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Mol. Cell. Biol., 06 1996, 2570-2578, Vol 16, No. 6
A Lasorella, A Iavarone and MA Israel
Cells which are highly proliferative typically lack expression of
differentiated, lineage-specific characteristics. Id2, a member of the
helix-loop-helix (HLH) protein family known to inhibit cell
differentiation, binds to the retinoblastoma protein (pRb) and abolishes
its growth-suppressing activity. We found that Id2 but not Id1 or Id3 was
able to bind in vitro not only pRb but also the related proteins p107 and
p130. Also, an association between Id2 and p107 or p130 was observed in
vivo in transiently transfected Saos-2 cells. In agreement with these
results, expression of Id1 or Id3 did not affect the block of cell cycle
progression mediated by pRb. Conversely, expression of Id2 specifically
reversed the cell cycle arrest induced by each of the three members of the
pRb family. Furthermore, the growth- suppressive activities of
cyclin-dependent kinase inhibitors p16 and p21 were efficiently antagonized
by high levels of Id2 but not by Id1 Id3. Consistent with the role of p16
as a selective inhibitor of pRb and pRb-related protein kinase activity,
p16-imposed cell cycle arrest was completely abolished by Id2. Only a
partial reversal of p21-induced growth suppression was observed, which
correlated with the presence of a functional pRb. We also documented
decreased levels of cyclin D1 protein and mRNA and the loss of cyclin
D1-cdk4 complexes in cells constitutively expressing Id2. These data
provide evidence for important Id2-mediated alterations in cell cycle
components normally involved in the regulatory events of cell cycle
progression, and they highlight a specific role for Id2 as an antagonist of
multiple tumor suppressor proteins.
Copyright © 1996, American Society for Microbiology
Id2 specifically alters regulation of the cell cycle by tumor suppressor proteins
Preuss Laboratory for Molecular Neuro-oncology, Department of Neurological Surgery 94143, USA.
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