Regulation of alternative splicing by steroid hormones.

Steroid hormone signaling pathways are critical for organismal development and act through binding to nuclear receptors driving transcriptional regulation. In this review, we summarize evidence for another - underrated - mechanism of action for steroid hormones: their ability to modulate the alternative splicing of pre-mRNA. Thirty years ago, pioneering studies used in vitro transfection of plasmids expressing alternative exons under the control of hormone responsive promoters in cell lines. These studies demonstrated that steroid hormone binding to their nuclear receptor impacted both gene transcription and alternative splicing outcomes. The advent of exon arrays and next generation sequencing has allowed researchers to observe the impact of steroid hormones at the whole transcriptome level. These studies demonstrate that steroid hormones regulate alternative splicing in a time-, gene-, and tissue-specific manner. We provide examples of the mechanisms by which steroid hormones regulate alternative splicing including 1) recruitment of dual function proteins that behave as coregulators and splicing factors, 2) transcriptional regulation of splicing factor levels, 3) the alternative splicing of splicing factors or transcription factors that feed-forward regulate steroid hormone signaling, and 4) regulation of elongation rate. Experiments performed in vivo and in cancer cell lines highlight that steroid hormone mediated alternative splicing occurs in both physiological and pathophysiologic states. Studying the impact of steroid hormones on alternative splicing is a fruitful avenue for research that should be exploited to discover new targets for therapeutic intervention.