The 9ORF1 gene encodes an adenovirus E4 region oncoprotein that requires a C-terminal region for transforming activity. Screening a gt11 cDNA expression library with a 9ORF1 protein probe yielded a novel cellular PDZ domain-containing protein, 9BP-1, which binds to wildtype, but not a transformation-defective, C-terminal, mutant 9ORF1 protein. The fact that PDZ domains complex with specific sequences at the free C-terminal end of some proteins led to the recognition that the 9ORF1 C-terminal region contained such a consensus-binding motif. This discovery prompted investigations into whether the 9ORF1 protein associates with additional cellular proteins having PDZ domains. It was found that the 9ORF1 protein interacts directly, in vitro and in vivo, with the PDZ domain-containing protein hDlg͞SAP97 (DLG), which is a mammalian homolog of the Drosophila discs large tumor suppressor protein and which also binds the adenomatous polyposis coli tumor suppressor protein. Of interest, in forming complexes, the 9ORF1 protein preferentially associated with the second PDZ domain of DLG, similar to adenomatous polyposis coli protein. Human T cell leukemia virus type 1 Tax and most oncogenic human papillomavirus E6 oncoproteins also possessed PDZ domainbinding motifs at their C termini and, significantly, human T cell leukemia virus type 1 Tax and human papillomavirus 18 E6 proteins bound DLG in vitro. Considering the requirement of the 9ORF1 C-terminal region in transformation, these findings suggest that interactions with the cellular factor DLG may contribute to the tumorigenic potentials of several different human virus oncoproteins.Human adenoviruses are organized into six subgroups, A through F, and in people cause primarily respiratory, gastrointestinal, and eye infections (1). After infection of rodents, however, subgroup A and B and some subgroup D adenoviruses are tumorigenic. In animals, subgroup A and B adenoviruses produce undifferentiated sarcomas at the site of virus injection, and the viral E1 region, consisting of the E1A and E1B genes, is both necessary and sufficient for this tumorigenicity. The transforming potentials of the nuclear E1A and E1B oncoproteins derive, at least in part, from an ability to complex with and inactivate the cellular tumor suppressor proteins pRB and p53, respectively (2).Compared with the subgroup A and B adenoviruses, subgroup D adenovirus type 9 (Ad9) is unique in eliciting only estrogen-dependent mammary tumors in female rats (3) and requiring the viral E4 region ORF1 gene (9ORF1) for oncogenicity (4, 5). The 9ORF1 gene codes for a 14-kDa cytoplasmic transforming protein (5, 6), and three separate regions of this viral polypeptide are important for transforming potential in cells (7), including a C-terminal region that mediates direct binding to several unidentified cellular proteins (p220, p180, p160, p155, p140͞p130; R.S.W. and R.T.J., unpublished work). To reveal the molecular mechanisms of the novel 9ORF1 oncoprotein, we sought to identify these 9ORF1-associated cel...

The oncoproteins of small DNA tumor viruses promote tumorigenesis by complexing with cellular factors intimately involved in the control of cell proliferation. The major oncogenic determinants for human adenovirus type 9 (Ad9) and high-risk human papillomaviruses (HPV) are the E4-ORF1 and E6 proteins, respectively. These seemingly unrelated viral oncoproteins are similar in that their transforming activities in cells depend, in part, on a carboxyl-terminal PDZ domain-binding motif which mediates interactions with the cellular PDZprotein DLG. Here we demonstrated that both Ad9 E4-ORF1 and high-risk HPV E6 proteins also bind to the DLG-related PDZ-protein MAGI-1. These interactions resulted in MAGI-1 being aberrantly sequestered in the cytoplasm by the Ad9 E4-ORF1 protein or being targeted for degradation by high-risk HPV E6 proteins. Transformation-defective mutant viral proteins, however, were de®cient for these activities. Our ®ndings indicate that MAGI-1 is a member of a select group of cellular PDZ proteins targeted by both adenovirus E4-ORF1 and high-risk HPV E6 proteins and, in addition, suggest that the tumorigenic potentials of these viral oncoproteins depend, in part, on an ability to inhibit the function of MAGI-1 in cells.

