MODULATION OF HOST CELL APOPTOTIC RESPONSES BY HPVE7

在正常细胞中，细胞的生长、分化和死亡过程错综复杂地耦合在一起。相比之下，这些过程在癌细胞中是不平衡的。在鳞状上皮细胞分化过程中，分化与细胞增殖密切相关，角质形成细胞在分化过程中永久退出细胞分裂周期。终末分化的角质形成细胞经历细胞死亡并脱落。人乳头瘤病毒(HPV)感染角质形成细胞，其生命周期与宿主上皮细胞的分化程序有关。为了允许它们的复制，HPV必须在受感染的宿主细胞中保持一个复制能力强的环境。因此，HPV编码的蛋白质允许在分化角质形成细胞时进行复制。在致癌过程中，病毒基因组通常整合到细胞基因组中。这导致这些病毒调节蛋白的表达失调。两种病毒蛋白E6和E7在HPV阳性的癌症中持续表达。我们之前已经证明，HPV E7癌蛋白可以通过灭活视网膜母细胞瘤肿瘤抑制蛋白pRb和细胞周期蛋白依赖激酶抑制物p21来灭活细胞周期检查点。在这里，我们提出的初步结果表明，E7也具有调节细胞死亡途径的能力。根据刺激的不同，HPVE7可以增强或抑制凋亡程序。表达HPVE7的细胞容易在缺乏生长因子的情况下发生凋亡，而在细胞因子肿瘤坏死因子α(TNF)的作用下，HPVE7表达的细胞受到保护而不发生凋亡。E7调节细胞死亡途径的能力与破坏视网膜母细胞瘤肿瘤抑制蛋白pRb和稳定P53肿瘤抑制蛋白的能力有关。在这里，我提出了一个综合方案，以确定pRb和p53的稳定性调节是否耦合，并分析pRb和/或pRb在这些凋亡途径中的相对重要性。此外，我将确定E7在肿瘤坏死因子途径中的作用点。我们的初步结果表明，这可能是在caspase 8(FLICE)与肿瘤坏死因子受体的偶联水平上。同时，这两个目标将提供对细胞死亡的关键调控电路的洞察。由于它们也可能在其他非HPV相关的癌症中功能失调，它们应该为抗癌治疗提供有用的靶点。

In normal cells, the processes of cellular growth, differentiation, and death are intricately coupled. In contrast, these processes are imbalanced in cancer cells. During differentiation of squamous epithelia, differentiation is tightly linked to cellular proliferation in that the keratinocytes withdraw permanently from the cell division cycle while they undergo differentiation. The terminally differentiated keratinocytes undergo cell death and are sloughed off. Human papillomaviruses (HPVs) infect keratinocytes and their life cycle is connected to the differentiation program of the host epithelial cells. To allow their replication, the HPVs have to maintain a replication-competent milieu in the infected host cell. Hence, the HPVs encode proteins that allow replication in differentiating keratinocytes. During carcinogenic progression the viral genome is often integrated into the cellular genome. This results in the dysregulated expression of these viral regulatory proteins. The two viral proteins E6 and E7 are consistently expressed in HPV-positive cancers. We have previously shown that the HPV E7 oncoprotein can inactivate cell cycle checkpoints by inactivating the retinoblastoma tumor suppressor protein, pRB, and the cyclin dependent kinase inhibitor p21. Here we present preliminary results that demonstrate, that E7 also has the capacity to modulate cell death pathways. Depending on the stimulus, HPV E7 can either enhance or inhibit the apoptotic program. HPV E7-expressing cells are predisposed to undergo apoptosis in response to growth factor deprivation while they are protected from undergoing apoptosis in response to the cytokine tumor necrosis factor alpha (TNF). The capacity of E7 to modulate cell death pathways correlates with ability to destabilize the retinoblastoma tumor suppressor protein, pRB and the stabilization of the p53 tumor suppressor. Here I propose an integrated plan to determine whether the regulation of the stabilities of pRB and p53 are coupled, and to analyze the relative importance of p53 and/or pRB in these apoptosis pathways. Furthermore I will determine the point of action of E7 in the TNF pathway. Our preliminary results indicate that this may be at the level of coupling of caspase 8 (FLICE) to the TNF-receptor. In concert, these two aims will provide insight into critical regulatory circuits of cell death. Since they may also be dysfunctional in other, non-HPV associated cancers they should provide useful targets for anticancer therapy.