Recombinant Mouse DnaJ homolog subfamily C member 15 (Dnajc15)

What is DNAJC15 and what are its primary cellular functions?

DNAJC15 is a mitochondrial co-chaperonin belonging to the DnaJ heat shock protein family (Hsp40). It localizes to the mitochondrial inner membrane where it serves multiple functions:

• Acts as a negative regulator of the mitochondrial respiratory chain, specifically regulating complex I activity

• Functions as an import component of the TIM23 translocase complex in mitochondria

• Stimulates the ATPase activity of HSPA9 (mitochondrial Hsp70)

• Prevents mitochondrial hyperpolarization and restricts mitochondrial ATP generation

• Regulates mitochondrial permeability transition pore (MPTP) complex

DNAJC15 stands apart from other DnaJC family members due to its C-terminal J domain (as opposed to the common N-terminal position) and its transmembrane domain, while most DnaJ proteins are soluble .

What is the tissue distribution pattern of mouse DNAJC15?

Mouse DNAJC15 displays a tissue-specific expression pattern that is conserved with its human ortholog:

• Highest expression in heart tissue

• Significant expression in liver and kidney

• Lower expression in lungs

• Within the immune system, high expression in CD8 T cells but almost undetectable in CD4 T cells and B cells

This expression pattern suggests tissue-specific roles for DNAJC15 and potentially differing mitochondrial regulation requirements across tissues.

What are the key structural features of mouse DNAJC15?

Mouse DNAJC15 shares approximately 75% identity with human DNAJC15, with nearly identical transmembrane and C-terminal DnaJ domain regions . Key structural elements include:

• A 147-amino acid protein with a molecular weight of ~16 kDa

• A J domain located at the C-terminus (atypical for DnaJ proteins)

• A transmembrane domain that anchors it in the mitochondrial inner membrane

• An N-terminal region that has no homology with other known proteins

What are the recommended protocols for expressing and purifying recombinant mouse DNAJC15?

For optimal expression and purification of recombinant mouse DNAJC15:

• Expression system selection: Use in vitro expression systems with cloned mouse DNAJC15 cDNA. These systems offer better specificity, sensitivity, and lot-to-lot consistency compared to traditional methods .

• Cloning strategy:

  • Clone the full DNAJC15 coding sequence into a PiggyBac vector (e.g., PB-Cuo-MCS-IRES-GFP-EF1α-CymR-Puro)

  • For inducible expression, utilize systems responsive to 4-isopropylbenzoic acid (15 μg/mL for strong induction)

• Cell selection: After transfection with the DNAJC15 expression construct and PiggyBac Transposase Expression Vector (0.2 μg/μL), select with puromycin for four consecutive days after reaching full confluence .

• Expression verification: Confirm expression by immunoblotting using DNAJC15-specific antibodies that recognize the N-terminal region .

How can I effectively detect mouse DNAJC15 in experimental samples?

Detection methods for mouse DNAJC15 depend on the experimental context:

• Western blotting:

  • Use antibodies specific to the N-terminal region of mouse DNAJC15

  • For recombinant tagged versions, detect using tag-specific antibodies (e.g., DDK-myc tag)

  • Expect a molecular weight band at approximately 16 kDa

• Protein fractionation:

  • Isolate mitochondrial fractions by differential centrifugation (8,000×g)

  • For higher purity, perform protease treatment of isolated mitochondria to remove non-imported preproteins

• Immunoprecipitation protocol:

  • Use a cross-linking approach with DSP (2 mM) for 30 min at room temperature

  • Quench with 100 mM Tris pH 7.4 for 15 min

  • Lyse cells in HEPES-NaCl buffer with digitonin

  • Pre-bind DNAJC15 antibody to Protein G magnetic beads

  • Use 1.4 mg of total protein for immunoprecipitation (120 min incubation)

  • Elute proteins using Laemmli buffer with DTT at 70°C

• Mass spectrometry-based detection:

  • SILAC labeling combined with cellular fractionation offers robust detection

  • LC-MS/MS analysis can quantify DNAJC15 levels across different cell fractions

What experimental approaches can be used to study DNAJC15 function in mitochondria?

