FURIN and central nervous system cancer: Similar to other cell surface receptor proteins [18], [19], [28], we observed that PTPRK protein is sequentially processed in glioma by three cleavage events involving 1) a furin-like protease, yielding a PTPRK P-subunit fragment non-covalently attached to the extracellular domains, PTPRK E-subunit; 2) an α-secretase, yielding a PΔE subunit (P-subunit without most of the extracellular region); and, 3) further processing by a γ-secretase ultimately generates a PTPRK-intracellular domain (ICD) fragment (Fig. S2).