The kinetics of simian virus 40-induced progression of quiescent cells into S phase depend on four independent functions of large T antigen.
Microinjection of purified simian virus 40 large-T-antigen protein or DNA encoding T antigen into serum-starved cells stimulates them to re-enter the cell cycle and progress through G1 into the S phase. Genetic analysis of T antigen indicated that neither its Rb/p107-binding activity nor its p53-binding activity is essential to induce DNA synthesis in CV1P cells. However, T antigens bearing missense mutations that inactivate either activity induced slower progression of the cells into the S phase than did wild-type T antigen. Inactivation of both activities resulted in a T antigen essentially unable to induce DNA synthesis. Missense mutations in either the DNA-binding region of the N terminus also impaired the ability of full-length T antigen to stimulate DNA synthesis in CV1P cells. The wild-type kinetics of cell cycle progression were restored by genetic complementation after coinjection of plasmid DNAs encoding different mutant T antigens or coinjection of purified mutant T-antigen proteins, suggesting that the four mitogenic functions of T antigen are independent. The maximal rate of induction of DNA synthesis in secondary primate cells and established rodent cell lines required the same four functions of T antigen. A model to explain how four independent activities could cooperate to stimulate cell cycle progression is presented.
Dickmanns
A
A
Institute for Biochemistry, Munich, Germany.
Zeitvogel
A
A
Simmersbach
F
F
Weber
R
R
Arthur
A K
AK
Dehde
S
S
Wildeman
A G
AG
Fanning
E
E
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000502:physiology*; D002453:Cell Cycle; D002460:Cell Line; D015967:Gene Expression Regulation, Viral; D005816:Genetic Complementation Test; D000882:Haplorhini; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein / Q000502:physiology; D013539:Simian virus 40 / Q000235:genetics*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000502:physiology
D000952:Antigens, Polyomavirus Transforming; D012333:RNA, Messenger; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53