Recombinant Pongo abelii DnaJ homolog subfamily C member 15 (DNAJC15)

What are the primary functions of DNAJC15 in mitochondrial physiology?

DNAJC15 serves multiple regulatory functions in mitochondria:

• Regulation of respiratory chain activity: DNAJC15 acts as a negative endogenous regulator of the mitochondrial respiratory chain, preventing mitochondrial hyperpolarization and restricting ATP generation .

• Protein import facilitation: It functions as an import component of the TIM23 translocase complex, enhancing the ATPase activity of mitochondrial heat shock protein 70 (HSPA9), and favoring the transport of proteins lacking a mitochondrial targeting sequence .

• Mitochondrial biogenesis: Through its interaction with the protein import machinery, DNAJC15 contributes to mitochondrial biogenesis .

• Oxidative phosphorylation control: DNAJC15 helps fine-tune mitochondrial respiration in CD8 T cells by interfering with the formation of electron transport chain (ETC) respiratory supercomplexes .

• Lipid metabolism regulation: The protein plays a role in regulating lipid metabolism and has been associated with lipid droplet accumulation in certain contexts .

How does DNAJC15 expression influence mitochondrial protein import?

DNAJC15 controls mitochondrial protein import specificity through its interaction with the TIMM23-TIMM17A protein translocase. Research using stable isotope labeling with amino acids in cell culture (SILAC) combined with cellular fractionation has demonstrated that:

• Depletion of DNAJC15 significantly reduces the steady-state levels of approximately 188 MitoCarta 3.0 annotated proteins in the mitochondrial fraction .

• After protease treatment of the mitochondrial fraction, steady-state levels of an additional 75 proteins were found to be significantly reduced in DNAJC15-depleted cells, suggesting these proteins remained associated with the outer mitochondrial membrane rather than being properly imported .

• Loss of DNAJC15 appears to specifically impact the import of OXPHOS-related proteins, limiting oxidative phosphorylation biogenesis under conditions of mitochondrial dysfunction .

• The import specificity of DNAJC15 appears distinct from that of DNAJC19, as depletion of DNAJC19 did not significantly reduce steady-state levels of mitochondrial proteins in the same experimental setup .

What are the optimal approaches for detecting and measuring DNAJC15 expression in research samples?

Based on current research methodologies, several approaches can be employed for DNAJC15 detection:

• Western Blotting: Anti-MCJ antibodies (such as ab167199) can be used at concentrations of approximately 1 μg/mL. The predicted band size is 16 kDa. For optimal results, use a secondary antibody such as goat anti-mouse HRP conjugated antibody at 1/2500 dilution .

• qRT-PCR: For measuring DNAJC15 mRNA levels, specific primers targeting the DNAJC15 gene can be designed. This approach has been successfully employed to demonstrate decreased DNAJC15 mRNA levels in cisplatin-resistant cancer cells compared to sensitive cells .

• Subcellular Fractionation: To confirm the mitochondrial localization of DNAJC15, isolate mitochondrial fractions by differential centrifugation. This can be followed by western blotting to detect DNAJC15 in mitochondrial extracts .

• Immunofluorescence microscopy: Can be used to visualize the co-localization of DNAJC15 with mitochondrial markers.

• SILAC labeling: For quantitative proteomics studies of DNAJC15's impact on the mitochondrial proteome, SILAC labeling combined with LC-MS/MS analysis allows for precise comparison of protein levels between wildtype and DNAJC15-depleted cells .

What experimental systems are most appropriate for studying DNAJC15 function in vitro?

Several experimental systems have proven effective for studying DNAJC15 function:

• Cell line models:

  • Human ovarian cancer cell lines (A2780, A2780cis, SKOV3, SKOV3cis, OC314) have been successfully used to study DNAJC15's role in chemoresistance .

  • HeLa cells have been employed for studying DNAJC15's role in mitochondrial protein import .

  • CD8 T cells for investigating DNAJC15's role in immune cell metabolism .

• Genetic manipulation approaches:

  • Overexpression using DNAJC15-DDK-myc tagged vectors has been effective in demonstrating DNAJC15's impact on chemosensitivity .

  • RNA interference using shRNAs (particularly shDNAJC15d) has been successful in downregulating DNAJC15 expression .

  • siRNA-mediated knockdown has been used to study DNAJC15's role in mitochondrial protein import .

• Functional assays:

  • Clonogenic assays to assess the impact of DNAJC15 expression on colony formation ability .

  • 3D spheroid culture to evaluate the effect of DNAJC15 on tumorigenic properties in a more physiologically relevant model .

