mTOR inhibition and levels of the DNA repair protein MGMT in T98G glioblastoma cells

Molecular Cancer

Research

Sarah Smalley¹  Simon J Morley¹  Anthony J Chalmers² 

[1] Department of Biochemistry, School of Life Sciences, University of Sussex, BN1 9QG, Brighton, UK;University of Glasgow, Beatson Institute for Cancer Research and Beatson West of Scotland Cancer Centre, 1053 Great Western Road, G12 0YN, Glasgow, UK;

关键词: MGMT;    Stability;    Translation;    mTOR;    Initiation of translation;    KU0063794;    Glioblastoma;    TMZ resistance;   

DOI  :  10.1186/1476-4598-13-144

 received in 2014-03-03, accepted in 2014-05-30,  发布年份 2014

来源: Springer

【 摘 要 】

BackgroundGlioblastoma multiforme (GBM), the most common and most aggressive type of primary adult brain tumour, responds poorly to conventional treatment. Temozolomide (TMZ) chemotherapy remains the most commonly used treatment, despite a large proportion of tumours displaying TMZ resistance. 60% of GBM tumours have unmethylated MGMT promoter regions, resulting in an overexpression of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT), which is responsible for tumour resistance to TMZ chemotherapy. Tumours also often exhibit hyperactive PI3-kinase/mTOR signalling, which enables them to resynthesise proteins quickly. Since MGMT is a suicide protein that is degraded upon binding to and repairing TMZ-induced O6-methylguanine adducts, it has been hypothesized that inhibition of translation via the mTOR signalling pathway could generate a tumour-specific reduction in MGMT protein and increase TMZ sensitivity.MethodsMGMT was monitored at the post-transcriptional, translational and protein levels, to determine what effect mTOR inhibition was having on MGMT protein expression in vitro.ResultsWe show that inhibiting mTOR signalling is indeed associated with acute inhibition of protein synthesis. Western blots show that despite this, relative to loading control proteins, steady state levels of MGMT protein increased and MGMT mRNA was retained in heavy polysomes. Whilst TMZ treatment resulted in maintained MGMT protein levels, concomitant treatment of T98G cells with TMZ and KU0063794 resulted in increased MGMT protein levels without changes in total mRNA levels.ConclusionsThese in vitro data suggest that, counterintuitively, mTOR inhibition may not be a useful adjunct to TMZ therapy and that more investigation is needed before applying mTOR inhibitors in a clinical setting.

【 授权许可】

CC BY   
© Smalley et al.; licensee BioMed Central Ltd. 2014