BPIFB6

BPIFB6 is an endoplasmic reticulum-resident member of the BPI-fold/lipid transfer-lipopolysaccharide binding protein (LT/LBP) family that functions as a positive regulator of secretory pathway trafficking and Golgi complex integrity (PMID:26962226). It localizes exclusively to the ER, where it associates with other BPIFB family members (PMID:26962226). Loss of BPIFB6 induces pronounced defects in both retrograde and anterograde secretory trafficking accompanied by dramatic Golgi fragmentation (PMID:26962226), and this disruption of the secretory pathway suppresses replication of multiple enteroviruses (coxsackievirus B, poliovirus, EV71) in a pan-viral manner, establishing BPIFB6 as a host factor required for enterovirus replication (PMID:26962226). The molecular basis of its trafficking function and the lipid/LPS-binding capacity inferred from its family membership have not been directly characterized in the available corpus.

1. 2002 Low

   Before any functional data existed, the question was what kind of protein BPIFB6 is; sequence and genomic analysis placed it in the LT/LBP family, framing an expectation of phospholipid/LPS-binding capacity.

   Evidence Sequence homology and exon/intron structural comparison with chromosomal mapping to 20q11

   PMID:12185532

   Open questions at the time

   • Family assignment is computational only — no direct lipid or LPS binding assay was performed
   • No cellular function or localization established at this stage
2. 2016 Medium

   To define where BPIFB6 acts, localization and association studies showed it is an ER-resident protein that forms complexes with other BPIFB family members, anchoring its function to the early secretory pathway.

   Evidence Fluorescence microscopy localization and co-association assays in cultured cells

   PMID:26962226

   Open questions at the time

   • Identity of the specific BPIFB partners and stoichiometry of the complexes not resolved
   • Single lab, single localization method
3. 2016 Medium

   To test whether BPIFB6 has a cellular trafficking role, loss-of-function showed that its depletion fragments the Golgi and disrupts both anterograde and retrograde trafficking, establishing it as a regulator of secretory pathway integrity.

   Evidence RNAi knockdown with trafficking assays and Golgi morphology imaging

   PMID:26962226

   Open questions at the time

   • The molecular mechanism linking an ER protein to Golgi integrity is unknown
   • No rescue or interactor mapping to explain how trafficking is controlled
4. 2016 Medium

   To connect BPIFB6 to a biological outcome, silencing showed it is required for enterovirus replication across multiple viruses, identifying it as a host dependency factor likely acting through its secretory-pathway role.

   Evidence RNAi knockdown with viral titer/plaque readouts across CVB, poliovirus, and EV71

   PMID:26962226

   Open questions at the time

   • Whether viral suppression is a direct consequence of Golgi/trafficking disruption versus another pathway is not formally separated
   • No direct interaction between BPIFB6 and viral proteins demonstrated

• The biochemical activity of BPIFB6 — whether it binds lipids or LPS as its family suggests, and how an ER protein controls Golgi morphology and trafficking — remains undefined.
• No direct lipid/LPS binding assay reported
• No structural model or substrate identified
• Mechanism coupling ER residence to Golgi integrity unknown