Structure-function relationship of ASH1L and histone H3K36 and H3K4 methylation

Area of Science:

• Epigenetics and Gene Regulation
• Molecular Biology
• Chromatin Biology

Background:

• ASH1L is a histone methyltransferase crucial for development and implicated in cancer.
• Its C-terminal region contains key functional domains: bromodomain (ASH1L_BD), plant homeodomain (ASH1L_PHD), and bromo-adjacent homology (ASH1L_BAH).

Purpose of the Study:

• To elucidate the biological functions and mechanisms of the C-terminal domains of ASH1L.
• To investigate the functional crosstalk between ASH1L_BD, ASH1L_PHD, and ASH1L_BAH.
• To understand how ASH1L interacts with chromatin and regulates its enzymatic activity.

Main Methods:

• Structural characterization of ASH1L domains.
• Biochemical assays to determine binding specificities (e.g., H3K4me2/3, DNA).
• Cellular localization studies (co-localization with histone marks).

Main Results:

• ASH1L_PHD binds H3K4me2/3; ASH1L_BD and ASH1L_BAH bind DNA.
• ASH1L_BAH DNA binding drives nucleosome association via linker DNA.
• ASH1L_PHD-ASH1L_BAH interaction forms a stable module; ASH1L regulates embryonic stem cell differentiation.
• ASH1L localizes with H3K4me3 at transcription start sites.
• ASH1L_PHD interaction with H3K4me3 inhibits ASH1L's H3K36me2 methyltransferase activity.

Conclusions:

• The C-terminal domains of ASH1L mediate chromatin association through DNA and histone mark recognition.
• ASH1L's enzymatic activity is regulated by its interaction with H3K4me3 via the ASH1L_PHD domain.
• These findings provide mechanistic insights into ASH1L's role in gene regulation and development.