Cbl has been identified in ternary complexes with CRKL and C3G (RAPGEF1)(Reedquist et al. 1996) a Rap1 GEF, suggesting a role for Cbl in linking cytokine stimulation to Rap1 activation. Consistent with this, stimulation of NB-4 promyelocytic cells by IFN-gamma causes tyrosine phosphorylation and association of Cbl with CRKL followed by activation of Rap1 (Alsayed et al. 2000) and tyrosine phosphorylation of Cbl and its association with CRKL correlated with an increase in Rap 1 activity in anergic T cells (Boussiotis et al. 1997).