  • Drug sensitivity assays using cisplatin (CDDP) to determine IC50 values in relation to DNAJC15 expression levels .

How can researchers effectively generate and validate DNAJC15 knockdown or overexpression models?

For robust DNAJC15 manipulation models, researchers should consider:

• Overexpression systems:

  • Utilize DNAJC15-DDK-myc tagged vectors for traceable expression .

  • Validate overexpression at both mRNA level (using qRT-PCR) and protein level (using western blotting) .

  • Confirm correct subcellular localization by isolating mitochondrial fractions and detecting the exogenous DNAJC15 in these fractions .

• Knockdown approaches:

  • Test multiple shRNAs or siRNAs to identify the most efficient construct for DNAJC15 downregulation .

  • For example, shDNAJC15d has been identified as particularly effective in some studies .

  • Validate knockdown efficiency at both mRNA and protein levels.

• Functional validation:

  • Assess changes in mitochondrial function using respirometry assays.

  • Evaluate alterations in protein import using mitochondrial fractionation followed by protease treatment .

  • Measure changes in sensitivity to relevant drugs (e.g., cisplatin for cancer cells) .

  • Assess colony formation and spheroid growth to validate phenotypic consequences .

What is the mechanistic link between DNAJC15 expression and chemoresistance in cancer?

DNAJC15 has been implicated in chemoresistance through several interrelated mechanisms:

• Epigenetic regulation: DNAJC15 expression is frequently downregulated due to methylation of its promoter CpG islands and the 5' coding sequence in various cancers including breast, ovarian, neuroblastoma, and brain cancers .

• Chemosensitivity regulation: High DNAJC15 levels correlate with increased sensitivity to various chemotherapeutic agents including paclitaxel, topotecan, and cisplatin (CDDP) in ovarian cancer cells .

• Ferroptosis induction: DNAJC15 overexpression induces increased lipid peroxidation and subsequent ferroptosis in ovarian cancer cells, making them more vulnerable to cisplatin toxicity .

• Drug efflux modulation: One mechanism linking therapy response to DNAJC15 expression involves regulation of multi-drug resistance protein activity. Loss of DNAJC15 enhances drug efflux, contributing to chemoresistance .

• Tumorigenic properties: DNAJC15 expression levels impact clonogenic capacity and spheroid formation. High DNAJC15 expression decreases colony formation ability and spheroid volume, suggesting reduced tumorigenic potential .

Experimental data demonstrating these relationships include:

How does DNAJC15 modulate ferroptosis in cancer cells?

DNAJC15 plays a critical role in modulating ferroptosis through the following mechanisms:

• Lipid droplet accumulation: High levels of DNAJC15 are associated with accumulation of lipid droplets in ovarian cancer cells .

• Lipid peroxidation induction: When overexpressed, DNAJC15 induces a phenotype displaying increased lipid peroxidation, a key process in ferroptosis initiation .

• Iron-dependent cell death: DNAJC15-induced ferroptosis involves iron-mediated unprogrammed cell death, which increases cancer cells' vulnerability to cisplatin toxicity .

• Recovery of resistant phenotype: Treatment with Ferrostatin-1 (a ferroptosis inhibitor) reduces lipid peroxidation in DNAJC15-overexpressing cells, decreasing their vulnerability to ferroptosis and recovering their cisplatin-resistant phenotype .

• Alternative cell death pathway: This DNAJC15-regulated ferroptosis represents an alternative anti-proliferative process beyond apoptosis that may be exploited therapeutically, particularly in ovarian cancer where chemoresistance is a significant clinical challenge .

This mechanism offers potential new therapeutic strategies for overcoming chemoresistance, as DNAJC15-mediated ferroptosis sensitivity could be exploited to enhance the efficacy of conventional treatments like cisplatin.

What is the role of DNAJC15 in immune cell function and metabolism?

DNAJC15 (also known as MCJ) plays a crucial role in regulating CD8 T cell metabolism and immune function:

• Mitochondrial respiration regulation: MCJ/DNAJC15 acts as an endogenous brake for mitochondrial respiration in CD8 T cells by interfering with the formation of electron transport chain (ETC) respiratory supercomplexes .

• Metabolic profiling: Loss of MCJ/DNAJC15 enhances mitochondrial metabolism in CD8 T cells, leading to increased oxidative phosphorylation and subcellular ATP accumulation .

• Cytokine secretion modulation: Interestingly, the increased ATP resulting from MCJ/DNAJC15 deficiency selectively enhances the secretion, but not the expression, of interferon gamma (IFNγ) .

