DNAJA4

DNAJA4 is an HSP40/DnaJ family co-chaperone with functionally distinct substrate specificity that operates at the intersection of cholesterol homeostasis, protein quality control, cytoskeletal regulation, and stress signaling. Its expression is transcriptionally controlled by SREBP2, and DNAJA4 promotes cholesterol synthesis by increasing HMG-CoA reductase protein content through a co-translational chaperone mechanism without altering mRNA or protein stability (PMID:16950652). DNAJA4 suppresses epithelial–mesenchymal transition and metastasis by recruiting the proteasome subunit PSMD2 to drive ubiquitin-proteasome degradation of the cytoskeletal protein MYH9 (PMID:37875476), negatively regulates NF-κB signaling and RhoA/ROCK1-dependent F-actin dynamics under heat stress in keratinocytes (PMID:29807809, PMID:32925288), and facilitates ubiquitin-independent proteasomal degradation of HBV HBx protein downstream of MSX1 (PMID:39883729). DNAJA4 also promotes ApoE expression, and its suppression by miR-199a and miR-1908 enhances melanoma metastasis (PMID:23142051).

1. 2006 High

   Establishing DNAJA4 as a SREBP2-regulated co-chaperone that enhances cholesterol biosynthesis resolved how a DnaJ protein could be transcriptionally coupled to lipid homeostasis and identified a co-translational mechanism for increasing HMG-CoA reductase protein without altering its mRNA.

   Evidence Subtractive hybridization, dominant-negative SREBP2 adenoviral expression, COS cell overexpression with 14C-acetate incorporation, Western blot, and mRNA analysis

   PMID:16950652

   Open questions at the time

   • Direct physical interaction between DNAJA4 and nascent HMG-CoA reductase not demonstrated
   • HSP70 partner identity for this co-translational function unknown
   • In vivo cholesterol phenotype in DNAJA4-deficient animals not tested
2. 2012 High

   Demonstrating that miR-1908, miR-199a-5p, and miR-199a-3p convergently suppress DNAJA4 and ApoE to promote melanoma metastasis placed DNAJA4 in a miRNA-regulated metastasis network and identified its role in sustaining ApoE expression.

   Evidence In vivo selection of metastatic human cancer cell populations, LNA inhibition, miRNA overexpression/inhibition, in vitro and in vivo metastasis assays

   PMID:23142051

   Open questions at the time

   • Mechanism by which DNAJA4 promotes ApoE expression not elucidated
   • Whether DNAJA4 chaperone activity is required for ApoE regulation not tested
3. 2015 Medium

   Identifying C2238/αANP-driven upregulation of miR-199a via ROS-Egr-1 as a pathway that suppresses DNAJA4 and consequently ApoE in vascular smooth muscle cells extended the miRNA-DNAJA4-ApoE axis to cardiovascular biology.

   Evidence miRNA overexpression/inhibition, NPR-C and Egr-1 knockdown, ROS inhibition, Western blot and RT-PCR in VSMCs

   PMID:26720342

   Open questions at the time

   • Single-lab finding without independent replication
   • Direct DNAJA4 3′-UTR reporter validation not shown in VSMCs
   • In vivo cardiovascular phenotype of DNAJA4 loss not examined
4. 2018 Medium

   CRISPR knockout of DNAJA4 in keratinocytes revealed it as a negative regulator of NF-κB signaling under heat stress, linking this co-chaperone to inflammatory cytokine control and cell survival during thermal injury.

   Evidence CRISPR/Cas9 KO in HaCaT cells, NF-κB inhibitor rescue, flow cytometry, MTS assay, RT-qPCR, Western blot

   PMID:29807809

   Open questions at the time

   • Direct molecular target through which DNAJA4 suppresses NF-κB not identified
   • Whether HSP70 partnership is required for NF-κB regulation unknown
   • In vivo skin phenotype not assessed
5. 2020 Medium

   Extending the keratinocyte KO model showed DNAJA4 restrains RhoA/ROCK1-dependent F-actin dynamics and modulates CLU/ERK protective signaling during hyperthermia, broadening its stress-response role beyond NF-κB to cytoskeletal and survival pathways.

   Evidence CRISPR/Cas9 KO in HaCaT cells, immunofluorescence, Western blot, CLU siRNA knockdown, ERK inhibitor rescue

   PMID:32277496 PMID:32925288

   Open questions at the time

   • Whether DNAJA4 directly binds RhoA or ROCK1 not tested
   • Relationship between NF-κB and cytoskeletal phenotypes in KO cells not dissected
   • CLU and ERK changes may be compensatory rather than direct
6. 2020 Medium

   Yeast complementation experiments demonstrated that DNAJA4 cannot substitute for Ydj1 under stress, establishing that DNAJA4 has distinct substrate specificity compared to DNAJA1 and DNAJA2.

   Evidence ydj1Δ yeast complementation with human DnaJA proteins, drug sensitivity and heat shock assays

   PMID:32149145

   Open questions at the time

   • Specific structural determinants of DNAJA4 substrate selectivity not mapped
   • Whether DNAJA4 cooperates with a different HSP70 partner than DNAJA1/A2 not addressed
7. 2023 High

   Discovery that DNAJA4 recruits the proteasome subunit PSMD2 to drive ubiquitin-proteasome degradation of MYH9, thereby suppressing EMT and metastasis in nasopharyngeal carcinoma, provided the first defined proteasome-targeting mechanism for DNAJA4.

   Evidence Co-IP identifying PSMD2 interaction, DNAJA4 overexpression/knockdown, MYH9 rescue, in vivo metastasis models, proteasome inhibitor experiments

   PMID:37875476

   Open questions at the time

   • Whether DNAJA4 directly ubiquitinates MYH9 or recruits an E3 ligase not clarified
   • Structural basis for PSMD2 recruitment unknown
   • Generality of PSMD2-mediated degradation to other DNAJA4 substrates not tested
8. 2025 Medium

   Showing that MSX1-induced DNAJA4 promotes ubiquitin-independent proteasomal degradation of HBV HBx protein demonstrated a second proteasome-targeting function and an antiviral role for DNAJA4.

   Evidence DNAJA4 overexpression, HBx protein stability by Western blot, HBV replication assays, correlation with MSX1

   PMID:39883729

   Open questions at the time

   • Direct physical interaction between DNAJA4 and HBx not demonstrated by reciprocal Co-IP or pulldown
   • Ubiquitin-independent degradation mechanism (proteasome subunit involvement) not defined
   • Single-lab finding without independent validation

• The identity of the HSP70 partner(s) through which DNAJA4 exerts its co-chaperone functions, the structural basis for its distinct substrate specificity relative to DNAJA1/A2, and whether its proteasome-targeting activities (via PSMD2 for MYH9; ubiquitin-independent for HBx) reflect a unified or context-dependent mechanism remain unresolved.
• No HSP70 partner identified for any DNAJA4 function
• No structural or domain-mapping studies on DNAJA4 substrate selectivity
• Relationship between cholesterol co-translational function and proteasome-targeting function not explored