Wei Qize
Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA.
J Biol Chem. 2005 Nov 11;280(45):37790-7. doi: 10.1074/jbc.M502974200. Epub 2005 Aug 29.
Binding of high risk human papillomavirus (HPV) E6 protein to E6-associated protein (E6AP), a cellular ubiquitin-protein ligase, enables E6AP to ubiquitinate p53, leading to p53 degradation in cervical cancer cells such as HeLa cells. Here we report that Pitx2a, a bicoid-type homeodomain transcription factor, can bind to HPV E6 protein and inhibit E6/E6AP-mediated p53 degradation. Deletion of the Pitx2a homeodomain abrogates its ability to bind to HPV E6 protein and to induce p53 accumulation in HeLa cells, suggesting that the homeodomain of Pitx2a is essential for inhibition of E6/E6AP-mediated p53 degradation. Recombinant Pitx2a can also block E6/E6AP-mediated p53 degradation in vitro, indicating that this function of Pitx2a is independent of its transcription activity. Pitx2a does not regulate Hdm2-mediated p53 degradation, because Pitx2a does not affect p53 protein levels in HPV-negative cells, such as HCT116, U2OS, and C33A cells. In addition, Pitx2a-induced p53 is transcriptionally active and maintains its specific DNA binding activity in HeLa cells. Taken together, these findings suggest that, by binding to E6, Pitx2a interferes with E6/E6AP-mediated p53 degradation, leading to the accumulation of functional p53 protein in HeLa cells.
高危型人乳头瘤病毒（HPV）E6蛋白与细胞泛素-蛋白连接酶E6相关蛋白（E6AP）结合，可使E6AP将p53泛素化，导致p53在宫颈癌细胞（如HeLa细胞）中降解。在此我们报告，双尾型同源域转录因子Pitx2a能够与HPV E6蛋白结合，并抑制E6/E6AP介导的p53降解。缺失Pitx2a同源域会消除其与HPV E6蛋白结合以及在HeLa细胞中诱导p53蓄积的能力，这表明Pitx2a的同源域对于抑制E6/E6AP介导的p53降解至关重要。重组Pitx2a在体外也能阻断E6/E6AP介导的p53降解，这表明Pitx2a的这一功能独立于其转录活性。Pitx2a不调节Hdm2介导的p53降解，因为Pitx2a不影响HPV阴性细胞（如HCT116、U2OS和C33A细胞）中的p53蛋白水平。此外，Pitx2a诱导产生的p53具有转录活性，并在HeLa细胞中保持其特定的DNA结合活性。综上所述，这些发现表明，通过与E6结合，Pitx2a干扰E6/E6AP介导的p53降解，导致HeLa细胞中功能性p53蛋白蓄积。
