Phosphorylated SHC1 in a complex with the activated EPOR binds GRB2 bound to VAV1 (Hanazono et al. 1995, Hanazono et al. 1996, Odai et al. 1997). GRB2 exists in pre-assembled complexes with VAV1 (Hanazono et al. 1995), SOS1 (Odai et al. 1997), or CBL (Odai et al. 1997). VAV1 and SOS1 are guanine nucleotide exchange factors that activate the RAS signaling pathway.