Cellular changes induced by low-risk human papillomavirus type 11 in keratinocytes that stably maintain viral episomes

Infections by low-risk papillomavirus types, such as human papillomavirus ( HPV) type 6 (HPV-6) and HPV-11, induce benign genital warts that rarely pro gress to malignancy. In contrast, lesions induced by high-risk HPV types ha ve the potential to progress to cancer. Considerable information is availab le concerning the pathogenesis of high-risk HPV types, but little is known about the life cycle of low-risk HPV types. Although functionally distinct, both high- and low-risk virus types infect keratinocytes and induce virion production upon differentiation. This information suggests that they may s hare common mechanisms for regulating their productive life cycles. Using t issue culture methods developed to study high-risk HPV types, we examined t he ability of BPV-11 to be stably maintained as episomes following transfec tion of normal human keratinocytes with cloned viral DNA. HPV-11 genomes we re found to be maintained in keratinocytes for extended passages in culture s in 14 independent experiments involving transfection of cloned HPV-11 DNA . Interestingly, the HPV-11-positive cells exhibited an extended life span that averaged approximately twofold longer than that of control neomycin-tr ansfected cells. In organotypic cultures, HPV-11-positive cells exhibited a ltered differentiation patterns, but the extent of disruption was less seve re than that seen with high-risk HPV types. In addition, the amplification of HPV-11 DNA, as well as the induction of several viral messages, was obse rved following differentiation of transfected cells in semisolid media. To determine whether global changes in cellular gene expression induced by HPV -11 were similar to those observed with high-risk HPV-31 (Y. E. Chang and L . A. Laimins, J. ViroL 74:4174-4182, 2000), microarray analysis of 7,075 ex pressed sequences was performed. A spectrum of cellular genes different fro m that previously reported for HPV-31 was found to be activated or represse d by HPV-11. The expression of only a small set of genes was similarly alte red by both high- and low-risk BPV types. This result suggests that differe nt classes of HPVs have distinct effects on global cellular transcription p atterns during infection. The methods described allow for a genetic analysi s of HPV-11 in the context of its differentiation-dependent life cycle.