Aj. Dasilva et al., BIOCHEMICAL-ANALYSIS OF P120 130 - A PROTEIN-TYROSINE KINASE SUBSTRATE RESTRICTED TO T-CELLS AND MYELOID-CELLS/, The Journal of immunology, 158(5), 1997, pp. 2007-2016
T cell activation is mediated by a cascade of intracellular events inv
olving protein-tyrosine kinases and their substrates. p56(lck) and p59
(fyn) are protein-tyrosine kinases that associate with CD4/CD8 and the
TCR zeta/CD3 complex, respectively. We previously reported the appear
ance of a protein doublet at 120 and 130 kDa that preferentially assoc
iates with p59(fyn) and undergoes tyrosine phosphorylation upon recept
or ligation. In this paper, we demonstrate that p120/130 is a novel pr
otein that is restricted in expression to T cells, thymocytes and myel
oid cells. Internal peptide sequencing and immunoblotting using an ant
i-p120/130 antisera showed that p120/130 is a unique protein that is d
istinct from p130(cas) and p125(cbl). By contrast, p120 and p130 share
d similar peptide patterns and are structurally related. Alkaline phos
phatase digestion of precipitates showed that they are not related due
to phosphorylation. p120/130 was found to associate constitutively wi
th a 55-kDa protein of unknown identity, but which is distinct from p5
6(lck) and Shc. p120/130 also undergoes a unique kinetics of phosphory
lation and associates with the Ag receptor in response to TCR ligation
. In keeping with the association with p59(fyn), T cells from p59(fyn)
-negative mice exhibit reduced phosphorylation of the protein. p120/13
0 therefore represents a novel TCR associated intracellular molecule w
ith potential to play a role in T cell signaling.