Core-binding factor leukemia hijacks the T-cell-prone PU.1 antisense promoter

Area of Science:

• Hematopoiesis and Cancer Biology
• Molecular Mechanisms of Gene Regulation
• Epigenetics and Chromatin Remodeling

Background:

• The blood system is a critical model for studying cell differentiation and cancer.
• PU.1 is a master regulator in hematopoietic systems; reduced PU.1 levels are a hallmark of acute myeloid leukemia (AML).
• Transcriptional dysregulation of PU.1 is implicated in AML pathogenesis.

Purpose of the Study:

• To elucidate the mechanism of PU.1 transcriptional downregulation in AML.
• To investigate the role of RUNX transcription factors and antisense transcription in PU.1 regulation.
• To identify potential therapeutic targets in core-binding factor AML (CBF-AML).

Main Methods:

• Analysis of PU.1 gene regulation using alternative promoters and antisense transcription.
• Investigating the role of RUNX transcription factors and CBF fusions (RUNX1-ETO, CBFβ-MYH11) in activating the PU.1 antisense promoter.
• Comparing antisense/sense transcript ratios and promoter accessibility in CBF-AML patients, normal karyotype AML, and healthy cells.
• Studying enhancer-promoter interactions to understand gene expression switching.

Main Results:

• Transcriptional downregulation of PU.1 is an active process involving an alternative promoter in intron 3, induced by RUNX factors driving antisense transcription.
• CBF fusions in t(8;21) and inv(16) AML activate the PU.1 antisense promoter, shifting transcription towards antisense and blocking myeloid differentiation.
• Elevated antisense/sense transcript and promoter accessibility ratios are characteristic of CBF-AML patients.
• A competitive interaction between an enhancer and promoters acts as a switch for myeloid or T-cell development.

Conclusions:

• Leukemic CBF fusions hijack a physiological sense/antisense promoter competition mechanism to perturb gene expression.
• This study reveals a novel mechanism of oncogene-induced gene expression alteration via promoter competition.
• The findings identify a previously unrecognized Achilles' heel for targeted therapies in oncogene-induced chromatin remodeling in AML.