A reduction of TrkB.T1 expression in the frontal cortex of a subpopulation of suicide completers is associated with the methylation state of the promoter region.

These results suggest broad reprogramming of promoter DNA methylation patterns in the hippocampus of suicide completers. This may help explain gene expression alterations associated with suicide and possibly behavioral changes increasing suicide risk.

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BACKGROUND: MicroRNAs are small RNA molecules that have the ability to repress target mRNAs through binding in their 3’ UTR. Prior work has shown that the expression of methyl binding domain protein 2 (MBD2) induces a variety of prometastatic genes through direct demethylation. HYPOTHESIS: MBD2 turns on microRNA expression through promoter demethylation that in turn suppress other genes. RESULTS: Methylated DNA Immunoprecipitation (mDIP) and MBD2 ChIP arrays identified a subset of microRNAs that change with the overexpression and transient knockdown of MBD2 in MCF10A and MCF7 cell lines, respectively. Methylation of these microRNAs with bisulfite sequencing and validation of MBD2 binding with quantitative PCR (qPCR) revealed the possible induction of hsa-mir-496 by MBD2. Expression of mir-496 was shown to be induced in MBD2 transfected MCF10A cells and repressed in MCF7 and MDA-231 cells with qPCR. Luciferase promoter assays revealed hsa-mir-496 promoter to be regulated by methylation and driven forward by co-transfection with MBD2. In silico scans of possible targets of hsa-mir-496 identified CPEB3 as a putative target. Expression of CPEB3 was shown to be inversely proportional to MBD2 in MBD2 transfected MCF10A cell lines and transient knockdowns of MBD2 in MCF7 and MDA-231 cell lines with qPCR. CONCLUSIONS: The discovery of microRNAs has shed a whole new light on transcriptional regulation and with it has raised several questions about specific cell states. Considering that MBD2 causes complete transformation of a cell and plays a large role in tumorigenicity it is essential to characterize the roles of microRNA action with regards to MBD2 and its respective network of action. More importantly to show MBD2 as a key regulator of microRNA expression can further reinforce its role as a DNA demethylase and a key regulator of cancer. FUTURE DIRECTIONS: Future work will involve testing mir-496 action in the cell with its putative target CPEB3 using 2-O-methyl primer assays in conjunction with luciferase reporter assays in order to probe the functionality of the CPEB3 3′UTR. The aforementioned results and directions will give us a refined picture of our model as well as attempt to define a system of MBD2-microRNA action. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 172.