CD77 BLA(Burkitt's lymphoma antigen), CTH(ceramide trihexoside), Gb3(globotriaocylceramide), pk blood group antigen
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Carbohydrate
B Cell
Epithelia
Germinal Center
Endothelia
Centroblast
B Lymphocyte
Burkitt lymphoma cell
Extrafollicular B cell
1 / 1

Expression
CD77 is expressed on germinal center B lymphocytes,  more strongly on centroblasts but can be induced on extrafollicular B cells.  Treatment of extrafollicular B cells with a high threshold level of CD40L induces expression of CD77.  CD77 is  highly expressed on Burkitt's lymphoma cells and weakly expressed on some follicular center lymphomas.  Expression is found on endothelia and epithelia. 

Structure
MOLECULAR FAMILY NAME:  Belongs to the carbohydrate group.

CD77 is a single-pass type-2 353 aa membrane protein.  CD77 is a neutral glycosphingolipid: Gala1 ->4Galb1 ->4Galcb1 ->Ceramide.  CD77 mAbs react with Gala1 ->4Galb1 -> 4Glc-ceramide (Gb3), which belongs to the globo-series of neutral glycosphingolipids.  CD77 is a rare Pk blood group antigen.  It contains of 3 carbohydrate molecules linked to a lipid moiety in the cell membrane.  Exposure depends on the length and extent of unsaturated of the fatty acid chain.

MOLECULAR MASS

CD77 has a formula Mr of 1052 with 1 kDa.

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION: No information

Ligands
Co-capping experiments suggest that CD77 is associated with CD19 on the surface of Daudi B cells, while CD77-deficient cells show concomitant decreased expression of CD19, suggesting that CD77 influences the surface expression of CD19.

LIGANDS AND MOLECULES ASSOCIATED WITH CD77
Molecule Comment
Shiga toxin Shiga toxin, produced by Shigella dysenteriae type 1 binds to Gb3/CD77
Verotoxin 1 (VT1) VT1 (also called Shiga-like toxin (SLT1) produced by strains of Escherichia coli binds to Gb3/CD77)
CD19 Based on sequence similarity with the binding (B) subunit of VT, CD19 has been described as a CD77-binding protein



Function
The function of is unknown, however, it may bind CD19.  CD77 is enriched in lipid rafts at the surface of B cells and it closely connected to Lyn and Sky kinases.  CD77 may be involved in the elimination process of the germinal center B cells that fail to produce high affinity antibody.  CD77+ B lymphocytes, both normal and tumoral, are prone to apoptosis.  Expression is lost when rescued from death by binding antigens on follicular dendritic cells.  Germinal center B cells which express CD77 have been shown to be engaged in programmed cell death.  CD77 is used as a centroblast marker.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD77 IN INTACT ANIMAL

CD77 antibodies and Verotoxin (VT-B) induce apoptosis of Burkitt's lymphoma cells.
CD77 is one of the critical cell surface molecules able to mediate an apoptic signal.  Its association with type 1 interferon receptor or with HIV coreceptor CXCR4 (CD184) seems to be critical for the functions of these receptors.  Crosslinking of CD77 induces apoptosis of Burkitt's lymphoma cells.  CD77 is a potential target used for cancer therapy particularily hematological malignancies such as follicular lymphoma, multiple myelona and chronic lymphocytic leukemia.  CD77 antibodies and Verotoxin (VT-B) induce apoptosis of Burkitt's lymphoma cells.  CD77 is a receptor for lectins on the pili of a certain strain of E. coli.  The verotoxin of E. coli and the Shiga toxin of Shigella dysenteriae which causes dysentery and hemolytic uremic syndrome specifically binds to Gb3. 


Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD77: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD77: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
Antibodies

Revised June 25, 2008


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