Regulation of expression and function of Lck tyrosine kinase by high cell density.
For many types of cells, an increase in cell density leads to characteristic changes in intracellular signalling and cell function. It is unknown, however, whether cell density affects the function of T lymphocytes. It is presented here that aggregation of Jurkat T cells, murine thymocytes or human peripheral blood T cells, results in gradual modification of the Lck tyrosine kinase. Within one hour of aggregation, Lck in the detergent-insoluble lipid raft fraction is dephosphorylated mainly at the carboxy-terminal tyrosine. Further aggregation leads to gradual loss of Lck protein from both lipid raft and non-raft fractions which is accompanied by increased protein ubiquitination, a process that is more evident in the detergent-soluble fraction. In contrast, the expression of LAT, which like Lck distributes to raft and non-raft membrane, or Csk, a kinase with a structure similar to Lck, is not affected by cell aggregation. Dephosphorylation of lipid raft-associated Lck, albeit with reduced kinetics, is observed in aggregated Jurkat CD45-deficient cells as well, suggesting involvement of additional tyrosine phosphatases. Changes in Lck structure and expression correlate with reduced ability of aggregated cells to fully activate protein tyrosine phosphorylation after stimulation of the TCR, and with changes in the activation of down-stream signalling cascades.
Ozegbe
Patricia
P
Bone & Joint Research Unit, William Harvey Research Institute, Queen Mary's School of Medicine & Dentistry, University of London, London, UK.
Chernajovsky
Yuti
Y
Kabouridis
Panagiotis S
PS
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D017493:Leukocyte Common Antigens / Q000378:metabolism; D018655:Lymphocyte Count; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D021962:Membrane Microdomains / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008811:Mice, Inbred DBA; D010766:Phosphorylation; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
D011948:Receptors, Antigen, T-Cell; D025801:Ubiquitin; D014443:Tyrosine; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017493:Leukocyte Common Antigens