Glioma is formed by active Akt1 alone and promoted by active Rad in transgenic zebrafish

摘要

Background. Ongoing characterization of glioma has revealed that Akt signaling plays a crucial role in glioma -genesis. In mouse models, however, Akt alone was not sufficient to induce glioma.Methods. We established transgenic zebrafish that overexpressed dominant-active (DA) human Aktl or Racl v (DARac1) at ptfla domain and investigated transgenic phenotypes and mechanisms leading to glio-magenesis.Results. Transgene expressions were spatiotemporally restricted without any developmental abnormality of embryos and persisted at cerebellum and medulla in adult zebrafish. DAAkt1 alone induced glioma (with visible bumps at the head), with incidences of 36.6% and 49% at 6 and 9 months, respectively. Histologically, gliomas showed various histologic grades, increased proliferation, and frequent invasion into the fourth ventricle. Preferential location of small tumors at periventricular area and coexpression of Her4 suggested that tumors originated from Ptfla- and Her4-positive progenitor cells at ventricular zone. Gliomagenesis was principally mediated by activation of survival pathway through upregulation of survivin genes. Although DARac1 alone was incapable of gliomagenesis, when coexpressed with DAAkt1, gliomagenesis was accelerated, showing higher tumor incidences (62.0% and 73.3% at 6 and 9 months, respectively), advanced histologic grade, invasiveness, and shortened survival. DARac1 upregulated survivin2, cyclin D1,β-catenin, and snail la but downregulated E-cadherin, indicating that DARac1 promotes gliomagenesis by enhancing proliferation, survival, and epithelial-to-mesenchymal transition. On pharmacologic tests, only Akt 1/2 inhibitor effectively suppressed gliomagenesis, inhibited cellular proliferation, and induced apoptosis in established gliomas.Conclusions. The zebrafish model reinforces the pivotal role of Akt signaling in gliomagenesis and suggests Racl as an important protein involved in progression.