A protein that is highly related to GTPase-activating protein-associated p62 complexes with phospholipase Cγ

p62 is a highly tyrosyl phosphorylated protein that was first identified in immunoprecipitates of the GTPase-activating protein (GAP) of p21(ras) from cells transformed by oncogenic nonreceptor tyrosine kinases or stimulated through tyrosine kinase receptors (C. Ellis, M. Moran, F. McCormick, and T. Pawson, Nature 343:377-381, 1991). In this article we describe a highly related 62-kDa protein that becomes tyrosyl phosphorylated and associated with phospholipase Cγ (PLCγ) in C3H10T1/2 cells stimulated with epidermal growth factor (EGF) or transformed by v-src. GAP-associated and PLCγ- associated p62 comigrated in one-dimensional sodium dodecyl sulfate- polyacrylamide gel electrophoresis and exhibited nearly identical phosphotryptic peptide patterns. That the association of p62 with PLCγ was direct and not mediated through binding of GAP-p62 to PLCγ or to the EGF receptor (and coprecipitation of the receptor with PLCγ) was demonstrated by (i) the inability to detect GAP in PLCγ immunocomplexes or PLCγ in GAP immunocomplexes, (ii) the association of p62 with PLCγ in v-src-transformed cells in the absence of EGF stimulation, and (iii) in vitro solution binding and direct blotting of p62 with a glutathione S-transferase fusion protein containing the Src homology 2 (SH2) domains of PLCγ. Unlike GAP, whose N- terminal SH2 mediates the interaction between GAP and p62, PLCγ was found to require both its N- and C-terminal SH2 regions for p62 binding. These studies demonstrate that a protein identical to or highly related to GAP-associated p62 binds PLCγ and suggest a means by which 'cross-talk' between PLCγ- and GAP-mediated signalling may occur.