CD81 TAPA-1(target of an anti-proliferative antigen-1), M38
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 3 glycoprotein, 4 span
B Cell
T Cell
Hematopoietic Cell
Leukocyte
Tumor Cell
Endothelial Cell
Epithelial Cell
Monocyte
Hematolymphoid cell
Granulocyte
Mesenchymal Cell
Neuroectodermal cell
26 / 26

Expression
CD81 is broadly expressed on hematopoietic cells, hematolymphoid, neuroectodermal and mesenchymal tumor cell lines.  Wide expression is on leukocytes, T and B cells and monocytes and the expression is increased after activations.  The lowest expression is in granulocytes, however a small subgroup of CD81+ granulocytes has high intensity levels per cell.  CD81 is absent from erythrocytes, platelets and neutrophils but is expressed on endothelial and epithelial cells.  Its pattern of expression suggests that the CD81 gene has a housekeeping function and a type promoter.


Structure
MOLECULAR FAMILY NAME: Belongs to the tetraspanin family.

CD81 is a multi-pass type-3, 4 span glycoprotein.  It contains 2 transmembrane domains of unequal size, 4 hydrophobic transmembrane domains and a cytoplasmic domain containing NH2- and COOH termini.  There is no N-glycosylation.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
B cells 26 kDa
Jurkat 26 kDa
K562 cells 26 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION: No information.

Ligands
Co-immunoprecipitation and flow cytometric energy transfer studies have shown that CD81 associates non-covalently with a number of other molecules like CD19, CD21 and Leu-13, MHC class I and II, CD20, CD37, CD53 and CD82 in B cells, CD4, CD8 and CD82 in T cells, CD9, CD63, the integrins CD29/CD49c VLA-3, CD29/CD49d VLA-4 and CD29/CD49f VLA-6 in several cell types.  No extracellular ligand has been identified for CD81.  CD81 associates with the envelope (E) protein of hepatitis C virus.

LIGANDS AND MOLECULES ASSOCIATED WITH CD81
Molecule Comment
Leu-13/9-29 CD19, CD21, Leu-13 and CD81 associate on the B cell to make a signaling complex
CD19 CD19, CD21, Leu-13 and CD81 associate on the B cell to make a signaling complex
CD21 CD19, CD21, Leu-13 and CD81 associate on the B cell to make a signaling complex



Function
CD81 mediates signal transduction events that play a role in the regulation of cell development, growth and motility.  CD81 is involved with CD19, CD21 and Leu13 that regulates the threshold response to antigen.  Surface expression of CD81 is downregulated on lymphocytes during infections.   Mouse CD81 appears to play a role in early T cell development.  Knockout mice show subtle defects in B-cell maturation and antibody production.  Engagement of CD81 with the mAb TAPA-1 induces B cell adhesion via the integrin CD29/CD49d (VLA-4).

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD81 IN INTACT ANIMAL

CD81 binds the envelope 2 protein of hepatitis C virus.  CD81 is a receptor for HCV and is required for hepatic infection by malarial parasities.  CD81 appears to promote muscle cell fusion and support myotube maintenance.  CD81 is located in the tumor-suppressor gene region and thus is a candidate gene for malignancies.  

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD81: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD81: No information.

ADDITIONAL INSIGHTS

Functions of this and other members of the tetraspan family are as yet poorly understood.

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 975P60033
MouseA46472P35762S45012
Antibodies
1D6   View Reactivity
JS-81   View Reactivity

Revised June 25, 2008


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