Recombinant Mouse RING finger protein 186 (Rnf186)

What is Recombinant Mouse RING finger protein 186 (Rnf186)?

Recombinant Full Length Mouse RING finger protein 186 (Rnf186) is a protein spanning amino acids 1-226 (Q9D241), typically expressed with an N-terminal His tag in E. coli expression systems. It belongs to the family of RING finger E3 ubiquitin ligases that mediate the transfer of ubiquitin to target proteins, thereby regulating their function, localization, or degradation . As an E3 ligase, Rnf186 plays crucial roles in various cellular processes, particularly in immune regulation and ER stress responses.

What are the key functional domains of Rnf186?

Rnf186 contains several important functional domains that are critical for its activity:

• A RING finger domain that mediates E3 ligase activity and interaction with E2 ubiquitin-conjugating enzymes

• A putative ER localization motif at position K219 that is essential for proper subcellular targeting

• A zinc finger domain that is required for substrate recognition and ubiquitination activities

• Transmembrane domains that facilitate its integration into the ER membrane

The integrity of these domains is essential for Rnf186's biological functions, including its role in immune signaling and ER stress responses .

How does Rnf186 localize within cells?

Rnf186 primarily localizes to the endoplasmic reticulum (ER) through specific localization motifs, including a key motif at position K219. Upon stimulation with microbial pattern recognition receptor (PRR) ligands, particularly NOD2 activators, Rnf186 shows enhanced localization to the ER. Mutation studies have demonstrated that substituting K219 with alanine (K219A) significantly reduces Rnf186's ER localization upon NOD2 stimulation, subsequently impairing its function in immune signaling pathways .

What are the optimal conditions for expressing and purifying recombinant Rnf186?

For optimal expression and purification of recombinant Rnf186:

• Expression system: E. coli provides an efficient system for expressing full-length mouse Rnf186 (amino acids 1-226)

• Tags: N-terminal His-tagging allows for efficient purification using immobilized metal affinity chromatography (IMAC)

• Buffer conditions: During purification, maintain reducing conditions to preserve the integrity of the zinc-containing RING domain

• Storage: Store the purified protein at -80°C in buffer containing 10% glycerol to maintain stability and activity

For functional studies, it's critical to verify that the recombinant protein retains E3 ligase activity through in vitro ubiquitination assays before proceeding with downstream applications .

How can researchers assess Rnf186 E3 ligase activity in vitro?

To assess the E3 ligase activity of Rnf186 in vitro:

• In vitro ubiquitination assay components:

  • Purified recombinant Rnf186 (50-200 ng)

  • E1 ubiquitin-activating enzyme (50-100 ng)

  • E2 ubiquitin-conjugating enzyme (preferably UBE2D family, 200-400 ng)

  • Ubiquitin (1-2 μg)

  • ATP regeneration system (2 mM ATP, 10 mM creatine phosphate, 3.5 U/ml creatine kinase)

  • Reaction buffer (50 mM Tris-HCl pH 7.5, 5 mM MgCl₂, 2 mM DTT)

• Incubate the reaction at 30°C for 1-2 hours, terminate with SDS-PAGE sample buffer

• Analyze ubiquitination by Western blotting using anti-ubiquitin antibodies or substrate-specific antibodies

For substrate-specific studies, include purified potential substrate proteins such as ATF6 or components of the NOD2 signaling pathway .

What methods can be used to study Rnf186-protein interactions?

Several complementary approaches can be employed to study Rnf186-protein interactions:

• Co-immunoprecipitation (Co-IP):

  • Transfect cells with tagged Rnf186 (e.g., Flag-Rnf186) and potential interacting proteins

  • Lyse cells under non-denaturing conditions

  • Immunoprecipitate using tag-specific antibodies

  • Analyze co-precipitated proteins by immunoblotting

• Mass spectrometry-based interactome analysis:

  • Immunoprecipitate Flag-Rnf186 from stably transfected cells

  • Elute and digest proteins for mass spectrometry analysis

  • Identify interacting proteins using database search tools like Sorcerer Sequest

  • Process data through Trans-Proteomics Pipeline (TPP) with Peptide Prophet filtering

• Proximity labeling techniques:

  • Create BioID or TurboID fusions with Rnf186

  • Allow proximity-dependent biotinylation of neighboring proteins

  • Enrich biotinylated proteins using streptavidin purification

  • Identify interacting proteins by mass spectrometry

These methods have been successfully employed to identify Rnf186 interactions with UPR sensors (PERK, IRE1α, ATF6) and immune signaling components like RIP2 .

How does Rnf186 regulate Pattern Recognition Receptor (PRR) signaling?

