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J. Virol., Jan 1998, 388-395, Vol 72, No. 1
JL Liu, Y Ye, LF Lee and HJ Kung
Marek's disease virus (MDV) induces the rapid development of overwhelming
T-cell lymphomas in chickens. One of its candidate oncogenes, meq (MDV Eco
Q) which encodes a bZIP protein, has been biochemically characterized as a
transcription factor. Interestingly, MEQ proteins are expressed not only in
the nucleoplasm but also in the coiled bodies and the nucleolus. Its novel
subcellular localization suggests that MEQ may be involved in other
functions beyond its transcriptional potential. In this report we show that
MEQ proteins are expressed ubiquitously and abundantly in MDV tumor cell
lines. Overexpression of MEQ results in transformation of a rodent
fibroblast cell line, Rat-2. The criteria of transformation are based on
morphological transfiguration, anchorage-independent growth, and serum-
independent growth. Furthermore, MEQ is able to distend the transforming
capacity of MEQ-transformed Rat-2 cells through inhibition of apoptosis.
Specifically, MEQ can efficiently protect Rat-2 cells from cell death
induced by multiple modes including tumor necrosis factor alpha,
C2-ceramide, UV irradiation, and serum deprivation. Its antiapoptotic
function requires new protein synthesis, as treatment with a protein
synthesis inhibitor, cycloheximide, partially reversed MEQ's antiapoptotic
effect. Coincidentally, transcriptional induction of bcl-2 and suppression
of bax are also observed in MEQ-transformed Rat-2 cells. Taken together,
our results suggest that MEQ antagonizes apoptosis through regulation of
its downstream target genes involved in apoptotic and/or antiapoptotic
pathways.
Copyright © 1998, American Society for Microbiology
Transforming potential of the herpesvirus oncoprotein MEQ: morphological transformation, serum-independent growth, and inhibition of apoptosis
Department of Molecular Biology and Microbiology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4960, USA.
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