ROR2 (Receptor Tyrosine Kinase-like Orphan Receptor 2) Protein

ROR2 (Receptor Tyrosine Kinase-like Orphan Receptor 2) Protein

Introduction

ROR2 is a member of the receptor tyrosine kinase-like orphan receptor (ROR) family that functions as a receptor for Wnt ligands, primarily Wnt5a. Initially classified as an "orphan" receptor due to incomplete characterization, ROR2 is now recognized as a critical mediator of non-canonical Wnt signaling with important roles in embryonic development, tissue patterning, and increasingly, in neurodegenerative disease pathophysiology. This page describes ROR2 structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.

<div class="infobox infobox-protein">
<div class="infobox-header">ROR2 (Receptor Tyrosine Kinase-like Orphan Receptor 2)</div>

ROR2 (Receptor Tyrosine Kinase-like Orphan Receptor 2) Protein

Introduction

ROR2 is a member of the receptor tyrosine kinase-like orphan receptor (ROR) family that functions as a receptor for Wnt ligands, primarily Wnt5a. Initially classified as an "orphan" receptor due to incomplete characterization, ROR2 is now recognized as a critical mediator of non-canonical Wnt signaling with important roles in embryonic development, tissue patterning, and increasingly, in neurodegenerative disease pathophysiology. This page describes ROR2 structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.

<div class="infobox infobox-protein">
<div class="infobox-header">ROR2 (Receptor Tyrosine Kinase-like Orphan Receptor 2)</div>

<div class="infobox-content">
<div class="infobox-row"><span class="infobox-label">Gene</span><span class="infobox-value">[ROR2](/genes/ror2)</span></div>
<div class="infobox-row"><span class="infobox-label">UniProt ID</span><span class="infobox-value">[Q9NQB0](https://www.uniprot.org/uniprot/Q9NQB0)</span></div>
<div class="infobox-row"><span class="infobox-label">PDB Structures</span><span class="infobox-value">6CGT, 6HCU</span></div>
<div class="infobox-row"><span class="infobox-label">Molecular Weight</span><span class="infobox-value">110 kDa (943 amino acids)</span></div>
<div class="infobox-row"><span class="infobox-label">Subcellular Localization</span><span class="infobox-value">Plasma membrane, Primary cilia</span></div>
<div class="infobox-row"><span class="infobox-label">Protein Family</span><span class="infobox-value">ROR family (RTK-like)</span></div>
<div class="infobox-row"><span class="infobox-label">Aliases</span><span class="infobox-value">NRR, BRK-2</span></div>
</div>
</div>

<p><strong>Associated Diseases:</strong> [Alzheimer's Disease](/diseases/alzheimers-disease), [Parkinson's Disease](/diseases/parkinsons-disease), [Robinow Syndrome](/dieses/robinow-syndrome), [Brachydactyly Type B1](/diseases/brachydactyly)</p>

Overview

ROR2 is a type I transmembrane receptor tyrosine kinase that serves as a primary receptor for Wnt5a, mediating non-canonical Wnt signaling pathways. Unlike canonical Wnt/β-catenin signaling, non-canonical pathways regulate planar cell polarity (PCP), Wnt/Ca²⁺ signaling, and receptor-mediated endocytosis. ROR2 is essential for embryonic development, particularly of the skeleton, heart, and nervous system, and is expressed in adult tissues including the brain.

The ROR family consists of two closely related members: ROR1 and ROR2. Both function as Wnt receptors but have distinct expression patterns and signaling outputs. ROR2 is particularly important in tissues undergoing morphogenetic movements and has emerged as a significant player in neuroinflammatory processes.

