A Drosophila Model for EGFR-Ras and PI3K-Dependent Human Glioma

Abstract

Gliomas, the most common malignant tumors of the nervous system, frequently harbor mutations that activate the epidermal growth factor receptor (EGFR) and phosphatidylinositol-3 kinase (PI3K) signaling pathways. To investigate the genetic basis of this disease, we developed a glioma model in Drosophila. We found that constitutive coactivation of EGFR-Ras and PI3K pathways in Drosophila glia and glial precursors gives rise to neoplastic, invasive glial cells that create transplantable tumor-like growths, mimicking human glioma. Our model represents a robust organotypic and cell-type-specific Drosophila cancer model in which malignant cells are created by mutations in signature genes and pathways thought to be driving forces in a homologous human cancer. Genetic analyses demonstrated that EGFR and PI3K initiate malignant neoplastic transformation via a combinatorial genetic network composed primarily of other pathways commonly mutated or activated in human glioma, including the Tor, Myc, G1 Cyclins-Cdks, and Rb-E2F pathways. This network acts synergistically to coordinately stimulate cell cycle entry and progression, protein translation, and inappropriate cellular growth and migration. In particular, we found that the fly orthologs of CyclinE, Cdc25, and Myc are key rate-limiting genes required for glial neoplasia. Moreover, orthologs of Sin1, Rictor, and Cdk4 are genes required only for abnormal neoplastic glial proliferation but not for glial development. These and other genes within this network may represent important therapeutic targets in human glioma.

Loss of PI3K blocks cell-cycle progression in a Drosophila tumor model

“…When we expressed an RNAi transgene targeting the negative PI3K pathway regulator, PI 3-phosphatase (Pten), we observed an increase in tumor size (Figures 1a and d) (Read et al, 2009). Again, the effects were much milder in wild-type tissues where PTEN RNAi only caused slight overgrowth (Figures 1e and h) (Read et al, 2009). Ras V12 , Dlg RNAi tumors are thus highly sensitive to perturbations in PI3K signaling.…”

“…Clones have the following genotypes: (i) Ras V12 , Dlg RNAi expression in wild-type clones and (j) Ras V12 , Dlg RNAi expression in clones homozygous mutant for PI3K (k) wild-type clones (l) clones homozygous mutant for PI3K. When we expressed an RNAi transgene targeting the negative PI3K pathway regulator, PI 3-phosphatase (Pten), we observed an increase in tumor size (Figures 1a and d) (Read et al, 2009). Again, the effects were much milder in wild-type tissues where PTEN RNAi only caused slight overgrowth (Figures 1e and h) (Read et al, 2009).…”

Axonal wrapping in theDrosophilaPNS is controlled by glia-derived neuregulin homolog Vein

“…To further validate these results, we performed gain-offunction experiments. Whereas the panglial expression of activated EGF receptor (λtop) results in the induction of cell proliferation in peripheral nerves (Read et al, 2009;Witte et al, 2009), the expression of activated EGF receptor only in the wrapping glia does not alter wrapping glial cell number (n=5 animals, counts of nrv2lamGFPEGFR λtop -positive nuclei in ten nerves per animal). In addition, we determined the ultrastructure and analyzed nine nerves of four animals.…”

Signalling Pathways in Development and Human Disease: A Drosophila Wing Perspective

“…In addition to genetic searches, Drosophila also permits to recapitulate the biology of particular diseases in vivo systems, an approach that is been applied to the study of tumorigenesis using among other tissues the imaginal discs (Janic et al, 2010). In this manner Drosophila tissues can be used not only to track down the steps leading to tumour initiation, progression and metastasis in vivo, but also to manipulate in genetic mosaics the activity of genes leading to tumoral growth and to assay therapeutic drugs (Kango-Singh and Halder, 2004;Vidal and Cagan, 2006;Jang et al, 2007;Januschke and Gonzalez, 2008;Read et al, 2009;Caldeira et al, 2009;Das and Cagan, 2010;Bina et al, 2010;Wu et al, 2010). This approach is contributing to dissect the effects of tumour-promoting and tumour-suppressing genes in the regulation of proliferation, apoptosis, cell-adhesion, trafficking and cell polarity, and revealed the importance of cellular interactions in the outcome of tumoral progression.…”