Human spleen tyrosine kinase p72Syk associates with the Src-family kinase p53/56Lyn and a 120-kDa phosphoprotein.
The 72-kDa spleen tyrosine kinase (Syk) and Src-family kinase p53/56Lyn (Lyn) contribute to signaling via the B-cell antigen receptor complex. Here we show that Syk and Lyn from human B lymphocytes can interact directly. Syk and Lyn coimmunoprecipitated from mature and activated B-cell lines, and gel-purified Syk and Lyn reassociated in vitro, demonstrating their direct interaction. This Syk-Lyn interaction may be dependent on the stage of B-cell differentiation, since Syk-Lyn associations were not detected in pre-B and myeloma cell lines and Syk from an immature B-cell line did not reassociate with Lyn in vitro. Serine/threonine kinase activity was also associated with Syk. Crosslinking of cell surface IgM led to rapid activation of both tyrosine and serine/threonine protein kinase activities that resulted in phosphorylation in vitro of proteins coprecipitating with Syk--in particular, a serine/threonine phosphorylated protein 120 kDa in size (pp120). Several phosphoproteins, including one of 72 kDa and one of 120 kDa, coprecipitated with phospholipase C-gamma 1 (PLC gamma 1). Sequential immunoprecipitation identified the 72-kDa protein associated with PLC gamma 1 as Syk. The 120-kDa serine/threonine phosphorylated protein that coprecipitated with PLC gamma 1 resembled the Syk-associated pp120 by several criteria. Thus, pp120 may serve as a link between Syk and PLC gamma 1, coupling the B-cell antigen receptor to the phosphatidylinositol pathway.
Department of Microbiology, University of Washington Medical Center, Seattle 98195.
S P
SP
Sidorenko
C L
CL
Law
K A
KA
Chandran
E A
EA
Clark
D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000378:metabolism*; D002460:Cell Line; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D051966:Phospholipase C gamma; D010750:Phosphoproteins / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology / Q000201:enzymology*; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D004792:Enzyme Precursors; D007075:Immunoglobulin M; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D010750:Phosphoproteins; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma