Phosphatidylinositol 3-kinase/AKT pathway activation in human vestibular schwannoma.
OBJECTIVE
The neurofibromatosis 2 gene, which encodes the tumor suppressor protein merlin, is frequently mutated in vestibular schwannomas (VS). Merlin can inhibit phosphatidylinositol 3 kinase (PI3 kinase) by binding to PI3 kinase enhancer long isoform. Therefore, we hypothesized that the PI3 kinase/AKT pathway is activated in VS.


BACKGROUND
Despite advances in diagnosis and treatment, VS continue to cause patient morbidity. A more thorough understanding of the signaling pathways deregulated in VS will aid in the development of novel medical therapeutics. Activation of the PI3 kinase/AKT pathway increases cell survival and cell proliferation and has been observed in a variety of human cancers. However, whether the PI3 kinase/AKT pathway is activated in human VS has not been reported.


METHODS
Complementary deoxyribonucleic acid microarrays were performed using cultured Schwann cells, 4 VS specimens, and 2 paired normal vestibular nerves. Immunohistochemical analysis using antibodies to activated phosphorylated-AKT was performed on 14 VS tissue sections. Western blots using various antibodies to components of the PI3 kinase/AKT pathways were conducted.


RESULTS
Microarray analysis demonstrated that total AKT gene expression was upregulated in VS, compared with normal vestibular nerves. Immunohistochemical analysis of 14 VS tissue sections detected positive staining for activated AKT phosphorylated at both serine-473 and threonine-308 in all tumors. Western blots comparing VS specimens with normal vestibular nerves showed that the AKT pathway was activated in VS but not in normal nerve. Total AKT, phosphorylated-AKT, PI3-kinase, phosphorylated-phosphatase and tensin homologue deleted on chromosome 10, phosphorylated-phosphoinositide-dependent protein kinase 1, phosphorylated-forkhead box O, phosphorylated-glycogen synthase kinase 3beta, and phosphorylated-mammalian target of rapamycin were upregulated in VS.


CONCLUSIONS
The PI3 kinase/AKT pathway is activated in VS. Using our recently reported quantifiable VS xenograft model, novel inhibitors of the PI3 kinase/AKT pathway may be tested for VS growth inhibition in vivo.
Jacob
Abraham
A
Department of Otolaryngology, The Ohio State University, Columbus, and Center for Childhood Cancer, Research Institute at Nationwide Children's Hospital, Department of Pediatrics 43210, USA. Abraham.jacob@osumc.edu
Lee
Tina X
TX
Neff
Brian A
BA
Miller
Shyra
S
Welling
Bradley
B
Chang
Long-Sheng
LS
D015153:Blotting, Western; D005576:Colforsin / Q000494:pharmacology; D004273:DNA, Neoplasm / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D009464:Neuroma, Acoustic / Q000235:genetics* / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D051058:Oncogene Protein v-akt / Q000235:genetics*; D016612:Paraffin Embedding; D010524:Peripheral Nervous System Neoplasms / Q000235:genetics* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D015398:Signal Transduction / Q000502:physiology*; D014404:Tubulin / Q000235:genetics; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D004273:DNA, Neoplasm; D014404:Tubulin; D005576:Colforsin; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt