biochemical cofactor requirement analysis (Fe(II), α-ketoglutarate).
• Nuclear Magnetic Resonance (NMR) spectroscopy to identify crucial motifs.

Main Results:

• hHR23A was identified as a histone H4K20 demethylase, reducing H4K20me1/2/3 levels in cells.
• hHR23A specifically demethylates H4K20me1/2/3 in vitro, requiring Fe(II), α-ketoglutarate, and its UBA domains.
• hHR23B also exhibits H4K20 demethylase activity in vitro and in vivo.
• hHR23A/B activate gene transcription by demethylating H4K20me1 and repetitive element transcription by demethylating H4K20me3.
• An HxxxE motif in the UBA1 domain is essential for iron binding and demethylase activity.

Conclusions:

• hHR23A and hHR23B are identified as novel histone H4K20 demethylases.
• These enzymes play a role in regulating gene transcription and repetitive element activity through H4K20 demethylation.
• The UBA domains and specific cofactors are crucial for their enzymatic function.