SH2 domain-mediated targeting, but not localization, of Syk in the plasma membrane is critical for FcepsilonRI signaling.
Aggregation of the high-affinity IgE receptor induces the tyrosine phosphorylation of subunits of the receptor and the subsequent association with the receptor of the cytosolic protein tyrosine kinase Syk. The current experiments examined the functional importance of membrane association of Syk and the role of the SH2 domain in receptor-mediated signal transduction. Wild-type Syk and chimeric Syk molecules with the c-Src myristylation sequence at the amino-terminus were expressed in a Syk-negative mast cell line. Chimeric Syk with the myristylation sequence was membrane associated, and a small fraction was constitutively colocalized with FcepsilonRI, Lyn, and LAT (linker for T-cell activation) in the glycolipid-enriched microdomains or rafts. However, even under these conditions, the tyrosine phosphorylation of Syk and the downstream propagation of signals required FcepsilonRI aggregation. This chimeric Syk was less active than wild-type Syk in FcepsilonRI-mediated signal transduction. In contrast, a truncated membrane-associated form of Syk that lacked the SH2 domains was not tyrosine phosphorylated by receptor aggregation and failed to transduce intracellular signals. These findings suggest that SH2 domain-mediated membrane translocation of Syk is essential for the FcepsilonRI-mediated activation of Syk for downstream signaling events leading to histamine release. Furthermore, the localization of Syk in glycolipid-enriched microdomains by itself is not enough to generate or enhance signaling events.
Receptors and Signal Transduction Section, Oral Infection and Immunity Branch, National Institutes of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA. rs53x@nih.gov
K
K
Sada
J
J
Zhang
R P
RP
Siraganian
D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D004792:Enzyme Precursors / Q000378:metabolism*; D006017:Glycolipids / Q000378:metabolism; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*; D000072377:Syk Kinase; D014162:Transfection; D014407:Tumor Cells, Cultured; D018909:src Homology Domains / Q000502:physiology*; D019061:src-Family Kinases
D004792:Enzyme Precursors; D006017:Glycolipids; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D017455:Receptors, IgE; D011993:Recombinant Fusion Proteins; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D000072377:Syk Kinase; C000606898:Syk protein, rat; D019061:src-Family Kinases