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Molecular and Cellular Biology, March 1999, p. 2169-2179, Vol. 19, No. 3
Department of Microbiology,
Received 13 July 1998/Returned for modification 24 August
1998/Accepted 18 November 1998
Reduced cell surface levels of major histocompatibility complex
class I antigens enable adenovirus type 12 (Ad12)-transformed cells to
escape immunosurveillance by cytotoxic T lymphocytes (CTL),
contributing to their tumorigenic potential. In contrast, nontumorigenic Ad5-transformed cells harbor significant cell surface levels of class I antigens and are susceptible to CTL lysis. Ad12 E1A
mediates down-regulation of class I transcription by increasing COUP-TF
repressor binding and decreasing NF-
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Reduced Phosphorylation of p50 Is Responsible for
Diminished NF-
B Binding to the Major Histocompatibility
Complex Class I Enhancer in Adenovirus Type
12-Transformed Cells
and
B activator binding to the class
I enhancer. The mechanism underlying the decreased binding of nuclear
NF-
B in Ad12-transformed cells was investigated. Electrophoretic
mobility shift assay analysis of hybrid NF-
B dimers reconstituted
from denatured and renatured p50 and p65 subunits from Ad12- and
Ad5-transformed cell nuclear extracts demonstrated that p50, and not
p65, is responsible for the decreased ability of NF-
B to bind to DNA
in Ad12-transformed cells. Hypophosphorylation of p50 was found to
correlate with restricted binding of NF-
B to DNA in Ad12-transformed
cells. The importance of phosphorylation of p50 for NF-
B binding was
further demonstrated by showing that an NF-
B dimer composed of p65
and alkaline phosphatase-treated p50 from Ad5-transformed cell nuclear
extracts could not bind to DNA. These results suggest that
phosphorylation of p50 is a key step in the nuclear regulation of
NF-
B in adenovirus-transformed cells.
*
Corresponding author. Mailing address: University of
Pennsylvania, Levy Research Building, Room 221, 4010 Locust St.,
Philadelphia, PA 19104. Phone: 215-898-3905. Fax: 215-898-8385. E-mail:
ricciardi{at}biochem.dental.upenn.edu.
Present address: Institute for Molecular Virology, University of
Wisconsin
Madison, Madison, WI 53706.
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