Adapter proteins FRS2 and FRS3 can both bind to the cytoplasmic tail of activated NTRK2 (TRKB) receptor, which is followed by NTRK2-mediated phosphorylation of FRS2 and FRS3. NTRK2 signaling through FRS3 has been poorly characterized (Easton et al. 1999, Yuen and Mobley 1999, Dixon et al. 2006, Zeng et al. 2014). Phosphorylated FRS2 is known to recruit GRB2 (presumably in complex with SOS1) and PTPN11 (SHP2) to activated NTRK2, leading to augmentation of RAS signaling (Easton et al. 1999, Easton 2006).