PTPRC Protein - Protein Tyrosine Phosphatase Receptor Type C

PTPRC Protein — Protein Tyrosine Phosphatase Receptor Type C (CD45)

<div class="infobox infobox-protein">
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<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">PTPRC Protein (CD45)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Protein Tyrosine Phosphatase Receptor Type C</td></tr>
<tr><td><strong>Gene</strong></td><td>[PTPRC](/genes/ptprc)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P08575](https://www.uniprot.org/uniprot/P08575)</td></tr>
<tr><td><strong>PDB ID</strong></td><td>5ln3, 5cms, 1YJ2</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>180-220 kDa (various isoforms)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cell membrane (type I transmembrane)</td></tr>
<tr><td><strong>Protein Family</strong></td><td>Receptor-type PTP family (CD45 family)</td></tr>
<tr><td><strong>Expression</strong></td><td>All nucleated hematopoietic cells, microglia</td></tr>
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<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">6 edges</a></td>
</tr>
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Overview

PTPRC Protein — Protein Tyrosine Phosphatase Receptor Type C (CD45)

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">PTPRC Protein (CD45)</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Protein Tyrosine Phosphatase Receptor Type C</td></tr>
<tr><td><strong>Gene</strong></td><td>[PTPRC](/genes/ptprc)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P08575](https://www.uniprot.org/uniprot/P08575)</td></tr>
<tr><td><strong>PDB ID</strong></td><td>5ln3, 5cms, 1YJ2</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>180-220 kDa (various isoforms)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cell membrane (type I transmembrane)</td></tr>
<tr><td><strong>Protein Family</strong></td><td>Receptor-type PTP family (CD45 family)</td></tr>
<tr><td><strong>Expression</strong></td><td>All nucleated hematopoietic cells, microglia</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">6 edges</a></td>
</tr>
</table>
</div>

Overview

PTPRC (Protein Tyrosine Phosphatase Receptor Type C), more commonly known as CD45, is a receptor-type protein tyrosine phosphatase that plays a central role in regulating immune cell signaling[@thomas1992]. As the prototypic member of the CD45 family, CD45 is expressed on all nucleated hematopoietic cells and serves as a critical regulator of signal transduction thresholds in immune cells. In the central nervous system, CD45 is expressed primarily on microglia, the resident immune cells of the brain, where it plays essential roles in modulating neuroinflammatory responses and microglial activation states[@wyss-coray2013].

CD45 is a large transmembrane protein characterized by an heavily glycosylated extracellular domain, a single transmembrane helix, and an intracellular tyrosine phosphatase domain. The protein undergoes extensive alternative splicing, generating multiple isoforms with distinct functions and tissue distributions. This complexity allows CD45 to finetune immune responses in different contexts, including within the brain where microglial CD45 critically influences neurodegenerative disease progression[@butters2003].

This comprehensive page covers CD45's molecular structure, its normal functions in the nervous system, its dysregulation in neurodegenerative diseases, and its potential as a therapeutic target.

Structure and Molecular Architecture

CD45 possesses a distinctive multi-domain architecture that enables its unique regulatory functions:

Domain Organization

Extracellular Domain (aa 1-583):

• Heavily O-glycosylated with multiple N-linked glycans
• Contains a variable region subject to alternative splicing
• Includes three fibronectin-type III repeats
• Determines isoform-specific functions

• Single alpha-helical transmembrane segment
• Anchors CD45 to the plasma membrane
• Couples extracellular signals to intracellular responses

• Contains tandem phosphatase domains
• The membrane-proximal domain (D1) is catalytically active
• The membrane-distal domain (D2) is regulatory
• Multiple phosphorylation sites for regulation

Isoforms

CD45 exists in multiple isoforms generated by alternative splicing:

CD45RO: Short isoform lacking exons 4-6 (extracellular domain)

• Expressed on activated and memory T cells
• Common in inflammatory conditions

• Expressed on naive T cells
• Used as T cell maturation marker

• B cell and macrophage expression
• Common in brain microglia

• T and B cell specific expression

Post-translational Modifications

Glycosylation:

• Extensive O-linked glycosylation in extracellular domain
• N-linked glycosylation sites
• Sialylation affects ligand interactions

• Tyrosine phosphorylation regulates activity
• Serine/threonine phosphorylation modulates function
• Kinase/phosphatase dynamics control signaling

Normal Physiological Functions

Immune Cell Signaling

CD45 is a master regulator of immune cell signal transduction:

Src Family Kinase Regulation:

• Dephosphorylates inhibitory tyrosine residues on Src family kinases
• Activates LCK, FYN, LYN in T cells
• Modulates signal intensity through BCR and TCR[@hermiston2001]

• Determines the sensitivity of immune cells to stimuli
• Prevents spontaneous activation
• Enables appropriate response to antigens

• Controls activation and differentiation outcomes
• Regulates cytokine production
• Modulates proliferation

Microglial Function

In the brain, CD45 performs critical microglial regulatory functions:

Activation State Modulation:

• Regulates microglial activation states
• Controls pro-inflammatory vs. anti-inflammatory phenotypes
• Influences phagocytic activity[@schwartz2003]

