MDM2 Overexpression Deregulates the Transcriptional Control of RB/E2F Leading to DNA Methyltransferase 3A Overexpression in Lung Cancer

Abstract

Purpose: Overexpression of DNA 5 0 -cytosine-methyltransferase 3A (DNMT3A), which silences genes including tumor suppressor genes (TSG), is involved in many cancers. Therefore, we examined whether the transcriptional deregulation of RB/MDM2 pathway was responsible for DNMT3A overexpression and analyzed the therapeutic potential of MDM2 antagonist for reversing aberrant DNA methylation status in lung cancer.Experimental Design: The regulation of DNMT3A expression and TSG methylation status by RB/MDM2 was assessed in cancer cell lines and patients. The effects of Nutlin-3, an MDM2 antagonist, on tumor growth in relation to DNMT3A expression and TSG methylation status were examined by xenograft model.Results: We found that RB suppressed DNMT3A promoter activity and mRNA/protein expression through binding with E2F1 protein to the DNMT3A promoter, leading to the decrease of methylation level globally and TSG specifically. In addition, MDM2 dramatically induced DNMT3A expression by negative control over RB. In clinical study, MDM2 overexpression inversely correlated with RB expression, while positively associating with overexpression of DNMT3A in samples from patients with lung cancer. Patients with high MDM2 and low RB expression showed DNMT3A overexpression with promoter hypermethylation in TSGs. Treatment with Nutlin-3, an MDM2 antagonist, significantly suppressed tumor growth and reduced DNA methylation level of TSGs through downregulation of DNMT3A expression in xenograft studies.Conclusions: This study provides the first cell, animal, and clinical evidence that DNMT3A is transcriptionally repressed, in part, by RB/E2F pathway and that the repression could be attenuated by MDM2 overexpression. MDM2 is a potent target for anticancer therapy to reverse aberrant epigenetic status in cancers.

p53 is essential for DNA methylation homeostasis in naïve embryonic stem cells, and its loss promotes clonal heterogeneity

“…Indeed, the corresponding genomic regions do not contain easily recognizable p53-binding motifs, suggesting that p53 may be recruited to those regions indirectly through association with other DNA-binding proteins. Repression of DNMTs by p53 has already been reported (Jinawath et al 2005;McCabe et al 2005;Lin et al 2010;Tang et al 2012;Ma et al 2015) and was partly ascribed to the ability of p53 to quench E2F transcriptional activity (Kimura et al 2003;Polager and Ginsberg 2009;Tang et al 2012). Furthermore, p53 transcriptionally induces miR-29, which targets all three DNMT transcripts (Yan et al 2015).…”

MDM2, MDMX and p53 in oncogenesis and cancer therapy

“…MDM2 may also have a role in the modification of the cellular epigenetic status. For example, MDM2-dependent degradation of RB can increase the levels and activity of the DNA methyltransferase DNMT3A 142 . This is associated with the silencing of tumour suppressor genes, and suggests that targeting this p53-independent function of MDM2 is a potential therapeutic strategy.…”

The MDM2-p53 pathway revisited

“…For example, MDM2 is able to affect processes such as DNA synthesis and repair by interaction with DNA polymerase ϵ[50],[51], DHFR[52], centrosome amplification[53] and the MRN DNA complex containing Nbs1[54],[55], etc. Similarly, MDM2 interacts with several proteins such as Rb/E2F-1 complex[55]–[57], the DNA methyltransferase DNMT3A[58], p107[59], MTBP[60],[61], the cyclin kinase inhibitor p21, independently of p53, and drives cell cycle progression (typically S-phase)[62],[63]. In an analogous fashion, the MDM2 oncoprotein interacts with the E2F1/Rb pathway to inhibit apoptosis[55].…”