A Computational-Based Approach to Identify Estrogen Receptor α/ß Heterodimer Selective Ligands.

The biologic effects of estrogens are transduced by two estrogen receptors (ERs), ERα and ERß, which function in dimer forms. The ERα/α homodimer promotes and the ERß/ß inhibits estrogen-dependent growth of mammary epithelial cells; the functions of ERα/ß heterodimers remain elusive. Using compounds that promote ERα/ß heterodimerization, we have previously shown that ERα/ß heterodimers appeared to inhibit tumor cell growth and migration in vitro. Further dissection of ERα/ß heterodimer functions was hampered by the lack of ERα/ß heterodimer-specific ligands. Herein, we report a multistep workflow to identify the selective ERα/ß heterodimer-inducing compound. Phytoestrogenic compounds were first screened for ER transcriptional activity using reporter assays and ER dimerization preference using a bioluminescence resonance energy transfer assay. The top hits were subjected to in silico modeling to identify the pharmacophore that confers ERα/ß heterodimer specificity. The pharmacophore encompassing seven features that are potentially important for the formation of the ERα/ß heterodimer was retrieved and subsequently used for virtual screening of large chemical libraries. Four chemical compounds were identified that selectively induce ERα/ß heterodimers over their respective homodimers. Such ligands will become unique tools to reveal the functional insights of ERα/ß heterodimers.

CARM1 automethylation is controlled at the level of alternative splicing.

Co-activator-associated arginine methyltransferase 1 (CARM1) is subjected to multiple post-translational modifications. Our previous finding that automethylation of CARM1 is essential for regulation of transcription and pre-mRNA splicing prompted us to investigate how automethylation is regulated. Here, we report that automethylation is regulated by alternative splicing of CARM1 mRNA to remove exon 15, containing the automethylation site. Specifically, we find that two major alternative transcripts encoding full-length CARM1 (CARM1FL) and CARM1 with exon 15 deleted (CARM1ΔE15) exist in cells, and each transcript produces the expected protein. Further biochemical characterizations of the automethylation-defective mutant and CARM1ΔE15 reveal overlapping yet different properties. Interestingly, other arginine methylation substrates also have missing exons encompassing the site(s) of methylation, suggesting that protein arginine methylation level may, in general, be controlled by the alternative splicing mechanism. Finally, we observed differential distribution of CARM1FL and CARM1ΔE15 in epithelial and stromal cells in normal mouse mammary gland. Thus, alternative splicing not only serves as the determinant for CARM1 automethylation but also generates cell type-specific isoforms that might regulate normal ERα biology in the mammary gland.