探討酵母菌Cip1調控之氧化壓力反應

Abstract

為了在大自然中生存，酵母菌必須針對多變的環境與外在壓力做出快速且適當的反應以提升其適存度。當細胞細胞受到環境壓力，如：滲透壓壓力、氧化壓力等可讓細胞週期停頓在G1期，使細胞適應並排除壓力。細胞週期G1至S期的轉換是由G1週期素和Cdc28週期素依賴性蛋白激酶複合體的活性來調控，G1週期素中的Cln3與Cdc28複合體可調控下游CLN2與CLN1以及其他G1期的基因表現。先前研究酵母菌YPL014W的基因產物Cip1蛋白是Cdc28/G1週期素複合體的其中一員，且受到轉錄因子Mcm1的調控，而過量表現Cip1會使細胞週期停頓在G1期；當遭遇滲透壓壓力，CIP1的表現量會受到轉錄因子Msn2/4調控而大幅提升，並同時藉由Hog1途徑將Cip1磷酸化，加強Cip1與Cdc28/G1週期素複合體的結合能力而達到暫時性的G1週期停頓，因此認為Cip1可能是週期素依賴性蛋白激酶的抑制物，並與人類p21在功能上是同源。氧化壓力可來自細胞外界環境、細胞老化或是粒線體損傷等等，嚴重時可能會造成DNA損傷。從先前文獻觀察到在遭遇氧化壓力時CIP1表現量是上升最多的，故本篇論文欲探討在氧化壓力下Cip1調控的細胞週期與反應，藉由LC/MS MS的分析找到氧化壓力誘導的Cip1磷酸化位點，並其可藉由與細胞週期素結合調控細胞週期。

To survive in the fluctuating environment, budding yeast Saccharomyces cerevisiae delay G1 progression under several stresses, such as osmotic stress and oxidative stress, so that cell can prevent itself from damage accumulation and improve its fitness. The G1/S transition is mediated by the activity of Cdc28/G1 cyclin complex, especially Cdc28/Cln3 complex can activates G1 downstream genes expression, including CLN1 and CLN2. Previous studies show that Cip1, which is encoded by YPL014W and mediated by transcription factor Mcm1, was suggested to be a component of Cdc28/G1 cyclin complex according to proteomic screening. Overexpression of Cip1 causes cyclin-mediated -cell cycle arrest at G1 phase. However, when confronted with stresses, CIP1 expression is up-regulated by transcription factor Msn2/4. Under osmotic stress, Cip1 protein was phosphorylated by SAPK Hog1 and enhanced its binding affinity with Cdc28/G1 complex, thus arrest cell cycle in G1 phase. Therefore, Cip1 was considered as new cyclin-dependent kinase inhibitor and serves as functional homologue of human p21. Oxidative stress comes from both endogenous and exogenous sources. Severe oxidative stress would damage DNA stability. I observed that CIP1 expression level was most upregulated under oxidative stress according to previous study. In this study, I want to determine how Cip1-mediated response affects yeast cell under oxidative stress. By LC/MS MS analysis, Cip1 has specific phosphorylation sites that can regulate cell cycle. Also, Cip1 could interact with cyclin to mediated the cell cycle.