Recombinant Mouse E3 ubiquitin-protein ligase RNF167 (Rnf167)

What is RNF167 and what are its primary cellular functions?

RNF167 is a transmembrane RING domain-containing E3 ubiquitin ligase that facilitates the transfer of ubiquitin from specific E2 ubiquitin-conjugating enzymes to target substrates. According to current research, RNF167 has several key functions:

• It acts as part of the E3 complex, accepting ubiquitin from specific E2 ubiquitin-conjugating enzymes such as UBE2E1

• It regulates AMPA receptor-mediated neurotransmission by controlling the surface expression and synaptic density of AMPA receptors

• It mediates atypical ubiquitylation and degradation of RIG-I-like receptors (RLRs) in antiviral immune responses

• It may play a role in growth regulation involved in G1/S cell cycle transition

The protein contains an N-terminal RING finger domain, which is essential for its E3 ligase activity, and a transmembrane domain that anchors it to cellular membranes, particularly in the endolysosomal system.

Where is RNF167 predominantly localized within cells?

RNF167 displays a distinct subcellular localization pattern that is critical for its function:

• It is predominantly localized to endosomes and lysosomes

• A subpopulation of RNF167 has been detected on the surface of cultured neurons

• Fluorescence microscopy has confirmed the interactions between RNF167 and conjugating E2 enzymes primarily occur in endosomes and lysosomes

This strategic localization allows RNF167 to participate in the regulation of endocytic trafficking of membrane proteins, particularly AMPA receptors in neurons, where it can influence receptor density at the postsynaptic surface.

What are the validated methods for studying RNF167 function in cells?

Several experimental approaches have proven effective for investigating RNF167 function:

Loss-of-function studies:

• Using a RING mutant RNF167 (which lacks E3 ligase activity) in overexpression studies

• Employing specific shRNA to eliminate endogenous RNF167 expression

• Dual whole-cell recordings from rat organotypic hippocampal slice cultures to assess functional effects

Protein-protein interaction studies:

• In vitro autoubiquitination and binding assays to identify E2 enzyme partners

• Fluorescence microscopy to visualize subcellular localization and co-localization with interaction partners

• Kinetic analyses to determine dissociation constants between RNF167 and selected conjugating E2 enzymes

Ubiquitination analysis:

• Detection of activity-dependent ubiquitination of target proteins (e.g., AMPARs)

• Analysis of specific ubiquitin chain linkages (K6, K11) on target proteins

How can researchers accurately measure RNF167-mediated ubiquitination of target proteins?

To effectively measure RNF167-mediated ubiquitination:

• In vitro ubiquitination assays:

  • Using purified components (E1, appropriate E2 enzymes, RNF167, substrate, and ubiquitin)

  • Detecting ubiquitinated products via Western blot

• Cell-based ubiquitination assays:

  • Expressing HA-tagged ubiquitin along with the substrate of interest and RNF167

  • Immunoprecipitating the substrate followed by detection of ubiquitin conjugates

• Analysis of specific ubiquitin linkages:

  • Using linkage-specific antibodies to detect K6- or K11-linked polyubiquitin chains

  • Employing mass spectrometry to identify precise ubiquitination sites and linkage types

• Activity-dependent ubiquitination:

  • For neuronal studies, stimulating neurons (e.g., with AMPA) before analyzing ubiquitination of target proteins

Studies have shown that pharmacological inhibition of UBE2N in cultured hippocampal neurons diminishes AMPA-induced GluA2 ubiquitination, demonstrating the specificity of this approach for studying RNF167 function .

How does RNF167 regulate AMPA receptor-mediated synaptic transmission?

RNF167 plays a critical role in regulating AMPA receptor density at synapses through ubiquitination-dependent mechanisms:

• Surface expression regulation:

  • Disruption of RNF167 activity (via RING mutation or shRNA knockdown) increases AMPAR surface expression in hippocampal neurons

  • This effect is specific to AMPARs, as NMDA receptor currents remain unaffected

• Functional consequences:

  • Expression of mutant RNF167 significantly increases evoked AMPAR EPSC amplitude by 77%

  • RING mutant RNF167 increases GluA2 surface expression compared with wild-type RNF167 or uninfected cultures (133.5 ± 7.9%, 109.4 ± 4.8%, and 100.0 ± 3.9%, respectively)

• Ubiquitination mechanism:

  • RNF167 promotes GluA2 ubiquitination in collaboration with E2 enzymes

  • In vitro polyubiquitination of GluA2 requires UBE2N after GluA2 has been primed by ubiquitin through the action of an initiating E2 enzyme

  • RNF167 is involved in activity-dependent ubiquitination of AMPARs, regulating their trafficking and stability

This mechanism provides a novel pathway for the dynamic regulation of synaptic strength through post-translational modification of AMPARs.

