The human papillomavirus (HPV) E7 protein is one of only two viral proteins that remain expressed in HPVassociated human cancers. HPV E7 proteins share structural and functional similarities with oncoproteins encoded by other small DNA tumor viruses such as adenovirus E1A and SV40 large tumor antigen. The HPV E7 protein plays an important role in the viral life cycle by subverting the tight link between cellular dierentiation and proliferation in normal epithelium, thus allowing the virus to replicate in dierentiating epithelial cells that would have normally withdrawn from the cell division cycle. The transforming activities of E7 largely re¯ect this important function. Oncogene (2001) 20, 7888 ± 7898.

The PE2 cleavage signal in a full-length cDNA clone of the alphavirus Venezuelan equine encephalitis virus (VEE) was ablated by site-directed mutagenesis. RNA transcripts derived from the resulting plasmids programmed the production of nonviable particles upon transfection of baby hamster kidney (BHK) cells. However, the mutant RNAs also gave rise to a small proportion of viable revertants. Analysis of these biological revertants and their molecularly cloned homologs demonstrated that second-site suppressor mutations at either E2 position 243 or E1 position 253 were able to restore viability to PE2 cleavage signal mutants. The viable revertants incorporated unprocessed PE2 into particles which showed normal infectivity for BHK cells, but reduced ability to grow in C6/36 mosquito cells. A mutant carrying a lethal PE2 cleavage signal mutation in combination with a suppressor at E1 253 was either avirulent or highly attenuated in adult mice when inoculated by the subcutaneous, intracerebral, or intranasal route and conferred complete protection against both intraperitoneal and intranasal challenge with virulent VEE. These results indicate the close functional association of the E2 and E1 proteins in the alphavirus spike. They also have implications for the design of recombinant live virus vaccines for VEE, for other alphaviruses, and for other viruses that use a similar mechanism for glycoprotein maturation.

Keratinocytes are the natural target cells for infection by human papillomaviruses (HPVs), most of which cause benign epithelial hyperplasias (warts). However, a subset of papillomaviruses, the "high risk" HPVs, cause lesions that can progress to carcinomas. Inflammatory mediators such as tumor necrosis factor-␣ (TNF-␣) and TNF-related apoptosis-inducing ligand (TRAIL) are produced by cells in response to a viral infection. To determine the effects of TNF-␣ and TRAIL on keratinocytes expressing the high risk HPV-16 oncoprotein E7, human foreskin keratinocytes stably expressing E7 were treated with TNF-␣ and TRAIL. Treatment with TNF-␣ alone, but not TRAIL, induced growth arrest and differentiation in keratinocytes that was almost completely overcome by expression of HPV-16 E7. Both cytokines induced apoptosis when administered in combination with the protein synthesis inhibitor cycloheximide, but the apoptotic response to TRAIL was significantly more rapid and efficient compared with the response seen after TNF-␣ treatment. HPV-16 E7-expressing keratinocytes were more prone to both TNF-␣-and TRAIL-mediated apoptosis compared with vector-infected controls.

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