The cyclin-dependent kinase inhibitor flavopiridol potentiates the effects of topoisomerase I poisons by suppressing Rad51 expression in a p53-dependent manner Journal Article
| Authors: | Ambrosini, G.; Seelman, S. L.; Qin, L. X.; Schwartz, G. K. |
| Article Title: | The cyclin-dependent kinase inhibitor flavopiridol potentiates the effects of topoisomerase I poisons by suppressing Rad51 expression in a p53-dependent manner |
| Abstract: | The results of a phase I clinical trial of the topoisomerase I (Topo I) poison CPT-11 followed by the cyclin-dependent kinase inhibitor flavopiridol in patients with advanced solid tumors indicate that patients whose tumors were wild-type, but not mutant, for p53obtained the most clinical benefit from this combination therapy. We elected to elucidate the mechanistic basis for this effect in isogenic-paired HCT116 colon cancer cells that were either wild-type (+/+) or null (-/-) for p53. With the combination therapy of SN-38 (the active metabolite of CPT-11) followed by flavopiridol, the induction of apoptosis was 5-fold greater in the p53+/+ cells compared with the p53-/- cells. This sequential treatment induced phosphorylation of p53 at Ser15, which interacted with Rad51, a DNA repair protein involved in homologous recombination. Rad51 bound to p53-Ser15 within the first 5 hours of combination therapy, and then was transcriptionally suppressed at 24 hours by flavopiridol only in p53+/+ cells. Microarray analysis also revealed suppression of Rad51 in a p53-dependent manner. Depletion of Rad51 by small interfering RNA (siRNA) sensitized both p53+/+ and p53-/- cells to SN-38-induced apoptosis with increase of γH2AX, a marker of DNA damage. Conversely, overexpression of Rad51 rescued p53+/+ cells from SN→F-induced apoptosis. Because flavopiridol inhibits Cdk9, we found that inhibition of Cdk9 by DRB or by siRNA could recapitulate the flavopiridol effects, with suppression of Rad51 and induction of apoptosis only in p53+/+ cells. In conclusion, after DNA damage by Topo I poisons, flavopiridol targets homologous recombination through a p53-dependent down-regulation of Rad51, resulting in enhancement of apoptosis. ©2008 American Association for Cancer Research. |
| Keywords: | controlled study; protein expression; protein phosphorylation; human cell; drug potentiation; mutant protein; biological marker; dna damage; dna repair; drug inhibition; gene overexpression; apoptosis; cyclin dependent kinase 9; serine; protein depletion; antineoplastic combined chemotherapy protocols; 7 ethyl 10 hydroxycamptothecin; small interfering rna; camptothecin; colonic neoplasms; down-regulation; hct116 cells; genetic transcription; protein interaction; phosphorylation; protein p53; irinotecan; drug synergism; protein kinase inhibitors; dna; reverse transcriptase polymerase chain reaction; rna, messenger; colon cancer; tumor suppressor protein p53; down regulation; flavonoids; flavopiridol; piperidines; dna microarray; cyclin dependent kinase inhibitor; rad51 protein; dna topoisomerase; dna topoisomerases, type i; cyclin-dependent kinase 9; rad51 recombinase; poison |
| Journal Title: | Cancer Research |
| Volume: | 68 |
| Issue: | 7 |
| ISSN: | 0008-5472 |
| Publisher: | American Association for Cancer Research |
| Date Published: | 2008-04-01 |
| Start Page: | 2312 |
| End Page: | 2320 |
| Language: | English |
| DOI: | 10.1158/0008-5472.can-07-2395 |
| PUBMED: | 18381438 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | --- - "Cited By (since 1996): 19" - "Export Date: 17 November 2011" - "CODEN: CNREA" - "Source: Scopus" |
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