RNA G-quadruplex secondary structure promotes alternative splicing via the RNA binding protein hnRNPF

It is generally thought that splicing factors regulate alternative splicing through binding to RNA consensus sequences. In addition to these linear motifs, RNA secondary structure is emerging as an important layer in splicing regulation. Here we demonstrate that RNA elements with G-quadruplex forming capacity promote exon inclusion. Destroying G-quadruplex forming capacity while keeping G-tracts intact abrogates exon inclusion. Analysis of RNA binding protein footprints revealed that G-quadruplexes are enriched in hnRNPF-binding sites and near hnRNPF-regulated alternatively spliced exons in the human transcriptome. Moreover, hnRNPF regulates an EMT-associated CD44 isoform switch in a G-quadruplex-dependent manner, which results in inhibition of EMT. Mining breast cancer TCGA datasets, we demonstrate that hnRNPF negatively correlates with an EMT gene signature and positively correlates with patient survival. These data suggest a critical role for RNA G-quadruplexes in regulating alternative splicing. Modulation of G-quadruplex structural integrity may control cellular processes important for tumor progression. PolyA-RNA-sequencing of two non-specific shRNA and two shhnRNPF HMLE cell lines