Which E2 ubiquitin-conjugating enzymes functionally interact with RNF167?

RNF167 functionally interacts with multiple E2 ubiquitin-conjugating enzymes, with varying specificities:

Key findings regarding these interactions include:

• Kinetic analyses reveal submicromolar dissociation constants between RNF167 and selected E2 enzymes

• Computed models of interaction between the RING domain of RNF167 and conjugating E2 enzymes provide structural insights into these interactions

• The E2 enzyme UBE2N can only facilitate polyubiquitination of GluA2 after it has been primed by ubiquitin through the action of an initiating E2 enzyme

• Pharmacological inhibition of UBE2N in cultured hippocampal neurons diminishes AMPA-induced GluA2 ubiquitination, confirming its importance in this pathway

These findings highlight the coordinated action of different E2 enzymes in RNF167-mediated ubiquitination processes.

What is the role of RNF167 in antiviral immunity?

Recent research has identified RNF167 as a negative regulator of RLR-triggered interferon signaling in antiviral immunity:

• Mechanism of action:

  • RNF167 facilitates both K6- and K11-linked polyubiquitination of RIG-I/MDA5

  • K6-linked ubiquitination occurs within CARD domains, while K11-linked ubiquitination targets CTD domains

  • These modifications lead to degradation of the viral RNA sensors through dual proteolytic pathways

• Dual degradation pathways:

  • RIG-I/MDA5 with K6-linked ubiquitin chains in CARD domains are recognized by autophagy cargo adaptor p62, leading to selective autophagic degradation in autolysosomes

  • K11-linked polyubiquitination in CTD domains leads to proteasome-dependent degradation

• Physiological significance:

  • This dual mechanism allows precise control over the amplitude and duration of type I interferon activation

  • It represents a sophisticated cross-talk between two protein quality control pathways in immune regulation

This research provides important insights into how atypical ubiquitination regulates antiviral signaling and maintains immune homeostasis.

How do different ubiquitin chain linkages mediated by RNF167 determine substrate fate?

RNF167 catalyzes the formation of atypical ubiquitin chains that direct substrates to different degradation pathways:

• K6-linked polyubiquitination:

  • Primarily targets CARD domains of RIG-I/MDA5

  • Recognized by autophagy cargo adaptor p62

  • Directs substrates to selective autophagic degradation in autolysosomes

• K11-linked polyubiquitination:

  • Primarily targets CTD domains of RIG-I/MDA5

  • Directs substrates to proteasome-dependent degradation

• Coordination between pathways:

  • The dual proteolytic systems work synergistically to control the amplitude and duration of interferon activation

  • This represents a sophisticated mechanism for fine-tuning cellular responses to viral infection

This differential ubiquitination demonstrates how the ubiquitin code can direct proteins to distinct cellular fates, extending our understanding beyond the classical K48-linked degradation pathway.

What is known about the structural determinants of RNF167 substrate recognition?

The structural basis for RNF167's substrate recognition remains an active area of research, with several key insights emerging:

• RING domain interactions:

  • The RING domain of RNF167 is essential for functional interaction with E2 enzymes

  • Computed models suggest specific interfaces between the RING domain and conjugating E2 enzymes

• Transmembrane domain:

  • The transmembrane domain anchors RNF167 to endosomal/lysosomal membranes

  • This localization is crucial for its ability to regulate membrane proteins like AMPARs

• Substrate-specific domains:

  • Different domains of substrates are targeted for different types of ubiquitination (e.g., CARD vs. CTD domains in RLRs)

  • This suggests distinct structural recognition motifs for different substrates

Future structural studies will likely provide more detailed insights into the precise molecular interactions that determine substrate specificity and recognition by RNF167.

What experimental approaches can resolve conflicting data on RNF167 function?

