探討川陳皮素在酵母菌中對紫外線照射引起DNA受損反應的影響

Abstract

川陳皮素(Nobiletin)為柑橘類果皮中含多甲基的酚類物質，目前已知其具有廣泛的生理活性，包括抗發炎及抗癌等。先前有研究指出由於川陳皮素的外圍含多個甲基，因此與一般常見富含氫氧基的酚類物質在生物體中的吸收與代謝途徑有所不同。此外，研究也證實川陳皮素經過生物體內代謝，會將其環上特定位置的甲基由氫氧基置換，產生去除單甲基或雙甲基的代謝物，而此置換的物質可能存在於生物體中作為某些功能使用。根據先前的研究顯示富含甲基的飲食，例如葉酸，可調節生物體中DNA或組蛋白的甲基化程度，而此種甲基化的調節可影響DNA受損後的修復途徑。因此，我們主要探討川陳皮素在UVB照射後的酵母菌中，對酵母菌DNA受損反應的影響。結果發現川陳皮素的添加會增加DNA受損指標γH2A的表現量，也會增加細胞週期檢查點蛋白Rad53的活化。而在細胞週期方面，川陳皮素的添加會使得細胞週期停滯在S期。組蛋白甲基化方面，川陳皮素的添加反而降低了H3K79三甲基化、對H3K4三甲基化無顯著影響並增加了H3K9乙醯化的程度。而在細胞內自由基表現量方面則沒有顯著差異。根據我們的研究，川陳皮素的添加會藉由增加γH2A的表現量進而活化檢查點蛋白Rad53，並使酵母菌停留在細胞週期的S期，使受損細胞DNA修復，最後達到增加酵母菌存活率的影響。

Nobiletin is a dietary phytochemical belonging to polymethoxy flavonoids from the peels of citrus fruits. It has a distinct metabolic feature compared to polyhydroxyflavonoids due to its high bioavailability. Nobiletin is shown to have health beneficial properties, including anti-inflammatory and anti-carcinogenic activities. We investigate how nobiletin affects DNA damage response after UVB treatment in unicellular model organism, baker’s yeast. The results show that nobiletin increases cell survival after UVB damage. UVB treatment induces histone H2A phosphorylation, a marker for DNA damage. The addition of nobiletin can increase both the phosphorylation levels of H2A and phosphotylation levels of Rad53, which is a DNA damage checkpoint protein, after UVB treatment. In the aspects of histone modification, nobiletin has no significant effect on H3K4 trimethylation and it reduces H3K79 trimethylation. Besides, nobiletin increases H3K9 acetylation, which represented that nobiletin promote cell arrest in cell cycle S phase. Furthermore, the addition of nobiletin also has no significant effect on reactive oxygen species (ROS) production after UVB treatment. Our results suggest nobiletin treatment increases the sensitivity of yeast cell to UV damage, promote cell cycle arrest and may facilitate cells to recruit repair proteins to DNA damage sites, thus, influence cell survival.