scholarly journals The amino-terminal transforming region of simian virus 40 large T and small t antigens functions as a J domain.

1997 ◽  
Vol 17 (8) ◽  
pp. 4761-4773 ◽  
Author(s):  
A Srinivasan ◽  
A J McClellan ◽  
J Vartikar ◽  
I Marks ◽  
P Cantalupo ◽  
...  
Keyword(s):  
Amino Acid ◽  
Atpase Activity ◽  
Mammalian Cells ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
Amino Terminal ◽  
J Domain ◽  
Small T Antigen

Simian virus 40 (SV40) encodes two proteins, large T antigen and small t antigen that contribute to virus-induced tumorigenesis. Both proteins act by targeting key cellular regulatory proteins and altering their function. Known targets of the 708-amino-acid large T antigen include the three members of the retinoblastoma protein family (pRb, p107, and p130), members of the CBP family of transcriptional adapter proteins (cap-binding protein [CBP], p300, and p400), and the tumor suppressor p53. Small t antigen alters the activity of phosphatase pp2A and transactivates the cyclin A promoter. The first 82 amino acids of large T antigen and small t antigen are identical, and genetic experiments suggest that an additional target(s) important for transformation interacts with these sequences. This region contains a motif similar to the J domain, a conserved sequence found in the DnaJ family of molecular chaperones. We show here that mutations within the J domain abrogate the ability of large T antigen to transform mammalian cells. To examine whether a purified 136-amino-acid fragment from the T antigen amino terminus acts as a DnaJ-like chaperone, we investigated whether this fragment stimulates the ATPase activity of two hsc70s and discovered that ATP hydrolysis is stimulated four- to ninefold. In addition, ATPase-defective mutants of full-length T antigen, as well as wild-type small t antigen, stimulated the ATPase activity of hsc70. T antigen derivatives were also able to release an unfolded polypeptide substrate from an hsc70, an activity common to DnaJ chaperones. Because the J domain of T antigen plays essential roles in viral DNA replication, transcriptional control, virion assembly, and tumorigenesis, we conclude that this region may chaperone the rearrangement of multiprotein complexes.

Simian virus 40 large T-antigen point mutants that are defective in viral DNA replication but competent in oncogenic transformation

1984 ◽  
Vol 4 (6) ◽  
pp. 1125-1133
Author(s):  
M M Manos ◽  
Y Gluzman
Keyword(s):  
Amino Acid ◽  
Dna Replication ◽  
Atpase Activity ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
Oncogenic Transformation ◽  
Viral Dna ◽  
Viral Dna Replication

The large T antigen of simian virus 40 (SV40) is a multifunctional protein that is essential in both the virus lytic cycle and the oncogenic transformation of cells by SV40. To investigate the role of the numerous biochemical and physiological activities of T antigen in the lytic and transformation processes, we have studied DNA replication-deficient, transformation-competent large T-antigen mutants. Here we describe the genetic and biochemical analyses of two such mutants, C2/SV40 and C11/SV40. The mutants were isolated by rescuing the integrated SV40 DNA from C2 and C11 cells (CV-1 cell lines transformed with UV-irradiated SV40). The mutant viral early regions were cloned into the plasmid vector pK1 to generate pC2 and pC11. The mutations that are responsible for the deficiency in viral DNA replication were localized by marker rescue. Subsequent DNA sequencing revealed point mutations that predict amino acid substitutions in the carboxyl third of the protein in both mutants. The pC2 mutation predicts the change of Lys----Arg at amino acid 516. pC11 has two mutations, one predicting a change of Pro----Ser at residue 522, and another predicting a Pro----Arg change at amino acid 549. The two C11 mutations were separated from each other to form two distinct viral genomes in pC11A and pC11B. pC2, pC11, pC11A, and pC11B are able to transform both primary and established rodent cell cultures. The C11 and C11A T antigens are defective in ATPase activity, suggesting that wild-type levels of ATPase activity are not necessary for the oncogenic transformation of cells by T antigen.

scholarly journals Simian virus 40 large T-antigen point mutants that are defective in viral DNA replication but competent in oncogenic transformation.

