J Biol Chem, Vol. 273, Issue 7, 3803-3807, February 13, 1998

An Important Role for the Retinoblastoma Protein in Staurosporine-induced G₁ Arrest in Murine Embryonic Fibroblasts

Michael S. Orr, William Reinhold, Lijia Yu, Nicole Schreiber-Agus^§, and Patrick M. O'Connor

From the  Laboratory of Molecular Pharmacology, Division of Basic Sciences, NCI, National Institutes of Health, Bethesda, Maryland 20892 and the ^§ Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 11724

In this study, we investigated the molecular basis of the ability of staurosporine to induce G₁ arrest in murine embryonic fibroblasts (MEFs). We used MEFs from transgenic mice lacking several negative regulators of the G₁/S phase transition including cells from mice lacking p53, p21, retinoblastoma (Rb), or p16 genes. We found that p53 function was not essential for staurosporine-induced G₁ arrest. In contrast, MEFs from mice lacking Rb genes showed approximately a 70% reduced capacity to arrest in the G₁ phase following staurosporine treatment. In support of a role for Rb in staurosporine-induced G₁ arrest, rat embryonic fibroblasts stably overexpressing cyclin D1/Cdk4^R24C exhibited approximately a 50% reduced G₁ arrest response to staurosporine. The role of Rb in determining the degree of staurosporine-induced G₁ arrest did not depend on the function of the cyclin-dependent kinase inhibitors p16 or p21 because MEFs lacking either of these genes were still capable of undergoing G₁ arrest following staurosporine exposure. Our studies provide evidence of an important role for the Rb protein in determining the degree of staurosporine-induced G₁ arrest in the first cell cycle.