Transformation-Defective Polyoma Middle T Antigen Mutants Defective in PLCγ, PI-3, or src Kinase Activation Enhance ERK2 Activation and Promote Retinoic Acid-Induced, Cell Differentiation Like Wild-Type Middle T

1999 ◽  
Vol 248 (2) ◽  
pp. 538-551 ◽  
Author(s):  
Andrew Yen ◽  
Van Cherington ◽  
Brian Schaffhausen ◽  
Kevin Marks ◽  
Susi Varvayanis
Keyword(s):  
Retinoic Acid ◽  
Cell Differentiation ◽  
Src Kinase ◽  
T Antigen ◽  
Wild Type ◽  
Kinase Activation ◽  
Polyoma Middle T Antigen ◽  
Erk2 Activation ◽  
Middle T Antigen

Polyoma Middle T Antigen in HL-60 Cells Accelerates Hematopoietic Myeloid and Monocytic Cell Differentiation

1998 ◽  
Vol 238 (1) ◽  
pp. 42-50 ◽  
Author(s):  
Joseph D. Platko ◽  
Mary E. Forbes ◽  
Susi Varvayanis ◽  
Megan N. Williams ◽  
S.Carroll Brooks ◽  
...  
Keyword(s):  
Cell Differentiation ◽  
T Antigen ◽  
Monocytic Cell ◽  
Polyoma Middle T Antigen ◽  
Middle T Antigen

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.

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.

scholarly journals A Transformation-Defective Polyomavirus Middle T Antigen with a Novel Defect in PI3 Kinase Signaling

2016 ◽  
Vol 91 (2) ◽  
Author(s):  
Deborah Denis ◽  
Cecile Rouleau ◽  
Brian S. Schaffhausen
Keyword(s):  
Tyrosine Phosphorylation ◽  
Tyrosine Kinases ◽  
T Antigen ◽  
Pi3 Kinase ◽  
Binding Motif ◽  
Wild Type ◽  
Pi3k Activity ◽  
Murine Polyomavirus ◽  
Middle T Antigen

ABSTRACT Middle T antigen (MT), the principal oncoprotein of murine polyomavirus, transforms by association with cellular proteins. Protein phosphatase 2A (PP2A), YAP, Src family tyrosine kinases, Shc, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-γ1 (PLCγ1) have all been implicated in MT transformation. Mutant dl1015, with deletion of residues 338 to 347 in the C-terminal region, has been an enigma, because the basis for its transformation defect has not been apparent. This work probes the dl1015 region of MT. Because the region is proline rich, the hypothesis that it targets Src homology domain 3 (SH3) domains was tested, but mutation of the putative SH3 binding motif did not affect transformation. During this work, two point mutants, W348R and E349K, were identified as transformation defective. Extensive analysis of the E349K mutant is described here. Similar to wild-type MT, the E349K mutant associates with PP2A, YAP, tyrosine kinases, Shc, PI3 kinase, and PLCγ1. The E349K mutant was examined to determine the mechanism for its transformation defect. Assays of cell localization and membrane targeting showed no obvious difference in localization. Src association was normal as assayed by in vitro kinase and MT phosphopeptide mapping. Shc activation was confirmed by its tyrosine phosphorylation. Association of type 1 PI3K with MT was demonstrated by coimmunoprecipitation, showing both PI3K subunits and in vitro activity. Nonetheless, expression of the mutants failed to lead to the activation of two known downstream targets of PI3K, Akt and Rac-1. Strikingly, despite normal association of the E349K mutant with PI3K, cells expressing the mutant failed to elevate phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in mutant-expressing cells. These results indicate a novel unsuspected aspect to PI3K control. IMPORTANCE The gene coding for middle T antigen (MT) is the murine polyomavirus oncogene most responsible for tumor formation. Its study has a history of uncovering novel aspects of mammalian cell regulation. The importance of PI3K activity and tyrosine phosphorylation are two examples of insights coming from MT. This study describes new mutants unable to transform like the wild type that point to novel regulation of PI3K signaling. Previous mutants were defective in PI3K because they failed to bind the enzyme and bring the activity to the membrane. These mutants recruit PI3K activity like the wild type, but fail to elevate the cellular level of PIP3, the product used to signal downstream of PI3K. As a result, they fail to activate either Akt or Rac1, explaining the transformation defect.

scholarly journals Regulation of cellular phenotype and expression of polyomavirus middle T antigen in rat fibroblasts.

1985 ◽  
Vol 5 (9) ◽  
pp. 2476-2486 ◽  
Author(s):  
L Raptis ◽  
H Lamfrom ◽  
T L Benjamin
Keyword(s):  
Maximum Level ◽  
Soft Agar ◽  
T Antigen ◽  
Metabolic Labeling ◽  
Morphological Transformation ◽  
Focus Formation ◽  
Tumor Virus ◽  
Polyomavirus Middle T Antigen ◽  
Polyoma Middle T Antigen ◽  
Middle T Antigen

Polyoma middle T antigen (mT) was expressed in rat F-111 cells under control of the dexamethasone-regulatable mouse mammary tumor virus promoter. Graded phenotypic responses to levels of mT induction by the hormone were seen, with morphological transformation, focus formation, and anchorage-independent growth requiring increasing levels of mT expression. The ability of different clones to form tumors reflected their maximum level of induction of mT-associated kinase and their ability to grow in soft agar. Expression of transformation parameters and tumorigenicity correlates with the level of mT phosphorylated by pp60c-src in immune complexes and not with the total amount of mT determined by metabolic labeling. We suggest that cellular factors regulate mT activity by forming a kinase-active fraction of mT molecules that controls the transformed state.

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