陰道滴蟲受鐵誘導之組蛋白轉譯後修飾

Abstract

鐵離子目前已知可活化陰道滴蟲蛋白激酶A相關訊息傳遞路徑，造成Myb3轉錄因子快速入核後遂行其功能，研究更發現此寄生蟲在鐵離子刺激後可誘發組蛋白脫乙醯酶TvHADC1的Ser391位點磷酸化。本實驗則利用蛋白激酶抑制劑發現鐵離子刺激透過PKC及MEK相關訊號傳遞路徑調控TvHDAC1入核，但H2O2刺激則非。TvHDAC1的過量表現亦造成組蛋白H3的Lys9以及H4的Lys5、Lys8、Lys16低乙醯化，然此現象不見於TvHDAC1的S391A點突變轉殖蟲株。藉由質譜分析細胞核蛋白，除發現鐵離子刺激快速改變組蛋白乙醯化與甲基化狀態，且變化趨勢異於H2O2刺激結果，鐵離子刺激亦同時活化組蛋白乙醯轉移酶TvHAT1與TvHAT2以及另外兩個組蛋白脫乙醯酶TvHDAC2與TvHDAC3磷酸化。免疫螢光染色分析驗證陰道滴蟲受鐵離子刺激後，可快速調控組蛋白特定位點乙醯化修飾。綜合以上數據顯示，陰道滴蟲受鐵刺激後，可能藉由訊號傳遞調控組蛋白乙醯轉移酶與脫乙醯酶，改變組蛋白密碼以控制下游基因活性，快速調節細胞生理因應環境中過量鐵離子。

Iron was shown to rapidly activate protein kinase A-mediated signaling to induce nuclear influx of a Myb3 transcription factor in the protozoan parasite, Trichomonas vaginalis. Site-specific phosphorylation of a histone deacetylase (HDAC), referred to as TvHDAC1, at Ser391 was previously found right after iron repletion. Here, the underlying mechanism of nuclear import of TvHDAC1 induced by iron but not H2O2 was investigated through inhibitor assay and the results indicate that PKC and MEK-related signaling pathways were activated to induce translocation of the enzyme from the endomembrane system toward the nucleus. Overexpression of TvHDAC1 resulted in hypoacetylation of histone H3 at Lys9 and histone H4 at Lys5, Lys8, Lys16, but this effect was aborted in the dominant negative mutant S391A. Exploring nuclei purification for LC-MS/MS based proteomics analysis, iron was found to induce rapid changes of acetylation and methylation on histones in a distinct way from H2O2 stimulation, and phosphorylation of two histone acetyltransferases (HAT), referred to as TvHAT1 and TvHAT2, and two additional HDACs, referred to as TvHDAC2 and TvHDAC3. The immunofluorescence assay was employed to confirm deacetylation of histones at specific sites upon iron repletion. These observations suggest that iron rapidly orchestrates multiple histone code writers through signal transduction to fine-tune gene expression in the parasite in response to iron overloading.