Several methodologies have proven effective for investigating DNAJC15 function:

• Respiratory chain analysis:

  • Measure complex I and complex II activity in isolated mitochondria from DNAJC15-manipulated cells

  • Assess oxygen consumption rates under both phosphorylation-coupled and uncoupled states

• Protein import assays:

  • SILAC labeling combined with mitochondrial isolation can track import of matrix and inner membrane proteins

  • Protease treatment of isolated mitochondria distinguishes imported from non-imported proteins

• Mitochondrial membrane potential:

  • Evaluate the effect of DNAJC15 manipulation on mitochondrial membrane potential, which is directly impacted by DNAJC15 activity

• Supercomplex formation analysis:

  • Assess the formation of respiratory chain supercomplexes in the presence or absence of DNAJC15

• ATP production measurement:

  • Quantify ATP levels to assess the impact of DNAJC15 on mitochondrial energy production

How does DNAJC15 influence chemoresistance in cancer models?

DNAJC15 has emerged as a key regulator of chemosensitivity, particularly in ovarian cancer:

• Expression patterns in chemoresistant cells:

  • DNAJC15 expression is significantly decreased in cisplatin (CDDP)-resistant compared to sensitive ovarian cancer cells

  • This downregulation positively correlates with the acquisition of chemoresistance

• Mechanistic insights:

  • DNAJC15 overexpression increases sensitivity to cisplatin in resistant cells by:

    • Reducing the CDDP IC50 values

    • Decreasing colony formation capacity

    • Reducing spheroid formation and growth

  • DNAJC15 knockdown in sensitive cells increases their resistance

• Relationship to ferroptosis:

  • DNAJC15 promotes vulnerability to ferroptosis in ovarian cancer cells

  • High DNAJC15 levels are associated with:

    • Accumulation of lipid droplets

    • Increased lipid peroxidation

    • Subsequent ferroptosis induction

• Therapeutic implications:

  • Ferroptosis inhibition via Ferrostatin-1 treatment decreases cells' vulnerability to ferroptosis and recovers the CDDP-resistant phenotype

  • This suggests that DNAJC15 modulates CDDP sensitivity through ferroptosis regulation

What is known about the epigenetic regulation of DNAJC15 in disease contexts?

DNAJC15 expression is heavily regulated by epigenetic mechanisms:

• Methylation patterns:

  • DNAJC15 gene expression is negatively regulated by methylation of CpG islands within the promoter and first exon/intron sequences

  • Hypermethylation of DNAJC15 CpG islands has been observed in multiple cancer types:

    • Ovarian cancer

    • Wilms' tumors

    • Malignant brain tumors

    • Melanoma

• Clinical correlations:

  • High levels of CpG island methylation in the DNAJC15 gene (associated with loss of expression) correlate with:

    • Diminished response to chemotherapy

    • Poor survival in ovarian cancer patients

  • DNAJC15 is expressed in chemosensitive breast and uterine cancer cells but not in multidrug-resistant cancer cells

• Experimental approaches to study epigenetic regulation:

  • Analyze methylation status using bisulfite sequencing

  • Compare methylation patterns between drug-sensitive and resistant cell lines

  • Assess the effect of demethylating agents on DNAJC15 expression and chemosensitivity

How does DNAJC15 regulate protein import specificity in mitochondria?

