Poster abstracts
Poster number 19 submitted by Claudia Kelly
Characterizing a novel mouse model with MDM2-ALT1 isoform overexpression
Claudia Kelly (Nationwide Childrens Hospital), Safiya Khurshid (Nationwide Childrens Hospital), Matias Montes (Nationwide Childrens Hospital, Ohio State University), Vincenzo Coppola (Ohio State University)
Abstract:
MDM2 plays an important role in cancer development by regulating the p53 pathway. Under stress conditions, MDM2 undergoes alternative splicing to yield several isoforms, including MDM2-Alt1, which has been shown to be upregulated in numerous cancers. Our lab works to understand the role of MDM2-Alt1 in cancer. Importantly, MDM2-Alt1 inhibits full-length MDM2, which results in increased p53 function. Although p53 is a tumor suppressor under normal conditions, the presence of the splice isoform MDM2-Alt1 may allow the overexpression of an oncogenic isoform of p53. Alternatively, MDM2-Alt1 may act independently of p53 to cause tumorigenesis. We have generated a CRISPR mouse model in which Mdm2-MS2 (the equivalent of human MDM2-Alt1) is overexpressed due to a mutation in Exon 11 (C7A). This novel mouse model allows us to study the effects of increased levels of Mdm2-MS2 on the development of cancer in vivo, without completely knocking out endogenous full-length Mdm2. Our hypothesis is that increased levels of the Alt1/MS2 isoform increases the incidence of cancer.
Our data show that over 50% of all mice carrying the C7A mutation in heterozygous (C7A/WT) or homozygous (C7A/C7A) form develop tumors by 18-20 months of age, whereas no wildtype (WT) mice in our cohort developed tumors by this timepoint. Additionally, we found that the incidence of tumors increases when we cross the C7A mutation onto a p53 heterozygous knock-out (+/-) background. In order to study the impact of stress on the expression of Mdm2-MS2, we exposed 3-month old mice to X-ray radiation. The DNA damage caused by X-ray led to an exaggerated induction of p53 expression in the spleen of C7A/C7A mice compared to irradiated WT mice. However, downstream targets of p53 that are normally upregulated in the spleen of C7A/C7A versus WT mice, including Bax, Gadd45, Killer, Puma, and Noxa, are not induced after irradiation in C7A/C7A mice. These data show that overexpression of Mdm2-MS2 potentially modulates the functional response of p53. Overall, our novel mouse model underlines the tumorigenic potential of the overexpression of Mdm2-MS2 and will provide crucial answers and uncover potential novel mechanisms about the role of MDM2 alternative splicing.
Keywords: alternative splicing, splicing and cancer