Km. Dennehy et al., THYMOCYTE ACTIVATION INDUCES THE ASSOCIATION OF THE PROTO-ONCOPROTEINC-CBL AND RAS GTPASE-ACTIVATING PROTEIN WITH CD5, European Journal of Immunology, 28(5), 1998, pp. 1617-1625
Studies of knockout mice indicate that the glycoprotein CD5, which is
expressed on T cells, most thymocytes and a subset of B cells, down-re
gulates TCR-and B cell receptor (BCR)-mediated signaling. CD5 is assoc
iated with the TCR and BCR, and is phosphorylated on cytoplasmic tyros
ine residues following antigen receptor ligation. Cross-linking of CD5
or pervanadate stimulation of thymocytes induces the association of a
120-kDa tyrosine-phosphorylated protein with CD5. The proto-oncoprote
in c-cbl associates with CD5 in pervanadate-stimulated thymocytes, and
reprecipitation analysis demonstrates that the major proportion of CD
5-associated pp120 is c-cbl. The GTPase-activating protein for ras (ra
s GAP), which is not tyrosine phosphorylated following CD5 cross-linki
ng, associates with CD5 in pervanadate-stimulated thymocytes. Using ty
rosine-phosphorylated peptides we show that ras GAP interacts in an SH
2-mediated manner with the phosphorylated Y429SQP sequence of CD5. Bot
h c-cbl and ras GAP have been proposed to suppress receptor-mediated s
ignaling, and may contribute to CD5-mediated suppression of TCR or BCR
signaling.