hnRNP L inhibits CD44 V10 exon splicing through interacting with its upstream intron

CD44 is a complex cell adhesion molecule that mediates communication and adhesion between adjacent cells as well as between cells and the extracellular matrix. CD44 pre-mRNA produces various mRNA isoforms through alternative splicing of 20 exons, among which exons 1-5 (C-1-C-5) and 16-20 (C-6-C-10) are constant exons, whereas exons 6-15 (V-1-V-10) are variant exons. CD44 V-10 exon has important roles in breast tumor progression and Hodgkin lymphoma. Here we show that increased expression of hnRNP L inhibits V-10 exon splicing of CD44 pre-mRNA, whereas reduced expression of hnRNP L promotes V-10 exon splicing. In addition, hnRNP L also promotes V-10 splicing of endogenous CD44 pre-mRNA. Through mutation analysis, we demonstrate that the effects of hnRNP L on V-10 splicing are abolished when the CA-rich sequence on the upstream intron of V-10 exon is disrupted. However, hnRNP L effects are stronger if more CA-repeats are provided. Furthermore, we show that hnRNP L directly contacts the CA-rich sequence. Importantly, we provide evidences that hnRNP L inhibits U2AF(65) binding on the upstream Py tract of V-10 exon. Our results reveal that hnRNP L is a new regulator for CD44 V-10 exon splicing. (C) 2015 Elsevier B.V. All rights reserved.