1984 ◽  
Vol 4 (6) ◽  
pp. 1125-1133 ◽  
Author(s):  
M M Manos ◽  
Y Gluzman
Keyword(s):  
Amino Acid ◽  
Dna Replication ◽  
Atpase Activity ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
Oncogenic Transformation ◽  
Viral Dna ◽  
Viral Dna Replication

The large T antigen of simian virus 40 (SV40) is a multifunctional protein that is essential in both the virus lytic cycle and the oncogenic transformation of cells by SV40. To investigate the role of the numerous biochemical and physiological activities of T antigen in the lytic and transformation processes, we have studied DNA replication-deficient, transformation-competent large T-antigen mutants. Here we describe the genetic and biochemical analyses of two such mutants, C2/SV40 and C11/SV40. The mutants were isolated by rescuing the integrated SV40 DNA from C2 and C11 cells (CV-1 cell lines transformed with UV-irradiated SV40). The mutant viral early regions were cloned into the plasmid vector pK1 to generate pC2 and pC11. The mutations that are responsible for the deficiency in viral DNA replication were localized by marker rescue. Subsequent DNA sequencing revealed point mutations that predict amino acid substitutions in the carboxyl third of the protein in both mutants. The pC2 mutation predicts the change of Lys----Arg at amino acid 516. pC11 has two mutations, one predicting a change of Pro----Ser at residue 522, and another predicting a Pro----Arg change at amino acid 549. The two C11 mutations were separated from each other to form two distinct viral genomes in pC11A and pC11B. pC2, pC11, pC11A, and pC11B are able to transform both primary and established rodent cell cultures. The C11 and C11A T antigens are defective in ATPase activity, suggesting that wild-type levels of ATPase activity are not necessary for the oncogenic transformation of cells by T antigen.

Dephosphorylation of simian virus 40 large-T antigen and p53 protein by protein phosphatase 2A: inhibition by small-t antigen

1991 ◽  
Vol 11 (4) ◽  
pp. 1996-2003 ◽  
Author(s):  
K H Scheidtmann ◽  
M C Mumby ◽  
K Rundell ◽  
G Walter
Keyword(s):  
Protein Phosphatase ◽  
P53 Protein ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
C Subunit ◽  
Phosphatase 2A ◽  
Small T Antigen

Simian virus 40 (SV40) large-T antigen and the cellular protein p53 were phosphorylated in vivo by growing cells in the presence of 32Pi. The large-T/p53 complex was isolated by immunoprecipitation and used as a substrate for protein phosphatase 2A (PP2A) consisting of the catalytic subunit (C) and the two regulatory subunits, A and B. Three different purified forms of PP2A, including free C, the AC form, and the ABC form, could readily dephosphorylate both proteins. With both large-T and p53, the C subunit was most active, followed by the AC form, which was more active than the ABC form. The activity of all three forms of PP2A toward these proteins was strongly stimulated by manganese ions and to a lesser extent by magnesium ions. The presence of complexed p53 did not affect the dephosphorylation of large-T antigen by PP2A. The dephosphorylation of individual phosphorylation sites of large-T and p53 were determined by two-dimensional peptide mapping. Individual sites within large-T and p53 were dephosphorylated at different rates by all three forms of PP2A. The phosphates at Ser-120 and Ser-123 of large-T, which affect binding to the origin of SV40 DNA, were removed most rapidly. Three of the six major phosphopeptides of p53 were readily dephosphorylated, while the remaining three were relatively resistant to PP2A. Dephosphorylation of most of the sites in large-T and p53 by the AC form was inhibited by SV40 small-t antigen. The inhibition was most apparent for those sites which were preferentially dephosphorylated. Inhibition was specific for the AC form; no effect was observed on the dephosphorylation of either protein by the free C subunit or the ABC form. The inhibitory effect of small-t on dephosphorylation by PP2A could explain its role in transformation.

scholarly journals The Molecular Chaperone Activity of Simian Virus 40 Large T Antigen Is Required To Disrupt Rb-E2F Family Complexes by an ATP-Dependent Mechanism

2000 ◽  
Vol 20 (17) ◽  
pp. 6233-6243 ◽  
Author(s):  
Christopher S. Sullivan ◽  
Paul Cantalupo ◽  
James M. Pipas
Keyword(s):  
Atp Hydrolysis ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Cellular Growth ◽  
Binding Motif ◽  
Large T Antigen ◽  
Consensus Binding Site ◽  
J Domain ◽  
Immortalized Cell

ABSTRACT The simian virus 40 large T antigen (T antigen) inactivates tumor suppressor proteins and therefore has been used in numerous studies to probe the mechanisms that control cellular growth and to generate immortalized cell lines. Binding of T antigen to the Rb family of growth-regulatory proteins is necessary but not sufficient to cause transformation. The molecular mechanism underlying T-antigen inactivation of Rb function is poorly understood. In this study we show that T antigen associates with pRb and p130-E2F complexes in a stable manner. T antigen dissociates from a p130–E2F-4–DP-1 complex, coincident with the release of p130 from E2F-4–DP-1. The dissociation of this complex requires Hsc70, ATP, and a functional T-antigen J domain. We also report that the “released” E2F–DP-1 complex is competent to bind DNA containing an E2F consensus binding site. We propose that T antigen disrupts Rb-E2F family complexes through the action of its J domain and Hsc70. These findings indicate how Hsc70 supports T-antigen action and help to explain the cisrequirement for a J domain and Rb binding motif in T-antigen-induced transformation. Furthermore, this is the first demonstration linking Hsc70 ATP hydrolysis to the release of E2F bound by Rb family members.

