DNAJB11 Human

What is the molecular structure of DNAJB11 and how does it function in normal cellular physiology?

DNAJB11 is a member of the HSP40-chaperone family consisting of three distinct domains: an N-terminal J-Domain that mediates binding to HSP70-chaperones, a substrate-binding domain, and a C-terminal dimerization domain . As an ER-resident protein, DNAJB11 serves as one of the main co-factors of the HSP70-chaperone BiP, contributing significantly to the folding and assembly of secretory and membrane proteins . Its ubiquitous expression pattern suggests fundamental importance across multiple tissue types, although research has highlighted its particular significance in kidney physiology .

How is DNAJB11 expression regulated during development and in adult tissues?

DNAJB11 demonstrates ubiquitous expression across tissues, as confirmed by protein atlas databases. Developmental studies using mouse models with LacZ cassettes (Dnajb11 tm1a/+ mice) have revealed that Dnajb11 expression is detectable throughout the entire embryo at E10.5 . In developing kidneys specifically, Dnajb11 expression is visible in all cell types across all investigated developmental timepoints . This expression pattern persists into adulthood, suggesting consistent roles in both developmental processes and maintenance of adult tissue homeostasis .

What are the known protein interaction partners of DNAJB11?

Unbiased proteomics screens have identified DNAJB11 as a significant interaction partner of polycystin-1 (PC1), a protein encoded by PKD1 that is critical in kidney tubule development and maintenance . This interaction was confirmed through co-immunoprecipitation studies, establishing DNAJB11 as one of the top hits in PC1 interaction screens . Additionally, DNAJB11 interacts extensively with BiP (an HSP70-chaperone) in the ER lumen, forming transient interactions with numerous client proteins to facilitate proper protein folding .

What types of DNAJB11 mutations have been identified in patients with kidney disorders?

Research has identified thirteen different loss-of-function variants in DNAJB11 across 20 pedigrees (54 affected individuals) through various sequencing approaches including targeted next-generation sequencing, whole-exome sequencing, and whole-genome sequencing . Disease-causing variants include missense mutations such as DNAJB11 p.Pro54Arg and DNAJB11 p.Leu77Pro . Experimental evidence indicates that while the p.Pro54Arg variant expresses at levels similar to wild-type DNAJB11, it fails to rescue PC1 cleavage defects in Dnajb11-deficient cells . The p.Leu77Pro variant shows significantly reduced expression levels, suggesting potential protein instability .

What is the estimated prevalence of DNAJB11-related disorders in the population?

Analysis of the publicly available GnomAD database has established the genetic prevalence of pathogenic DNAJB11 variants at approximately 0.85 per 10,000 individuals in the general population . Additional evidence from the Genomics England 100,000 genomes project identified pathogenic DNAJB11 variants in nine out of 3,934 probands with various kidney and urinary tract disorders, primarily presenting with cystic kidney disease (eight probands) and nephrocalcinosis (one proband) . These findings suggest that DNAJB11 mutations represent a significant cause of atypical cystic kidney disease that may be underdiagnosed in clinical practice .

How does the clinical presentation of DNAJB11-associated kidney disease differ from classical ADPKD?

DNAJB11-associated kidney disease presents with several distinctive features compared to classical ADPKD:

These clinical differences highlight the importance of precise diagnosis in atypical cystic kidney disease patients, with significant implications for patient follow-up, genetic counseling, prognosis, treatment strategies, and donor selection for transplantation .

How does DNAJB11 deficiency affect polycystin-1 processing and function?

DNAJB11 deficiency profoundly impacts polycystin-1 (PC1) processing, specifically impairing GPS (G protein-coupled receptor proteolytic site) cleavage of PC1 . This impairment represents a critical mechanism underlying DNAJB11-dependent cyst formation. In experimental models, loss of DNAJB11 results in a significant reduction in the PC1 C-terminal fragment to full-length protein ratio, indicating defective maturation of PC1 . This processing defect has been confirmed both in vitro in cell models and in vivo in mouse models with Dnajb11 inactivation . The functional consequence is dosage-dependent kidney cyst formation, establishing a shared pathogenic mechanism with classical ADPKD .

What is the relationship between DNAJB11 and the unfolded protein response (UPR) in kidney disease?

Contrary to initial hypotheses suggesting DNAJB11-kidney disease might represent an overlap between ADPKD and autosomal dominant tubulointerstitial kidney disease (ADTKD) pathogenesis, research demonstrates that Dnajb11 loss does not activate the unfolded protein response (UPR) . This finding establishes a fundamental distinction from typical ADTKD pathogenesis, where UPR activation is central to disease development . While DNAJB11 expression is reportedly upregulated by UPR activation (particularly the ATF6 and IRE1α/Xbp1s branches), the loss of DNAJB11 does not induce UPR activation . This suggests that fibrosis in DNAJB11-kidney disease likely represents an exaggerated response to polycystin-dependent cysts rather than a primary consequence of prolonged UPR activation .

How does the timing of DNAJB11 inactivation influence disease phenotypes?

The timing of Dnajb11 inactivation strongly influences disease severity in experimental models . Studies with constitutive and conditional Dnajb11 knockout mice reveal that cyst formation begins in utero, and constitutive inactivation results in more severe disease compared to postnatal conditional inactivation . These findings suggest a developmental component to DNAJB11-related cystogenesis, with early embryonic loss producing more profound effects than later inactivation . This temporal influence on disease severity might explain phenotypic variability observed in human patients and has implications for understanding disease progression mechanisms .

