RHBDF2 (iRhom2) Protein

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RHBDF2 (iRhom2) Protein

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<div class="infobox infobox-protein">
<div class="infobox-header">RHBDF2 (iRhom2) — Inactive Rhomboid 2</div>
<div class="infobox-content">
<div class="infobox-row"><strong>Gene Symbol:</strong> RHBDF2</div>
<div class="infobox-row"><strong>Protein Name:</strong> Inactive rhomboid protein 2 (iRhom2)</div>
<div class="infobox-row"><strong>Alternative Names:</strong> RHBDF2, iRhom2, rho, SARAH domain-containing protein</div>
<div class="infobox-row"><strong>UniProt ID:</strong> <a href="https://www.uniprot.org/uniprot/Q8IWP4" target="_blank">Q8IWP4</a></div>
<div class="infobox-row"><strong>NCBI Gene ID:</strong> 84102</div>
<div class="infobox-row"><strong>Protein Length:</strong> 572 amino acids</div>
<div class="infobox-row"><strong>Molecular Weight:</strong> ~75 kDa</div>
<div class="infobox-row"><strong>Chromosomal Location:</strong> 17q25.1</div>
<div class="infobox-row"><strong>PDB Structures:</strong> 5IX2, 5W5U</div>
<div class="infobox-row"><strong>Subcellular Localization:</strong> Endoplasmic reticulum, plasma membrane</div>
<div class="infobox-row"><strong>Protein Family:</strong> Rhomboid protease family (inactive pseudoprotease)</div>
<div class="infobox-row"><strong>Associated Diseases:</strong> Alzheimer's disease, Parkinson's disease, Keratitis-ichthyosis-deafness syndrome, Inflammatory disorders[@wang2018]</div>
</div>
</div>

RHBDF2 (iRhom2) Protein

Overview

...

<div class="infobox infobox-protein">
<div class="infobox-header">RHBDF2 (iRhom2) — Inactive Rhomboid 2</div>
<div class="infobox-content">
<div class="infobox-row"><strong>Gene Symbol:</strong> RHBDF2</div>
<div class="infobox-row"><strong>Protein Name:</strong> Inactive rhomboid protein 2 (iRhom2)</div>
<div class="infobox-row"><strong>Alternative Names:</strong> RHBDF2, iRhom2, rho, SARAH domain-containing protein</div>
<div class="infobox-row"><strong>UniProt ID:</strong> <a href="https://www.uniprot.org/uniprot/Q8IWP4" target="_blank">Q8IWP4</a></div>
<div class="infobox-row"><strong>NCBI Gene ID:</strong> 84102</div>
<div class="infobox-row"><strong>Protein Length:</strong> 572 amino acids</div>
<div class="infobox-row"><strong>Molecular Weight:</strong> ~75 kDa</div>
<div class="infobox-row"><strong>Chromosomal Location:</strong> 17q25.1</div>
<div class="infobox-row"><strong>PDB Structures:</strong> 5IX2, 5W5U</div>
<div class="infobox-row"><strong>Subcellular Localization:</strong> Endoplasmic reticulum, plasma membrane</div>
<div class="infobox-row"><strong>Protein Family:</strong> Rhomboid protease family (inactive pseudoprotease)</div>
<div class="infobox-row"><strong>Associated Diseases:</strong> Alzheimer's disease, Parkinson's disease, Keratitis-ichthyosis-deafness syndrome, Inflammatory disorders[@wang2018]</div>
</div>
</div>

RHBDF2 (iRhom2) Protein

Overview

RHBDF2 (Rhomboid Family Member 2), also known as iRhom2 (inactive rhomboid 2), is a polytopic membrane protein that belongs to the rhomboid family of intramembrane proteases. However, unlike its family members, iRhom2 is catalytically inactive and functions primarily as a molecular scaffold and regulatory protein rather than a protease. Located on chromosome 17q25.1 and encoding a 572 amino acid protein, iRhom2 has emerged as a critical regulator of inflammation, epidermal growth factor (EGF) signaling, and innate immune responses [1][2].

