大腸直腸癌是世界上最常見的癌症之一，但是目前仍有許多的挑戰存在於大腸直腸癌的診斷以及治療中。先前雙特異性去磷酸酶-2(Dual-Specificity Phosphatase-2, DUSP2)，一種可以將同一個受質上的磷酸化絲氨酸以及磷酸化蘇氨酸去磷酸化的去磷酸酶，已經被發現主要透過抑制細胞外調節蛋白激酶(Extracellular signal Regulated-Kinase, ERK)訊息傳遞在大腸直腸癌中扮演抑制腫瘤的角色。然而，目前仍然不知道DUSP2是否能夠透過辨識並去磷酸化其他的受質來調控其他訊息傳遞路徑。先前透過質譜分析而鑑定出蛋白質精氨酸甲基轉移酶4 (Protein Arginine Methyl Transferase 4, PRMT4)是一個和DUSP2互動的蛋白質。PRMT4是一個表觀遺傳調控子，主要是造成啟動子上組蛋白H3的第17個精氨酸的非對稱性雙甲基化修飾來促使靶基因表現。為了驗證PRMT4和DUSP2的交互作用，我們利用PRMT4和DUSP2的免疫共沈澱實驗展示出DUSP2會透過PRMT4上的蘇氨酸-任意氨基酸-酪氨酸模體與PRMT4互動。這項發現進一步被共軛焦免疫螢光顯微鏡所拍攝的影像所證實，結果顯示PRMT4與DUSP2的表現位置相互重疊。為了進一步推斷DUSP2對於PRMT4的調節性效果，我們利用基因富集分析(Gene Set Enrichment Analysis, GSEA)來分析過度表現PRMT4的細胞以及過度表現DUSP2的細胞之表現資料譜(expression profile)，結果發現DUSP2可能負向調控PRMT4的功能。這個假說被進一步透過PRMT4和DUSP2共表現實驗所證實了，結果顯示DUSP2透過磷酸酶活性破壞PRMT4的穩定性。為了進一步調查PRMT4上調如何參與在大腸直腸癌惡化中，我們利用免疫墨點法來偵測PRMT4在多種大腸直腸癌細胞株中的表現量，結果發現，相對於正常結腸上皮細胞， PRMT4在大腸直腸癌細胞株中有較多的表現量，表示PRMT4可能和較差的預後有關。為了更進一步描繪PRMT4的致癌性角色，我們分析了公開的染色質免疫沈澱定序(Chromatin ImmunoPrecipitation Sequencing, ChIP-seq)和核糖核酸定序(RNA Sequencing, RNA-seq)來鑑定出PRMT4的下游調控基因，MYC原致癌基因蛋白(MYC Proto-Oncogene Protein, MYC)，PRMT4的其中一個下游調控基因被發現在抑制PRMT4表現後進而導致其表現下調的情形，而在抑制DUSP2表現後則重現表現上調的情形，顯示MYC是PRMT4-DUSP2軸的下游調控基因。更進一步的實驗顯示PRMT4敲落會延後細胞週期的進程，也會敏化細胞對於歐利普（Oxaliplatin）的處理。總的來說，我們發現了PRMT4是DUSP2的一個新穎的受質且由於DUSP2喪失所造成的PRMT4上調會促進大腸直腸癌的進程。

Colorectal cancer is one of the most prevalent cancer around the world, however, there are many challenges for the diagnosis and treatment of colorectal cancer. Previously, dual-specificity phosphatase-2 (DUSP2), a phosphatase that is able to dephosphorylate phosphothreonine and phosphotyrosine residues within the same substrate, has been shown to play a tumor suppressive role in colorectal cancer primarily through inactivating ERK signaling. Nevertheless, it remains a question as to whether DUSP2 recognizes and dephosphorylates other substrates to control other signaling pathways. Previously, protein arginine methyltransferase 4 (PRMT4) was identified as a DUSP2-interacting protein through mass spectrometry analysis. PRMT4 is an epigenetic regulator shown to promote gene expression through catalyzing asymmetric dimethylation of histone H3 at arginine 17 (H3R17me2a) on promoters of its target genes. To validate the interaction between PRMT4 and DUSP2, we utilized co-immunoprecipitation of PRMT4 and DUSP2 to show that DUSP2 interacts with PRMT4 through threonine-X-tyrosine (TXY) motif of PRMT4. This finding was further supported by the confocal fluorescence microscopic images showing PRMT4 colocalized with DUSP2. To infer the regulatory relationship between PRMT4 and DUSP2, we performed the gene set enrichment analysis (GSEA) with the expression profiles of PRMT4-overexpressing and DUSP2-overexpressing cells. The analysis showed that DUSP2 might negatively regulate function of PRMT4. This hypothesis was further validated by the co-expression experiment of PRMT4 and DUSP2 in colorectal cancer cell line. Results showed that DUSP2 destabilized PRMT4 through its phosphatase activity. To further investigate how PRMT4 upregulation is involved in colorectal cancer progression, expression levels of PRMT4 were detected in colorectal cancer cell lines. Results showed that the expression level of PRMT4 was higher in colorectal cancer cell lines compared to normal colon epithelial cell line, suggesting PRMT4 might be associated with poor prognosis of patients with colorectal cancer. To further delineate the oncogenic role of PRMT4, we analyzed the publicly available chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) data to identify target genes of PRMT4. One of the target genes, c-Myc, was shown to be downregulated upon PRMT4 knockdown and upregulated upon DUSP2 knockdown, suggesting c-Myc as a downstream mediator of DUSP2-PRMT4 axis. Further experiments showed that PRMT4 knockdown delayed cell cycle progression and sensitized cells to oxaliplatin treatment. Taken altogether, we have identified PRMT4 as a novel substrate of DUSP2 and the upregulation of PRMT4 resulting from loss-of-DUSP2 would promote colorectal cancer progression.

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