scholarly journals Role of the Three Polyoma Virus Early Proteins in Tumorigenesis

1983 ◽  
Vol 3 (8) ◽  
pp. 1451-1459 ◽  
Author(s):  
Claude Asselin ◽  
Celine Gelinas ◽  
Marcel Bastin
Keyword(s):  
Cultured Cells ◽  
Virus Genome ◽  
T Antigen ◽  
Polyoma Virus ◽  
Transformed Cells ◽  
Newborn Rats ◽  
Wild Type ◽  
Complementary Function ◽  
Small T Antigen ◽  
Middle T Antigen

A modified polyoma virus genome which can encode the middle T protein but not the large or small T proteins transforms rat cells in culture with an efficiency about 20% that of the wild-type genome. Although middle T-transformed cells grow as tumors when transplanted into nude mice or syngeneic rats, the middle T gene alone is totally inactive when used in a more stringent and rigorous assay for tumorigenicity such as the injection of DNA into newborn rats. Thus, functions other than those expressed by middle T antigen are required for the elaboration of all the properties associated with tumorigenesis. To assess whether a complementary function could be exerted by the large or the small T antigen, we constructed plasmids containing two modified early regions which independently encoded middle T and one of the two other proteins. Both recombinants were tumorigenic in newborn rats. Cell lines derived by transfer of these plasmids under no special selective conditions did not acquire the property of growth in low-serum medium but exhibited the same tumorigenic properties as wild-type polyoma DNA-transformed cells. Furthermore, a recombinant which encoded the middle and small T antigens, but not the large T antigen, was tumorigenic in newborn rats. Although the small T antigen provides a complementary function for tumorigenicity, it cannot complement the middle T antigen for an efficient induction of transformation of cultured cells. This suggests that the complementary function exerted by the small T antigen is different from that of the N-terminal fragment of the large T protein.

Role of the Three Polyoma Virus Early Proteins in Tumorigenesis

1983 ◽  
Vol 3 (8) ◽  
pp. 1451-1459 ◽  
Author(s):  
Claude Asselin ◽  
Celine Gelinas ◽  
Marcel Bastin
Keyword(s):  
Cultured Cells ◽  
Virus Genome ◽  
T Antigen ◽  
Polyoma Virus ◽  
Transformed Cells ◽  
Newborn Rats ◽  
Wild Type ◽  
Complementary Function ◽  
Small T Antigen ◽  
Middle T Antigen

A modified polyoma virus genome which can encode the middle T protein but not the large or small T proteins transforms rat cells in culture with an efficiency about 20% that of the wild-type genome. Although middle T-transformed cells grow as tumors when transplanted into nude mice or syngeneic rats, the middle T gene alone is totally inactive when used in a more stringent and rigorous assay for tumorigenicity such as the injection of DNA into newborn rats. Thus, functions other than those expressed by middle T antigen are required for the elaboration of all the properties associated with tumorigenesis. To assess whether a complementary function could be exerted by the large or the small T antigen, we constructed plasmids containing two modified early regions which independently encoded middle T and one of the two other proteins. Both recombinants were tumorigenic in newborn rats. Cell lines derived by transfer of these plasmids under no special selective conditions did not acquire the property of growth in low-serum medium but exhibited the same tumorigenic properties as wild-type polyoma DNA-transformed cells. Furthermore, a recombinant which encoded the middle and small T antigens, but not the large T antigen, was tumorigenic in newborn rats. Although the small T antigen provides a complementary function for tumorigenicity, it cannot complement the middle T antigen for an efficient induction of transformation of cultured cells. This suggests that the complementary function exerted by the small T antigen is different from that of the N-terminal fragment of the large T protein.

Polyoma virus middle T antigen: relationship to cell membranes and apparent lack of ATP-binding activity

1982 ◽  
Vol 2 (10) ◽  
pp. 1187-1198 ◽  
Author(s):  
B S Schaffhausen ◽  
H Dorai ◽  
G Arakere ◽  
T L Benjamin
Keyword(s):  
Kinase Activity ◽  
T Antigen ◽  
Polyoma Virus ◽  
Intact Cells ◽  
Apparent Lack ◽  
Permeabilized Cells ◽  
Kinase Reaction ◽  
Middle T Antigen

Middle T antigen of polyoma virus is associated principally with the plasma membrane. Comparison of the trypsin sensitivity of middle T in intact cells and "inside out" membrane preparations showed that middle T is oriented towards the inside of the cell. This was confirmed by labeling of middle T in permeabilized cells, but not in intact cells, using [gamma-32P]ATP. Middle T molecules active in the in vitro kinase reaction could be differentiated from the bulk (metabolically labeled) middle T based on resistance to trypsin treatment. The active fraction also behaved differently from the bulk when cell frameworks were prepared with Triton-containing buffers; whereas the bulk middle T was evenly distributed in the soluble and cell framework fractions, the kinase-active forms were largely associated with the framework. Middle T molecules labeled in vivo with 32PO4 were found largely in the framework fraction, like the molecules that show kinase activity in vitro. Experiments with ATP affinity reagents 8-azido-ATP and 2,3-dialdehyde ATP have failed to label the middle T antigen. However, 2,3-dialdehyde ATP could be used to inhibit the kinase reaction. This raises the question of whether middle T antigen possesses intrinsic kinase activity or, rather, associates with a cellular tyrosine kinase.

scholarly journals Dual inhibition of MDM2 and MDM4 in virus-positive Merkel cell carcinoma enhances the p53 response

