Phosphorylation of ERBB2 on tyrosine residue Y877 by SRC family kinases significantly increases trans-autophosphorylation rate of ERBB2 heterodimers, presumably by enabling the kinase domain of ERBB2 to achieve a conformation that positively affects ERBB2 kinase activity. The downstream signaling of phosphorylated ERBB2 heterodimers that are phosphorylated on Y877 of ERBB2, in addition to the known trans-autophosphorylation sites, has not been studied extensively; it is assumed that the behavior of Y877-phosphorylated ERBB2 heterodimers is qualitatively similar to the behavior of trans-autophosphorylated ERBB2 heterodimers which do not harbor this modification.