PTK7/CCK4
PTK7, historically called CCK4, is a receptor of the tyrosine kinase family whose intracellular kinase domain lacks several catalytic residues and shows little or no measurable activity, effectively making it a pseudokinase that signals through protein-protein interactions. Its extracellular region carries seven immunoglobulin-like domains, and the full-length receptor is cleaved by membrane-type metalloproteases to release a soluble ectodomain. PTK7 participates in Wnt/planar cell polarity signaling during development, and its loss produces neural tube and planar polarity defects in model organisms. Highly expressed in colon carcinoma, acute myeloid leukemia, and other malignancies, PTK7 is the target of antibody-drug conjugate and CAR-T programs in clinical development.
