SLC35A5

SLC35A5 is a Golgi-resident nucleotide sugar transporter that contributes to the selective import of UDP-sugars required for glycoconjugate biosynthesis (PMID:30641943). It localizes exclusively to the Golgi apparatus with its C-terminus facing the cytosol (PMID:30641943), and its inactivation in HepG2 cells reduces Golgi uptake of UDP-glucuronic acid, UDP-N-acetylglucosamine, and UDP-N-acetylgalactosamine while leaving UDP-galactose transport intact, defining a substrate-selective transport role (PMID:30641943). SLC35A5 functions within a multiprotein assembly, forming homomers and heteromers with other SLC35A subfamily members (PMID:30641943). Beyond these features, the downstream consequences of SLC35A5 transport activity—including its links to chondroitin sulfate proteoglycan biosynthesis and to cellular paclitaxel resistance—have only been characterized at low confidence in the available corpus.

1. 2012 Low

   Before any biochemical role was known, a functional genomics screen first connected SLC35A5 to a cellular phenotype, implicating it in drug response.

   Evidence RNAi knockdown in HapMap lymphoblastoid cell lines with paclitaxel cytotoxicity assay

   PMID:22437668

   Open questions at the time

   • Single method (RNAi + cytotoxicity) with no molecular mechanism linking SLC35A5 to paclitaxel handling
   • No connection drawn at this stage to transport activity or Golgi function
   • Not independently confirmed
2. 2017 Low

   Interaction mapping began to place SLC35A5 within the SLC35A subfamily by showing it associates selectively with SLC35A4 but not other members.

   Evidence FLIM-FRET in vivo interaction analysis (SLC35A5 a secondary finding in an SLC35A4-focused study)

   PMID:28167211

   Open questions at the time

   • Single lab, single method; SLC35A5 was a secondary observation
   • Functional consequence of the SLC35A4–SLC35A5 interaction not established
   • No reciprocal or biochemical validation of the complex
3. 2019 Medium

   A focused study established SLC35A5's core identity—its Golgi localization, membrane topology, substrate-selective transport activity, and oligomeric state—answering what the protein physically is and does.

   Evidence Immunofluorescence and topology assays, CRISPR-Cas9 knockout with nucleotide sugar uptake assays, and FLIM-FRET/co-IP interaction analysis in HepG2 cells

   PMID:30641943

   Open questions at the time

   • Direct transport by purified SLC35A5 not reconstituted; uptake measured in a knockout cell context
   • Stoichiometry and composition of the SLC35A multiprotein complex undefined
   • Whether SLC35A5 is the direct transporter or a regulatory complex subunit not resolved
4. 2019 Low

   Knockout linked SLC35A5 transport activity to a downstream glycan output, connecting it to proteoglycan biosynthesis.

   Evidence CRISPR-Cas9 knockout in HepG2 cells followed by glycan analysis

   PMID:30641943

   Open questions at the time

   • Only a slight change in chondroitin sulfate proteoglycan levels observed
   • Single lab, single method
   • Causal chain from substrate transport to proteoglycan change not directly demonstrated

• The mechanism linking SLC35A5's nucleotide sugar transport to drug resistance and to its specific complex partners remains open.
• No molecular mechanism connects SLC35A5 transport to paclitaxel resistance
• The functional role of SLC35A5 heteromers with specific SLC35A members is undefined
• No structural model or reconstituted transport assay exists