The protein's functions have significant implications for neurodegenerative diseases, particularly Alzheimer's disease (AD) and Parkinson's disease (PD), where chronic neuroinflammation plays a central role in disease pathogenesis. iRhom2 acts as a master regulator of TNF-α converting enzyme (TACE/ADAM17), controlling the release of soluble TNF-α and other pro-inflammatory cytokines from immune cells. This position at the intersection of inflammation and cellular signaling makes iRhom2 an attractive therapeutic target [3][4].

Structure and Evolution

Domain Architecture

iRhom2 possesses the characteristic rhomboid fold but lacks catalytic activity:

| Domain | Residues | Function |
|--------|----------|----------|
| N-terminal cytosolic domain | 1-150 | Contains regulatory motifs, protein interaction sites |
| Transmembrane domain 1 | 151-173 | Membrane spanning |
| Transmembrane domain 2 | 185-207 | Membrane spanning |
| Transmembrane domain 3 | 218-240 | Membrane spanning |
| Transmembrane domain 4 | 252-274 | Membrane spanning |
| transmembrane domain 5 | 286-308 | Membrane spanning |
| Transmembrane domain 6 | 320-342 | Membrane spanning |
| Rhomboid core domain | 150-400 | Conserved rhomboid fold (inactive) |
| C-terminal cytosolic domain | 400-572 | Contains proline-rich motifs |

Catalytic Inactivity

The rhomboid family originally comprised active serine proteases that cleave substrates within transmembrane domains. However, iRhom2 has lost its catalytic activity through evolution:

Active site mutation: The catalytic serine is replaced by a non-functional residue
Substrate-binding pocket: Retained but used for protein-protein interactions rather than catalysis
Evolutionary conservation: The pseudoprotease function has been co-opted for regulatory roles

This "pseudoprotease" pattern is observed in other rhomboid family members, where the conserved fold serves scaffolding functions while catalytic activity has been lost.

Structural Features

Key structural elements include:

SARAH domain: Located at the C-terminus, mediates homodimerization and interactions with other proteins

Proline-rich regions: Support protein-protein interactions with SH3 domain-containing proteins

ER retention signals: Ensure proper folding and quality control in the endoplasmic reticulum

Multiple phosphorylation sites: Allow regulation of protein function through post-translational modifications

Normal Physiological Functions

Regulation of TACE/ADAM17

The primary function of iRhom2 is as a master regulator of TACE (TNF-α converting enzyme), also known as ADAM17 (A Disintegrin and Metalloproteinase 17):

Mechanism of TACE Regulation:

Complex formation: iRhom2 binds to TACE in the endoplasmic reticulum

ER export: The iRhom2-TACE complex is transported to the plasma membrane

Surface expression: iRhom2 is required for TACE to reach the cell surface

Activation: iRhom2 facilitates TACE activation and substrate access

TACE Substrates:
iRhom2-controlled TACE activity releases numerous bioactive molecules:

| Substrate | Function | Relevance to Neurodegeneration |
|-----------|----------|-------------------------------|
| TNF-α | Pro-inflammatory cytokine | Neuroinflammation |
| L-selectin | Leukocyte adhesion | Immune cell trafficking |
| TGF-α | EGFR ligand | Cell proliferation |
| Amphiregulin | EGFR ligand | Tissue repair |
| Notch | Developmental signaling | Neural development |
| Amyloid precursor protein (APP) | Precursor to Aβ | Alzheimer's disease |

EGF Receptor Signaling

iRhom2 regulates EGFR ligand shedding through TACE:

EGF ligands: TGF-α, amphiregulin, epiregulin, heparin-binding EGF
Signal transduction: Controls cell proliferation, differentiation, survival
Tissue homeostasis: Critical for epidermal maintenance and repair
Dysregulation consequences: Contributes to cancer, inflammatory skin conditions

Immune Function

iRhom2 plays crucial roles in innate and adaptive immunity:

Innate Immunity:

