Activation and repression by oncogenic MYC shape tumour-specific gene expression profiles

Area of Science:

• Molecular Biology
• Oncology
• Gene Regulation

Background:

• The MYC oncoprotein is a key regulator of gene expression in mammalian cells.
• MYC overexpression is implicated in various cancers, altering gene expression profiles.
• Understanding MYC's role in normal versus tumor cells is crucial for cancer therapy.

Purpose of the Study:

• To investigate the specific gene expression changes driven by MYC in tumor cells compared to normal cells.
• To elucidate the mechanisms underlying MYC's context-dependent regulation of gene expression.
• To identify factors contributing to the distinct gene expression signatures in MYC-driven tumors.

Main Methods:

• Inducible expression and depletion of MYC in human cell lines.
• Utilized murine tumor models to study MYC's effects in vivo.
• Analyzed MYC occupancy at promoters and its correlation with gene expression changes.
• Investigated MYC's role in transcription initiation and elongation.
• Examined the role of MIZ1 (ZBTB17) in MYC-mediated gene repression.

Main Results:

• MYC levels dictate specific gene activation and repression patterns characteristic of tumor cells.
• MYC promoter occupancy and E-box sequence affinity correlate with the magnitude and direction of gene response.
• MYC influences both transcription initiation and elongation, with distinct effects on different target genes.
• Complex formation with MIZ1 mediates MYC-driven gene repression, with the MYC/MIZ1 ratio determining the outcome.

Conclusions:

• MYC's oncogenic function arises from specific alterations in target gene expression, not just widespread gene activation.
• Promoter affinity, transcription initiation regulation, and MIZ1 complex formation are key determinants of MYC's specificity.
• These findings provide insights into MYC's role in tumorigenesis and potential therapeutic strategies targeting MYC.