SLAP, a dimeric adapter protein, plays a functional role in T cell receptor signaling

Abstract

Engagement of the T cell antigen receptor (TCR) leads to rapid activation of protein tyrosine kinases, which in turn phosphorylate downstream enzymes and adapter proteins. Some adapter proteins, such as SLP-76, Vav, and LAT, positively regulate TCR-mediated signal transduction, whereas others, such as Cbl, play an inhibitory role. SLAP (Src-like adapter protein), an adapter protein containing a Src homology 3 and a Src homology 2 domain, was isolated from a yeast interacting screen by using N-terminal Cbl as bait. N-terminal Cbl interacts with SLAP in vivo and in vitro in a tyrosine phosphorylation-independent manner. We observed that SLAP is expressed in T cells, and upon TCR activation, SLAP interacts with ZAP-70, Syk, LAT, and TCR chain in Jurkat T cells. In transiently transfected COS-7 cells, SLAP forms separate complexes with ZAP-70, Syk, and LAT through its Src homology 2 domain. Overexpression of a C-terminal-truncated SLAP mutant down-regulates nuclear factor of activated T cells-AP1 activity. We have evidence that SLAP forms homodimers through its C-terminal region. Serial truncations and mutations in the C terminus of SLAP demonstrate that there is a correlation between the loss of dimerization and the inhibition of nuclear factor of activated T cells-AP1 activity. The in vivo association of SLAP with key signaling molecules and its inhibition of T cell activation suggests that SLAP plays an important role in TCR-mediated signal transduction.

c-Cbl-facilitated cytoskeletal effects in v-Abl-transformed fibroblasts are regulated by membrane association of c-Cbl

“…SLAP was a good candidate having been identified as a binding partner of c-Cbl TKB-independent of tyrosine phosphorylation. Furthermore, SLAP is myristoylated and binds to the membrane (Tang et al, 1999;Manes et al, 2000). Binding of SLAP with c-Cbl was confirmed to be independent of the SH2-type TKB interactions and to enhance membrane association of c-Cbl (Figure 4).…”

“…It has been shown previously that Src-like adaptor protein (SLAP), a ubiquitously expressed, membrane-associated, SH2-and SH3-containing adaptor, binds to the N-terminus of Cbl in a TKB/phosphotyrosine-independent manner (Pandey et al, 1995;Tang et al, 1999;Manes et al, 2000). The c-Cbl-binding region was mapped to the C-terminal portion of SLAP.…”

“…Functional cooperation between SLAP and c-Cbl is required for SLAP-facilitated increase in cell spreading and adhesion SLAP interacts with multiple proteins, including Vav and several PTKs (Roche et al, 1998;Tang et al, 1999;Sosinowski et al, 2000). Some of these proteins have been implicated in the regulation of cytoskeletal events.…”

Src-like adaptor protein (SLAP) regulates B cell receptor levels in a c-Cbl-dependent manner

“…Insights into how SLAP regulates TCR levels were obtained from studies where SLAP was shown to associate with c-Cbl in vitro (3,13). Interestingly, mice deficient in c-Cbl, SLAP, or both have similar thymic phenotypes, suggesting that SLAP and c-Cbl may function in the same biochemical pathway (14)(15)(16).…”

“…Src-like adaptor protein (SLAP) is a protein that regulates lymphocyte signaling pathways (3,4). The N terminus of SLAP has sequence and domain similarity to Src family kinases, containing Src homology 3 (SH3) and SH2 domains that are able to bind to activated components of the T cell receptor (TCR) complex (5).…”