2018 ◽  
Vol 116 (3) ◽  
pp. 1027-1032 ◽  
Author(s):  
Donglim Esther Park ◽  
Jingwei Cheng ◽  
Christian Berrios ◽  
Joan Montero ◽  
Marta Cortés-Cros ◽  
...  
Keyword(s):  
Target Genes ◽  
Underlying Mechanism ◽  
T Antigen ◽  
Sequencing Analysis ◽  
Merkel Cell ◽  
Wild Type ◽  
Synergistic Activation ◽  
P53 Response ◽  
P53 Activation ◽  
Small T Antigen

Merkel cell polyomavirus (MCV) contributes to approximately 80% of all Merkel cell carcinomas (MCCs), a highly aggressive neuroendocrine carcinoma of the skin. MCV-positive MCC expresses small T antigen (ST) and a truncated form of large T antigen (LT) and usually contains wild-type p53 (TP53) and RB (RB1). In contrast, virus-negative MCC contains inactivating mutations in TP53 and RB1. While the MCV-truncated LT can bind and inhibit RB, it does not bind p53. We report here that MCV LT binds to RB, leading to increased levels of ARF, an inhibitor of MDM2, and activation of p53. However, coexpression of ST reduced p53 activation. MCV ST recruits the MYC homologue MYCL (L-Myc) to the EP400 chromatin remodeler complex and transactivates specific target genes. We observed that depletion of EP400 in MCV-positive MCC cell lines led to increased p53 target gene expression. We suspected that the MCV ST–MYCL–EP400 complex could functionally inactivate p53, but the underlying mechanism was not known. Integrated ChIP and RNA-sequencing analysis following EP400 depletion identified MDM2 as well as CK1α, an activator of MDM4, as target genes of the ST–MYCL–EP400 complex. In addition, MCV-positive MCC cells expressed high levels of MDM4. Combining MDM2 inhibitors with lenalidomide targeting CK1α or an MDM4 inhibitor caused synergistic activation of p53, leading to an apoptotic response in MCV-positive MCC cells and MCC-derived xenografts in mice. These results support dual targeting of MDM2 and MDM4 in virus-positive MCC and other p53 wild-type tumors.

scholarly journals Expression of biologically active middle T antigen of polyoma virus from recombinant baculoviruses

1989 ◽  
Vol 17 (4) ◽  
pp. 1427-1443 ◽  
Author(s):  
Jitka Forstová ◽  
Nina Krauzewicz ◽  
Beverly E. Griffin
Keyword(s):  
T Antigen ◽  
Polyoma Virus ◽  
Biologically Active ◽  
Recombinant Baculoviruses ◽  
Middle T Antigen

scholarly journals Transformation by Polyomavirus Middle T Antigen Involves a Unique Bimodal Interaction with the Hippo Effector YAP

2016 ◽  
Vol 90 (16) ◽  
pp. 7032-7045 ◽  
Author(s):  
Cecile Rouleau ◽  
Arun T. Pores Fernando ◽  
Justin H. Hwang ◽  
Nathalie Faure ◽  
Tao Jiang ◽  
...  
Keyword(s):  
Transcriptional Activation ◽  
T Antigen ◽  
Tumor Formation ◽  
Ras Signaling ◽  
Hippo Signaling ◽  
Control Mechanisms ◽  
Positive Contribution ◽  
Activation Functions ◽  
Wild Type ◽  
Middle T Antigen

ABSTRACTMurine polyomavirus has repeatedly provided insights into tumorigenesis, revealing key control mechanisms such as tyrosine phosphorylation and phosphoinositide 3-kinase (PI3K) signaling. We recently demonstrated that polyomavirus small T antigen (ST) binds YAP, a major effector of Hippo signaling, to regulate differentiation. Here we characterize YAP as a target of middle T antigen (MT) important for transformation. Through a surface including residues R103 and D182, wild-type MT binds to the YAP WW domains. Mutation of either R103 or D182 of MT abrogates YAP binding without affecting binding to other signaling molecules or the strength of PI3K or Ras signaling. Either genetic abrogation of YAP binding to MT or silencing of YAP via short hairpin RNA (shRNA) reduced MT transformation, suggesting that YAP makes a positive contribution to the transformed phenotype. MT targets YAP both by activating signaling pathways that affect it and by binding to it. MT signaling, whether from wild-type MT or the YAP-binding MT mutant, promoted YAP phosphorylation at S127 and S381/397 (YAP2/YAP1). Consistent with the known functions of these phosphorylated serines, MT signaling leads to the loss of YAP from the nucleus and degradation. Binding of YAP to MT brings it together with protein phosphatase 2A (PP2A), leading to the dephosphorylation of YAP in the MT complex. It also leads to the enrichment of YAP in membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that may depart from YAP's canonical oncogenic transcriptional activation functions.IMPORTANCEThe highly conserved Hippo/YAP pathway is important for tissue development and homeostasis. Increasingly, changes in this pathway are being associated with cancer. Middle T antigen (MT) is the primary polyomavirus oncogene responsible for tumor formation. In this study, we show that MT signaling promotes YAP phosphorylation, loss from the nucleus, and increased turnover. Notably, MT genetics demonstrate that YAP binding to MT is important for transformation. Because MT also binds PP2A, YAP bound to MT is dephosphorylated, stabilized, and localized to membranes. Taken together, these results indicate that YAP promotes MT transformation via mechanisms that depart from YAP's canonical oncogenic transcriptional activation functions.

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