• Adaptation during immune response: MCJ/DNAJC15 helps adapt effector CD8 T cell metabolism during the contraction phase of an immune response .

• Enhanced memory response: Memory CD8 T cells lacking MCJ/DNAJC15 demonstrate superior protection against influenza virus infection, suggesting a role in long-term immune memory .

These findings highlight DNAJC15 as a potential target for enhancing CD8 T cell-mediated immunity in contexts such as vaccination or cancer immunotherapy.

How does stress adaptation regulate DNAJC15 function in mitochondrial protein import?

Recent research has uncovered a sophisticated regulatory mechanism involving DNAJC15 during cellular stress adaptation:

• OMA1-mediated regulation: The stress-regulated mitochondrial peptidase OMA1 orchestrates adaptive responses to cellular stress, including regulation of DNAJC15 .

• Proteolytic processing: OMA1 cleaves the mitochondrial chaperone DNAJC15 and promotes its degradation by the m-AAA protease AFG3L2 .

• Import specificity modulation: Loss of DNAJC15 reduces the import of OXPHOS-related proteins via the TIMM23-TIMM17A protein translocase, limiting oxidative phosphorylation biogenesis under conditions of mitochondrial dysfunction .

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

• Organelle crosstalk: This mechanism highlights the interdependence of proteostasis regulation between different organelles, particularly the mitochondria and endoplasmic reticulum .

This adaptive response represents a stress-dependent change in protein import specificity as part of the OMA1-mediated mitochondrial stress response.

What are the molecular determinants of DNAJC15's role in regulating mitochondrial respiratory complexes?

DNAJC15's regulation of mitochondrial respiratory function involves several molecular aspects:

• Respiratory supercomplex formation: DNAJC15/MCJ interferes with the assembly of electron transport chain (ETC) respiratory supercomplexes, which are crucial for efficient oxidative phosphorylation .

• Differential protein import: DNAJC15 appears to selectively regulate the import of OXPHOS-related proteins. When DNAJC15 is depleted, 188 MitoCarta 3.0 annotated proteins show reduced steady-state levels in mitochondria .

• TIMM23-TIMM17A translocase interaction: DNAJC15 specifically interacts with this protein translocase complex to modulate the import of a subset of mitochondrial proteins .

• Mitochondrial hyperpolarization prevention: DNAJC15 prevents mitochondrial hyperpolarization states and restricts mitochondrial generation of ATP, serving as a natural regulator of respiratory activity .

• Chaperone-like activity: As a member of the DnaJ family, DNAJC15 stimulates the ATPase activity of HSPA9 (mitochondrial heat shock protein 70), influencing protein folding and complex assembly .

These molecular interactions position DNAJC15 as a key regulatory node that links mitochondrial protein import, respiratory complex assembly, and cellular energy production.

What experimental approaches can address contradictory findings regarding DNAJC15 function across different cell types?

To resolve contradictory findings about DNAJC15 function across different cell types, researchers should consider:

• Comparative multi-cell type analysis:

  • Simultaneously analyze DNAJC15 function in multiple cell types (e.g., cancer cells, immune cells, and normal cells) using identical experimental conditions.

  • Quantify baseline DNAJC15 expression levels across cell types using both RT-qPCR and western blotting to identify intrinsic differences.

• Context-dependent interaction mapping:

  • Employ proteomics approaches such as BioID or proximity labeling to identify cell type-specific DNAJC15 interaction partners.

  • Use co-immunoprecipitation followed by mass spectrometry to compare DNAJC15 protein complexes across cell types.

• Conditional knockout/knockin models:

  • Generate tissue-specific or inducible DNAJC15 knockout models to assess cell type-specific phenotypes.

  • Create reporter systems to track DNAJC15 expression and localization in real-time across different cellular contexts.

• Integrated multi-omics analysis:

  • Combine transcriptomics, proteomics, and metabolomics data from DNAJC15-manipulated cells of different origins.

  • Use computational approaches to identify convergent and divergent pathways affected by DNAJC15 across cell types.

• Functional domain mapping:

  • Create chimeric proteins with domains from different species or paralogs to identify critical functional regions.

  • Perform site-directed mutagenesis of key residues to determine their importance across cell types.

• Stress response profiling:

  • Compare how different cellular stressors (oxidative stress, ER stress, hypoxia) affect DNAJC15 function across cell types.

  • Analyze the role of post-translational modifications in regulating DNAJC15 function under various stress conditions.

These approaches can help reconcile seemingly contradictory findings by revealing how DNAJC15 function adapts to different cellular contexts and identifying the core conserved functions versus context-dependent roles.

