Abstract 4208: Post-translational modification of E2F1 in malignant melanoma

Abstract

Abstract Malignant melanoma has the highest fatality among all skin cancers. No current treatment significantly enhances survival once metastasis is established. Previous studies have shown that E2F1, a transcription factor, is over-expressed in melanoma cells. However, the mechanism through which E2F1 is elevated remains unknown. E2F1 is known to be involved in many important biological processes, including cell cycle progression, DNA damage, DNA repair, differentiation, development, autophagy and apoptosis. This underscores the importance of E2F1 in carcinogenesis. Normally in late S phase, E2F1 is recognized by the E3 ligase p45 SKP2 and undergoes ubiquitination and finally degradation in 26S proteasome. Our overall hypothesis is that E2F1 escapes proteasomal degradation in melanoma cells due to changes in post-translational modification. In this study we have used melanoma cells of increasing disease progression. Our results show that although the primary melanoma cells have high level of E2F1 message and protein, it is unstable. On the other hand the more metastatic melanoma cells have low levels of E2F1 which is however very stable. Consistent with this result, post-translational modification of E2F1 including the phosphorylation at Serine 337 and the acetylation at Lysine 117 increase with melanoma progression, which suggests that these post-translational modification sites might play an important role in stabilization of E2F1 and keep it functionally active in the more metastatic cell lines. E2F1 knockdown data also shows that E2F1 KD can inhibit cell proliferation in early stage melanoma cells but not in the more metastatic cells, which also suggest that inhibition of post-translational modifications and stability of E2F1 may be a more effective way to inhibit melanoma progression to more advanced stages. Abrogation of acetylation is expected to cause E2F1 protein instability. On the other hand, if acetylation is potentiated, the stabilized E2F1 will continue to promote progression through the cell cycle. We are currently testing whether the ectopic expression of the continuously acetylated E2F1 protein can rescue proliferation inhibition caused by E2F1 down-regulation, and drive metastasis and a mutant E2F1 with abrogated acetylation can block rescue of the proliferation inhibition in the E2F1 down-regulated melanoma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4208. doi:1538-7445.AM2012-4208