scholarly journals Simian Virus 40 Large T Antigen's Association with the CUL7 SCF Complex Contributes to Cellular Transformation

2005 ◽  
Vol 79 (18) ◽  
pp. 11685-11692 ◽  
Author(s):  
Jocelyn S. Kasper ◽  
Hiroshi Kuwabara ◽  
Takehiro Arai ◽  
Syed Hamid Ali ◽  
James A. DeCaprio
Keyword(s):  
Tumor Suppressor ◽  
Mouse Embryo ◽  
Family Members ◽  
Simian Virus 40 ◽  
Cellular Transformation ◽  
Simian Virus ◽  
T Antigen ◽  
Mouse Embryo Fibroblasts ◽  
Embryo Fibroblasts ◽  
F Box Protein

ABSTRACT Simian virus 40 large T antigen (T Ag) is capable of immortalizing and transforming rodent cells. The transforming activity of T Ag is due in large part to perturbation of the tumor suppressor proteins p53 and the retinoblastoma (pRB) family members. Inactivation of these tumor suppressors may not be sufficient for T Ag-mediated cellular transformation. It has been shown that T Ag associates with an SCF-like complex that contains a member of the cullin family of E3 ubiquitin ligases, CUL7, as well as SKP1, RBX1, and an F-box protein, FBXW8. We identified T Ag residues 69 to 83 as required for T Ag binding to the CUL7 complex. We demonstrate that Δ69-83 T Ag, while it lost its ability to associate with CUL7, retained binding to p53 and pRB family members. In the presence of CUL7, wild-type (WT) T Ag but not Δ69-83 T Ag was able to induce proliferation of mouse embryo fibroblasts, an indication of cellular transformation. In contrast, WT and Δ69-83 T Ag enabled mouse embryo fibroblasts to proliferate to similarly high densities in the absence of CUL7. Our data suggest that, in addition to p53 and the pRB family members, T Ag serves to bind to and inactivate the growth-suppressing properties of CUL7. In addition, these results imply that, at least in the presence of T Ag, CUL7 may function as a tumor suppressor.

scholarly journals Differential ability of a T-antigen transport-defective mutant of simian virus 40 to transform primary and established rodent cells.

1985 ◽  
Vol 5 (5) ◽  
pp. 1043-1050 ◽  
Author(s):  
R E Lanford ◽  
C Wong ◽  
J S Butel
Keyword(s):  
Cell Lines ◽  
Mouse Embryo ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
Mouse Embryo Fibroblasts ◽  
Established Cell Lines ◽  
Established Cell ◽  
Embryo Fibroblasts

The transforming potential and oncogenicity of a simian virus 40 (SV40) mutant affecting T-antigen (T-ag), SV40(cT)-3, was examined in an effort to dissect T-ag functions in transformation. SV40(cT)-3 has a point mutation at nucleotide 4434 that abolishes the transport of T-ag to the nucleus but does not affect its association with the cell surface. Transfection-transformation assays were performed with primary cells and established cell lines of mouse and rat origin. The efficiency of transformation for established cell lines by SV40(cT)-3 was comparable to that of wild-type SV40, indicating that transformation of established cell lines can occur in the absence of detectable amounts of nuclear T-ag. Transformation of primary mouse embryo fibroblasts by SV40(cT)-3 was markedly influenced by culture conditions; the relative transforming frequency was dramatically reduced in assays involving focus formation in low serum concentrations or anchorage-independent growth. Immunofluorescence tests revealed that the transformed mouse embryo fibroblasts partially transport the mutant cT-ag to the cell nucleus. Transformed cell lines induced by SV40(cT)-3 did not differ in growth properties from wild-type transformants. SV40(cT)-3 was completely defective for the transformation of primary baby rat kidney cells, a primary cell type unable to transport the mutant T-ag to the nucleus. The intracellular localization of cellular protein p53 was found to mimic T-ag distribution in all the transformants analyzed. The mutant virus was weakly oncogenic in vivo: the induction of tumors in newborn hamsters by SV40(cT)-3 was reduced in incidence and delayed in appearance in comparison to wild-type SV40. These observations suggest that cellular transformation is regulated by both nuclear and surface-associated forms of SV40 T-ag.

Differential ability of a T-antigen transport-defective mutant of simian virus 40 to transform primary and established rodent cells

1985 ◽  
Vol 5 (5) ◽  
pp. 1043-1050
Author(s):  
R E Lanford ◽  
C Wong ◽  
J S Butel
Keyword(s):  
Cell Lines ◽  
Mouse Embryo ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
Mouse Embryo Fibroblasts ◽  
Established Cell Lines ◽  
Established Cell ◽  
Embryo Fibroblasts

The transforming potential and oncogenicity of a simian virus 40 (SV40) mutant affecting T-antigen (T-ag), SV40(cT)-3, was examined in an effort to dissect T-ag functions in transformation. SV40(cT)-3 has a point mutation at nucleotide 4434 that abolishes the transport of T-ag to the nucleus but does not affect its association with the cell surface. Transfection-transformation assays were performed with primary cells and established cell lines of mouse and rat origin. The efficiency of transformation for established cell lines by SV40(cT)-3 was comparable to that of wild-type SV40, indicating that transformation of established cell lines can occur in the absence of detectable amounts of nuclear T-ag. Transformation of primary mouse embryo fibroblasts by SV40(cT)-3 was markedly influenced by culture conditions; the relative transforming frequency was dramatically reduced in assays involving focus formation in low serum concentrations or anchorage-independent growth. Immunofluorescence tests revealed that the transformed mouse embryo fibroblasts partially transport the mutant cT-ag to the cell nucleus. Transformed cell lines induced by SV40(cT)-3 did not differ in growth properties from wild-type transformants. SV40(cT)-3 was completely defective for the transformation of primary baby rat kidney cells, a primary cell type unable to transport the mutant T-ag to the nucleus. The intracellular localization of cellular protein p53 was found to mimic T-ag distribution in all the transformants analyzed. The mutant virus was weakly oncogenic in vivo: the induction of tumors in newborn hamsters by SV40(cT)-3 was reduced in incidence and delayed in appearance in comparison to wild-type SV40. These observations suggest that cellular transformation is regulated by both nuclear and surface-associated forms of SV40 T-ag.