How can researchers distinguish between the direct effects of DNAJC15 on mitochondrial protein import versus secondary metabolic consequences?

To differentiate direct import effects from secondary metabolic consequences:

• Time-course analysis:

  • Implement inducible DNAJC15 expression or depletion systems to track the temporal sequence of events following DNAJC15 manipulation.

  • Perform rapid kinetic analysis to identify immediate versus delayed responses.

• In vitro import assays:

  • Isolate mitochondria from DNAJC15-manipulated cells and perform in vitro protein import assays using radiolabeled precursor proteins.

  • This approach directly measures import efficiency independent of cellular metabolic adaptations.

• Selective substrate analysis:

  • Test import of diverse mitochondrial precursor proteins targeting different submitochondrial compartments to identify substrate specificity.

  • Use chimeric proteins with different targeting signals to determine which import pathways are DNAJC15-dependent.

• Rescue experiments:

  • Perform rescue experiments with wild-type DNAJC15 versus mutants lacking specific functional domains.

  • Use metabolic inhibitors or metabolite supplementation to determine if the observed phenotypes can be rescued independently of DNAJC15 manipulation.

• Interaction analysis with import machinery:

  • Use proximity labeling or crosslinking mass spectrometry to capture transient interactions between DNAJC15 and components of the protein import machinery.

  • Perform in vitro binding assays with purified components to establish direct interactions.

• Comparative analysis with other import factors:

  • Compare the effects of DNAJC15 depletion with depletion of established import factors (e.g., TIMM23, TIMM17A).

  • Identify overlapping and distinct phenotypes to delineate DNAJC15-specific effects.

These methodological approaches can help establish causality and distinguish primary from secondary effects of DNAJC15 on mitochondrial function.

How might targeting DNAJC15 expression or function be exploited for cancer therapy?

Based on current research findings, several strategies for targeting DNAJC15 in cancer therapy show promise:

• Epigenetic modification:

  • Development of demethylating agents specifically targeting the DNAJC15 promoter region to restore expression in cancers where it is epigenetically silenced .

  • Combination of such agents with conventional chemotherapeutics to enhance chemosensitivity.

• Ferroptosis induction:

  • DNAJC15 overexpression induces ferroptosis in ovarian cancer cells, making them more vulnerable to cisplatin toxicity .

  • Developing therapies that mimic or enhance DNAJC15's effect on lipid peroxidation could synergize with existing chemotherapeutics.

• Chemoresistance modulation:

  • Targeting pathways downstream of DNAJC15 that contribute to drug efflux and chemoresistance .

  • Using DNAJC15 expression as a biomarker to predict response to conventional chemotherapeutics.

• Metabolic targeting:

  • Exploiting the metabolic vulnerabilities created by altered DNAJC15 expression in cancer cells.

  • Developing inhibitors that target the compensatory metabolic pathways activated in DNAJC15-deficient cancer cells.

• Combinatorial approaches:

  • Combining DNAJC15-targeted therapies with other approaches such as immunotherapy, particularly given DNAJC15's role in immune cell function .

These approaches could be particularly valuable in ovarian cancer, where DNAJC15 loss correlates with cisplatin resistance and poor clinical outcomes .

What are the potential implications of DNAJC15 modulation for immune-based therapies?

DNAJC15/MCJ modulation presents several opportunities for enhancing immune-based therapies:

• Enhanced T cell function:

  • Inhibition of DNAJC15/MCJ in CD8 T cells could enhance their mitochondrial metabolism, leading to increased oxidative phosphorylation, subcellular ATP accumulation, and improved effector functions, particularly IFNγ secretion .

• Memory T cell enhancement:

  • MCJ-deficient memory CD8 T cells show superior protection against viral infection, suggesting that targeting DNAJC15 could improve the longevity and efficacy of memory responses induced by vaccines or adoptive cell therapies .

• Metabolic reprogramming for CAR-T or TCR-T therapies:

  • Engineering adoptively transferred T cells with reduced DNAJC15/MCJ expression could enhance their metabolic fitness and anti-tumor activity.

  • This approach might be particularly valuable for overcoming the metabolic barriers in the tumor microenvironment.

• Checkpoint inhibitor combination:

  • DNAJC15/MCJ inhibition could potentially synergize with immune checkpoint blockade by enhancing the metabolic fitness of tumor-infiltrating lymphocytes.

• Biomarker development:

  • DNAJC15 expression levels in tumor or immune cells could serve as biomarkers for predicting response to immunotherapies.