ERBB4s80 interacts with a co-transcriptional activator YAP1 through its WW-domain binding motifs in the C-tail. Feng et al. established that the PY2 motif, present in CYT1 isoforms of ERBB4 only, has the highest affinity for YAP1 binding. PY1 and PY3 motifs, shared between CYT1 and CYT2 isoforms, have lower binding affinity for YAP1, with PY1 motif being the least important for YAP1 interaction (Komuro et al. 2003, Omerovic et al. 2004, Feng et al. 2009).