Abstract 2480: Chronic radiation exposure increases uPA and cMyc expression levels but decreases nMyc expression levels in neuroblastoma cells
Authors: Gnanamony Manu , Pinson David , Antony Reuben , Fernández Karen S. , Lin Julian , Joseph Pushpa A. , Gondi Christopher S. 
Published: July 2016

Neuroblastoma is the most common extra-cranial solid tumor in children. Despite aggressive therapy prognosis of high risk neuroblastoma remains guarded and also unpredictable because of heterogeneity of tumor response to treatment. Radio-resistance has been recognized as a significant contributor to aggressive clinical behavior of neuroblastoma. Characterization of genetic alterations have been used for predicting clinical outcome in neuroblastomas and one of the most studied genetic markers in aggressive neuroblastoma is nMyc/MYCN. The MYCN gene belongs to the MYC family of transcription factors and nMyc expression is to a large extent inversely correlated with cMyc expression and nMyc expression is also associated poor clinical outcomes. In this study, we have attempted to correlate the expression of nMyc in neuroblastoma cells NB1691 and SKNBE2 to radiation resistance. We exposed neuroblastoma cells NB1691 and SKNBE2 to chronic radiation doses with a cumulative high energy X-ray radiation dose of 25Gy achieved by dosing at 5Gy increments over a period of 15 days. Cells surviving after the 25Gy cumulative radiation dose were selected and designated as NB1691R and SKNBE2R. Expression levels of nMyc, cMyc and uPA were determined. We observed that the radiation tolerant cells showed at least 164 fold increase in the expression of uPA in NB1691R cells and at least 97 fold increase in SKNBE2R cells. We also observed that the expression levels of nMyc decreased in both NB1691R and SKNBE2R cells to almost undetectable levels. Further, the expression levels of cMyc revealed that NB1691R cells showed a 208 fold increase and SKNBE2R a 71 fold increase when compared to parental cells. We further determined whether the expression of uPA can modulate the expression of nMyc. We silenced uPA expression in NB1691 cells and observed that downregulation of uPA moderately rescued nMyc expression. Cell cycle analysis revealed that acute radiation of NB1691 cells induced accumulation of cells in the G2/M phase and un-radiated NB1691R cells continued to show cells accumulated in the G2/M phase similar to acute radiated NB1691 cells.

Our study shows that:

1. Chronic radiation exposure suppresses the expression of nMyc and induces the expression of cMyc.

2. cMyc expression was accompanied with the expression of uPA and suppression of uPA expression moderately rescued the expression of nMyc.

Our preliminary findings suggest that chronic exposure to radiation alters the nMyc/cMyc ratio in neuroblastoma cells and induces the expression of the pro-invasive molecule uPA.

Citation Format: Manu Gnanamony, David Pinson, Reuben Antony, Karen S. Fernández, Julian Lin, Pushpa A. Joseph, Christopher S. Gondi. Chronic radiation exposure increases uPA and cMyc expression levels but decreases nMyc expression levels in neuroblastoma cells. [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 2480.