PIK3R3 and medulloblastoma: However, mRNA transcripts for components of the PI-3 kinase enzyme complex, Pik3r3 and Pik3cb, and downstream targets of PI-3 kinase signaling, Mapk8 (Jnk) and Frap1 were up regulated 2.8, 1.9, 1.5, and 1.2-fold, respectively (Figure 2C,Table S3) in Pten deficient medulloblastomas.