The nuclear receptor NR2E1/TLX controls senescence
Ana O'Loghlen1,2, Nadine Martin1, Benjamin Krusche3
1Cell Proliferation Group, MRC Clinical Sciences Centre, Imperial College London, Hammersmith Campus, London W12 0NN, UK.
Abstract:
The nuclear receptor NR2E1 (also known as TLX or tailless) controls the self-renewal of neural stem cells (NSCs) and has been implied as an oncogene which initiates brain tumors including glioblastomas. Despite NR2E1 regulating targets like p21(CIP1) or PTEN we still lack a full explanation for its role in NSC self-renewal and tumorigenesis. We know that polycomb repressive complexes also control stem cell self-renewal and tumorigenesis, but so far, no formal connection has been established between NR2E1 and PRCs. In a screen for transcription factors regulating the expression of the polycomb protein CBX7, we identified NR2E1 as one of its more prominent regulators. NR2E1 binds at the CBX7 promoter, inducing its expression. Notably CBX7 represses NR2E1 as part of a regulatory loop. Ectopic NR2E1 expression inhibits cellular senescence, extending cellular lifespan in fibroblasts via CBX7-mediated regulation of p16(INK4a) and direct repression of p21(CIP1). In addition NR2E1 expression also counteracts oncogene-induced senescence. The importance of NR2E1 to restrain senescence is highlighted through the process of knocking down its expression, which causes premature senescence in human fibroblasts and epithelial cells. We also confirmed that NR2E1 regulates CBX7 and restrains senescence in NSCs. Finally, we observed that the expression of NR2E1 directly correlates with that of CBX7 in human glioblastoma multiforme. Overall we identified control of senescence and regulation of polycomb action as two possible mechanisms that can join those so far invoked to explain the role of NR2E1 in control of NSC self-renewal and cancer.
Insights
The nuclear receptor NR2E1 (also known as TLX) regulates neural stem cell self-renewal and brain tumor initiation by controlling senescence and polycomb repressive complexes, notably CBX7.
Area of Science:
- Molecular Biology
- Stem Cell Biology
- Cancer Research
Background:
- The nuclear receptor NR2E1 (TLX) is crucial for neural stem cell (NSC) self-renewal and implicated in brain tumor development.
- Existing knowledge on NR2E1's role in NSC self-renewal and tumorigenesis is incomplete, particularly regarding its connection to polycomb repressive complexes (PRCs).
Purpose of the Study:
- To investigate the regulatory relationship between NR2E1 and PRCs.
- To elucidate the mechanisms underlying NR2E1's function in NSC self-renewal and tumorigenesis, focusing on senescence and polycomb action.
Main Methods:
- Screening for transcription factors regulating CBX7 expression.
- Analyzing NR2E1 binding to the CBX7 promoter.
- Assessing the impact of NR2E1 and CBX7 on cellular senescence.
- Evaluating NR2E1 and CBX7 expression in human glioblastoma samples.
Main Results:
- NR2E1 directly binds to and induces the expression of CBX7, a component of PRCs.
- A feedback loop exists where CBX7 represses NR2E1.
- NR2E1 inhibits cellular senescence and extends cell lifespan by regulating p16(INK4a) and repressing p21(CIP1).
- NR2E1 knockdown induces premature senescence in human cells and NSCs.
- NR2E1 expression positively correlates with CBX7 expression in glioblastoma.
Conclusions:
- NR2E1 regulates CBX7, linking NR2E1 to polycomb repressive complex function.
- NR2E1's role in restraining senescence is a key mechanism in NSC self-renewal and cancer suppression.
- These findings provide novel insights into NR2E1's multifaceted roles in stem cell biology and oncogenesis.
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