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A general theme that has emerged from studies of DNA tumor viruses is that otherwise unrelated oncoproteins encoded by these viruses often target the same important cellular factors. Major oncogenic determinants for human adenovirus type 9 (Ad9) and high-risk human papillomaviruses (HPV) are the E4-ORF1 and E6 oncoproteins, respectively, and although otherwise unrelated, both of these viral proteins possess a functional PDZ domain-binding motif that is essential for their transforming activity and for binding to the PDZ domain-containing and putative tumor suppressor protein DLG. We report here that the PDZ domainbinding motifs of Ad9 E4-ORF1 and high-risk HPV-18 E6 also mediate binding to the widely expressed cellular factor MUPP1, a large multi-PDZ domain protein predicted to function as an adapter in signal transduction. With regard to the consequences of these interactions in cells, we showed that Ad9 E4-ORF1 aberrantly sequesters MUPP1 within the cytoplasm of cells whereas HPV-18 E6 targets this cellular protein for degradation. These effects were specific because mutant viral proteins unable to bind MUPP1 lack these activities. From these results, we propose that the multi-PDZ domain protein MUPP1 is involved in negatively regulating cellular proliferation and that the transforming activities of two different viral oncoproteins depend, in part, on their ability to inactivate this cellular factor.Human adenovirus type 9 (Ad9) is a unique oncogenic virus that generates estrogen-dependent mammary tumors in rats (22). Whereas the viral E1A and E1B oncoproteins are responsible for tumorigenesis by most human adenoviruses (44), the primary oncogenic determinant for Ad9 is its E4-ORF1 (9ORF1) transforming protein (21,23,52,59). Mutational analyses of the 125-amino-acid (aa) 9ORF1 protein implicate three separate regions (regions I, II, and III) as being critical for transformation (56). Although the activities associated with regions I and II have not been determined, region III at the extreme carboxyl terminus of 9ORF1 mediates interactions with multiple cellular polypeptides (p220, p180, p160, p155, and p140/p130) (57). This carboxyl-terminal 9ORF1 domain was recently discovered to define a functional PDZ domainbinding motif (28) and, consistent with this finding, 9ORF1-associated protein p140/130 was identified as the cellular PDZ protein DLG (28), a mammalian homolog of the Drosophila discs large tumor suppressor protein dlg-A (29, 33).In humans, infections with human T-cell leukemia virus type 1 and high-risk human papillomaviruses (HPV) are associated with the development of adult T-cell leukemia and cervical carcinoma, respectively (5, 43). Finding a functional PDZ domain-binding motif at the carboxyl terminus of 9ORF1 subsequently led us to discover that human T-cell leukemia virus type 1 Tax and high-risk but not low-risk HPV E6 oncoproteins possess similar binding motifs at their carboxyl termini and, in addition, bind DLG (28). Although it is well established that transformation by high-risk HPV E6 pro...

More than a decade ago, three viral oncoproteins, adenovirus type 9 E4-ORF1, human T-lymphotropic virus type 1 Tax, and high-risk human papillomavirus E6, were found to encode a related carboxyl-terminal PDZ domain-binding motif (PBM) that mediates interactions with a select group of cellular PDZ proteins. Recent studies have shown that many other viruses also encode PBM-containing proteins that bind to cellular PDZ proteins. Interestingly, these recently recognized viruses include not only some with oncogenic potential (hepatitis B virus, rhesus papillomavirus, cottontail rabbit papillomavirus) but also many without this potential (influenza virus, Dengue virus, tick-borne encephalitis virus, rabies virus, severe acute respiratory syndrome coronavirus, human immunodeficiency virus). Examination of the cellular PDZ proteins that are targets of viral PBMs reveals that the viral proteins often interact with the same or similar types of PDZ proteins, most notably Dlg1 and other members of the membrane-associated guanylate kinase protein family, as well as Scribble. In addition, cellular PDZ protein targets of viral PBMs commonly control tight junction formation, cell polarity establishment, and apoptosis. These findings reveal a new theme in virology wherein many different virus families encode proteins that bind and perturb the function of cellular PDZ proteins. The inhibition or perturbation of the function of cellular PDZ proteins appears to be a widely used strategy for viruses to enhance their replication, disseminate in the host, and transmit to new hosts.The PDZ domain is a protein-protein interaction module that is widespread throughout evolution, being found in bacteria, fungi, and metazoans (76). PDZ domains generally consist of approximately 90 amino acid residues that adopt a structure composed of six ␤-strands and two ␣-helices (reviewed in reference 57). The term PDZ is an abbreviation for the first three proteins found to share this structural domain: PSD-95, Dlg, and ZO-1. PDZ domains are typically found in cytoplasmic and membrane adapter proteins that are involved in a variety of cellular processes of significance to viral infection: maintenance of cell-cell junctions, cellular polarity, and signal transduction pathways. In metazoans, PDZ proteins often contain multiple PDZ domains and additional proteinprotein interaction elements, such as SH3, L27, or leucine-rich repeat (LRR) domains. In the mouse genome, over 700 individual PDZ domains are found in over 300 proteins, while in the human genome, over 900 PDZ domains are found in over