Lck phosphorylation status of Lck Tyr192 and Tyr192/Tyr505 mutantsLck phosphorylation status of Lck Tyr192 and Tyr192/Tyr505 mutants

ABSTRACT: Lymphocyte-specific protein tyrosine kinase (Lck) is crucial for signaling from the T cell receptor (TCR) and is controlled through tyrosine phosphorylations. Phosphorylated Tyr505 (pTyr505) promotes a closed, inactive conformation of Lck, while pTyr394 is critical for kinase activity. Additionally, pTyr192 has been suggested to regulate Lck activity by changing the specificity of the Lck Src-homology 2 (SH2) domain and/or by affecting Lck association with CD45 thus drastically increasing pTyr505. However, little is known about how pTyr192 affects endogenously expressed Lck. Here we used CRISPR/Cas9 genome editing to generate Jurkat cell lines expressing Lck Glu192 mimicking Lck pTyr192, or Lck Phe192 mimicking unphosphorylated Lck Tyr192. We confirmed that Lck Glu192 is hyperphosphorylated on Tyr505, possibly explaining reduced association of Lck Glu192 with prototypic Lck-SH2 ligands. To isolate the effect of Lck Tyr192 mutations from the effect on Lck pTyr505, we subsequently generated Jurkat cells doubly mutated on Lck Tyr192 and Lck Tyr505. Both Lck Phe192/Phe505 and Lck Glu192/Phe505 mutants co-precipitated similar amounts of binding partners. Moreover, both mutants displayed hyperphosphorylation of Tyr394. Our results indicate that CD45 is the main phosphatase controlling Lck pTyr394 in steady-state T cells. Additionally, our data demonstrate that the prototypic specificity of the Lck SH2 domain (owned by the Lck Phe192 mutants) promotes transphosphorylation of Tyr394. These observations pinpoint the fundamental role of Tyr192 in regulation of Lck activity and simultaneously reveal the most potent Lck mutants so far described

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): T Cell

SUBMITTER: Tuula Nyman  

LAB HEAD: Tuula Nyman

PROVIDER: PXD014470 | Pride | 2021-04-02

REPOSITORIES: Pride