CD326 TACSTD1 (tumor associated calcium signal transducer 1),
Ep-CAM, EGP40, MIC18, TROP1, EGP, hEGP-2, KSA, M4S1, MK-1, GA733-2
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Epithelial Cell
Erythroblast
Carcinoma Cell
Colon
Lung
40 / 40

Expression
CD326 is expressed on almost all epithelial cell membranes with the exception of adult squamous cells of the skin and a few specific epithelial cell types such as hepatocytes and not on mesodermal or neural cell membranes.  Expression is only in neoplasms of epithelial cell origin and immature erythroblasts.  Expression is found on the surface of adenocarcinomas and some colon astrointestinal carcinomas, normal colon and in lung.



Structure
MOLECULAR FAMILY NAME

CD326 is a single-pass type-1 293 aa  glycoprotein.  It contains a 21 aa signal sequence, a 246 aa extracellular domains which contains 2 epidermal growth factor (EGF)-like repeats,  a 122 aa cysteine-poor stretch and 2 putatuve N-linked glycosylation sites, a 21 aa transmembrane domain and a 26 aa cytoplasmic domain with 2 binding sites for α-actinin.
Both EGF repeats were required for the formation of homophilic adhesions.  Deletion of either EGF-like repeat was sufficient to inhibit the adhesion properties of the molecule.  The first repeat is required for reciprocal interactions between CD326 molecules on adjacent cells as demonstrated with blocking antibodies.  The second repeat is mainly required for lateral interactions between CD326 molecules.  Lateral interactions result in tetramers which might be a necessary step in formation of CD326-mediated intercellular contacts.  CD326 is an adhesion molecule but does not bear homology to other known cell adhesion molecules.
   
MOLECULAR MASS

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION

CD326 has 2 putative N-linked glycosylation sites.

Ligands
LIGANDS AND MOLECULE ASSOCIATED WITH CD326:

CD326 associates with CD305 (LAIR-1), CD306 (LAIR-2) and Ep-CAM.  CD326 displays homophilic binding.

Function
CD326 is a 9-exon gene that encodes a carcinoma associated antigen.  CD326 mediates calcium-independent homophilic cell-cell adhesion with its extracellular domain and is linked to the actin cytoskeleton via its intracellular domain.  The antigen may function as a growth factor receptor and functions as a homotypic calcium-independent cell adhesion molecule but is weaker than that mediated by cadherins and is thought to be involved in maintaining cells in position during proliferation.  Expression levels of CD326 correlate inversely with that of CD324 (E-cadherin) and cellular differentiation.  Hence CD326 expression declines during cell differentiation and CD324 expression increases.  A recent study suggests that CD326-mediated adhesion between IELs and intestinal epithelial cells helps to maintain an immunological barrier which is the first line of defense against mucosal infection. 

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD326 IN INTACT ANIMAL

CD326 is a marker of epithelial cells, and immunohistochemistry is a means of distinguishing tumors of epithelial and non-epithelial origin.  This epithelial glycoprotein, CD326, is now recognized as having an important role in tumor biology.  The antigen is being used as a target for immunotherapy treatment of human colorectal carcinomas.  CD326 binds CD305 and CD306 to inhibit cellular activation and inflammation. 




Comments
MOLECULAR INTERACTIONS-
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD326: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD326: No information.

ADDITIONAL INSIGHTS

For further information see Balzar, M. et al (2001) Mol. Cell Biol. 21: 2570-2580.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 4072P16422
Antibodies

Revised June 25, 2008


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