抑癌基因p53及其相关蛋白,p63和p73可以合成为缺少部分N-或C-末端区域的多种同种型。具体来说,ΔNp73α同种型的高表达与以预后不良为特征的各种人类恶性肿瘤有关。这种亚型也是由致癌病毒积累的,例如爱泼斯坦-巴尔病毒(EBV),以及似乎与致癌作用有关的β人乳头瘤病毒(HPV)属。为了获得对ΔNp73α机制的更多了解,我们使用β-HPV38型病毒E6和E7蛋白转化的人角质形成细胞作为实验模型(38HK)进行了蛋白质组学分析.我们发现ΔNp73α通过与E2F4的直接相互作用与E2F4/p130阻遏复合物结合。ΔNp73同种型特征的p73的N末端截短有利于这种相互作用。此外,它独立于C端拼接状态,表明它可以代表ΔNp73同工型的一般特征(α,β,γ,δ,ε,ζ,θ,η,和η1)。我们表明,ΔNp73α-E2F4/p130复合物抑制特定基因的表达,包括编码增殖负调节因子的基因,在38HK和HPV阴性癌症来源的细胞系中。在缺乏ΔNp73α的原代角质形成细胞中,E2F4/p130不会抑制此类基因,表明与ΔNp73α的相互作用重新连接了E2F4转录程序。总之,我们已经鉴定并鉴定了一种新的转录调控复合物,该复合物在肿瘤发生中具有潜在的意义。重要性TP53基因在约50%的人类癌症中突变。相比之下,TP63和TP73基因很少突变,而是在广泛的恶性肿瘤中表达为ΔNp63和ΔNp73亚型,它们充当p53拮抗剂。与化学抗性相关的ΔNp63和ΔNp73的积累,可由致癌病毒如EBV或HPV感染引起。我们的研究集中在高度致癌的ΔNp73α亚型上,并使用了细胞转化的病毒模型。我们揭示了ΔNp73α和参与细胞周期控制的E2F4/p130复合物之间的物理相互作用,它重新连接了E2F4/p130转录程序。我们的工作表明,ΔNp73同工型可以与不与TAp73α肿瘤抑制因子结合的蛋白质建立相互作用。这种情况类似于支持细胞增殖的p53突变体的功能获得相互作用。
Tumor suppressor p53 and its related proteins, p63 and p73, can be synthesized as multiple isoforms lacking part of the N- or C-terminal regions. Specifically, high expression of the ΔNp73α isoform is notoriously associated with various human malignancies characterized by poor prognosis. This isoform is also accumulated by oncogenic viruses, such as Epstein-Barr virus (EBV), as well as genus beta human papillomaviruses (HPV) that appear to be involved in carcinogenesis. To gain additional insight into ΔNp73α mechanisms, we have performed proteomics analyses using human keratinocytes transformed by the E6 and E7 proteins of the beta-HPV type 38 virus as an experimental model (38HK). We find that ΔNp73α associates with the E2F4/p130 repressor complex through a direct interaction with E2F4. This interaction is favored by the N-terminal truncation of p73 characteristic of ΔNp73 isoforms. Moreover, it is independent of the C-terminal splicing status, suggesting that it could represent a general feature of ΔNp73 isoforms (α, β, γ, δ, ε, ζ, θ, η, and η1). We show that the ΔNp73α-E2F4/p130 complex inhibits the expression of specific genes, including genes encoding for negative regulators of proliferation, both in 38HK and in HPV-negative cancer-derived cell lines. Such genes are not inhibited by E2F4/p130 in primary keratinocytes lacking ΔNp73α, indicating that the interaction with ΔNp73α rewires the E2F4 transcriptional program. In conclusion, we have identified and characterized a novel transcriptional regulatory complex with potential implications in oncogenesis. IMPORTANCE The TP53 gene is mutated in about 50% of human cancers. In contrast, the TP63 and TP73 genes are rarely mutated but rather expressed as ΔNp63 and ΔNp73 isoforms in a wide range of malignancies, where they act as p53 antagonists. Accumulation of ΔNp63 and ΔNp73, which is associated with chemoresistance, can result from infection by oncogenic viruses such as EBV or HPV. Our study focuses on the highly carcinogenic ΔNp73α isoform and uses a viral model of cellular transformation. We unveil a physical interaction between ΔNp73α and the E2F4/p130 complex involved in cell cycle control, which rewires the E2F4/p130 transcriptional program. Our work shows that ΔNp73 isoforms can establish interactions with proteins that do not bind to the TAp73α tumor suppressor. This situation is analogous to the gain-of-function interactions of p53 mutants supporting cellular proliferation.