ERBB4s80 binds STAT5A through STAT5A SH2 domain. This interaction likely depends on STAT5A activation induced by prolactin and mediated by JAK2. Heterodimers of prolactin receptor (PRLR) and JAK2 are activated by prolactin binding, resulting in STAT5 recruitment and phosphorylation, and subsequent formation of phosphorylated STAT5 homodimers. There is evidence that ERBB4 may be part of the PRLR:JAK2 complex and that it may be activated by JAK2-mediated phosphorylation, in the absence of ERBB4 growth factors (Muraoka-Cook et al. 2008).