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Mol. Cell. Biol., Oct 1997, 6076-6086, Vol 17, No. 10
DP Satijn, DJ Olson, J van der Vlag, KM Hamer, C Lambrechts, H Masselink, MJ Gunster, RG Sewalt, R van Driel and AP Otte
Polycomb (Pc) is involved in the stable and heritable repression of
homeotic gene activity during Drosophila development. Here, we report the
identification of a novel human Pc homolog, hPc2. This gene is more closely
related to a Xenopus Pc homolog, XPc, than to a previously described human
Pc homolog, CBX2 (hPc1). However, the hPc2 and CBX2/hPc1 proteins
colocalize in interphase nuclei of human U-2 OS osteosarcoma cells,
suggesting that the proteins are part of a common protein complex. To study
the functions of the novel human Pc homolog, we generated a mutant protein,
delta hPc2, which lacks an evolutionarily conserved C-terminal domain. This
C-terminal domain is important for hPc2 function, since the delta hPc2
mutant protein which lacks the C-terminal domain is unable to repress gene
activity. Expression of the delta hPc2 protein, but not of the wild-type
hPc2 protein, results in cellular transformation of mammalian cell lines as
judged by phenotypic changes, altered marker gene expression, and
anchorage-independent growth. Specifically in delta hPc2-transformed cells,
the expression of the c-myc proto-oncogene is strongly enhanced and serum
deprivation results in apoptosis. In contrast, overexpression of the
wild-type hPc2 protein results in decreased c-myc expression. Our data
suggest that hPc2 is a repressor of proto-oncogene activity and that
interference with hPc2 function can lead to derepression of proto-oncogene
transcription and subsequently to cellular transformation.
Copyright © 1997, American Society for Microbiology
Interference with the expression of a novel human polycomb protein, hPc2, results in cellular transformation and apoptosis
E. C. Slater Instituut, University of Amsterdam, The Netherlands.
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