title: HnRNP L and L-like cooperate in multiple-exon regulation of CD45 alternative splicing.
abstract: 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.
authors.affiliation: Institute of Biochemistry, Justus Liebig University of Giessen, D-35392 Giessen, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Preussner
authors.forename: Silke
authors.initials: S
authors.lastname: Schreiner
authors.forename: Lee-Hsueh
authors.initials: LH
authors.lastname: Hung
authors.forename: Martina
authors.initials: M
authors.lastname: Porstner
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Jäck
authors.forename: Vladimir
authors.initials: V
authors.lastname: Benes
authors.forename: Gunnar
authors.initials: G
authors.lastname: Rätsch
authors.forename: Albrecht
authors.initials: A
authors.lastname: Bindereif
mesh_terms: D017398:Alternative Splicing; D001402:B-Lymphocytes / Q000378:metabolism; D002460:Cell Line; D005091:Exons; D006367:HeLa Cells; D034664:Heterogeneous-Nuclear Ribonucleoprotein L / Q000378:metabolism*; D006801:Humans; D017493:Leukocyte Common Antigens / Q000235:genetics*; D009154:Mutation; D038621:Regulatory Sequences, Ribonucleic Acid
chemical_list: D034664:Heterogeneous-Nuclear Ribonucleoprotein L; D038621:Regulatory Sequences, Ribonucleic Acid; D017493:Leukocyte Common Antigens