Recent research has uncovered sophisticated mechanisms by which DNAJC15 controls mitochondrial protein import:

• Protein import specificity:

  • DNAJC15 supports the import of many matrix and inner membrane proteins with OXPHOS-related functions

  • Loss of DNAJC15 impairs import primarily of proteins localized to the matrix and inner membrane

  • DNAJC15 particularly affects proteins with higher turnover rates compared to the median stability of the mitochondrial proteome

• Interactome analysis:

  • 73 proteins with reduced levels after DNAJC15 depletion are significantly enriched in the DNAJC15 interactome

  • These proteins likely bind to DNAJC15 during membrane translocation into mitochondria

• Impact on OXPHOS components:

  • DNAJC15 depletion significantly impairs complex I activity in both phosphorylation-coupled and uncoupled states

  • Complex II activity is moderately reduced in DNAJC15-depleted mitochondria

• Effect on cellular stress responses:

  • Non-imported mitochondrial preproteins accumulate at the endoplasmic reticulum in DNAJC15-deficient cells

  • This accumulation disrupts ER proteostasis and triggers an ATF6-related unfolded protein response

What is the role of DNAJC15 in stress adaptation of mitochondrial protein import?

DNAJC15 plays a key role in adapting mitochondrial function during cellular stress:

• Regulation by OMA1 peptidase:

  • The stress-regulated mitochondrial peptidase OMA1 cleaves DNAJC15 during cellular stress

  • This cleavage promotes DNAJC15 degradation by the m-AAA protease AFG3L2

• Functional outcomes of stress-mediated regulation:

  • Loss of DNAJC15 reduces import of OXPHOS-related proteins via the TIMM23-TIMM17A protein translocase

  • This limits OXPHOS biogenesis under conditions of mitochondrial dysfunction

  • Non-imported mitochondrial preproteins accumulate at the endoplasmic reticulum and induce an ATF6-related unfolded protein response

• Physiological significance:

  • These mechanisms represent stress-dependent changes in protein import specificity

  • They are part of the OMA1-mediated mitochondrial stress response

  • They highlight the interdependence of proteostasis regulation between different organelles

How does DNAJC15 regulate the mitochondrial permeability transition pore complex?

DNAJC15 has been identified as a regulator of the mitochondrial permeability transition pore (MPTP) complex:

• Functional impact:

  • Overexpression of DNAJC15 results in MPTP opening and induction of apoptosis

  • Reduced DNAJC15 levels suppress MPTP activation upon cisplatin treatment

• Molecular mechanism:

  • DNAJC15 exerts its proapoptotic function through cyclophilin D (CypD), an essential component of MPTP

  • DNAJC15 plays a specific role in recruitment and coupling of CypD with mitochondrial permeability transition

• Connection to protein translocation machinery:

  • This function establishes a link between the mitochondrial inner membrane protein translocation machinery and regulation of cell death pathways

  • It provides insight into how DNAJC15 may influence chemoresistance through modulation of apoptotic pathways

What are common challenges in working with recombinant DNAJC15 and how can they be addressed?

Researchers may encounter several challenges when working with recombinant DNAJC15:

• Expression level issues:

  • Problem: Overexpression of DNAJC15 can cause rapid depolarization of mitochondria and mitochondrial swelling

  • Solution: Use inducible expression systems with titratable inducers (e.g., 4-isopropylbenzoic acid at 8-15 μg/mL) to control expression levels

• Protein localization confirmation:

  • Problem: Confirming proper localization to the mitochondrial inner membrane

  • Solution: Perform subcellular fractionation to isolate mitochondria followed by protease protection assays to distinguish outer vs. inner membrane localization

• Protein-protein interaction detection:

  • Problem: Transient or weak interactions with DNAJC15 may be difficult to capture

  • Solution: Use in situ crosslinking approaches (e.g., DSP crosslinker) prior to cell lysis and immunoprecipitation

• Distinguishing direct vs. indirect effects:

  • Problem: Separating primary effects of DNAJC15 manipulation from secondary consequences

  • Solution: Employ acute induction or depletion strategies and monitor temporal responses in mitochondrial function

How can I design experiments to specifically study the role of DNAJC15 in ferroptosis sensitivity?

