Role of BET family of transcription regulators in DNA replication stress

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Bowry, Akhil (2020). Role of BET family of transcription regulators in DNA replication stress. University of Birmingham. Ph.D.

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Abstract

BET proteins function as epigenetic readers, and BET inhibition has been shown to have activity against many different cancers. BET inhibitors have been fast-tracked into first clinical trials, however the effects of these inhibitors are still poorly understood. A more detailed understanding about the physiological effects of BET inhibition is important and may lead to improved clinical applications as well as allowing safer use of BET inhibitor drugs.

In this thesis we have been able to identify that BET inhibition unexpectedly leads to an increase in RNA synthesis that is associated with conflicts between transcription and replication, leading to replication fork slowing, a sign of replication stress. We have identified BRD4 as the main target of BET inhibition in this process which is needed for normal fork progression. Interestingly, our data suggest that increased RNA synthesis requires free P-TEFb to be released from its inhibitor complex HEXIM1 to allow increased RNA polymerase II phosphorylation. HEXIM1 is required for BET inhibitor-induced replication-transcription conflicts.

We have shown that BET inhibitor-induced fork slowing does not activate the canonical ATR-Chk1 replication stress response pathway. However, it activates the homologous recombination factor RAD51, which is recruited into nuclear foci in response to BET inhibitor treatment. RAD51 depletion followed by BET inhibition prevents replication fork slowing but activates the replication stress response. HEXIM1 depletion has the same effect, preventing fork slowing and activating the replication stress response. These data suggest that i) replication fork slowing is required to prevent DNA damage formation in presence of BET inhibitors and ii) this depends on HEXIM1, which is upstream of transcription-replication conflicts, and RAD51, which acts downstream of transcription-replication conflicts.

Our data shed light on the initial stress response during the first 8 hours of BET inhibition. They implicate HEXIM1 and RAD51, which both play potential roles in BET inhibitor resistance, in the BET inhibitor-induced replication stress pathway.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):