Plasmids expressing CCN1, wild-type PIK3R1, mutant PIK3R1, or a combination of these plasmids were transfected into U87MG glioma cells, which carry low CCN1 expression29, no PIK3R1 somatic mutations30 and PIK3R1Met326Ile germline mutation (Fig. 6A). Here, PIK3R1 is linked to central nervous system cancer.