Orphan receptor tyrosine kinase (RTK) that plays a role in epithelial cell differentiation and regionalization of the proximal epididymal epithelium. May activate several downstream signaling pathways related to cell differentiation, proliferation, growth and survival including the PI3 kinase-mTOR signaling pathway. Mediates the phosphorylation of PTPN11, an activator of this pathway. May also phosphorylate and activate the transcription factor STAT3 to control anchorage-independent cell growth. Mediates the phosphorylation and the activation of VAV3, a guanine nucleotide exchange factor regulating cell morphology. May activate other downstream signaling proteins including AKT1, MAPK1, MAPK3, IRS1, and PLCG2. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Inhibited by dephosphorylation by PTPN6. Interacts with PTPN11; may activate the PI3 kinase-mTOR signaling pathway. Interacts with VAV3; constitutive interaction mediating VAV3 phosphorylation (By similarity). Interacts with PTPN6 (via SH2 1 domain); the interaction is direct and promotes ROS1 dephosphorylation. Expressed by epithelial cells of the caput epididymis (at protein level). Phosphorylated. Probably autophosphorylates. Phosphorylation at Tyr-2267 and/or Tyr-2327 recruits PTPN11 (By similarity). Phosphorylation at Tyr-2267 is required for the interaction with PTPN6 that mediates ROS1 dephosphorylation. Phosphorylation at Tyr-2267 stimulates the kinase activity and the activation of the ERK1 signaling cascade. Mice are viable and healthy. Females display normal fertility while males are sterile due a non-cell autonomous defect in sperm maturation. It is associated with the absence of tall columnar epithelial cells with long microvilli in the proximal part of the caput epididymidis. Belongs to the protein kinase superfamily. Tyr protein kinase family. Insulin receptor subfamily.