MAML1-Dependent Notch-Responsive Genes Exhibit Differing Cofactor Requirements for Transcriptional Activation

Area of Science:

• Molecular biology
• Gene regulation
• Cancer research

Background:

• Mastermind proteins regulate Notch target gene transcription, but their precise molecular function is unclear.
• Notch signaling can activate genes at promoters or enhancers, with differential MAML1 dependence.

Purpose of the Study:

• To investigate the molecular basis of Mastermind-like 1 (MAML1) function in Notch-dependent gene transcription.
• To identify specific MAML1 regions and activities required for regulating Notch target genes.

Main Methods:

• Gene knockout and add-back experiments using MAML1 variants in Jurkat T-ALL cells.
• Analysis of target gene expression (HES4, DTX1) and histone modifications (H3K27 acetylation).
• Functional assessment of MAML1-p300 fusion proteins.

Main Results:

• MAML1 knockout abolished Notch-responsive activation of HES4 and DTX1, decreasing H3K27 acetylation.
• Residues 151-350 of MAML1 were identified as essential for both genes' expression.
• A MAML1-p300 fusion rescued HES4 but not DTX1 expression, indicating distinct MAML1 roles.

Conclusions:

• The MAML1 region spanning residues 151-350 is critical for Notch-dependent transcription.
• MAML1 exhibits differential recruitment activities at promoter- and enhancer-bound Notch targets.
• This highlights the molecular complexity of MAML1 in orchestrating Notch-stimulated gene expression.