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Principal Investigator: Andrew Volk
Organization: CINCINNATI CHILDRENS HOSP MED CTR
Fiscal Year: 2024
Award: $397,500
Funding agency: National Institute of General Medical Sciences
PROJECT SUMMARY:
Comprehensive regulation of transcription is a major mechanism by which immature cells functionally
determine their identity. The epigenetic factors responsible for this transcriptional regulatory activity are some
of the most potent, and most commonly mutated, factors implicated in tissue homeostasis and disease. We
understand the role of many epigenetic factors responsible for activating transcription, but we have a limited
understanding of the factors that repress transcription associated with differentiation. Additionally, we know
many of the epigenetic transcriptional regulators present on the chromatin before and after replication, but we
have a limited understanding of how these factors interact during replication. The relative lack of understanding
of how the replication machinery regulates transcription associated with cell identity is a key knowledge gap
in the field of epigenetics. Our studies suggest that the Chromatin Assembly Factor 1 (CAF1) complex,
functioning in its canonical role of replication-linked chromatin assembly, is the critical factor responsible for
directly regulating fate-specific transcription during replication.
CAF1 is a heterotrimeric protein complex responsible for facilitating histone H3/H4 heterodimer
assembly at the replication fork during the S phase of cell cycle. Our lab focuses on the functional contributions
of CAF1 through studying its p60 subunit: Chromatin Assembly Factor 1B (CHAF1B). We are using CHAF1B
as a model for CAF1 function because of the abundance of tools and expertise we have generated to study
CHAF1B and the overwhelming evidence that readouts of CHAF1B and the CAF1 complex are functionally
identical. CHAF1B is highly expressed in uncommitted stem cells, and its expression decreases as cells
differentiate. We recently reported that CHAF1B directly binds chromatin at promoters and enhancers of
differentiation genes, repressing their expression by blocking transcription factor binding. Depletion of CHAF1B
in independent models led to massive upregulation of gene activation caused by transcription factors flooding
regions of chromatin previously occupied by CHAF1B. This led to our hypothesis: CHAF1B is a master
regulator of cell identity through a novel role as transcriptional repressor of fate genes in immature cells.
Our long-term goal is to understand how cells regulate transcription associated with cell fate
throughout differentiation. Our short-term goal is to understand how the chromatin assembly machinery
affects transcriptional repression of fate genes in immature cells. In this proposal we will study the functional
roles of the factors responsible for CHAF1B direct binding to chromatin on transcription and phenotype (Focus
1), and the contributions of the DNA/protein complexes recruited by CHAF1B to the chromatin on transcription
and phenotype (Focus 2). Discoveries about CHAF1B, the CAF1 complex, and the larger DNA/protein
chromatin landscape it promotes, have the potential for driving sweeping changes in the way we understand
functional epigenetics and treat disease.
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