Abstract 5002: Posttranslational modification of E2F1 during melanoma progression

Abstract

Abstract Melanoma, the malignant tumor of melanocytes, accounts for approximately 78% of skin cancer related deaths. No current treatment significantly enhances disease-free survival once distant metastases have established. To facilitate the development of effective treatment strategies, it is imperative that we obtain a better understanding of the biology of melanoma cells as they progress through the various stages of disease. Previous studies have shown that E2F1, a transcription factor, is over-expressed in melanoma cells. Interaction between E2Fs and tumor suppressor, Rb is essential for regulation of cell cycle progression. E2F1 is known to be involved in other important biological processes, including DNA damage, DNA repair, differentiation, development, autophagy and apoptosis. However, the mechanism through which E2F1 is elevated in melanoma remains unknown. In normal cells in late S phase, E2F1 is recognized by the E3 ligase p45 SKP2, undergoes ubiquitination and is finally degraded in 26S proteasome. Since multiple post-translational modifications have been reported to affect the stability and functions of E2F1, we have hypothesized that during melanoma progression E2F1 fails to undergo degradation and this failure is due to post-translational modification of E2F1. In this study we have used melanoma cells of increasing disease progression. Our results show that primary melanoma cells have high level of E2F1 message and protein. We also found that E2F1 protein levels are not tightly regulated during cell cycle progression. Levels of E2F1 remain constantly high during cell cycle progression in the less metastatic melanoma cells. Consistent with these results, phosphorylation of E2F1 at Serine 337 is almost unchanged during cell cycle progression in the less metastatic melanoma cells. These results taken together suggest that this post-translational modification site may play an important role in stabilization of E2F1 in the primary melanoma cells that represent the radial and vertical growth phases of melanoma. Since modifications usually induce conformational changes, which may affect any following modifications, it is necessary to study the crosstalk among different modifications like acetylation and phosphorylation. The modifications towards the same direction may generate a specific array of modifications that can induce markedly stronger functional effects compared with those produced by the sum of single modifications. Therefore, it is intriguing to detect the coordination of different modifications and determine if there is such a modification array that regulates the stabilization and degradation of E2F1 resulting in the elevated E2F1 levels in melanoma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5002. doi:10.1158/1538-7445.AM2011-5002