SRC-LIKE ADAPTER PROTEIN (SLAP) IS A NEGATIVE REGULATOR OF MITOGENESIS

The Src-like adaptor protein (Slap) is a recently identified adaptor p rotein containing Src homology 3 (SH3) and SH2 domains. Slap is found in a wide range of cell types and was shown to interact with the Eck r eceptor tyrosine kinase in a yeast two-hybrid interaction screen [1]. Here, we found that Slap is expressed in NIH3T3 cells and could associ ate with the activated platelet-derived growth factor (PDGF) receptor. Using mutated versions of the PDGF receptor and phosphopeptide compet ition experiments, we determined that Slap has the highest affinity fo r the Src-binding site of the PDGF receptor. Our inability to produce cell lines that stably expressed Slap suggested that Slap inhibited ce ll growth. We further investigated this issue by transiently expressin g Slap by microinjection, Overexpression of Slap by this method inhibi ted DNA synthesis induced by PDGF and serum, whereas overexpression of the adaptor proteins Grb2 and Shc did not. Finally, microinjection of a Slap antibody into NIH3T3 cells that had been stimulated with subop timal doses of growth factors potentiated the effects of the growth fa ctors. These data suggest that, unlike other adaptor proteins, Slap is a negative regulator of signalling initiated by growth factors.