miR-7 inhibits glioblastoma growth by simultaneously interfering with the PI3K/ATK and Raf/MEK/ERK pathways

Abstract

Epidermal growth factor receptor (EGFR) signaling regulates glioblastoma cell proliferation, survival, migration and invasion and plays a key role in tumor progression. We show that microRNA-7 (miR-7) is a common regulator of the phosphoinositide-3-kinase (PI3K)/ATK and Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathways, both of which are launched by EGFR through its two direct targets, the transcription factors PI3K and Raf-1, respectively. Enforced expression of miR-7 markedly decreased expression of PI3K, phosphorylated Akt, Raf-1, phosphorylated MEK 1/2, and cyclin D1, as well as slightly reduced expression of EGFR. Forced expression of PI3K or Raf-1 transcripts lacking the 3'-untranslated region (3'-UTR) partially reversed the effects of miR-7 on cell growth inhibition and cell cycle arrest in glioma cells. Additionally, transient expression of miR-7 in glioblastoma cells strongly inhibited in vivo glioblastoma xenograft growth. We conclude that miR-7 is a potential tumor suppressor in glioblastoma that acts by targeting multiple oncogenes related to the downstream pathway of EGFR and may serve as a novel therapeutic target for malignant gliomas.