Rnf186 plays a critical role in regulating PRR signaling, particularly NOD2-mediated responses, through multiple mechanisms:

• Complex assembly: Rnf186 promotes the assembly of the NOD2 signaling complex by facilitating the interaction between:

  • RIP2 (receptor-interacting protein kinase 2)

  • IRAK1 (interleukin-1 receptor-associated kinase 1)

  • TRAF6 (TNF receptor-associated factor 6)

• Ubiquitination: Rnf186 enhances ubiquitination of the RIP2-associated complex, which is crucial for:

  • MAPK activation (ERK, p38)

  • NF-κB signaling

  • Downstream cytokine production

• ER localization: Upon NOD2 stimulation, Rnf186 localizes to the ER and associates with a complex composed of:

  • ATF6, PERK, IRE1α (UPR sensors)

  • RIP2 (NOD2 pathway adaptor)

Knockdown or mutation of Rnf186 significantly impairs these processes, resulting in reduced inflammatory responses to bacterial components .

What is the relationship between Rnf186 and the Unfolded Protein Response (UPR)?

Rnf186 serves as a critical link between innate immune signaling and the UPR pathway:

• UPR sensor interaction: Upon NOD2 stimulation, Rnf186 associates with UPR sensors:

  • ATF6 (Activating Transcription Factor 6)

  • PERK (Protein kinase R-like ER kinase)

  • IRE1α (Inositol-requiring enzyme 1α)

• ATF6 regulation: Rnf186 mediates the ubiquitination of ATF6, promoting ER stress responses

• Complex formation: Rnf186 is required for optimal formation of the NOD2-induced RIP2 complex with UPR sensors

• Specificity: This relationship appears pathway-specific, as Rnf186 does not associate with Dectin-1-induced signaling complexes

These interactions highlight the role of Rnf186 as an integrator of microbial sensing and ER stress responses, which is particularly important in intestinal epithelial cells and macrophages .

How does Rnf186 contribute to autophagy regulation?

Rnf186 has been identified as an important regulator of autophagy, particularly in colonic epithelial cells:

• EFNB1-EPHB2 pathway: Rnf186 regulates the EFNB1 (ephrin B1)-EPHB2-induced autophagy pathway

• Ubiquitination: Mass spectrometry analysis has identified EPHB2 as a substrate for Rnf186-mediated ubiquitination

• Intestinal homeostasis: Through its regulation of autophagy, Rnf186 contributes to intestinal homeostasis and epithelial cell function

The ubiquitination of EPHB2 by Rnf186 appears to modulate autophagy pathways that are critical for maintaining intestinal epithelial cell function and potentially protecting against intestinal inflammation .

What are the implications of Rnf186 genetic variants in inflammatory bowel disease (IBD)?

Both rare and common genetic variants in the Rnf186 gene have been associated with inflammatory bowel disease through distinct mechanisms:

These genetic variants lead to impaired Rnf186 function through different mechanisms but converge on reducing bacterial clearance in primary human macrophages. The identification of these variants highlights the importance of Rnf186 in intestinal immune homeostasis and suggests it may be a potential therapeutic target for IBD .

How does Rnf186 differ functionally from other RING finger E3 ligases in immune regulation?

Rnf186 exhibits several distinctive features compared to other RING finger E3 ligases involved in immune regulation:

• Cooperativity with TRAF6: Unlike many E3 ligases that function redundantly, Rnf186 and TRAF6 function in a non-redundant, cooperative manner in NOD2 signaling:

  • Combined knockdown of both Rnf186 and TRAF6 leads to greater reduction in signaling than individual knockdowns

  • This suggests complementary rather than redundant roles in the same pathway

• ER localization: Rnf186 uniquely localizes to the ER and serves as a bridge between PRR signaling and UPR activation

• Pathway specificity: Rnf186 selectively regulates NOD2-mediated responses but not Dectin-1-induced outcomes, demonstrating pathway specificity

• Disease association: Rnf186 has specific genetic associations with inflammatory bowel disease, particularly ulcerative colitis

Understanding these unique features of Rnf186 is crucial for developing targeted therapeutic approaches that modulate specific immune pathways without broadly affecting E3 ligase functions.

What experimental models are best suited for studying Rnf186 function in vivo?

Several experimental models are particularly valuable for investigating Rnf186 function in vivo:

• Genetic mouse models:

  • Rnf186 knockout mice: To study complete loss of function

  • Rnf186 conditional knockout mice: For tissue-specific deletion (particularly intestinal epithelium and macrophages)

  • Knock-in models of disease-associated variants: To study specific mutations (K219A, zinc finger domain mutations)

• Organoid systems:

  • Intestinal organoids derived from wild-type or Rnf186-deficient mice

  • Human intestinal organoids with CRISPR-edited RNF186

  • These provide physiologically relevant 3D systems to study intestinal epithelial functions

• Experimental colitis models:

  • DSS (dextran sodium sulfate)-induced colitis

  • TNBS (2,4,6-trinitrobenzene sulfonic acid)-induced colitis

  • These models help assess the role of Rnf186 in intestinal inflammation and recovery

• Bacterial infection models:

  • Citrobacter rodentium: To study intestinal infection and clearance

  • Adherent-invasive E. coli: To model pathogenic bacterial interactions relevant to IBD

When designing in vivo studies, researchers should consider the tissue-specific expression patterns of Rnf186 and its dual roles in immune signaling and ER stress responses .

How do mouse and human Rnf186/RNF186 compare in structure and function?

