SR proteins regulate V6 exon splicing of CD44 pre-mRNA

Abstract

CD44 pre-mRNA includes 20 exons, of which exons 1-5 (C1-C5) and exons 16-20 (C6-C10) are constant exons, whereas exons 6-15 (V1-V10) are variant exons. V6-exon-containing isoforms have been known to be implicated in tumor cell invasion and metastasis. In the present study, we performed a SR protein screen for CD44 V6 splicing using overexpression and lentivirus-mediated shRNA treatment. Using a CD44 V6 minigene, we demonstrate that increased SRSF3 and SRSF4 expression do not affect V6 splicing, but increased expression of SRSF1, SRSF6 and SRSF9 significantly inhibit V6 splicing. In addition, using a constitutive exon-specific primer set, we could not detect alterations of CD44 splicing after SR protein-targeting shRNA treatment. However, using a V6 specific primer, we identified that reduced SRSF2 expression significantly reduced the V6 isoform, but increased V6-10 and V6,8-10 isoforms. Our results indicate that SR proteins are important regulatory proteins for CD44 V6 splicing.