SP110 核蛋白與p53及MYBBP1A蛋白的交互作用

Abstract

人類的 SP110 基因是小鼠 Ipr1 基因的同源體，且這兩個基因所對應產生的SP110 與Ipr1 蛋白均屬於核蛋白。先前報導指出，Ipr1蛋白在調控宿主對抗肺結核感染時的免疫反應上扮演重要角色。SP110蛋白主要有三種不同異構型：SP110a、SP110b、SP110c。在這些不同形式的SP110蛋白中，又以SP110b與Ipr1蛋白同源性最高。 SP110蛋白在人體中主要的角色可能是調節基因轉錄作用和免疫反應，但到目前為止對SP110蛋白還沒有很清楚的了解。p53是一個有名的抑癌基因，其功能包含調控細胞週期、細胞凋亡、老化等等。先前的研究指出，小鼠中的Mybbp1A蛋白會與Ipr1蛋白有交互作用的現象。除此之外，人類的MYBBP1A蛋白還會幫助p53與p300產生交互作用，促使p53發生乙醯化及活化反應。 在本研究中，我們首先發現p53蛋白與SP110b蛋白具有直接性的交互作用。且在細胞中，他們都會位在細胞核內。此外，我們也發現MYBBP1A蛋白在細胞的分佈會伴隨著p53蛋白的表現而跟著改變; 但在SP110b蛋白存在下，MYBBP1A蛋白與p53蛋白皆會隨著SP110b蛋白的表現而改變細胞的分佈。根據p53 promoter-luciferase reporter assay的結果，我們發現同時表現p53與SP110b時，SP110b會穩定p53活性並促使p53表現，而且當MYBBP1A 再加入後，更能促使p53的表現上升。這些結果顯示此三個蛋白會有交互作用而影響細胞的功能。

SP110, a nuclear body protein, is the human orthologue of mouse Ipr1 (Intracellular pathogen resistance 1) protein, which has been previously identified as an important genetic factor regulating host innate immunity against Mycobacterium tuberculosis infection. SP110 protein has three major isoforms, SP110a, SP110b and SP110c, which are produced by the alternative splicing of mRNA. However, the distinct functions of SP110 isoforms are still under investigation. Among the isoforms, SP110b is the closest human homologue to Ipr1 protein, and both proteins are indicated to play multiple functions in cells in our previous studies. p53, a well-known tumor suppressor, has functions on regulating cell cycle arrest, apoptosis, senescence and genomic DNA stability. It has been demonstrated that mouse Mybbp1a protein (Myb-binding protein 1a) interacts with Ipr1 protein. Besides, human MYBBP1A also facilitates the p53-p300 interaction to enhance p53 acetylation and activation. However, the relationship of these three proteins (SP110, p53, and MYBBP1A) and the role of their interactions in cellular functions are still unknown. In the studies, we first confirmed the interaction between p53 and SP110b by pull-down assay. We also found that these proteins were partially co-localized in the nucleus. Moreover, we observed that the cellular distribution of MYBBP1A was accompanied with the cellular localization of p53 and the cellular distributions of both proteins were further concomitant with the localization of SP110b. It has been previously demonstrated that the expression of p53 was stabilized by SP110b. Here we further showed that the expression of p53 and SP110b in HEK293T and H1299 cells were much increased in the presence of MYBBP1A than in the absence of the protein and the transcription level of p53 was also increased in the presence of SP110b. The results indicated that SP110b interacted with p53 and MYBBP1A and these proteins were localized in the nucleus. In the presence of SP110b, MYBBP1A regulated the transcription of p53. The studies suggested that interaction of the three proteins may affect cellular functions.