NSRP1

NSRP1 (NSrp70) is a nuclear speckle-resident alternative splicing regulator essential for embryonic development, T cell maturation, and suppression of epithelial-mesenchymal transition. It physically interacts with the SR proteins SC35 and ASF/SF2 via its central domain (aa 290–471), uses its N-terminal region (aa 107–161) for pre-mRNA splicing activity, and requires a C-terminal nuclear localization signal (aa 531–540, including an RD motif) for nuclear targeting (PMID:21296756, PMID:38808951). NSRP1 directly binds target pre-mRNAs such as NUMB to control exon skipping, thereby promoting TGFβ receptor degradation and suppressing SMAD-mediated EMT, and regulates NSD2 exon inclusion to modulate interferon signaling and CDK4/6 inhibitor sensitivity in breast cancer cells (PMID:35568738, PMID:39667501). Biallelic loss-of-function variants in NSRP1 that ablate the C-terminal NLS cause a severe autosomal recessive neurodevelopmental disorder in humans (PMID:34385670).

1. 2011 High

   Identification of NSRP1 as a nuclear speckle-resident splicing regulator resolved what molecular function this uncharacterized coiled-coil protein performs, establishing it as an alternative splicing factor that interacts with canonical SR proteins and requires distinct domains for localization, protein interaction, and splicing activity.

   Evidence Co-IP, co-localization imaging, deletion mutagenesis, and splicing minigene reporter assays (CD44, Tra2β1, Fas) in cultured cells; mouse knockout showing embryonic lethality

   PMID:21296756

   Open questions at the time

   • Direct RNA-binding activity of NSRP1 was not demonstrated
   • Endogenous splicing targets were not identified genome-wide
   • Mechanism by which the N-terminal region (107–161) activates splicing was not defined
2. 2015 Medium

   Discovery of physical interactions between NSRP1, RanBP9, and DISC1 in neuronal cells suggested a connection to neuronal signaling pathways beyond its core splicing function.

   Evidence Yeast two-hybrid, GST pull-down, and confocal co-localization in human neuronal cell lines

   PMID:26475744

   Open questions at the time

   • Interactions were not validated by reciprocal endogenous co-IP in neuronal tissue
   • Functional consequence of NSRP1-DISC1 interaction on splicing or neuronal function was not tested
   • No in vivo neuronal phenotype was assessed
3. 2016 Medium

   Demonstration that NSRP1 is required for gastrulation and dorsal mesoderm induction in Xenopus extended the essential developmental role beyond mouse, establishing an evolutionarily conserved requirement during early body axis formation.

   Evidence Morpholino knockdown in Xenopus embryos with animal cap assays and gene expression analysis

   PMID:27638308

   Open questions at the time

   • Specific splicing targets mediating the gastrulation defect were not identified
   • Rescue with human NSRP1 was not shown to confirm ortholog equivalence
   • Morpholino off-target effects were not ruled out with a second independent reagent
4. 2021 High

   Conditional knockout in thymocytes revealed that NSRP1 controls alternative splicing of cell-cycle and survival genes including SRSF1 during T cell maturation, answering how it functions in a specific lineage and explaining why its loss blocks the double-positive to single-positive thymocyte transition.

   Evidence CD4Cre conditional knockout in mice, RNA-seq global splicing profiling, flow cytometry

   PMID:34037780

   Open questions at the time

   • Direct RNA-binding sites in thymocytes were not mapped (e.g., by CLIP)
   • Whether NSRP1 splicing targets differ between immune and non-immune lineages is unknown
   • Mechanism by which NSRP1 loss leads to insufficient TCR signaling was not fully delineated
5. 2021 Medium

   Identification of biallelic frameshift variants removing the C-terminal NLS in human families established NSRP1 as a Mendelian neurodevelopmental disease gene, linking the previously characterized NLS domain to human pathology.

   Evidence Exome sequencing and family-based rare variant analysis with molecular transcript characterization

   PMID:34385670

   Open questions at the time

   • Functional rescue of patient-derived cells with wild-type NSRP1 was not performed
   • Neuronal splicing targets disrupted by the truncation were not identified
   • Only a small number of families were reported
6. 2022 High

   Demonstration that NSRP1 directly binds NUMB pre-mRNA and controls its exon skipping to suppress TGFβ/SMAD-mediated EMT answered how NSRP1 acts as a metastasis suppressor and identified the first direct RNA target with a defined downstream signaling consequence.

   Evidence RNA immunoprecipitation, RNA pull-down, in vitro splicing assays, in vivo metastasis assays, RNA-seq

   PMID:35568738

   Open questions at the time

   • The RNA-binding domain or motif within NSRP1 responsible for NUMB recognition was not mapped
   • Whether NSRP1 acts alone or requires SR protein co-factors for NUMB splicing regulation was not tested
   • Structural basis for NSRP1-RNA recognition is unknown
7. 2024 Medium

   A patient-derived missense variant (Val532Glu) within the NLS directly demonstrated that a single residue change causes cytosolic mislocalization, providing the strongest direct evidence that the C-terminal NLS is necessary and sufficient for nuclear targeting.

   Evidence GFP-tagged wild-type and V532E NSRP1 transfection in HEK293T cells with fluorescence microscopy

   PMID:38808951

   Open questions at the time

   • The import receptor recognizing the NSRP1 NLS has not been identified
   • Whether cytosolic NSRP1 retains any residual splicing-independent function is unknown
8. 2024 Medium

   Identification of NSD2 as a splicing target whose exon 2 inclusion is suppressed by NSRP1 revealed a mechanism linking splicing regulation to interferon pathway activation and CDK4/6 inhibitor resistance in breast cancer.

   Evidence RNA-seq and alternative splicing analysis, NSRP1 knockdown/overexpression in MCF7 and palbociclib-resistant derivatives, drug sensitivity assays

   PMID:39667501

   Open questions at the time

   • Direct binding of NSRP1 to NSD2 pre-mRNA was not demonstrated
   • Whether the NSD2-IFN axis operates in non-breast cancer contexts is unknown
   • In vivo validation of NSRP1-NSD2-drug resistance axis is lacking

• The genome-wide RNA-binding landscape of NSRP1, the structural basis for its interaction with SR proteins and RNA, and the specific splicing programs disrupted in the developing nervous system to cause neurodevelopmental disease remain undefined.
• No CLIP-seq or equivalent transcriptome-wide binding map exists
• No structural or cryo-EM model of NSRP1 or its SR protein complexes has been reported
• Neuronal-specific splicing targets are uncharacterized