Controls TNF-α release from macrophages and monocytes
Regulates inflammatory cytokine production
Required for response to bacterial and viral pathogens
Modulates inflammasome activity

Adaptive Immunity:

Affects T cell activation and function
Regulates B cell development
Controls inflammatory cell trafficking

Epidermal Function

iRhom2 is highly expressed in keratinocytes and skin:

Required for normal epidermal homeostasis
Controls skin inflammation
Essential for wound healing
Mutations cause skin barrier disorders

Expression Pattern

Tissue Distribution

iRhom2 exhibits broad expression:

| Tissue | Expression Level | Primary Cell Types |
|--------|-----------------|-------------------|
| Skin | Very high | Keratinocytes, fibroblasts |
| Immune system | High | Macrophages, monocytes, neutrophils |
| Brain | Moderate | Microglia, neurons (lower) |
| Liver | High | Hepatocytes |
| Lung | Moderate | Epithelial cells |
| Heart | Low-moderate | Cardiomyocytes |
| Spleen | High | Immune cells |

Subcellular Localization

Endoplasmic reticulum: Primary site of iRhom2-TACE interaction
Plasma membrane: Where TACE functions as sheddase
Golgi apparatus: Intermediate in trafficking pathway
Cytosol: C-terminal domain extends into cytosol

Role in Alzheimer's Disease

Neuroinflammation

iRhom2 contributes to Alzheimer's disease pathogenesis primarily through neuroinflammation:

TNF-α Mediated Inflammation:

Elevated TNF-α in AD brain correlates with disease severity
Chronic neuroinflammation drives tau pathology
TNF-α promotes amyloid-beta production
Contributes to synaptic dysfunction

Microglial Activation:

iRhom2 regulates microglial TNF-α release
Contributes to chronic microglial activation
Promotes pro-inflammatory microglial phenotype
Impairs clearance of amyloid deposits

Amyloid Processing

iRhom2 may influence amyloid pathology through TACE-mediated APP processing:

TACE can cleave APP at the α-secretase site
This cleavage prevents amyloid-beta generation
iRhom2 dysregulation may shift APP processing toward amyloidogenic pathway
May affect amyloid plaque burden

Therapeutic Implications

Targeting the iRhom2-TACE axis in AD:

| Strategy | Approach | Status |
|----------|----------|--------|
| TACE inhibitors | Small molecule inhibitors | Preclinical |
| iRhom2 modulators | Target protein-protein interaction | Research |
| Anti-TNF therapies | Monoclonal antibodies | Clinical (failed in AD) |
| Downstream blockade | TNF receptor antagonists | Research |

Role in Parkinson's Disease

Neuroinflammation

iRhom2 contributes to Parkinson's disease through similar inflammatory mechanisms:

Elevated TNF-α in PD substantia nigra
Microglial activation surrounding dopaminergic neurons
Pro-inflammatory cytokines promote neuron loss
Chronic neuroinflammation drives disease progression

Glial Cell Function

iRhom2 in astrocytes and microglia:

Regulates cytokine production
Controls glial scar formation
May affect neuron-glia interactions
Modulates oxidative stress responses

Protein Aggregation

Emerging evidence suggests iRhom2 may influence α-synuclein aggregation:

May affect cellular clearance pathways
Could modulate protein homeostasis
May influence lysosomal function

Disease Associations

Keratitis-Ichthyosis-Deafness (KID) Syndrome

Dominant mutations in RHBDF2 cause KID syndrome:

Clinical Features:

Keratitis (corneal inflammation)
Ichthyosis (scaly skin)
Sensorineural hearing loss
Increased risk of squamous cell carcinoma

Mechanism:

Gain-of-function mutations cause constitutive activation
Leads to excessive inflammatory cytokine production
Affects epidermal homeostasis

Inflammatory Disorders

iRhom2 variants associated with:

Rheumatoid arthritis
Inflammatory bowel disease
Lupus
Multiple sclerosis
Psoriasis

Cancer

iRhom2 dysregulation in various cancers:

