Figure S1. The activity of BET family members is required for the growth of T-47D cells. Figure S2. BET proteins are required for E2-dependent gene expression in T-47D cells. Figure S3. JQ1 does not affect the expression of ERα, SRC2, and SRC3 in MCF-7 cells. Figure S4. JQ1 inhibits the E2-dependent expression of enhancer RNAs (eRNAs) in MCF-7 cells. Figure S5. E2-dependent Myc upregulation is not affected by JQ1. Figure S6. BET proteins are critical regulators of E2-dependent gene expression in T-47D cells. Figure S7. BRD3 is enriched at a subset of ERBSs. Figure S8. E2-induced genes affected by JQ1 are associated with ERα binding sites enriched with BRD3. Table S1. Gene ontologies associated with E2 up-regulated genes repressed by JQ1.
ARTICLE ABSTRACT
The bromodomain family member proteins (BRD; BET proteins) are key coregulators for estrogen receptor alpha (ERα)-mediated transcriptional enhancers. The use of BRD-selective inhibitors has gained much attention as a potential treatment for various solid tumors, including ER-positive breast cancers. However, the roles of individual BET family members have largely remained unexplored. Here, we describe the role of BRDs in estrogen (E2)-dependent gene expression in ERα-positive breast cancer cells. We observed that chemical inhibition of BET family proteins with JQ1 impairs E2-regulated gene expression and growth in breast cancer cells. In addition, RNAi-mediated depletion of each BET family member (BRDs 2, 3, and 4) revealed partially redundant roles at ERα enhancers and for target gene transcription. Furthermore, we found a unique role of BRD3 as a molecular sensor of total BET family protein levels and activity through compensatory control of its own protein levels. Finally, we observed that BRD3 is recruited to a subset of ERα-binding sites (ERBS) that are enriched for active enhancer features, located in clusters of ERBSs likely functioning as “super enhancers,” and associated with highly E2-responsive genes. Collectively, our results illustrate a critical and specific role for BET family members in ERα-dependent gene transcription.
BRD3 is recruited to and controls the activity of a subset ERα transcriptional enhancers, providing a therapeutic opportunity to target BRD3 with BET inhibitors in ERα-positive breast cancers.