To investigate DNAJC15's role in ferroptosis, consider the following experimental design:

• Modulation of DNAJC15 expression:

  • Generate cell lines with stable overexpression or knockdown of DNAJC15

  • For ovarian cancer models, use A2780cis and SKOV3cis (resistant) and OC314 (sensitive) cell lines as established models

• Ferroptosis assessment:

  • Measure lipid peroxidation using C11-BODIPY fluorescent probe or MDA assays

  • Evaluate glutathione peroxidase 4 (GPX4) activity, a key regulator of ferroptosis

  • Assess iron accumulation using iron-specific dyes

• Connection to chemotherapy sensitivity:

  • Determine IC50 for cisplatin in cells with modulated DNAJC15 expression

  • Test the effect of ferroptosis inhibitors (e.g., Ferrostatin-1) on cisplatin sensitivity

  • Analyze cell death mechanisms using appropriate markers

• Phenotype characterization:

  • Evaluate clonogenic capacity using colony formation assays

  • Assess 3D growth dynamics using spheroid formation assays

  • Monitor changes in both spheroid formation (0 days) and growth (5 and 10 days)

What controls should be included when studying the effect of DNAJC15 on mitochondrial function?

Robust experimental design for DNAJC15 studies should include the following controls:

• Expression controls:

  • Empty vector controls (mock) for overexpression studies

  • Scrambled shRNA/siRNA for knockdown experiments

  • Verification of DNAJC15 levels by both mRNA (qPCR) and protein (Western blot) analyses

• Localization controls:

  • Confirmation of mitochondrial localization using fractionation

  • Verification that exogenous DNAJC15 correctly localizes to mitochondria

• Functional controls:

  • Parallel assessment of DNAJC19 (another mitochondrial J-protein) effects to distinguish DNAJC15-specific functions

  • For protein import studies, include TIM23 complex component manipulations as comparative controls

• Rescue experiments:

  • Reintroduction of wild-type DNAJC15 in knockout cells

  • Use of DNAJC15 variants (e.g., cleavage-resistant forms) to validate mechanisms

• Stress response controls:

  • Include established stress inducers (e.g., oligomycin treatment) to confirm that cells remain responsive to mitochondrial stress

What emerging areas of DNAJC15 research hold promise for therapeutic development?

Several promising research directions may yield therapeutic applications:

• Targeting DNAJC15 expression in chemoresistant cancers:

  • Development of epigenetic modifiers to reverse DNAJC15 promoter methylation

  • Screening for small molecules that can mimic DNAJC15 function in chemoresistant cells

• Exploiting the DNAJC15-ferroptosis connection:

  • Combination therapies linking DNAJC15 modulation with ferroptosis inducers

  • Biomarker development using DNAJC15 levels to predict ferroptosis sensitivity

• Modulating mitochondrial stress responses:

  • Targeting the OMA1-DNAJC15 axis to influence mitochondrial adaptation

  • Developing approaches to manipulate protein import specificity during disease states

• Cardiac intervention in hypoxic conditions:

  • Exploring DNAJC15 as a mitochondrial target for cardiac intervention in pulmonary hypertension

  • Understanding how DNAJC15 modulates mitochondrial response to chronic hypoxia

How might advanced technologies further illuminate DNAJC15 function?

Cutting-edge technologies could address remaining questions about DNAJC15:

• Cryo-electron microscopy:

  • Determine the structure of DNAJC15 within the TIM23 complex

  • Visualize how DNAJC15 interacts with client proteins during import

• Single-cell proteomics:

  • Analyze cell-to-cell variability in DNAJC15 expression and function

  • Identify rare cell populations with distinct DNAJC15-dependent phenotypes

• Organoid and in vivo models:

  • Develop tissue-specific DNAJC15 knockout/knockin models

  • Generate patient-derived organoids to study DNAJC15 in personalized disease contexts

• Multi-omics integration:

  • Combine proteomics, metabolomics, and transcriptomics to build comprehensive models of DNAJC15 function

  • Apply machine learning approaches to predict context-dependent roles of DNAJC15