MDM2 overexpression deregulates the transcriptional control of RB/E2F leading to DNA methyltransferase 3A overexpression in lung cancer.
OBJECTIVE
Overexpression of DNA 5'-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.


METHODS
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.
Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Republic of China.
Yen-An
YA
Tang
Ruo-Kai
RK
Lin
Yo-Ting
YT
Tsai
Han-Shui
HS
Hsu
Yi-Chieh
YC
Yang
Chih-Yi
CY
Chen
Yi-Ching
YC
Wang
D000818:Animals; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics*; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D050687:E2F1 Transcription Factor / Q000235:genetics*; D005260:Female; D015870:Gene Expression; D015972:Gene Expression Regulation, Neoplastic; D016161:Genes, Retinoblastoma; D006801:Humans; D007093:Imidazoles / Q000378:metabolism; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D010879:Piperazines / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D014158:Transcription, Genetic
D002843:Chromatin; C000717967:DNMT3A protein, human; C000715535:Dnmt3a protein, mouse; D050687:E2F1 Transcription Factor; D007093:Imidazoles; D010879:Piperazines; C482205:nutlin 3; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2