Browsing by Subject "BRD4"

Understanding the differences between normal and malignant tissue is required to find vulnerabilities in cancer that can be exploited. One of the hallmarks of cancer is its ability to sustain proliferative signaling, leading to unbridled cellular replication. This puts an increased pressure on the cell’s ability to maintain genome integrity and creates a potential vulnerability to be targeted by cancer therapies. Targeting how a cancer cell prevents or responds to DNA damage is one way to take advantage of this vulnerability.

My dissertation work aims to better understand this DNA damage response in cancer and tests two hypotheses: The first is whether inhibition of the transcriptional regulator BRD4 leads to an increase in transcription-replication conflicts, DNA damage, and cell death. The second is whether the tumor microenvironment alters the way cancer cells respond to DNA damage induced by radiation therapy in glioblastoma.

Effective spatio-temporal control of transcription and replication during S-phase is paramount to maintain genomic integrity and cell survival. My work shows that BRD4, a BET bromodomain protein and known transcriptional regulator, is important for preventing dysregulation of these systems leading to conflicts between the transcription and replication machinery in S-phase. We demonstrate that inhibition or degradation of BET bromodomain proteins leads to an accumulation of RNA:DNA hybrids, a known cause of transcription-replication conflicts, and causes increased DNA damage and cell death in cancer cells actively undergoing replication. Furthermore,

over-expression of full-length BRD4, which contains a P-TEFb interacting domain known to activate efficient transcription, is necessary and sufficient to rescuing this effect. These results give mechanistic insight into chemotherapeutics that target BRD4 currently in clinical trials.

In complementary work, we explored the effect that the extracellular environment of cancer plays in its response to DNA damage caused by radiation therapy. Standard methods of culturing cancer cells, which do not replicate the extracellular environment of a native tumor, have led to an incomplete understanding of response to therapies such as ionizing radiation in vivo. To understand the role that the tumor environment plays on the radiation response, we used both human and murine glioblastoma cells to show that organotypic brain slice culture was better able to recapitulate the expression profiles of in vivo tumors. Specifically, we saw that pathways involved in multicellular processes, cell morphogenesis, and the extracellular matrix were not only significantly upregulated in glioblastoma cells cultured on brain slices compared to in vitro culture but were also critically important to radiation survival.

Collectively, this dissertation provides novel understandings of how cancer cells prevent and respond to DNA damage as well as a framework for future work in cancer biology.