What mouse models have been developed to study DNAJB11-associated kidney disease?

Several complementary mouse models have been developed to investigate DNAJB11 function:

• Constitutive knockout models: Generated based on alleles from the European Conditional Mouse Mutagenesis Program (EUCOMM), these Dnajb11−/− mice are live-born below the expected Mendelian ratio and develop severe cystic kidney disease, dying around weaning age .

• Reporter models: Dnajb11 tm1a/+ mice harboring a LacZ cassette enable monitoring of Dnajb11 expression through X-Gal staining, revealing ubiquitous expression patterns during development .

• Conditional knockout models: These models utilize conditional floxed alleles (after removing the LacZ cassette) to enable tissue-specific and temporally controlled Dnajb11 inactivation, facilitating investigation of cell type-specific contributions to disease pathogenesis .

These diverse mouse models allow researchers to investigate the genetic mechanisms underlying autosomal dominant inheritance, identify specific cell types driving cyst formation, and elucidate molecular mechanisms of DNAJB11-dependent polycystic kidney disease .

What cell culture systems are effective for studying DNAJB11 function in vitro?

Researchers have developed several cell culture systems to investigate DNAJB11 function:

• Dnajb11-deficient renal epithelial cell lines: Generated through CRISPR/Cas9 technology, these cell lines allow assessment of PC1 C-terminal fragment (CTF) formation and its ratio to immature full-length protein (FL) .

• Rescue experimental systems: These systems involve re-expression of wild-type or mutant DNAJB11 in Dnajb11−/− cells to test functional rescue of observed phenotypes, particularly PC1 cleavage defects .

• Proteomic analysis platforms: These systems enable comparative proteomics between Dnajb11- and Pkd1-deficient cells to identify common and distinct pathways and dysregulated proteins .

These complementary in vitro approaches provide valuable tools for mechanistic studies of DNAJB11 function and for screening the functional impact of DNAJB11 variants identified in patients .

What biochemical assays can be used to assess PC1 cleavage in DNAJB11 research?

The assessment of PC1 cleavage represents a critical readout in DNAJB11 research. Key biochemical approaches include:

• PC1 CTF/FL ratio quantification: Western blot analysis to measure the ratio between PC1 C-terminal fragment (CTF) and full-length (FL) protein provides a quantitative readout of GPS cleavage efficiency .

• Co-immunoprecipitation assays: These assays confirm physical interactions between DNAJB11 and PC1 during processing and maturation .

• Variant functional testing: Expression of disease-causing DNAJB11 variants in Dnajb11−/− cells followed by PC1 CTF/FL ratio quantification serves as a biochemical readout for assessing the pathogenicity of DNAJB11 variants of unknown significance .

These methodologies provide crucial insights into the molecular mechanisms by which DNAJB11 facilitates proper PC1 processing and how mutations disrupt this essential function .

How do proteomic profiles differ between DNAJB11-deficient and PKD1-deficient cells?

Quantitative proteomic analysis of Dnajb11- and Pkd1-deficient cells has revealed both common and distinct pathways and dysregulated proteins . This comparative approach provides a foundation for understanding phenotypic differences between different forms of ADPKD . While specific proteomic differences aren't fully detailed in the available search results, this research direction represents a promising approach for identifying unique molecular signatures of DNAJB11-associated kidney disease versus classical ADPKD . Future research may leverage these proteomic differences to develop targeted therapeutic approaches specific to DNAJB11-mutant patients .

What explains the autosomal dominant inheritance pattern of DNAJB11-related disease despite evidence suggesting a cellular recessive mechanism?

A key paradox in DNAJB11-related disease is the apparent disconnect between its autosomal dominant inheritance pattern in humans and evidence from mouse models suggesting a cellular recessive mechanism of cyst formation . Studies show that mice with monoallelic inactivation of Dnajb11 show no apparent phenotype, while biallelic loss causes cystic disease . This suggests that in humans with heterozygous DNAJB11 mutations, additional factors likely contribute to disease manifestation . Possible explanations include:

• Somatic second-hit mutations in the wild-type allele within kidney cells

• Haploinsufficiency effects that manifest over decades in humans but not in shorter-lived mouse models

• Dominant-negative effects of specific human mutations not replicated in mouse knockout models

• Environmental or genetic modifiers that influence disease penetrance

Understanding this inheritance discrepancy represents an important area for future research .

What mechanisms explain the predominant involvement of proximal tubules in DNAJB11-associated cyst formation?

Unlike classical ADPKD, DNAJB11-associated kidney disease demonstrates a striking predilection for cyst formation in proximal tubules . This cell type specificity represents a fundamental difference from PKD1/PKD2-associated disease and raises important questions about underlying mechanisms. Possible explanations include:

• Cell type-specific differences in DNAJB11 expression or function

• Variations in PC1 processing requirements between tubule segments

• Proximal tubule-specific client proteins of DNAJB11 beyond PC1

• Differential sensitivity of tubule segments to defects in protein folding and trafficking

Elucidating these mechanisms could provide insights into tubule segment-specific vulnerabilities and potentially reveal targeted therapeutic approaches for DNAJB11-associated disease .