HnRNP L and L-like cooperate in multiple-exon regulation of CD45 alternative splicing.

Marco Preussner, Silke Schreiner, Lee-Hsueh Hung, Martina Porstner, Hans-Martin Jäck, Vladimir Benes, Gunnar Rätsch, Albrecht Bindereif

Institute of Biochemistry, Justus Liebig University of Giessen, D-35392 Giessen, Germany.

Nucleic acids research 2012 Jul

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CD45 encodes a trans-membrane protein-tyrosine phosphatase expressed in diverse cells of the immune system. By combinatorial use of three variable exons 4-6, isoforms are generated that differ in their extracellular domain, thereby modulating phosphatase activity and immune response. Alternative splicing of these CD45 exons involves two heterogeneous ribonucleoproteins, hnRNP L and its cell-type specific paralog hnRNP L-like (LL). To address the complex combinatorial splicing of exons 4-6, we investigated hnRNP L/LL protein expression in human B-cells in relation to CD45 splicing patterns, applying RNA-Seq. In addition, mutational and RNA-binding analyses were carried out in HeLa cells. We conclude that hnRNP LL functions as the major CD45 splicing repressor, with two CA elements in exon 6 as its primary target. In exon 4, one element is targeted by both hnRNP L and LL. In contrast, exon 5 was never repressed on its own and only co-regulated with exons 4 and 6. Stable L/LL interaction requires CD45 RNA, specifically exons 4 and 6. We propose a novel model of combinatorial alternative splicing: HnRNP L and LL cooperate on the CD45 pre-mRNA, bridging exons 4 and 6 and looping out exon 5, thereby achieving full repression of the three variable exons.

Citation

Marco Preussner, Silke Schreiner, Lee-Hsueh Hung, Martina Porstner, Hans-Martin Jäck, Vladimir Benes, Gunnar Rätsch, Albrecht Bindereif. HnRNP L and L-like cooperate in multiple-exon regulation of CD45 alternative splicing. Nucleic acids research. 2012 Jul;40(12):5666-78