SLC35F6

SLC35F6 is an orphan member of the SLC35 nucleotide-sugar transporter family that localizes to lysosomes through a cytoplasmic C-terminal EQERLL360 sorting signal, as demonstrated by domain-swap and mutagenesis experiments (PMID:38928424). SLC35F6 physically interacts with the mitochondrial adenine nucleotide translocase ANT2 and influences mitochondrial membrane potential; its knockdown induces apoptosis via the Bcl2/BAX/caspase3 pathway and suppresses cancer cell proliferation (PMID:19154410, PMID:39482997).

1. 2008 Medium

   The initial characterization of C2orf18/SLC35F6 established that it localizes to mitochondria, physically interacts with ANT2, and is required for cancer cell survival — linking an uncharacterized ORF to mitochondrial function and apoptosis regulation.

   Evidence Subcellular fractionation, co-immunoprecipitation with ANT2, and siRNA knockdown with apoptosis/growth readouts in pancreatic cancer cell lines

   PMID:19154410

   Open questions at the time

   • Interaction with ANT2 demonstrated by co-IP only; no reciprocal or in vitro binding validation
   • Transport substrate of SLC35F6 not identified
   • Mitochondrial versus other organelle localization not resolved with high-resolution methods
2. 2024 High

   Precise subcellular mapping resolved SLC35F6 as a lysosomal protein rather than exclusively mitochondrial, and identified the EQERLL360 cytoplasmic motif as both necessary and sufficient for lysosomal targeting — establishing the molecular basis of its trafficking.

   Evidence Fluorescence microscopy, C-terminal tail swaps between SLC35F1 and SLC35F6, site-directed mutagenesis of EQERLL360, and cell surface biotinylation

   PMID:38928424

   Open questions at the time

   • Transport substrate remains unknown
   • Whether the earlier reported mitochondrial localization reflects a dual-organelle distribution or a methodological discrepancy is unresolved
   • Adaptor protein(s) recognizing the EQERLL signal not identified
3. 2024 Low

   An independent model (piglet) confirmed SLC35F6 involvement in apoptosis through Bcl2/BAX/caspase3 and mitochondrial membrane potential changes, extending the pro-survival role beyond cancer cell lines.

   Evidence Gene expression modulation with apoptosis pathway and mitochondrial membrane potential readouts in a pig model

   PMID:39482997

   Open questions at the time

   • Single study in a non-standard model with limited mechanistic depth; awaits independent replication
   • Direct biochemical mechanism connecting a lysosomal transporter to mitochondrial apoptosis signaling unknown
   • No reconstitution of SLC35F6 transport activity
4. 2025 Low

   SLC35F6 knockdown in hepatocellular carcinoma cells elevated TP53 levels and reduced growth, placing SLC35F6 within a miR-542-3p/SLC35F6/TP53 regulatory axis and suggesting it normally restrains TP53 accumulation.

   Evidence siRNA knockdown, miRNA overexpression, Western blot for TP53, and cell growth assays in HCC cell lines

   PMID:40118430

   Open questions at the time

   • No direct biochemical interaction between SLC35F6 and TP53 demonstrated; mechanism of TP53 regulation unknown
   • Pathway placement based on correlative expression changes in a single study
   • Relationship between lysosomal localization and TP53 regulation unexplained

• The transport substrate of SLC35F6 remains entirely unknown, leaving its primary molecular function unresolved despite clear links to apoptosis regulation and lysosomal localization.
• No substrate identification or transport reconstitution has been performed
• Structural basis of SLC35F6 function not determined
• How a lysosomal transporter mechanistically influences mitochondrial membrane potential and apoptotic signaling is unexplained