OCLN

OCLN (occludin) is an integral tight junction protein that controls epithelial and endothelial barrier integrity and also serves as an essential host entry factor for hepatitis C virus (HCV) (PMID:20463075, PMID:32056224). Cell-surface localization and HCV permissiveness depend on the MARVEL domain: splice isoforms retaining it localize to the membrane and support viral interaction, whereas variants lacking it are cytoplasmic and non-permissive (PMID:20463075). Together with CD81, OCLN constitutes a minimal set of factors sufficient to render even non-hepatic cells competent for HCV entry and replication (PMID:32056224). Beyond its membrane role, the OCLN carboxy-terminus links tight junction cargo to the minus-end-directed motor by binding the dynein light intermediate chain (LIC) in a phosphorylation-dependent manner — S471 phosphorylation is required for LIC binding and S490 phosphorylation for trafficking — and this trafficking activity drives endothelial proliferation and collateral angiogenesis, with full-length OCLN loss being embryonic lethal. OCLN abundance is tightly regulated post-transcriptionally and post-translationally: its 3' UTR is directly targeted by miR-122, miR-144, and miR-122-5p to lower protein levels and increase barrier permeability across hepatic, intestinal, and brain microvascular contexts (PMID:25302477, PMID:29258088, PMID:34150006), and its protein stability is controlled by autophagosomal degradation and ubiquitination (PMID:38497494, PMID:40392484). Pathogen-driven OCLN loss is a route to barrier failure, as S. pneumoniae StkP phosphorylates BECN1 to trigger autophagy-dependent OCLN degradation and alveolar barrier dysfunction (PMID:38497494).

1. 2010 High

   Established that OCLN's MARVEL domain dictates both its cell-surface localization and its function as an HCV entry factor, defining the structural determinant of viral permissiveness.

   Evidence Recombinant isoform expression with localization studies and in vitro HCV infectivity assays

   PMID:20463075

   Open questions at the time

   • Does not define the molecular interface between the MARVEL domain and HCV
   • Does not address OCLN's tight-junction barrier function
2. 2014 High

   Showed that OCLN levels are set post-transcriptionally via direct 3' UTR targeting by miR-122, coupling host miRNA control to HCV entry efficiency.

   Evidence Dual-luciferase 3' UTR reporter, miR-122 overexpression, and HCV pseudoparticle entry assay in hepatocytes

   PMID:25302477

   Open questions at the time

   • Does not establish the upstream regulators of miR-122 in this context
   • Effect on barrier permeability not measured
3. 2017 Medium

   Extended miRNA control of OCLN to barrier permeability, demonstrating miR-144 directly represses OCLN (and ZO1) to increase intestinal epithelial permeability.

   Evidence Dual-luciferase reporter, miRNA mimic/inhibitor transfection, and OCLN overexpression rescue in IBS-D rat colonic epithelium

   PMID:29258088

   Open questions at the time

   • Single-lab finding
   • Relative contribution of OCLN versus ZO1 to the permeability phenotype not resolved
4. 2020 Medium

   Placed OCLN downstream of a probiotic-modulated miR-144 axis and confirmed CD81/OCLN as a minimal sufficient module for HCV entry in non-hepatic cells.

   Evidence miRNA microarray with OCLN rescue (L. casei study) and CD81/OCLN transduction of tree shrew BM-MSCs with HCV infection assay

   PMID:32056224 PMID:32807750

   Open questions at the time

   • CD81/OCLN cooperation mechanism at the membrane not defined
   • Probiotic regulation of miR-144 mechanism not established
5. 2021 Medium

   Generalized OCLN's miRNA regulation to the neurovascular unit, showing miR-122-5p directly targets OCLN to increase brain microvascular endothelial apoptosis and permeability.

   Evidence Dual-luciferase reporter, miRNA mimic transfection, and OCLN overexpression rescue with flow cytometry in BMECs

   PMID:34150006

   Open questions at the time

   • Single-lab finding
   • Link between OCLN loss and apoptosis mechanism not defined
6. 2024 High

   Defined a pathogen-driven post-translational route to OCLN loss, in which bacterial StkP phosphorylates BECN1 to trigger autophagosomal OCLN degradation and barrier failure.

   Evidence pEV proteomics, co-IP, BECN1 phosphorylation assays, autophagy inhibition, TEER, and stkP deletion in vivo

   PMID:38497494

   Open questions at the time

   • Mechanism targeting OCLN specifically to autophagosomes not defined
   • Whether host autophagy regulators reproduce this in the absence of bacteria unaddressed
7. 2025 Medium

   Revealed a previously uncharacterized motor-adaptor function: the OCLN C-terminus binds dynein LIC in a phosphorylation-dependent manner to traffic tight junction cargo and drive endothelial proliferation and collateral angiogenesis.

   Evidence Reciprocal co-IP, S471A/S490A mutagenesis with functional readouts, in vivo collateral angiogenesis, and exon 5-targeted deletion (preprint)

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Kinase(s) phosphorylating S471/S490 not identified
   • Cargo identity transported by the OCLN-dynein complex not defined
8. 2025 Low

   Implicated ubiquitination as an additional OCLN stability control point, with a miR-20a/DUSP3 axis modulating OCLN ubiquitination during sepsis-associated barrier dysfunction.

   Evidence CLP mouse model and LPS-treated NCM460 cells with OCLN knockdown/overexpression, western blot, and immunofluorescence

   PMID:40392484

   Open questions at the time

   • DUSP3-to-OCLN ubiquitination link is indirect and ubiquitination assay details unspecified
   • Responsible E3 ligase not identified
   • Single-lab finding

• How OCLN integrates its membrane barrier role, viral receptor function, and dynein-dependent cargo trafficking into a single regulated program remains unresolved.
• No structural model of the OCLN-dynein LIC complex
• Identity of kinases and E3 ligases controlling OCLN trafficking and turnover unknown
• Causal Mendelian disease link not established in the corpus