The differential staurosporine-mediated G1 arrest in normal versus tumor cells is dependent on the retinoblastoma protein

• Published in: Cancer research (Chicago, Ill.) Vol. 66; no. 19; pp. 9744 - 9753
• Main Authors: MCGAHREN-MURRAY, Mollianne, TERRY, Nicholas H. A, KEYOMARSI, Khandan
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01.10.2006
• Subjects: Animals; Antineoplastic agents; Biological and medical sciences; Breast - cytology; Camptothecin - pharmacology; Cell Line, Transformed - drug effects; Cell Line, Transformed - metabolism; Cyclin-Dependent Kinase 4 - metabolism; Doxorubicin - pharmacology; Drug Resistance - physiology; Enzyme Induction - drug effects; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Female; Fibroblasts - drug effects; Fibroblasts - metabolism; G1 Phase - drug effects; G1 Phase - physiology; Genes, p53; Genes, Retinoblastoma; Humans; Medical sciences; Mice; Neoplasm Proteins - physiology; Pharmacology. Drug treatments; Phosphorylation - drug effects; Protein Processing, Post-Translational - drug effects; Retinoblastoma Protein - antagonists & inhibitors; Retinoblastoma Protein - deficiency; Retinoblastoma Protein - physiology; RNA, Small Interfering - pharmacology; Staurosporine - pharmacology; Tumor Suppressor Protein p53 - deficiency; Tumor Suppressor Protein p53 - physiology; Tumors; Retinoblastoma protein; G1 Phase; Tumor cell; Comparative study; Cell cycle
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-06-1809

Previously, we reported that breast cancer cells with retinoblastoma (pRb) pathway-defective checkpoints can be specifically targeted with chemotherapeutic agents, following staurosporine-mediated reversible growth inhibition in normal cells. Here we set out to determine if the kinetics of staurosporine-mediated growth inhibition is specifically targeted to the G(1) phase of cells, and if such G(1) arrest requires the activity of wild-type pRb. Normal human mammary epithelial and immortalized cells with intact pRb treated with low concentrations of staurosporine arrested in the G(1) phase of the cell cycle, whereas pRb-defective cells showed no response. The duration of G(1) and transition from G(1) to S phase entry were modulated by staurosporine in Rb-intact cells. In pRb(+) cells, but not in Rb(-) cells, low concentrations of staurosporine also resulted in a significant decrease in cyclin-dependent kinase 4 (CDK4) expression and activity. To directly assess the role of pRb in staurosporine-mediated G(1) arrest, we subjected wild-type (Rb(+/+)) and pRb(-/-) mouse embryo fibroblasts (MEFs) to staurosporine treatments. Our results show that whereas Rb(+/+) MEFs were particularly sensitive to G(1) arrest mediated by staurosporine, pRb(-/-) cells were refractory to such treatment. Additionally, CDK4 expression was also inhibited in response to staurosporine only in Rb(+/+) MEFs. These results were recapitulated in breast cancer cells treated with siRNA to pRb to down-regulate the pRb expression. Collectively, our data suggest that treatment of cells with nanomolar concentrations of staurosporine resulted in down-regulation of CDK4, which ultimately leads to G(1) arrest in normal human mammary epithelial and immortalized cells with an intact pRb pathway, but not in pRb-null/defective cells.