Gene

Restriction point

Cell biology

Biology

Cell cycle

Regulator

Cell culture

Apoptosis

Start point

Cancer research

Ectopic expression

Genetics

Mathematics

Cyclin

Embryonic stem cell

Cyclin D1

End point

Geometry

Carcinogenesis

Cancer

Oncogene

The restriction (R)-point decision is fundamental to normal differentiation and the G1-S transition, and the decision-making machinery is perturbed in nearly all cancer cells. The mechanisms underlying the cellular context-dependent R-point decision remain poorly understood. We found that the R-point was dysregulated in Runx3-/-mouse embryonic fibroblasts (MEFs), which formed tumors in nude mice. Ectopic expression of Runx3 restored the R-point and abolished the tumorigenicity of Runx3-/-MEFs and K-Ras-activated Runx3-/-MEFs (Runx3-/-;K-RasG12D/+). During the R-point, Runx3 transiently formed a complex with pRb and Brd2 and induced Cdkn1a (p21Waf1/Cip1/Sdi1; p21), a key regulator of the R-point transition. Cyclin D-CDK4/6 promoted dissociation of the pRb-Runx3-Brd2 complex, thus turning off p21 expression. However, cells harboring oncogenic K-Ras maintained the pRb-Runx3-Brd2 complex and p21 expression even after introduction of Cyclin D1. Thus, Runx3 plays a critical role in R-point regulation and defense against cellular transformation.

Runx3 plays a critical role in restriction-point and defense against cellular transformation