title: The differential staurosporine-mediated G1 arrest in normal versus tumor cells is dependent on the retinoblastoma protein.
abstract: 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.
authors.affiliation: Department of Experimental Radiation Oncology, M.D. Anderson Cancer Center, Houston, TX 77030-4095, USA.
authors.forename: Mollianne
authors.initials: M
authors.lastname: McGahren-Murray
authors.forename: Nicholas H A
authors.initials: NH
authors.lastname: Terry
authors.forename: Khandan
authors.initials: K
authors.lastname: Keyomarsi
mesh_terms: D000818:Animals; D001940:Breast / Q000166:cytology; D002166:Camptothecin / Q000494:pharmacology; D002461:Cell Line, Transformed / Q000187:drug effects / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D004351:Drug Resistance / Q000502:physiology; D004790:Enzyme Induction / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects* / Q000502:physiology; D016161:Genes, Retinoblastoma; D016158:Genes, p53; D006801:Humans; D051379:Mice; D009363:Neoplasm Proteins / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000502:physiology
chemical_list: D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D004317:Doxorubicin; C495900:CDK4 protein, human; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D019311:Staurosporine; D002166:Camptothecin