Leukocyte tyrosine kinase (LTK) receptor is an orphan receptor with a tyrosine-protein kinase activity [, , ]. This receptor is activated by ALKAL1 or ALKAL2 ligands at the cell surface and transduces an extracellular signal into an intracellular response [, ]. Ligand-binding to the extracellular domain induces tyrosine kinase activation, leading to activation of the mitogen-activated protein kinase (MAPK) pathway [].The exact function of this protein is not known. Studies with chimeric proteins (replacing its extracellular region with that of several known growth factor receptors, such as EGFR and CSFIR) demonstrate its ability to promote growth and specifically neurite outgrowth, and cell survival. LTK is involved in regulation of the secretory pathway involving endoplasmic reticulum (ER) export sites (ERESs) and ER to Golgi transport [, , ].
