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The interactions of LCK in T cells and its regulation by CD45 Lefebvre, Dennis C.
Abstract
Lck is a Src-family tyrosine kinase whose activity is essential for T cell activation and development. The phosphorylation of two key tyrosine residues in Lck, Tyr 505 and Tyr 394, regulate its activation by inducing profound changes in conformation. In vitro, CD45, a leukocyte-specific tyrosine phosphatase, preferentially dephosphorylated Tyr 394, as opposed to Tyr 505, and this specificity depended on the Lck non-catalytic domains and not the sequence specificity of the phosphatase catalytic pocket. The Lck non-catalytic domains enhanced the rate of CD45-mediated Tyr 394 dephosphorylation, and inhibited, but did not block catalysis at Tyr 505. A direct, specific, non-catalytic interaction was observed between the second phosphatase domain of CD45 (D2) and subdomain X(SD10) of Lck. This interaction was also shown to influence CD45 substrate specificity as the replacement of Erkl SD10 with that of Lck resulted in the conversion of Erkl into a more efficient CD45 substrate. In T cells, the majority of CD45 is constitutively associated with a smaller protein aptly named CD45-associated protein (CD45AP). An interaction between Lck and CD45AP was determined to occur independently of CD45 in T cells. A direct CD45AP:Lck interaction was confirmed in vitro, and was shown to antagonize the ability of CD45 to interact with Lck. Moreover, the presence of CD45AP significantly inhibited CD45-mediated Lck dephosphorylation at Tyr 394, but not Tyr 505, suggesting a role for CD45AP in sustaining Lck activity in the cell. CD44 is a widely expressed transmembrane adhesion molecule that requires the activity of Src-family kinases in T cells to induce cytoskeletal changes associated with cell adhesion. Here, Src-family kinases Lck and Fyn were both shown to associate with CD44 in T cells. In vitro, the CD44 cytoplasmic domain bound to Lck directly in a zinc dependent manner, but did not bind to Fyn. The treatment of T cells with cation chelator 1,10-phenanthroline both disrupted the CD44:Lck association and blocked CD44-induced cytoskeletal changes. This suggests that the zinc-dependent Lck association with CD44 plays a key role in mediating CD44-induced cell signaling events required for cell adhesion.
Item Metadata
Title |
The interactions of LCK in T cells and its regulation by CD45
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2003
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Description |
Lck is a Src-family tyrosine kinase whose activity is essential for T cell activation
and development. The phosphorylation of two key tyrosine residues in Lck, Tyr 505 and
Tyr 394, regulate its activation by inducing profound changes in conformation. In vitro,
CD45, a leukocyte-specific tyrosine phosphatase, preferentially dephosphorylated Tyr
394, as opposed to Tyr 505, and this specificity depended on the Lck non-catalytic
domains and not the sequence specificity of the phosphatase catalytic pocket. The Lck
non-catalytic domains enhanced the rate of CD45-mediated Tyr 394 dephosphorylation,
and inhibited, but did not block catalysis at Tyr 505. A direct, specific, non-catalytic
interaction was observed between the second phosphatase domain of CD45 (D2) and
subdomain X(SD10) of Lck. This interaction was also shown to influence CD45
substrate specificity as the replacement of Erkl SD10 with that of Lck resulted in the
conversion of Erkl into a more efficient CD45 substrate.
In T cells, the majority of CD45 is constitutively associated with a smaller protein
aptly named CD45-associated protein (CD45AP). An interaction between Lck and
CD45AP was determined to occur independently of CD45 in T cells. A direct
CD45AP:Lck interaction was confirmed in vitro, and was shown to antagonize the ability
of CD45 to interact with Lck. Moreover, the presence of CD45AP significantly inhibited
CD45-mediated Lck dephosphorylation at Tyr 394, but not Tyr 505, suggesting a role for
CD45AP in sustaining Lck activity in the cell.
CD44 is a widely expressed transmembrane adhesion molecule that requires the
activity of Src-family kinases in T cells to induce cytoskeletal changes associated with
cell adhesion. Here, Src-family kinases Lck and Fyn were both shown to associate with CD44 in T cells. In vitro, the CD44 cytoplasmic domain bound to Lck directly in a zinc
dependent manner, but did not bind to Fyn. The treatment of T cells with cation chelator
1,10-phenanthroline both disrupted the CD44:Lck association and blocked CD44-induced
cytoskeletal changes. This suggests that the zinc-dependent Lck association with CD44
plays a key role in mediating CD44-induced cell signaling events required for cell
adhesion.
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Extent |
23324041 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-11-17
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0091217
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2003-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.