The human papillomavirus (HPV) E2 protein regulates viral gene expression and is also required for viral replication. HPV-transformed cells often contain chromosomally integrated copies of the HPV genome in which the viral E2 gene is disrupted. We have shown previously that re-expression of the HPV 16 E2 protein in HPV 16-transformed cells results in cell death via apoptosis. Here we show that the HPV 16 E2 protein can induce apoptosis in both HPV-transformed and non-HPV-transformed cell lines. E2-induced apoptosis is abrogated by a trans-dominant negative mutant of p53 or by overexpression of the HPV 16 E6 protein, but is increased by overexpression of wild-type p53. We show that mutations that block the DNA binding activity of E2 do not impair the ability of this protein to induce apoptosis. In contrast, removal of both N-terminal domains from the E2 dimer completely blocks E2-induced cell death. Heterodimers formed between wild-type E2 and N-terminally deleted E2 proteins also fail to induce cell death. Our data suggest that neither the DNA binding activity of E2 nor other HPV proteins are required for the induction of apoptosis by E2 and that E2-induced cell death occurs via a p53-dependent pathway.Papillomaviruses infect epithelial cells and generally induce the formation of benign hyperproliferative lesions. However, some papillomavirus types are associated with cancer. For example, human papillomavirus (HPV) 1 types 16 and 18 have been linked to cervical cancer in women (1) and bovine papillomavirus (BPV) types 2 and 4 have been linked to bladder cancer and cancer of the upper alimentary canal respectively, in cattle (2, 3). Human cervical cancers express the viral E6 and E7 oncogenes, and the products of these genes increase cell proliferation and promote cell immortalization (for a review, see Ref. 4). The human papillomavirus E2 gene, or lack thereof, is also thought to play a major role in the development of cervical cancer. Most cervical cancers contain chromosomally integrated copies of the HPV genome in which the viral E2 gene has been disrupted (5). Furthermore, mutations in the E2 gene increase the immortalization capacity of HPV 16 (6).The papillomavirus E2 genes encode sequence-specific DNAbinding proteins that regulate viral gene expression and are also required for viral DNA replication (reviewed in Ref. 7). The E2 proteins bind as dimers to multiple copies of an inverted repeat sequence found within the viral long control region. Depending on the particular virus and the particular E2 protein being studied, the binding of E2 to these sites can either activate or repress transcription of the E6 and E7 oncogenes. For example, the HPV 16 E2 protein activates transcription from the P97 promoter located at the 3Ј end of the HPV 16 long control region, whereas, under exactly the same conditions, the BPV1 E2 protein represses P97 promoter activity (8,9). Each subunit of the E2 dimer contains two domains separated by a flexible hinge: the N-terminal domain of each subunit mediates the regulation o...

Heat shock proteins (HSPs) have shown promise for the optimization of protein-based vaccines because they can transfer exogenous antigens to dendritic cells and at the same time induce their maturation. Great care must be exercised in interpretating HSP-driven studies, as by-products linked to the recombinant generation of these proteins have been shown to mediate immunological effects. We generated highly purified human recombinant Hsp70 and demonstrated that it strongly enhances the cross-presentation of exogenous antigens resulting in better antigen-specific T cell stimulation. Augmentation of T cell stimulation was a direct function of the degree of complex formation between Hsp70 and peptides and correlated with improved antigen delivery to endosomal compartments. The Hsp70 activity was independent of TAP proteins and was not inhibited by exotoxin A or endosomal acidification. Consequently, Hsp70 enhanced cross-presentation of various antigenic sequences, even when they required different post-uptake processing and trafficking, as exemplified by the tumor antigens tyrosinase and Melan-A/MART-1. Furthermore, Hsp70 enhanced cross-presentation by different antigen-presenting cells (APCs), including dendritic cells and B cells. Importantly, enhanced cross-presentation and antigen-specific T cell activation were observed in the absence of innate signals transmitted by Hsp70. As Hsp70 supports the cross-presentation of different antigens and APCs and is inert to APC function, it may show efficacy in various settings of immune modulation, including induction of antigen-specific immunity or tolerance.Cytotoxic CD8 T cells have an essential role in cellular immunity in that they destroy infected or malignantly transformed cells. They are activated by the recognition of complexes of major histocompatibility complex (MHC) 4 class I and antigenic peptides present on the surface of antigen-presenting cells (APC). Conventionally, the antigenic peptides presented by MHC class I are derived from endogenous cytosolic antigens. In specialized situations, MHC class I molecules additionally present peptides derived from exogenous antigens. This noncanonical MHC class I presentation, which is referred to as cross-presentation, requires that the exogenous antigen is internalized by APCs, subsequently enzymatically processed into peptides, and channeled into the MHC class I loading pathway (1, 2). Cross-presentation is crucial for the generation of CD8 T cell responses against antigens that are not endogenously produced by APCs, such as tumor antigens and pathogen-derived proteins. In an applied setting, cross-presentation is the required pathway for the generation of protein-based vaccines that are intended to stimulate antigen-specific CD8 responses. Critical parameters that define the efficacy of a vaccine are the amount of delivered antigen and the context in which the antigen is presented to the T cells. As the physiological capacity of APCs to cross-present antigen is generally low (3), there is significant interest to de...