Abstract 3703: MDM2 regulation of MYC and MYCN in pediatric neural cancers

Abstract

Abstract Background MYC and MYCN have critical roles in a wide range of cancers and can be deregulated through diverse transcriptional and post-transcriptional mechanisms. Recent studies have shown that the high-level MYCN expression needed to drive retinoblastoma and MYCN-amplified neuroblastoma proliferation depends upon efficient MYCN translation mediated by highly expressed MDM2 and acting via a p53-independent mechanism. Here, we assessed MDM2-mediated regulation of MYC as well as MYCN in other pediatric neural tumors, specifically in Group 3 medulloblastoma and in MYC-overexpressing neuroblastoma. We also assessed MDM2-mediated regulation of MYCN in small cell lung cancer (SCLC), which has genetic and morphologic features in common with retinoblastoma. Methods MDM2, MYCN, and MYC expression were defined in Group 3 medulloblastoma lines D283, D425, D341; in MYC-overexpressing neuroblastoma lines CHLA 255 and SY-5Y; and in p53-wild type and p53-mutant SCLC lines H69 and H526 by western blotting. Cells were infected with shMDM2 and scrambled control lentivirus and effects on MDM2, MYC, and MYCN protein expression defined using western blot and effects on cell growth defined using Cell Titer-Glo. In neuroblastoma cells, MDM2 knockdown effects were defined with or without p53 co-knockdown. Results Group 3 medulloblastoma lines D283, D341, D425 highly expressed MYC but not MYCN. MDM2 knockdown did not decrease MYC expression in these cells. MDM2 knockdown decreased MYC expression In CHLA 255 and SY5Y neuroblastoma cells, along with p53 induction and cell death, and MYC down-regulation and cell death were mitigated by co-knockdown of p53. MDM2 knockdown decreased MYCN expression and impaired viability in p53-wild type H69 SCLC cells and in p53-mutant H526 SCLC cells. Conclusions MDM2 is not needed to sustain high-level MYC expression in three Group 3 medulloblastoma cell lines. MDM2 sustains high-level MYC in two MYC-overexpressing neuroblastoma cell lines via a p53-dependent mechanism distinct from the p53-independent MYCN regulation in MYCN-amplified neuroblastomas. In SCLC, MDM2 sustains high-level MYCN expression and viability in a p53-independent manner, similar to MDM2 effects in retinoblastoma and in MYCN-amplified neuroblastoma. These findings suggest that MDM2 selectively sustains MYCN but not MYC expression through a p53-independent mechanism and raise the possibility that cis-acting elements specific to MYCN-RNA mediate MDM2 regulation. Citation Format: Hung N. Tran, Donglai Qi, David Cobrinik. MDM2 regulation of MYC and MYCN in pediatric neural cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3703.