The CYT1 isoforms of ERBB4 possess a C-tail tyrosine residue that, upon trans-autophosphorylation, serves as a docking site for the p85 alpha subunit of PI3K - PIK3R1 (Kaushansky et al. 2008, Cohen et al. 1996). Binding of PIK3R1 to CYT1 isoforms of ERBB4 is followed by recruitment of the p110 catalytic subunit of PI3K (PIK3CA), leading to assembly of an active PI3K complex that converts PIP2 to PIP3 and activates AKT signaling (Kainulainen et al. 2000).