scholarly journals Human Cytomegalovirus pp71 Stimulates Cell Cycle Progression by Inducing the Proteasome-Dependent Degradation of the Retinoblastoma Family of Tumor Suppressors

2003 ◽  
Vol 23 (6) ◽  
pp. 1885-1895 ◽  
Author(s):  
Robert F. Kalejta ◽  
Jill T. Bechtel ◽  
Thomas Shenk
Keyword(s):  
Cell Cycle ◽  
Human Cytomegalovirus ◽  
Tumor Suppressors ◽  
Family Members ◽  
Simian Virus 40 ◽  
Cellular Transformation ◽  
Simian Virus ◽  
T Antigen ◽  
Cellular Growth ◽  
Dependent Manner

ABSTRACT The oncoproteins of the DNA tumor viruses, adenovirus E1A, simian virus 40 T antigen, and papillomavirus E7, each interact with the retinoblastoma family of tumor suppressors, leading to cell cycle stimulation, apoptosis induction, and cellular transformation. These proteins utilize a conserved LXCXE motif, which is also found in cellular proteins, to target the retinoblastoma family. Here, we describe a herpesvirus protein that shares a subset of the properties of the DNA tumor virus oncoproteins but maintains important differences as well. The human cytomegalovirus pp71 protein employs an LXCXD motif to attack the retinoblastoma family members and induce DNA synthesis in quiescent cells. pp71 binds to and induces the degradation of the hypophosphorylated forms of the retinoblastoma protein and its family members p107 and p130 in a proteasome-dependent manner. However, pp71 does not induce apoptosis and fails to transform cells. Thus, the similarities and differences in comparison to E1A, T antigen, and E7 make pp71 an interesting new tool with which to further dissect the role of the retinoblastoma/E2F pathway in cellular growth control and carcinogenesis.

scholarly journals Enterocyte Proliferation and Intestinal Hyperplasia Induced by Simian Virus 40 T Antigen Require a Functional J Domain

2007 ◽  
Vol 81 (17) ◽  
pp. 9481-9489 ◽  
Author(s):  
Abhilasha V. Rathi ◽  
M. Teresa Sáenz Robles ◽  
James M. Pipas
Keyword(s):  
Transgenic Mice ◽  
Family Members ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
Morphological Examination ◽  
Enterocyte Proliferation ◽  
J Domain ◽  
Intestinal Hyperplasia

ABSTRACT Transgenic mice expressing the simian virus 40 large T antigen (TAg) in enterocytes develop intestinal hyperplasia that progresses to dysplasia with age. This induction requires TAg action on the retinoblastoma (Rb) family of tumor suppressors and is independent of the p53 pathway. In cell culture systems, the inactivation of Rb proteins requires both a J domain in TAg that interacts with hsc70 and an LXCXE motif that directs association with Rb proteins. Together these elements are sufficient to release E2Fs from their association with Rb family members. We have generated transgenic mice that express a J domain mutant (D44N) in villus enterocytes. In contrast to wild-type TAg, the D44N mutant is unable to induce enterocyte proliferation. Histological and morphological examination revealed that mice expressing the J domain mutant have normal intestines without loss of growth control. Unlike mice expressing wild-type TAg, mice expressing D44N do not reduce the protein levels of p130 and are also unable to dissociate p130-E2F DNA binding complexes. Furthermore, mice expressing D44N in a null p130 background are still unable to develop hyperplasia. These studies demonstrate that the ectopic proliferation of enterocytes by TAg requires a functional J domain and suggest that the J domain is necessary to inactivate all three pRb family members.

scholarly journals Cell-Specific Modulation of Papovavirus Replication by Tumor Suppressor Protein p53

2000 ◽  
Vol 74 (10) ◽  
pp. 4688-4697 ◽  
Author(s):  
Dina Lepik ◽  
Mart Ustav
Keyword(s):  
Tumor Suppressor ◽  
Cell Lines ◽  
P53 Protein ◽  
Chinese Hamster ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
S Phase ◽  
Human Papillomaviruses ◽  
Mouse Cells

ABSTRACT Small DNA tumor viruses like human papillomaviruses, simian virus 40, and adenoviruses modulate the activity of cellular tumor suppressor proteins p53 and/or pRB. These viruses replicate as nuclear multicopy extrachromosomal elements during the S phase of the cell cycle, and it has been suggested that inactivation of p53 and pRb is necessary for directing the cells to the S phase. Mouse polyomavirus (Py), however, modulates only the pRB protein activity without any obvious interference with the action of p53. We show here that Py replication was not suppressed by the p53 protein indeed in all tested different mouse cell lines. In addition, E1- and E2-dependent papillomavirus origin replication was insensitive to the action of p53 in mouse cells. We show that in hamster (Chinese hamster ovary) or human (osteosarcoma 143) cell lines the replication of both Py and papillomavirus origins was efficiently blocked by p53. The block of Py replication in human and hamster cells is not caused by the downregulation of large T-antigen expression. The deletion analysis of the p53 protein shows that the RPA binding, proline-rich regulatory, DNA-binding, and oligomerization domains are necessary for p53 action in both replication systems. These results indicate that in mouse cells the p53 protein could be inactive for the suppression of papovavirus replication.

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