Department of Pathology, Georgetown University Medical Center, Washington, D.C., United States of America.
PLoS Pathog. 2013;9(4):e1003284. doi: 10.1371/journal.ppat.1003284. Epub 2013 Apr 4.
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.
先前的研究表明，野生型人端粒酶逆转录酶（hTERT）蛋白可以在功能上替代人乳头瘤病毒 16 型（HPV-16）E6 蛋白，E6 蛋白与病毒 E7 蛋白协同作用，使原代角质形成细胞永生化。在本研究中，我们惊人地发现，催化失活的 hTERT（hTERT-D868A）、延伸缺陷的 hTERT（hTERT-HA）和端粒募集缺陷的 hTERT（hTERT N+T）也与 E7 合作，介导绕过衰老阻断并实现细胞永生化。这表明 hTERT 具有独立于其端粒维持功能的活性，介导跨越这一限制点的转移。由于 hTERT 已被证明在基因激活中具有作用，我们进行了微阵列研究，发现 E6、hTERT 和突变型 hTERT 蛋白改变了高度重叠的一组细胞基因的表达。最重要的是，E6 和 hTERT 蛋白诱导 Bmi1 的 mRNA 和蛋白水平，Bmi1 是多梳组（PcG）复合物 1 的核心亚基。我们进一步表明，Bmi1 替代 E6 或 hTERT 进行细胞永生化。最后，组织阵列研究表明，Bmi1 的表达随宫颈发育不良的严重程度而增加，提示其在宫颈癌进展中可能具有潜在作用。总之，这些数据表明 hTERT 具有端粒外的活性，促进细胞永生化，其诱导 Bmi1 是介导这种活性的一种潜在机制。
