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 PTPN6 (via SH2 1 domain); the interaction is direct and promotes ROS1 dephosphorylation (By similarity). Interacts with PTPN11; may activate the PI3 kinase-mTOR signaling pathway. Interacts with VAV3; constitutive interaction mediating VAV3 phosphorylation. Expressed in brain. Expression is increased in primary gliomas. Phosphorylated. Probably autophosphorylates. Phosphorylation at Tyr-2274 is required for the interaction with PTPN6 that mediates ROS1 dephosphorylation (By similarity). Phosphorylation at Tyr-2274 stimulates the kinase activity and the activation of the ERK1 signaling cascade (By similarity). Phosphorylation at Tyr-2274 and/or Tyr-2334 recruits PTPN11. A chromosomal aberration involving ROS1 is found in a glioblastoma multiforme sample. An intra-chromosomal deletion del(6)(q21q21) is responsible for the formation of GOPC-ROS1 chimeric protein which is localized to the Golgi and has a constitutive receptor tyrosine kinase activity. A SLC34A2-ROS1 chimeric protein produced in non-small cell lung cancer cells also retains a constitutive kinase activity. A third type of chimeric protein CD74-ROS1 was also identified in those cells. Belongs to the protein kinase superfamily. Tyr protein kinase family. Insulin receptor subfamily.