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Updated: Mar 28, 2026
Techniques to Induce and Quantify Cellular Senescence
Published on: May 1, 2017
NSun2 delays replicative senescence by repressing p27 (KIP1) translation and elevating CDK1 translation
Hao Tang1, Xiuqin Fan1, Junyue Xing1
1Department of Biochemistry and Molecular Biology, Beijing Key Laboratory of Protein Posttranslational Modifications and Cell Function, School of Basic Medical Sciences, Peking University Health Science Center, Beijing 100191, China.
Abstract:
A rise in the levels of the cyclin-dependent kinase (CDK) inhibitor p27KIP1 is important for the growth arrest of senescent cells, but the mechanisms responsible for this increase are poorly understood. Here, we show that the tRNA methyltransferase NSun2 represses the expression of p27 in replicative senescence. NSun2 methylated the 5'-untranslated region (UTR) of p27 mRNA at cytosine C64 in vitro and in cells, thereby repressing the translation of p27. During replicative senescence, increased p27 protein levels were accompanied by decreased NSun2 protein levels. Knockdown of NSun2 in human diploid fibroblasts (HDFs) elevated p27 levels and reduced the expression of CDK1 (encoded by CDK1 mRNA, a previously reported target of NSun2), which in turn further repressed cell proliferation and accelerated replicative senescence, while overexpression of NSun2 exerted the opposite effect. Ectopic overexpression of the p27 5'UTR fragment rescued the effect of NSun2 overexpression in lowering p27, increasing CDK1, promoting cell proliferation, and delaying replicative senescence. Our findings indicate that NSun2-mediated mRNA methylation regulates p27 and CDK1 levels during replicative senescence.
Insights
The tRNA methyltransferase NSun2 represses p27 expression in senescent cells. NSun2-mediated methylation of p27 mRNA controls cell proliferation and senescence, impacting CDK1 levels.
Area of Science:
- Molecular Biology
- Cell Biology
- Epigenetics
Background:
- Cellular senescence is a state of irreversible growth arrest.
- The cyclin-dependent kinase (CDK) inhibitor p27KIP1 is crucial for growth arrest in senescent cells.
- Mechanisms regulating p27KIP1 levels during senescence are not fully understood.
Purpose of the Study:
- To investigate the role of tRNA methyltransferase NSun2 in regulating p27KIP1 during replicative senescence.
- To elucidate the molecular mechanisms by which NSun2 affects p27KIP1 expression and cellular proliferation.
Main Methods:
- In vitro and cellular methylation assays of p27 mRNA 5'-UTR by NSun2.
- NSun2 knockdown and overexpression in human diploid fibroblasts (HDFs).
- Analysis of p27KIP1, CDK1 mRNA, and protein levels.
- Assessment of cell proliferation and senescence markers.
Main Results:
- NSun2 directly methylates p27 mRNA's 5'-UTR, inhibiting its translation.
- NSun2 levels decrease during replicative senescence, correlating with increased p27KIP1.
- NSun2 knockdown elevates p27KIP1, reduces CDK1 expression, and accelerates senescence.
- NSun2 overexpression has opposite effects, promoting proliferation and delaying senescence.
Conclusions:
- NSun2-mediated mRNA methylation is a novel regulatory mechanism controlling p27KIP1 and CDK1 levels.
- This pathway plays a significant role in regulating cell proliferation and replicative senescence.
- Targeting NSun2 could offer therapeutic strategies for age-related diseases and cancer.
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