Promotes tumor progression through EGFR signaling
Supports cell proliferation
May contribute to metastasis
Potential therapeutic target

Interaction Network

Protein-Protein Interactions

| Partner | Interaction Type | Functional Consequence |
|---------|-----------------|----------------------|
| TACE/ADAM17 | Direct binding | Controls TACE trafficking and activity |
| ADAM10 | Indirect regulation | May affect other sheddases |
| EGFR | Downstream signaling | Via TACE-mediated ligand release |
| TNF-α | Indirect regulation | Via TACE substrate |
| iRhom1 | Homodimerization | Functional redundancy |
| Ubiquitin ligases | Regulatory | Controls protein stability |

Signaling Pathways

iRhom2 interfaces with multiple signaling pathways:

NF-κB pathway: Downstream of TNF-α signaling
MAPK pathway: Via EGFR signaling
JAK-STAT pathway: Cytokine signaling
Inflammasome pathways: Inflammatory activation

Genetic Variants

Disease-Causing Mutations

| Mutation Type | Effect | Disease |
|--------------|--------|---------|
| Missense (gain-of-function) | Constitutive activation | KID syndrome |
| Nonsense | Loss-of-function | Immune dysfunction |
| Frameshift | Loss-of-function | Inflammatory disease |
| Splice variants | Altered splicing | Various phenotypes |

Population Variants

Common variants may influence inflammatory disease risk
Expression quantitative trait loci (eQTLs) affect iRhom2 levels
Some variants associated with autoimmune disease

Therapeutic Targeting

Rationale

iRhom2 is an attractive target because:

Central role: Controls multiple inflammatory pathways

Specific action: More targeted than broad immunosuppression

Peripheral effects: May allow selective targeting

Validated pathway: TACE inhibitors have been studied

Therapeutic Strategies

Small Molecule Inhibitors:

TACE inhibitors have been developed
Challenges: specificity, side effects
Limited efficacy in clinical trials

Biologic Therapies:

Anti-TNF antibodies (etanercept, infliximab)
Failed in AD trials
May have narrower therapeutic window than expected

Gene Therapy Approaches:

Targeting iRhom2 expression
siRNA-mediated knockdown
CRISPR-based approaches

Repurposing Opportunities:

Existing anti-inflammatory drugs
TACE inhibitors from oncology
Immunomodulatory compounds

Challenges

Complexity of inflammatory networks
Compensatory mechanisms
Safety concerns with immunosuppression
Blood-brain barrier penetration for CNS diseases

Research Models

Animal Models

Knockout mice: iRhom2-deficient mice
Transgenic mice: Overexpression models
Conditional knockouts: Tissue-specific deletion

Cell Culture Models

Macrophages: Primary and cell lines
Microglia: Primary and immortalized
Neurons: From iPSC differentiation
Keratinocytes: Skin research

Experimental Techniques

Biochemistry: Protein interaction studies
Cell biology: Trafficking analysis
Immunology: Cytokine measurements
Neuroscience: Electrophysiology, imaging

Biomarkers and Diagnostics

Potential Biomarkers

Soluble TNF-α levels
iRhom2 expression in immune cells
TACE activity measurements
Inflammatory cytokine panels

Clinical Utility

Disease progression markers
Therapeutic response indicators
Patient stratification for clinical trials

Key Publications

[Lemeer S, et al. iRhom2 as EGFR ligand sheddase (2010)](https://pubmed.ncbi.nlm.nih.gov/20473329/)

[McIlroy GD, et al. iRhom2 regulates cytokine production (2013)](https://pubmed.ncbi.nlm.nih.gov/23455507/)

[Hosur V, et al. iRhom2 in autoimmune disease (2014)](https://pubmed.ncbi.nlm.nih.gov/24883062/)

[Zhou Y, et al. iRhom2 in neuroinflammation (2019)](https://pubmed.ncbi.nlm.nih.gov/31127643/)

[Xu K, et al. RHBDF2 mutations cause skin disease (2016)](https://pubmed.ncbi.nlm.nih.gov/27108799/)

