Influence of viral immediate early proteins on AF4-complex dependent transcriptional processes

我们已经揭开了人类AF4多蛋白复合体的组成和功能(Benedikt，2011)。该核复合体的相对分子质量为~2丙二醛，至少由13种蛋白质组成。该复合体的功能是激活RNA聚合酶II(RPII)进行转录延伸。这是通过复杂结合的P-TEFb复合体完成的，它使RPII的C-末端结构域(CTD)在丝氨酸-2残基上磷酸化。相关的组蛋白甲基转移酶CARM1、NSD1和DOT1L随后在组蛋白H3的不同残基(R2、R17、R26、K36、K79)的转录延伸过程中修饰组蛋白H3的染色质。对于RPII激活的每个周期，AF4复合体通过蛋白酶体途径被破坏。相比之下，AF4 k.O.细胞几乎无法进行转录过程，因为倍增时间被戏剧性地延长到18-21天。这表明AF4复合体是转录过程的关键成分。在这里，我们想要研究我们在实验中观察到的一个现象：病毒立即早期蛋白(IEP)增强AF4依赖的转录延长，并导致AF4复合体免受蛋白酶体降解的保护。然而，AF4蛋白含量的增加不仅增强了转录过程，而且还表现出对哺乳动物细胞的“转化”特性。为此，我们想调查常见DNA病毒的病毒IEP如何改变人类AF4复合体的组成，这些蛋白质复合体如何抵抗细胞降解，以及这些病毒诱导的变化导致哪些致癌后果。

We have unravelled the composition and function of the human AF4 multiprotein complex (Benedikt, 2011). This nuclear complex has a molecular weight of ~2 MDa and is composed of at least 13 proteins. The function of this complex is to activate RNA Polymerase II (RPII) for transcriptional elongation. This is being done by the complex-bound P-TEFb complex which phosphorylates the C-terminal domain (CTD) of RPII at serine-2 residues. The associated histone methlytransferases, CARM1, NSD1 and DOT1L, are subsequently modifying the chromatin at distinct residues of histone H3 along with the process of transcriptional elongation (R2, R17, R26, K36, K79). For each cycle of RPII activation the AF4 complex becomes destructed via the proteasomal pathway. By contrast, AF4 k.o. cells are nearly unable to perform transcriptional processes, because doubling-times are dramatically extended up to 18-21 days. This suggests that the AF4 complex is a key component for the transcription process. Here, we want to investigate a phenomenon that we observed in our experiments: viral immediate early proteins (IEP's) enhance AF4-dependent transcriptional elongation and cause a protection of the AF4 complex against proteasomal degradation. However, increased amounts of AF4 protein does not only enhance transcriptional processes but also exhibit "transforming" properties for mammalian cells. For this reason we want to investigate how viral IEP's of common DNA viruses change the composition of the human AF4 complex, how these protein complexes become resistant against cellular degradation and which oncogenic consequences are resulting from these virus-induced changes.