Abstract
Gaining pharmacologic access to the potential of ARID1A, a tumor suppressor protein, to mediate transcriptional control over cancer gene expression is an unresolved challenge. Retinoid X receptor ligands are pleiotropic, incompletely understood tools that regulate breast epithelial cell proliferation and differentiation. We found that low-dose bexarotene (Bex) combined with the nonselective beta-blocker carvedilol (Carv) reduces proliferation of MCF10DCIS.com cells and markedly suppresses ARID1A levels. Similarly, Carv synergized with Bex in MCF-7 cells to suppress cell growth. Chromatin immunoprecipitation sequencing analysis revealed that under nonestrogenic conditions Bex + Carv alters the concerted genomic distribution of the chromatin remodeler ARID1A and acetylated histone H3K27, at sites related to insulin-like growth factor (IGF) signaling. Several distinct sites of ARID1A enrichment were identified in the IGF-1 receptor and IRS1 genes, associated with a suppression of both proteins. The knock-down of ARID1A increased IGF-1R levels, prevented IGF-1R and IRS1 suppression upon Bex + Carv, and stimulated proliferation. In vitro IGF-1 receptor neutralizing antibody suppressed cell growth, while elevated IGF-1R or IRS1 expression was associated with poor survival of patients with ER-negative breast cancer. Our study demonstrates direct impact of ARID1A redistribution on the expression and growth regulation of IGF-1-related genes, induced by repurposed clinical drugs under nonestrogenic conditions. Implications: This study underscores the possibility of the pharmacologic modulation of the ARID1A factor to downregulate protumorigenic IGF-1 activity in patients with postmenopausal breast cancer undergoing aromatase inhibitor treatment.