© 2001 by Society
© 2001 by the Society forNeuro-Oncology
Decreased cyclin B1 expression contributes to G2 delay inhuman brain tumor cells after treatment with camptothecin
Divisions of Neurology (A.J.J., C.B.T., P.C.P.), Oncology (A.J.J., P.C.P.), and Neurosurgery (L.S.), Children's Hospital of Philadelphia,324 South 34th St., Philadelphia, PA 19104-9786; and Departments of Radiation Oncology (A.M., W.G.M.) and Pathology and Laboratory Medicine (R.J.M.), University ofPennsylvania School of Medicine, Philadelphia, PA 19104
2 Address correspondence and reprint requests to Anna J. Janss, Division ofNeurology, Children's Hospital of Philadelphia, 324 South 34th St.,Philadelphia, PA 19104-9786.
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Abstract |
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DNA damage produces delayed mitosis (G2/M delay) inproliferating cells, and shortening the delay sensitizes human malignantglioma and medulloblastoma cells to cytotoxic chemotherapy. Althoughactivation of the cyclin-dependent kinase CDC2 mediates G2/Mtransition in all tumor cells studied to date, regulation of CDC2 variesbetween tumor types. Persistent hyperphosphorylation of kinase and reducedcyclin expression have been implicated as mediators of treatment-inducedG2 delay in different tumor models. To evaluate regulation ofG2/M transition in human brain tumors, we studied the expressionand/or activity of CDC2 kinase and cyclins A and B1 in U-251 MG and DAOYmedulloblastoma cells after their treatment with camptothecin (CPT).Synchronized cells were treated during S phase, then harvested atpredetermined intervals for evaluation of cell cycle kinetics, kinase activitymRNA, and protein expression. CPT produced G2 delay associated withdecreased CDC2 kinase activity and cyclin B1 expression. Kinase activity wasassociated with CDC2 bound to cyclin B1, not cyclin A, in both cell lines.Cyclin A mRNA and protein expression were reduced after CPT treatment;however, decreased protein expression was short lived and moderate in theglioma and primitive neuroectodermal tumor/medulloblastoma cells,respectively. We conclude that G2 delay is a common response ofbrain tumor cells to chemotherapy with topoisomerase I inhibitors and that amechanism of this delay may be reduced expression of cyclin B1.
Received April 5, 2000; Accepted August 17, 2000