探討酵母菌組蛋白去甲基酶Rph1對於光解酶基因PHR1之轉錄調控機制

組蛋白甲基化修飾涉及許多重要的生物性功能，如：轉錄調節、DNA修復、異染色質之形成、抑制X染色體之基因表現以及細胞分化。組蛋白甲基化修飾在過去曾一度被認為是一種穩定的修飾作用，並且為不可逆之反應。然而直到2004年，第一個組蛋白去甲基酶LSD1(Lysine-Specific Demethylase 1)首度被發現，才改變了這項觀點。　　近期的研究新發掘出另一類的組蛋白去甲基酶。含有JmjC(Jumonji C) domain的蛋白質成員當中，可能具有潛在的組蛋白去甲基酶活性，然而目前對於這些蛋白質的生物性功能並不清楚。基於這樣的前提，JmjC蛋白質除了可能具有組蛋白去甲基酶之活性外，尚可能在維持生物性功能上扮演重要角色。於是我首先使用生長表現型分析來研究在出芽酵母菌(S. cerevisiae)當中五個的JmjC蛋白質成員的生物性功能。我發現過度表現其中兩個H3K36專一性之組蛋白去甲基酶：Rph1(Repressor of PHR1)與Jhd1(JmjC domain-containing Histone Demethylase 1)，能夠增加酵母菌對於6-azauracil之耐受性，這顯示兩者可能參與調節轉錄作用之延長階段。除此之外，過度表現 RPH1 可導致酵母菌對於UV傷害之耐受性較差。先前曾有研究推測 Rph1可能是光解酶基因PHR1之抑制子。為了釐清上述所觀察到的現象是否與Rph1的功能有關，我使用RT-PCR分析Rph1對於PHR1轉錄活性之影響。我發現過度表現RPH1會造成PHR1的基礎表現量下降，同時也會降低PHR1在受到UV傷害所誘導增幅之表現量。過度表現失活性rph1H235A也有類似的作用，但是相對較弱。為進一步了解Rph1之酵素活性是否參與其中，我使用染色質免疫沉澱法分析PHR1啟動子的甲基化修飾狀態。在一般狀態下，Rph1會結合至該區並減少該區H3K36me3之層次。當細胞受到UV傷害後，Rph1會與該區之DNA分離，相對地同時該區H3K36me3之層次亦回升。基於上述實驗所觀察到的現象，我推測Rph1調節PHR1轉錄活性的作用雖並非絕對性地依賴其酵素活性，但其酵素活性仍對此調節功能有相當程度的重要性。

關鍵字

組蛋白去甲基酶

並列摘要

Histone methylation is involved in several important biological processes such as transcriptional regulation, DNA repair, the formation of heterochromatin, X-chromosome inactivation and differentiation. Histone methylation was once considered extremely stable and irreversible. However it is not until the first histone demethylase LSD1 has been discovered in 2004, this view has been changed. Recently, a novel histone demethylase activity has been reported. The JmjC domain-containing proteins which may encode potential histone demethylase activity, but little is known about the biological functions of these proteins. Based on the prediction of the JmjC domain-containing proteins may has potential histone demethylase activity and play several important roles in maintain biological functions. First, I preformed several phenotype screening to investigate the biologic content of the five JmjC proteins in S. cerevisiae. I found overexpression of two H3K36 demethylases (Rph1and Jhd1) result in slightly resistant to 6-azauracil. This data indicated two H3K36 demethylases may participate in transcriptional elongation. In addition, overexpression of RPH1 is hypersensitivity to UV-irradiation. Previous report suggested that Rph1 may functional act as a repressor of PHR1, a photolyase gene. To elucidate whether this phenotype is linked to this function of Rph1, I next performed RT-PCR analysis to characterize the relationship between Rph1 and transcription activity of PHR1. I found overexpression of RPH1 reduces the basal transcription level and the induction level of PHR1 upon UV damage. Overexpression of rph1H235A has similar patterns but has a milder effect. To further elucidate whether this effect is associated with the histone demethylase activity, I next performed ChIP assay to observe the methylation patterns at promoter region of PHR1 . In normal conditions, Rph1 binds to the promoter region of PHR1 and overexpression of RPH1 reduces the H3K36me3 level . When cells were exposed to UV-irradiation, Rph1 disassociated from the promoter region of PHR1 and the H3K36me3 level was increased. Based on these observations, it may indicate the repressive functions of Rph1 to PHR1 may partially but not totally depend on the histone demethylase activity.

並列關鍵字

Rph1 ； PHR1 ； JmjC

參考文獻

Berger, S. L. (2007). "The complex language of chromatin regulation during transcription." Nature 447(7143): 407-12.

Chen, Z., J. Zang, et al. (2006). "Structural insights into histone demethylation by JMJD2 family members." Cell 125(4): 691-702.

Christensen, J., K. Agger, et al. (2007). "RBP2 belongs to a family of demethylases, specific for tri-and dimethylated lysine 4 on histone 3." Cell 128(6): 1063-76.

Cloos, P. A., J. Christensen, et al. (2006). "The putative oncogene GASC1 demethylates tri- and dimethylated lysine 9 on histone H3." Nature 442(7100): 307-11.

Driscoll, R., A. Hudson, et al. (2007). "Yeast Rtt109 promotes genome stability by acetylating histone H3 on lysine 56." Science 315(5812): 649-52.

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探討酵母菌組蛋白去甲基酶Rph1對於光解酶基因PHR1之轉錄調控機制

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