The There is convincing epidemiological and experimental evidence linking specific types of human papillomavirus (HPV) with the etiology of cervical cancer (1, 2). HPV-16 and -18 are present in >70% of cervical dysplasias and carcinomas, whereas HPV-6 and -11 are usually found in benign genital condyloma acuminata (3, 4). The E6-E7 genes of HPV-16, which are expressed at high levels in cervical carcinomas, encode proteins that are capable of transcriptional regulation and cellular transformation through interactions with cellular proteins, such as the tumor suppressor gene products pRB and p53 (5). These functions suggest an important role of HPV-16 in the initiation of cervical cancers.The HPV-16 DNA is frequently found in metastases of cervical cancers in either local lymph nodes (6)(7)(8)(9)(10)(11)(12)(13)(14) or distant site (15). The same HPV DNA sequences are consistently detected in metastases and primary tumors from the same patients, suggesting the same origin of viral DNA, and in situ hybridization has demonstrated the HPV DNA within the nuclei of metastatic cells (9, 10). HPV-16 DNA can also be detected in histologically negative lymph nodes (8, 11), suggesting that it may provide a sensitive indicator for early metastases. It is not known, however, whether the expression of HPV genes influences the ability of a tumor to metastasize, and it is controversial whether human cervical cancers with HPV-16 DNA are more invasive than those associated with nononcogenic HPV types or HPV-negative cancers (16)(17)(18).To investigate the relationship between the expression of HPV-16 genes and tumor metastasis, we have assessed the ability of murine cell lines expressing the E6 and E7 genes from oncogenic HPV-16 or nononcogenic HPV-6b to formThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. metastasis in a nude mouse model. We report here that the expression in mouse cell lines of the E6 and E7 genes from HPV-16, but not from HPV-6b, results in metastatic conversion.
MATERIALS AND METHODSMice. Female BALB/c (nu/nu) mice, 4-8 weeks old, and C3H/HeN mice, 6-8 weeks old, were bought from HarlanSprague-Dawley.Cell Lines. NCTC2555 is a fibrosarcoma line of C3H/HeN mouse origin (19), and the NIH 3T3 fibroblast line is BALB/c mouse origin. The CaSki line was derived from a HPV-16-positive squamous cell carcinoma of human cervix. PA317 and t-2 are packaging cell lines for amphotropic or ecotropic retroviruses, respectively. YAC-1 is a natural killer (NK) cell-sensitive lymphoma line and EL-4 is a NK-resistant lymphoma line. All cells were purchased from American Type Culture Collection and were maintained at 37°C with Dulbecco's modified Eagle's medium (DMEM) containing 10% fetal calf serum (HyClone) in a humidified atmosphere of 5% C02/95% air.Gene Transfer by Recombinant Retroviruses. Retroviruses were prepared as described (20,21) at biosafety level 2....