Abstract 3063: MicroRNA-605: A novel genetic modifier in Li-Fraumeni Syndrome.

Abstract Background: Li-Fraumeni syndrome (LFS) is a rare autosomal-dominant disorder, typically involving germ-line mutations in the prototypical tumour suppressor gene, TP53. Despite the high penetrance of TP53 mutations, LFS patients display striking differences in the age of disease onset, suggesting the presence of additional genetic modifiers. To date, functional polymorphisms in TP53 (Arg72Pro), MDM2 (SNP 309), as well as DNA copy number variations (CNVs) and telomere attrition, have been associated with cancer risk in LFS. However, it is likely that additional modifiers exist and that a combination of these low-penetrance risk factors act together to predispose TP53 mutation carriers to a spectrum of susceptibilities. Recently, the TP53 signalling network has been linked to a small number of non-coding RNAs, called microRNAs (miRNAs), whose main function is to negatively regulate gene expression. One particular member of this family, called miR-605, has been found to target the MDM2 gene, an important inhibitor of p53 function. Importantly, a common Single Nucleotide Polymorphism (SNP) within miR-605 was also found to modulate gastrointestinal cancer risk. By affecting miR-605 expression, this SNP could impact cancer risk in TP53 mutation carriers. Hypothesis: In this study, we hypothesized that SNP-mediated miR-605 deregulation might modify cancer risk in LFS by eliciting important transcriptional changes in the levels of p53 and/or MDM2. Methods: miR-605 was overexpressed in two TP53 mutant cell lines (RD and Rh30) in order to assess its tumor suppressive functions. MDM2 and TP53 protein expression were analyzed through Western Blotting. Additionally, blood-derived DNA samples from 47 Caucasian TP53 mutation carriers were genotyped for the miR-605 variant by SNP-RFLP. Results: Overexpressing miR-605 in two TP53 mutated cell lines led to a significant attenuation in cell viability as measured by MTS assay. The capacity of these cell lines to form macroscopic colonies was also compromised following transfection by a miR-605 commercial mimic. Moreover, miR-605-transfected cells also displayed higher sensitivity to a wide range of chemotherapeutic drugs. In RD cells, MDM2 downregulation was detected following miR-605 overexpression but TP53 levels remained unchanged. Genotyping our aforementioned study population revealed the G-allele of the miR-605 SNP to be associated with an earlier age of cancer onset (p=0.02). The median age of cancer onset in carriers of the G-allele (n= 15) was 3.75 years compared to 21.5 years in patients with the common homozygous A/A genotype (n= 32). Conclusion: Together, our results identify miR-605 deregulation as a potential cancer modifying event in TP53 mutation carriers. Future work will focus on elucidating the functional consequences of the miR-605 SNP whilst also pursuing a more general understanding of miR-605 tumor suppression. Citation Format: Badr Idsaid, David Malkin. MicroRNA-605: A novel genetic modifier in Li-Fraumeni Syndrome. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3063. doi:10.1158/1538-7445.AM2013-3063

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