Musashi-1 透過表觀遺傳學以及非典型訊息路徑調控 大腸癌幹細胞之可塑性

Abstract

近年來，越來越多研究證明了大腸癌的盛行率與飲食習慣以及食品安全之間的關係。除此之外，大腸癌也是台灣罹患率最高的癌症之一。雖然大腸癌患者整體的存活率在病程的前期非常的高，可達九成以上，但是當患者被診斷出為超過IIb期之大腸癌時，其存活率就會大幅下降。這個現象主要是由於癌細胞晚期的抗藥性、轉移以及再復發等能力所導致。而癌症幹細胞被認為是使腫瘤具有上述難以治療能力的元兇之一。至目前為止，癌症幹細胞是如何和外界環境因子交流並進一步造成其可塑性調控之機制尚未十分明確。壓力顆粒是一種由核酸以及蛋白所構成的複合體，並透過外界環境壓力刺激而產生此結構，而外界壓力包含了缺氧、熱刺激以及藥物處理等等。最近的研究指出這種壓力顆粒的生成可能和癌症的抗藥性有所關聯。Msi-1是一個核酸結合蛋白，而在有外界壓力刺激的情況下它會移動至壓力顆粒的結構內；同時它也是神經以及上皮細胞的幹細胞標記。雖然Msi-1具有許多重要的特質，但是其導致癌症兇猛化的機轉仍然未解。而我們從病人檢體中發現在stage II後期之病人其Msi-1表現量皆會增加，同時表現這個基因的細胞在spheroid assay中生長情形明顯較好。綜合先前研究以及上述實驗結果，我們做了一個假設：Msi-1這個基因有可能在外界壓力的影響下會引發細胞特性的轉變，如造成癌幹細胞特性之調控以及獲得遠端轉移之能力等。透過在大腸癌細胞株中過量表現Msi-1，我們發現到MTSS1蛋白會被抑制，同時DNMT3b以及STAT3蛋白質表現量會隨之上升。因此我們提出了一個STAT3/DNMT3b/MTSS1的細胞訊息路徑調控假說。最後透過使用病人檢體所建立出的大腸癌疾病模型來初步驗證我們的假說。本實驗希望透過以上實驗數據建立出一個大腸癌可塑性轉變之非典型調控路徑，進而去改善現今對於大腸癌的了解與治療。

Nowadays, increasing evidences have shown that the prevalence of colorectal cancer (CRC) is correlated to food safety issues. CRC is a disease with the highest incident rate in all cancers in Taiwan. Although the survival rate of CRC patients is high in early stage, it has poor prognosis after stage IIb due to drug-resistance, metastasis and relapse. Cancer stem cells (CSCs) are recognized as one of the prime culprits for clinical difficulties. It is poorly studied about the underlying mechanism of CSCs plasticity related to environmental factors for cancer adaptation. Stress granules (SGs) are ribonuclear protein complex induced by environmental stress, such as hypoxia, heat stress, drug treatment. Recently, studies about SGs may regulate drug resistance have been reported. Musashi-1 (Msi-1), an RNA binding protein, is recruited to SGs under stress condition, and recognized as both neural and epithelial stem cell marker. Although Msi-1 contains several important characteristics, the mechanism about how Msi-1 affects tumor malignancy is largely unknown. We found increased Msi-1 level in stage II CRC patients, and overexpression of Msi-1 increases spheroid formation in CRC cell lines. Here we proposed a mechanism that Msi-1 mediates stress-induced tumor transformations including the switch of CSCs lineages and the acquisition of metastasis property. By overexpressing Msi-1 in CRC cell line, our data suggests that Msi-1 downregulates metastasis suppressor protein 1 (MTSS1) and increases DNMT3b and STAT3 expressions. The signal transduction axis of STAT3/DNMT3b/MTSS1 to metastasis phenotype needs further exploration. And we preliminarily validated the hypothesis by patient-derived organoid culture system. According to these preliminary results, we aim to elucidate CRC transformations by non-canonical pathways which may pave the way for drug development for improving CRCs treatment.