SP110b調節p53造成的細胞死亡

Abstract

人類的SP110 基因為小鼠Ipr1基因的同源體 (Ortholoque)。這兩個基因所對應產生的Ipr1 和SP110 蛋白質均是屬於核蛋白。目前已知 Ipr1 在調節宿主對抗肺結核感染時的免疫反應上扮演重要的角色。SP110 主要有三種不同的異構體 (Isoforms)，分別是 SP110a、SP110b及SP110c，其中又以 SP110b 和 Ipr1 的相似性最高。SP110 在人體中主要的角色是調節基因轉錄作用和免疫反應，但是這三種 Isoforms 實際在人體內所扮演的角色目前還不太清楚。p53 是一種抑癌基因，它的功能包括調節細胞週期、細胞凋亡和細胞老化的現象。在這篇研究中，我們發現 SP110b蛋白和 p53蛋白之間有交互作用，且它們在細胞核中有(共位) Co-localization的現象。此外，當這兩個蛋白共同表現四天後，p53 在細胞中的分布會因 SP110b 蛋白的表現而改變，使得 p53 在細胞的位置由原本分布在整個細胞變成只分布在細胞核內。我們發現這樣的影響，可能導致 SP110b 抑制 p53 在細胞中的功能，使得癌細胞的死亡情形降低。我們接著加入抗癌藥物，發現在抗癌藥物的處理之下，SP110b 同樣也會抑制 p53 造成的細胞死亡。但是，我們發現在沒有 p53 的存在時無論有無藥物的處理之下，SP110b 反而是會增加癌細胞的死亡。根據 Real-time PCR 的結果，我們發現 SP110b 抑制 p53 造成的細胞死亡不是透過調控它的下游基因所導致的。然而，利用 LC MS/MS 的分析，我們發現 SP110b 會改變 p53 的後轉譯修飾作用。由以上這些結果我們可以推測，SP110b 是透過改變 p53 的後轉譯修飾作用，進而影響p53在細胞中的分布，使得p53在細胞中的功能受到調控。另外，在沒有 p53 的存在時，SP110b 則是透過 p53 非依賴型的細胞凋亡而造成細胞死亡。

SP110, a component of nuclear bodies, is the human orthologue of mouse Ipr1 protein, which plays an important role in the regulation of host innate immunity to Mycobacterium tuberculosis infection. SP110 has three major isoforms: SP110a, SP110b, and SP110c. Among these isoforms, SP110b is the closest human homologue to mouse Ipr1 protein. SP110 has functions in regulating gene transcription and immune response, but the distinct functions of individual SP110 isoform are still under investigation. p53, a tumor suppressor, has functions in regulating cell cycle, apoptosis, and senescence as well as conserving the genome stability by preventing genome mutation. In the studies, we demonstrated that SP110b protein interacted with p53 and that both proteins were partially co-localized in the nucleus. We also found that in the presence of SP110b the cellular distribution of p53 was changed from cytoplasm to nucleus 4 days post expression of both proteins. Ectopic expression of p53 in H1299 cells, which are p53 deficient, induced apoptotic cell death; however, the expression of SP110b inhibited the apoptosis induced by p53 in H1299 cells. Moreover, overexpression of SP110b suppressed the late apoptosis of p53-expressing H1299 cells treated with anti-cancer chemotherapy drugs, Cisplatin or Docetaxel. To further investigate the effect of SP110 on cancer cell death, we expressed SP110b in H1299 cells to observe whether and how SP110b affected cell survival in the absence of p53. The results showed that SP110b increased apoptosis of cancer cells in the absence of p53. According to real-time PCR analysis, SP110b didn’t significantly change the expression of p53 target genes including p21 and Puma in H1299 cells. Finally, we found that expression of SP110b caused phosphorylation of p53 at Thr312 assessed by LC MS/MS, suggesting that SP110b regulated p53 function through post-translation modification of p53. Taken together, the results indicated that SP110b interacted with p53 and negatively modulated the p53-dependent apoptotic cell death and, in the absence of p53 expression, SP110b induced a p53-independent apoptotic cell death.