The role of phosphorylation of serine 59 of Lck on T-cell receptor mediated signaling

Maria Movafegh, Purdue University

Abstract

Lck, a member of the Src family of protein tyrosine kinases, is activated through the T cell receptor (TCR) and plays a major role in the TCR signaling cascade. It is responsible for phosphorylating the immuno-regulated tyrosineactivated motifs (ITAMs) of the TCR and for phosphorylating the tyrosine kinase Zap-70 when Zap-70 binds the ITAMs. Activation of Zap-70 leads to a signaling cascade that leads to a release of intracellular calcium and the activation of the downstream Ras/Raf/Mek/Erk signaling cascade, resulting in the activation of selected transcription factors. Lck's ability to bind and phosphorylate other proteins, a necessary part of its role in the signaling cascade, is a result of its structure; Lck contains a SH2, a SH3, a kinase domain, a membrane associating domain and a unique domain, which is unique in amino acid sequence, but is a common motif in to Src family protein tyrosine kinases. One feature of Lck's unique domain is serine 59, which is phosphorylated by the serine/threonine proline-directed Erk MAP kinase. Cells that expressing a mutant form of Lck with the serine 59 residue replaced by glutamic acid exhibit a signaling defect. When stimulated with anti-CD3å these cells no longer support the phosphorylation of tyrosine 319 in Zap-70. This phosphorylation event has been correlated with Zap-70 activation. Despite the fact that Zap-70 phosphorylation was impaired in S59DLck expressing cells, these cells were still able to support Erk phosphorylation. This project interrogated the mechanism underlying the ability of S59DLck expressing cells to activate the Ras/Raf/Mek/Erk signaling pathway in the absence of supporting Zap-70 tyrosine 319 phosphorylation. In particular, I investigated the activation status of PLC-γ, a downstream effector of Zap-70 signaling. Following stimulation through the TCR, S59DLck expressing cells showed no defect in the activation of PLC-γ, indicating that the phosphorylation fo tyrosine 319 in Zap-70 is not necessary for the activation of PLC-γ and its downstream effectors.

Degree

M.S.

Advisors

Harrison, Purdue University.

Subject Area

Immunology

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