GRK3 and glioblastoma: GRK3 expression is down-regulated by EGFR signaling in GBM compared to normal astrocytes, which leads to a corresponding increase in tumor growth.[14] Published data by others have also shown that down-regulation of GRK6 in medulloblastoma [15] and Lewis lung carcinoma [60] can similarly regulate tumor size, migration, and metastasis.