When addressing contradictory findings about RNF167 function, researchers should consider:

• Methodological considerations:

  • Use multiple loss-of-function approaches (RING domain mutation, shRNA knockdown, CRISPR/Cas9)

  • Validate findings with rescue experiments (e.g., expressing shRNA-resistant RNF167 constructs)

  • Employ complementary functional assays (e.g., surface expression measurements and electrophysiological recordings)

• Context-specific functions:

  • Compare results across different cell types and tissues

  • Consider developmental stage-specific effects

  • Examine cell state-dependent functions (e.g., activity-dependent vs. basal conditions)

• Substrate-specific effects:

  • Distinguish between direct and indirect effects on different substrates

  • Characterize specific ubiquitin chain topologies using linkage-specific antibodies or mass spectrometry

  • Use reconstituted in vitro systems with purified components

One successful approach demonstrated in the literature combines dual whole-cell recordings from rat organotypic hippocampal slice cultures with molecular manipulations, allowing direct comparison of synaptic effects between manipulated and control neurons .

What is the potential role of RNF167 in neurological disorders?

Given its critical role in regulating AMPAR-mediated synaptic transmission, RNF167 may have significant implications for neurological disorders:

While direct evidence linking RNF167 dysfunction to specific neurological conditions remains limited, its fundamental role in synaptic regulation suggests potential involvement in disorders affecting cognition, learning, and memory.

How might targeting RNF167 be leveraged for therapeutic development?

The emerging understanding of RNF167 function suggests several potential therapeutic approaches:

• Neurological applications:

  • Modulating RNF167 activity could potentially normalize AMPAR surface expression in conditions with altered synaptic strength

  • Small molecule inhibitors of specific RNF167-E2 interactions could provide targeted approaches to modulate particular substrates

• Immunological applications:

  • As a negative regulator of RLR-triggered interferon signaling, RNF167 modulation might enhance antiviral responses

  • The dual proteolytic pathways regulated by RNF167 offer multiple potential intervention points

• Drug development considerations:

  • Targeting the RING domain could disrupt E3 ligase activity

  • Disrupting specific E2-E3 interactions may provide more selective effects

  • Pharmacological inhibition of collaborating E2 enzymes (as demonstrated with UBE2N) represents another potential approach

Development of such therapeutics would require careful consideration of RNF167's multiple cellular functions to minimize off-target effects while maximizing efficacy in the targeted pathway.

What are the most pressing unanswered questions about RNF167 function?

Several critical areas require further investigation to fully understand RNF167 biology:

• Comprehensive substrate identification:

  • Beyond AMPARs and RLRs, what other proteins are regulated by RNF167-mediated ubiquitination?

  • Are there tissue-specific substrates in non-neuronal and non-immune contexts?

• Regulation of RNF167 itself:

  • How is RNF167 expression and activity regulated under different physiological conditions?

  • Are there post-translational modifications that control RNF167 function?

• Structural biology:

  • What is the complete three-dimensional structure of RNF167, including its transmembrane domain?

  • How does RNF167 achieve substrate specificity at the molecular level?

• In vivo significance:

  • What are the phenotypic consequences of RNF167 knockout or mutation in animal models?

  • Are there human genetic variants in RNF167 associated with specific disorders?

Addressing these questions will provide a more comprehensive understanding of RNF167's biological roles and potential as a therapeutic target.

What novel methodologies could advance RNF167 research?

Emerging technologies that could significantly advance our understanding of RNF167 include:

• Proximity labeling approaches:

  • BioID or APEX2-based approaches to identify the full interactome of RNF167 in its native cellular context

  • TurboID to capture transient interactions with substrates and regulatory proteins

• Advanced imaging:

  • Super-resolution microscopy to better visualize RNF167 localization and trafficking

  • Live-cell ubiquitination sensors to monitor RNF167 activity in real-time

• Ubiquitinomics:

  • Proteome-wide identification of RNF167-dependent ubiquitination sites using quantitative mass spectrometry

  • Linkage-specific ubiquitin chain analysis to map the full spectrum of chain types catalyzed by RNF167

• CRISPR-based screening:

  • Genome-wide screens to identify genes that modify RNF167 phenotypes

  • Base editing to introduce specific mutations in endogenous RNF167