ZAP-70 enhances IgM signaling independent of its kinase activity in chronic lymphocytic leukemia.
We transduced chronic lymphocytic leukemia (CLL) cells lacking ZAP-70 with vectors encoding ZAP-70 or various mutant forms of ZAP-70 and monitored the response of transduced CLL cells to treatment with F(ab)(2) anti-IgM (anti-mu). CLL cells made to express ZAP-70, a kinase-defective ZAP-70 (ZAP-70-KA(369)), or a ZAP-70 unable to bind c-Cbl (ZAP-YF(292)) experienced greater intracellular calcium flux and had greater increases in the levels of phosphorylated p72(Syk), B-cell linker protein (BLNK), and phospholipase C-gamma, and greater activation of the Ig accessory molecule CD79b in response to treatment with anti-mu than did mock-transfected CLL cells lacking ZAP-70. Transfection of CLL cells with vectors encoding truncated forms of ZAP-70 revealed that the SH2 domain, but not the SH1 domain, was necessary to enhance intracellular calcium flux in response to treatment with anti-mu. We conclude that ZAP-70 most likely acts as an adapter protein that facilitates B-cell receptor (BCR) signaling in CLL cells independent of its tyrosine kinase activity or its ability to interact with c-Cbl.
Moores UCSD Cancer Center, University of California-San Diego, 3855 Health Sciences Drive No. 0820, La Jolla, CA 92093, USA.
Liguang
L
Chen
Lang
L
Huynh
John
J
Apgar
Li
L
Tang
Laura
L
Rassenti
Arthur
A
Weiss
Thomas J
TJ
Kipps
D048868:Adaptor Proteins, Signal Transducing / Q000276:immunology; D000256:Adenoviridae; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology; D051925:CD79 Antigens / Q000276:immunology; D020013:Calcium Signaling; D004247:DNA; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology* / Q000276:immunology*; D050505:Mutant Proteins / Q000276:immunology; D051966:Phospholipase C gamma / Q000276:immunology; D010766:Phosphorylation; D010957:Plasmids; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D015398:Signal Transduction; D014161:Transduction, Genetic; D014162:Transfection; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000276:immunology*
D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; D051925:CD79 Antigens; D007075:Immunoglobulin M; D050505:Mutant Proteins; D011947:Receptors, Antigen, B-Cell; D004247:DNA; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D051966:Phospholipase C gamma