SP110b核蛋白在p53核仁轉移上的角色

Abstract

核仁是細胞核中的一個區域，不僅在核醣體生物合成中非常的重要，而且在壓力反應中發揮著至關重要的作用，使細胞能夠在惡劣的條件下生存。當核醣體生物合成因發生刺激而中斷時，核仁壓力反應被激活，導致核仁完整性被破壞。 p53 是一種維持基因組穩定性的轉錄因子，通常因多種方式的壓力反應而被活化。蛋白酶體抑制劑 MG132 誘導的核仁壓力會導致 p53 在細胞核中積聚、核仁易位以及p53 轉錄活性減弱。然而，MG132誘導p53核仁轉移的機制仍不清楚。我們先前的研究顯示，SP110 蛋白的主要亞型 SP110b 與 p53 蛋白能相互作用，減弱 p53誘導的細胞死亡，並影響 p53 細胞分佈。因此，本研究的目的是確定在 MG132處理下 SP110b 是否會改變 p53 轉移到核仁中。為了了解SP110b介導的p53核仁轉移效應，研究使用了SP110b突變體SP110b M1+3，其中核仁定位訊號（NoLS）為突變型，並被證明比野生型SP110b核仁定位訊號具有更明顯的核仁定位能力。由於SP110b M1+3 和p53蛋白之間較微弱的交互作用，SP110b M1+3在MG132處理下對 p53 核仁轉移幾乎沒有影響。此外，MG132 誘導的 p53 核仁轉移在缺乏SP110 的細胞中也不受影響。基於上述結果，MG132誘導的p53核仁轉移似乎不依賴SP110b。未來的研究可以利用在類似壓力條件下與p53共轉移到核仁中的蛋白質，或是使用將SP110b轉移到核仁中的缺氧條件來觀察p53核仁轉移的變化。

The nucleolus, a compartment in the nucleus, plays a crucial role not only in ribosome biogenesis, but also in stress responses, which enable cells to survive harsh conditions. The nucleolus stress response is activated when the ribosome biogenesis is interrupted by the stimuli, resulting in the destruction of nucleolus integrity. p53, a transcription factor that maintains genome stability, is often activated as a consequence of stress responses in many ways. Nucleolar stress induced by MG132, a proteasome inhibitor, results in p53 accumulation in the nucleus, nucleolar translocation, and dulled transcriptional activity of p53. However, the mechanism of MG132-induced nucleolar translocation of p53 is still unclear. Our previous studies demonstrated that SP110b, the major isoform of speckle protein 110 (SP110), interacts with p53 protein, attenuates the p53-induced cell death, and affects p53 cellular distribution. Therefore, the purpose of this study is to determine whether SP110b alters the localization of p53 into the nucleolus under MG132 treatment. In order to examine the SP110b-mediated effect on p53 nucleolar translocation, an SP110b mutant, SP110b M1+3, in which the nucleolar localization signal (NoLS) has been mutated and demonstrated to be more obvious nucleolar localization capabilities than that of the wild-type SP110b protein was used. Due to the weak interaction between SP110b M1+3 and p53 protein, SP110b M1+3 has little to no impact on p53 nucleolus localization under MG132 treatment. Furthermore, MG132-induced nucleolar translocation of p53 remained unaffected in cells lacking SP110. Based on the results above, it appears that MG132-induced p53 nucleolar translocation is independent of SP110. Future studies could use proteins that are co-translocated with p53 into the nucleolus under similar stress conditions or use a hypoxic condition for SP110b translocation into the nucleolus to observe changes in p53 nucleolar translocation.