AKT2-knockdown suppressed viability with enhanced apoptosis, and attenuated chemoresistance to temozolomide of human glioblastoma cells in vitro and in vivo

The AKT2 kinase (protein kinase Bβ) is overexpressed in high-grade gliomas. Upregulation of the AKT2 gene has been previously observed in glioblastoma patients suffering from chemotherapy failure and tumor progress. In this study, we aimed to evaluate the effect of AKT2 on viability and chemoresistance in the human glioblastoma cell line U251. The U251 cell line was stably transfected with short hairpin RNA (shRNA) targeting AKT2. U251 cells underexpressing AKT2 were then examined for viability with temozolomide (TMZ) treatment, and tested for cell apoptosis both in vitro and in tumor-implanted mice. Next, expressions of several chemoresistance-related molecules were measured by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and western blot analysis. The results showed that the 50% inhibitory concentration (IC(50)) of AKT2 shRNA-transfected cells was significantly lower compared with Lenti-GFP-transfected and nontransfected controls and that the tumor growth of the AKT2-shRNA and TMZ combined-treated mice was obviously suppressed in either mass or volume. Concomitantly, the apoptosis of TMZ-treated tumor cells was significantly enhanced after knockdown of AKT2, as measured by flow cytometry and in situ terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analysis. Furthermore, AKT2-inhibition in TMZ-treated glioblastoma U251 cells upregulated apoptotic effector caspase-3, whereas it downregulated antiapoptotic protein Bcl-2, DNA repairing protein MGMT, and drug efflux pump protein MRP1. Our study identified AKT2 as an important gene in presenting chemoresistance in glioblastoma, and a potential target to potentiate the clinical effect of chemotherapy in glioma treatment.