Engagement of CD81 induces ezrin tyrosine phosphorylation and its cellular redistribution with filamentous actin.
CD81 is a tetraspanin family member involved in diverse cellular interactions in the immune and nervous systems and in cell fusion events. However, the mechanism of action of CD81 and of other tetraspanins has not been defined. We reasoned that identifying signaling molecules downstream of CD81 would provide mechanistic clues. We engaged CD81 on the surface of B-lymphocytes and identified the induced tyrosine-phosphorylated proteins by mass spectrometry. This analysis showed that the most prominent tyrosine phosphorylated protein was ezrin, an actin-binding protein and a member of the ezrin-radixin-moesin family. We also found that CD81 engagement induces spleen tyrosine kinase (Syk) and that Syk was involved in tyrosine phosphorylation of ezrin. After engagement of CD81, it colocalized with ezrin and F-actin, and this association was disrupted when Syk activation was blocked. Taken together, these studies suggest a model in which CD81 interfaces between the plasma membrane and the cytoskeleton by activating Syk, mobilizing ezrin, and recruiting F-actin to facilitate cytoskeletal reorganization and cell signaling. This mechanism might explain the pleiotropic effects induced in response to stimulation of cells by anti-CD81 antibodies or by the hepatitis C virus, which uses this molecule as its key receptor.
Coffey
Greg P
GP
Stanford University, School of Medicine, Division of Oncology, Stanford, CA 94305, USA.
Rajapaksa
Ranjani
R
Liu
Raymond
R
Sharpe
Orr
O
Kuo
Chiung-Chi
CC
Krauss
Sharon Wald
SW
Sagi
Yael
Y
Davis
R Eric
RE
Staudt
Louis M
LM
Sharman
Jeff P
JP
Robinson
William H
WH
Levy
Shoshana
S
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D000072377:Syk Kinase; D060225:Tetraspanin 28; D014443:Tyrosine / Q000378:metabolism; D000099149:Ezrin
D000199:Actins; D015703:Antigens, CD; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; D060225:Tetraspanin 28; D014443:Tyrosine; D000099149:Ezrin; C554798:CD81 protein, human; C000606896:SYK protein, human