A comparative analysis of mouse Rnf186 and human RNF186 reveals important similarities and differences:

While the core functions appear largely conserved, researchers should be cautious when extrapolating findings between species, particularly regarding specific protein-protein interactions and regulatory mechanisms .

What are the major technical challenges in studying Rnf186 function?

Researchers face several technical challenges when investigating Rnf186 function:

• Protein solubility issues:

  • As a transmembrane protein, full-length Rnf186 can be difficult to express and purify in soluble form

  • Solution: Use detergent-based extraction methods or express soluble domains separately

• Identifying specific substrates:

  • Ubiquitination is often transient and context-dependent

  • Solution: Employ proteasome inhibitors, tandem ubiquitin binding entities (TUBEs), or ubiquitin remnant profiling

• Distinguishing direct vs. indirect effects:

  • Rnf186 functions in complex regulatory networks

  • Solution: Use in vitro reconstitution assays with purified components to verify direct effects

• Temporal dynamics:

  • PRR-induced Rnf186 translocation and function occur within specific time windows

  • Solution: Employ time-course experiments with precise temporal resolution

• Cell type specificity:

  • Rnf186 functions may vary between macrophages and intestinal epithelial cells

  • Solution: Compare results across relevant primary cells and cell lines

Addressing these challenges requires combining multiple complementary approaches and carefully designed controls to generate reliable and physiologically relevant data .

How can researchers differentiate between the ubiquitination activities of Rnf186 and other E3 ligases in the same pathway?

Differentiating between the ubiquitination activities of Rnf186 and other E3 ligases (such as TRAF6) in the same signaling pathway requires specialized approaches:

• Structure-function analysis:

  • Generate Rnf186 mutants with specific defects in E3 ligase activity (e.g., RING domain mutations)

  • Compare the ubiquitination patterns with wild-type Rnf186 to identify specific substrates

• Ubiquitin linkage analysis:

  • Different E3 ligases often generate distinct ubiquitin chain topologies (K48, K63, M1, etc.)

  • Use linkage-specific antibodies or mass spectrometry to identify Rnf186-specific ubiquitin chain types

• Sequential immunoprecipitation:

  • First immunoprecipitate known TRAF6 substrates

  • Then re-immunoprecipitate Rnf186-associated complexes

  • This helps distinguish sequential or cooperative ubiquitination events

• Reconstitution experiments:

  • Use cells deficient in both Rnf186 and the other E3 ligase (e.g., TRAF6)

  • Sequentially reintroduce each ligase to identify their specific contributions

• Temporal analysis:

  • Rnf186 and other E3 ligases may act at different time points in the signaling cascade

  • Detailed time-course experiments can reveal the sequence of ubiquitination events

Research has demonstrated that Rnf186 and TRAF6 function in a non-redundant manner, suggesting they target different substrates or sites within the NOD2 signaling complex .

What are the unexplored aspects of Rnf186 biology that warrant further investigation?

Several important aspects of Rnf186 biology remain underexplored and represent promising areas for future research:

• Non-immune functions:

  • While its immune roles are well-studied, potential functions in cellular metabolism, proliferation, or differentiation remain largely unexplored

  • Investigation of Rnf186 in diverse cell types beyond immune and intestinal cells could reveal novel functions

• Transcriptional regulation:

  • The mechanisms controlling Rnf186 expression in different contexts are poorly understood

  • Analysis of the Rnf186 promoter and potential enhancers could identify key regulatory factors

• Post-translational modifications:

  • How Rnf186 itself is regulated by phosphorylation, ubiquitination, or other modifications

  • Identification of enzymes that modify Rnf186 and how these affect its function

• Interplay with microbiome:

  • How the intestinal microbiota shapes Rnf186 function and vice versa

  • Potential role in maintaining microbiome homeostasis beyond innate immune signaling

• Therapeutic targeting:

  • Development of small molecules or peptides that can modulate Rnf186 activity

  • Potential for targeting Rnf186 in inflammatory bowel disease or other conditions

These research directions could significantly expand our understanding of Rnf186 biology and potentially reveal new therapeutic opportunities .

How might advanced technologies enhance our understanding of Rnf186 function?

Emerging technologies offer exciting opportunities to deepen our understanding of Rnf186 function:

• Cryo-electron microscopy:

  • Determining the precise structure of Rnf186 in complex with its partners

  • Visualizing conformational changes during activation

• Genomic screens:

  • CRISPR-Cas9 screens to identify synthetic lethal interactions with Rnf186

  • Identification of genes that modulate Rnf186 function

• Single-cell approaches:

  • Single-cell RNA-seq to capture heterogeneity in Rnf186 expression and response

  • Single-cell proteomics to analyze Rnf186 protein levels and modifications

• Intravital imaging:

  • Real-time visualization of Rnf186 dynamics in living tissues

  • Tracking Rnf186 responses to microbial challenges in vivo

• Protein engineering:

  • Development of optogenetic or chemically-inducible Rnf186 variants

  • Creation of biosensors to monitor Rnf186 activity in real-time

These advanced technologies would provide unprecedented insights into the spatial, temporal, and molecular details of Rnf186 function in health and disease .