Conditional Astroglial Rictor Overexpression Induces Malignant Glioma in Mice

Abstract

BackgroundHyperactivation of the mTORC2 signaling pathway has been shown to contribute to the oncogenic properties of gliomas. Moreover, overexpression of the mTORC2 regulatory subunit Rictor has been associated with increased proliferation and invasive character of these tumor cells.Methodology/Principal FindingsTo determine whether Rictor overexpression was sufficient to induce glioma formation in mice, we inserted a Cre-lox-regulated human Rictor transgene into the murine ROSA26 locus. This floxed Rictor strain was crossed with mice expressing the Cre recombinase driven from the glial fibrillary acidic protein (GFAP) promoter whose expression is limited to the glial cell compartment. Double transgenic GFAP-Cre/RictorloxP/loxP mice developed multifocal infiltrating glioma containing elevated mTORC2 activity and typically involved the subventricular zone (SVZ) and lateral ventricle. Analysis of Rictor-dependent signaling in these tumors demonstrated that in addition to elevated mTORC2 activity, an mTORC2-independent marker of cortical actin network function, was also elevated. Upon histological examination of the neoplasms, many displayed oligodendroglioma-like phenotypes and expressed markers associated with oligodendroglial lineage tumors. To determine whether upstream oncogenic EGFRvIII signaling would alter tumor phenotypes observed in the GFAP-Cre/RictorloxP/loxP mice, transgenic GFAP-EGFRvIII; GFAP-Cre/RictorloxP/loxP mice were generated. These mice developed mixed astrocytic-oligodendroglial tumors, however glioma formation was accelerated and correlated with increased mTORC2 activity. Additionally, the subventricular zone within the GFAP-Cre/RictorloxP/loxP mouse brain was markedly expanded, and a further proliferation within this compartment of the brain was observed in transgenic GFAP-EGFRvIII; GFAP-Cre/RictorloxP/loxP mice.Conclusion/SignificanceThese data collectively establish Rictor as a novel oncoprotein and support the role of dysregulated Rictor expression in gliomagenesis via mTOR-dependent and mTOR-independent mechanisms. Furthermore, oncogenic EGFRvIII signaling appears to potentiate the in vivo proliferative capacity of GFAP-Cre/RictorloxP/loxP gliomas.

Phosphorylation of the Hippo Pathway Component AMOTL2 by the mTORC2 Kinase Promotes YAP Signaling, Resulting in Enhanced Glioblastoma Growth and Invasiveness

“…We and others (3,4) have demonstrated increased expression of Rictor in GBM. This results in hyperactivated mTORC2 signaling leading to accelerated GBM growth, motility, and invasive characteristics (3,5).…”

“…In this study, we utilized a recently developed GEM model, in which glial fibrillary acidic protein Cre (Gfap-Cre)-mediated conditional Rictor overexpression induced intermediate grade gliomas (5). Using a retroviral gene-trapping strategy to identify modifiers that accelerate transformation and growth of cell lines derived from gliomas from these mice, we identified AMOTL2 as a relevant signaling node linking mTOR complex 2 (mTORC2) signaling and the Hippo pathway.…”

“…These cells are derived from glial tumors from Gfap-Rictor mice and overexpress Rictor resulting in heightened mTORC2 activity (5). A retroviral gene trap cassette (Fig.…”

Overexpression of Rictor protein in colorectal cancer is correlated with tumor progression and prognosis

“…Blocking Rictor phosphorylation, which was able to lessen the inhibition of the mTORC2-Akt signaling pathway, was applied to stop tumor progression and cancer cell proliferation (17). Bashir et al reported that the Rictor gene was involved in cancer cell proliferation in malignant glioma and had a high recurrence rate in hepatic carcinoma (18). A previous study indicated that integrin-linked kinase (ILK), a focal adhesion adaptor, is an STK that regulates cell proliferation, survival and EMT.…”

Evaluation of function of RICTOR gene in gga-mir-142-3pknockdowned developing chicken embryo

“…Studies in mice also reported that over expression of RICTOR gene was associated with increased proliferation of cells along with invasion of tumor cells (Bashir et al, 2012). Mammalian TORC2 plays a role in actin cytoskeleton reorganization and similar to yeast TORC2, the Rho-type GTPases were involved in these functions.…”