Abstract
Lck, a lymphocyte-specific tyrosine protein kinase, is bound to cellular membranes as the result of myristoylation and palmitoylation of its amino terminus. Its activity is inhibited by phosphorylation of tyrosine 394. The Tyr-505 --> Phe mutant of Lck (F505Lck) exhibits elevated biological activity and constitutive phosphorylation of Tyr-394 in vivo. Mutations at sites of fatty acylation that prevent F505Lck from associating with cellular membranes abolish the biological activity as a protein kinase in vivo and in vitro, and eliminate the phosphorylation of Tyr-394. Here, we show that exposure of cells expressing cytoplasmic or nuclear forms of F505Lck to H2O2, a general inhibitor of tyrosine protein phosphatases, restores the catalytic activity of these mutant proteins through stimulation of phosphorylation of Tyr-394. H2O2 treatment induced the phosphorylation of Tyr-394 therefore need not occur by autophosphorylation. Thus, there appear to be two mechanisms through which the phosphorylation of Lck at Tyr-394 can occur. One is restricted to the plasma membrane and does not require the presence of oxidants. The other is operational in the nucleus as well as the cytosol and is responsive to oxidants.
Highlights
P56lck, a member of the Src family of tyrosine protein kinases (1, 2), is expressed exclusively in lymphoid cells and predominantly in T cells
We show that exposure of cells expressing cytoplasmic or nuclear forms of F505Lck to H2O2, a general inhibitor of tyrosine protein phosphatases, restores the catalytic activity of these mutant proteins through stimulation of phosphorylation of Tyr-394
A Form of Activated Lck Localized to the Nucleus Does Not Induce an Increase in Tyrosine Phosphorylation of Cellular Substrate—To determine if Lck, which had been both activated by mutation (F505) and retargeted to the nucleus, was able to transform fibroblasts, we constructed a form of Lck in which the nuclear localization signal from SV40 large T antigen was attached to the amino terminus, Gly-2 was mutated to alanine, and Tyr-505 was mutated to phenylalanine
Summary
P56lck, a member of the Src family of tyrosine protein kinases (1, 2), is expressed exclusively in lymphoid cells and predominantly in T cells. We show that exposure of cells expressing cytoplasmic or nuclear forms of F505Lck to H2O2, a general inhibitor of tyrosine protein phosphatases, restores the catalytic activity of these mutant proteins through stimulation of phosphorylation of Tyr-394.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
