Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human papillomaviruses (HPVs) are associated with the majority of cervical cancers and encode a transforming protein, E6, that interacts with the tumor suppressor protein p53. Because E6 has p53-independent transforming activity, the yeast two-hybrid system was used to search for other E6-binding proteins. One such protein, E6BP, interacted with cancer-associated HPV E6 and with bovine papillomavirus type 1 (BPV-1) E6. The transforming activity of BPV-1 E6 mutants correlated with their E6BP-binding ability. E6BP is identical to a putative calcium-binding protein, ERC-55, that appears to be localized in the endoplasmic reticulum.
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PMID:Interaction of papillomavirus E6 oncoproteins with a putative calcium-binding protein. 762 74

While the bovine papillomavirus type 1 (BPV-1) E6 induces tumorigenic transformation of murine C127 cells, it does not bind or promote the degradation of p53. We recently showed the cellular protein ERC-55/E6BP binds BPV-1 E6 as well as the cancer-related human papillomavirus (HPV) E6 proteins. BPV-1 E6 also binds E6-AP, a ubiquitin ligase necessary for HPV E6-induced p53 degradation. We previously reported that the transforming activity of a set of BPV-1 E6 mutants correlated with their E6BP-binding ability. Another function of BPV-1 E6 is stimulation of transcription when targeted to a promoter, although cellular promoters responsive to BPV-1 E6 have not been identified. To examine whether its transcriptional function is required for oncogenic activity, or is related to its interactions with E6-AP or E6BP, a series of BPV-1 E6 mutants were analyzed as fusions to a sequence-specific DNA binding domain for activity in yeast and in mammalian cells. We show that some transformation defective mutants retained substantial levels of transcriptional activation activity. These mutants also distinguish transcriptional activation from E6-AP and E6BP binding. These results suggest the transcriptional activation function of BPV-1 E6 is not sufficient for cell transformation.
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PMID:Mutational analysis of transcriptional activation by the bovine papillomavirus type 1 E6. 929 14

The E6 proteins from cervical cancer-associated human papillomavirus (HPV) types such as HPV type 16 (HPV-16) induce proteolysis of the p53 tumor suppressor protein through interaction with E6-AP. We have previously shown that human mammary epithelial cells (MECs) immortalized by HPV-16 E6 display low levels of p53. HPV-16 E6 as well as other cancer-related papillomavirus E6 proteins also binds the cellular protein E6BP (ERC-55). To explore the potential functional significance of these interactions, we created and analyzed a series of E6 mutants for their ability to interact with E6-AP, p53, and E6BP in vitro. While there was a similar pattern of binding among these E6 targets, a subset of mutants differentiated E6-AP binding, p53 binding, and p53 degradation activities. These results demonstrated that E6 binding to E6-AP is not sufficient for binding to p53 and that E6 binding to p53 is not sufficient for inducing p53 degradation. The in vivo activity of these HPV-16 E6 mutants was tested in MECs. In agreement with the in vitro results, most of these p53 degradation-defective E6 mutants were unable to reduce the p53 level in early-passage MECs. Interestingly, several mutants that showed severely reduced ability for interacting with E6-AP, p53, and E6BP in vitro efficiently immortalized MECs. These immortalized cells exhibited low p53 levels at late passage. Furthermore, mutants defective for p53 degradation but able to immortalize MECs were also identified, and the immortal cells retained normal levels of p53 protein. These results imply that multiple functions of HPV-16 E6 contribute to MEC immortalization.
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PMID:Multiple functions of human papillomavirus type 16 E6 contribute to the immortalization of mammary epithelial cells. 1043 18

Recent analyses have identified a number of binding partners for E6, including E6AP, ERC55, paxillin, hDlg, p300, interferon regulatory factor 3, hMCM7, Bak, and E6TP1. Notably, association with E6 targets p53, E6TP1, myc, hMCM7, and Bak for degradation. However, the relative importance of the various E6 targets in cellular transformation remains unclear. E6 alone can dominantly immortalize normal human mammary epithelial cells (MECs), permitting an assessment of the importance of various E6 targets in cellular transformation. Studies in this system indicate that E6-induced degradation of p53 and E6 binding to ERC55 or hDlg do not correlate with efficient immortalization. Here, we have examined the role of E6TP1, a Rap GTPase-activating protein, in E6-induced immortalization of MECs. We tested a large set of human papillomavirus type 16 E6 mutants for their ability to bind and target E6TP1 for degradation in vitro and in vivo. We observed a strict correlation between the ability of E6 protein to target E6TP1 for degradation and its ability to immortalize MECs. Recent studies have identified telomerase as a target of E6 protein. Previous analyses of E6 mutants have revealed this trait to closely correlate with MEC immortalization. We examined our entire panel of E6 mutants for rapid induction of telomerase activity and found in general a strong correlation with immortalizing ability. The tight correlation between E6TP1 degradation and MEC immortalization strongly supports a critical role of functional inactivation of E6TP1 in E6-induced cellular immortalization.
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PMID:Human papillomavirus type 16 E6-induced degradation of E6TP1 correlates with its ability to immortalize human mammary epithelial cells. 1128 1

