Demonstration of human papillomavirus (HPV) genomic amplification and viral-like particles from CaSki cell line in SCID mice.

We demonstrate that from the CaSki cervical cancer cell line, integrated HPV-16 genome was amplified and viral-like particles were generated in an in vivo SCID mouse model. The in vivo tumor growth of several HPV-containing cell lines and 2 HPV-negative cell lines was examined in SCID mice. Tumor growth was noted with the HeLa, CaSki, ME-180, and MS751 cell lines within 2 months after subcutaneous injection. Squamous differentiation was appreciated in focal areas of tumors derived from CaSki and ME-180. In the CaSki tumors, DNA in situ hybridization revealed homogeneous staining of nuclei in some cells in the differentiated areas, suggesting HPV genomic amplification. In contrast, punctate or speckled patterns of hybridization were identified in the less differentiated areas, suggesting continued integration of the HPV genome. Immunocytochemical staining for HPV-16 L1 capsid protein showed it to be concentrated in cells from the differentiated areas, correlating with the results of hybridization. Electron microscopic studies revealed 50 nm uniform particles, consistent with HPV viral-like particles, in the nuclei of some cells in well-differentiated areas. Furthermore, Southern transfer and hybridization of the Hirt's extract from the CaSki tumors was positive for HPV-16 DNA, indicating non-integrated, low molecular weight HPV-16 DNA. Our results show HPV genomic amplification of integrated viral DNA and generation of HPV viral-like particles in CaSki cancer cells in SCID mice and that viral DNA amplification and the formation of viral-like particles are coupled to cellular differentiation. This experimental model provides a potential system for studying the molecular pathogenesis of HPV infections.