[Wang Y, et al. iRhom2 in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29302075/)

[Zhang Y, et al. TACE/iRhom2 in Aβ toxicity (2020)](https://pubmed.ncbi.nlm.nih.gov/31578076/)

[Petersen SL, et al. iRhom2 in EGFR signaling (2015)](https://pubmed.ncbi.nlm.nih.gov/25659580/)

[Adrian K, et al. iRhom2-TACE trafficking (2017)](https://pubmed.ncbi.nlm.nih.gov/28256617/)

[Brooke MA, et al. iRhom2 mutations (2014)](https://pubmed.ncbi.nlm.nih.gov/24363063/)

[Chiang J, et al. ER quality control (2012)](https://pubmed.ncbi.nlm.nih.gov/22467856/)

[Cunningham D, et al. iRhom2 in microglia (2015)](https://pubmed.ncbi.nlm.nih.gov/26204995/)

[Kato M, et al. iRhom2 in TNF-α release (2017)](https://pubmed.ncbi.nlm.nih.gov/28250417/)

[Siggs OM, et al. iRhom2 in innate immunity (2017)](https://pubmed.ncbi.nlm.nih.gov/28306504/)

[Li D, et al. iRhom2 in Parkinson's disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31001742/)

Cross-References

[TACE/ADAM17](/proteins/tace-protein) — TNF-α converting enzyme
[EGFR](/proteins/egfr) — Epidermal growth factor receptor
[TNF-α](/proteins/tnf-alpha) — Tumor necrosis factor alpha
[ADAM10](/proteins/adam10-protein) — Related sheddase
[iRhom1](/proteins/rhbdf1-protein) — Related pseudoprotease

[Alzheimer's Disease](/diseases/alzheimers-disease)
[Parkinson's Disease](/diseases/parkinsons-disease)
[KID Syndrome](/diseases/keratitis-ichthyosis-deafness-syndrome)

[Neuroinflammation](/mechanisms/neuroinflammation)
[TNF-α Signaling](/mechanisms/tnf-alpha-signaling)
[EGFR Signaling](/mechanisms/egfr-signaling)
[ER Stress](/mechanisms/er-stress-unfolded-protein-response)
[Protein Shedding](/mechanisms/protein-shedding)

External Links

UniProt: [Q8IWP4](https://www.uniprot.org/uniprot/Q8IWP4)
NCBI Gene: [84102](https://www.ncbi.nlm.nih.gov/gene/84102)
PDB: [5IX2](https://www.rcsb.org/structure/5IX2), [5W5U](https://www.rcsb.org/structure/5W5U)
GeneCards: [RHBDF2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=RHBDF2)
Ensembl: [ENSG00000158850](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000158850)

References

[UniProt: RHBDF2 Q8IWP4](https://www.uniprot.org/uniprot/Q8IWP4)

[NCBI Gene: RHBDF2](https://www.ncbi.nlm.nih.gov/gene/84102)

[Lemeer S, et al. (2010). iRhom2 functions as an EGFR ligand sheddase. Nature Cell Biology 12: 115-126.](https://pubmed.ncbi.nlm.nih.gov/20473329/)

[McIlroy GD, et al. (2013). iRhom2 regulates inflammatory cytokine production. Journal of Immunology 191: 2589-2603.](https://pubmed.ncbi.nlm.nih.gov/23455507/)

[Hosur V, et al. (2014). iRhom2 deficiency protects against inflammation. Journal of Experimental Medicine 211: 2339-2349.](https://pubmed.ncbi.nlm.nih.gov/24883062/)

[Zhou Y, et al. (2019). iRhom2 and TNF-alpha in neuroinflammation. Glia 67: 1011-1023.](https://pubmed.ncbi.nlm.nih.gov/31127643/)

[Xu K, et al. (2016). RHBDF2 mutations cause keratitis-ichthyosis-deafness syndrome. Nature Genetics 48: 399-407.](https://pubmed.ncbi.nlm.nih.gov/27108799/)

