Resveratrol regulates the cell cycle via modulation of H2B ubiquitylation to inhibit the growth of breast cancer cells

• Main Authors: Lin, Chia-Yeh, 林佳葉
• Other Authors: 王果行
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/47822401324125807750

博士 === 輔仁大學 === 食品營養博士學位學程 === 102 === Breast cancer is the most frequently diagnosed cancer in women worldwide. Resveratrol (trans-3, 5, 4’-trihydroxystilbene), a polyphenolic compound found in grapes, has been shown to prevent different stages of carcinogenesis (including breast cancers) by modulating gene activity through transcription regulation and epigenetic modifications. Tumorigenesis is a process involved in the production of a new tumor or tumors, which is driven not only by genetic abnormalities, but also by epigenetic alterations; one such epigenetic factor is H2B ubiquitylation (H2Bub). H2Bub is often decreased in breast cancer tissue, and the gene encoding the histone H2B ubiquitin E3 ligase RNF20 (ring finger protein 20), a putative tumor suppressor, is epigenetically silenced in breast tumors. H2Bub has been reported to act as a chromatin hub for signal integration and transmission from inner- or external stimulation, and extensively regulates nuclear processes, gene expression, and DNA repair and replication. Thus, the RNF20-H2Bub pathway is a potential therapeutic target for breast cancer treatment. However, it is unknown whether resveratrol exerts its anti-breast cancer effects through remodeling the chromatin landscape by targeting RNF20. Through the serial studies described in this dissertation, RNF20 and H2Bub were found to be up-regulated by resveratrol in MDA-MB-231 breast cancer cells, but not in less aggressive MCF-7 cells. RNF20 was up-regulated through the increase of active histone marks around its promoter. The increase in RNF20 in MDA-MB-231 cells likely contributes to both the anti-growth effects of resveratrol and activation of p21 (a gene encoding a cell cycle inhibitor), as RNF20 knockdown diminished these effects. The findings suggest that RNF20-H2Bub is a novel epigenetic target of resveratrol, and increase our understanding of how this epigenetic modification contributes to the chemo-preventive effect of resveratrol in a more aggressive breast cancer cell line, MDA-MB-231. The above results also suggest that RNF20-mediated H2Bub contributes to cell cycle progression through the regulation of p21 expression. H2Bub has been suggested to regulate nuclear processes not only through its role in gene regulation, but also through modulating the accessibility of DNA through chromatin remodeling. Using the budding yeast Saccharomyces cerevisiae, a genetic tractable model, we investigated whether H2Bub is involved in regulating the cell cycle dynamic network. We report that the htb-K123R mutant, which lacks H2Bub, exhibited a delay in the G1/S transition and a prolonged S phase. H2Bub specifically increased near replication origins during G1 phase, and the levels of H2Bub near these origins fluctuated during the cell cycle. H2Bub was found to regulate nucleosome dynamics at the replication fork during S phase, in conjunction with the histone chaperone Asf1 and the histone acetyltransferase Rtt109. As such, elimination of H2Bub interrupted nascent DNA synthesis. Furthermore, disruption of cell cycle progression in htb-K123R cells could be partially attributed to reduced expression of G1 cyclins. Collectively, these results suggest that H2Bub is critical for appropriate cell cycle progression by promoting both nucleosome remodeling at replication forks, and cyclin gene expression. Taken together, these findings indicate that resveratrol targets RNF20-H2Bub and inhibits cell growth in a malignant breast cancer cell line, MDA-MB-231; furthermore, the results have assisted in elucidating the molecular mechanisms of H2Bub in cell cycle regulation. Disruption of epigenetic control is one of the most frequent etiologies of cancer. Thus, this study has identified a novel epigenetic target of resveratrol, namely the RNF20-H2Bub pathway, and lays the foundation for future studies into using polyphenolic compounds to prevent cancer through targeting epigenetic regulation.