BRM is a subunit of the master gene-regulating complex SWI/SNF. This complex controls the expression of a wide variety of genes and plays a critical role in growth control, differentiation, and development. Because of these roles, it is not surprising that BRM expression is frequently targeted and disrupted in a variety of human cancers. When BRM is silenced in these cancers, it is not mutated or altered, but rather it is epigenetically silenced. Hence it is clinically possible to restore BRM expression in cancers that lack its expression. The re- expression of BRM in cancer cell lines devoid of its expression results in cell cycle arrest and senescence;this observation indicates the potential clinical benefit of restoring BRM expression. To further advance BRM as a targeted therapy, we must understand how BRM expression is silenced in cancer cells. Part of the answer lies with two polymorphic sites that lie in the promoter region of the BRM gene. The presence of these two polymorphic sites strongly correlates with the loss of BRM expression in both cancer cell lines and in primary tumors and is also strongly associated with lung cancer risk, with an odds ratio of 2.2. Hence, understanding how these polymorphic sites function is central to determining how BRM is silenced in cancer. Furthermore, analysis of the sites shows that they are highly similar if not identical to the MEF2 binding sites. To this end, we have found that knockdown of MEF2D or HDAC3 induces BRM expression. Moreover, MEF2 transcription factors recruit HDACs to the promoter region in order to silence genes. It appears that these BRM polymorphic sites function to attract MEF2D, which then recruits HDAC3, resulting in the silencing of the BRM gene. In this proposal, we will test this hypothesis with a series of experiments in Aim 2. As a first step in developing BRM- activating drugs, we have developed an assay to identify compounds that can restore BRM expression. The main focus of this grant is to adapt this assay so it can be used for high throughput screening:
Aim1. We will then screen compounds from both the Michigan High Throughput Screening Facility and the University of Michigan Center for Chemical Genomics, approximately 150,000 compounds, to identify those that restore BRM expression. We will then rescreen these potential hits with series of secondary screens to identify true hits. We will then determine which of these compounds activate BRM by targeting either MEF2D or HDAC3. The proposed research will further determine how BRM is suppressed, the roles that BRM promoter polymorphisms play in the suppression of BRM, and if HDAC and MEF2D inhibit BRM via these polymorphisms. We expect that this work will give the prerequisite knowledge necessary to develop the restoration of BRM as a viable clinically targeted therapy.
This research is focused of the development of a High Through Assay to find drugs which reactivate BRM. Such drugs are needed because of the important roles that BRM plays in cell cycle control and other anticancer process.
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