DNAJC5

DNAJC5 (CSPα) is a palmitoylated, membrane-anchored HSC70 co-chaperone that operates at endolysosomes to maintain cellular proteostasis through two coupled activities: misfolding-associated protein secretion (MAPS) of cytosolic misfolded proteins such as α-synuclein and TDP-43, and ESCRT-dependent endosomal microautophagy (PMID:29531792, PMID:36626307, PMID:35506243). Palmitoylation by DHHC acyltransferases is required for DNAJC5 membrane anchoring, oligomerization, and unconventional secretion; the depalmitoylase PPT1 regulates its turnover, and the interactor SLC3A2/CD98hc directs a perinuclear MAPS-competent pool distinct from the microautophagy-associated lysosomal pool (PMID:41657026, PMID:26659577, PMID:35506243). In neurons, DNAJC5 also interacts with the synaptic proteins SNAP-25 and Munc18-1 in an HSC70-dependent manner (PMID:38193346). Dominant mutations (L115R, L116Δ) in the cysteine-string domain cause adult-onset neuronal ceroid lipofuscinosis (Kufs disease/CLN4) through a toxic gain-of-function mechanism involving excessive oligomerization and prelysosomal aggregation that damages lysosomal membranes, a process counteracted by CHIP ubiquitin ligase–mediated microautophagy (PMID:21820099, PMID:31663851, PMID:40397740, PMID:40855364).

1. 2011 High

   Establishing that DNAJC5 cysteine-string domain mutations cause a human neurodegenerative disease (CLN4/Kufs) and affect palmitoylation-dependent sorting answered the question of whether CSPα dysfunction is pathogenic in humans.

   Evidence Linkage mapping, exome sequencing across 20 families, and cellular palmitoylation/sorting assays in neuronal cells

   PMID:21820099 PMID:22073189

   Open questions at the time

   • Mechanism by which mutations cause neurodegeneration (loss-of-function vs. gain-of-function) was unresolved
   • No animal model yet recapitulated the disease
2. 2015 High

   Identifying CSPα as a PPT1 substrate and showing global palmitoylation disruption in CLN4 brains revealed that DNAJC5 sits at the intersection of two ceroid lipofuscinosis pathways and that its disease state perturbs broader lipid-modification homeostasis.

   Evidence PPT1 enzymatic activity assays and quantitative palmitome proteomics in CLN4 patient versus control brain tissue

   PMID:26659577

   Open questions at the time

   • Whether PPT1 dysregulation is cause or consequence of DNAJC5 aggregation was unclear
   • No reconstitution of PPT1-mediated CSPα depalmitoylation in a defined system
3. 2018 High

   Demonstrating that DNAJC5 is essential for MAPS and acts downstream of USP19–HSC70 on late endosomes/lysosomes defined CSPα's non-synaptic proteostasis function — the secretion of misfolded cytosolic proteins via the endolysosomal system.

   Evidence Knockdown/knockout secretion assays, co-immunoprecipitation, subcellular localization, and epistasis experiments in human cells

   PMID:29531792

   Open questions at the time

   • Cargo selectivity and translocation mechanism for misfolded substrates into endosomes was unknown
   • In vivo relevance of MAPS not yet tested
4. 2019 High

   Genetic epistasis in Drosophila resolved the loss- vs. gain-of-function debate by showing CLN4 mutations cause excessive CSPα oligomerization and prelysosomal accumulation in a hypermorphic, HSC70-dependent manner.

   Evidence Transgenic Drosophila expressing CLN4 mutant human CSPα with genetic reduction of dCSP and Hsc70, immunofluorescence, and ultrastructural analysis

   PMID:31663851

   Open questions at the time

   • Whether the same gain-of-function mechanism operates in mammalian neurons remained untested
   • Direct demonstration of lysosomal membrane damage was lacking
5. 2022 High

   Uncovering that DNAJC5 drives two coupled but separable activities — ESCRT-dependent microautophagy and SLC3A2-dependent MAPS — from distinct endosomal pools explained how its dysfunction generates lipofuscin-like storage material.

