HPV16 E7 protein and hTERT proteins defective for telomere maintenance cooperate to immortalize human keratinocytes.
HPV16 E7 protein and hTERT proteins defective for telomere maintenance cooperate to immortalize human keratinocytes.
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DOI：
10.1371/journal.ppat.1003284
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发表时间：
2013
期刊：
影响因子：
6.7
通讯作者：
Liu X
中科院分区：
文献类型：
--
作者：
Miller J;Dakic A;Chen R;Palechor-Ceron N;Dai Y;Kallakury B;Schlegel R;Liu X
以往的研究表明，野生型人端粒酶逆转录酶（hTERT）蛋白可以在功能上取代人乳头瘤病毒16型（HPV-16）E6蛋白，后者与病毒E7蛋白在原代角质形成细胞永生化中协同作用。在目前的研究中，我们取得了令人惊讶的发现，无催化活性的hTERT（hTERT-D868 A），延长缺陷的hTERT（hTERT-HA），和端粒募集缺陷的hTERT（hTERTN +T）也与E7在介导绕过衰老阻滞和影响细胞永生化。这表明hTERT具有独立于其端粒维持功能的活动，该功能介导通过该限制点的转运。由于hTERT已被证明在基因激活中发挥作用，我们进行了微阵列研究，发现E6，hTERT和突变hTERT蛋白改变了高度重叠的细胞基因组的表达。最重要的是，E6和hTERT蛋白诱导Bmi 1的mRNA和蛋白质水平，Bmi 1是Polycomb组（PcG）复合物1的核心亚基。我们进一步表明，Bmi 1替代E6或hTERT在细胞永生化。最后，组织芯片研究表明，Bmi 1的表达随着宫颈不典型增生的严重程度而增加，这表明在宫颈癌的进展中具有潜在的作用。总之，这些数据表明hTERT具有促进细胞永生化的额外端粒活性，并且其对Bmi 1的诱导是介导该活性的一种潜在机制。人乳头瘤病毒（HPV）是宫颈癌以及其他几种人类癌症病因学中的关键因素。E6蛋白与这些病毒的E7蛋白组合，使上皮细胞永生化并增加hTERT蛋白的表达。在目前的研究中，我们表明，hTERT的酶活性是不需要合作的细胞永生化。我们进一步证明，hTERT蛋白增加Bmi 1蛋白的表达，这也是能够合作的细胞永生化。我们预计这些发现将刺激端粒酶在HPV生物学、癌症病因学和干细胞重编程中的新研究。
Previous studies have shown that wild-type human telomerase reverse transcriptase (hTERT) protein can functionally replace the human papillomavirus type 16 (HPV-16) E6 protein, which cooperates with the viral E7 protein in the immortalization of primary keratinocytes. In the current study, we made the surprising finding that catalytically inactive hTERT (hTERT-D868A), elongation-defective hTERT (hTERT-HA), and telomere recruitment-defective hTERT (hTERT N+T) also cooperate with E7 in mediating bypass of the senescence blockade and effecting cell immortalization. This suggests that hTERT has activities independent of its telomere maintenance functions that mediate transit across this restriction point. Since hTERT has been shown to have a role in gene activation, we performed microarray studies and discovered that E6, hTERT and mutant hTERT proteins altered the expression of highly overlapping sets of cellular genes. Most important, the E6 and hTERT proteins induced mRNA and protein levels of Bmi1, the core subunit of the Polycomb Group (PcG) complex 1. We show further that Bmi1 substitutes for E6 or hTERT in cell immortalization. Finally, tissue array studies demonstrated that expression of Bmi1 increased with the severity of cervical dysplasia, suggesting a potential role in the progression of cervical cancer. Together, these data demonstrate that hTERT has extra-telomeric activities that facilitate cell immortalization and that its induction of Bmi1 is one potential mechanism for mediating this activity. The human papillomaviruses (HPVs) are critical elements in the etiology of cervical cancer, as well as several other human cancers. The E6 protein, in combination with the E7 protein of these viruses, immortalizes epithelial cells and increases the expression of the hTERT protein. In the current study we show that the enzymatic activity of hTERT is not required for cooperating in cell immortalization. We further demonstrate that hTERT proteins increase the expression of the Bmi1 protein, which is also capable of cooperating in cell immortalization. We anticipate that these findings will stimulate new studies of telomerase in HPV biology, cancer etiology, and stem cell reprogramming.
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