Transfection of the E6 gene of human papillovirus (HPV) 16 into primary human keratinocytes (PHKs) generates proliferating cell colonies which are resistant to serum- and calcium-induced terminal differentiation. The extreme C-terminus of E6 was shown to be dispensable for this activity. To map further the amino acid sequences required for inducing resistance to serum and calcium, and to address the functional significance of E6 interactions with p53 and E6BP (ERC-55) in this function, we evaluated the activities of a series of E6 mutants. Small deletions within the central portion of the second putative zinc-finger abolished, or markedly reduced, E6 biological activity, while mutations affecting the cysteine residues in the base of the finger were less effective in this respect. When these mutants were assayed for their ability to degrade p53 in vitro and in vivo and to inhibit p53 transcriptional activation (TA), we found that there was a dissociation of these activities in some mutants. We mapped one mutant which was highly efficient in p53 degradation and inhibition of p53 TA, yet displayed severely reduced activity in the biological assay, and conversely, a subset of mutants that showed moderate activities in the colony assay while being severely impaired in p53 degradation and inhibition of p53 TA. These data argue that p53 inactivation or even elimination are not sufficient, and may not be essential, for altering the response of PHKs to serum and calcium. When these E6 mutants were evaluated for E6BP binding in vitro, there was a similar dissociation between the biological and biochemical activities of several mutants. We mapped mutants with moderate activity in the biological assay that lacked the ability to bind to E6BP and a mutant that showed high biological activity with only marginal binding to E6BP. Thus, there is no absolute correlation between the ability of E6 mutant proteins to induce alterations in keratinocyte differentiation responses to calcium and serum and to induce p53 degradation, inhibit p53 mediated transactivation, or bind E6BP. Evidently there are additional cellular targets for E6 which mediate this alteration in cellular differentiation.
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PMID:Inhibition of serum- and calcium-induced terminal differentiation of human keratinocytes by HPV 16 E6: study of the association with p53 degradation, inhibition of p53 transactivation, and binding to E6BP. 1187 33

Cervical cancers evolve from lesions generated by genital human papillomaviruses (HPV). "Low-risk" genital HPVs cause benign proliferations whereas "high-risk" types have the potential to progress into cancer. High-risk HPV E6 oncoproteins interact with the ubiquitin ligase E6AP and target several cellular proteins, including p53 and proteins of the MAGI family, towards ubiquitin-mediated degradation. E6AP, like other E6 binding proteins such as E6BP, IRF-3 and paxillin, interacts with E6 via a consensus leucine-charged motif. Here we have investigated the kinetics of the interactions of a 15-mer peptide containing the LxxvarphiLsh motif of E6AP with E6. For this we have developed a Biacore assay based on antibody-capture on the sensor surface of GST- and/or MBP-E6AP peptide constructs followed by E6 protein injection. Our experiments show that E6 oncoproteins from four major high-risk (16, 18, 33 and 58) HPV types bind to E6AP with equilibrium dissociation constants in the low micromolar range. The kinetic dissociation parameters of these interactions are remarkably similar. On the other hand, low-risk HPV 11 E6 does not interact with E6AP even at relatively high concentrations. We also show that the two zinc-binding domains of E6 are required for E6AP recognition. Finally, we have analysed the binding properties of site-directed mutants of the E6AP-derived peptide. We demonstrate the importance for binding of conserved aliphatic side-chains and the moderate role of the global negative charge of the peptide. This work provides the first quantitative data on an HPV E6-mediated interaction, which support the current models of E6AP-mediated degradation.
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PMID:Kinetic analysis of the interactions of human papillomavirus E6 oncoproteins with the ubiquitin ligase E6AP using surface plasmon resonance. 1589 Feb 4