SKAP55 Negatively Regulates T Cell Receptor Signaling

Burnham Institute For Medical Research, La Jolla CA

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Abstract

DESCRIPTION (provided by applicant): Engagement of the T cell antigen receptor (TCR) initiates a cascade of signaling events that ultimately leads to cytokine gene expression, cellular proliferation and induction of T-cell effector functions. Non-receptor protein tyrosine kinases (PTKs) link the TCR with proximal signaling events through tyrosine phosphorylation of multiple adapter and effector proteins. These events lead to the activation of multiple biochemical pathways in the cytoplasm and signals to the nucleus. One of the key cytoplasmic enzymes activated upon TCR ligation by the PTKs is phospholipase C-gamma1 (PLC-gamma1). The enzymatic role of PLC-gamma1 in generating second messengers has been well documented. More recently, studies done using genetically deficient Jurkat T cell lines and gene-targeted mice have shown that optimal tyrosine phosphorylation of PLC-gamma1 requires the activity of multiple PTKs and adapter proteins. We have identified the adapter SKAP-HOM in a three-hybrid screen designed to find phosphoproteins that interact with PLC-gamma1. Using the powerful new technique of siRNA, we have knocked down expression ot SKAP55, a SKAP-HOM related protein, in Jurkat T cells and found a novel role for this adapter as a negative regulator of TCR signaling. The specific aims of this proposal are: (1) to elucidate the molecular mechanism by which SKAP55 negatively regulates PLC-gamma1 signaling in the Jurkat T cell line (2) to determine the basis of the SKAP55-PLC-gamma1 interaction and the role of the SKAP55 PH domain (3) to use knock-down technology to explore the function of SKAP55 and SKAP-HOM in non-transformed human T cells.