American Cancer Society awards grant to Hollings researcher studying protein linked to ovarian cancer

There are many good ideas deserving of further investigation that haven’t received funding dollars to support the research. That was the impetus behind the American Cancer Society’s announcement in August that it would begin funding a new series of grants called Catalyst awards, meant for research proposals that had received high marks from reviewers but had not yet been funded.

In the first round, the cancer society awarded MUSC Hollings Cancer Center researcher David Long, Ph.D., a one-year grant to expand his work investigating a previously unknown interaction between the well-studied proteins BRD4 and ATM.

Interaction with ATM acts like a switch, telling BRD4 to stop doing one job and start doing a different one. Long’s lab thinks that when cells make too much BRD4, or it gets mutated, that it will cause problems with the switching mechanism, causing mass confusion, or genomic instability, as BRD4 attempts to do both jobs at once.

Long’s lab will drill down into the mechanics of what’s happening as well as how it affects genomic instability, which is a major driver of cancer development and progression.

Ultimately, this knowledge could then lead to new ideas for how to treat cancer.

“We would love to develop an inhibitor that blocks the interaction between BRD4 and ATM and then ask, ‘Does this help kill cancer cells?’ Instead of hitting BRD4 all the time or ATM all the time, we would just stop them from coming together, which could be more selective and less toxic to patients.”

Catch-and-release

ATM is not an unknown player.

“ATM has been studied for a long time. It's known to phosphorylate over 700 different proteins,” Long said. Phosphorylation is a process that regulates protein function and sends signals.

BRD4, however, was not among those 700-plus proteins known to be phosphorylated by ATM. Not until Long’s lab tried to answer the question of how BRD4 knew when it was supposed to be working on job No. 1, transcription, and when it was supposed to switch to job No. 2, DNA repair.

The team discovered that ATM interacts with BRD4 just long enough to pull it off the DNA where it’s working on transcription, in a process that Long described as “catch-and-release.”

“This is a very unusual mechanism, and we think that’s why no one had ever identified BRD4 as an ATM substrate because this phosphorylation is really transient. It gets taken off really quickly,” Long said. “And, so, we were really interested in understanding how this is regulated. And then, what role does it play in cancer development?”

Cells are very particular about doing one job at a time, he noted – for good reason. Attempting to transcribe DNA at the same time as carrying out repair is a recipe for conflict – actually creating even more damage to the DNA. But if you have overexpression, or too much, of BRD4, then ATM can’t get to every individual BRD4 protein to pull them all away from their transcription duties.

BRD4 and ovarian cancer

BRD4 is overexpressed in multiple cancers, including almost a fifth of high-grade serous ovarian cancer, and is associated with worse outcomes for patients. That’s been assumed to be because of BRD4’s role in promoting the expression of oncogenes, but Long’s work indicates that its role in DNA repair – and the conflict that arises when too much BRD4 ends up doing both jobs at once – could also contribute to poor outcomes.

“We would love to develop an inhibitor that blocks the interaction between BRD4 and ATM and then ask, ‘Does this help kill cancer cells?’ Instead of hitting BRD4 all the time or ATM all the time, we would just stop them from coming together, which could be more selective and less toxic to patients.”

David Long, Ph.D.

Because the catch-and-release function happens so quickly, it hasn’t shown up on traditional screens. Long’s lab uses a cell-free “protein soup” of frog egg extract that allows the team to single out specific interactions.

But to move into a cell model, the team needed to look to new technologies to capture this fast, transient interaction.

The lab will use a new technology developed at Johns Hopkins Medicine called very fast CRISPR, or vfCRISPR, to study what happens when there’s a double-strand DNA break. With vfCRISPR, researchers use RNA that’s been modified to be photocleavable. They can ready the experiment and put all the pieces in the exact spots that they want to study – but nothing happens until they turn on a quick flash of UV light, which prompts vfCRISPR to slice through the DNA, creating a double-strand break.

In these experiments, the researchers will create the break at the c-MYC gene that’s involved in normal cell growth but is also at the root of many cancers when it’s not expressed properly.

Long anticipates that with the vfCRISPR approach, they’ll be able to see BRD4 begin to fall off DNA at the break and then for that damage signal to start traveling down the line, with more and more BRD4 falling off as damage signals get turned on.

“We're applying this technique in a way that hasn't been done before,” Long explained. “So, we think using this really quick system will let us study these really dynamic events that are normally too fast to see.”

BRD4 and cancer

Although BRD4 is often overexpressed in ovarian cancer, it can also cause problems in many other types of cancer.

Long expects that this study will expand the understanding of how BRD4 typically regulates its activity to protect against genomic instability and, through that understanding, show ways to target these mechanisms with more precise therapies.

There are already inhibitors against BRD4, but they have had limited effects when used alone, he said.

“More recent studies have shown promise by combining them with DNA-damaging agents,” he said. “These findings highlight the important role that genomic instability plays in sensitizing cells to BRD4 inhibitors and treating cancers with altered BRD4 expression. The proposed studies will provide novel insight into BRD4’s role in genome maintenance and help lay the foundation for the development of new therapeutic strategies.”

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