Effect of basic and nonbasic amino acid substitutions on transport induced by simian virus 40 T-antigen synthetic peptide nuclear transport signals

1988 ◽  
Vol 8 (7) ◽  
pp. 2722-2729
Author(s):  
R E Lanford ◽  
R G White ◽  
R G Dunham ◽  
P Kanda
Keyword(s):  
Amino Acid ◽  
Synthetic Peptide ◽  
Mammalian Cells ◽  
Positive Charge ◽  
Nuclear Transport ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Amino Acid Substitutions ◽  
Positively Charged

A previous study demonstrated the ability of a synthetic peptide homologous to the simian virus 40 T-antigen nuclear transport signal to induce the nuclear transport of carrier proteins and the dependence of peptide-induced transport on a positive charge at the lysine corresponding to amino acid 128 of T antigen. In this investigation synthetic peptides were utilized to examine the effect on transport of amino acid substitutions within the T-antigen nuclear transport signal. Nuclear transport was evaluated by immunofluorescence after microinjection of protein-peptide conjugates into the cytoplasm of mammalian cells. Substitution of other basic amino acids at position 128 revealed a hierarchy for nuclear transport. The rate of nuclear transport was most rapid when a lysine was at position 128 followed in descending order by arginine, D-lysine, ornithine, and p-aminophenylalanine. Peptide-induced nuclear transport was dependent upon a positively charged amino acid at positions 128 and 129, since substitutions of neutral asparagines at these positions abolished transport. However, partial transport was observed with the peptide having an asparagine at position 128 when a high number of peptides were conjugated to the carrier protein.

scholarly journals Membrane interactions of simian virus 40 large T-antigen: influence of protein sequences and fatty acid acylation.

1984 ◽  
Vol 4 (8) ◽  
pp. 1542-1550 ◽  
Author(s):  
U Klockmann ◽  
M Staufenbiel ◽  
W Deppert
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Fatty Acid ◽  
Protein Sequences ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Membrane Association ◽  
Large T Antigen ◽  
Amino Terminal

To sort out possible influences of protein sequences and fatty acid acylation on the plasma membrane association of simian virus 40 large T-antigen, we have analyzed the membrane interactions of carboxy-terminal fragments of large T-antigen, encoded by the adenovirus type 2 (Ad2+)-simian virus 40 hybrid viruses Ad2+ND1 and Ad2+ND2. The 28,000 (28K)-molecular-weight protein of Ad2+ND1 as well as the 42K and 56K proteins of Ad2+ND2 associate preferentially with membranous structures and were found in association with the membrane system of the endoplasmic reticulum and with plasma membranes. Neither the endoplasmic reticulum membrane- nor the plasma membrane-associated 28K protein of Ad2+ND1 is fatty acid acylated. We, therefore, conclude that fatty acid acylation is not necessary for membrane association of this protein and suggest that an amino acid sequence in this protein is responsible for its membrane interaction. In contrast, the 42K and 56K proteins of Ad2+ND2 in plasma membrane fractions contain fatty acid. However, the interaction of these proteins with the plasma membrane differs from that of the 28K protein of Ad2+ND1: whereas the 28K protein of Ad2+ND1 interacts stably with Nonidet P-40-soluble constituents of the plasma membrane, the 42K and 56K proteins of Ad2+ND2 are tightly bound to the Nonidet P-40-insoluble plasma membrane lamina. Thus, an amino acid sequence in the amino-terminal region of the 28K protein confers membrane affinity to these proteins, whereas a region between the amino-terminal end of the 42K protein of Ad2+ND2 and the amino-terminal end of the 28K protein of Ad2+ND1 contains a reactive site for fatty acid acylation. This posttranslational modification correlates with the stable association of the 42K and 56K proteins with the plasma membrane lamina. We suggest that the same sequences also mediate the proper plasma membrane association of large T-antigen in simian virus 40-transformed cells.

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