MLL4/KMT2D histone methyltransferase and JUNB cooperate in a feed-forward loop to support AP-1-dependent TGF-β...

Area of Science:

• Cellular Biology
• Molecular Biology
• Epigenetics

Background:

• Transforming growth factor beta (TGF-β) signaling regulates crucial cellular processes, including development, homeostasis, and cancer.
• Chromatin regulators are essential for controlling TGF-β-responsive gene transcription.
• The specific roles of MLL3/MLL4 histone methyltransferase complexes in TGF-β signaling require further elucidation.

Purpose of the Study:

• To investigate the distinct functions of MLL3 and MLL4 histone methyltransferase complexes in TGF-β transcriptional responses.
• To elucidate the molecular mechanisms underlying MLL4's role in TGF-β signaling pathways.

Main Methods:

• CRISPR/Cas9 genome editing was used to inactivate KMT2C/MLL3 or KMT2D/MLL4 genes in human diploid epithelial cells.
• Time-course RNA-sequencing (RNA-seq) and CUT&RUN experiments were performed to analyze gene expression and protein-DNA interactions.
• Inhibitor studies targeting AP-1, BAF chromatin remodeler, and CBP/p300 histone acetyltransferase were conducted.

Main Results:

• MLL4, but not MLL3, is essential for TGF-β-induced transcriptional responses.
• TGF-β treatment increases MLL4 binding, particularly at AP-1 transcription factor binding sites, correlating with H3K27ac modifications.
• A feed-forward loop involving SMAD2-induced JUNB, MLL4, AP-1, BAF complex, and CBP/p300 sustains TGF-β-driven transcription.

Conclusions:

• Distinct roles for MLL3 and MLL4 paralogs in TGF-β transcriptional regulation were revealed.
• MLL4 plays a critical role in sustaining TGF-β transcriptional activation through a novel feed-forward regulatory loop.
• The findings highlight the importance of MLL4 and associated chromatin regulators in mediating TGF-β signaling pathways.