Topology Dictates Evolution of Regulatory Cysteines in a Family of Viral Oncoproteins

ABSTRACT The pocket domain of pRB is required for pRB to arrest the cell cycle. This domain was originally defined as the region of the protein that is necessary and sufficient for pRB's interaction with adenovirus E1A and simian virus s40 large T antigen. These oncoproteins, and other pRB-binding proteins that are encoded by a variety of plant and animal viruses, use a conserved LXCXE motif to interact with pRB. Similar sequences have been identified in multiple cellular pRB-binding proteins, suggesting that the viruses have evolved to target a highly conserved binding site of pRB that is critical for its function. Here we have constructed a panel of pRB mutants in which conserved amino acids that are predicted to make close contacts with an LXCXE peptide were altered. Despite the conservation of the LXCXE binding site throughout evolution, pRB mutants that lack this site are able to induce a cell cycle arrest in a pRB-deficient tumor cell line. This G1 arrest is overcome by cyclin D-cdk4 complexes but is resistant to inactivation by E7. Consequently, mutants lacking the LXCXE binding site were able to induce a G1 arrest in HeLa cells despite the expression of HPV-18 E7. pRB mutants lacking the LXCXE binding site are defective in binding to adenovirus E1A and human papillomavirus type 16 E7 protein but exhibit wild-type binding to E2F or DP, and they retain the ability to interact with CtIP and HDAC1, two transcriptional corepressors that contain LXCXE-like sequences. Consistent with these observations, the pRB mutants are able to actively repress transcription. These observations suggest that viral oncoproteins depend on the LXCXE-binding site of pRB for interaction to a far greater extent than cellular proteins that are critical for cell cycle arrest or transcriptional repression. Mutation of this binding site allows pRB to function as a cell cycle regulator while being resistant to inactivation by viral oncoproteins.

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Expression andIn SilicoAnalysis of the Recombinant Bovine Papillomavirus E6 Protein as a Model for Viral Oncoproteins Studies

BioMed Research International ◽

10.1155/2013/421398 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 5

Author(s):

J. Mazzuchelli-de-Souza ◽

R. F. Carvalho ◽

R. M. Ruiz ◽

T. C. Melo ◽

R. P. Araldi ◽

...

Keyword(s):

Recombinant Proteins ◽

In Silico ◽

Cell Transformation ◽

Bovine Papillomavirus ◽

Viral Oncoprotein ◽

Viral Oncoproteins ◽

Biotechnological Products ◽

Clone And Express ◽

E6 Protein

Bovine papillomaviruses (BPVs) are recognized as the causal agents of economical relevant diseases in cattle, associated with the development of tumors in skin and mucosa. The oncogenesis process is mainly associated with different viral oncoprotein expressions, which are involved in cell transformation. The expression and characterization of recombinant viral oncoproteins represent an attractive strategy to obtain biotechnological products as antibodies and potential vaccines, Thus, the aim of this work was to clone and express the BPV-1 and BPV-2 E6 recombinant proteins and performin silicoanalysis in order to develop a strategy for the systematic study of other papillomaviruses oncoproteins. The results demonstrated that BPV-1 and BPV-2 E6 recombinant proteins were expressed and purified from bacterial system as well as itsin silicoanalysis was performed in order to explore and predict biological characteristics of these proteins.

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Cell Cycle Targets of Viral Oncoproteins

The Cell Cycle ◽

10.1007/978-1-4615-2421-2_10 ◽

1994 ◽

pp. 91-97

Author(s):

Joseph R. Nevins

Keyword(s):

Cell Cycle ◽

Viral Oncoproteins

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Bovine Papillomavirus E7 Oncoprotein Inhibits Anoikis

Journal of Virology ◽

10.1128/jvi.00422-07 ◽

2007 ◽

Vol 81 (17) ◽

pp. 9419-9425 ◽

Cited By ~ 31

Author(s):

Joseph DeMasi ◽

Michael C. Chao ◽

Ashu S. Kumar ◽

Peter M. Howley

Keyword(s):

Cellular Transformation ◽

Cellular Protein ◽

Site Directed Mutagenesis ◽

Bovine Papillomavirus ◽

Viral Oncoproteins ◽

Anchorage Independence ◽

E7 Oncoprotein ◽

Transformation Activity ◽

Antiapoptotic Activity ◽

E6 And E7

ABSTRACT The bovine papillomavirus type 1 (BPV-1) E7 oncoprotein is required for the full transformation activity of the virus. Although BPV-1 E7 by itself is not sufficient to induce cellular transformation, it enhances the abilities of the other BPV-1 oncogenes to induce anchorage independence. We have been exploring the mechanisms by which E7 might affect the transformation efficiency of other viral oncoproteins and in particular whether it might protect cells from apoptosis. We report here that BPV-1 E6 and E7 can each independently inhibit anoikis, a type of apoptosis that is induced upon cell detachment. Using site-directed mutagenesis, we determined regions of the E7 protein that were essential for its antiapoptotic activity. The ability of E7 to inhibit anoikis did partially correlate with an ability to enhance anchorage independence of BPV-1 E6-transformed cells. In addition, the antiapoptotic activity of E7 also only partially correlated with its ability to bind p600, a cellular protein that has previously been reported to play a role in anoikis. We conclude that the contribution of E7 to BPV-induced cellular transformation may involve its ability to inhibit anoikis but that additional functional activities must also be involved.

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Cyclin E2, a novel human G1 cyclin and activating partner of CDK2 and CDK3, is induced by viral oncoproteins

Oncogene ◽

10.1038/sj.onc.1202505 ◽

1998 ◽

Vol 17 (21) ◽

pp. 2787-2798 ◽

Cited By ~ 66

Author(s):

Maimoona Zariwala ◽

Jidong Liu ◽

Yue Xiong

Keyword(s):

Viral Oncoproteins ◽

Cyclin E2 ◽

G1 Cyclin

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Papillomaviruses and Endocytic Trafficking

International Journal of Molecular Sciences ◽

10.3390/ijms19092619 ◽

2018 ◽

Vol 19 (9) ◽

pp. 2619 ◽

Cited By ~ 7

Author(s):

Abida Siddiqa ◽

Justyna Broniarczyk ◽

Lawrence Banks

Keyword(s):

Infectious Virus ◽

Critical Role ◽

Productive Infection ◽

Endocytic Trafficking ◽

Infection Cycle ◽

Transport Pathways ◽

Viral Oncoproteins ◽

Infectious Entry ◽

Golgi Network ◽

Dna Complex

Endocytic trafficking plays a major role in transport of incoming human papillomavirus (HPVs) from plasma membrane to the trans Golgi network (TGN) and ultimately into the nucleus. During this infectious entry, several cellular sorting factors are recruited by the viral capsid protein L2, which plays a critical role in ensuring successful transport of the L2/viral DNA complex to the nucleus. Later in the infection cycle, two viral oncoproteins, E5 and E6, have also been shown to modulate different aspects of endocytic transport pathways. In this review, we highlight how HPV makes use of and perturbs normal endocytic transport pathways, firstly to achieve infectious virus entry, secondly to produce productive infection and the completion of the viral life cycle and, finally, on rare occasions, to bring about the development of malignancy.

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