Structure

Domain Architecture

ROR2 is a 943-amino acid type I transmembrane receptor with the following domain organization:

| Domain | Position | Function |
|--------|----------|----------|
| Signal Peptide | 1-19 aa | Directs protein to secretory pathway |
| cysteine-rich domain (CRD) | 20-130 aa | Wnt ligand binding; resembles Frizzled CRD |
| Kringle Domain 1 | 131-220 aa | Protein-protein interactions |
| Kringle Domain 2 | 221-310 aa | Protein-protein interactions |
| Transmembrane Domain | 311-335 aa | Membrane anchoring |
| Tyrosine Kinase Domain | 336-620 aa | Catalytic domain (kinase-inactive in ROR2) |
| Serine/Threonine-Rich Region | 621-750 aa | Regulatory sequences |
| C-terminal Tail | 751-943 aa | Cytoplasmic tail with signaling motifs |

Structural Features

• CRD (Cysteine-rich Domain): The extracellular CRD directly binds Wnt5a and other Wnt ligands. Unlike Frizzled receptors, ROR2 CRD shows distinct binding specificity for non-canonical Wnts.
• Kringle Domains: These domains mediate protein-protein interactions and may contribute to receptor oligomerization.
• Inactive Kinase Domain: ROR2 possesses a kinase domain with mutations that impair catalytic activity. Instead, it functions as a scaffoldsome assembly platform, recruiting downstream signaling proteins.
• Primary Cilia Localization: ROR2 localizes to primary cilia, where it participates in cilia-dependent signaling pathways.

Post-Translational Modifications

• Glycosylation: Heavily N-glycosylated in the extracellular domain
• Phosphorylation: Several tyrosine and serine/threonine phosphorylation sites
• Proteolytic Processing: May be cleaved at the extracellular domain

Normal Function

Wnt5a Receptor

ROR2 functions primarily as a receptor for Wnt5a:

Non-Canonical Wnt Signaling

ROR2 mediates several non-canonical Wnt pathways:

Planar Cell Polarity (PCP) Pathway

• Convergent Extension: ROR2-mediated PCP regulates cell movement during embryonic morphogenesis
• Tissue Patterning: Essential for establishing planar cell polarity in epithelia
• Neurulation: Critical for neural tube closure and spinal cord development

Wnt5a/Ca²⁺ Signaling

• Calcium Release: ROR2 activation leads to intracellular Ca²⁺ release
• PKC Activation: Activates protein kinase C isoforms
• NFAT Regulation: Modulates NFAT transcriptional programs

Ciliogenesis

• Primary Cilia Formation: ROR2 is required for primary cilia assembly
• Cilia Signaling: Participates in hedgehog and other cilia-dependent pathways
• Centrosome Function: Regulates centrosome duplication and function

Tissue-Specific Functions

| Tissue | Function |
|--------|-----------|
| Bone | Endochondral ossification, bone morphogenesis |
| Heart | Cardiac morphogenesis, valve formation |
| Brain | Neuronal migration, axon guidance, synapse formation |
| Kidney | Ureteric bud branching morphogenesis |

Role in the Nervous System

Neural Development

During brain development, ROR2 regulates:

• Neuronal Migration: Controls radial and tangential neuronal migration
• Axon Guidance: Mediates Wnt5a-dependent axon pathfinding
• Synapse Formation: Regulates synaptic assembly and function
• Corpus Callosum: Essential for callosal neuron axon guidance

Adult Brain Function

In the adult brain, ROR2 continues to play roles in:

• Synaptic Plasticity: Modulates excitatory synaptic transmission
• Neurogenesis: Affects neural stem cell behavior
• Circuit Maintenance: Supports long-term neuronal health

Role in Neurodegeneration

Alzheimer's Disease

ROR2 contributes to AD pathophysiology through multiple mechanisms:

Neuroinflammation: ROR2 on [microglia](/cell-types/microglia-neuroinflammation) mediates Wnt5a-induced pro-inflammatory responses. This process involves:

• Microglial activation and cytokine production
• Enhanced phagocytic activity
• Reactive oxygen species generation

• Altered Wnt5a/ROR2 signaling in APP transgenic mice
• Potential feedback between Aβ and non-canonical Wnt pathways

• Cross-talk between Wnt and GSK-3β pathways
• Potential effects on tau kinases

Parkinson's Disease

ROR2 connections to PD include:

Genetic Association: ROR2 variants have been associated with PD risk in genome-wide studies

Dopaminergic Neuron Development: ROR2 is expressed during dopaminergic neuron development:

• Regulates midbrain dopaminergic neuron specification
• May affect vulnerability of dopaminergic neurons

• Inflammatory amplification may affect synucleinopathy progression
• Microglial ROR2 contributes to chronic neuroinflammation

Neuroinflammation Mechanisms

ROR2-mediated neuroinflammation involves several mechanisms:

Key Signaling Pathways:

• NF-kappaB Activation: ROR2 activates canonical NF-kappaB signaling
• MAPK Pathways: ERK, JNK, and p38 pathways are engaged
• STAT3 Activation: JAK/STAT3 signaling contributes to inflammation

Other Neurodegenerative Conditions

ROR2 has been implicated in:

• Amyotrophic Lateral Sclerosis (ALS): Altered expression in motor neuron disease
• Multiple Sclerosis: Demyelination and neuroinflammation
• Huntington's Disease: Potential modifier of disease progression

Therapeutic Targeting

Current Strategies

| Strategy | Approach | Development Status |
|----------|----------|------------------|
| Anti-ROR2 Antibodies | Neutralize ROR2-Wnt5a interaction | Preclinical |
| Wnt5a Inhibition | Block Wnt5a activity | Preclinical |
| Small Molecule Inhibitors | Target kinase domain or protein-protein interactions | Research |
| RNAi Approaches | siRNA/shRNA-mediated knockdown | Experimental |

Challenges

Future Directions

• Blood-Brain Barrier Penetrant Small Molecules
• Cell-Type Specific Targeting (e.g., microglial-selective)
• Pro-drug Approaches

Animal Models

Knockout Mice

Ror2 knockout mice exhibit:

• Perinatal Lethality: Die at birth or shortly after
• Skeletal Abnormalities: Severe truncating and patterning defects
• Cardiac Defects: Valve and septal defects
• Neural Tube Defects: Exencephaly, spina bifida

Conditional Knockouts

Brain-specific Ror2 knockout reveals:

• Social Behavior Deficits: Reduced social interaction
• Learning Impairments: Defects in spatial learning
• Microglial Alterations: Changed microglial morphology

Transgenic Models

Several transgenic models have been developed:

• Wnt5a Overexpression: Constitutive non-canonical signaling
• ROR2 Gain-of-Function: Neuroinflammation models

Key Publications

Cross-references

• Gene: [ROR2](/genes/ror2)
• Protein: [Wnt5a Protein](/proteins/wnt5a-protein)
• Protein: [ROR1 Protein](/proteins/ror1-protein)
• Protein: [Frizzled Receptor Family](/proteins/frizzled-proteins)
• Protein: [GSK-3β Protein](/proteins/gsk3b-protein)
• Disease: [Alzheimer's Disease](/diseases/alzheimers-disease)
• Disease: [Parkinson's Disease](/diseases/parkinsons-disease)
• Pathway: [Wnt Signaling Pathway](/mechanisms/wnt-signaling-neurodegeneration)
• Cell Type: [Microglia](/cell-types/microglia-neuroinflammation)

See Also

• [ROR2 Gene](/genes/ror2)
• [Wnt Signaling in Neurodegeneration](/mechanisms/wnt-signaling-neurodegeneration)
• [Non-Canonical Wnt Pathways](/mechanisms/wnt-planar-cell-polarity)
• [Microglial Neuroinflammation](/cell-types/microglia-neuroinflammation)
• [Robinow Syndrome](/diseases/robinow-syndrome)

External Links

• [UniProt: Q9NQB0](https://www.uniprot.org/uniprot/Q9NQB0)
• [PDB structures](https://www.rcsb.org/search?q=uniprot:Q9NQB0)
• [GeneCards: ROR2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=ROR2)
• [OMIM: ROR2](https://www.omim.org/entry/606361)

References