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Proteasome-dependent regulation of Syk tyrosine kinase levels in human basophils.
J Allergy Clin Immunol 2002; 110(3):366-73JA

Abstract

BACKGROUND

In human basophils, FcepsilonRI signal initiation, leading to histamine release, relies on activation of Syk protein tyrosine kinase. Basophils from approximately 10% of unselected donors do not degranulate in response to FcepsilonRI cross-linking. Their unresponsiveness has been linked to the absence of Syk protein despite apparently normal levels of Syk mRNA.

OBJECTIVE

The aim of this study was to explore pathways of Syk protein degradation as a possible posttranslational mechanism for downregulating Syk protein levels in human basophils and other leukocytes.

METHODS

Highly purified basophils, lymphocytes, and monocytes were incubated in the presence or absence of a panel of cell-permeable inhibitors of proteolytic degradation pathway(s). Subsequently, the protein level of Syk tyrosine kinase was determined by means of Western blotting. In vitro assays were conducted through use of immunoprecipitated basophil Syk and a rabbit reticulocyte lysate system.

RESULTS

Three inhibitors of proteasome-mediated degradation-PSI, lactacystin, and ALLN-substantially increased Syk levels in releaser basophils and restored Syk expression in nonreleaser basophils. Caspase inhibitors were less effective, and inhibitors of calpain-mediated proteolysis had no effect. Among other leukocytes tested, only naive CD4(+) T cells had more Syk after proteasome inhibitor treatment. In vitro ubiquitination assays demonstrated that Syk is readily ubiquitinated in vitro and also that Syk ubiquitination is associated with a substantial decrease in total levels of Syk protein.

CONCLUSION

These data provide evidence for a ubiquitin/proteasome-dependent mechanism that contributes to Syk regulation in human basophils and might also be relevant to naive T cells. Understanding this regulatory pathway might lead to strategies for suppressing allergic inflammation while preserving essential Syk-mediated functions in other hematopoietic cells.

Authors+Show Affiliations

Department of Pathology, University of New Mexico School of Medicine, Albuquerque 87131, USA.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

12209081

Citation

Youssef, Lama A., et al. "Proteasome-dependent Regulation of Syk Tyrosine Kinase Levels in Human Basophils." The Journal of Allergy and Clinical Immunology, vol. 110, no. 3, 2002, pp. 366-73.
Youssef LA, Wilson BS, Oliver JM. Proteasome-dependent regulation of Syk tyrosine kinase levels in human basophils. J Allergy Clin Immunol. 2002;110(3):366-73.
Youssef, L. A., Wilson, B. S., & Oliver, J. M. (2002). Proteasome-dependent regulation of Syk tyrosine kinase levels in human basophils. The Journal of Allergy and Clinical Immunology, 110(3), pp. 366-73.
Youssef LA, Wilson BS, Oliver JM. Proteasome-dependent Regulation of Syk Tyrosine Kinase Levels in Human Basophils. J Allergy Clin Immunol. 2002;110(3):366-73. PubMed PMID: 12209081.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Proteasome-dependent regulation of Syk tyrosine kinase levels in human basophils. AU - Youssef,Lama A, AU - Wilson,Bridget S, AU - Oliver,Janet M, PY - 2002/9/5/pubmed PY - 2002/10/9/medline PY - 2002/9/5/entrez SP - 366 EP - 73 JF - The Journal of allergy and clinical immunology JO - J. Allergy Clin. Immunol. VL - 110 IS - 3 N2 - BACKGROUND: In human basophils, FcepsilonRI signal initiation, leading to histamine release, relies on activation of Syk protein tyrosine kinase. Basophils from approximately 10% of unselected donors do not degranulate in response to FcepsilonRI cross-linking. Their unresponsiveness has been linked to the absence of Syk protein despite apparently normal levels of Syk mRNA. OBJECTIVE: The aim of this study was to explore pathways of Syk protein degradation as a possible posttranslational mechanism for downregulating Syk protein levels in human basophils and other leukocytes. METHODS: Highly purified basophils, lymphocytes, and monocytes were incubated in the presence or absence of a panel of cell-permeable inhibitors of proteolytic degradation pathway(s). Subsequently, the protein level of Syk tyrosine kinase was determined by means of Western blotting. In vitro assays were conducted through use of immunoprecipitated basophil Syk and a rabbit reticulocyte lysate system. RESULTS: Three inhibitors of proteasome-mediated degradation-PSI, lactacystin, and ALLN-substantially increased Syk levels in releaser basophils and restored Syk expression in nonreleaser basophils. Caspase inhibitors were less effective, and inhibitors of calpain-mediated proteolysis had no effect. Among other leukocytes tested, only naive CD4(+) T cells had more Syk after proteasome inhibitor treatment. In vitro ubiquitination assays demonstrated that Syk is readily ubiquitinated in vitro and also that Syk ubiquitination is associated with a substantial decrease in total levels of Syk protein. CONCLUSION: These data provide evidence for a ubiquitin/proteasome-dependent mechanism that contributes to Syk regulation in human basophils and might also be relevant to naive T cells. Understanding this regulatory pathway might lead to strategies for suppressing allergic inflammation while preserving essential Syk-mediated functions in other hematopoietic cells. SN - 0091-6749 UR - https://www.unboundmedicine.com/medline/citation/12209081/Proteasome_dependent_regulation_of_Syk_tyrosine_kinase_levels_in_human_basophils_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0091674902001227 DB - PRIME DP - Unbound Medicine ER -