PIK3CA and glioblastoma: Another subnetwork identified four genes, PTEN, PRKG2, MAPK8IP2, and ELK1. PTEN is a negative regulator of PI3K signaling [107,108], frequently dysregulated in GBM; the PRKG2 gene encodes cyclic guanosine monophosphate (cGMP)-dependent protein kinase II and is responsible for anti-proliferative signals in human gliomas [109]; the MAPK8IP2 gene encodes a JNK-interacting protein, influencing JNK and p38MAPK signaling [110], which are pivotal in GBM [111,112]; and ELK1 is a downstream target of PKCη-, and its activation results in increased proliferation in GBM cell lines [113].