Figure 8.

Model of density-dependent p27^kip1-induced growth arrest. The proliferation of cells at high density requires an event that is inhibited by pocket protein complexes containing Rb and/or p130. Growth of cultures to high density results in G₀ arrest, an increase in p27^kip1 levels (+), and a decrease in cyclin/cdk activity (−). As a consequence, Rb- and p130-containing complexes remain intact, and expression of gene products required for the proliferation of high-density cells is prevented.