LSM14A

LSM14A is a multifunctional RNA-binding protein that serves as a core organizer of cytoplasmic mRNA ribonucleoprotein granules and an innate immune sensor of cytosolic nucleic acids. Its N-terminal LSm domain and C-terminal FDF/RGG motifs direct it to P-bodies, where it represses translation and is required for P-body integrity; PRMT1-mediated asymmetric dimethylation of arginine residues is necessary for its P-body localization (PMID:16484376, PMID:17074753, PMID:22614839). Upon viral infection, LSM14A binds cytosolic RNA and DNA and translocates from P-bodies to peroxisomes to activate IFN-β signaling through the RIG-I–VISA and MITA/STING pathways; in dendritic cells it additionally controls MITA/STING protein levels by promoting proper nuclear mRNA precursor processing (PMID:22745163, PMID:27183626). LSM14A also localizes to the mitotic spindle, directly binds tubulin, and stabilizes DDX5 in the cytoplasm to regulate CDK4/P21-dependent cell cycle progression (PMID:26339800, PMID:39040050).

1. 2006 High

   Defining LSM14A as a structural organizer of P-bodies and stress granules resolved how this protein integrates into cytoplasmic mRNA decay and storage compartments, with its FDF motif directing P-body localization and its second RGG domain directing stress granule localization.

   Evidence GFP-tagged domain-deletion constructs, siRNA knockdown, and colocalization with DCP1a/Ge-1 in human cells; complemented by Xenopus in vitro translation and mRNA tethering assays showing direct translational repression

   PMID:16484376 PMID:17074753

   Open questions at the time

   • Endogenous mRNA targets of LSM14A-mediated repression were not identified
   • Whether translational repression and P-body integrity functions are mechanistically separable was not resolved
   • Structural basis of LSm domain–mRNA interaction unknown
2. 2012 High

   Discovery that LSM14A functions as a cytosolic nucleic acid sensor upstream of RIG-I–VISA and MITA/STING established an unexpected innate immune role, showing that upon viral infection LSM14A relocates from P-bodies to peroxisomes to activate IRF3 and IFN-β.

   Evidence RNA/DNA binding assays, siRNA knockdown with IFN-β reporter, co-immunoprecipitation with RIG-I/VISA/MITA, peroxisome colocalization by immunofluorescence and subcellular fractionation

   PMID:22745163

   Open questions at the time

   • The structural determinants of LSM14A nucleic acid sensing versus translational repression remain unmapped
   • Whether LSM14A directly senses nucleic acids or acts as a co-receptor is unclear
   • The signal triggering P-body-to-peroxisome translocation is uncharacterized
3. 2012 High

   Identification of PRMT1-dependent asymmetric arginine dimethylation as a requirement for LSM14A P-body localization established post-translational regulation of its granule-targeting function, while influenza NS1 was shown to co-opt LSM14A to disrupt P-bodies and promote viral replication.

   Evidence Mass spectrometry mapping of dimethylarginine sites, PRMT1 siRNA knockdown with P-body phenotype; reciprocal CoIP and NS1 mutagenesis with plaque assay readout

   PMID:22614839 PMID:22973032

   Open questions at the time

   • Whether arginine methylation affects the innate immune function of LSM14A is untested
   • Methylation-deficient point mutant phenotypes were not assessed
   • Whether other viruses exploit the same NS1–RAP55 interface is unknown
4. 2015 Medium

   Localization of LSM14A to the mitotic spindle and its direct binding to tubulin expanded its functional repertoire beyond mRNA metabolism, with depletion causing mitotic arrest.

   Evidence GFP-tagged LSM14A imaging during mitosis in HeLa cells, in vitro tubulin binding, siRNA knockdown with mitotic phenotype

   PMID:26339800

   Open questions at the time

   • Single-lab finding; independent confirmation needed
   • The domain mediating tubulin binding was not mapped
   • Relationship between spindle function and P-body/mRNA roles during mitosis unclear
5. 2016 High

   Generation of Lsm14a knockout mice revealed a cell-type-specific mechanism: in dendritic cells, LSM14A is required for proper nuclear mRNA precursor processing of MITA/STING, explaining how LSM14A deficiency selectively impairs DNA virus–triggered antiviral responses.

   Evidence Lsm14a KO mice, cell-type-specific analysis, nuclear mRNA precursor processing assay, Western blot for MITA/STING, cytokine assays

   PMID:27183626

   Open questions at the time

   • The mechanism by which LSM14A promotes MITA/STING mRNA processing is unknown
   • Why the requirement is dendritic cell–specific is unexplained
   • In vivo viral challenge phenotype not fully characterized across virus types
6. 2021 Medium

   SFTSV NSs protein was found to hijack LSM14A through an LRRD motif, forming a complex that binds viral RNA but blocks downstream IRF3 phosphorylation, providing a second example of pathogen subversion of LSM14A innate sensing.

   Evidence CoIP, colocalization, LRRD motif mutagenesis, IRF3 phosphorylation/dimerization assays

   PMID:34244294

   Open questions at the time

   • Single-lab study without independent replication
   • Whether the NSs–LSM14A complex sequesters viral RNA or actively inhibits signaling is unresolved
   • In vivo relevance of LRRD mutant virus not tested
7. 2024 Medium

   LSM14A was shown to stabilize DDX5 protein during G1/S phase to regulate CDK4 and P21 expression, linking it to cell cycle control in glioblastoma, while METTL1-mediated m7G methylation of LSM14A mRNA provides an upstream layer of post-transcriptional regulation.

   Evidence CoIP/MS, protein half-life assay, MeRIP for m7G, cell cycle assays, xenograft model

   PMID:39040050

   Open questions at the time

   • Single-lab study; whether DDX5 stabilization occurs outside glioblastoma is unknown
   • The domain on LSM14A that mediates DDX5 interaction was not mapped
   • How m7G methylation selectively affects LSM14A mRNA versus other targets is unclear

• How LSM14A coordinates its distinct roles in P-body organization, innate immune signaling, spindle assembly, and cell cycle regulation—and whether these functions involve shared or separable domains—remains a central unresolved question.
• No structural model of full-length LSM14A exists
• Genome-wide identification of endogenous mRNA targets is lacking
• Whether the innate sensing and mRNA metabolism functions are coupled or independent is unknown