腸出血性大腸桿菌是一種新出現的人畜共通的病原體，其引起全世界人類的出血性腹瀉甚至死亡。腸出血性大腸桿菌藉由誘發肌動蛋白細胞骨架重排導致附著性和抹除性病變 (A/E lesions)。和過去二十年中對於腸出血性大腸桿菌引起的附著性機制深入研究相比，腸出血性大腸桿菌引起的腸道微絨毛抹除的潛在機制仍是未知。在我們先前研究發現，腸出血性大腸桿菌導致微絨毛肌動蛋白異位 (ACT-5 mislocalization)，即是微絨毛肌動蛋白從原本的腸細胞的尖端 (apical site) 進而轉變為在腸細胞的細胞質出現，並伴隨著秀麗隱桿線蟲消化道中附著性和抹除性的病變。微絨毛肌動蛋白參與形成核心束結構以支撐腸道微絨毛的正常結構，並且核心束結構中的組件處於持續著不斷更替的狀態。因此，我們認為研究線蟲微絨毛被腸出血性大腸桿菌抹除的機制，腸出血性大腸桿菌誘導的微絨毛肌動蛋白異位是好的生物記號。於是，我們創建了反向遺傳篩選，以尋找參與在出血性大腸桿菌誘導的微絨毛肌動蛋白異位的宿主因子。我們的研究結果顯示cyb-3基因是腸出血性大腸桿菌誘導微絨毛肌動蛋白異位所需的潛在宿主因子。CYB-3蛋白是調控G2/M細胞週期的細胞週期蛋白B3，細胞週期蛋白B3會結合並活化細胞週期蛋白依賴性激酶1 (CDK-1)。我們的結果發現，細胞週期蛋白依賴性激酶1的活性對於腸出血性大腸桿菌誘導的微絨毛肌動蛋白異位是必要的。為了找出CYB-3 / CDK-1信號軸的下游，我們使用RNAi篩選出會影響肌動蛋白動力學的基因。我們的結果發現，腸出血性大腸桿菌誘導的微絨毛肌動蛋白異位需要cyk-1基因和pfn-1基因，並且CYK-1和PFN-1蛋白作用在CYB-3 / CDK-1信號軸的下游。為了在哺乳動物中確認上述的發現，我們使用了人類的腸上皮細胞 (Caco-2 cells) 作為我們的體外細胞模型。我們發現在人類的腸上皮細胞，CCNB3 / CYB-3和CDK1 / CDK-1也是腸出血性大腸桿菌誘導微毛抹除所必需的宿主因子。此外，我們發現RfaD是腸出血性大腸桿菌誘導微絨毛肌動蛋白異位和微毛抹除所必需的細菌因子。總結，我們的實驗結果顯示CYB-3 / CDK-1-CYK-1 / PFN-1信號軸和細菌因子RfaD，在腸出血性大腸桿菌誘導的微絨毛肌動蛋白異位和微毛抹除中扮演重要角色。

Enterohemorrhagic E. coli (EHEC) is an emerging zoonotic pathogen that causes bloody diarrhea and even death in humans worldwide. EHEC induces the characteristic attaching and effacing (A/E) lesion resulted from rearrangements of the actin cytoskeleton. Compared with the mechanism of the EHEC-induced attachment, which have been thoroughly studied in the past two decades, the underlying mechanism of the EHEC-induced effacement of intestinal microvilli remained largely unknown. Our previous studies have demonstrated that EHEC causes mislocalization of the microvillus-specific actin (ACT-5) from the apical site to the cytoplasm in their intestinal cells and concomitant A/E lesion formation in the alimentary tract in Caenorhabditis elegans. The microvillar ACT-5 forms a core bundle structure to support the normal morphology of intestinal microvilli, and the core microvillar assemblies are in a constant turnover state. Therefore, we thought this EHEC-induced mislocalization of microvillar ACT-5 might be a biomarker for studying the microvillar effacement in C. elegans. We, therefore, created a reverse genetic screening to identify the host factors involved in the EHEC-induced ACT-5 mislocalization in C. elegans. In a reverse genetic screening, we found that cyb-3 gene encodes a potential host factor required for this EHEC-induced ACT-5 mislocalization. CYB-3 is a Cyclin B protein that binds to and activates the Cyclin-dependent kinase 1 (CDK-1) in G2/M phase of cell cycle. Our results showed that the CDK-1 activity is indispensable for this EHEC-mediated mislocalization phenotype. To identify downstream of the CYB-3/CDK-1 signaling axis, we used RNAi screening for genes that affect actin dynamics. Our results showed that cyk-1 gene which encodes diaphanous formin and pfn-1 gene which encodes actin-binding profilin are required for the EHEC-induced microvillar actin mislocalization and act downstream to the CDK-1/CYB-3 signal axis. To reconfirm the above findings in mammals, we used cultured human Caco-2 intestinal epithelial cells as our in vitro cell model. We found that CCNB3/CYB-3 and CDK1/CDK-1 are also indispensable for the EHEC-induced microvillar effacement in human intestinal Caco-2 cells. Moreover, we found that bacterial factor, RfaD, is required for this EHEC-induced ACT-5 mislocalization and is also indispensable for the EHEC-induced microvillar effacement in human intestinal Caco-2 cells. Together, all of our data support that the CYB-3/CDK-1-CYK-1/PFN-1 signal axis and bacterial factor, RfaD, play an important role for this EHEC-induced ACT-5 mislocalization and microvillar effacement.

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