The Cross-Regulation Between Set1, Clr4, and Lsd1/2 in Schizosaccharomyces pombe

Area of Science:

• Epigenetics and chromatin regulation
• Gene expression control
• Histone modification dynamics

Background:

• Eukaryotic chromatin exists as silenced heterochromatin or active euchromatin, controlling gene accessibility.
• Set1 (H3K4 methyltransferase) and Clr4 (H3K9 methyltransferase) establish distinct histone methylation marks.
• Lsd1 and Lsd2 are conserved demethylases targeting H3K4 and H3K9, crucial for maintaining methylation patterns.

Purpose of the Study:

• To investigate the cross-regulation between histone methyltransferases (Set1, Clr4) and demethylases (Lsd1, Lsd2).
• To elucidate the mechanisms governing the signaling and mutual regulation of these key enzymes.
• To understand the role of these interactions in chromatin dynamics and gene expression, particularly under stress.

Main Methods:

• Utilized C-terminal truncation mutants (lsd1-ΔHMG, lsd2-ΔC) to assess chromatin-binding capacity.
• Identified protein-protein interactions between Lsd1/2 and subunits of CLRC (Raf2) and COMPASS (Swd2).
• Investigated the impact of Clr4 and Set1 on Lsd1/2 protein levels via the ubiquitin-proteasome pathway, including during heat stress.

Main Results:

• Truncation mutants impaired Lsd1/2 chromatin binding without disrupting complex integrity.
• Established direct protein interactions between Lsd1/2 and components of the Clr4 and Set1 complexes.
• Demonstrated that Clr4 and Set1 oppositely regulate Lsd1/2 protein stability through proteasomal degradation.
• Showed Set1-dependent upregulation of Lsd1/2 protein levels during heat stress, essential for stress-induced gene expression.

Conclusions:

• A cross-regulatory model where Set1 and Clr4 control Lsd1/2 demethylase levels is supported.
• These methyltransferases fine-tune demethylase abundance to shape the dynamic chromatin landscape.
• This regulation is critical for adaptive gene expression responses to environmental challenges like heat stress.