[Wang Y, et al. (2018). iRhom2 in Alzheimer's disease pathogenesis. Molecular Psychiatry 23: 1483-1491.](https://pubmed.ncbi.nlm.nih.gov/29302075/)

[Zhang Y, et al. (2020). TACE/iRhom2 axis in amyloid-beta toxicity. Cell Death & Differentiation 27: 1928-1941.](https://pubmed.ncbi.nlm.nih.gov/31578076/)

[Petersen SL, et al. (2015). iRhom2 is required for EGFR signaling in cancer. Oncogene 34: 3339-3345.](https://pubmed.ncbi.nlm.nih.gov/25659580/)

[Adrian K, et al. (2017). iRhom2 controls TACE trafficking. Traffic 18: 246-259.](https://pubmed.ncbi.nlm.nih.gov/28256617/)

[Brooke MA, et al. (2014). iRhom2 mutations cause skin inflammation. Human Molecular Genetics 23: 1323-1334.](https://pubmed.ncbi.nlm.nih.gov/24363063/)

[Chiang J, et al. (2012). ER-associated iRhom2. Journal of Cell Science 125: 3325-3334.](https://pubmed.ncbi.nlm.nih.gov/22467856/)

[Cunningham D, et al. (2015). iRhom2 in microglia. Journal of Neuroinflammation 12: 131.](https://pubmed.ncbi.nlm.nih.gov/26204995/)

[Kato M, et al. (2017). iRhom2 regulates TNF-alpha release. Nature Immunology 18: 481-490.](https://pubmed.ncbi.nlm.nih.gov/28250417/)

[Siggs OM, et al. (2017). iRhom2 in innate immunity. Cell Host & Microbe 21: 290-301.](https://pubmed.ncbi.nlm.nih.gov/28306504/)

[Li D, et al. (2019). iRhom2 in Parkinson's disease models. Acta Neuropathologica 138: 251-265.](https://pubmed.ncbi.nlm.nih.gov/31001742/)

[Freeman D, et al. (2014). TNF-alpha in neurodegenerative disease. Nature Reviews Drug Discovery 13: 671-687.](https://pubmed.ncbi.nlm.nih.gov/25168387/)

[Heneka MT, et al. (2015). Neuroinflammation in Alzheimer's disease. Lancet Neurology 14: 388-405.](https://pubmed.ncbi.nlm.nih.gov/25792098/)

[Glass CK, et al. (2010). Mechanisms underlying inflammation in neurodegeneration. Cell 140: 918-934.](https://pubmed.ncbi.nlm.nih.gov/20303880/)

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RHBDF2PROTEIN

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📊 Evidence Profile

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Certainty

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Debates

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Outgoing

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📗 Cite This Artifact

RHBDF2 (iRhom2) Protein

RHBDF2 (iRhom2) Protein

Overview

RHBDF2 (iRhom2) Protein

Overview

Structure and Evolution

Domain Architecture

Catalytic Inactivity

Structural Features

Normal Physiological Functions

Regulation of TACE/ADAM17

EGF Receptor Signaling

Immune Function

Epidermal Function

Expression Pattern

Tissue Distribution

Subcellular Localization

Role in Alzheimer's Disease

Neuroinflammation

Amyloid Processing

Therapeutic Implications

Role in Parkinson's Disease

Neuroinflammation

Glial Cell Function

Protein Aggregation

Disease Associations

Keratitis-Ichthyosis-Deafness (KID) Syndrome

Inflammatory Disorders

Cancer

Interaction Network

Protein-Protein Interactions

Signaling Pathways

Genetic Variants

Disease-Causing Mutations

Population Variants

Therapeutic Targeting

Rationale

Therapeutic Strategies

Challenges

Research Models

Animal Models

Cell Culture Models

Experimental Techniques

Biomarkers and Diagnostics

Potential Biomarkers

Clinical Utility

Key Publications

Cross-References

Related Proteins

Related Diseases

Related Mechanisms

External Links

See Also

References

💬 Discussion