Abstract
Medulloblastomas are highly malignant, poorly differentiated childhood tumours arising in the cerebellum. These tumors rarely lose TP53, which is the most commonly mutated gene in cancer. Recent work has shown that the basal level of p53 plays an important role in maternal reproduction by maintaining the expression of LIF in the uterus. Since LIF can maintain the undifferentiated state of stem cells we set out to ask if p53 regulates LIF in the human medulloblastoma cell lines DAOY and D283MED. We also used p53−/− and p53+/+ isogenic HCT116 colorectal carcinoma cell lines, already reported to exhibit p53-dependent expression of the LIF D transcript, to establish the extent of p53-dependency for LIF M and T alternative transcripts. Whilst all three known, full-length alternative transcripts are more abundant in p53+/+ cells, the alternative LIF M and T transcripts appear particularly sensitive to p53. In the p53 wild-type medulloblastoma cell line D283MED chromatin immunoprecipitation experiments showed p53 binding to the LIF gene. The mutant p53 expressed in line DAOY did not bind to this region or to the p21WAF1 p53 binding site. RNA interference against either WIP1 or SIRT1 stabilized p53 and enhanced the transcription of LIF in D283MED cells. Interestingly, siRNA against WIP1 or SIRT1 also induced increased apoptosis in the medulloblastoma line D283MED and, over a longer time period, in DAOY cells. We speculate that suppression of p53 function by combined WIP1-mediated dephosphorylation and SIRT1 deacetylation enables medulloblastoma cell survival but p53-dependent and independent apoptotic pathways remain intact. Thus small molecule inhibitors of SIRT1 may be useful in treatment of medulloblastoma.
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Abbreviations
- LIF:
-
Leukemia inhibitory factor
- ChIP:
-
Chromatin immunoprecipitation
- qRT–PCR:
-
Quantitative real time PCR
- STAT3:
-
Signal transducer and activator of transcription 3
- SIRT1:
-
Human Sirtuin 1 member of the silent information regulator 2 (Sir2) gene family
- WIP1/PPM1D:
-
Wild type p53-induced phosphatase 1/protein phosphatase magnesium-dependent 1 delta
- NAD+:
-
Nicotinamide adenine dinucleotide
- RNAi:
-
RNA interference
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Acknowledgments
We are grateful to Dr Bert Vogelstein for the HCT116 p53 −/− and +/+ cell lines. We thank the members of the YCR p53 Research Unit for helpful discussions. This work was supported by Yorkshire Cancer Research Fund core funding to JM.
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Supplementary Fig. 1
The LIF antibody shows a lower signal in LIF siRNA-treated HepG2 cells.A band of approximately 40 kDa is seen using antibodies against LIF; this signal is reducedmarkedly in cells treated with LIF D siRNA compared with a control siRNA transfection (laminA/C), transfection using the reagent only “oligofectamine” and untreated cells. An actin blot isincluded as a loading control (PDF 52 kb)
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Baxter, E.W., Milner, J. p53 regulates LIF expression in human medulloblastoma cells. J Neurooncol 97, 373–382 (2010). https://doi.org/10.1007/s11060-009-0043-x
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DOI: https://doi.org/10.1007/s11060-009-0043-x