RESTORATION OF TELOMERES IN HUMAN PAPILLOMAVIRUS-IMMORTALIZED HUMAN ANOGENITAL EPITHELIAL-CELLS

Loss of telomeres has been hypothesized to be important in cellular se nescence and may play a role in carcinogenesis. In this study, we have measured telomere length in association with the immortalization and transformation of human cervical and foreskin epithelial cells by the human papillomavirus type 16 or 18 E6 and E7 open reading frames. By u sing a telomeric TTAGGG repeat probe, it was shown that the telomeres of precrisis normal and E6-, E7-, and E6/E7-expressing cells gradually shortened with passaging (30 to 100 bp per population doubling). Cell s that expressed both E6 and E7 went through a crisis period and gave rise to immortalized lines. In contrast to precrisis cells, E6/E7-immo rtalized cells generally showed an increase in telomere length as they were passaged in culture, with some later passage lines having telome res that were similar to or longer than the earliest-passage precrisis cells examined. No consistent association could be made between telom ere length and tumorigenicity of cells in nude mice. However, of the t hree cell lines that grew in vivo, two had long telomeres, thus arguin g against the hypothesis that cancer cells favor shortened telomeres. Our results indicate that arrest of telomere shortening may be importa nt in human papillomavirus-associated immortalization and that restora tion of telomere length may be advantageous to cells with regard to th eir ability to proliferate.