Poster Presentation 27th Lorne Cancer Conference 2015

E6AP is a novel regulator of the INK4/ARF locus: implications for NSCLC (#165)

Cristina Gamell 1 , Yaara Levav-Cohen 2 , Twishi Gulati 3 , Kamil Wolyniec 3 , Richard J Young 3 , Hongdo Do 3 , Imogen Elsum 4 , Patrick Humbert 3 , Michael Cater 5 , Prudence A Russell 6 , Gavin Wright 6 , Doron Ginsberg 7 , Alex Dobrovic 8 , Ben Solomon 3 , Sue Haupt 3 , Ygal Haupt 3
  1. Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  2. The Hebrew University of Jerusalem, Jerusalem 91904, Israel
  3. Peter MacCallum Centre, Melbourne, Vic, Australia
  4. Burnet Institute, Melbourne, Vic, Australia
  5. Deakin University, Burwood Campus, Melbourne, Australia
  6. St. Vincent's Hospital, Melbourne, Vic, Australia
  7. Bar-Ilan University, Ramat-Gan, Israel
  8. Ludwig Institute For Cancer Research at the Olivia Newton John Cancer Centre, Melbourne, Vic, Australia

The E6-Associated Protein (E6AP) is an E3 ubiquitin ligase, initially characterized for its role in p53 degradation in HPV-infected cells. We recently demonstrated that E6AP-deficient cells evade oncogene and stress-induced senescence [1, 2]. We now report that E6AP knockout MEFs show reduced levels of the genes encoded by the INK4/ARF locus, providing a molecular mechanism by which E6AP controls cellular senescence. The INK4/ARF locus is the most frequently inactivated locus in human cancer and it encodes for the key tumor suppressors p15INK4b, p16INK4a and p19ARF. p16INK4a, specifically, is lost at high frequency in several cancers, including non-small cell lung carcinoma (NSCLC) [3], and while hypermethylation is responsible for its loss in nearly half the cases, the mechanism for the remaining cases is unknown. Our results demonstrate that E6AP regulates the INK4/ARF locus by inhibition of Cdc6, a key repressor of this locus. This finding is supported by mouse models of lung cancer, whereby E6AP deficiency promotes oncogenesis. Importantly, in a subset of NSCLC patients, E6AP low/Cdc6 high/p16 low expression profile is associated with worse overall survival and a low frequency of p16INK4a hypermethylation. Overall, our study provides a novel mechanism for the silencing of the INK4/ARF locus.

1. Levav-Cohen, Y., et al., E6AP is required for replicative and oncogene-induced senescence in mouse embryo fibroblasts. Oncogene, 2012. 31(17): p. 2199-209.

2. Wolyniec, K., et al., The E6AP E3 ubiquitin ligase regulates the cellular response to oxidative stress. Oncogene, 2012.

3. Gonzalez-Quevedo, R., et al., Differential impact of p16 inactivation by promoter methylation in non-small cell lung and colorectal cancer: clinical implications. Int J Oncol, 2004. 24(2): p. 349-55.