TY - JOUR
T1 - High-density growth arrest in Ras-transformed cells: low Cdk kinase activities in spite of absence of p27Kip Cdk-complexes
AU - Groth, Anja
AU - Willumsen, Berthe Marie
N1 - Keywords: Ras; High-density growth arrest; Cdk
PY - 2005
Y1 - 2005
N2 - The ras oncogene transforms immortalized, contact-inhibited non-malignant murine fibroblasts into cells that are focus forming, exhibit increased saturation density, and are malignant in suitable hosts. Here, we examined changes in cell cycle control complexes as normal and Ras-transformed cells ceased to grow exponentially, to reveal the molecular basis for Ras-dependent focus formation. As normal cells entered density-dependent arrest, cyclin D1 decreased while cyclin D2 was induced and replaced D1 in Cdk4 complexes. Concomitantly, p27Kip1 levels rose and the inhibitor accumulated in both Cdk4 and Cdk2 complexes, as these kinases were inactivated. Ras-transformed cells failed to arrest at normal saturation density and showed no significant alterations in cell control complexes at this point. Yet, at an elevated density the Ras-transformed cells ceased to proliferate and entered a quiescent-like state with low Cdk4 and Cdk2 activity. Surprisingly, this delayed arrest was molecularly distinct from contact inhibition of normal cells, as it occurred in the absence of p27Kip1 induction and cyclin D1 levels remained high. This demonstrates that although oncogenic Ras efficiently disabled the normal response to contact inhibition, a separate back-up mechanism enforced cell cycle arrest at higher cell density.
AB - The ras oncogene transforms immortalized, contact-inhibited non-malignant murine fibroblasts into cells that are focus forming, exhibit increased saturation density, and are malignant in suitable hosts. Here, we examined changes in cell cycle control complexes as normal and Ras-transformed cells ceased to grow exponentially, to reveal the molecular basis for Ras-dependent focus formation. As normal cells entered density-dependent arrest, cyclin D1 decreased while cyclin D2 was induced and replaced D1 in Cdk4 complexes. Concomitantly, p27Kip1 levels rose and the inhibitor accumulated in both Cdk4 and Cdk2 complexes, as these kinases were inactivated. Ras-transformed cells failed to arrest at normal saturation density and showed no significant alterations in cell control complexes at this point. Yet, at an elevated density the Ras-transformed cells ceased to proliferate and entered a quiescent-like state with low Cdk4 and Cdk2 activity. Surprisingly, this delayed arrest was molecularly distinct from contact inhibition of normal cells, as it occurred in the absence of p27Kip1 induction and cyclin D1 levels remained high. This demonstrates that although oncogenic Ras efficiently disabled the normal response to contact inhibition, a separate back-up mechanism enforced cell cycle arrest at higher cell density.
U2 - 10.1016/j.cellsig.2004.11.021
DO - 10.1016/j.cellsig.2004.11.021
M3 - Journal article
C2 - 15993748
SN - 0898-6568
VL - 17
SP - 1063
EP - 1073
JO - Cellular Signalling
JF - Cellular Signalling
IS - 9
ER -