DNAJB14

DNAJB14 is an ER-resident, single-pass transmembrane J-domain co-chaperone that recruits cytosolic Hsc70 and SGTA to the ER membrane to regulate transmembrane protein quality control, ion channel assembly, aggregate clearance, and ER-to-cytosol protein reflux. Its cytosol-facing J-domain binds Hsc70 and accelerates ERAD of misfolded transmembrane substrates such as CFTRΔF508 via the ubiquitin–proteasome system, and it forms a complex with DNAJB12 that protects against mutant FUS aggregation in an HSP70-dependent manner (PMID:23018488, PMID:35082301). Through an HSP70-independent mechanism, DNAJB14 promotes tetrameric assembly of K⁺ channel subunits (hERG, Kv4.2) and can rescue trafficking-defective hERG mutants linked to long QT syndrome (PMID:27916661). DNAJB14 also drives ER-to-cytosol reflux (ERCYS) of ER-resident proteins including PDI family members, and its J-domain-dependent recruitment of SGTA enables cytosolic accumulation of factors that inhibit caspase-3 and wt-p53, thereby conferring chemoresistance in cancer cells (PMID:40202782, PMID:41120732).

1. 2012 High

   Establishing DNAJB14 as an ER-anchored co-chaperone resolved how a J-protein could act specifically at the ER membrane to accelerate degradation of misfolded transmembrane — but not luminal — substrates via Hsc70 and the proteasome.

   Evidence Immunofluorescence, protease protection, co-IP with Hsc70, and CFTRΔF508 degradation assays with MG132 in mammalian cells

   PMID:23018488

   Open questions at the time

   • Identity of endogenous ERAD substrates beyond CFTRΔF508 not determined
   • How DNAJB14 discriminates transmembrane versus luminal misfolded clients is unclear
   • Relationship to other ER-resident J-proteins such as DNAJB12 not yet defined
2. 2014 Medium

   Overexpression-induced formation of nuclear membranous structures (DJANGOS) containing DNAJB14, DNAJB12, Hsc70, and ER markers revealed that DNAJB14's chaperone activity can remodel ER-nuclear envelope connections.

   Evidence Immunofluorescence, cryo-EM, J-domain mutation analysis, and live-cell imaging

   PMID:24732912

   Open questions at the time

   • DJANGOS observed only upon overexpression; physiological relevance at endogenous levels unestablished
   • Mechanism by which J-domain activity drives membrane reorganization unknown
3. 2016 High

   Demonstrating that DNAJB14 promotes tetrameric assembly of hERG and Kv4.2 K⁺ channels via an HSP70-independent mechanism established a chaperone-independent scaffolding function and linked DNAJB14 to cardiac ion channelopathies.

   Evidence C. elegans genetic screen, in vitro assembly assay, electrophysiology, and hERG mutant rescue in human cells

   PMID:27916661

   Open questions at the time

   • Structural basis for HSP70-independent assembly promotion unknown
   • Whether DNAJB14 acts on other multimeric membrane protein complexes beyond K⁺ channels not tested
4. 2022 High

   Identifying a full-length DNAJB14–DNAJB12 complex that suppresses mutant FUS aggregation in an HSP70-dependent manner showed that DNAJB14 functions as part of a heteromeric ER-tethered disaggregation system relevant to ALS-linked proteotoxicity.

   Evidence Reciprocal co-IP, FRAP on mutFUS aggregates, proteostasis reporters, and knockdown/overexpression in primary neurons

   PMID:35082301

   Open questions at the time

   • Whether the DNAJB14–DNAJB12 complex acts on other cytosolic aggregate-prone proteins not explored
   • How an ER-tethered complex accesses cytosolic/nuclear aggregates mechanistically unresolved
5. 2023 Medium

   Showing that DNAJB14 knockdown impairs ER-to-cytosol translocation of PDI under ER stress, and that DNAJB14 is itself degraded by the proteasome upon reductive challenge, established DNAJB14 as a regulated component of the ERCYS pathway with non-redundant function relative to DNAJB12.

   Evidence Knockdown, subcellular fractionation, proteasome inhibitor treatment, sulfenic-acid trapping, and UPR activation in mammalian cells

   PMID:37925033

   Open questions at the time

   • Cargo selectivity of DNAJB14-dependent ER reflux beyond PDI not defined
   • How DNAJB14's DUF1977 luminal domain contributes to non-redundancy with DNAJB12 unclear
   • Mechanism of DNAJB14 redox-dependent proteasomal turnover not elucidated
6. 2023 Medium

   DNAJB14 knockout alters PINK1 stabilization kinetics and mitochondrial morphology under mitochondrial stress, linking DNAJB14 to ER–mitochondria crosstalk and mitophagy regulation.

   Evidence CRISPR knockout, PINK1/p-Drp1 western blot, and mitochondrial morphology imaging under CCCP treatment

   PMID:37851175

   Open questions at the time

   • Direct physical interaction between DNAJB14 and PINK1 or Drp1 not demonstrated
   • Whether mitochondrial phenotype is secondary to general ER chaperone dysfunction not excluded
   • Mechanism connecting ER-localized DNAJB14 to mitochondrial fission/fusion machinery unknown
7. 2025 High

   J-domain mutagenesis and SGTA interaction studies established the molecular mechanism by which DNAJB14 drives ERCYS: its J-domain recruits HSC70 and SGTA to translocate ER-resident proteins (AGR2, PDIA4) to the cytosol, where they inhibit caspase-3 and wt-p53, conferring chemoresistance in cancer cells.

   Evidence J-domain point mutations, co-IP, siRNA knockdown of DNAJB14/DNAJB12/SGTA, subcellular fractionation, p53 and caspase-3 activity assays, and cisplatin/doxorubicin cytotoxicity in cancer cell lines

   PMID:40202782 PMID:41120732

   Open questions at the time

   • Whether ERCYS operates in non-cancer cell contexts at physiological expression levels is unresolved
   • Structural basis of the DNAJB14–SGTA interaction not determined
   • Full repertoire of ERCYS cargoes beyond AGR2 and PDIA4 not mapped
8. 2025 Medium

   DNAJB14 knockdown selectively impaired HBV virion morphogenesis without affecting subviral particle secretion, and also reduced infectious HDV production, revealing an unexpected role in hepatitis virus assembly.

   Evidence siRNA knockdown, virion and subviral particle secretion assays, HDV infectivity assay

   PMID:41684842

   Open questions at the time

   • Direct interaction between DNAJB14 and HBV envelope or core proteins not shown
   • Whether this role involves DNAJB14's co-chaperone, scaffolding, or ERCYS activity is unknown
   • Not independently confirmed by a second laboratory

• The structural basis for DNAJB14's dual HSP70-dependent and HSP70-independent activities, the full client/cargo repertoire of ERCYS, and the mechanism linking ER-tethered DNAJB14 to mitochondrial dynamics and viral assembly remain unresolved.
• No atomic-resolution structure of DNAJB14 or its complexes available
• Comprehensive substrate identification (e.g., proximity labeling) not reported
• In vivo phenotype of DNAJB14 knockout in animal models not described