Suppression of 5 ' splice-sites through multiple exonic motifs by hnRNP L

Abstract

Selection of 5 ' splice-sites (5 ' SS) in alternative splicing plays an important role in gene regulation. Although regulatory mechanisms of heterogeneous nuclear ribonucleoprotein L (hnRNP L), a well-known splicing regulatory protein, have been studied in a substantial level, its role in 5 ' SS selection is not thoroughly defined. By using a KLF6 pre-mRNA alternative splicing model, we demonstrate in this report that hnRNP L inhibits proximal 5 ' SS but promotes two consecutive distal 5 ' SS splicing, antagonizing SRSF1 roles in KLF6 pre-mRNA splicing. In addition, three consecutive CA-rich sequences in a CA cassette immediately upstream of the proximal 5 ' SS are all required for hnRNP L functions. Importantly, the CA-cassette locations on the proximal exon do not affect hnRNP L roles. We further show that the proximal 5 ' SS but not the two distal 5 ' SSs are essential for hnRNP L activities. Notably, in a Bcl-x pre-mRNA model that contains two alternative 5 ' SS but includes CA-rich elements at distal exon, we demonstrate that hnRNP L also suppresses nearby 5 ' SS activation. Taken together, we conclude that hnRNP L suppresses 5'SS selection through multiple exonic motifs. (C) 2017 Elsevier B.V. All rights reserved.