探討 Irisin 對人類大腸直腸癌之影響與其分子機制

Abstract

缺乏運動和肥胖與提高罹患大腸直腸癌的風險之間具有相當密切的關聯，研究也顯示運動可以降低罹患大腸直腸癌的機率並延緩癌症的進程。然而，運動如何預防癌症發展的機制尚不清楚。近年的研究發現，irisin是一種運動時肌肉細胞所分泌出來的肌肉激素，irisin會作用於白色脂肪細胞並促進脂肪細胞的褐化以減少肥胖的情況。研究發現irisin會抑制多種類癌細胞的細胞侵襲、遷移和增生的能力。因此本篇論文的研究目的為探討irisin對於不同時期的人類大腸直腸癌細胞的影響及其分子機制。在本篇研究中，以大腸桿菌和酵母菌來表現人類irisin重組蛋白質，並探討irisin對於人類大腸直腸癌細胞的影響。我們的結果顯示irisin會降低大腸直腸癌細胞的增生能力，但不影響正常大腸細胞的增生，irisin也會抑制大腸直腸癌細胞的侵襲能力，但不影響細胞遷移。Irisin會藉由誘導週期蛋白依賴性激酶 (CDK) 的抑制劑p21的表現和抑制細胞週期調控因子cdc2的活化，以促使大腸直腸癌細胞的細胞週期停滯於S和G2期，進而降低細胞的增生能力。接著我們進一步探討irisin如何透過分子機制來調控對於癌細胞生理功能的影響，我們的結果顯示irisin會結合到大腸直腸癌細胞表面，並進一步抑制兩個在整合素 (integrin) 所觸發的信息傳導路徑中的重要分子FAK和AKT的磷酸化。而結果亦顯示irisin可能會結合到細胞表面的integrin β4，並藉由integrin β4來調控對於大腸直腸癌細胞增生能力的影響。此外我們也利用轉錄體學分析來鑑定出irisin所調控的基因，並藉由小分子干擾RNA (siRNA) 來抑制所篩選出的基因表現以評估該基因所參與調控的生理功能，結果顯示irisin會藉由誘導癌細胞轉移抑制因子 (metastasis suppressor) NDRG1的表現來抑制大腸直腸癌細胞的侵襲能力。總結上述的結果，本篇論文提議irisin可以延緩大腸直腸癌惡化的進程，並且具有發展為用於大腸直腸癌治療藥物的潛力。

Insufficient physical activity and obesity are strongly linked to the increased risk of colorectal cancer (CRC). Epidemiological studies also indicate that exercise can reduce the risk of CRC and delay cancer progression. However, the underlying mechanism of how exercise prevents cancer development is still unclear. Recently, irisin is discovered as a myokine released from muscle cells during exercise. Irisin targets white adipocytes and promotes browning of adipocytes to reduce obesity. Several studies found that irisin inhibits cell invasion, migration and proliferation in various types of cancer cells. Thus, the research purpose of this thesis is to study the effect and the molecular mechanism of irisin on different stages of human CRC cells. In this research, recombinant human irisin was produced in E.coli and Pichia pastoris, and its effects on CRC cells were investigated. Our results showed that irisin reduced cell proliferation of CRC cells, but did not affect normal colon cells. Irisin also inhibited cell invasion of CRC cells, but did not affect cell migration. Irisin induced the expression of p21 and inhibited the activation of cdc2, a cell cycle regulator, and further contributed to S and G2 phase arrest of cell cycle in CRC cells to reduce cell proliferation. We further investigated the molecular mechanism of how irisin mediates effects on cancer cells. Our results showed irisin bound to the cell surface of CRC cells and further inhibited phosphorylation of FAK and AKT which are key components of the signal transduction pathway triggered by integrins. Irisin might bind to integrin β4 on the cell surface and mediate effects on CRC cells. Moreover, transcriptome NGS analysis was performed to identify irisin-regulated genes, and the biological function of the selected gene was assessed by siRNA knockdown. The results showed that irisin inhibited cell invasion of CRC cells by inducing the expression of NDRG1 which is known as a metastasis suppressor. In conclusion, we proposed that irisin could delay CRC progression and might be a potential target of CRC treatment.