SEC14L1

SEC14L1 is a multi-domain cytosolic protein that functions as a negative regulator of RIG-I-mediated innate antiviral signaling (PMID:23843640). It directly binds the RIG-I CARD domain through its PRELI-MSF1 and CRAL-TRIO domains and competes with the adaptor VISA/MAVS for RIG-I association, thereby dampening downstream IFN-β production and restraining the antiviral response to RNA virus infection (PMID:23843640). Independently, SEC14L1 engages the cholinergic vesicular machinery: its GOLD domain mediates interaction with the vesicular acetylcholine transporter VAChT, and it co-precipitates with the high-affinity choline transporter CHT1; co-expression of these transporters recruits cytosolic SEC14L1 to vesicle-like organelles, and SEC14L1 overexpression modestly reduces high-affinity choline transport (PMID:17092608). The protein's CRAL/TRIO domain shows homology to lipid/retinoid-binding proteins, but a direct lipid-transfer activity has not been demonstrated in the available corpus (PMID:8697811, PMID:11707779).

1. 1996 Medium

   Establishing the gene's existence and a candidate role: cloning revealed a SEC14-homologous protein, framing SEC14L1 as a putative intracellular transport factor before any biochemical function was known.

   Evidence cDNA cloning, sequence homology analysis, FISH mapping to 17q25, and Northern blot expression survey

   PMID:8697811

   Open questions at the time

   • Function inferred from homology only, not from direct assay
   • No binding partner or substrate identified
   • No subcellular localization established
2. 2001 Low

   Defining the gene structure and domain content: identification of alternatively spliced transcripts and a CRAL/TRIO domain homologous to TTPA and CRALBP suggested a retinoid/lipid-binding capacity.

   Evidence Genomic sequencing, exon mapping, RT-PCR splice variant analysis, sequence homology

   PMID:11707779

   Open questions at the time

   • CRAL/TRIO lipid-binding activity inferred from homology, not biochemically validated
   • Functional significance of the exon 17 VNTR splice variation unknown
3. 2006 Medium

   Linking SEC14L1 to cholinergic vesicular transport: it was shown to bind VAChT via its GOLD domain and to associate with CHT1, with transporter co-expression redistributing it to vesicles and reducing choline uptake.

   Evidence Yeast two-hybrid of brain cDNA library, reciprocal Co-IP in mammalian cells, GOLD-domain mapping, fluorescence localization, choline uptake assay

   PMID:17092608

   Open questions at the time

   • Mechanism by which SEC14L1 reduces choline transport not defined
   • Physiological relevance in neurons not tested
   • Single-lab finding
4. 2013 High

   Assigning a defined signaling function: SEC14L1 was shown to negatively regulate RIG-I antiviral signaling by binding the RIG-I CARD domain and competing with the adaptor VISA/MAVS, establishing a molecular mechanism for dampening IFN-β induction.

   Evidence Yeast two-hybrid, reciprocal endogenous and transfected Co-IP, domain mapping, knockdown/overexpression with IFN-β reporter and viral replication readouts (NDV, Sendai virus) in HEK293T and HT1080

   PMID:23843640

   Open questions at the time

   • Structural basis of CARD competition not resolved
   • Whether lipid binding by CRAL-TRIO contributes to RIG-I regulation unknown
   • In vivo relevance in immune cells/animals not tested

• Whether the cholinergic transport role and the RIG-I regulatory role reflect a single unifying biochemical activity (e.g., lipid/cargo binding by its CRAL-TRIO/GOLD domains) remains unresolved.
• No demonstrated lipid ligand for the CRAL-TRIO domain
• No mechanistic link connecting transporter binding and innate immune signaling