• Modulates cytokine production
• Controls chemokine expression
• Regulates inflammatory responses[@zhu2011]

• Affects microglial phagocytosis of debris
• Regulates amyloid clearance
• Controls synaptic pruning

Role in Alzheimer's Disease

Microglial Dysfunction

CD45 plays a complex role in Alzheimer's disease pathogenesis:

Amyloid Clearance:

• CD45 deficiency enhances microglial amyloid clearance
• Reduced CD45 leads to improved Aβ removal
• Suggests CD45 may limit beneficial microglial responses[@tan2008]

• Elevated CD45 in AD microglia
• Dysregulated signaling contributes to chronic inflammation
• May promote neurotoxicity

• Altered CD45 isoform expression in AD brain
• Changes correlate with disease severity
• Potential biomarker potential[@lalANC2010]

Pathological Mechanisms

Neuroinflammation:

• CD45 drives pro-inflammatory microglial responses
• Contributes to chronic neuroinflammation
• Promotes cytokine-mediated toxicity

• Microglial-mediated synapse loss
• Pruning dysregulation
• Contributes to cognitive decline

• CD45 modulation could reduce harmful inflammation
• Could enhance beneficial microglial functions
• Potential for immunotherapy approaches["@liu2014"]

Role in Parkinson's Disease

Microglial Activation

CD45 is implicated in Parkinson's disease through microglial pathways:

Dopaminergic Neuron Vulnerability:

• Activated microglia with altered CD45 in substantia nigra
• Chronic inflammation contributes to neuron loss
• CD45-regulated cytokines affect survival[@zhang2019]

• Elevated CD45 in PD brain
• Enhanced pro-inflammatory signaling
• Contributes to disease progression

• CD45 affects microglial mitochondrial function
• Altered energy metabolism in PD
• Potential therapeutic target

Expression Changes

• Increased CD45 expression in PD substantia nigra
• Correlation with disease severity
• Changes in CD45 isoforms

Role in Other Neurodegenerative Disorders

Amyotrophic Lateral Sclerosis

• Altered CD45 on microglia in ALS
• Contributes to motor neuron inflammation
• Potential therapeutic target

Multiple Sclerosis

• CD45 in demyelinating lesions
• Regulates autoimmune responses
• T cell regulation role

Huntington's Disease

• Microglial CD45 dysregulation
• Contributes to striatal degeneration
• Inflammatory component

Interaction Network

Immune Cell Signaling

| Partner Protein | Interaction Type | Functional Consequence |
|-----------------|-------------------|------------------------|
| LCK | Dephosphorylation | T cell activation |
| FYN | Dephosphorylation | Signal initiation |
| SYK | Dephosphorylation | B cell signaling |
| ZAP-70 | Dephosphorylation | TCR signaling |

Microglial Interactions

| Partner | Interaction | Effect |
|---------|-------------|--------|
| Tyrosine kinases | Regulation | Activation state |
| Cytokine receptors | Modulation | Inflammatory response |
| Phagocytic receptors | Coordination | Clearance function |

Animal Models

Knockout Studies

CD45 Knockout Mice:

• Severe combined immunodeficiency
• Impaired T and B cell development
• Altered immune responses

• Microglial-specific knockouts reveal brain functions
• Neurological phenotypes
• Inflammation-related changes

Disease Models

• AD mouse models show CD45 involvement
• PD models demonstrate microglial CD45 role
• Therapeutic intervention studies

Therapeutic Implications

Targeting Strategies

Immunomodulation:

• CD45 antibodies for immune modulation
• Small molecule phosphatase modulators
• Cytokine pathway targeting[@liu2014]

• Modulating microglial activation states
• Enhancing beneficial functions
• Reducing harmful inflammation

Challenges

Specificity:

• CD45 is ubiquitously expressed
• Systemic effects possible
• Achieving brain specificity

• Multiple isoforms with different functions
• Context-dependent effects
• Balancing inflammation and immunity

Genetic Variation

Polymorphisms

• CD45 variants associated with autoimmune diseases
• Some variants may modify neurodegenerative disease risk
• Effect on protein expression and function[@chen2018]

Biomarker Potential

• CD45 as disease progression marker
• Cerebrospinal fluid CD45 measurements
• Imaging of microglial activation[@zhou2021]

Future Directions

Research Priorities

Unanswered Questions

• What is the precise role of CD45 in different disease stages?
• Can CD45 modulation achieve therapeutic benefits safely?
• What are the optimal biomarkers for patient selection?

See Also

• [PTPRC Gene](/genes/ptprc)
• [Microglial Activation](/mechanisms/microglial-activation)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Immune Signaling](/mechanisms/immune-signaling)
• [Phagocytosis](/mechanisms/microglial-phagocytosis)

External Links

• [UniProt: PTPRC (P08575)](https://www.uniprot.org/uniprot/P08575)
• [NCBI Gene: PTPRC](https://www.ncbi.nlm.nih.gov/gene/5756)
• [PDB: CD45 Structures](https://www.rcsb.org/)
• [PubMed: CD45 Research](https://pubmed.ncbi.nlm.nih.gov/?term=CD45+neurodegeneration)