The pathogenesis of cervical cancer is influenced by a variety of cytokines that regulate keratinocyte growth or mediate the host's response to papillomavirus (HPV) infection. Our studies examine mechanisms by which HPVs perturb the ability of cervical keratinocytes to respond to or secrete specific cytokines. Keratinocytes were infected with high-titer recombinant retroviruses encoding the HPV-16 E6 or E7 genes alone or in combination; cytokine release was monitored by ELISA assay. E6 and E7 stimulated a 10 to 20-fold increase in release of interleukin-1a (IL-1a), a key mediator of inflammation and immunity (relative effectiveness E7E6/E7E6vector control). IL-1a release occurred selectively as secretion of the IL-1 receptor antagonist and IL-1 soluble receptor2, competitive inhibitors of IL-1 binding, were increased only slightly. E7 and E6/E7 stimulated a 10-fold increase in apoptosis, a recognized pathway for IL-1a release. Furthermore, functional innactivation of the retinoblastoma protein (Rb) was important as E7 proteins from 'low risk' types that bound Rb less effectively did not liberate IL-1a. In contrast, E6 and E7 decreased release of biologically active TGF-b2, an autocrine growth factor that inhibits proliferation of normal keratinocytes. Furthermore, normal ecto-cervical keratinocytes and HPV-immortalized cells responded differently to these two cytokines. IL-1a stimulated proliferation of several HPV-immortalized and cervical carcinoma-derived cell lines whereas normal cells were not effected. In addition, low levels of TGF-b stimulated proliferation and inhibited squamous differentiation of the immortal cells but not normal keratinocytes. TGF-b also increased the number of epidermal growth factor (EGF) receptors by stimulating transcription of the gene. Molecular analyses indicated that both cytokines stimulated proliferation by induction of an autocrine growth factor, amphiregulin, a member of the EGF peptide family. Thus, HPV-16 E6 and E7 proteins perturb expression and responsiveness to cytokines that regulate keratinocyte proliferation and host response to infection. These results suggest that differential responsiveness to IL-1a and TGF- b provides a selective growth advantage for abnormal cervical cells in vivo.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Intramural Research (Z01)
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Special Emphasis Panel (LBGY)
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National Cancer Institute Division of Basic Sciences
United States
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