LUC7L3

LUC7L3 is a nuclear mRNA-binding protein that functions as a pre-mRNA splicing factor within transcription and RNA-processing complexes. It directly associates with poly(A) mRNA, as demonstrated by UV crosslinking interactome capture in multiple human cell lines (PMID:22658674, PMID:22681889). LUC7L3 cooperates with the splicing factor RBM25 to regulate alternative splicing of the cardiac sodium channel SCN5A pre-mRNA; its upregulation in human heart failure promotes production of a truncated SCN5A transcript, reducing sodium channel current by approximately 91% and contributing to arrhythmic risk (PMID:21859973). It resides in the nucleus, where it participates in soluble protein complexes associated with RNA metabolism (PMID:35271311, PMID:22939629).

1. 2007 Medium

   Establishing that LUC7L3 is embedded in the human transcription and RNA-processing machinery resolved its broad functional neighborhood, linking it to splicing-related complexes rather than placing it as an isolated RNA-binding protein.

   Evidence AP-MS of tagged transcription/RNA processing components in human cells

   PMID:17643375

   Open questions at the time

   • Specific direct binding partners for LUC7L3 were not individually validated
   • No functional consequence of these interactions was tested
   • Identity of the RNA targets remained unknown
2. 2011 High

   Demonstrating that LUC7L3 overexpression drives aberrant SCN5A pre-mRNA splicing and drastically reduces sodium channel current established its first defined substrate-level splicing function and linked it to heart failure pathophysiology.

   Evidence Overexpression in Jurkat cells and human embryonic stem cell-derived cardiomyocytes with RT-PCR and patch-clamp electrophysiology; gene array profiling of heart failure tissue

   PMID:21859973

   Open questions at the time

   • Whether LUC7L3 binds SCN5A pre-mRNA directly or acts through RBM25 was not resolved
   • Loss-of-function validation (knockdown/knockout) was not reported
   • Scope of LUC7L3-dependent splicing events genome-wide was unknown
3. 2012 High

   UV crosslinking interactome capture in two independent cell lines confirmed LUC7L3 as a direct poly(A) mRNA-binding protein, establishing its biochemical identity as a bona fide RNA-binding protein rather than an indirect complex component.

   Evidence UV crosslinking and oligo(dT) purification with quantitative mass spectrometry in HeLa (conventional UV) and HEK293 (PAR-CLIP-based) cells

   PMID:22658674 PMID:22681889

   Open questions at the time

   • Specific RNA sequence or structural motifs recognized by LUC7L3 were not identified
   • Whether RNA binding is required for its splicing regulatory function was untested
4. 2012 Medium

   Co-fractionation mass spectrometry placed LUC7L3 within stable soluble protein complexes, providing evidence that it operates as part of multi-subunit assemblies rather than as a monomeric factor.

   Evidence Biochemical fractionation of human cell extracts combined with quantitative tandem mass spectrometry

   PMID:22939629

   Open questions at the time

   • The identity and stoichiometry of LUC7L3-containing complexes were not individually characterized
   • Whether complex membership is RNA-dependent was not tested
5. 2015 Medium

   Large-scale AP-MS interactome studies expanded the catalog of LUC7L3 co-complex partners, reinforcing its integration into RNA metabolism networks and providing stoichiometric interaction data.

   Evidence High-throughput AP-MS in HEK293T (BioPlex) and quantitative GFP-tagged AP-MS in HeLa cells

   PMID:26186194 PMID:26496610

   Open questions at the time

   • Specific LUC7L3 interactions were not individually validated by reciprocal pull-down
   • Functional significance of individual partners was not assessed
6. 2022 Medium

   Endogenous GFP tagging confirmed LUC7L3 nuclear localization by live-cell imaging and identified RNA-related co-immunoprecipitation partners, consolidating its assignment as a nuclear RNA-processing factor.

   Evidence Endogenous GFP tagging via genome engineering, live-cell confocal imaging, and AP-MS (OpenCell) in human cells

   PMID:35271311

   Open questions at the time

   • Sub-nuclear localization (e.g., nuclear speckles vs. nucleoplasm) was not resolved
   • Functional consequence of mis-localization was not tested

• The genome-wide repertoire of LUC7L3-dependent splicing events, the RNA-binding specificity determinants, and whether its splicing function is essential for normal cardiac conduction remain unresolved.
• No CLIP-seq or equivalent map of direct LUC7L3 RNA targets exists in the timeline
• Loss-of-function (knockout/knockdown) phenotype data are absent
• Structural basis of LUC7L3 RNA recognition is unknown