CCK4
The CCK4 family of the protein-tyrosine kinase group centers on PTK7 (CCK4, colon carcinoma kinase 4), an immunoglobulin-superfamily receptor first identified through its overexpression in colon cancer. PTK7 carries seven extracellular Ig-like domains, a single transmembrane helix, and a kinase domain with substitutions at conserved catalytic positions, so its annotation alternates between weak kinase and pseudokinase across classification schemes. It functions in Wnt planar cell polarity signaling, cell adhesion, and migration, and proteolytic cleavage of its ectodomain releases biologically active fragments. High expression across many solid tumors makes PTK7 a target for CAR-T and antibody-drug conjugate programs.
