ABSTRACT
Eukaryotic translation initiation factor 4E binding protein 1 (EIF4EBP1) encodes the 4EBP1 protein, a negative regulator of mRNA translation and a substrate of the mechanistic target of rapamycin (mTOR), whose function and relevance in cancer is still under debate. Here, we analyzed EIF4EBP1 expression in different glioma patient cohorts and investigated its mode of transcriptional regulation in glioblastoma cells. We verified that EIF4EBP1 mRNA is overexpressed in malignant gliomas, including isocitrate dehydrogenase (IDH)-wildtype glioblastomas, relative to non-neoplastic brain tissue in multiple publically available datasets. Our analyses revealed that EIF4EBP1 overexpression in malignant gliomas is neither due to gene amplification nor to altered DNA methylation, but rather results from aberrant transcriptional activation by distinct transcription factors. We found seven transcription factor candidates co-expressed with EIF4EBP1 in gliomas and bound to the EIF4EBP1 promoter, as revealed by chromatin immunoprecipitation (ChIP)-sequencing data. We investigated the ability of these candidates to activate the EIF4EBP1 promoter using luciferase reporter assays, which supported four transcription factors as candidate EIF4EBP1 regulators, namely MYBL2, ETS1, HIF-1A, and E2F6. Finally, by employing transient knock-down experiments to repress either of these transcription factors, we identified MYBL2 and ETS1 as the relevant transcriptional drivers of enhanced EIF4EBP1 expression in malignant glioma cells. Taken together, our findings confirm enhanced expression of EIF4EBP1 in malignant gliomas relative to non-neoplastic brain tissue and characterize the underlying molecular pathomechanisms.
ABSTRACT
Neuroblastoma (NB) accounts for 15% of cancer-related deaths in childhood despite considerable therapeutic improvements. While several risk factors, including MYCN amplification and alterations in RAS and p53 pathway genes, have been defined in NB, the clinical outcome is very variable and difficult to predict. Since genes of the mechanistic target of rapamycin (mTOR) pathway are upregulated in MYCN-amplified NB, we aimed to define the predictive value of the mTOR substrate-encoding gene eukaryotic translation initiation factor 4E-binding protein 1 (EIF4EBP1) expression in NB patients. Using publicly available data sets, we found that EIF4EBP1 mRNA expression is positively correlated with MYCN expression and elevated in stage 4 and high-risk NB patients. In addition, high EIF4EBP1 mRNA expression is associated with reduced overall and event-free survival in the entire group of NB patients in three cohorts, as well as in stage 4 and high-risk patients. This was confirmed by monitoring the clinical value of 4EBP1 protein expression, which revealed that high levels of 4EBP1 are significantly associated with prognostically unfavorable NB histology. Finally, functional analyses revealed that EIF4EBP1 expression is transcriptionally controlled by MYCN binding to the EIF4EBP1 promoter in NB cells. Our data highlight that EIF4EBP1 is a direct transcriptional target of MYCN whose high expression is associated with poor prognosis in NB patients. Therefore, EIF4EBP1 may serve to better stratify patients with NB.
ABSTRACT
Osteoporosis is characterized by reduced bone mineral density (BMD) and increased bone fragility, which may be modified by lifestyle behaviors. In observational studies, chronic moderate ethanol consumption is associated with higher BMD, but results are inconsistent and underlying mechanisms are unknown. To understand the influence of chronic ethanol consumption on true bone density (Archimedes principal), bone mechanical properties (Young's Modulus of bend), and osteogenic gene expression, 12-month-old male Wistar rats were randomly assigned to a control group or ethanol intervention (20% ethanol in drinking water on alternate days) group for 13 weeks and tibiae and femurs were collected. Blood was collected to assess alcohol content and antioxidant enzyme activities. We hypothesized that chronic ethanol consumption would increase true bone density and mechanical properties and increase osteoblastic gene expression and serum antioxidant enzyme activity. Ethanol consumption did not influence femoral or tibial true bone density but did result in lower tibial Young's modulus of bend (p = 0.0002). However, there was no influence of ethanol on other measures of mechanical properties. Femoral pro-osteoclastic gene expression of Dkk1 was lower (p = 0.0006) and pro-osteoblastic gene expression of Ctnnb1 was higher (p = 0.02) with ethanol consumption. We observed no differences in circulating antioxidant activities between groups, other than a tendency for greater (p = 0.08) glutathione peroxidase in the ethanol group. Results showed chronic ethanol consumption did not influence true bone density, only modestly reduced tibial mechanical properties (lower Young's modulus of bend), and moderately impacted expression of genes within the femur known to regulate both osteoblast and osteoclast activities.