Loss of syk kinase during IgE-mediated stimulation of human basophils.
BACKGROUND
Ongoing secretion from human basophils is a balance of activation and deactivation events. Recent studies have focused on downregulatory steps that appear to modify the presence of the activated state of various signaling molecules. We now examine downregulation regulated by mechanisms related to proteasome processing.


OBJECTIVE
To determine the long-term effects of FcepsilonRI aggregation on expression of syk kinase.


METHODS
Peripheral blood basophils were examined for changes in the expression of syk kinase after stimulation with optimal and suboptimal stimulation.


RESULTS
Stimulation results in a 20% loss of syk in 1 hour and an 80% loss of syk in longer incubations (>18 hours). Loss of syk in this time frame can occur at levels of stimulation that do not result in observable mediator release. Loss of syk occurs after stimulation with either anti-IgE antibody or antigen. Activation is shown to result in c-Cbl phosphorylation, and its association with syk and immunoblotting reveals the appearance of a ladder of syk species with molecular weights that are consistent with ubiquitylation of syk. Stimulation in the presence of a proteasome inhibitor such as lactacystin A results in the sustained presence of very high-molecular-weight ubiquitylated species, although it does not alter the presence of the syk ladder.


CONCLUSIONS
Although the loss of syk is probably too slow to account for downregulation of ongoing secretion of histamine or leukotriene C4 release, it may lead to longer-term alterations in basophil function that explain characteristics of clinical procedures like rapid drug desensitization.
Macglashan
Donald
D
Johns Hopkins Asthma and Allergy Center, Baltimore, MD 21224, USA. dmacglas@jhmi.edu
Miura
Katsushi
K
D001491:Basophils / Q000201:enzymology* / Q000473:pathology; D015536:Down-Regulation; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D007073:Immunoglobulin E / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl; D017455:Receptors, IgE / Q000502:physiology; D000072377:Syk Kinase; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D017455:Receptors, IgE; D007073:Immunoglobulin E; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C067419:CBL protein, human