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Journal of Virology, June 2000, p. 5280-5290, Vol. 74, No. 11
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
J Domain-Independent Regulation of the Rb Family by
Polyomavirus Large T Antigen
Qing
Sheng,
Tara M.
Love, and
Brian
Schaffhausen*
Department of Biochemistry, Tufts University
School of Medicine, Boston, Massachusetts
Received 13 October 1999/Accepted 10 March 2000
The ability of polyomavirus large T antigen (LT) to promote cell
cycling, to immortalize primary cells, and to block differentiation has
been linked to its effects on tumor suppressors of the retinoblastoma susceptibility (Rb) gene family. Our previous studies have shown that
LT requires an intact N-terminal DnaJ domain, in addition to an Rb
binding site, for activation of simple E2F-containing promoters and
stimulation of cell cycle progression. Here we show that some LT
effects dependent on interaction with the Rb family are largely DnaJ
independent. In differentiating C2C12 myoblasts, overexpression of LT
caused apoptosis. Although this activity of LT completely depended on
Rb binding, LTs with mutations in the J domain remained able to kill.
Comparisons of Rb
and J
LTs revealed
additional differences. Wild-type but not Rb
LT activated
the cyclin A promoter under serum starvation conditions. Genetic
analysis of the promoter linked the Rb requirement to an E2F site in
the promoter. LTs with mutations in the J domain were still able to
activate the promoter. Finally, J mutant LTs caused changes in
phosphorylation of both pRb and p130. In the case of p130, Thr-986 was
shown to be a site that is regulated by J mutant LT. Taken together,
these observations reveal that LT regulation of Rb function can be
separated into both DnaJ-dependent and DnaJ-independent pathways.
*
Corresponding author. Mailing address: Department of
Biochemistry, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6876. Fax: (617) 636-2409. E-mail:
bschaffh_pol{at}opal.tufts.edu.
Journal of Virology, June 2000, p. 5280-5290, Vol. 74, No. 11
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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