As suggested by the mRNA expression profiling of human glioblastomas26, the protein levels of PTPRZ-B, the major PTPRZ isoform in both glioblastoma cell lines6, 13, were 1.2-fold higher in C6 cells and 3.8-fold higher in U251 cells under sphere culture than under normal culture conditions (Fig. 1B). Here, PTPRZ1 is linked to glioblastoma.