Abstract: 【Abstract】 Objective To construct human immortalized keratinocytes stably expressing human papillomavirus type 16 （HPV16） E6/E7 gene, and provide a cell model for studying mechanisms underlying HPV16 E6/E7-induced cell immortalization and malignant transformation. Methods Primary human foreskin keratinocytes （HFKs） were isolated by sequential two-step enzymatic digestion. Cultured HFKs were stably transfected with a HPV16 E6/E7 gene-overexpressing lentiviral vector LV5-HPV16 E6/E7, and consecutively cultured for more than 30 passages. Then, immortalized keratinocytes were screened out and divided into 3 groups: （1） blank control group: second-passage primary HFKs; （2） experimental group: HFKs transfected with LV5-HPV16 E6/E7 at different passages, and the second-passage primary HFKs transfected with LV5-HPV16 E6/E7 were referred to as A0 cells, thereafter, the transfected HFKs were named according to their passage number, such as A1, A2, ... A30; （3） positive control group: the HPV16-positive cervical cancer cell line SiHa. Real-time fluorescence-based quantitative PCR （qRT-PCR） and Western blot analysis were performed to determine the mRNA expression of HPV16 E6/E7 and protein expression of HPV16 E6/E7 and CK14, respectively, in the blank control group, experimental group and positive control group. Cell counting kit-8 （CCK8） assay and Transwell insert invasion assay were conducted to assess the cellular proliferative and invasive activity. In vivo tumor formation experiment in nude mice was conducted to investigate the tumorigenicity of A30 cells in the experimental group and SiHa cells in the positive control group. Results Primary HFKs were successfully isolated. After the primary HFKs were transfected with the recombinant plasmid LV5-HPV16 E6/E7, the blank control group showed no fluorescence in the cells, but showed senescent phenotypes after serial passages, while in the experimental group, the volume and morphology of A30 cells were similar to those of the primary HFKs with the proportion of fluorescence-positive cells being 100%. Compared with the blank control group, the experimental group showed significantly increased mRNA expression levels of HPV16 E6 and E7 in A1, A10, A20 and A30 cells （HPV16 E6: t = 7.12, 8.07, 6.53, 5.66, P < 0.001, < 0.001, = 0.001, = 0.005, respectively; HPV16 E7: t = 3.20, 4.29, 3.75, 4.22; P = 0.024, 0.008, 0.013, 0.014, respectively）. The protein expression of HPV16 E6/E7 was absent in the blank control group, but was observed in A30 and SiHa cells. CCK8 assay showed that the proliferative activity of A10, A20 and A30 cells was significantly higher than that of the blank control group （t = 6.49, 7.55, 9.43, P = 0.003, 0.002, 0.001, respectively）, while there was no significant difference in the proliferative activity between A1 cells and the blank control group（t = 2.40, P = 0.074）. Transwell insert invasion assay showed that A30 cells could not cross the basement membrane, but SiHa cells could pass through the basement membrane and were stained blue. Two months after the inoculation with A30 cells in the nude mice, no visible tumors were found, which was confirmed by a histological study. Subcutaneous tumors were formed in the nude mice after the inoculation with SiHa cells. Conclusion Human immortalized keratinocytes were successfully established by lentivirus-mediated transfection with HPV16 E6/E7 gene, and can serve as an ideal cell model for HPV-related research.

Key words: Human papillomavirus 16, Keratinocytes, Lentivirus infections, Cell line, transformed, HPV16 E6/E7