RNA-binding protein that acts as a pre-mRNA splicing factor (PubMed:15694343, PubMed:24795046, PubMed:28302793, PubMed:28437394, PubMed:31271494). Acts by promoting exon inclusion via regulation of exon cassette splicing (PubMed:31271494). Also acts as a transcriptional coactivator for steroid nuclear receptors ESR1/ER-alpha and ESR2/ER-beta, and JUN/AP-1, independently of the pre-mRNA splicing factor activity (By similarity).