High-density growth arrest in Ras-transformed cells: low Cdk kinase activities in spite of absence of p27(Kip) Cdk-complexes

TY - JOUR

T1 - High-density growth arrest in Ras-transformed cells

T2 - low Cdk kinase activities in spite of absence of p27(Kip) Cdk-complexes

AU - Groth, Anja

AU - Willumsen, Berthe M

PY - 2005/9

Y1 - 2005/9

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, p27(Kip1) 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 p27(Kip1) 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, p27(Kip1) 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 p27(Kip1) 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.

KW - Animals

KW - CDC2-CDC28 Kinases

KW - Cell Cycle Proteins

KW - Cell Line, Transformed

KW - Cell Proliferation

KW - Contact Inhibition

KW - Cyclin D1

KW - Cyclin D2

KW - Cyclin-Dependent Kinase 2

KW - Cyclin-Dependent Kinase 4

KW - Cyclin-Dependent Kinase Inhibitor p27

KW - Cyclin-Dependent Kinases

KW - Cyclins

KW - Mice

KW - NIH 3T3 Cells

KW - Oncogene Protein p21(ras)

KW - Proto-Oncogene Proteins

KW - Retinoblastoma Protein

KW - Tumor Suppressor Proteins

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 -