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Molecular and Cellular Biology, October 2000, p. 7624-7633, Vol. 20, No. 20
Dana-Farber Cancer Institute and Harvard
Medical School, Boston, Massachusetts 02115
Received 11 May 2000/Returned for modification 8 June 2000/Accepted 26 July 2000
At least three domains of simian virus 40 large T antigen (TAg)
participate in cellular transformation. The LXCXE motif of TAg binds to
all members of the retinoblastoma protein (pRB) family of tumor
suppressors. The N-terminal 70 residues of TAg have significant homology to the J domain of Hsp40/DnaJ and cooperate with the LXCXE
motif to inactivate the pRB family. A bipartite C-terminal domain of
TAg binds to p53 and thereby disrupts the ability of p53 to act as a
sequence-specific transcription factor. The contribution of these three
domains of TAg to cellular transformation was evaluated in cells that
contained inactivating mutations in the pRB and p53 pathways. Cells
that stably expressed wild-type or selected mutant forms of TAg were
generated in mouse embryo fibroblasts (MEFs) containing homozygous
deletions in the RB, INK4a, and ARF loci. It was determined that the J domain, the LXCXE motif, and the
p53-binding domain of TAg were required for full transformation of
wild-type and RB
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Loss of p19ARF Eliminates the Requirement
for the pRB-Binding Motif in Simian Virus 40 Large T
Antigen-Mediated Transformation
/
MEFs. In contrast,
INK4a
/
MEFs that lacked expression of
p16INK4a and p19ARF and
ARF
/
MEFs that lacked
p19ARF but expressed
p16INK4a acquired anchorage-independent growth
when expressing wild-type TAg or mutant derivatives that disrupted
either the pRB-binding or p53-binding domain. The expression and
function of the pRB family members were not overly disrupted in
ARF
/
MEFs expressing LXCXE mutants of TAg.
These results suggest that inactivating mutations of
p19ARF can relieve the requirement for the
LXCXE motif in TAg-mediated transformation and that TAg may have
additional functions in transformation.
*
Corresponding author. Mailing address: Dana-Farber
Cancer Institute, Mayer 457, 44 Binney St., Boston, MA 02115. Phone:
(617) 632-3825. Fax: (617) 632-4760. E-mail:
james_decaprio{at}dfci.harvard.edu.
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