   Evidence BioID proximity labeling, SLC3A2 knockout, ESCRT inhibition, ANCL-mutant expression, and Drosophila neurodegeneration assay

   PMID:35506243

   Open questions at the time

   • How SLC3A2 recruits DNAJC5 to the perinuclear compartment was not defined
   • Relative contribution of microautophagy failure vs. MAPS failure to disease unclear
6. 2023 High

   Reconstituting palmitoylation-dependent DNAJC5 oligomerization and α-synuclein translocation into endosomal membranes established the minimal biochemical requirements for MAPS cargo capture.

   Evidence Reconstitution of α-syn secretion by DNAJC5 expression in HEK293T cells, palmitoylation-deficient mutagenesis, membrane-targeting rescue, validated in SH-SY5Y and iPSC-derived dopamine neurons

   PMID:36626307

   Open questions at the time

   • Whether oligomerization directly forms a translocation channel or recruits additional machinery unknown
   • Stoichiometry of DNAJC5 oligomers on endosomal membranes not determined
7. 2024 Medium

   Proximity labeling in neuronal cells revealed that DNAJC5 interacts with SNAP-25 and Munc18-1, and that the CLN4 L115R mutation selectively abolishes these interactions while preserving HSC70 binding, separating chaperone engagement from synaptic client interactions.

   Evidence MiniTurbo BioID in stable PC12 lines expressing WT or L115R CSPα, LC-MS proteomics, western blot validation

   PMID:38193346

   Open questions at the time

   • Reciprocal pull-down or endogenous-level validation not shown
   • Functional consequence of lost SNAP-25/Munc18-1 interaction for synaptic transmission not tested in this study
8. 2025 High

   Convergent studies in transgenic/knockout mice, iPSC-derived neurons, and CRISPR screens established that CLN4 is a cell-autonomous toxic gain-of-function disease in which mutant DNAJC5 aggregates directly damage lysosomal membranes, counteracted by CHIP-mediated microautophagy.

   Evidence Transgenic and conditional-KO mouse neuropathology; in vitro lysosomal membrane damage assay; genome-wide CRISPR screen identifying CHIP; CHIP rescue in CLN4 iPSC neurons and Drosophila

   PMID:40397740 PMID:40855364

   Open questions at the time

   • Whether CHIP-based therapeutic strategies are viable in vivo in mammals remains untested
   • Structural basis of mutant CSPα membrane-damaging activity unresolved
9. 2025 High

   Defining a minimal palmitoylation module (DC95) comprising the cysteine-string domain plus C-terminal residues as sufficient for DHHC-dependent palmitoylation, Golgi translocation, and unconventional secretion delineated the domain architecture governing DNAJC5 membrane targeting.

   Evidence Systematic mutagenesis of palmitoylation sites, DHHC overexpression, subcellular fractionation, and secretion assays in human cells

   PMID:41657026

   Open questions at the time

   • Which DHHC isoform is the physiologically dominant palmitoylase in neurons not resolved
   • Structural basis of how the C-terminal residues cooperate with the cysteine-string for palmitoylation unknown
10. 2025 Medium

    Identifying TDP-43 and hnRNP K as regulators of canonical DNAJC5 splicing revealed a transcriptional-level control point, connecting TDP-43 proteinopathy to DNAJC5-dependent endosomal trafficking.

    Evidence TDP-43/hnRNP K knockdown, splice isoform analysis, RNA-dependent co-immunoprecipitation, binding-site mutagenesis in DNAJC5 pre-mRNA

    PMID:41983529

    Open questions at the time

    • In vivo relevance of aberrant DNAJC5 splicing in TDP-43 proteinopathies not demonstrated
    • Whether mis-spliced DNAJC5 produces a dominant-negative or loss-of-function allele unclear

• The structural basis of DNAJC5 oligomerization on endosomal membranes, the mechanism by which cytosolic misfolded cargoes are translocated across the endosomal membrane, and the in vivo therapeutic potential of modulating CHIP or DHHC enzymes in CLN4 remain open questions.
• No high-resolution structure of membrane-associated DNAJC5 oligomer
• Translocation mechanism for MAPS cargo across endosomal membrane undefined
• Therapeutic targeting of CHIP or palmitoylation for CLN4 not tested in mammalian models