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Mol. Cell. Biol., 05 1995, 2672-2681, Vol 15, No. 5
H Hirai, MF Roussel, JY Kato, RA Ashmun and CJ Sherr
Cyclin D-dependent kinases act as mitogen-responsive, rate-limiting
controllers of G1 phase progression in mammalian cells. Two novel members
of the mouse INK4 gene family, p19 and p18, that specifically inhibit the
kinase activities of CDK4 and CDK6, but do not affect those of cyclin
E-CDK2, cyclin A-CDK2, or cyclin B-CDC2, were isolated. Like the previously
described human INK4 polypeptides, p16INK4a/MTS1 and p15INK4b/MTS2, mouse
p19 and p18 are primarily composed of tandemly repeated ankyrin motifs,
each ca. 32 amino acids in length, p19 and p18 bind directly to CDK4 and
CDK6, whether untethered or in complexes with D cyclins, and can inhibit
the activity of cyclin D-bound cyclin- dependent kinases (CDKs). Although
neither protein interacts with D cyclins or displaces them from
preassembled cyclin D-CDK complexes in vitro, both form complexes with CDKs
at the expense of cyclins in vivo, suggesting that they may also interfere
with cyclin-CDK assembly. In proliferating macrophages, p19 mRNA and
protein are periodically expressed with a nadir in G1 phase and maximal
synthesis during S phase, consistent with the possibility that INK4
proteins limit the activities of CDKs once cells exit G1 phase. However,
introduction of a vector encoding p19 into mouse NIH 3T3 cells leads to
constitutive p19 synthesis, inhibits cyclin D1-CDK4 activity in vivo, and
induces G1 phase arrest.
Copyright © 1995, American Society for Microbiology
Novel INK4 proteins, p19 and p18, are specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
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